(NASA-CB-146253)

STUDY O F G K O U N D HANDLIUG
C H A B A C T E H I S T I C S OF A H A R I T I f l E PATROL A i E S H I Y
Coutcactor Fioai Heport, O c t . 1 9 8 0
Mar.
1981 (Goodyear Aerospace Corp.)
280 p
nc A13/flE A01
CSCL 01E C3/09

N8L-16690
Unclas
05555

NASA CR- I66253

STUDY OF
GROUND HANDLING CHARACTERISTICS
OF A MARITIME PATROL AIRSHIP

MARCH 1981

PREPARED UNDER CONTRACT NO. NAS2-10448

BY
GOODYEAR AEROSPACE CORPORATION
AKRON, OHIO
FOR

AMES RESEARCH CENTER

NATIONAL AERONAUTlCS AND SPACE ADMINISTRATION

1. h m f t MR

?.-mwWht.-Mo.

~ h b b t k Q W I ) h

CR- 166258
I

&TLl(rllll(LIYII))

kIkprcDHI

, M m h 1981
a-owll~a-ea

Study of Ground Handling Characterintics of a

Maritime Petrol Airship
7. 4ItbftJ

@.--mt4onmMo.

QER- 16948
1RYkrtWWs.

a.

~ r o r m i q ~ r c k n ) ( n r n d ~

Ooodyear Aerospace Corporation

1210 Massillon Road
Akron, Ohio 44315

11.

NAS2- 10448

12. - + w b l t m r d ~

ca

~ w am~ l I Jn~ . ~

NASA
Ames Research Center
Moffett Field, Calif.

ia TW

n w

%TE"'?!rt

contractor
, Oct 1980 - March

la

*~ncr
OI

14.

on

Prepared based on memorandum of agreement between U .S. Coast Guard

and NASA.
t6 Abrabcl

Mooring concepts appropriate for maritime patrol airship (MPA) vehicles are
investigated.
The evolution of ground handling systems and procedures for all airship types
is reviewed to ensure that appropriate consideration i s given to past experiences.
A tri-rotor maritime patrol airship is identified and described. Wind loads on a
moored airship and the effects of these loads on vehicle design are analyzed.
Several mooring concepts are assessed with respect to the airship design, wind
loads, and mooring site considerations. Basing requirements and applicability
of expeditionary mooring aiso are addressed.

( 7 R*V Word Ifyyt@d

bv A u W t a Jl

18. ~ i b u l i SUlanmt
a

Lighter-t han-Air (LTA)

Maritime Patrol Airship (MPA)
Ground Handling
Mooring
19 ~ W I V Oluc.(of 1~ m t l
*

Unclassified

70. suurctv cmtl, lof INI -1

Unclassif'ied

] ? I . b.at P m

280

QRECDMG PAGE BLANK NOT FILM#)

ABSTRACT
Mooring concepts appropriate for maritime patrol airship (MPA)
vehicles are investigated.
The evolution of ground handling systems and procedures for
all airship types is reviewed to ensure that appropriate consideration is given to past experiences.

A tri-rotor maritime

patrol airship is identified and described.

Wind loads on a

moored airship and the effects of these loads on vehicle design

are analyzed.

Several mooring concepts are assessed with re-

spect to the airship design, wind loads, and mooriug site considerations.

Basing requirements and applicability of expedi-

tionary mooring also are addressed.

PRECEDlNG PAGE BLANK NOT FILMED

FOREWORD
With t'.e recent advent of the Coast Guard's 200-mile coastal patrol zone, a renewed
interest has developed in applying lighter-than-air (LTA) technology to developing
high-performance and fuel-efficient maxitime patrol vehicles (MPA's)

. The U .S.

Coast Guard and U .S. Navy launched a joint effort to investigate their feasibility.
A s part of this on-going program, it was concluded that modern hybrid airships may
be cost-effective and fuel-efficient vehicles capable of carrying out many maritime
patrol missions.
One area identified as requiring in-depth technical study was the ground handling
characteristics and associated equipment for this new class of vehicles.

Historically,

ground handling has been a severe problem for lighter-than-air vehicles due to their
inherent lack of low-speed controllability.

Even i f modem hybrid airships exhibit a

substantial increase in available control power, ground handling is still a concern.

In 1980, NASA and the U .S. Coast Guard signed a memorandum of agreement to coordinate development efforts in LTA technology.

Based on this agreement, a timely

decision was made to augment an on-going NASA-sponsored ground handling study

contract (specifically aimed at the hybrid heavy lift airship) in order to analyze
ground handling problems associated with maritime patrol airship configurations.
Funds were made available by the U.S. Coast Guard. The original contracted study
was carried out by Goodyear Aerospace Corporation (GAC) between December 1,
1979 and July 31, 1980. The augmented portion of the contract (for MPA vehicles)
also was perfcrmed by Goodyear Aerospace and covered October 1, 1980 through
February 28, 1981. The contractor's report number is GER-16948.
The objective of this ground handling study is to define several ground handling
systems appropriate for MPA vehicles and to assess their impact on vehicle design
and mooring operations. This report is the result of additional study performed
under NASA-Ames Contract NAS2- 10448. Accordingly, several portions of the NASA's
Contractor Report CR-166130, "Preliminary Study of Ground Handling Characteristics
of Buoyant Quad Rotor Vehicles,'' are repeated within this report.
Dr. H . Miura served as the NASA technical monitor for the augmented MPA ground
handling study.
Cornmanier K

Cognizant technical personnel for the U .S. Coast Guard were

. Williams and M r .

L. Nivert. Within Goodyear Aerospace, M r . Dale E.

Williams, LTA program manager, and Mr. Donald B

. Block, chief LTA engineer, pro-

vided overall program guidance. M r . Ronald G . E. Browning was the project engineer.
Prime contributors were M r . F. Bloetscher, M r . W, Trumpold, M r . A. Ahart, Mr. L.
Cermak, and M r . P. Jacobs.

- v-

PRECEDING PAGE BLANK

NOT FILMED

TABLE OF CONTENTS
Page
LIST OF FIGURES
LIST OF TABLES

...........................
...........................

Section
I

Item

....................
Early Approaches . . . . . . . . . . . .
a. General . . . . . . . . . . . . . . .
6.
- Floating Hangar . . . . . . . . . . .
c. Manpower . . . . . . . . . . . . . .
d. Docking Rails and Trolleys . . . . . . . . . . . . .
- Ground Cable Landing System . . . . . . . . . . . .
e.
f . Mooring-by-Wire . . . . . . . . . . . . . . . . . .
-g.
Vickers Masterman Mast . . . . . . . . . . . . . . .
- Nose Mooring Systems . . . . . . . . . . . . . . . .
h.
...

HISTORICAL REVIEW

1.

i.

Belly Mooring Mast System (Non-Rigid Airships)

.............
.................
.....................
...............
3. Maritime Experience . . . . . . . . . . . . . . . . . . .
a. General. . . . . . . . . . . . . . . . . . . . . . .
- Ship-Mounted Masts . . . . . . . . . . . . . . . . .
6.
-c. Aircraft Carrier Operations . . . . . . . . . . . . .
d.
- Water Takeoffs and Landings. . . . . . . . . . . . .
4. Summary . . . . . . . . . . . . . . . . . . . . . . . .
THE MPA VEHICLE CONCEPT . . . . . . . . . . . . . . . .
1. General. . . . . . . . . . . . . . . . . . . . . . . . .
2. ZP3G Configuration . . . . . . . . . . . . . . . . . . .
3. Major Characteristics . . . . . . . . . . . . . . . . . .
MOORING SYSTEM ALTERNATIVES . . . . . . . . . . . . .
1. General. . . . . . . . . . . . . . . . . . . . . . . . .
2. Systems Permitting Rotation . . . . . . . . . . . . . . .
a. Bow Mooring . . . . . . . . . . . . . . . . . . . .
b.
Mooring . . . . . . . . . . . . . . . . . . . .
-c . Belly
Center
Point Mooring . . . . . . . . . . . . . . . .
2.

Developments After World War I1

a. Expeditionary Mast
b.
- MobileMast
-c. Mobile Winches (Mules).

xi
xiv

Section

Title

. Complete
Restraint S y ~ t e m s. . . . . . . . . . . . . .
a . Car Secured . . . . . . . . . . . . . . . . . . .
6 . Envelope Secured . . . . . . . . . . . . . . . . .
4 . Protective Systems . . . . . . . . . . . . . . . . . .
a . Wind Screens . . . . . . . . . . . . . . . . . . .
6
-. Hangars . . . . . . . . . . . . . . . . . . . . .
5 . Maritime Systems . . . . . . . . . . . . . . . . . . .
a . General . . . . . . . . . . . . . . . . . . . . . .
6
. Sea Anchors . . . . . . . . . . . . . . . . . . .
.
6 . Summary . . . . . . . . . . . . . . . . . . . . . . .
3

IV

STRUCTURAL ANALYSIS OF A FULLY RESTRAINED

AIRSHIP

.........................

. Static Aerodynamic Forces and Moments . . . . . . . .

3 . Loads of a Fully Restrained Airship . . . . . . . . . .
a . General . . . . . . . . . . . . . . . . . . . . . .
2

c.

...........
..........
Restrained Airship . . . . .

Vertical Landing Gear Forces

. Horizontal Landing Gear Forces

4
V

Computer Model for Fully

DYNAMIC ANALYSIS OF A MASTED AIRSHIP

.
2.
3.
1

........................
Dynamic Forces and Moments Acting on the Airship . .
General

Computer Model for Systems with Rotational

Capability
a
Data Inputs
Computed Inputs
c
Outpqts
-

.
-..

.........
......................
.........
...................
...................
.................
IMPACTS OF VEHICLE DESIGN ON GXOUND HANDLING .
1. Tail Configuration . . . . . . . . . . . . . . . . . .
2 . Effect of Buoyancy Ratio . . . . . . . . . . . . . . .
4

VI

......................
....................
.................
.....................

Computer Model Results and Analysis

a
General
6
Mast
Forces Versus Mast Location
c
Bow Mooring
a Belly Moored
-e Equilibrium Angle

.
.
.
-..

Page

Section

Title

VII

........
4 . Prapulsion Units . . . . . . . . . . . . . . . . . . .
OPERATIONAL CHARACTERISTICS AND COSTS . . . . . .
1. General . . . . . . . . . . . . . . . . . . . . . . . .
2 . Site Considerations . . . . . . . . . . . . . . . . . .
a . General . . . . . . . . . . . . . . . . . . . . . .
6
. Topography . . . . . . . . . . . . . . . . . . . .
c . Soil Conditions . . . . . . . . . . . . . . . . . .
a . Site Size and Shape . . . . . . . . . . . . . . . .
e . Weather Conditions . . . . . . . . . . . . . . . .
3

Envelope and Suspension System Weight

.....................
..............
............
.......
.
..................
.
...
.......................
4 . Belly Mooring . . . . . . . . . . . . . . . . . . . . .
a . Structural Requirements . . . . . . . . . . . . . .
6
-. Mooring Area Requirements . . . . . . . . . . . .
c . Operations and Mobility . . . . . . . . . . . . . .
a-. Environmental and Maintenance Considerations . . .
e
-. Costs . . . . . . . . . . . . . . . . . . . . . . .
5 . Complete Vehicle (Total) Restraint . . . . . . . . . .
a . Structural Requirements . . . . . . . . . . . . .
-. Mooring Area Requirements . . . . . . . . . . . .
6
c . Operational Concept . . . . . . . . . . . . . . .
d . Costs . . . . . . . . . . . . . . . . . . . . . . .
6 . Hangar Systems . . . . . . . . . . . . . . . . . . . .
a . Operational Concept and Requirements . . . . . . .
Bow Mooring
a
Structural Requirements
Mooring
Area Requirements
.6.
Operational Concept and Requirements
c
a. System Mobility
e
Environmental and Maintenance Considerations
- Costs

.
.

-. Additional Utility for Airship Operations

6

.
a-.
c

.
8.
9.
7

.....................
...
.......................

Support
Additional Support for Other USCC Operations
Costs

............
Permanent Versus Remote Base Requirements . . . . .
Concept Summary . . . . . . . . . . . . . . . . . . .
General . . . . . . . . . . . . . . . . . . . . . .
-ab .. Attributes
....................
-c . Iiangar Systems
-d . Rating . . . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
Operational Scenario Suitability

Page
6-8

Section
VIII

.
2.
3.
4

5.

.
8.
7

....
Historical Review . . . . . . . . . . . . . . . . . . . .
Vehicle Concept . . . . . . . . . . . . . . . . . . . .
Mooring System Alternatives . . . . . . . . . . . . . . .
Structural Analysis of a Fully Restrained Airship . . . .
Dynamic Analysis of a Masted Airship . . . . . . . . . .
Impact of Vehicle Desigil on Ground Handling . . . . . .
Operational Characteristics and Costs . . . . . . . . . .

SUMMARY. CONCLUSIONS. AND RECOMMENDATIONS

1

IX

Page

Title

....................
LIST OF SYMBOLS . . . . . . . . . . . . . . . . . . . . .
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . .
Recommendations

Appendix

...................

ADDED MASS FORCES

AIRSHIP MOORING LOADS ANALYSIS:

MODEL OUTPUTS

SIMULATION

...................

8- 1
8- 1
8- 1
8- 1
8- 1

8- 2
8- 2
8- 2
8- 4

9- 1
10-1

LIST OF FIGURES
Figure

Page

1-6

.........
Italian Docking Rail and Trolley ( 1923) . . . . . . .
Docking Rail Trolley (1923) . . . . . . . . . . . . .
Italian Single Rail and Trolley (1923) . . . . . . . .
Three-Wire Mooring System . . . . . . . . . . . . .
Vickers Mooring Mast ( 1923) . . . . . . . . . . . . .

1-7

Terry-Type Mooring Mast (1923)

1-8

English High Mast (Cardington. England). 1930

1-1
1-2

1-3
1-4
1- 5

Early Examples of Floating Airdocks

...........

...

1-11

...
Stub or Expeditionary Mast (1927) . . . . . . . . . .
Self-Propelled Mobile Mast ( 1932) . . . . . . . . . .

1- 1 2

Rail-Type Hauling-Up and Mooring-Out Circles (1930)

1- 13

Belly Mooring Mast ( 1964)

1- 9
1- 10

Navl High Mast (Lakehurst. New Jersey). 1925

1- 1 4

..............
Early Belly Mooring System ( 1930) . . . . . . . . .

1-15

Modern Goodyear Bus with Belly Mooring Mast (1979)

1- 16

Mooring Mast after Raising

1-17
1- 18
1- 19

..................
Anchor Layout (Reference 11) . . . . . . . . . . . . . . . . .
Coodyear Expeditionary Mast ( 1964) . . . . . . . . . . . . . .

ZPG-3W Airship Mooring to Type V Mast with MC-3

Mules on Nose Lines (1958)

..................

Coodyear Commercial Airship Ground Handling Equipment

(Rome. Italy). 1973

......................
MC-3 Mobile Winch (1958) . . . . . . . . . . . . . . . . . . .
U.S.S. Patoka High Mast (1928) . . . . . . . . . . . . . . . .
.....
.
............

The Shenandoah Leaving Mast on the U.S S. Patoka

Suggested Warship Modifications ( 1924)

1-2
1-4
1-5
1-6
1-7
1-10

1-12
1-14
1-15
1-18
1-19
1-20

1-22
1-23

1-25
1-26
1-27
1-28

Figure

LIST OF FIGURES (CONTINUED)

3- 3

.........
K Ship Landing Aboard Aircraft Carrier . . . . . . . . . . .
L-1 Airship Taking Off from Lake Erie . . . . . . . . . . . .
Inboard Profile . . . . . . . . . . . . . . . . . . . . . . . .
ZP3G Airship . . . . . . . . . . . . . . . . . . . . . . . . .
Barrier Height Requirement . . . . . . . . . . . . . . . . . .
Section View of Candidate Conventional Airship Hangar . . . .
WDLts Air-Supported Hangar . . . . . . . . . . . . . . . . .

3- 4

Proposed Sea Anchor System on ZPGl (Reference 17)

4- 1

Coordinate System

4- 2

Force and Moment Coefficient Values About Center of

Buoyancy of Airships with Tails versus Angle of Yaw
(Pitch and Roll Angles of Zero)

1-25
1-26

1-27
2- 1
2- 2
3- 1
3- 2

Disposition of Landing Crew on Carrier Deck

.....
......................

................

Moments About Y=O. Z=0; View Looking Forward Along

Centerline

..........................

Moments About lCB Z=O. View Looking Port to

Starboard

..........................
Vertical Loads. View Looking Port to Starboard . . . . . . . .
Moments About Vertical Axis through CB. View Looking
Down at Airship

.......................
Maximum Gear Forces versus Wind Speed . .
........
Maximum Gear Forces versus Idanding Gear Placement . . . . .
Force Coefficient versus Airship Length for Various
Yaw Angles

..........................
..by
Segments. N o s e t o T a i l ( - ) . . . . . . . . . . . . . . .
Cy by Segments. Centerline to Starboard (+)
........
Signs of Forces and Moments . . . . . . . . . . . . . . . . .
Moored Airship Dynamic Simulation Logic Sequence . . . . . .
Peak FMAST versus Mast Location

...............

Peak FLATR versus Mast Location

...............

Page
1-40

Figure
5- 8
5- 9
5- 10
5- 11
5- 12
5- 13
6- 1

6- 2

LIST OF FIGURES (CONTINUED)

.,.............
Peak Mast Forces versus Wind Angle for Bow Moored MPA . . .
Peak FLONG versus Mast Location

..
Peak Mast Forces versus Wind Angle for Belly Mwred MPA. . .
Peak Mast Forces versus Wind Speed for Belly Moored MPA . .
Equilibrium Position with Respect to Mast Location , . , . . .
Terra-Tire Anti-Kiting Device. . . . . . , . . . . . . . . - .
Buoyancy Ratio versus Maximum Upward Vertical Load for
Fully Restrained MPA . . . . , . . . . . . . . . . . . . . . .
Suspension System Forces for Total Restraint System , . . . .
Effect of Complete Vehicle (Total) Restraint Mooring on
...........
Suspension System and Envelope Weight
Land Requirements for Mooring Systems with Rotational
Capability . . . . . . . . . . . . . . . . . . . . . . . . . . .
Annual Extreme Wind Speeds (rnph). . . . . . . . . . . . . . .
Bow Mooring Mast Arrangement . . . . . . . . . . . . . . . .
Wind Speed versus Landing Gear Load for Belly-Moored MPA. .
Hypothetical Landing Gear and Truss Configuration . . . . . .
Fleet Airship Wing One Deployment During World War I1 . . . .
Peak Mast Forces versus Wind Speed for Bow Moored MPA ,

Page
5- 13

5- 15
5- 16
5- 17
5- 18
5- 19

6- 6

LIST OF TABLES

Page

Table
1- 1
2- 1

2- 2
4- 1
4- 2
4- 3

...
Major Characteristics . . . . . . . . . . . . . . . . . . . .
ZP3G Performance Summary . . . . . . . . . . . . . . . . .
d
of Data Used in References . . . . . . . .
Type a ~ Scope
Body Axis Static Aerodynamic Forces and Moments . . . . .

Mast and Airship Wind Speed Mooring Limitations (MPH)

Assumed Distribution of Landing Gear Forces in Three

Different Axial Directions

.................
Coordinate System . . . . . . . . . . . . . . . . . . . . . .

Cotnparison of Full-Scalc Empennage Geometric

Characteristics

.......................

Comparison of Measured Stability Derivatives for Various

Tail Configurations (Based on 1/48-Scale DTMR Wind
Tunnel Tests)

.......................

Computation of Dynamic Stability Criteria

Tail Configurations

for Various

.....................

...........
.............

Suspension System Weight Factor (Kws)

Suspension System Weight Fraction

Envelope Weight Fractions for Fixed Number of

Suspension Systems

....................
Typical CBR Ratings . . . . . . . . . . . . . . . . . . . .
Soil Classification Data . . . . . . . . . . . . . . . . . . .
Characteristics of Single-Helix Screw Anchors . . . . . . . .
Tire Pressure Recommendations . . . . . . . . . . . . . . .
Equipment Weight for Bow Mooring System . . . . . . . . . .
Equipment Weight for Belly Mooring System . . . . . . . . .
USCG Aircraft Characteristics . . . . . . . . . . . . . . .
Hangar System Costs . . . . . . . . . . . . . . . . . . . .

1-31

LIST OF TABLES (CONTINUED)

Table
.

7-9
7- 10

....................
Mooring Concept Summary . . . . . . . . . . . . . . . . . .
Levels of MPA Bases

Page

7-22
7- 26

SECTION I

1.

WRLY APPROACHES

-a.

General

- HISTORICAL REVIEW

The evolution of ground handling systems has, by necessity, paralleled the

advancement of airship design and opcrztional capabilities (References 1-11)

Early craft, due to their Zrnited size, were easily ground handltd to and from
mooring sheds by smdl groups of men.

However, as envelope size increased,

more effective and efficient ground support became necessary.

b.

Floatin6 Hangar
Not unexpectedly. Von Zeppelin extended his innovative skills t o airship
mooring.

The use of a floating hangar on Lake Constance was the culmi-

nation of his assessment of how to satisfy three mair, requirements for

airship mooring operations :

1. Provide a flat surface

2.

Provide unobstructed approaches

3.

Enable the airship always to carry out docking procedures

in line with the prevailing wind direction.

This also marked the inception of mechanical handling systems through the
use of small boats acting a s tugs.
The downfall of this approach was i t s sensitivity to stormy weather.

Due

to this, the concept was eventually abandoned and a return to land facilities was implemented.

c.

Two early examples a r e shown in Figure 1-1.

Manpower
For several years, no attempt was made to change the operation of walking 2n
airship to and from its protective h-gar.

Since most airship flights during

this period (World War I ) were conducted by the military, a sufficiently

large contingent of personnel was always available for ground handling.
This system remained, however, closely dependent on wind conditions.
Numerous flights either were cancelled o r extended due to incompatible
winds at the scheduled undocking or docking times, respectively.

d.

Docking Rails and Trolleys

In keeping with the philosophy of providing hangar space for an airship
when it was not in flight, early attempts at ground

handling were aimed

at improving the efficiency of moving the airship t o m d f r o m the hangar,

rather than providing an exterior mooring system.

The result was the

development of docking rails and trolleys (see Figures 1-2 and 1-3).

Initial

design and use of this equipment was undertaken by the Germans and
Italians.

System refinements were instituted at a later date in both the

United States and England.

Docking rails were built along the inside of each hangar wall and extended
some distance out onto the airfield (see Figure 1-4).

These rails provided a

rigid base along which mobile trolleys could r u n , thereby establishing a

control system for the critical portion of the airship undocking ldocking
sequence.
A typical docking operation utilizing the rail /trolley system is :

1.

The airship kinds and is walked to the external rail end

by the ground crew.

2.

A rope tackle is attached from the left and right trolleys

to bow mooring points on the airship.

3.

The airship is walked forward until trolleys can be attached in the same manner to s t e m mooring points.

4.

The airship, now secured fore and aft, is walked into the
hangar.

Eight crewmen were used on each trolley.

The remaining available per-

sonnel were assigned to :he bow hauling rope to ease the airship forward
and underneath the car to krep it from contacting the ground.
Ground
-e. --

Cable Landing System

Another tar'y attempt at minimizing ground crew personnel requirements was

the grounc' cable landing.

