NASA TECHNICAL N O T E TN .

-D-3960
NASA -
.cs, -
t i

WIND-TUNNEL TESTS OF A SERIES

OF PARACHUTES DESIGNED FOR
CONTROLLABLE GLIDING FLIGHT

by James A. Weiberg and Kenneth W. Mort

Ames Research Center
Moffett Field, Cali$

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. MAY 1967

 TECH LIBRARY KAFB, "I

IIllilIllllOlLll3llLllOllLl7lll11 I1
l
NASA T N D-3960

WIND-TUNNEL TESTS O F A SERIES O F PARACHUTES

DESIGNED FOR CONTROLLABLE GLIDING FLIGHT

By James A. W e i b e r g and Kenneth W. M o r t

Ames Research Center

Moffett Field, Calif.

NATIONAL AERONAUT ICs AND SPACE ADMINISTRATION

For s a l e by the Clearinghouse for Federal Scientific and Technical Information
Springfield, Virginia 22151 - CFSTI price.$3.00
 WIND-!LV"EL TESTS OF A SERIES OF PARACHUTES

DESIGNED FOR CONTROLLABLE GLIDING FLIGHT

By James A. Weiberg and Kenneth W. Mort

Ames Research Center

SUMMARY

It was found that the glide capability of parachutes was affected by the
canopy configuration. The maximum lift-drag ratio achieved was approximately
2.1 and was attained by two parachutes, a rectangular canopy and a 3-lobe
canopy. This performance was generally obtained with some loss in stability,
particularly at low lift-drag ratios corresponding to nearly vertical
descent. Limited results of an investigation of two reefed configurations
are also presented.

INTRODUCTION

The characteristics desired of a recovery parachute are high maximum

lift-to-drag ratio (L/D) with ability to control the glide angle from
vertical descent (L/D = 0) to the maximum L/D. Research reported in refer-
ence 1 showed that the glide path of a parachute could be controlled by use
of an extendable flap in one side of the canopy. The maximum glide path
angle of these parachutes was limited by distortion and collapse of the
leading edge of the canopy. Additional tests were made of parachute con-
figurations designed to maintain canopy shape to higher glide angles and the
results are presented in this report. The tests were conducted in the Ames
40- by 80-foot wind tunnel.

NOTATION

b reference span of rectangular parachutes, ft

drag
CD drag coefficient,
9so

CL lift coefficient, lift

9so

CR resultant force coefficient, J c L ~+ cD2

DO nominal diameter of uninflated parachute, ft

 h suspension line length, ft

L
- lift-drag ratio
D
9 free-stream dynamic pressure, psf

d o 2 , or reference area, sq ft
nominal uninflated parachute area -
SO 4

v free-stream velocity, f p s

Ali internal control line extension (see figs. 2(c) and 2(f))

control line extension, ft

MODEL AND APPARATUS

Parachutes

The parachutes primarily have solid canopies. Single- and multiple-

lobe canopies and clusters of single canopies were tested. Photographs of
the parachutes in the tunnel are shown in figure 1. The geometry of the
parachutes is given in figure 2. Configurations 1 to 6 (figs. 2(a) to 2(d))
are single circular canopies. The three devices investigated to prevent
canopy leading-edge collapse are shown in figure 2(e) and consist of (1)a
curved aluminum tube inserted into the leading edge of the canopy, (2) a
torus inflated to 0.8 psi with nitrogen and attached to the skirt of the
canopy, and (3) triangularly shaped struts attached to the leading edge of
the canopy at the suspension lines. Configurations 7 and 8 (fig. 2(f)) are
multiple-lobe canopies and represent a cluster of three parachutes in a
single canopy. Configurations 9, 10, and 11 (figs. 2(g) to 2(i)) are rec-
tangular canopies. The sailcloth porosity (cfm/sq ft at a differential pres-
sure of 0.3 inch of water) was 2 for configurations 1 to 8 and 0.5 for
configurations 9 to 11.

The circular and multiple-lobe canopies (configurations 1 to 8) had

controllable trailing-edge flaps. Configurations 5 and 7 also had control-
lable internal suspension lines (see figs. 2( c) and 2 ( f)). The rectangular
canopies (configurations 9, 10, and 11) had control lines attached as shown
in figures 2(g), (h), and (i).

Parachute configurations 1 to 8 were designed and fabricated by the

Ventura Division of Northrop Corporation. Configurations 9, 10, and 11
were designed and fabricated by Barish Associates, Inc.

2
 Control Mechanism and Tunnel Mounting

The mechanism which operated the control lines is shown in figure 3,

and is similar to the one described in reference 1.
The parachutes were mounted in the tunnel either on one of the con-
ventional model support struts (fig. 4(a)) or on a short strut (fig. 4(b)).
On the conventional strut, the control mechanism was attached rigidly to the
strut and the parachute was "flown" in an approximately horizontal plane
near the center of the tunnel. On the short strut, the control mechanism
was mounted on a gimbal arrangement which allowed the mechanism to pivot
about a horizontal axis so that the parachute was "flown" in a vertical
plane.

Tests and Corrections

The parachutes were tested for a range of control settings and tunnel
velocities. Tests of configurations 1 to 8 began with a low stable flap
setting. The flap extension was then increased until the parachute oscil-
lated. Tests of configurations 9 to 11 began at maximum L/D, which
occurred just prior to the collapse of the leading edge. The control lines
were then retracted until the canopy oscillated. The data presented in the
figures represent the maximum range of control settings with which the
parachutes could be flown without oscillating violently.

Parachutes.5 and 7 were also tested in several reefed conditions. The

parachutes were reefed at the skirt for several skirt diameters, and the
drag was then determined for each diameter.

Lift and drag were measured by the regular wind-tunnel balance system.
The drag data have been corrected for the drag of the supports. No cor-
rections have been applied to the data for blockage or the effects of the
tunnel walls because these corrections are estimated to be less than
1 percent.

RESULTS AND DISCUSSION

Glide Performance

The aerodynamic characteristics of various sin le canopy configurations

are shown in figure 5 by presenting CL, CD, and LTD as functions of con-
trol line setting. Results are shown for various forward velocities, canopy
sizes, and suspension line lengths. If not indicated, the parachutes were
flown in a vertical plane. Three of the configurations were flown both
vertically and horizontally to evaluate the test technique. Figures 5(a),
(