The end points of a long cable were secured,

through sy .ings, to ground anchor points.

The airship's objective was to

engage the cable with a suspended grappling hook while flying overhead.
The results of this experiment were unsuccessful.

Several variations of a mooring by wire system were suggested and tried

(see Figure 1-51.

Although experiences with t h ~ s esystems wcre not totally

unsatisfactory, some significant drawbacks made them impractical.

Figure 1-2

- Italian Dc-eking Rail and Trolley ( 1 9 2 3 )

Figure 1-3

- Docking

Rail Trolley (1923)

ORIGINAL PAW
OF POOR g u

1s

WlND

WlND

Figure 1-4

- Italian Single Rail and Trolley

(1923)

(A) THREE-WIRE SYSTEM

GROUND CABLES

(8) FREE THREE-WIRE SYSTEM

L
Y

(CI 81 MODIFICATION OF FREE THREE-WIRE SYSTEM

Figure 1-5

- Three-Wire Mooring System

Four variations were attempted:

1.

The Usborne system consisted of two vertical wires attached

to t h e car.
2.

This proved to be unstable in high winds.

The basic three-wire system utilized wires attached at one

point on the airship t o form an equilateral pyramid.

This

configuration was used to bring the rigid airships to their

mooring masts even through the system itself proved to be
too unstable for mooring out.

3.

The free-three-wire system enables the three cables to feed

from the apex of the equilateral pyramid through sheave
blocks anchored to the ground and attached to a free-moving
central ring.

This concept eliminated the rigidity of the

fixed cable system.

As a result, the free-three-wire system

provided the airship with more stable riding out characteristics.

4.

A four-wire systen, had one additional wire from the ring

(described above) to a ground anchor point.

This, in

effect, formed the ring into a parallelogram.

Although this

system was tested, it was not successful.

Conclusions resulting from experiences with mooring-by-wire systems were:

1.

For maximum stability, an airship would have to be trimmed

four to five degrees down by the tail and held a similar
amount off wind.

2.

Since heating and cooling causes rapid change in the airship

static condition, a rapid ballasting system would have had
to be developed.

3.

To keep tension on the wires, the airship would have to be

maintained in a light static condition.

4.

Ballasting and fueling an airship moored in this manner

would be very difficult.

5.

A crew would have to remain on board at all times.

Crew

changes would be very difficult.

6.

The mooring area would be large.

The mooring b y wire system was proven to be too unstable and cumbersome
:o be practical, except possibly as an alternative emergency mooring system.

g.

Vickers Masteman Mast

The Vickers mast was an early development by the Englirh for non-rigid
airships.

I t r unique design enabled the airship to be cradled in a yoke

rather than be constrained a t a single attachment point (ree Figure 1-6).

Two pads were fastened to the envelope r e v e r d feet behind the nose to reinforce the contact areas between the d r s h i p and the end points of the yoke.
To initiate the mooring procedure, the ground crew, with handling guys,
would walk the airship upwind toward the mast.
be stationed at a winch in each yoke.

At the yoke, a man would

Once the airship was properly po-

sitioned in the yoke, cables would be attached to the envelope and reeled
in such a manner that the airship was securely attached to the mast.
While the Vickers mast saw limited use for several years, deficiencies in the
following areas accounted for its final demise:
The mooring patches were cumbersome and had sufficient

1.

weight to cause the airship to become nose heavy

2.

The patches were difficult to attach

3.

The mooring operation was extremely sensitive to high, gusty

winds and therefore required an excessive number of ground

4.

personnel
There was insufficient positive maneuvering action during

5.

mooring
The positioning of two men on the yoke of the mast was
hazardous

h.

Nose Mooring Systems

( a ) General
The expansion of military airship programs stimulated the searcn for acceptable mooring systems.
in cost.
tory.

Hangars were operationally effective but prohibitive

Thus, development of an outside mooring technique was manda-

The nose mooring system appeared to be the most suitable.

Consistent with this approach was the development of nose battens in

non-rigid airships. While early airships were slow enough to obviate this
need, newer and faster craft required nose stiffening to prevent in-flight
fabric deformation. Similarly, a nose mooring approach necessitated the
development of a system to distribute the mooring loads. A fabric-covered
metal noat cone structure satisfied both these needs.

Figure 1-6

- Vickers Mooring Mast

(1923)

This led to new airships with a grooved, bearing-mounted rpindle installed

in the nose cone and a flexible steel pull-in cable aecured to the spindle.
Battens were attached to the bare of the nose cone to distribute the mooring loads evenly over the envelope aurface. Initially, there battens were
made of wood but were eventually replaced by mtrongoa and lighter
aluminum battens. The rpindle in the nose cone wae mated to a device atop
a mooring mart. These early maets were rimply variations of guyed built-up
steel structures with a hand winch at the bottom and a buffer a t the top
against which the airship would be drawn. As airships increased in size,
more efficient and stronger masts were produced,
( b ) Terry Mast (for Non-Rigid Airships)
One t y ~ eof mast developed early by the military was known as the t e r r y
mast (see Figure 1-7)
This mast consisted of a structural steel center

pole supported by eight guys anchored in the ground. On top of the mast a
13-foot-diameter cone-shaped buffer was mounted. The buffer ring had felt
pads secured around the lip to reduce envelope wear at the contact points.
The buffer was attached to an arm of a circular casting that rotated on
bearings on top of the mast. Counterweights were attached to another
casting arm opposite to the buffer.
A pull-in line was attached to two nose patches and run through a sheave

on the mast head, down through the mast, and out through another sheave
at the bottom, finally to a winch. Once the hookup was made, the winch
reeled in the airship until the envelope nose was snug inside the buffer
cone.

Tension was kept on the pull-in line, and the winch was locked.

While this configuration had merit in terms of minimizing ground crew requirements, it had several drawbacks:
1.

The cone and counterweight were heavy and exhibited a

flywheel ch:,ra 3eristic in shifting winds.

2.

Load distribution was unsatisfactory.

The buffer cone

should have been extended by four to six feet and contoured

to the envelope's shape.
3.

The nose patches were unable to suritain the pull-in cable

4.

load.
Considerable stresses built up in tne envelope immediately
aft of the buffer ring.

In actual recorded cases, battens

were broken and envelope fabric torn due to these stresses.

ORIGINAL PAGE IS
OF POOR QUALITY

HAS BEEN RAISED

H CLEARANCE
0 MAKE DECISION

Figure 1-7

- Terry-Type Mooring Mast (1923)

5.

Forward and aft shocks around the buffer ring were

experienced during mooring operations in guaty winds.

(c) High Mast

Coincident with the rapid development of rigid airships for intercontinental

travel in the 1920's was the design of a high mast.

This ayrtem rerulted

in the elimination of a hangar as a necearity for airship operations, thereby
providing a rolution for more efficient (both operationally and economically)
mooring hardware that could be made available at a-veral terminal locations
(see Figure 1-8). This apprtach, however, was not devoid of drawbacks. A
moored airship was, in fact, always being flown at the mast. Consequently,
an on-board flight crew was a continuous requirement. In addition, undesirable air currents were occh. )nally encountered at the mooring height,
thus causing extreme airship attitudes.
In the same decade, the U. S. Navy entered the rigid airship world with
the delivery of the ZR-1 Shenandoah in the fall of 1923 and the ZR-3
Los Angeles one year later. Accommodation in the form of a 100-foot high
mast was provided at Lakehurst, New Jersey (see Figure 1-9). A sequential
description of the airship's operations at this site is as follows:
1. The mast and airship are prepared for the mooring
operation.
2.

When all is ready, the airship approaches the mast into

the wind.

3.
4.

When near the 500-foot circle, the main mooring wire is

dropped.
The ground rrew connects the airship and mast wires.

5, The airship then rises until the mooring lines are taut,
discharging ballast if necessary to ac;omplish this.
6 . The main winch starts to haul in the airship.
7. After the main hauling line is taut, the left yaw line
i s let down on a messenger block carrying the end of
the line to the mast cup.
8. The same operation is repeated for the right yaw line.
9. When the a i r ~ h i p ' syaw lines are coupled to tne mast
yaw lines, they are cast a d r ~ f tirom the mast platform
and hauling is begun.

10.

Each mast yaw winch is operated until a predetermined

mark on its guy appear8 at the snatch block anchorage,
which indicates that there i s f u r t enough line between the
snatch block8 and the bow of the d r r h i p to aUow the
airship's cone to be brought down into the mast cup,

The

mart yaw winches a r e than ~ t o p p s dand the liner held.

11. hthe airship's cone i8 about 25 feet from the mart CUP,
the speed is reduced and maintained "deadn .low.
12.

The main hauling line continues t o draw the airrhip forward and down until the airship's cone enter8 the revolving
cup on the mast and locks itself into place with the three

13.

spring locks.
When the airship is secured to the mast. all airship Uneo
are returned to the airship.

14.

The airship is immediately readied for flight qo that an

emergency unmasting could be accomplished if a situation
required it.

15.

Ballast lines and the tail-drag are hooked up.

T h e egress operation is as follows:

1.

The airship is trimmed and weighed ~ f light

i
so that it
will rise immediately after relccrse.

2.

The release pendant is slacked off a

Sew

inches to allow

movement of the cone in the mast cup.

3.

The releasing hook is tripped, and the airship rises carrying the releasing pendant out through the ram and cup.

4.

The releasing pendant is retrieved and secured in the

airship and the tail-drag is dropped.

Fifteen ground personnel were required for high mast rigid airship mooring
l~prrations.

(d) USN "Stubn or Expeditionary M a t (for Rigid Airships)

In the late 1920's. the U. S. Navy became interested in the
expeditionary mast.

8 tub

or

I t had several advantages over the high mast.

Since

the s t u b mast was designed for quick assembly and disassembly, it could
be made transportable.

This made it usable for temporary mooring-out sites

(see Figure 1-10). The stub mast's low height meant that the airship would

be moored horizontally a few feet above the ground. A detachable castel.ng,

pneumatic wheel was designed for attachment to the aft power c a r . This
allowed the airship to swing around the mast without damage.
some conditions would cause the airship to kite.

Hcwever,

Various systems were tried

to counter this phenomenon such as drag chains, drag wheels, and railmounted mooring-out cars.

All of these concepts met with limited success.

(el Self-Propelled Mobile Mooring Mast (for Rigid Airships)

To facilitate ground handling of the large rigid airships, the U. S. Navy
experimented with a 100-ton. self-propelled, mobile mooring mast (see
Figure 1- 11). This pyramid mast was 60 feet on a side and was mounted on
crawlers.

The wide base and mass of this mast overcame the overturning

moment imposed by moderate wind loads on the rigid airships.

By mounting
each corner of the triangular base on crawlers, and through the use of a
self-contained power source, the mast unit was able to traverse the

Lakehurst terrain s~ccessfully A similar self-propelled mobile mast was

used on the Akron and Macon airships in Akron, Ohio.
( f ) Rail-Type Hauling-Up and Mooring-Out Circles

The U . S. Navy rigid airship program expanded dramatically in the early

1930's with the addition of the ZR-4 Akron and the ZR-5 Macon to the
fleet.

Ground handling equipment and techniques had improved, but further

development was required such as:

1.

A method of eliminating the hazardous transfer of an airship

from a fixed mooring mast to a mobile mast for docking

operations

Figure 1- 12

- Rail-Type Hauling-Up and Mooring-Out Circles ( 1930)

, locomotive-powered , mobile mooring

4.

A rd-mounted

5.
6.

A rail-mounted stern handling beam coupled t o

mast.

A second locomotive mounted on the hauling-up circle to

swing the s t e m beam.

The airship was towed in or out of the hangar secured between the mobile

mooring m a s t at the nose and the 178,000-pound s t e m handling beam.

mobile mast would be stopped a t the center of the hauling-up circle.
stern beam was transferred from the

The
The

hauling-up circular track to the

straight track by means of jacking trucks.

The s t e m locomotive would po-

sition the s t e m beam a s required for the docking or undocking operations.

If the airship were to be moored out, it would be positioned into the wind
and disconnected from the s t e m beam.

A taxi wheel supporting the aft

part of the airship was attached, and then the mobile mast would pull the
airship out to the mooring circle.

i-

Belly Mooring Mast System (Non-Rigid Airships)

In the late 19201s, The Goodyear Tire & Rubber Company developed a belly
mooring system that was unique to its commercial airship fleet. Because of
its limited load sustaining ability, it was eventually replaced by an expeditionary mast as the main mooring system. The belly mooring system (see
Figure 1-13) consists of a metal disc mounted in the underside of tne airship
envelope approximately half way between the nose and the front of the car.
Several cables attached radiate from the periphery of tho disc and have their
ends attached to envelope finger patches.

A gimbaled spindle is mounted in

the center of the disc, with a short pull-in cable attached to it.
A modified bus (see Figure 1-14) was the original mobile ground support

vehicle.

I t contained cornpartment s to carry auxiliary blowers, power sup-

plies, and tools.

Facilities to accommodate the crewmen and their luggage

were also provided inside the bus.

collapsible mast.

Atop the bus was mounted a short

When erected, it was anchored to the roof of the bus;

outrigger wheels on eac'r side of the bus were engaged for lateral stability.
A cup and locking device were attached to the top of the mast.

The airship would land to the ground crew and be held in place.

One man

would pull on the tail lines to raise the belly mooring disc a few feet higher
than the top of the bus-mounted mast.

Linemen would man two nose lines

to keep the nose of the airship steady and into the wind.

A mast man was

positioned on the mast to direct the spindle into the cup.

He would thread

a pull-in rope down through the cup to a pull-in man rtanding alongside
the bus on the grou..il.

The bus would be driven under the nore of the

airship, a t which time the m a s t man would couple the ground pull-in rope
to the short pull-in cable orr the belly mooring disc.

The pull-ir. man then

pulled down on the rope at the same time the tail line man slowly slacked
off his pull on the tail line. This allowed the nose of the airship to slowly
lower until the spindle slid into the mast cup. The mast man then locked
the spindle in the cup, thereby securing the airship to the mast.

With the

airship secured to the bus mast, the bus could be driven to any location on
the field o r into a hangar if men were put on tail lines to maintain directional stability.
Though the buses used in the early operations have gradually evolved into
a modem configuration, the mooring operation described above has remained
the same Iaee Figure 1- 15)

AFTER WORLD WAR

a.

Expeditionary Mast
An air-transportable mast was developed for the Navy by Meckum Engineering, Inc. (see Figure 1-16). The mast was an aluminum structure supported
by steel cables and anchors.

By removing or adding sections, the mast

could accommodate models SG , M , or ZPC airships.

Figure 1-17 shows the

anchor layout of the system.

A similar mast was developed for Goodyear's

commercial airship operation (see Figure 1- 18).
A description of the mooring technique used with expeditionary masts fol-

lows :

1.

Right and left nose lines and a pull-in line attached to the
nose of the airship hang free during the landing approach.

2.

The airship is flown upwind to the g a u n d crew.

Linemen
grab the nose lines and spread them out approximately 45

degrees to the airship.

ping the airship.

The ground crewman assists in stop-

Once the airship is stopped, the nose

lines are further spread 90 degrees to the airship. Sufficient tension is then maintained on the lines to keep the
nose of the airship into the wind.
3.

Another group of ground crewmen called the car party moves

in around the airship car. Their responsibilities include
ballasting and maneuvering the airship as required.

ORIGINAL PAGE IS
OF POOR QUALrrY

SECOND MCHOR
LOCATION

OUY C A K t

rae WI CAUI
ITAND 1 PLACES

BETWEEN

mcnous
2s' R

.A9

CENTER
POINT
VERTICAL

CENTERANCWR
ROD EYE
TO? OF

GROWD LINE

4"

Aw

/-

CtntEa LINE

tar

AND ANCHOR

- w ~ w

Figure 1-17

- Ar~chorLay.otit (Reference i i )

'8.

w@g

4.

Directing the ground handling operation froar a position

under the nose of the airship stands the crew chief.

5.

The airship is maneuvered to a position 50 fect downwind

from the mast.

6.

A t this point, the mast and airship pull-in lines are connected.

7.

The mast p a - i n line is cxtended until tension is experienced

in the line.
8.

A four-point mooring control is now effected.

a.

Nose linemen pull right and left on the nose lines for cup
alignment.

b.

Pull-in men pull the airship forward tcrarard the mast cup.

c.

The pilot uses reverse thrust to keep the airship from

ovemding the mast cup.

9.

The airship is eased forward until the airship nose spindle mates
with the mast cup, a t which time a top man on the mast throws a
locking lever engaging four dogs into a groove on the spindle
securing the airship to the mast.

A total of 16 ground personnel was required.

b.

Mobile Mast
Since the rigid airship self-propelled masts were too large for the non-rigid
airships, a smalle,- towed mast was developed prior to World War 11.

As

airships bf -3me larger. modifications and improvements were made to accommodate the new airships.

Various types of mobile masts are described

below :
1.

Type 111 mast

- weight of

39,000 pounds, used with ZS2G-1

and ZSC-21314 airships

2.

Type I V mast

- weight

of 44,020 pounds, used with ZPC-2/2VJ,

ZSZG-I, and ZSG-21314 airships

3.

Type IVB mast

4.

Type IVB mod mast

5.

Type v tnast (see Figure 1- 19) - weight of 128,670 pounds,

used with ZPG-2laW and ZPG-3W airships

weight of 47,900 pounds

weight of 55,900 pounds

Ground handling maneuvers are affected by many variables such as shifting of wind velocities, ground effects, hangar effects, variable mule line
tension

tractor speed and direction, and mule speed and direction.

Table 1-1 [Reference 10) reflects the mast and airship mooring wind limitations
imposed by tale Navy while utilizing the various mobile masts.
is assumed to be colinear with the major axis of the airship.

The wind direction

The table assumes

no accounting for side loading.

TABLE 1-1

--

- MAST AND AIRSHIP WIND SPEED MOORING LIMITATIONS (MPH)

Airship condition*
ZPG-3W
3

Mast
1A

1B 2

78 71 58 14 58

IVBmod
IVB

IV
I11

- - - -

- -

- - -

1A

ZPC-212W
1B 2 3

ZS2G-1
1A

1B 2

ZSC-21314
1A 1B 2 3

66 66 66

12

- - - -

63

58

42

12

56 66 60

14

66 66 66

63

54

36

12

66 66 55

14

66 66 65

32 12

66 61 52

14

46 28

11

61 52

49

- -

14

14
66 66 61 14
58 58 38 13

Mast dogged - airship free to weather vane.

1B: Mast undogged (tied to tractor) - airship free to weather vane.
2:
Mast towed and maneuvered at 5 mph with a i r s h p free to
weather vane.
3:
Mast undogged (tied to tractor) - standard docking and undocking
4.
hlast undogged (tied to tractor) - upper tube extending or retracting.
1A:

c.
-

hfobile Winches (Mules)

The K-type airship required from 50 to 100 men, depending on wind velocity
and direction, for ground handling.

The Navy became interested in de-

veloping a technique that could reduce this manpower requirement, which

led to the development of mobile winches, commonly called mules (see
Figures 1-19 and 1-20). These units are basically four-wheel drive, fore and
aft steering tractors with a winch mounted on the back. The Navy referred
to a 30,000-pound type as an MC-3 (see Figures 1- 19 and 1- 21) and a lighter
17,500-pound type as an MC-4 (see (see Figure 1-20)

Heavy takeoffs and landings on non-rigid airship main landing gears were
standard practice by the beginning of World War 11. The installation of
reverse pitch propellers provided the pilot with the capability of braking
the airship.

Integrating these innovations with the mobile mast and mules

resulted in landing and mooring procedures as follows:

1.

The slightly heavy airship lands into the wind.

2.

A t touchdown, the pilot applies reverse thrust to slow the airship.

Fieure 1-20

BLACK AND WHITE FHOTOGiiAFk4

Commercial Airship Grouttd Nand!ing

Equrpmcnt { R o m e . Ita'lyf , 1973

- Goadyear

Mulea otationed on each side of the approach end of the

landing area swing in and run parallel to the airship.
Linemen run in and pick up nose Lines and spread them out.
The mules move in and the winch cables u e connected to
the nose b a s .
Tendon is taken on the winch cables, and the mules
assist

ill

bringing the airship to a stop, a s required.

The mules are driven outward and abreast of the airship

nose.
The airship is held in position by mule winch cable tension,
pilot engine, and empennage control.
The mobile mast is brought into and stationed in front of
the airship until the airship pull-in line is coupled to the
mast pull-in line.
Slowly. the airship is winched in to the mast until the nose
spindle locks into the mast cup.
Thc nose lines are then disconnected fron the mules and
stored out of the way of the airship.
The mast tractor tows the mast and airship to a safe
position in front of the airdock.
The mules proceed to each side of the airship tail, where
tail lines are attached between the airship tail handling
points and the winch cables.
Tension is taken on the winch cable tail lines.
When all is ready, the mules pull the tail into the wind
as the mast is maneuvered until the airship lines up with
the airdock.

The airship is then moved into the airdock

and secured.
Those Coodyear airship operations bases equipped with hangars (Houston,
Texas and Rome, Italy) still use the MC-4 type mule for docking and
undocking

3.

MARITIME EXPERIENCE

a.
-

General
In order to completely integrate airship ser*Aces into Naval operations, several
attempts have been made to develop hardware and operational procedures that
would accomplish this goal. This objective has been manifested In several oreas :
ship-mounted masts, aircraft-carrier operations, and water takeoffs and landings.

b.
-

Ship-Mounted Masts
The only mast ever to be erected on a ship was a reproduction of the Lakehurst
high mooring mast on the U S .S Patoka (see Figures 1-22 and 1-23) A sister
ship, the Ramapo, had been scheduled for a mast but this was never accomplished. Originally classed a s an oiler, the Patoka was delivered in 1919. Its
overall dimensions were 463.25 x 60 x 26.25 feet (mean draught) with a displacement of 5375 tons.

--

. .

The Patokt3 was equipped with two 80-foot steel lattice-work booms. The horizontal angle between each bcom and the ship's centerline was 60 degrees from
aft. A small boat carried the haul-in line end astern of the Patoka. With the
Patoka steaming 45 degrees into the wind, an airship would fly across the
haul-in line. A grappling hook suspended from the airship would snatch the
haul-in line, and slack would be taken up. The Patoka would then turn into
the wind. The rest of the mooring would proceed in the manner a s previously
described for land-based high masts. The only airships to use this mast were
the Los Angeles, Shenandoah, and Akron, with the Los Angeles' 44 moorings
being the most numerous.
Though it enjoyed only limited success, the Patoka experience precipitated
other designs such a s the one shown in Figure 1-24. This concept was never
developed.
c-. Aircraft Carrier Operations (References 12, 13)
Though the Los Angeles landed aboard the aircraft carrier Saratoga on January
27, 1928 and despite the occasional airship landing on a carrier deck during
World War 11, a serious investigation into the feasibility of airship fleet operations from a carrier was not initiated until early 1950. By the close of the following year. however. all Navy airship pilots were required to qualify for
carrier operations.

The deployment of a carrier deck landing party is shown in Figure 1-25. During
landing and takeoffs, the carrier would maintain a heading into the wind
(210 deg) and vary its speed to provide a relative wind velocity of 24 to 28
knots over the deck. The following procedures would then prevail:
Landings :
1. As the airship approaches the carrier from astern, the pilot
attempts to have the short lines reach the carrier deck so
that the two men at station (A) can each grab one line and
rush it to the short line crew ( D ) a s the airship moves in.
2. When the rear end of the airship car is over the carrier deck,
the drag rope is dropped and taken by the drag rope crew (B)
to hold back.
3. When the forward hand rail of the car comes within reach,
the car crew (C) takes hold and tries to keep the landing
wheel down on the deck.
4. During this time, the short line crews ( D ) help to hold the
airship back and also try to keep it near the center of the
deck.
5. With the airship now in the hands of crews (B), (C) , and
(D! , the bow is brought down so that the two catwalk ropes
(R can be connected to the short cable pendants by the
men ( E ) , after which the catwalk crews (F) take over (two
short cable pendants are added at the short line patch
assembly for carrier operations).
6. This relieves crews (D), and the short lines are brought in
toward the car.
7. If the airship is to be held on deck for an extended period
of time, a center rope or cable (R2) is hooked into a strong
point at the forward end of the car.
Takeoffs :
1. The LSO signals the pilot to rev up the engines and then the
crews ( B ) and (C ) to clear the area.
2. The LSO then signals the men (E) to pull the quick releases
of the catwalk ropes, leaving the sirship free to take off.
3. The airship takeoff is with a turn to the port, away from the
carrier island structure.

ORIGINAL PAGE IS
OF POOR QUALITY

AFT END OF FLIGHT DECK.

!
I

'

PULLEY ON DECK

I I

Figure 1 - 2 5
(A)

Disposition of Landing Crew on Carrier Deck

- Men near aft end of carrier deck to catch short lines and rush them to
crews ( D )

(B) - Drag rope crew, three o r four men

(C ) - Car crew (forward hand rail), three or four men

(D) - Short line crews (six to eight men each)
(El - Two men each to connect catwalk ropes (R1) on landing, one of them to
operate quick release at takeoff
(F) - Catwalk crew, below deck level ( 10 to 1 2 men each)
(G) - Safety man with hatchet to cut catwalk rope in case quick release fails at
takeoff
{LSO) - Landing officer
(R1) - Catwalk ropes
(Rz) - Center
rope o r cable

4.

The two safety men ( 0 ) are there to cut the catwalk ropes
in case of a quick-release failure

The total ground party crew numbered 47 to 57 men.

3

Carrier suitability tests of the XZS 2G- 1 airship were conducted aboard the
CVS class aircraft carrier U .S .S. Antietam duxdng May and June, 1956.
These tests were to determine the ability of the ZS2G-1 a h h i p to operate
beyond the useful range of the airship from land bases, Results of the test
were favorable. It was concluded, however, that operations in conjunction
with smaller carrier types would require the utilization of inflight replenishment features for fuel, armament, personnel, and provisionc.
The K-type airships were the only models qualified for aircraft carrier operations (see Figure 1-26). The larger airships that followed were capable of
extended operations through airborne replenishment systems, tnereby
obviating the need for carrier deck landings. Although thC requirement of
pilot qualification was maintained, no ,?xtensive operational use of aircraft
carriers as mobile airship bases was u ldertaken.
Watei* Takeoffs and Landings (Refere~..c;i!
i4)
The U. S. Navy, recognizing that thc possibilities of water operations had
not been fully explored, experimented in 1939 with the 5-4 airship. Two
inflated strips mounted along the bottom of the car were used for flotation
when the airship landed on the water. No formal results of these experiments
were docilmented

Goodyear experimented in 1.930 and 1931 with water landings and takeoffs
using both single and double floats. It is reported by personnel who flew
both flotation devices that the twin float system provided more stability,
especially when side gusts were encountered. The twin floats, however, were
set only ihree to five feet apart.
In 1946, Goodyear was &wardeda Navy contract to conduct an airship i m -

provement test program. One item of the contract was to investigate water
tekeoffs and landings utilizing the Navy's L-type airship, L-1. Tests on
single and twin fixed floats were conducted. A single swivel float concept
was investigated but never tested.
The stated objectives of these tests were to determhe the limiting wind and
water conditions for water takeoffs and landings;

to develop a flying technique to land on the water without the aid of ground
personnel; and to determine the effect of the arrangement on speed and fuel
consumption.
In general, the single fixed float was found to be unsatisfactory because of

its poor stability in lateral rolls. Twin float operations, however, with the
floats 10 feet apart, demonstrated greatly improved stability against roll (see
Figure 1-27). On at least one occasion, however, the airship rolled far over
on the starboard side and partially submerged the starboard engine. Although
the report concluded that the results obtained exceeded expectations, no further development of floatation systems for airships was pursued by tlie Navy
or Goodyear.
4.

SUMMARY
The historical development of ground handling systems has been adversely
impacted by two items: (1) the lack of low-speed controlability of an airship;
and (2) the large surface area of the airship.
In order to compensate for the first item above, airships have traditionally
been designed to accommodate external loads applied through ground handling
Snet to some point on the ship.

The availability of large numbers of ground

personnel was a prerequisite for airship operations.

The large rigid airships

built in Akron typically required 300 men for ground handling.

A s the airshi9

industry evolved and large non-rigids became dominant, the desire to develop
a ground handling approach that was less dependent on manpower grew.

This

resulted in the mobile mast/mule system, which still remains a s the state-of-theart for ground handling.
Once the airship was on the ground, its susceptibility to weather conditions
became obvious. Early airships were placed in hangars to avoid environmental
effects, but the limitation this placed on the airship as a viable transportation
mode was intolerable. Hence, a variety of experiments was undertaken in
order to develop a mooring system that would permit the airship to sustain
most weather conditions. The eventual outcome, when the various cable systems and mast types had proven unsuccessful, was the bow mooring concept.
While this approach still has limitations, it has proven to be the best solution
to date.

1-44

1- 7

1 -1irsf)ip l';lltints Off' f r c r r n T,:iE:c I. ric*

SECTION 11 - THE MPA VEHICLE CONCEPT

GENERAL
The baseline MPA design used in this study is the 875,000-cu f t ZP3G model
a s defined in References 15 and 16 prepared for the Naval Air Development
Center by Goodyear Aerospace. Pertinent extracts a m provided below.
ZP3G CONFIGURATION
The conceptual design of the ZP3G is shown in Figures 2- 1 and 2- 2. Its
overall length is 324 f t , the maximum diameter of the envelope is 73.4 ft. In
this configuration, the propulsion systems are shown in the cruise or convenCionnl takeoff position. The forward propellers, however, do rotate plus or
minus 90 Oeg and the stern propulsion system rotates a plus 90 deg for VTOL
operation.
The conceptional design uses four ballonets. The forward and aft ballonets
serve to trim the airship in addition to compensating for large altitude
changes. The center ballonets permit nominal changes in altitude. which are
repeatedly required in some missions, without affecting the airship trim con dition. Ballonet configuration is governed by geometric restrictions and size.
To maintain trim fore and aft. ballonets are n e a ~ l yequal in volume and location relative to the center of buoyancy. The catenary system on the ZF3G
restricts the size of the forward ballonet ; therefore, the geometry of the aft
ballonet is controlled. The remaining ballonet air volume i s mode up in the
center section of the envelope. outboard of the car suspension system. Although the ballonets are less efficient weightwise, the huge surging air mass
plus the flapping and flexing of the ballonet fabric, during partial inflation,
is minimized when the ballonet consists of several compartments.
Bow s t i f f e n i n g and t h e X-type tail for t h e ZP3G concept a r e of conventional dcs i g n . a s flight dynamics a n d performance c h a r a c t e r i s t i c s of a similar sized N airs h i p with t h i s volume a n d configuration have beet1 s u b s t a n t i a t e d .

Furtherrnorc.

the X-type empennage provides the necessary ground clearance for short
takeoffs witb a reuso~ableangle of attnck. A base structure for the fin suse s fin catenary and
pension cables is an added feature since it e l l n ~ i n ~ t the
reduces the number of brace cables. In the concept. the car is supported at
the floor level by the i n t e r n ~ land external catenaries. A separate catenary
system for the forward propulsion system divorces the powerplant from the

Figure 2- 1

- Inboard Profile
P(4

Figure 2- 2 - ZP3C Airship

car to permit a more stable platform and reduce the noise level for the crew.
Location of the forward propellers in this position is also necessary t o balance
the thrust forces during the hover mode of operation. The stern propulsion
system is mounted on an inverted V tail, which provides the tilt capability for
the propeller. The V tail also supports the deflectable ruddervator, which
greatly improves control effectiveness in both hover and low-speed cruise via
ruddervator deflection in the propeller slip stream.
3.

MAJOR CHARACTERISTICS
Principal characteristics of the ZP3G conceptual design are listed in Table 2- 1.
The e ~ v e l o p evolume of 875,000 cu f t is the design volume. With Dacron fabric, the increase in volume due to stretch is assumed to be two percent. A
ballonet volume of 216,250 cu f t permits the airship to fly missions a t 5000-ft
altitude. Under standard atmospheric conditions, it l i m i t s the ballonet ceiling
to 9700 ft. The dynamic lift of 8500 lb in hover is established a s follows. The
total propeller thrust a t maximum power setting is 12,500 lb. On the stern
propeller, 1500 lb of thrust is reserved for low-speed attitude control; 2500 lb
of excess thrust i s required for acceleration from hofer to climb, leaving a
total of 8500 lb for dynamic lift. A 3900-lb negative lift is also available with
the propulsion system to counteract excess static lift during landing. This
capability is provided by rotating the forward propellers down 90 deg. The
3900 lb is limited by an assumed maximum acceptable negative pitch attitude
of 10 deg for the vehicle and not by the available propeller thrust. The
pitching moment resulting from this force is counteracted only by the metecentric center of the airship since the negative thrust of the stern engine is
minimal in this mode of operation. Again, this negative lift feature should be
used only when necessary because. the loss of thrust on the stern propeller
greatly reduces the attitude control capability. The gross weight of 60,664 lb
could be increased 3200 lb when a vectored thrust STOL operation is incorporated. This, in turn, would increase the useful payload to 25,704 lb.
The performance summary is listed in Table 2-2. Illaximum speeds are taken
at sea level using the takeoff thrust of all engines. Range i s listed at 40 and
50 kncts minimum speed. Although the 40-knot velocity obtains an additional
100 naut mi. the 50-knot speed reduces flight time by 25 percent. The maximum available horsepower for climb occurs at 55 knots. However, catenary
limitations restrict the pitch angle of the airship to 30 deg; with this limitation,
the velocity for maximum climb is 71 knots. The air system, proposed in the

TABLE 2-1

- MAJOR CHARACTERISTICS

Design item

Characteristic

Envelope volume

B allonet volume
Fineness ratio
Beta factor
Static lift a t 2000-ft altitude
Dynamic lift
Maximum gross weight
Weigh: empty including fixed
mission payload
Useful load
Powerplant
Allison GMA-500 (3)

800 SHP each

concept, limits the maximum rate of climb to 2400 f t per minute; therefore,
climb at the normal rated power is restricted unless the air valve system
discharge rate is increased.
For conventional takeoff, the vehicle attitude assumes a maximum pitch angle
of 6 deg to ensure a margin of safety for tail clearance. The performance for
acceleration and deceleration uses maximum power at sea level. To accelerate
from zero velocity, the airship is considered to be neutrally buoyant.

For the

time to decelerate, from the 97-knot maximum speed, a six-second transition

phase is assumed to change the propeller from zero to full reverse thrust.

In

Table 2- 2, range and endurance assume that the vehicle is operating at the
2000-ft altitude with a useful payload of 6370 1b. Liftoff is STOL with vectored
thrust, and the performance is based on 90 percent of the maximum fuel load of
23,750 lb.

TABLE 2-2

- ZP3G PERFORMANCE SUMMARY

Design item

Performance

Maximum speed (8500 lb heavy)

94 knots

Maximum speed (8500 lb heavy, rear engine only)

(maximum continuous power)

52 knots

Maximum speed (neutrally buoyant )

97 knots

Range at 40 knots

3407 naut mi

Range at 50 knots

3290 naut mi

Best climb velocity

71 knots

Rate of climb at maximum power

3375 ftlmin

Rate of climb limited by air system

2400 ftlmin

Conventional takeoff distance (8500 lb heavy)

1025 ft

Velocity at liftoff

50 knots

Distance to clear 50-ft object

2400 ft

Velocity at clearance height

65 knots

Time to acceieraie to 40 knots (neutrally buoyant)

15 sec

Time to accelerate to 92 knots

( 95%maximum speed, neutrally buoyant)

64 sec

Time to decelerate from 97 knots to 0 knots

(neutrally buoyant)

55 sec

Altitude liinit

5000 ft

B allonet ceiling

9700 ft

Endurance: less than or equal to 25 knots

101 h r

SECTION 111 - MOORING SYSTEM ALTERNATIVES

GENERAL
Several potential mooring systems could be utilized with t h e maritime patrol airship with varying degrees of effectiveness.

To assess those systems that have

the highest probability of success, it i s first necessary to identify all candidate

solutions and perform a preliminary distinction for t h e airship mooring systems
that warrant additional investigation.
The approaches to securixg the MPA while on the ground can be divided into
t h e following categories:

those that secure the airship a t a single point and per-

mit the vehicle to rotate about that point a s required due to wind loads; those
that completely restrain the MPA from motion while on t h e ground; those that
protect the airship from being subjected to the weather elements.

In addition,

those that have maritime applications a r e asressed.

A rudimentary description of each of these systems i s provided.

Details of

structural and operational analyses a r e givel: in later sections of this report.

SYSTEMS PERMITTING ROTATION
Bow Mo0rir.g
Bow mooring the MPA requires the securing of the airship by the bow t o a mast
with the airship weight near equilibrium but slightly heavy.
mast types are the stick mast and the mobile mast.

The two standard

The stick mast i s transport-

able and requires a system of cables and ground anchors in order to achie-de
structural acceptability.

The mobile mast i s normally employed a t a hangar site.

I t is a pyramidic shaped structure with a triangular base that is on wheels, I t

i s used primarily to move airships to and from the hangar and is normally towed
by a tractor o r ground handling mule.
A significant attribute of the bow mooring system is that i t does not necessitate

any structural changes to the airship.

Nose battens that are developed for aerodynamic loads a r e equally effective at transferring bow mooring loads over a

sufficiently large envelope area. Since no rolling moments are introduced by

bow mooring, no changes are required in the envelope and suspension systems.
A more detailed oeprational description of previous and existing bow mooring

approaches i s given in Section I .

b.
-

Placing a mast on the underside of t h e envelope at a point between the bow and
the control car constitutes belly mooring.

The advantages to this sytem over

bow mooring a r e that it requires a shorter mast and requires a smaller area for
rotation.

The operational approach i s similar to baw mooring.

The primary drawbacks a r e that i t precipitates a number of changes to the airship. At the very least, some type of attachment capability must be built into
Since this point i s below the centerline of the airship, rolling

the envelope.

moments are introduced into t h e airship that must be dissipated through t h e envelope and suspension system to the mast.

Therefore, stronger envelope fabric

and increased structural capability in the catenaries is mandated.

For the MPA considered in this report, a design change incorporating a tricycle
landing gear was provided in order to counteract the effects of the rolling moment.

The single gear was placed on the car a t a point 104 feet from the nose,

while the aft gear are 148 feet from the nose and are laterally displaced from
the centerline a distance of 30 feet.

Though the use of anything other than

a single landing gear is uncommon, it is not without prededent.

The ZPG-3W,

the largest non-rigid airship ever built, had a tricycle gear.

c.
-

Center Point Mooring

The concept of center point mooring is simply the extension of belly mooring to
its extreme.

This approach was an integral part of the original Goodyeer heavy

lift airship design that incorporated a tail-less symmetrical envelope and four
rotor systems attached to an interconnecting structure (Reference 36).
When an airship is moored about its center point and is struck by the wind,
it will reach an equilibrium angle that does not coincide with the original wind
angle.

For example, the heavy lift model mentioned previously had an equilibrium

position whereby the main axis was normal to the wind direction.
to its symmetric shape.

This w a s due

For the MPA, which has a traditional airship profile and

is equipped with tail surfaces, t h e equilibrium position i s 40 degrees to the wind

direction.

This, in effect, becomes a total restraint system in which the direc-

tion of the wind is a constant.

in this report.

Therefore, this approach is not f u r t h e r addressed

3.

COMPLETE RESTRAINT SYSTEMS

-a.

Car Secured
The firm attachment of the MPA's control car to the ground can be effected b y
providing four landing gears placed on outriggers a t some variable distance
from the airship centerline - which, in t u r n , a r e secured to the ground

- or by

providing direct attachment of the car to the ground through the use of cables
and the replacement of the landing gear with a skid arrangement.

A s with any mooring system other than bow mooring, t h e loads that t h e airship
i s subjected to while on the ground must b e transferred through t h e envelope
and suspension system to t h e ground. The additional disadvantage with total
restraint i s that no energy can be dissipated through motion- This will result
in significant structural penalties should t h e airship design be driven by this
approach to mooring

Envelope Secured
A secoild possible total restraint system would be to directly secure the envelope

to the ground.

This would be accomplished by attaching external catenary

curtains on each side of the envelope and providing cable attachments to anchor
points on the ground.

Though this concept would relieve the envelope and in-

ternal catenary system of exposure to mooring loads, it creates several other

problems.

There would be considerable additional drag; there would be the

potential interference with the operation of the forward propulsion units; there
would be logistic difficulties in actually providing cable attachments to the curtain and in maintaining ground location while the cables were being attached to
previously set anchors.

4.

PROTECTIVE SYSTEMS

a.
-

Wind Screens
To provide adequate protection from wind loads, a wind screen must be sufficiently tall to direct the wind above the airship.

A pr~liminarypragmatic investi-

gation based on pressure distributions of an airdock-style building (Reference 39)

suggests that a 76-foot vertical wall would be required (see Figure 3-1).

Based

on the overall length of the MPA, the total wall area per side would b e approximately 25,000 square feet.

The structural requirements for the walls alone

would appear to outweigh ally advantage that this approach might have.

I t is

Figure 3-1

Barrier Height Requirement

f u r t h e r compounded, however, by the following:

t h e airship must still b e secured

within the confines of the two walls to account f o r wind angles that a r e colinear
to the airship and to resist upward motion caused b y t h e negative p r e s s u r e a s a
result of the air flow above the wall; the need for a mobile ,.last to place the airship between t h e walls; and t h e permanency dictated by t h e size of the s t r u c tures.
b.
-

Hangars
The ultimate a p p r o x h to airship mooring is to provide all-weather protection
with a hangar.

Though undoubredly the most expensive approacl-, to mooring,

t h e r e a r e severai benefits that accrue to the operator with a hangar.

These

include the virtual elimination of mooring-related airship damage; the convenience of maintaining a single facility for erection and maintenance needs; and the
utility of a large protected area to service other aircraft.
An appropriate hangar for the MPA would have the following attributes:

Dimensions:

Length
Width
Height

425 feet
150 feet
128 feet

Structural:

DesignedforlocationanywhereincontinentalU.S,A,
Definition of major structural elements include a concrete
floor (6-inch minimum) with anchor points (6000 Ib) laid
+ it on a 20-foot by 20-foot grid.

Architectural: Includes insulated roof and siding, some truck doors and
man doors, access to the roof, louvres, smoke curtains, and
SO forth.
Mechanical:

The mechanical services include conventional heating for

localized areas ; adequate lighting t 60 cycle power a t 120 v 1
240 ~ 1 4 6 0
v 480 v ; water and sewer; air
100 psi and
30 psi ( d r y ) ; overhead monorails (4000 pound) the full
length of the building with service platform and appropriate access ladders.

Main doors:

Sliding o r rolling type; entire front of hangar must be clear

when t h e doors are open.

A section view of a possible hangar is shown in Figure 3-2.

Additional cost

items required with airship hangar operations are a mobile mast and a pair of
ground handling mules.
The use of air-supported s t r u c t u r e s a s airship hangars is also being touted by
Environmental Structures, Inc. (ESI) of Cleveland, Ohio.

There has been a

precedent in this area, however, a s Westdeutsche Luftwerbung (WDL) has had

experience with an air-supported airship hangar (see Figure 3-3).

Unfortun-

ately, the hangar has twice been d m a g e d by high winds and has collapsed with
an airship inside.

The airship suffered considerable damage.

The advent of new materials has apparently marked the beginning of a new era
for air-supported s t r u c t u r e s , and experiences such as WDL's will not be repeated.

This is the claim of ESI and a description of their approach follows.

The advanced air-supporied structures concept was developed by Coodyear to

enclose l a r g ~areas economically. I t utilizes steel cables about five feet apart
as the main load-carrying elements. The film between the cables acts as the
gas barrier and can be anything from window clear to opaque.

I t i s dieiectric-

ally s'.aled t o the cables and usually comes in a double layer with dead air insulating space in between.

This insulating layer can be created o r eliminated

at will through the use of a special sill channel at the perimeter of the s t r u c t u r e .

To date, no size limitation has been encountered, and spans up to 1000 feet
have been investigated. The recommended width-to-height ratio for high
stability is 4-5 to 1. For the height krquired for the MPA, this translates to
a span wrdth of about 600 feet, making \he total coverage area 255,000 squzre
feet.

3- 6

Figure 3-2

Section View of Candidate Conventional Airship Hangar

5.

MAETIME SYSTEMS

-a.

Generd
Two types of maritime operations are discussed in Section I: aircraft carrier
operations and water landings and takeoffs. Since these capabilities have been
demonstrated in the past, it is unlikely that any worthwhile innovation could be
made.

Furthermore, remanning and refueling operations at sea have been dem-

onstrated by Navy airships.

b.
-

Sea Anchors
The feasibility of using sea anchors t 3 moor airships was the basis of a study
undertaken by Goodyear for t5e U.S. Navy in 1956 (Reference 17). The motivation was to develop a system whereby the airship would remain airborne at a
low altitude above the water while suspending ASW detection devices in the
water.

The design goal was to limit the airship to a four-knot drift in a 35-knot

The airship considered in the study was the ZPG1, which was the base
vehicle in the design of the MPA (see Figure 3-4).

wind.

The results of the study were gemrally positive.

It was anticipated that the

most risk involved would be during "blow-downs" resulting from sudden and
strong wind shifts.
recommended

Some type of flotation gear installation on the airship u:zs

the event the water surface was contacted.

This stcdy was initiated as an attempt. to overcome the control inefficiencies of

the airship at low speeds.

The predicted inherent capabilities of the MPA

should overcome these deficiencies.

6.

SUMMARY
1he purpose of identifying alternate m~oringsystems was to define those sys-

tems that warrant additional investigation as to their suitability for the maritime
patrol airship.

The following systems are subjected to a more in-depth review;

bow mooring, belly mooring, total restraint, and hangar systems.

Figure 3-4

ORIGINAL PAGE IS
OF PGbR QUALIm

Proposed Sea Anchor System on ZPGl (Reference 17)

SECTION IV

- STRUCTURAL ANALYSIS OF A FULLY RESTRAINED AIRSHIP

1. GENERAL
A first-order study of airship empty weights versus wind velocity for different

mooring concepts and structural concepts (different internal suspension systems,

envelope pressures, o r other attachment approaches) was initiated to establish
practical steady-state wind velocity 0peratil.g limits.

The following anal, ;is

is limited t r a static condition, and envelope deformation is not considered.

The

static analysis i s appropriate for fully restrained airship.

2.

STATIC AERODYNAMIC FORCES AND MOMENTS

The first task was to estimate the static aerodynamic forces and moments acting
on the different configurations for the differeat mooring concepis.

The static

data for these curves was selected from References 18 through 26. The type
and scope of data presented in tach reference are listed in Table 4-1.

The

model description, test Reynolds number, range of data collected, and any simulation of the ground effect a s indicated by the vertical velocity gradient are presented in T3ble 4-1.
In Reference 18, the authors considered that direct extrapolation by continuation
of the curves for model results to the Reynolds number of the full-size airships
is not justified or satisfactory, inasmuch as an extension of a curve too many
times its original length can lead to erroneous conclusions. They suggest instead that a more satisfactory method is to consider the flows about the bodies
for the two cases of model and full size to see if any critical change in the flow
is expected in passing from model scale to full scale.

For 90 degree yaw angles,

a section of the hull becomes circular, and two types of flow occur.

For Reynolds

numbers less than 4 to 5 x 105, based on diameter, the flow is characterized by

early separation.

For Reynolds numbers greater than this value, the flow be-

comes turbulent, and separation occurs further back on the cylinder. Once the
Reynolds number for this critical range has been exceeded, the flow in cylinder
tests has shown no marked changes with increasing Reynolds number.

Thus, i t

is believed that the flow over the full-size airships will be generally similar to
~11eflow over models tested above the critical Reynolds number range.

I t was

further pointed out that the effects due to the ground gradient should scale
almost directly with the larger Reynolds number.

The system of coordinates

O
R
E
W PAGE IS
OF POOR QUALITY
TABLE 4-1

- TYPE AND SCOPE OF DATA USED IN REFERENCES

selected is based on that used in Reference 18 and is repeated in Figure 4-1.

The data used from the references to establish aerodynamic loads for the analysis
are presented in Figure 4-2.

POSITIVE DIRECTION OF
AXES AND ANGLES IS
SHOWN BY ARROWS

Figure 4- 1 - Coordinate System

Figure 4-2 includes data presented as a curve from the extensive testing of a
large airship model of the Akron in a large wind tunnel at yaw angles from 0 to
180 degrees (Reference 181, testing of a mode! of the heavy lifter in the 7 x 10
wind tunnel at yaw angles presented as a c w v e from 0 to 90 degrees (Reference
21). testing of a model of the 2PN in a water basin at yaw engles from C to 180

degrees (References 22 and 2 3 ) . and wind tunnel tests of tethered balloon shapes

(References 24 and 26) The coefficient va'tues for the forces based or, V 213
are similar despite the different model fineness ratios and testing facilities and
techniques. The coefficient values from References 18. 21, 22, 23. 24. and 26

are most similar for Cy which corresponds to the largest force acting on an airship at yaw angles from 60 to 120 degrees. The second largest force acting at
yaw angles from 60 to 120 degrees is lift corresponding to minus values of C,.

ORIGINAL PAGE IS
OF POOR QUALrrY

trtlutd
Ref 18 - Akron

v a h1I7
2.2
2.0

Ref 21 Heavy Lifter

Re! 23 ZPN Water Tests A

Ref 22- ZPN

- Water Tests A .

~ . f24

- Navy "C" Balloon CZVS

Cx's.

C, '.s

1.4
1.2

1.0
1133

vel. Gradient A v hl,,

Vel. Gradient B V t h

Yaw Angle, Deg.

Yaw Angle, Deg.

Figure 4 - 2

1.6

Ref 26 - 1649 Balloon

T b Fins

1.8

.a

YW Angle. Deg.

Yaw Angle. Deg.

- Force and Moment Coefficient Values About Center of Buoyancy

of Airships with Tails versus Angle of Yaw (Pitch and Roll
Angles of Zero)

Agreement of the CZ values at 90 5egrces of yaw is very good between Reference

18, 21, and 22 with the velocity gradient B ivahl").

cient values at 60 degret

The difference in coeffi-

of yaw may be due to the differences in the values of

fineness ratio of the different models, the selected test velocity gradients over
the models, and the test H I D ratios (distance from groundlmodel diameter).
The least similar values are associated with the longitudinal forces that have
the smallest

eri1,ient values, and the values appear to be very sensitive to

the selected test velocity gradients and the test HID ratios.
The simi!arity of values for the moment coefficients based on Y from the different references is not always as good as for the force values.

The yawing mo-

ment coefficient, Cn, which corresponds to the largest moment, has fair correlation between Refezences 18, 21, 22, and 24 a t 90 degrees of yaw. The pitching
moment coefficient, Cm, is very sensitive to made1 fineness ratio and relative
tail sizes as can be observed from the data of Reference 18 a s compared to the
data from References 21, 22. and 23 at a yaw angle of 90 degrees. From these
data, specific coefficient values were selected at 60. 90, and 120 degrees of yaw
for use in the structural weights analysis.
Table 4-2.

The selected valugs are listed in

3.

LOADS ON A FULLY RESTRAINED AIRSHIP

-a .

General
A preliminary analysis was conducted to determine the loads imposed on the landing

gear due to winds acting on the airship when t h e landing gear totally constrains the
airship's motion.

For this first-order analysis, the airship is considered t o be a

rigid body with a rigid four-point landing gear.

The assumed distribution of the

landing gear forces in the different directions due to the different aerodynamic
forces and moments acting on the airship is listed in Table 4- 3. Sketches defining
the aerodynamic sign conventions follow this table.

The coordinates used a r e

further defined in Table 4-4 and Figures 4-3 through 4-6. The analysis determines
the landing gear forces due to the different aerodynamic forces and moments, proportions the forces between each of the four landing gear points, and superimposes
the values at each point of the corresponding components and ~ d d them
s
t o determine the total force values in the vertical, longitudinal, and lateral directions a t
each landing gear point.

The signs in t h e resulting equations were made so that

tensions between the landing gear and the constraint are positive (+).
This investigation is a pragmatic approach to the generation of a solution. Implicit with this are the assumptions that (1) the landing gear positions are at
the corners of a rectangle with the location of the CB at the center of that rectangle and ( 2 ) the stiffness of the the landing gear support s t r u c t u r e s are
symmetric with respect to both the X-Z plane and Y-Z plane.
b
-.

Vertical Landing Gear Forces

Transferring the rolling moments to the plane of the landing gear, the components
of the vertical forces can be determined by the sum of the morents due to the
values of C q v z i 3about y = 0 , and Z = 0; that i s , the intersection of verticzl
Y
centerline and the ground and ClqV (see Figure 4-3).

TABLE 4 - 3

- ASSljMED DISTRIBUTION OF LANDING GEAR FORCES IN

THREE DIFFERENT AXIAL DIRECTIONS
-

k r d m l e forcer Tkou@b CB
lan(:tudlarl

Vattieal

s,

4r
Cxq

Lateral

c.

21 J

CIPV

Loads d w to Lateral Force

213
cy9v
(Cad View)

(End V i e r )

TABLE 4 - 4

CP
.V

(Slda Vier)

C O O R D I N A T E SYSTEhf

T h e aerodynamic forces pass through the coordinates o i the CB

where:

~CB

"CB

B = 0 a t nose; (+) toward tail

y = 0 a t c e ~ t e r l i n e ;(+) centerline to starboard

Z = 0 a t ground level;

-0.

l o d e due t o L o n ~ i t u d l r v lForce
cxqvZ/'

located at:

=n

Load* due to R o l l i w
ltaont ClqV

A.

~ e r o d y n r i cm n t r About CB
Rollin@
Cltehl~
Yaw In8

(+) downward

Landing gear coordinates are :

Landing gear
A1

~ L G -~ Y L G ~

Figure 4-3

- Moments About

Y=O, Z=O; View Looking Forward Along Centerline

Assuming all four landing gear points share the vertical forces equally
(symmetrical stiffness), then these components are:
Vertical force at A ~ B, ~ A,* , B ~ =

ClqV

cyqv2/3(zLG

(YCB

- ZCB)

- VLC)

where: ZLG = 0

YCB = 0

ZCB = height of airship center of buoyancy above ground ( I t )

YLC = lateral locations of A1, B1, A2, B2 ( f t )

Tension = (+)
Again, transferring the pitching moment to the plane of the landing gear,
the components of the vertical forces can be determined by the sum of the
moments due to the valuer of
Figure 4- 4 1.

cxqv2I3about

lCB and Z = 0, and CmqV (see

Figure 4-4

- Moments About

lCB.Z=O, View Looking Port to Starboard

Assuming all four landing gear points share the vertical forces equally, then
the -:slues of these vertical force components are:

Vertical force at A

Where:

1'

A2, B2 -

C,,qV

--cxqv2 I3 (ZLG - ZCB)

(2)

lCB = distance of airship center of buoyancy from nose ( f t )

lLG = longitudinal location of A

1' B1, A 2 , B2 ( I t )

The vertical forces due t o the vertical loads.

c ~ ~buoyancy
v ~ and~ weight,
~ .

can be determined by summing only the vertical forces assuming the forces
are in a l i g ~ m e r ~(see
t Fig urc 4- 5 ) .

Figure 4-5

- Vertical Loads, View Looking Port to Starboard

Assuming all four landing gear pointr c e equally spaced forward and aftward
of the CB, they will share the vertical forces equally.

T h e values of these

vertical force components are:

Vertical force at A1, B1. A2. B2

- cZqv2I3- weight

= *;,V

Where: A p = difference in the densities of air and helium (Ib/cu ft)

w t = Weight of airship (Ib)

Superpositioning and adding t h e vertical components from (1) , ( 2 ) , a n d (3)
results in the total vertical landing gear forces at A1, B1, A2. B2 o r

Total vertical force at A1, B1, A * . B 2 =

c 1 ~ v + c y ~ v 2(zLG-zcB)
'3
+

Where tension a t restraint = (+)

c.

Horizontal Landinn Gear Forces

The horizontal forces in the longitudinal and lateral directions were established
in a similar manner.

Longitudinal landing gear forces were determined assuming

one-half of the yawing moment results in longitudinal landing gear forces and
the other half results in lateral forces; the longitudinal forces can b e determined
from t h e value of

cXqv2I3acting through

and about lCBand 0.2

(see Figure 4 - 4 )

and a 0.5 C q V acting abot:t a vertical centerline through the CB (see Figure 4 - 6 ) .
n

Figure 4-6

- Moments About

Vertical Axis througi. CB,

View Looking Down a t Airship

Arruming all four landing gear pointr r h r r e each of the longitudinal forcer
equally, then the total longitudinal forcer imposed by each landing point are:
Total longitudinal landing gear force. at Al,

Where a force forward

B1, A2, B2

(+)

The lateral landing gear forces were determined assuming the value. of CyqV 2 I3
and 0.5CnqV acting through and about a vertical centerline through the CB (see
Figure 4- 3) and 0,5C,qV

acting about l C and

~ Z=0 (see Figure 4- 4).

Assuming all four landing gear points share each of the lateral forcer equally,
then the total lateral forces imposed by each landing gear point are:
Total lateral landing gear forces at A1.

Where a force from port to s a r b o a r d

B1, A2, and B2 =

(+)

The aerodynamic coefficients to be used with the prior equations were presented
as curves in Figure 4-2.
4.

COIvlPUTER MODEL FOR FULLY RESTRAINED AIRSHIP

A computer model to evaluate the static loads developed at the gea? points in a

fully restrained airship mooring system was developed in accordance with the
equations presented in the preceding section.

F o r c e n the vertical, lateral,

and longitudinal directions are computed for various landing gear spans.

Figure

4-7 shows the effect of wind speed on these forces. Note that the maxima do not
occur at the same: wind angle.

The highest vertical load is a result or

.I

90-degree

cross wind, while both the lateral and longitudinal peaks occur at 120 degrees.
The effect of landing gear placement with respect to the main axis of the airship
is shown in Figure 4-8.

vertical load diminishes.

Naturally, as tne moment arm i s increased, the peak

Figure

- 7 - blaximum Gear Forces versus Wind Speed

900-

L A X I M U M VER'TICAL

800-

7OO

600

',
i

MAXIMUM LATERAL

-_

--.-----.
1
-

10

20

MAXIICWM LONGITUDINAL

30

LATEUAL DISPLACEMENT OF AFT GEAR FROM AIRSHIP CENTERLINE (FEET)

Fiy.

.-

4-8 - Maximum G e h r Forces versus Landing Gear Placement

SECTION V

- DYNAMIC ANALYSIS OF

A MASTED AIRSHIP

1. GENERAL
Dynamic loads analysis and associated computer programs were developed to
determine mooring loads for each mooring application for systems with rotational capability. A description of the logic and results of the calculations are
presented.

-.

DYNAMIC FORCES AND MOMENTS ACTING ON THE AIRSHIP

For those mooring styles in which the akship is free to rotate (bow moored,
belly moored, and center point moored), consideration must be given to dynamic
forces and moments. The static analysis is therefore extended to encompass
this realm.
The airship was divided into ten equal-length segments.

The total aerodynamic

forces acting on the airship were considered for the analysis to be the sum of
the aerodynamic forces acting on each segment.

The segmented approach w a s

chosen because the relative wind speed and relative wind direction change
drastically over the length of the airship a s its angular velocity increases.
For instance, with bow mox:.

.&

the relative wind velocity acting on the tail

becomes negative long before the airship reaches its maximum rotational velocity
caused by a wind direction shift.
Th? segmented method was selected as a first-order engineering approach since
it did not require the generation of damping term coefficients associated with
more conventional analyses.

Simulations using the segmented approach predict

that the airship will. respond to the wind as expected with little overshoot as i t
aligns with the wind.
The following assumptions are integral with this approach:
1.

A ateady-staid wind condition is assumed.

A more rigorous investiga-

tion ~ o u l dinvolve a review of gust response and accelerative effects

that are beyond the scope of this study. Appendix A summarizes
approaches that may be appropriate.
2.

The aerodynamic forces and moments acting on the entire airship are
a summation of the individual forces and moments for each segment.
The fortes on each segment are simply a function of the localized airspeed ~ n yaw
d
angle, while the individual moments consist of the product of segmental forces and their moment arms.

3.

The airship rotates in the horizontal plane only. I t is recognized that

kiting of a moored airship w i l l undoubtedly occur, but the magnitude
of the kiting forces is insignificant compared to the lateral forces a t
large yaw angles.

The vertical forces were uncoupled from the hori-

zontal forces.
4.

The rotational accelerations of the airships tire limited only by the

effects of rotational inertia.

No attempt was made to quantify forces

such as those to initiate rolling in the landing gear to overcome rolling

resistance.
5.

The rot2 tional velocity is limited when the sum of the moments about
the mast due to the aerodynamic forces acting on the segments becomes
zero.

The values of C, o r Cy over the length of the airship for yaw angles from 0 to

2C degrees were developed from force distribution data for airships versus
angle of yaw (Reference 33).

The values of Cx or Cy over the iength of the

airship for yaw a ~ g l e sgreater than 20 degrees were calculated using pressure
distribution data (References 33 and 34) and the relative projected area of the
segments. The resulting force distribution values for Cy versus the airship
length for different angles of yaw are presented in Figure 5-1.

The Cy values

for each yaw angle were integrated over the airship length for comparison with
the corresponding Cy values for the total a r s h i p , and the curve values were
adjusted until the values were equal.

The curve was-then divided into ten

equal-length segments of the airship.

The average Cy value for each segment

was then calculated from the curve valiles within each segment.
The values of the yawicg moment coefiicients were calculated next from the
values of the force coefficients for each of the ten segments and their positions
from the center of pressure of the airship.

These calculated values were com-

pared with the yawing moment coeificient (Cn) values measured for the total
airship. If the values did not correspond, the shape of the force coefiicient
curve was slightly adjusted while preserving the area under the curve that
corresponds to the value of Cy for the total airship. This precess was repeated
until the calculat~dvalues of Cy and C, based on the segments equaled the
values of Cy and Cn measured for the total airship.
This calculation process can lead to moaeethan just one solution for the iorce
distribution curves.

Eiowever, the force distribution curves belong to a family

with the values corresponding to the forward portion of the a'rship being well

Figure 5-1

- Force Coefficient versus Airship Length for Various Yaw Angles

5-3

defined at yaw angles of less tha

20 degrees and reasonably defined from

pressure distributions at angles of yaw greater than 20 degrees.

The portion

of the curves requiring judgment for the iterative solution is related to the tail
region.

With these constraints, the shapes and values for the force distribu-

tion curves a r e limited to within a reasonably narrow range that is compatible

with an engineering analysis of the forces acting on the airship during its rotation about a mast.
The resulting average values of Cx and Cy for each of the ten segments versus
angle of yaw are precented

i11

Figcres 5-2 and 5-3, respectively.

The sign

conventions used in the analysis a r e indicated in Figure 5-4.

The aerodynmic forces and moments acting on the airship segments were calculated using a computer program that allowed the airship to rotate i n a horizontal plane about a vertical mooring mast.

The program allowed positioning the

mast a t any positicn along the airship.

The relative wind velocity (vector) a t

each airship segment due to the selected wind velc-ity and the velocity of the
airship segment determined the value of the coefficient and dynamic pressure
acting

011

each segment. Initially, the resistance to rotation is due to inertia

of the airship and i t s virtual mass.

A s time passes, the airship's rotational

velocity increases and ;he aerodynamic forces acting on the tail of the airship
becorne less, and then they resist the actions of the aerodynamic forces on the
more forward sections.

Fi:-ally, it was calculated that the aerodynamic forces

resist rotation of the airship and slow the rotational velocity of the airship to
small values as the airship heads into the wind.

The airship rotates onIy a few

d-3;ees beyond heading into the wind because of the small rotational momentum
remaining.
The f llowing equations were d e v e l ~ p e dfor this analysis:

10
F

latr = i=1 F y i - g i=l

( L i L m ) F yi

ORIGINAL PAGE IS
OF POOR QUALITY

Figure 5-2

- C, by

Segments, Nose to Tail ( - )

OlrrOlNAL PAGE IS
OF POOR QUALITY

Figure 5- 3

-C

by Segments. Centerline tc Starboard (+)

Figure 5-4

Sign of Forces and Moments

where

V$

= v W sin

(+-el +

[vw -

cos

(k0)

- Q ( L -~L,)]

(22)

and

3.

COMPUTER MODEL FOR SYSTEMS WITH ROTATIONAL CAPABILITY

The computer program deals with the dynamic loads analysis for bow, belly, and
center point mooring situations.

An annotated logic sequence for the program

i s shown in Figure 5- 5.

-a.

Data Inputs
A description of the data input requirements is as follows:

1. Airship profile table of distance from the nose versus envelope radius
2. Segment location identifying the location of each analyzed segment
with respect to the nose

3.

C, and Cy tables providing tabular data of the information that i s

graphically illustrated in Figures 4-1 and 4-2

4.

Moment of inertia about t h e center of grz'vity

, including

the effect of

virtual mass

5. Airship mass, including virtual mass

6.

1,ocation of the mast with respect to the nose of the airship

7.

Location of the airship's center of buoyancy with respect to its nose

8.

Time and iteration intervals

9.

Height of tne airship's center line

10.

Initial values for angular displacement, angular velocity, wind speed,

and wind direction

Read
Titles
>

Sum Forces
w

Read
Envelope
Tables

A
4

Read
Constants
i

t
Read
Initial
Conditions

Calculate Forces
On ME?!

1
I

II
w

7'

Compute
Wind Velocity
And Relative
Angle

Calculate Angular
Acceleration

Initialize
Counters

Integrate
Acceleration
Twice For
Velocity
And Displacement

II

'

t
iI

Initialize
Sums

T=T+ I

I
Look Up
Aerodynamic
Coefficients

t
Calculate
Longitudinal
Force At
Segment I

i
L

Calcclate
Lateral
Force At
Segment I

Calculate
Torque At
Segment I
h

Figure 5-5

- Moored Airship Dyi9ar:~ic Simulation Logic Sequence

b.
-

Computed Inputs
Two computed inputs for the simulation node1 are:

(1) mast height, which is a

function of mast location and the airship profile; and (2) moment of inertia about
the mast.

-c.

Outputs

A tabular listing of the airship configuration data, mooring style data, and
initial conditions is provided at the beginning of a computation.

Computed val-

ues of angular acceleration (THEDD) , a.lgular velocity (THED) , angular Cisplacement with respect to the original airshlp location (THE), the transverse
load on the mast (FLATR) , the longitudinal force on the mast (FLONC) , and
the total force on the mast (FMAST). Since there is no rolling moment associated with bow mooring, there are no landing gear forces to compute.

However,

belly mooring introduces significant landing gear loads which are tabulated
(FLCA 1, FLGB 1, FLGB 2) for the forward, port, and starboard gears, respectively.

The mannitude of these loads i s determined by their geometric

locations in apporticning the overall lateral and longitudinal forces on the airship.
4.

COMPUTER MODEL RESULTS AND ANALYSIS

-a.

General
A series or' graphs was generated to identify predicted performance attributes
of the dynamic mooring systems for varying input conditions.

Initial wind char-

acteristics (speed and direction) are inditated on the graphs. Peak forces are
defined as the highest ocurring force over the i n t e g r a t i ~ ntime.

- Mast Forces Versus Mast 1,ocation

b.
Three graphs plotting the peak mast forces ageinst the mast locatio~!a r e shown
in Figures 5-6, 5-7, and 5-8 for total rnast force, lateral mast force, and longitudinal mast force, respectively. Distance "0" represents bow mooring, 143.6
indicates center point mooring. and all intermediate values are belly mooring.
As the mast is moved from the bow taward the center of the airship, FLATR

increases while FLONG decreases.

The net effect on FMAST is to increase as

the mast distance from the bow increases.

90 DEG
WIND SPEED

60 KNOTS

30 OEG

MAST DISTANCE FROM NOSE (FEET)

Figure 5-6

- Peak FMAST versus Mast Location

90 DEG

MASS DISTANCE F R O M NOSE (FEET)

Figure 5-7

Peak FLATR versus Mast Location

90 DEG

WIND SPEED = g0 KNOTS

60 DEG

45 DEG

30 DEG

20

40

60

80

100

MAST DISTANCE FROM NOSE (FEET)

Figure 5-8

- Peak FLONG

versus Mast Location

110

140

- Bow Mooting,

c.

The peak forces generated on the m e t are sensitive to both the wind's originating direction with respect to the d r s h i p and i t s s p e d . Figures 5-9 and 5- 10
illustrate these relationships.

d.

Belly Moored
For this analysis, the mast location for a belly moored airship was arbitrarily
assigned at 75 feet from the nose.

This value coincides with the longitudinal

placement of the envelope-mounted powerplant and represents a point that does

not fall within the forward ballonet.

In this case, as shown in Figures 5-11

and 5-12, the lateral force i s predominant for all angles.

e.
-

Equilibrium Angle
In these dynamic mooring concepts, the wincl causes the airship to rotate about
the mast.

A s indicated in Figure 5-13, however. once the mast distance from

the nose exceeds 90 feet, the airship no longer lines up with the prevailing
wind.

For example. at an initial wind direction of 30, with the mast at 120 fret

from the nose. the airship would be at equilibrium at approximately (30

7O) o r

23O.
Appendix B contains listings and graphs for both bow and belly mooring conditions at 60-knot wind speeds for a ~ g l e sbetween 15 degrees and 90 dt.gret?s
in 15-degree increments.

WIND ANGLE RELATIVE TO AIRSHIP (DEGREES)

Figul e 5-9

- Peek Mast Forces versus Wind Angle

for Bow Moored MPA

20

10

30

40

WIND SPEED (KNOFSI

Figure 5-10

Peak Mast Forces versus Wind Speed

for Bow Moored MPA

60

WIND ANGLE RELATIVE TO AIRSHIP (DEGREES)

Figure 5- 11

- Peak Mast Forces versus Wind Angle

for Belly Moored MPA

140

120

WIND ACTING AT 90 OEG

100

80

60

FLONG

20

10

20

30

43

50

WIND SPEED (KNOTS)

Figure 5-12

- Peak

Mast Forces versus Wind Speed

for Belly Moored MPA

DIFFERENCE BETWEEN I N I T I A L W I N D ANGLE

A N D AIRSHIP E U U I L I B R I U M ANGLE (DEGREESI

SECTION VI

- IMPACTS OF VEHICLE DESIGN

ON GROUND HANDLING

1. TAIL CONFIGURATION
Tests were conducted by the David Taylor Model Basin (DTMB) to determine the
effects of varying tail configuration; on a conventional airship hull (Reference

2 9 ) . The following empennage configurations were investigated:

1.

Conventional

2.

Modified conventional

3.

X-type

4.

Modified X-type

5.

Inverted Y-type

6.

Modified inverted Y-type

7.

End- p l a i d

The various empennage configurations are compared in Table 6-1.

Stability and

control derivztives for each empennage c o n f i g ~ r a t ~ owere

n
determined experimentally and are reported in Reference 29.
Aerodynamic derivatives of particular interest in the ground handling case are
zero lift drag coefficient (CDo), side force-slope in yaw ( C ) , and yaw momenty4'
slope in yaw (C ). Table 6-2 compares these derivatives for the various empen-

"JI

nage configurations. The conventional or cruciform configuration is used as a

basis for comparison and is given a designated value of 100. .
The following conclusions are apparent based on Table 6-2:

1.

Zero lift drag coefficient is a minimum for the two inverted Y

configurations.

2.

The end-plated tail has excessive drag as tested.

3.

Static directional stability (Cn ) is a maximum and approximately

4'

equal for the X-type and end-plated fins.

The dynamic stability of the various configurations was also analyzed in Reference 29. Dynamic stability was judged on the basis of the following stability
criteria:

TABLE 6-2

- COMPARISON OF MEASURED STABILITY DERIVATIVESFOR

VARIOUS TAIL CONFIGURATIONS (BASED ON
1148-SCALE DTMB WIND TUNNEL TESTS)

Modified
Modified Inverted inverted
Modified
Configuration Conventional conventional X -type X - type Y -type Y -type End-pletc J

C ~ *
C ~ w

Cnv

100

100

100

100

94

94

114

100

88

142

116

129

121

129

100

103

76

86

84

87

78

= m 8 -

m' = C

per r,qdian

"JI

n' = C

per radian

Y~
ml'= Cn (V /V "'3)
r
nu = C
yr

per radian per sec

( v I v ~per
~ ~radian
) per

sec

kx = longitudinal inertia coefficient

Dynamic stability of a configuration e x i s t s when t h e index i s negative; that i s ,

I is less than o r equal to 0. Based on t h e measured and estimated derivatives at

small angles of yaw, t h e stability criteria for each configuration a r e given in
Table 6- 3.

TABLE 6-3

- COMPUTATION OF DYNAMIC STABILITY CF.ITERIA

FOR

VARIOUS TAIL CONFIGURATIONS

Modified
inverted
Y -type

Modified
D.kectiona1 stability

Based on Table 6-3, the following conclusions can be drawn:

1.

The modified conventional empennage (lower fin left off) is directionally unstable.

2.

The modified X-type empennage has marginal directional stability,

3.

The inverted Y-type configuration is less stable than the X-type

empennage.

4.

The end-plated configuration has only marginal directional stability.

With regard to ground handling qualities, the data of Reference 29 indicate that
the inverted Y configuration is very suitable.

Directional stability character-

istics are better than for the conventio!lal cruciform type but not a s good as the
X-type,

Drag is less with the Y configuration than the X-type or cruciform.

Both the X-type and inverted Y-type configurations have good tail ground
clearance qualities as opposed to the cruciform tail.

The inverted Y has the

further advantage of having the best (lowest) snow accumulation characteristics.

The only configuration that appears to be absolutely unacceptable from a

ground handling standpoint is the modified conventional tail due to its directional instability

2.

EFFECT OF BUOYANCY RATIO

Buoyancy ratio ( 6 ) is defined as the static lift divided by the gross weight of
the airship. The design value of 6 for thia MPA is 0.66.
With the airship moored at the bow and free to awing, any shifting of the prevailing wind sets up a yaw angle, which causes the airship not only to wecthervane but also to kite. If the wind shifts leus than 90 degrees, the negative l i f t
due to pitch and static heaviness in combination with the metacentric moment
opposes the kiting tendency and defines maximum kiting angle for a given yaw
angle. A s the yaw angle is reduced by weathervaning, the airship L forced to
the ground. If the wind shifts more than 90 degrees (a tail-to-wind condition),
both the lift due to y3.w and the lift due to pitch may cause the airship to kite
to large angles, If the wind shift and velocity are severe enough, high impact
loads may result on contact with the ground (References 38 and 41).
In order to prevent any damage caused by kiting, the following alternatives
exist :
1. Apply an anti-kiting moment sufficient either to prevent or limit

kiting for all weather conditions. This can be accomplished by:

a.
b.

Decreasing the buoyancy ratio by adding weight to the car

Attaching a weight to the stern handling lines, leaving the
airship free to weathervane

c.

Applying up deflection of the elevator before kiting and varying elevator deflection during kiting

d. Trimming the airship tail-heavy with ballonet

2.

Tie the tail to a stern riding-out car an.chored to circular rails

3.

Increase the load capacity of the landing gear and its supporting
structure to withstand all reasonable impact loads which may be
experienced

4.

Moor the airship to a high mast

The anti-kiting moment, which is applied by adding weight to the car, is limited
by the capacity of the landing gear. Should kiting occur in spite of this static
heaviness, the impact velocity on contact with the ground is thereby increased.
The concept of attaching a weight to the stern lines culminated in the development of the Terra-Tire anti-kiting device by Goodyear (see Figure 6-1).

The

anti-kiter w a s 10-112 feet long, 11 feet wide, and approximately 6 feet high, I t
weighed 10,300 pounds comple'ely loaded with shot and 5465 poucds without shot(

The unit consisted of a tubular steel frame, which vould carry 2600 pounds of
shot when filled, with slack-abscrbing springs through which passed the attach-

ing cables, and all mounted on two 60 x 42 x 18.OC Terra-Tires. The capacity
of each Terra-Tire was 6000 pounds with a pressure of 10 psi. The anti-kiter
was attached to the s t e m bridles of the airship by quick disconnects and bridle
sheaves at the end of the cable which passed through the slack absorber. Approxhatdy 90 inches of vertical travel were absorbed by the springs before
they bottomed and allowed the anti-kiter to leave the ground. A shot bag frame
allowed the addition or removzl of 2249 pounds of weight.

The anti-kiter also in-

corporated a retractable tow hitch, retractable screw hand crank, and retractable stowage stand, Unfortunately, the anti-kiter suffered from the same problem as adding weight to the car. It did nat entirely prevent kiting and resdted

in considerable damage when it recontacted the ground.

The provision of a tail car anchored to rails appears to be too costly for nonrigid airship operatins.

In winds greater than 25 knots, proper use of the elevators can be quite effective to prevent or limit kiting and to reduce ground contact speeds should kiting
occur. By fully deflecting the elevators up, kiting can be appreciably delayed
and reduced.

However. to minimize landing gear loads in high winds, the ele-

vators should not be deflected full up until the airship starts to kite.

After

the maximum kiting angle is attained, the ground contact velocity can be reduced by holding down the elevator.
Consequently, effective use of the elevators requires that they should be controlled either manually ar automaticdly durin3 kiting. In low winds (less than

20 knots), the elevators have limited effectiveness a i d should be kept in neutral.

The anti-kiting mcment due to trimming the airship tail down will not greatly reduce kiting.

Should the airship kite, this moment increases the impact velocity

slightly.
The added weight needed to increase the gear strength can reduce the performance in flight noticeably. Some solution may be obtained by the installation of
special ground handling gears, which can be removed for flight.
The aerodynamic forces that cause kiting in shifting winds are basically due to
ground effects. Consequently, by mooring the airship to a high mast, kiting
tendencies can be reduced.

The kiting that remains while moored high is less

likely to reault in dunage. However, t h e overall diradvontagea associated with

high mast w r i n g greatly outweigh this particular attribute.

T h e solution t h a t appears t o p m v i d a tlrc b e s t overall r e s u l t s i s t o maintain t h e
airship a t equilibrium, b u t slightly heavy while a t t h e mast.

When t h o airship

is fully restrained. a Iowar buoyancy ratlo would be y m f a r r u d in o r d e r t o ra-

slat the o v e r t u r n i n g moment.

Howevar, a s shown in F i j ~ u r e6 - 2 , t h e effects sf

reducing fl a r e not that substarltlcrl.

l n fact, a decrease in buoyancy ratio

fro111

1.0 to 0.5 in a b0-krttrl wiird corrditlot~results in only about r 10-percent rcduction in t h e aiaxin\um upward vertical force.
3.

E N V a O P E ANXI SUSPENSICN SYSTEM '.JElCIIT

The weight of t h e s u s p t t ~ ~ s i osystcnr
n
is a functiotr of the susyetrded Iclait.
cotrvetrtiotral airship, t h e ~ \ l ~ p ~ r . rload
i ~ risi a p p m ~ i n r a t c l y50 percetrt

L)!

In a

the

gross weight. wlrere t h e prwss u*cilrht is t h e pmxiuct of t h e ~iisplrcccivolutrre

. ~ t r i t t l ~ clocal

(0.07bS)V.

.tir density. Fur st.rtrci \-,I .rtniosphere, t h e susperrdc~ilo.\ri i s (0.5)

The si~spet\sio:r systenr is r * ~ g ~ . n i dcsigrrcd

~llv
to c.\rrv .rtr AJdition.rl

,\cct.lrr.tt~~vr
f.\ctor of 0.3g.

The t i r s i ~ sustlens;.rvl
t~
syaterri loud is ~tetitredAS

lase wl1rt.e

I'lrr. ccwf fir-icstrt C,,.s varit's ~011rc3wtr~t

with coirfigtir.rt iotr ~ i r c iI~l,\ci(list ribi~tiorr
t

ittrt.I

4).

t c r . I s

Arr . r v r r . r ~ ehas been usc-ti (se-t- l'crblr

Hc..rtr.\it-ing the .rirshrp b y rigldlv .rtraching t h r c a r to thc- grourrri result^ ~ t rt h r

.rirlr).a~l ctit\g
t

011

ttrc* C - I ~ V C I O ~tlt-ltrg
O
t r . ~ t r s t ~ - r r rbcyl the suupetrsiotl systcnr to

it I i t i o t i t11i.1s u e t i t I . .

'l'hese lo,rrts

,\-t*

.rdrlrcl vrctor.tllv tt, ricfitrc t h e resul!.rnt st~spctrslor-rsystrrra luu~i'snragttituclr .\rrrt

clir~*~tiorr.I'trrrc forces ,rt.r irletrtifir~iit\ F ~ g u r r .t, 1.
.rre:
the sarne ))lar\r. rtreir tltbtitr~trc~trs

tlll tori-cs .\re .rctlnp irr

Figure 6-2

Buoyancy Ratio versus Maximum Upward Vertical Load for

Fully Restrained MPA
6- 9

Fy = effective horizontal component of external wind loads

F, = effective vertical component of external wind loads
L
Pds = static lift load

(= 6 )

Ps
8,

= resultant load
= direction of resultant lead
= location of internal suspension curtain

TABLE 6-4

Ship
ZS 2G- 1

I
Note:

- SUSPENSION
- - SYSTEM WEIGHT COEFFICIENT
Volume

(ft3)

(lbs)

(Actual)

650,000

1001

0.0268

W'

'we

Mean

0.0244

(C,,)

(lbs
910

W i s the actual suspension weight of the airship.

W' is the
weight defined b y the product of the mean value of C,, and
(0.0574V).

Figure 6- 3 - Suspension Systcm Forccs for Total Restraint System

6-10

Assume the pitching and yawing moments are reacted by linearly varying loads
over the length of the suspension system. The average increase in load (fAVG)
over one-half the length of the suspension system of length, L, is defined as:

The length, L, of the suspension system is estimated at 55 percent of the over-

,
all length of the ship, The ship length, L

is related to the volume by

where A is the length-to-diameter ratio and C( is the prismatic coefficient. Appropriate values for the MPA are p = 0.643 and X = 4.37. Inserted in the above
equation :

Since

L = 0.55Lm,

therefore

L = 1.85V 113

The average increase in the load component on the suspension system is

Since
where

Ci is the pitching or

yawing moment coefficient.

Therefore:

The

total design vertical load component is defined aa:

F, = F,
where

and

F,

+ Pdl

PI' + FI!I

( c ~ ~ v ~+ ("1 ). 6

(cX+

2 ~ 213)
~ ~ 8

1 . 6 2 ~ gv
~ )21s

F = F 1 + F "
Y

= ( C ~ ~ V ~+ ' (1.62
~ ) CnpV 219)

(cY+

1.62

c,) qv 219

Using a NASA standard atmosphere,

where (KT), is the wind velocity, and substituting in the above equation,

Therefore, referring again to Figure 6- 3,

e* = Tan - 1
+

[11*293

1-62 Cm

(KT):

for (KT),

If (KT), is equal to zero, then 0, = 0.

The load in the heavily loaded side of the suspension system, Ps 12, for values
of Os equal to o r less than 4 is:

;q (sin
-+
2

Ps12

Bin

Cos

When 0 is greater than 4 , the load on one-half the suspension system is assumed
to be Ps.

If it is assumed that the airship is free to roll, the centerline plane

of the suspension system will align itself with the vector, Ps, and the load on
each half of the suspension system is 0.5 P,.
Since the weight of the suspension system is proportional to the load in the
suspension system, the suspension system weight multiplier, Kws, can be defined as:

For

es 2 0,

K"s

sines
-+Sin

sin os

cos

es

Cos )

cos

eg

(KT+G)

[(11'205

vl/S

= 0.0591 (KT)'

"I3+ Cz + 6

(KT),2

+ (CY +

1.62

Cn)]

In conventional airship design, side loads are very limited and are assumed
negligible. Typical values of 19 are approximately 30 degrees.

Total restraint

of an airship introduces substantial side forces, however, that result in flattening the suspension system plane.
count for this.

A value of

+ = 40 degrees i s selected

to ac-

Now, using this value of 4 and the airship volume of 875,000

cubic feet, Equation 37 can be solved at various yaw angles and various speeds.
The results are given in Table 6-5.
TABLE 6-5

SUSPENSION SYSTEM WEIGHT FACTOR (K,,)

Yaw angle (deg)

=If
deg

(knots)

90 deg

120 deg

The suspension system weight for a restrained airship would be impacted by

the weight factor defined above so that the system weight, Ws, is

As previously defined, CWs = 0.0244 and Ls = (0.0574)V. Defining the weight

fractioz, %Ws, as the suspensien syster?! p e r c e ~ of
t the gmss lift

and

i-?eine

0.06 lb lcu ft as the nminal lift of helium (gross lift equals 0.06V) ,

Results of Equation 39 combined with the maximum values of Kws in Table 6-5
are given in Table 6-6.
TABLE 6-6

- SUSPENSION SYSTEM WEIGHT FRACTION

(KT)w

Maximum

(knots)

Table 6-6 indicates that the suspension system weight increases from the 2.3:
percent of the conventional airship gross static lift to a l m ~ s t9 percent at 30
knots and 29 percent at 60 knots.
The effect of total restraint mooring on the envelope weight is a function of how
the increase in si~.spensionsystem strength i s obtained. The increase in suspension system strength can be obtained by either increasing the size of a fixed
number of suspension systems or increasing the number of suspension systems.

If ihe number of suspension systems is increased by the required factor, the

load per envelope attachment line is constant.

Therefore, there is no increase

in envelope weight.
If a fixed number of suspension systems is increased in strength by the required
factor, the envelope structural weight is increased by some factor- The errwlope structural weight is the envelope weight minus ballonets, airlines, patches,
fairings, etc.

The envelope structural weight is a function of the maximum de-

sign velocity of the airship and is not directly controlled by the suspended load
effects.

The structural weight fraction of conventional ships designed to fly 75

knots is 12.5 percent of the gross lift.

The airship experiences loads that pro-

duce fabric stress greater than that required to carry the suspended load. A
factor greater than the required factor of safety is inherent in the envelope
structural weight with respect to the strength required to carry the suspended
load.

This factor varies with several design parameters:

speed, configuration,

pitch angle, gas valve size, and ascent and descent rate.
mated to be 2.25 for a 75-knot airship.

The factor is esti-

The envelope weight fraction is increased

by the ratio of the suspension system weight factor to the 2.25 inherent factors
in the envelope for a conventional suspension configuration and suspended load.

The total weight fraction for the structural envelope plus the suspension system is the algebraic sum of %We and %Ws as shown in Table 6-7.

Whereas the

(%We + %Ws) for a conventional airship is 14.83 percent, the weight penalty

associated with a restrained airship is considerably higher.

Depending on the

wind speed, the end result would vary from a significant decrease in payload
capability to being too heavy to fly. For those conditions below the dotted line
in Table 6-7, alternate airship designs would require consideration.
Graphic representations of the data in Tables 6-6 and 6-7 are shown in Figure

6- 4.
Regardless of the type of airship (non-rigid, semi-rigid, or rigid), the transference of large lateral forces through the airship will require sufficient structure to accommodate the load.

It is anticipated that any vehicle designed on

this premise will result in structural weights similar to those predicted above.

TABLE 6-7

- ENVELOPE WEIGHT FRACTIONS FOR

FIXED NUMBER OF SUSPENSION SYSTEMS

For the concept of directly attaching the envelope to an anchor system as opposed to securing the control car, there appears to be little structural weight
adva.ntage. Since the weight of a structure is a linear function of the load in
the structure, the external catenary system would have approximately the same
impact as the internal system defined above.

The loads will be identical, and

any improvement in the geometric position of the system i s offset by the increased
length t o ground.
Assuming a more optional location of the attachment between the envelope and
the restraining system, the envelope weight penalty may be somewhat less than
determined for the rigid c a r restraint.
Even assuming that part of the restraint system can be detached and not become
part of the airborne shi; weight, incorporating such a system will, depending
on design wind speed, vary from a significant decrease in payload capability to
being too heavy to fly,
4.

PROPULSION UNITS
In terms of ground handling operations, the placement of the propulsion units
has both advantages and disadvantages.

On the positive side, the large verti-

cal clearance distance between the propellers and the ground add an additional

FIXED NUMBER OF
SUSPENSION SYSTEMS

CONVENTIONAL SUSPENSION SYSTEM WEIGHT I%W, = 2.3396)

WIND SPEED (KNOTS)

Figure 6 4

- Effect of Complete Vehicle (Total) Restraint Mooring on

Suspension System and Envelope Weight

dimension of safety for ground handling personnel and equipmeat. The engines
can be kept running in order to provide thrust without jeopardizing other operations.
A disadvantage of the propulsion unit placement relates to servicing the engines,

With the airship on a mast, maintenance of the propulsion system is limited to

minor overhaul. Access to the forward engines is gained from the car, to the
air duct, through the cross-beam tunnel to the engine cowl. For access to the
stern engine, the nose pendant cable is payed out of the mooring cap to permit
mechanical mules, with constant tension winches, to pull and hold the stern of
the airship down to ground level, With the engine in the vertical attitude, a
work platform is latched to the support structure fcr maintenance.

This per-

mits the airship to weathervane to some degree when tensions in the winch
cables are reduced. In a hangar,

>jar overhaul should be no problem. The

vehicle may be tied down to minimize rnovement and positioned such that the
maximum engine height above ground level is 25 feet. On a comparable basis,
the DC-10 fin engine exceeds a ground height of 35 feet.
The selection of the Allison CMA-500 engines for the MPA was premised on an
evaluation of proposed maritime missions as defined in Referei. e 15. This
choice was not impacted by any consideration of ground handling operation.
The attribute that the powerplants should exhibit to aid in ground handling is
the ability to supply sufficient thrust to enable the airship to taxi or hold a position on the ground. This capability would significantly reduce the need for
superfluous personnel and equipment. This topic, however, falls within the
realm of overall airship performance analysis and is beyond the scope of this
report.

SECTION VII
1.

- OPERATIONAL CHARACTERISTICS AND COSTS

GENERAL

A s previously indicated in this report, four mooring concepts are inv.-.stigated

for the MPA:

1. Bow mooring
2. Belly mooring

3.

Complete vehicle (total) restraint

4.

Hangar systems

For each mooring concept, a series of system attributes is reviewed tncompassing ground handling manpower and equipment requirements, mooring area requirements, impact on maintenance procedures, environmental considerations,
and mooring system mobility.
In order to assess the alternatives, certain operational assumptions a1.e made.
These assumptions are not intended as design criteria but rather as reference
pu'nts for ground handling applications.

The major assumed features are:

1.

The MPA is capable of VTOL operation.

2.
3.

The MPA i s capable of taxiing.

Aerodynamic lift on the MPA with empennage is approximately
8500 pounds.

4.

The crew is composed of not fewer than four members.

2.

SITE CONSIDERATIONS

;.

General
The selection and operation of an airship mooring site depends on a number of
physical constraints imposed by the geography sf the area. The p r i n ~ i p : ~geo:
yraphic factors are topography, soil type, site size and shape, and weather
conditions

b.
-

Topography
Fundamental to celecting a mooring site is consideration of site topography.
Ideally, a smooth, flat, level surface of apprcpriate size will be available; realistically, such a site will rarely be found in a remote environment, Certain
civil engineering functions will then be required in order to ~ n v e r tthe available area to a suitable mooring site. These functions will typically involve using
a bulldozer to provide a generally smooth, flat area free from significant relief

differences and stumps.

The degree to which this must be accomplished is de-

fined by the mooring styles.

-c .

Soil Conditions
The ability of a soil to support a given load is paramount in the provision of a
mooring site both in terms of a load applied by the airship through its landing
gear and the forces incurred a t any mast anchor points.
The California Bearing Ratio (CBR) test serves as a standard procedure for
determining load bearing capability.

The CBR number is a ratio of the unit load

(psi) required to generate a certain penetration in the test sample to a standard

unit load (Reference 30). The CBR is generally used to rate the predicted p e r
formance of soils.

Table 7-1 gives typical ratings (Reference 30).

TABLE 7-1

General
CBR No. Rating
0- 3

3-7

7-20
20-50
>SO

1 Very Poor
1 Poor to Fair
I Fair
1 Good
Excellent

- TYPICAL

CBR RATINGS

Typical Soil Types

I Clays of high plasticity. Hme silts

I Same a s above
I Low plasticity clays, inorganic silts. fine sands
I Silty. sandy. or clayey grounds
Well graded gravels with few fines

More empirical data has been developed by industry, particularly with respect
to the "holding power" of ground anchors. In essence. a soil p r a e was developed for field testing to provide instant access to anchor design charts. A
typical soil classification system is shown in Table 7-2 (Reference 31).
The use of single-helix anchors appear to be appropriate '.or the mooring systems considered in this report.

These anchors would be installed with a hand-

held portable pipethreader adapted for this purpose.

Due to 5he torque lirnita-

tions on this equipment. the efficiency of setting the anchors rirops quickly
above the eight-inch helix size. It can be either electrically or gas driven.
The arthors have differently sized helixes available mounted on a 1.25-inch rod.
Various attributes of these anchors are given in Table 7-3 (Reference 31).

TABLE 7-2

1I

- SOIL CLASSIFICATION DATA

--

Solid Bed Rock

Dm- Clay; Compact Gravel; Denra Fine Sand;

Laminated Rockr Slate; Schirtr Surdrtone

pi
4

Shale; Broken Bed Rock ; Hardpan : Compact,

Clay-Gravel Mlxturer

Gravel, Compact Gravel and Sand; Claypan

Medium-Firm Clay; Loose Sand and Gravel;

Compact Coarse Sand

6'
8**

Soft-Plastic Clay; Loose t o a r s e Sand: Clayey

Silt; Compact Fine Sand
Fill; Loose Fine Sand; Wet Clays; Silt
Swamp; Marsh; Saturated Silt: HbInus

*Includes a r e a s only seasonally wet with slow drain a s i n

fairly flat terrain.
**Install anchors deep enough. b y the use of extensions,
to penetrate a Clara 5. 6. o r 7 underlying tne Class 8 Soil.

TABLE 7- 3

- CHARACTERlSTICS

OF SINGLE-HELIX
-

SCREW ANCHORS

Hc*lix
Diametcr
(in. )

A re;\
(sq in.)

tlolding Strength b y Soil

",lass (Ibl*

Unit
Weight

11.000

9.000

6.000

13.000

1o.ooo

7,000

45.2

15.000

13.000

10,000

113

51.6

17.000

15.000

12.000

176

61.6

20.000

17,000

14,000

(Ib)

50

35.0

13,000

10

?e

41.5

15,000

11-5116

100

13- 11 2
15

*Rt,fcr to Table 7-1 for soil classes.

The forces developed a t t h e landing gear when t h e airship lands o r when it is

moved and i t s resisting rolling moment must also b e addressed.

Landing gear

and tire arrangements and types a r e sensitive to the bearing strength of t h e

Table 7-4 gives the recommended maximum tire pressures

contacted surface.

for various landing surfaces ( Reference 32)

TABLE 7-4

- TIRE PRESSURE RECOMMENDATIONS

M a x Tire
Pressure (psi)

Landing Surface
Aircraft carrier deck

Large military airport pavement

L u g e civil airport pavement
Small tarmac runway; good foundation
Small tarmac runway; poor foundation
Temporary metal runway

I
II

70- 90
50- 70

50- 70

Hard grass, depending on soil

Wet, boggy grass
Hard desert sand
Soft, looser desert sand

d.
-

Site Size and Shape

The size of a landing and mooring area needed to support one MPA should be
determined based on the minimum width that will permit an airship to land without damaging any airship components, obscurring visibility, or causing ingestion in the engines from blowing soil and debris due to dynamic pressure.

The

airship mooring style must also be considered.

For those mooring systems with rotational capabilities (bow and belly), the required circular land area was generated based on a radius equal to the distance
from the s t e r n to the mast plus 50 feet.

In developing the minimum area require-

ments, it was assumed that - under certain conditions

it would not be necessary

to completely clear the area of brush under the aft portion of the ship.
arbitrarily assumed that a clearance of 20 feet be obtained in any event.

I t was
Thus,

for bow mooring, a point on the underside of the envelope 220 feet from the
nose is 20 feet above ground.

This 220 feet represents the absolute minimum

radius acceptable for a bow mooring circle. For belly mooring, the same approach
was taken, but under no circumutance should the radius be less than one-half

the ship's length plus 50 feet. Figure 7-1 illustrates this requirement.
The amount of blowing soil and debris that is generated while the engines are
operating is a function of the soil type, soil strength, and amount of vegetation.

If soil erosion becomes a problem due to vegetation degradation, steps should be

taken w minimize its effect through soil consolidation and stabilication with
either chemical o r soil cement treatments. Cost would vary considerably depending on the extent of the problem. While various concepts exist for landing mats,
they would t e uneconomical for MPA applications unless a specific long-term
site on previously unprepared soil was a dictum.

e.

Weather Conditions (References 34 to 36)

The major weather factor influencing MPA mooring capabilities is wind. Strong
gusts attacking a moored airship at large angles with respect to the centerline
axis can impart tremendous loads that either must be handled by the envelope
and suspension system or transferred to the mooring mast.

Failure in either

mode could lead to catastrophy.

An investigation into extreme wind distributions in the United States (Reference
40) ir,dicates that the annual predicted extreme wind speed at a point 30 feet

10 '

-i<
V)

8.
MAXIMUM AREA REQUIREMENT

6 *

Lu

4 .

"

MINIMUM AREA REQUIREMENT

2.

00
YUlf DISTANCE FROM NOSE (FEETI

100

120
--

140

Figure 7- 1 - Land Requirements for Mooring Systems

with Rotational Capability

above ground, based on a 10-year mean recurrence interval for the East Coast,
ranges from 75 to 85 mph (65 to 74 knots).

The Gulf Coast is generally restrict-

ed to 70 mph (61 knots), while the West Coast maximum is approximately 60 mph
( 52 knots).

A pocket of very high winds in excess of 90 mph ( 78 knots) exists

along the west coast of Washington (see Figure 7-2).

Peak gust speeds at the

30-ft elevation would be 30 percent higher than these values.

In order to compare the relative merits of the various mooring techniques, a

reference wind velocity of 69 mph (60 knots) is selected that approximates the
predicted annual extreme in most coastal areas.
The buildup of snow or ice on a moored airship i s a critical problem.

Due to

the immense size of the surface of the airship, relatively small depths can impact a significant load on the envelope system and landing gear.

Assuming that

the snow buildup occurs over one-fourth of the total envelope area and based
on an average snow density of eight pounds per cubic foot, each inch of accunlulated snow adds 10,000 pounds of weight.

Figure 7-2

- Annual

Extreme Wind Speeds (mph)

The problem of snow removal has been investigated for many years, but as yet
no completely satisfactory solution has b u n generated.

Some approaches that

have been tried or hypothesized arc as follows:

1.

Scraping and brushing, a technique using a rope, was slow and

required constant attention during storms.

Rope action also

chafed the envelope, and the development of larger airships

precluded its use.
2.

Vibration met with limited success. The major problem of inducing

a vibration in the envelope was difficult to satisfy.

3.

Envelope distortion was discarded due to the Fotential of fabric

damage. It would not have been effective for snow.

4.

External heat required too much power and equipmeat, and the
problem was compounded by inaccessibility to upper envelope
surfaces.

5.

Super heating the helium was experimented with but was not further
developed despite its apparent feasibility.

6.

Chemical systems, the application of substances to reduce ad-hesion or act as freeze depressants, have been effective.

7.

Water systems have also been used.

The most widely used

technique was to attempt to spray the snow from the envelope.

Though this approach has some limitations it remained tl.e
recommended approach of the Navy and is presently prescribed
for the Goodyear public relations airship fleet.
Though other weather factors can adversely affect the operation of an airship
mooring system, none have the capability of impacting the airship and mooring
equipment in the same manner as high, off-angle winds or large accumulations
of snow or ice.
3.

BOW MOORING

-a ,

Structural Requirements
Fundamental to the design of a mast for a bow mooring system is the load transference from the airship through the nose to the mast.

This minimizes the mag-

nitude of the mooring loads on the envelope or suspension system. In the most
extreme case as defined in this report (a 60-knot wind attacking at 90 degrees
to the centerline axis), the maximum forces are approximately 48,000 pounds for
FLATR and 4 5,000 pounds for FLONG. The maximum resultant force (FMAST) ,

which in this instance coincides with the maximum FLONG, equals 66,000 pounds.
Both the maximum moment developed by the forces and the determination of the
ultimate axial load are of critical design importance.
The peak vertical force on the mast is determined by summing the system forces

the aerodynamic load and the force created by the pitching moment. The result,
based on Table 4-2, is a net upward vertical force of 40,000 pounds that must be
restrained.
A tubular aluminum mast has been selected to satisfy the design criteria. I t
would be constructed ir, two sections.
The top half, equipped with the mast head and mooring cup, would have a 16inch outside diameter and a one-inch wall thickness.
would be 14 inches and 0.75 inch, respectively.
feet.

The lower half dimensions

The baseplate diameter is six

A t a point three feet from the top of the mast, 20 cables would emanate.

These cables would be attached to ground anchors placed on the circumference

of a circle of radius 35 feet about the mast; this would result in anchors every
11 feet.

The cables are one-half inch in diameter and 59 feet long, with an

ultimate load requirement of 21,000 pounds.

In order to provide bending support, cables are also provided at the midpoint

of the mast.

Ten would be required; these cables would be attached to the same

anchors as above but at 22-foot placements.

Each cable is 41 feet long with a

diameter of 5/16 inch. Ultimate load i s 9800 pounds (see Figure 7-3).
Tests conducted by Goodyear have shown that ground anchor holding strength
is additive. That is, a set of two anchors holding a single cable will develop
double the resistance of a single anchor.

For this particular case, the eight-

inch single-helix anchor (see Table 7-3) used in tandem would be sufficient in
C:ass 5 or better soils.
b.
-

Mooring Area Requirements

The bow mooring concept rcquires a large tract of land. For the MPA with an
effective required radius of 375 feet, this land amounts to a cleared area of 10
acres.
In a previously unprepared site, it may be possible to take advantage of the
ground clearance in the aft portion of the airship.

This could effectively re-

duce the cleared area to the minimum amount indicated in Figure 7-1.

Figure 7-3

- Bow Mooring Mast Arrangement

O~erationalConcent and Reauirexnents

The operational sequence for establishing a base begins with the MPA delivering
the mast, mart baseplate, anchors, portable power drive system, winch, ancillary tools, and a two-man crew.

The airship then departs the area temporarily

while the m a s t baseplate i s centrally located in the field and all anchors installed.
The mast is drawn toward the baseplate with the winch, and all cables (slack)
are attached to their respective anchors.

The mast is hoisted to a vertical po-

sition atop the baseplate by the winch and a block and tackle.

All guy cables

are then secured. Total estimated time for this effort is six to eight hours.
The airship lands near the mast and taxis toward it. When the airship is sufficiently close, a noseline is attached to a line leading through the mooring cup,
through the mast to the winch.

The vehicle is then drawn into the mast and

secured in position.
To unmast the airship, the nose pin is manually removed, and the MPA can then
move up and away from the mast.
lation sequence.

The mast is removed by reversing the instal-

The anchors can be removed and reused.

The mast is stowed

under and attached to the car during flight.

-d.

System Mobility
The provision of a large ground support team with associated equipment is inconsistent with the mission goals of the MPA.

The airship and its crew must be

capable of establishing a base without assistance, provided the topography and

soil conditions are conducive.

Two main system attributes are prerequisites for

such operations:

(1) the ability of the airship to land unaided and ten~porarily

hold a position on the ground (that is, low-speed controllability) and ( 2 ) the
ability of the airship to transport all necessary mooring equipment.
T t e first attribute must be assumed as a capability at this point.

In the second,

however, the total weight of the mooring system n,,~stexceed the load-carrying
capabilities of the airship.

The total useful load defined for the MPA is 22,504

pounds.
A weight breakdown of the ground equipment used for the bow mooring system

is given in Table 7-5.

By carrying this equipment, the useful load of the MPA

would be reduced to 16,680 pounds.

TABLE 7-5

- EQUIPMENT WEIGHT FOR BOW MOn:UNG SYSTEM

-

--

--

Item

Estimated Weight (lb)

Mast head
Mast
Cables and fittings

B aseplat e

Anchors (40)
Winch
Tool kits and power drive
Total

e.

IL

Environmental
- and Maintenance Considerations
The bow 1,r.mring concept meets the wind load criteria of sustaining a 60-knot
gust that hits the envelope perpendicular to i t s centerline axis.

Although

still susccptible t o snow loads, this mooring system approaches the all-weather
capability feature that would be required for any operator.
Maintenance service for the engines is addressed in Section V I .

Any major

work will necessitate the use of a hangar.

-f .

Costs
Total acquisition cost of a bow mooring system is estimated at $375,000.

This

cost is based on historical records maintained within Goodyear and is tempered

by a pzrametric extension of the costs associated with the Goodyear public
relatians fleet.
4.

BELL'.!

MOORING

-a.

S t r u r t ~ l r a lRequirements
--A mooring mast placed a t any location other than the bow necessitates assess-

ing the rolling moment effects on the airship as well as on the mooring system.
The critical areas are:

(1) the point of attachment for the mooring mast to

the airship; ( 2 ) the landing gear; and (3) the mast and anchors.

The oper-

ational capability of a belly mooring concept i s limited by the least capable of

these areas.
selected.

For this analysis, a mast position 75 feet from the nose has been

This position coincides with the plane of t.he forward engines and

does not interfere with the location of the forward ballonet.

In addition,

tne car is assumed to be equipped with a tricycle landing gear.

The forward

gear is 104 feet from the nose, while the aft gear is 148 feet from the nose.
Lateral displacement varies from 10 to 30 feet.
In order to secure a mast to the underside of the airship, all forces occurring
at that point must be distributed over a sufficiently large envelope area so
that the strength limits of the fabric are not exceeded.

For the case of the

mast at a point 75 feet from the nose, the maximum FMAST is 121,000 pounds.
Since the design limit for the fabric is 150 pounts per inch, a total external
catenary curtain of 67 feet would be required on each side of the airship to
accommodate this load.

It is unlikely that the force could be evenly distri-

buted over such a length, even if the curtain could be physically placed.
An alternative would be to provide an internal curtain to support this point.
Again, however, the physical arrangement of the system is inhibited by the
forward ballonet and the support structure for the engines.
above, significant redesign of the airship would be required.

In view of the
Assuming this

redesign is feasible, an acceptable mooring suspension system would weigh

approximately 2700 pounds more than the weight required for the standard
suspension system, based on the findings of Section 6.3.
The forces required to resist the overturning moment of the airship are substantial.

Figure 7-4 shows the relationship between wind speed and the force

required at a single gear point to maintain the ship in equilibrium with respect
to rolling.

At 60 knots, this force is 67,000 pounds when the aft gears are

at the widest spacing.

In order to scope the magnitude of this force, a preliminary support truss
and landing gear were designed for the MPA.

Using the maximum load indi-

cated above at a distance 30 feet from center and using tires similar to those
used on the ZPC-3W, the result was a 16-wheel landing gear and a support
structure weight in excess of 10,000 pounds (see Figure 7-5).
is unacceptable.

This result

Even by going to a higher rated tire that would possibly

result ix a castering two-tired gear, the structural weight penalty would still
exist.
A more realistic approach would be to offset the landing gear 10 feet on each

side and use two wheels per side.

The allowable load would be 12,600 pounds

at 45 psi, which would permit mooring on a grassy surface (see Table 7 - 4 ) .

10

20

WIND SPEED (KNOTSI

Figure 7-4

- Wind Speed Versus

Landing Gear Load

for Belly-Moored MPA

4130 STtRL TRUSS

5.00 r 0.156 WALL
hAIU TUBLS

ESTIMATED WEIGHT

TOTAL
(POUNDS)

Figure 1-5

13520

Hypothetical Landing Gear an.3 Truss Configuration

If a more subrtantial ruxface was available, the allowable load would be increased to 25,200 poundr per gear at a tire preruure of 68 pri.

Them valuer
correspond to maximum wind rpeeds of 15 and 21 knots, respectively.
9ased on the original design requirements of withstanding a 60-knot wind
afting at 90 degrees to the m a h axis and using the same approach used for
the bow mast, a tubular aluminum mast with the following dimensions could
withstand the predicted FMAST of 121,000 pounds:

14.3 feet high, 18 inches

outside diameter, wall thickness of 0.75 inches. For a 20-cable arrangement,
an ultimate cable load of 33,300 pounds must be restrained. Referring to

Table 7- 3, a pair of 13.5-inch-diameter single-helix screw anchors would b+.

required. Recall, however, that the capability of the hand-held power drive
unit is limited. I t therefore might be more feasible to use three of the eightinch anchors at each point. For the purpose of comparison to other systems,
it will be assumed that the larger units are used.

b.

Mooring Area Requirements

A s indicated in Figure 7-1, the recommended mwrmg area for the MPA belly

moored at a point 75 feet from the nose is approximately 6.4 acres. Uilder
certain conditions, this area could be reduced to 3.3 acres provided vertical
clearances were maintained.
Operations and Mobility
Procedurally, belly mooring is similar to bow mooring.

The mast is somewhat

easier to erect due to its shorter length, but additional work would be necessary to install the anchors.
The weight summary for the belly mooring concept is given in Table 7-6.
This concept is 567 pounds lighter than the bow mooring system.

TABLE 7-6

EQUIPMENT WEIGHT FOR BELLY MOORING SYSTEM

Estimated Weight (lb)

Item
Mast head
Mast
Cables and fittings
Baseplate
Anchors (40)
Winch
Tml kits and power drive
Total

d.

Environmental and Maintenance Considerations

As indicated previously, the belly mooring concept is severely limited by the

rolling moment.

This limitation would drive the design and substantially re-

duce the structural requirements indicated above.

Maintenance procedures

for bow r r r i n g would also apply to this concept.

e.
-

Costs
The acquisition cost of a b d y mooring system would approximate that of the

bow mooring system.

be considered.

However, significant changes to the airship also must

These changes include the provision of a tricycle landing

gear and associated structure, a belly mooring patch, and substantial suspension system enhancements.

In addition, this concept could also deteriorate

airship performance due to increased weight and drag.

5.

COMPLETE VEHICLE (TOTAL) RESTRAINT

-a.

Strucf.ural Requirements
A major problem in assessing complete vehicle restraint for the MPA is to define

an attachment point.

Unlike the heavy-lift airship designs that incorporate a

massive interconnecting structure, the MPA is equipped solely with a control

car that is not structurally designed to handle large ground handling loads.
There are two possible approaches to consider.

The first is to assume that the

airship car is firmly fixed to the ground by cable or other mechanical attachment device. If no changes were made to the envelcpe or suspension system,
there would be little resistance to the rolling rnornertt and the airship would be
destroyed in any significant cross wind. If a suspension system was installed
to compensate for the load developed by a 60-knot wind, it would weigh 15,060
pounds, an increase of 13,850 pounds (refer to Table 6-5).

This weight would

diminish the useful load to 8654 pounds, aboat equal to the dynamic lift, which
wodd significantly inhibit airship operations.
If the susper.sion system design was left uncharged and the envelope structure
improved, the results would be even worse.

At 60 knots, the envelope would

weigh more than ;5,000 pounds (see Table 6-6).

A compromise is to relax the wind-speed requirement to where the added struc-

tural weight of the suspension system is tolerable.

At 20 knots, for example,

the weight of the suspension would be slightly more than double the norniai,

or 2600 pounds.

This additional weight probably could be tolerated, but addi-

tional structural development would still be required for the car.

The second approach would be to develop a quad-gear arrangement similar to
the tricycle gear setup for belly mooring. Unfortunately, this arrangement
suffers from the same weight problercs and hence is disregarded.

-b .

Mooring Area Requirements

The complete vehicle (total) restraint concept is the most frugal in terms of
land requirements.

A rectangular area with the dimensions of vehicle length

plus 100 feet by vehicle width plus 100 feet would probably suffice, assuming
the VTOL characteristics of the MPA. The total area would be 1.8 acres.

-c .

Operational Concept
Operationally, the MPA could follow a routine similar to the bow and belly mooring concepts.

A small ground party crew would have to set anchors in place

prior to bringing the ship in for mooring. Since the airship would normally
land into the wind, the anchors should be arranged to accommodate this.

This

approach is sensitive to changes in wind direction.

d.
-

Costs
Due to the absence of a need for large amounts of ground handling hardware,
the complete vehicle (total) restraint system has some economic advantage.
Even at the comparatively low wind speed of 20 knots, however, the car structure and suspension system must be improved. The costs of these modifications
as well as the reduction in airship operating capabilities due to increased weight

would have to be included in a comprehensive system cost analysis.

6.

HANGAR SYSTEMS

-a.

Operational Concept and Requirements

Both the conventional and air-supported hangars defined in Section

~uld
conduct airship operations in a manner similar to those developed by the Navy
and currently practiced by Goodyear. In essence, the airship would enter and
leave a hangar with the assistance of a mobile mast and two ground ha.ndling
mules. The function of this eqmpment is to prevent cross winds at the hangar
door from causing a collision between the airship and the hangar.
tion is detailed in Item 2c- of Section I.

This opera-

Equipment needs at the hangar associated with ground handling are:

1. Mobile mooring mast

2,

Mast tractor

3.

Two ground hanclling mules

4,

Water ballast system

5,

Auxiliary power unrt for t h e mast

6.

Mobile service vehicle

7.

Fire-fighting equipment

8.

Mooring circle

A s an airship mooring concept, a hangar is unequaled.

I t provides all-weather

protection and facilitates maintenance and servicing operations.

b
-, Additional Utility for Airship Operations Support

Given the investment requirement tor :he construction of a hangar, i t s use

cannot be restricted t o simply housing t h e airship.

Complete airship assembly,

erection. component testing, and overhaul work could be accommodated.

Such

operations would require significantiy more equipment. however, such as:

Test stand equipment
Magirus ladders
Scaffolding
Ground cloths
inflation net
Rope racks
Ballonet ladders
Fin slings

Suspended work platforms

Helium supply
Helium purifier
In flation tunnels
Bosun's chairs
Pressure watch blowers
Engine handling equipment
All necessary tools
Since the above equipment does nqt specifically encompass the realm of ground
handling, it is not included in the cost estimate.

-c.

Additional Support for Other USCC Operations

Should a hangar be erected, i t s cost effectiveness is enhanced by additional
utility.

Since an immediate buildup of an airship fleet is impossible, there will

be significant time periods when t h e hangar i s unoccupied by an airship.

ing these times, use by nther USCG vehicles is recommended.
of these aircraft a r e given in Table 7-7.
TABLE 7-5
-

Dur-

Characteristics

Dimensionally, there is no problem.

- USCG AIRCRAFT CHARACTERJSTICS

Model
Length
Width /span
(including rotor)
Height
Max gross
weight (lb)
The 150-foot door opening would permit access by any of the aircraft.

Sim-

ilarly, height and length restrictions a r e not compromised.

There would be significant economic benefit to maintaining a hangar for all operations rather than limiting its use to airships through more effective use of personnel and equipment.
Costs
The hangar erection costs and equipment acquisition costs are detailed below
(see Table 7-8).

The conventional hangar cost is based on the description in

Section 111 and was provided by A S F Building Systems of Houston, Texas.

This

firm designed and built the existing Goodyear hangar in Houston.

The air-supported h.mgar cost is based on a clear height equal to the conventional hangar (128 feet) and a width of 500 feet ( 4 to 1 ratio).
425 feet.

The length is

Unit cost estimate provided bv ESI for materials and erection i s $6

per square foot for a long-term material.

This estimate is assumed to include

all necessary hardwara and equipment but is exclusive of a foundation pad,

whose cost is estimated at $325,000.
In both cascs, land acquisition and clearing costs a r e not considered.

TABLE 7-8

- HANGAR SYSTEM COSTS

Item

Estimated Cost ( $1981)

Building erection
Conventional

6,100,000
1,600,000

A i r supported
Fquipmen t
Mooring mast
Mast tractor
Mules ( 2 )
Ballast system
APU
Service vehicle
Mooring circle
Fire- fighting equipment
Totals
8.

8,053,000

3,553,000

OPERATIONAL SCENARIO SUITE BILITY

A s indicated in Item 2d
- of Section V I I , high winds and snow can severely
impact ground handling operations.

Some of t h e record wind speeds

for domestic coastal sites are well beyond proposed design limits.

However,

due to advanced weather-prediction techniques, it is unlikely that an airship

would remain in an area scheduled for such inclement conditions.
The ability of maritime patrol airships to survive is well documented.

The

history of their use during World War 11 lends credibility to their predicted
ability to operate in a wide variety of environmental circumstances.

This ability

is best demonstrated by the identification of t h e World W a r I1 airship operational wings:

kirship Wing One operated off the East Coast and was headquartered

at iaicehurst (see Figure 7- 6) ; Wing Two covered t h e Caribbean with headquarters in Richmond, Florida; Houma, Louisiana; and Jamaica: Wing Three
covered the West Coast with headquarters at Tillimook, Moffett Field, and Santa
Ana: Wing Four consisted of two squadrons and protected the South Atlantic
from its headquarters in Brazil: and Wing Five covered the lower Antilles from
an operating base in Trinidad.

In 1944, a squadron was deployed to North Africa to patrol the Western Mediterranean and Straits of Gibraltar. These ships were the first non-rigids tc make
a transatlantic flight.

An airship utility squadron headquartered in Key West

provided many service and utility operations, including ASW training.

9.

PERMANENT VERSUS REMOTE BASE REQUIREMENTS

Two distinct levels of basing exist within the realm of MPA operations (see Table
7- 9). Level I, which would serve as the home base or headquarters, would be
the maintenance depot equipped with a spare parts inventory to handle all service functions. A mooring circle would be established with a paved surface, p e r
manently installed anchors, and mast baseplate.

TABLE 7-9

- LEVELS OF

A hangar is optional.

MPA BASES

Attribute

I
I1

Permanent base; operational headquarters

Remote base; MPA commutes daily Lo mission site

Level I1 would constitute a base away from the headquarters.

I t would typically

be a site that did not require any clearing o r leveling prior to establishing the
base.

An open field near a small airport would be a candidate location.

From

this site, the MPA would travel daily to the mission site. The mast would remain erected at this location for the duration of the mission.

Similar to operating

from a Level I base, an MPA could service several mission sites from a single
location.

10. CONCEPT SUMMARY

-a.

General
The key attributes of each mooring concept (bow, belly, and complete vehicle
restraint) are assessed below with respect to their predicted operational effectiveness.

Hangars are discussed separately.

-b .

Attributes

( 1) Manpower

A basic premise of the MPA is that it will permit the ground handling function
to be executed by members of the flight crew.

The basis for this statement is

that the MPA has substantially improved low-speed controllability over previous
airships and is also capable of VTOL and taxiing.

Thus, for all concepts ex-

amined, a ground crew party of two men (from an airship complement of four
men) properly equipped could perform the necessary tasks.
( 2) Equipment

For both the bow- and belly-mooring concepts, a full complement of mast, baseplate, and ancillary equipment is required.
assigned to the airship.

This equipment would always be

The airship associated with total restraint would have

substantially less equipment as an integral part of its inventory but is much

tnore dependent on engineering services that must be undertaken in advance of
the airship's arrival.

Spontaneous mooring is therefore precluded.

( 3 ) Impact on Vehicle Empty Weight

Assuming that the operational design speed of 60 knots must be attained with
each concept, the effect of this speed on the vehicle's empty weight can be
estimated.
For bow mooring, no additional envelope o r suspension system weight would be
required since all mooring loads are transferred directly to the mast.

The only

adverse impact would be the weight of the mooring equipment that would become
an integral part of the airship in the ferry mode, During missi~nexecution,
however, there would be no weight penalty since all ground handling equipment
would be off-loaded.
The belly mooring concept is impacted by ground equipment loads similar to
those indicated above.

This approach is further impacted, however, by addi-

tional weight requirements for the suspension system, envelope, and landing
gear assemblies. The probability of advancing a vehicle design based on large
wind loads and belly mooring (heavy-duty gear assemblies; complex catenary
system to support mast lairship interface point) is remote.
Complete vehicle (total) restraint mooring would result in extremely large weight
penalties for high-wind conditions. Even at reduced wind speeds where the
additional suspension weight requirements are smaller, substantial improvements
to the car's structure would be needed.
7-23

( 4) Mooring Area Requirements

The amount of cleared land required for effective ground handling varies from
a maximum of 11 acres for a barrier to a minimum of 1.8 acres for a fully restrained airship.

Some savings can be realized in those concepts with rotational

capability by only partially clearing the area to maintain vertical clearance requirements in the aft portion of the airship.
( 5 ) hlaximum Wind Speed
For thc MPA vehicle specified in Section 11, there are identifiable wind-speed
limitations for each mooring concept.
A bow-moored MPA is capable of withstanding 60 knots at 90 degrees with the
ground equipment specified. As the wind direction approaches colinearity to
the airship, the allowable wind speed increases dramatically.
The belly-mooring concept cannot withstand wind speeds in excess of 15 knots
on a grasry surface or 2 1 knots on a paved surface. The critical element is the
landing gear, but the development of an effective mooring point on the underside of the envelope and the retention capability of the ground anchors also are
limiting factors.
The totally restrained airship is limited by its envelope and suspension system
capabilities to 20 knots, but this speed would likely be further diminished by
structural limitations of the car.

(6) System Mobility

The transportability of the bow- and belly-mooring systems is implicit in their
designs.

The masts, complete with guy cables, would be attached to the car

with all support equipment stowed as required.

Thus, each airship would have

a mooring system as an integral vehicle component. The total restraint system

may need some advance preparation to provide suitable anchor systems since
the screw anchors described for mast retention would not be sufficient.

(7) Cost
The costs of building a mast for either bow or belly mooring are approximately

$375,000.

However, the belly-moored airship would require additional features

that would impact both its initial cost and its operational costs due to increased
weight and drag. The cost of the complete vehicle restraint system depends on
the method of securing the airship to the ground.

-c.

Hangar Systems
Though not specifically a mooring system, the hangars defined herein represent
the ultimate approach to protecting an airship on the ground.

However, mov-

ing an airship to and from the hangar necessitates additional mobile equipment,
which in fact represents a bow mooring operation. Tota! minimum manpower is
six (two per mule, one on the mast tractor, and oqe supervisor).
Despite operational similarities, the costs of the two hangar systems are considerably different.

The lower purchase price of the air-supported structure

must be assessed in the light of a shorter life (material Is good for only five to
six years) and the development required for moving an airship through a large
opening in the structure without seriously impacting the support system.

d.

Rating
Since all mooring concepts represent some degree of risk, the preferred approach to mooring is the use of a hangar.

Unfortunately, the large cost and

immobility of such a structure are major detriments.

The impact of the former

can diminish somewhat by using it to house and service other vehicles.

The bow-mooring concept is the only approach that fulfilled the operational wind
load requirements without adversely affecting the overall MPA design. There
was no weight penalty associated with this concept, although some adverse performance effects in the ferry mode could result due to the overall weight of the
mooring equipment.

The large land area associated wit11 the bow mooring is a

disadvantage.
A distant third in terms of overall effectiveness is the belly-mooring concept.

The structural integrity of the system is jeopardized at wind speeds in excess

of 15 knots.

In addition, this concept would suffer from performance degrada-

tion due to increased airship weight.

The complete vehicle (total) restraint approach has only limited applicability as
defined above due to structural weight implications.
Table 7-10 su--1marizes the key attributes of each mooring concept.

SECTION VIII

- SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS

1. HISTORICAL REVIEW
The development of ground handling systems for lighter-than-air vehicles has
evolved from man-handling to the mechanized state established for large nonrigid Navy airships in the 1950's. Throughout the nearly 200 years since the
Montgolfier brothers first ascended in a hot-air balloon, a plethora of mooring
techniques have been attempted. Of all these efforts, however, the bow-mooring
concept has consistently represented the optimum approach for securing airships on the ground.

Though marine capabilities have been demonstrated, they

have not been further developed.

2,

VEHICLE CONCEPT
The baseline vehicle for this study was the ZP-36 maritime patrol airship developed by Goodyear Aerospace for NADC (Reference 15). It has a tri-rotor propulsion system with the forward engines supported on a structure above and
ahead of the control car and the aft engine mounted on the stern. The envelope
volume is 875,000 cubic feet.

3.

MOORING SYSTEM ALTERNATIVES

Several mooring alternatives were described and assessed: bow mooring, belly
mooring , center point mooring, ccmplete vehicle (total) restraint mooring, hangar
systems, and maritir,,z systems. After preliminary investigation, it was determined that center point mooring and all maritime systems did not warrant additional investigation.

4.

STRUCTURAL ANALYSIS OF A FULLY RESTRAINED AIRSHIP

An investigation of airship empty weights versus wind velocity was undertaken
for the two vehicle concepts but was limited to a static condition in which envelope deformation was not considered.

Previously defined aerodynamic coefficients

that are based on experimental data for various airship models were found to have
sufficient correlation to be applicable to the vehicle being considered.

The co-

efficients appear to be insensitive to fineness ratio.

A static analysis of the rooring loads developed in a fully restrained airship was
defined and coded for a computer program. Results indicate that the lateral
ioads are the most significant followed by vertical and longitudinal.

5.

DYNAMIC ANALYSIS OF A MASTED AIRSHIP

In order to extend the results of the rtatic analysis to encompass the dynamic
effects of an airship rotating about a mast, a segmented approach was taken to
determine the overall forces acting on the airship.

For each segment, the vari-

ous forces were computed and then summed to yield results for the entire airship.

Calculations were performed by a computer simulation model in which the

airship physical properties, mooring mast location, and wind information were
input. Results of this model, presented graphically, indicate that the mast
forces increase as the mast location moves from the airship nose toward the
center point. For both bow- and belly-mooring concepts, mast forces increase
due to increased wind speeds and increased yaw angles. The airship equilibrium
position was fourid to be colinear with the wind provided the mast is no further
than 100 feet from the nose.

6.

IMPACT OF VEHICLE DESIGN ON G 3 0 U N D HANDLING

With respect to ground handling qualrties, the X-t;,pe empennage configuration
is very suitable, with good ground clearance quali4.ies. I t also has the advantage of having good (low) snow accumulation char; cteristics

The effect of buoyancy ratio on the vertical forces of a fully restrained airship
is also addressed at various wind speeds,
When mooring, attempts are made to exclude ground handling loads from acting
on the envelope and suspension system by transferring the loads to a mast.

If

this opportunity is not provided, however, the envelope and suspension system
must be structurally capable of withstanding these forces. This results in a
severe weight penalty due to increases in envelope fabric strength or increased
size or quantity of catenary cables. Operationally, this would result in a serious
degradation of airship performance efficiency.
Propulsion unit selection should address the need for sufficient power requirements for ground handling purposes.

Unit placement in this particular design

makes engine servicing somewhat inconvenient ui~lesshangared.

7.

OPERATIONAL CHARACTERISTICS AND COSTS

The main factors to consider in the establishment of a mooring site are the local
topography, soil conditions, weather conditions, and the mooring concept.

The rite topography wiil dictate the overall suitability of a mooring location.
Significant relief would not bn tolerable, and the rite would require extensive
renovation.
Soil conditions and bearing strength wifl ultimately define the operational l i m i t s
of the mooring systems. The ability of the soil to withatand loads at landing
gear contact points and to develop sufficient strength f r o m anchors is of paramount importance. Similarly, the landit~gsite's resistance to degradation through
erosion must be addressed.
The two weather factors that most severely affect airship mooring are wind and
snow. This analysis has attempted to quantify wind loads and minimize their
effects through the use of +.heappropriate mooring concept.

Snow loads, how-

ever, will require additional study since no completely effective means of snow
removal has been developed.
Four mooring concepts were exmined : bow-mooring ; belly-rnoc~ring; complete
vehicle (total) restraint ; and hangars.
Bow mooring is the most conventional and is designed to hold the airship at the
nose, thus permitting it to rotate. Loads are transferred through the airship
to the mast so that mooring loads do not act as the design loads on the vehicle.
While it does permit the airship to rotate, belly moaring results in significant
loads due to the rolling moment that must be resisted.

Some structural penalty

would be involved with this concept. Complete vehicle (total) restraint mooring
offers distinct disadvantages since extreme envelope and suspension system
weight penalties would accrue, if a satisfactory means of attachment could be
develob ed for high wind speeds.
Hangar systems are the optimun~appropch although construction and operating
costs are major factors.
For t h e non-hangar systems, bow mooring is preferred, despite the large land
area requirements. The attributes that distinguish it as most attractive are:
load transference to the mast and hence no design impact on the airship; ability
to withstand extreme wind speeds; transportability; and relative ease of installation.
In terms of permanent versus remote temporary basing, two levels exist:

(1) a

permanent base to serve as the operational headquarters arld ( 2 ) a remote base

from which the airship commutes on a daily basis to the mission site. Another
advantage of the bow-mooring system is that it is appLcable to each of these

levels without needing any mooring equipment changes relative to base location.
The only elements that would probably be required in a permanent base would
be a paved mooring area with anchors permanently installed.
8.

RECOMMENDATIONS
As a result of the findings of this study, the following recomnendations for

additional study art suggested:

1.

Future design studies to further develop and enhance a

transportable bow-mooring mast system

2.

Additional study of snow and ice removal as well as identification of critical opew.tional limits in cold weather areas

3.

More detailed analysis of wind load effects that w i l l examine

the overall airship reactions to these forces : wind accelerative
impacts, envelope deformation, landing gear deflections, other
structural deflections

4.

Additional study of the dynamic effects on a moored airship,

including kiting effects

5.

Additicnal study of ground anchors and enhancement of

theii holding power capabilities

SECTION IX

- LIST OF SYMBOLS

Symbol

Definition
Rolling moment coefficient
Pitching moment coefficient
Yawing mornznt coefficient
Axial force coefficient
Lateral force coefricient
Vertical force coefficient
Suspension system weight coefficient
Total lateral force

Flong

Total longitudinal force

Fmast

Total resuitant force

Fxi

Axial force on element i

Lateral force on element i

Yi

Icg

Moment of inertia about center of gravity, including

virtual mass
Moment of inertia about r a s t , including virtu,d mass
Design velocity (knots)
Wind velocity (knots)
Center of gravity location along X
Element location along X
Mast location along X
Mass of airship, including virtual mass
Resultant force in suspension system
Instantaneous relative wind velocity at element i
Prevailing i:ind velocity

Symbol

Definition
Suspension system weight
Buoyancy ratio

Airship heading
Angular velocity about the mast
Angular acceleration about the mast
Length- to-diameter ratio
Prismatic coefficient
Wind azimuth angle
Air density

SECTION X

- LIST OF REFERENCES

Walker, H.. Jr. : Mooring and Ground Handling Future for Large Airships,
AIAA Paper 75-941. Vero Beach, Florida, July 15, 1975.
Kolesnik. Eugene; and Lord Ventry:

Jane's Pocket Book of Airships, 1976.

Dill, V. H. : "Balloon and Airship Ground Handling Eguipment , Hangars.

Etc , Circa 1925- 30.

Rosendahl , C E. : The Moorin and Handling of a Rigid Airship (Paper

presented a t the Fiftli-T?Nataon Aeronautic Meeting of t h e American Society
of Mechanical Engineers, May 1933), Archives File No. LOIO12.
Bolster, C. M. : Mechanical Equipment for Handling Large Rigid Airships
(Paper presented at the Fifth National Aeronautic Meeting of the American
society bf Mechanical Engineers. May, 1933), Archives ~ 3 No.
e L01012.
Rosendahl. C. E. : Non-Rigid Airship Ground Handling, Mechanization of;
Memorandum to All Activities, July 1945.
"Mooring Mast Descriptions and Operational Te~hxliques,"Archives File No.
L01006. Circa 1926.
"Stub Mast For Mooring The Los Angeles," Archives File No. L00124.
Cround Facilities for Handling Airships, Archives File No. L009i 1.
Airqhip Cround Handling Instructions Handbook, NAVAER 01-1F- 501, 1 November 1958.

Meckum Engineering, Inc : Handbook of Operation and Service Instructions

with Parts List for Air Transportable Airships Mooring Mast, NAVAER 14-1501.
"Observations of Carrier Deck Landings and Carrier to Airship Refueling
Practices (Carrier U S S . Palm ) ," Coodyear Aircraft Corporation, Akron,
Ohio. SM-1882. SQ-396. August 6, 1951.

..

"Report of Model ZSZC- 1. Report No. 2, Carrier Suitability Evaluation, 'I

Sub-Board of Inspection and Survey, U S. Naval Air Station, Lakehurst ,
New Jersey, November 27, 1956.

"Water Takeoffs and Landings," Navy Contract NOa(s)-4743, Item I , Goodyear Aircraft Corporation, Akron, Ohio, December 16, 1946.
"Maritime Patrol Airship ZP3G, Coodyear Aerospace Conceptual Design,"
prepared for Naval Air Development Center, 1978.

."

Bailey, D. B. , and Rappoport, H. K . "Maritime Patrol Airship Study

(MPAS) Naval Air Development Center Report No. 80149-60, March 19,
1980.

"The Feasitlity of Mooring Airships to Sea Anchors While Dunking ASW

Detecting Devices, Navy Contract NOas 56- 217, Goodyear Aircraft Corporation GER-7380, March 30, 1956.
Silverstein, Abe and Gulick, B. G. : Ground-Handling Forces on a 1140Scale Model of the U .S. Airship Akron, NACA Report No. 566, Langley
Memorial Aeronautical Laboratory, Langley Field, Va , April 8, 1936.

Abbott, L. H. : Airship Model Tests in the Variable-Density Wind Tunnel,

NACA Report No. 394, Langley Memorial Aeronautical Laboratory, Langley
Field, Va., January 27, 1931.
Bierman, D. ; and Herrnstein, W. H., Jr. : The Interference Between Struts
in Various Combinations, NACA Report No. 468, Langley Memorial Aeronautical Laboratory, Langley Field, V a . , June 5, 1933.
Nielsen, J. N. ; and et al: Determination of the Aerodynamic Characteristics
of the Heavy Lifter, NEAR TR113, Nielsen Engineering & Research, Inc. ,
Mountain View, California, April 1976.
Boldt. T. R.:

Towed Model Tests of 1/75 Scale ZPN Airship During UndockGeneral Development Corporation, Elkton,
Maryland, December 31, 1953.
i s , GDC Report RSO-8- 1.

Boldt T. R. : Towed Model Tests of 1175th Scale ZPN Airships, GDC Report
R50-8- 2. General Development Corporation, Elkton, Maryland, March 22,
1954.

Swarthout , Colburn D : Aerodynamic Forces on Logging Balloons, Master

of Science Thesis, Civil Engineering, University of Washington, 1967.
Wind Tunnel Test of the General Mills Aerocap Model,
Davenport, E. L.:
Part I , University of Detroit Wind Tunnel Project 314, Detroit, Michigan,
March 1960.
Wind Tunnel Test of a Single Hull Balloon Model, CER-12972.
Aerospace Corporation, December 1967.
Freeman, Hugh B

., Pressure-Distribution

Goodyear

Measurements on the Hull and Fins

of a 1/40 Scale Model of the U .S. Airship Akron, NACA Report No. 443,

Langley Field, Virginia, June 1932.

Davenport, E. L. , Wind T u n - : ~ lTest of the General Mills Aerocap Model,
Part 111, University of Detroit, Detroit, Michigan, March 1960.
"Comparative Aerodynamic Characteristics of the XZPSK Airship Having Various Empennage Configurations, I' U . S. Navy Contract NOa(s) 51-007F, Goodyear Aircraft Corporation, 1953.
Bowles , Joseph E. : Engineering Properties of Soils and Their Measurement.
McGraw Hill Book Company, 1970.
A . B. Chance Company Utility Products Catalog No. C726, Centralia,
Missouri, 1972.

32. Conway, H. G., Landing Gear Design, Chapman

& Hall Ltd.,

London, 1958.

Daughty, L. E., J r . ; et al: "Rapid Site Preparation Techniques for VTOL

Aircraft, " Technical Report AFAPL-TR-66- 116, Volume 11, Part ILI, July 1969.
"Climates of the States, National Oceanic and Atmospheric Administration,
Water Information Center, Inc., Port Washington, N. Y. , 1974.
"Water Atlas of the United States,
Washington, N. Y., 1973.

Water Information Center, Inc., Port

Bryson, R. A . , ed. : "World Survey of Climatology, Volume 11, Climates

of North America," Elsevier Scientific Publishing Co. , N. Y., 1974.
Preliminary Study of Ground Handling Characteristics of Buoyant Quad Rotor
Vehicles, NASA Contractor Report NASZ- 10446, Goodyear Aerospace Corporation, Akron, Ohio, July 1980.
"Aerodynamic Evaluation of Kiting Prevention as Determined from the ZPM-4
Airship Anti-Kiting Tests, " Contract NOa(s) 53-571-C, Amendment 9; Goodyear Aerospace GER-8458 Rev B , January 17, 1958, Akron, Ohio.
Hoerner, Sighard F. : Fluid Dynandc Drag, 1958.

Thom , H. C. S. : "New Distributions of Extreme Winds in the United States, "

Journal of the Structural Division, Proceedings or the American Society of
Civil Ergineers July 1968.

"The Kiting Motion of a Masted Airship as Determined by Analytical Evaluation

of Water Model Tests, " Contract NOW 60-029c; Goodyear Aerospace GER- 10052;
Akron, Ohio, May 1, 1961.

APPENDIX A

- ADDED MASS FORCES

1. INTRODUCTION
The treatment of added mass forces in the literature is inadequate even in the
following references :

1.

"Hydrodynamics, " by Sir Horace Lamb

2.

The Complete Expressions for Added Mass of Rigid Body

Moving in an Ideal Fluid, It by F. H. Imlay

Several articles were published in the literature with erroneous concepts and
conclusions; some appeared as recently as July 1981. Even for the topics that were
adequately treated, the approaches were obsolete in the following sense:

1.

The approaches were not easily amenable for extensions

2.

A modern-day airplane aerodynamicist was unfamiliar with

the notation and the approaches

Thus, a comprehensive approach is presented here for the treatment of added
The advantages of the approach a r e as follows:

mass forces.

1.

The limitations and assumptions are clear.

2.

A modem-day aerodynamicist can easily read and follow

the trcatnient.

3.

Formulation is appealing because the existing fluid dynamics

programs can be used for calculation of added mass constants
of arbitrary three-dimensional bodies on digital computers.

4.

Formulation can easily be extended to elastic bodies.

5.

In addition to the gross added mass coefficients, the distribution of the added masses can also be obtained.

Finally, six examples are carefclly selected to demonstrate the concepts.

may clear up the erroneous assumptions that exist in the literature.

2.

EQUATIONS OF MOTION AND IFVISCID FLOWS

The governing equations of mobon of inviscid flows are given by
Continuity equation:

Momentum equation:

2+

div Q = 0

grad p
0

Some

$1

2
Energy equation: &[t
Y-1+
where:

la'

= P at

= fluid density
= i u + j v + k w = total velocity vector

.c

D
fi -- aY + ? grad
a
y
p

= speed of sound
= ratio of specific heats
= pressure

For potential flows (barotropic irxotational flows), Equations A-1 to A-3 boil
down to the following nonlinear potential flow equation:

where:

($)I

02(

= grad 4

~2

=g *Q

= speed of sound

32
a2
= Laplace operator = +-+-

32

ay2

322

+9

grad

0-2

=0

in cartesian system

The boundary conditions of the problem are:

1.

At each point of the solid-fluid surface, at every instant,

the component normal to the surface of the relative velocity
between the fluid and the solid must vanish.

2.

The conditions at infinity are to be specified. Further, it

is required that the velocity due to the motion of the body

be finite o r zero at infinity.

The equation of the surface of a three-dimensional arbitrary body moving in a
time-dependent fashion can be written as

F (x,y,z.t) = 3
The first boundary condition can then be written mathematically as

E+
Q
at

grad F = 0

(A-5)

Equations A-4 to A-6 are valid for incompressible and compressible fluid flows
including subsonic, transonic, supersonic, and hypersonic unsteady flows. For incompressible flows, the nonlinear potential flow equa.tion (Equation A-4) reduces to

The most general flow that is governed by the Laplace equation is unsteady, incompressible, irrotational , and large disturbance flows. There is no unsteady term
in the Laplace equation, but the time dependency comes through the boundary condition given by Equation A-6.
For small disturbances, the nonlinear potential flow equation can be linearized
to the following equation
(A- 8)
where $' is perturbation velocity potential over the steady-state velocity vector

Q = i U and a,
.y

is free-stream speed of sound.

I t can be observed from Equation

A-8 that only incompressible flows can be represented by Laplace's equation even

for steady flows,

Consider a region, R , that is enclosed by a surface, S , and that contains only

fluid in motion. The kinetic energy, T , of the fluid in R is given by

(A- 9 )

The first form of Green's theorem says

v2( + grad

grad ( ) d r =

Substituting the above result (after specializing JI= 4 ) in Equation A - 9 yields

(A- 10)

If the flow is governed by Laplace's equation ( V 2 4 = O ) , then Equation A-11

becomes

(A- 12)
S
-

Since the governing equation and the boundary conditions for the flows under consideration are linear, one can seek a solution for in the following form for a body
moving in incompressible potential flow by virtue of linearity and time variable separability of the problem:

(A- 13)
where u l , u2, u3. u4,

and ug are linear and angular velocities about an arbitrary system axes that is neither an inertial space nor a set of body axes. SubstiUS.

tuting Equation A-13 into A-12 yields

(A- 14)

Interchanging summation and integration in the above equation:

(A- 15)

(A- 16)

where
( A - 17)

The second form of Green's theorem says

(A- 18)

If 41 and

$J

are both harmonic functions, then Equation A-18 becomes

(A- 19)

The application of Equation A- 19 to Equation A- 17 yields

(A-20)

M =M
ij

ji

The kinetic energy given by Equation A-16 can be expressed in matrix form a s

The matrix [Mij] is known as added m a s s matrix. This matrix is symmetric by virtue
of Equation A-20. The Lagrange equation of a rigid body referred to an arbitrary
system axes is

whcre

u 1 = U; u2 = V; u 3 = W ; u4 = p ; u5 = q ;

U6

=r

Expanding Equations A-22 and A-23

(A- 26)

(A- 27)

(A- 30)

Substituting Equations A-16 and A-20 In Equations A-26 to A-31:

F1 = ;
Mll

+ ;M12 + ;hil3 + ;Ml4 + 4 M l 5 + ;hil6

- u2 M13 -

u v M23

- u w M3) - u p M34 - u q Ms5 - U r Mg6

(A- 36)

F ~ = ; M ~ ~ + ; M ~ ~ ~ ; M ~ ~ + ~ M ~ ~ + ; ~ M ~ ~ + ; M ~ ~

In the special case where u l . u 2 u3, u 4 us, and u b refer LO a coordinate systern with the center at the center of mass, Bquations A-35 to A-37 reduce to the
following :

+q

M16

4- q

MZb

q w M36 +

P M46 q2 M56
+

"
(A- 38)

(A-40)
Thc analysis performed so far leads to the following conclusions.
1,

When a body is moving in an inviscid incompressible fluid (which

is at rest otherwise) and a velocity potential can be defined for
the resulting disturbance flow field, then the fluid forces that
arise due to accelerations and due to certain velocity product
terms are given by Equations A - 2 6 to A-31.
these equations are called

G=

The coefficients in

added masses and inertias (also known

as apparent or virtual).
2.

The added mass and inertia coefficients can be put into matrix
form of order 6 X 6 as shown in Equation A-21.

This added mass

matrix is symmetric by virtue of Equation A-20 and hence there

are 21 independent coefficients.
3.

Some of the adfied mass or inertia coefficients will be zero when the
body has certain geometrical properties. In the case of a body with
mutually orthogonal planes of symmetry, the number of co. fficients
will be as follows: one plane of symmetry, 1 2 coefficients; two
planes of symmetry, 8 coefficients; three planes of symmetry, 6
coefficients; and cyclic symmetry, 1 coefficient.

The unsteady Bernoulli's equation for incompressable flows can be written as

The function F(t) may be eliminated from the right side of Equation A-41 by
redefining the velocity potential.

Thus, 4 may be replaced by [ 4

without altering the velocity field in any respect.

- / F(t) dt)

Hence, Equation A-41 can be

written as
(A- 42)

at

The added masses are acceleration dependent aerodynamic forces; hence, for
determination of these forces, Equation A-42 can be written as

eP + a t

= constant

(A-43)

Differentiate the governing differential equation of motion given by Equati~n

A-7 with respect to t

3
3
3
LL+22L+LL.(,
2

ar;~

atax

ataz

(A- 44)

Substitute Equation A-43 in Equation A-44, then

(A- 45)

The boundary condition of the problem can be written on the surface of the
body as

(Q - Q s )

where

2=0

(A- 46)

CI

= velocity vector of the fluid

.c)

QS = -relocity vector of the surface of the body

h . .

nicferentiate Equation A-47 with respect to t

Perform gradient operation on Equation A-43 and take dot product with unit
vector a

[e
+ grad
P

(%)I

g=0

(A- 50)

Compare Equations A - 4 8 and A-50.

Let Q n s = QS
Then

= normal velocity of t h e body sllrface

a Q ~ =s a (Qs 9 = anS s normal accelerztion of

-at
at

the body surface.

Then Equation A-51 car. be written as

The solution of Equations A-45 and A - 5 2 gives the pressure distribution due to
the acceleration of body.

The integration of this pressure gives the acceleration-

dependent aerodynamic forces or added mass coefficients.

p

and anS must be specified.

To solve this problem,

If the accelerations are specified in the direction other

than the normal directions, the normal accelerations have to be computed.

If accelerations are specified as

;=

1,

;= 0. k = 0. 1; = 0,

4 = 0.

and

;= 0,

then

the corresponding Fressure distribution can be obtained by solving Equations A-45

and A-52.

In solving this problem, the unit acceleration

the normal direction accordirlg to Equation A-52.

;has

to be resolved in

By integrating this pressure and

the moments due to this pressure, the forces defined in Equations A-32 to A-37 can
be obtained.

These forces are related to added mass coefficients as shown below.

Similarly. by specifying different s e t s of body accelerations, the remaining

added mass coefficients can be determined.

The sets of prcjblems to be solved to

determine the 21 added mass coefficients are gih-en below.

Accelerations

Added Mass Coefficients

For solution of the above sets of problems, the normal accelerations are to be
specified.

They can be obtained as described below. If F ( x , y ,z) = 0 is the body

surface equation, then the unit outward drawn normal is given by:

=1- f

rad F

(A- 53)

Let linear acceleration vector of the origin 0 relative to the stationary fluid at
infinity be

h and let body

LI

angular acceleration be

;.

.y

If the position vector of a

point on the body is g and the outward normal is n , then the normal acceleration at
the body surface is:

Example 1: Sphere Problem for Validation of the Formulation

For application of the above formulation, consider a sphere of radius, a ,
F ( r , 8. S s r - a = O

The unit ~ e c t o ris given by:

v I'

"IF1

= i sin 8 cos w + uj sin 8 sin w + k cos 8

(A- 55)

The normal acceleration of the body is given by:

=(Q+;x3*%

anS

Acceleration

1.
2.

3.
4.

. . .
.
. .
;=&;rppqq::;=O, ; = 1
. .
. . .
u = v = p - q = r = O .
. .
.
u = v = w - q - , r = O , p = l
a

v = w = p = q = r = O .u - 1

(A- 56)

Norma3 acceleration

= sin

0 cos w

an^, = sin

8 sin w

a
nS1

a
= cos 0
nS3
a
=0
nS4

Zrom the boundary condition.

apl
an = -

p sin 8 cos w

ap2
=an

p sir1 8 sin w

3~

=an

p EOS 8

The governing equation (Laplace's equation) in spherical coordinates is given by:

Three :;elutions for this equation can be written as:

p1 =

f sin

cos w

r
3

1 a
pZ = 2
k 7 sin 9 sin w

r
1 a3
P 3 = Z k T ~0 ~ ~
r
where k is an arbitrary constant.
The validity of t h e above solutions can be verified by substituting these into the
Laplace's equation.

The radial derivatives of these solutions a r e given by:

apl
an

ap2

= - k sin 8 cos

= - k sin

e sir:

r=a

aPj
an

r =a

k cos 8

r=a

The comparison of Equations A-60 and A-57 gives:

k =

(A- 60)

Substituting Equation A-61 into Equa:ion A-59 gives,

1
p 1 = 2 p a s i n Ocos u
(A- 62)

1
p 2 = 2 p a sin 8 s i n w
1
p 3 = ~ apc o s 6

Integrate over the bcdy surface,

sl

=Jf-

p l sin

ff

F2 =

coa u r 2 sin 0 ci ~d r

p 2 sin 6 sin

ur2

sin 8 d 8 d w

0 0

F3 =//-

p3 cos 8 r 2 sin 8 d 0 d w

By substituting A-62 into the above equations gives

The above result agrees with the classical r e s u l t , and there is only one non-zero
coefficient.
Observations
The formul.:tion

presented here to determine the 21 added mass coefficients is

valid and is applicable to arbitrarv three-dimensional bodies.

The formulation is

appealing because (1) existing fluid dynamics programs can be used for calculations on digital computers and ( 2 ) the formulation can be extended to elastic
bodies.
Formulation not only gives gross added mass but also added distribution.

Example 2:

Two-Dimensional Circular Cylinder Accelerating

in a Stationary Fluid

Laplace's equahons in polar coordinates can be written as:

give a unit acceleration in x direction; then:

= cos 0
a
nS
The boundary condition of the problem can b e written as

The pressure function, p , can be written as

2

.P'

cR

cos

This pressure function satisfies Laplace's equation and

hence:

where k = 1; a = 1; M

= p n R2

Observations
This example just demonstrates t h e conventional added mass calculation when
the body is accelerating in a fluid and the result agrees with the classical result.
Added mass distribution for this problem is also known.
Example 3:

Stationary Two-Dimensional Circular Cylinder

-a Fluid with a Steady Acceleration

in

Consider the following velocity field without the body:

ux = U (constant)
u

= Vt

Convert the above velocity ~omponentsin terms of polar coordinates.

ur = U cos 8 + V't sin 8

- U sin 8 + Vt cob; 8

Flow is potential without t h e body since

$ (r.8)

= U r cos

.?A
ar

= U cos

-' 2

=-

ae

Vt r sin 8

0 + Vt sin 8

sin

e + ~t

= ur

cos e = us

Seek an inviscid solution when the body is placed in this stream, then

The velocity field i s chosen s o that i t satisfies boundary condition on t h e cylinder. The flow rcmsins potential even with the body since a potential of the foC~wing form can be defined:

4 ,r.~, = (r +

9
ar

-2
r 30

<)(u

- $)(u
r

+ )

cos 0 + t,

-.

sin 8,

cos e + v t sin 0, = u r

sin e

+ ~t

cos 8) = u

Unsteady Bernoulli's equation can be written as

7

The pressure distribution to determine the added inass forces can be obtained
from the following equation:

E! +
P

at

= constant

= - 2 p R V sin 8

+k

/,=A

dFx=2
dF

= 2 p

R V sin 0 cos 8 R d 8 - k c o s 8 R d 0
RVsin

8 R d 8 - k s i n 8 R d 0

2a

F =
Y

~ sin~2 0 d~ 0 = 2 p l r R 2 V

Hence

Now compute the substantial accelerations without the body.

Without the body:

DQ
aQ
~t
at

+Q

- - jV

grad Q

15

Hence :

k = 1 from Example 2

Observations

Flow is unsteady potential without the body.

Unsteady acceleration is uniform.
Body is placed in this stream and the flow remained potential.
The acceleration-dependent aerodynamic force can be written as:
F
Mass of the
fluid replaced
by the body

Example 4:

n R

( 1 + k)

Pressure
gradient
portion

(+)D u

Conventional
added mass
term

Substantial
acceleration
of the flow
without the
body

Stationary Two-Dimensional Circular Cylinder

in a Fluid with an Unsteadv Acceleration

Consider the following velocity field without the body:

ux

= U (constant)

uY =

(1

)I

cos T

Define a velocity potential ( as:

Hence, flow i s potentid without the body.

Convert the velocity components in

terms of polar coordinates

= - U sin

lTt
+ 21 (1 - cos -1
cos
f

Place a circular cylinder in this stream and seek an inviscid solution; then:

The velocity field is chosen so that it satisfies t h e inviscid boundary conditions

on the cylinder. Define 4 as:
4 ( r . 0 ) = (r

+ R)
r
[U

cos 0 +

5 ( - cos c)sin e]

Flow remains potential

at

( :') r;
1

lrt sin 9
.in T

Pressure distribution to determine the added mass forces i s

Observations
Same relation holds good even for fluids with unsteady acceleration.

not be true for nonuniform accelerations.

This may

Example! 5:

Uniformly ,\ccelerat,hfi Curt Front Penetrates a

Two-Dimensional Ckcular Cylinder

VUt
u =---

Vx

Express velocitj components in tcrms of polar coordinate

Ur

=U

u =
0

COS

0+

U sin 0

v-

a (Ut - r cor

+ 2v (Ilt

- r cos

8) sin 0

8) cos 0

Seek an inviscid solution after the body is placed into the stream. Let:

Ur = 0 when r = R

=>

satisfies inviscid b o u n t - ~ condition

y
on the cylinder.

Continuity equation: diV Q

=0
.c.

+ ur (1 -

Momentum equation :

G
L=

,-

aQ

+Q

grad (I =

grad

a!?

-+
at

zQ =

p,

CI

a
--1 r

3r

ur

grad($)-

9
cI

a
12
P = Z Ppa e
CI

Curl

cos e s i n 0

grad

Dt

2
at

$)( &

curl Q

Tangential momentum :

a u

2U

=-

cos 8

u (sin e + a cos 8

2 U (cos 8 - a sin d - 2 b cos 8 sin t3)

+ b cos2 0)

r=R

21

r=R

=--- U V B cos e + 4 u 2 (cos Q sin 0

- -1 -3 4
P aejrZR
a
- a sin2 8 - 2 b cos 0 sin2 8 ia cos 28-a2
-

2 ab cos 2 8 sin 8 + b cos3 8

2 b2 cos3 8 sin 8)

cos 8 sln 8

ab sin 8 cos2 8

- 2b sin3

sin 8 cos 8

-'

UVR
a sin e + r

'IR=-

2
2
a cos 8

u2

+ j sin cos

[T

2
cos 8 ( a 2 - 1) + a sin 8 cos 8

b sin3 8 + ab cos3 8 + b sin 8 + 7

= - 3 U2

Vt
~

Fx = - 23 R R2

VR

Tp - 2 u a

p~

v2

Ut

a
F

= y5

~R'-VU
a

3
2
FX = - 2 p n R

v2
-

Ut

Substantial acceleration without the body:

Q = i U + j l
ly

(Ut-X)

'c.

- - aQ-

DQ

~t

3Q
5

-at

- - + grad($)
at

- Q

- x curl (1
.c

= ,ja -V~

grad

($1

= grad

2 (Ut

2a

X)

(ut

2
u

$1

x ) 2 2a

B x c u r l rCI
Q

;(ut-x)

hr

--v
a

= - -*i a2 ( ~ - tX)

L'v

+jLe

Observations
Substantial accelerauons of the gust front are zero. Even then, the body
experiences non- zero forces.
Example 6: Stationary Two-Dimensional Circular Cylinder
in a Convecting Vortex Core

Coordinates of point p are ( x , y)

Center of the coordi ;ate system is at the

center oi the cylinder. A t t = 0 , the center of the vorrex core coincides with center
of the cylinder.

A- 27

= radius of the vortex core

V
U

= velocity at the edgeof the vortex core

= velocity of translating vortex

COS

e =

- Ut

=u

coa 8 = !

urf = ux cos 4 + u

U$f

rf

(x

J(x - ut) 2 + y 2

- Utj

sin 4

= - u X sin 4 + uY cos 4

urf = (U

; sin 8

y)cos 4

- ) -V

= U cos 4

~ t sin
)

cos)+ v
- (r cos 4

+ !?
2 (x -

-VUt sin
II

~ t sin
) 4

U(f

- (u - Vr
'jn2)
a

sin 4

2
= - U sin ( + -Vr
a sin

( r cos 4

-~

t cos
!

VUt cos
+aEcos 2 4 - -?-

usin^$+ in^$+Vr - -VUt

R
a

+ -va

cos

I$

Velocity urf is the radial velocity in the vortex core far from the cylinder.
This velocity will be .nod:'ied by the presence o f the cylinder in the vicinity of the
cylinder so that the radial velocity on the surface of the cylinder is zero since the
Hence, ur in the vicinity of the cylinder can

fluid cannot penetrate the cylinder.

be written as

Now, u e has to satisfy the continuity equation.

iontinuity equahon:

div Q = 0=

= - U

a
ar

( sin

( r ur) +

)-V

I++

Compare this equation with (B\ ; then

f(r) =

Vr
-

P.

a ue = 0
ae

+ f(r)

-u

fi

$)

+r

(sin 4

+ ~ta

cos 4,

vr

+a

Momentum equation: D s = - Brad

aQ

Q~
a t + grad T - Q
CI

curl Q =
5

rC,

Curl Q = p Z
CI

-1
[r

ar

Momentum equation can now be written as

- grad
P
P

(r u 1

a
-a+

(ur)]

-8

4
*

-I

-8

T
3

I-'

*I 2

h)

I: k

CIJwN

I-'

5'

-1 rn5

5-

$.

\sl

qJww

-1

IQ

DIP
w w
C1
II

B y observing the form of ur

one can conclude that terms 3, 4, 5 , 6 do not contribute to the pressure on the
cylinder.

+IrzR=

-u

a u

(L

$)iy

'3

a + R = - Z U (cos 4

a,~R=pi-

- 3

UV
a

+ a cos 2
where

cos

"0s (

r=R

+ + 4 u2 (sin

- a 2 cos

41 sin $

sir

p cos

+ - a sin2 4

- b cos ) + ab sin

+ a sin

4 cos 41

+,

a sin 4 cos 4

- b sin 4 - ab cos 4
2n

=-/
Fx

p cos ( ~d b =

-p

11

2
2
nab R =- P V t R n x 4 U 2

2a2u

2n
F =-/
Y

psin(Rde=-

R 2 UVR
R

Substantial acceleration without body

-Dt - -a Q + ($)-

DQ

CI

at

grad

P_

curl Q
rn

CurlQ

i
*

-a

ax

*u

a
a?

3,

-a

"-y ;

=k

(T +;)

= L11 U

(x-ut)

k
Cy

2 v2
"x
= v2
-2 ( x - Ut) - 2
Dt

11

11

(X

Ut) =

=i-

v2 ( X -7

(X

Ut)

Ut)

11

The right-hand side expressions of Equations A-32 to A-37 represent the fluid
dynamic forces experienced by the body when i t is accelerating in an incompressible
inviscid fluid that is otherwise at rest.

These expressions contain 2 1 independent

coefficients called added mass coefficients (also called virtual o r apparent). In the
case of a body with mutually orthogonal planes of symmetry, the number of coefficients will be reduced as follows: one plane of symmetry, 1 2 coefficients; two planes
of symmetry, eight coefficients; three planes of symmetry, six coefficients; anci
cyclic symmetry, one coefficient.

If a body is kept stationary in an unsteady in-

compressible potential flow, then the body experiences unsteady forces.

Part of

these body forces are due to the pressuie gradient that is required to be present in
fluid to accelerate the flow. The remainder of the body forces accounts for the

resistance resuring from the acceleration of the fluid particles induced by the body,
as would be the case if the body were accelerated through an inviscid fluid a t rest,
If the fluid flow problem is solved directly to determine the pressure distribution
and the resulting body forces, then this distinction between the pressure gradient
forces and added mass force would be unnecessary.

In the literature, this distinc-

tion i s usually made since the added mass force can be expressed as
Forte = k M a
where

k = added mass coefficient

M = mass of the fluid displaced by the body

a = acceleration of the ambient flow
The evaluation of this coefficient, k , is demonstrated in Examples 1 and 2 , If
zi1 particles of the fluid are subject to the same substantial acceleration, then the
total force experienced by the body can be expressed as
Force = (1 + k ) M a
This fact is demonstrated in Examples 3 and 4 for steady and unsteady accelerations.
In Example 5, a ramp gust front propagating with constant velocity U is considered.
The substantial acceleration components of this gust front are uniform and zero.
When this gust front passes over a body, then the body experiences unsteady
forces that are unrelated to added mass coefficients and substzntial accelerations
(uniform and zero in the present example) of fluid particles of the ambient flow.
In Example 6, a body is placed in a convecting vortex core; substantial accelerations
of the fluid particles of the ambient flow are nonuniform in this case. In this case,
the body experiences unsteady forces unrelated to added mass coefficients.

The

added mass coefficient approach would give wrong r e s u l s , particularly when the
velocity gradients are very high as in Examples 5 and 6.

APPENDIX B
AIRSHIP MOORING LOADS ANALYSIS
SIMULATION MODEL OUTPUTS
NOTES
1.

The airship is submerged in the steady-state wind with given yaw angle at the
initial condition. It i s then released to start moving freely about the mast.

2.

Refer to Figure 2-2 for airship geometric properties.

INDEX

Bow moored at 60 knots

Angle (deg)

Page

15

B-2

30

B- 9

45

B-16

60

B-23

75

B-30

90

B- 37

Belly moored at 60 knots

15
30
45
60
75

90

******&*r***t**&**L&efi****b*h*******t***

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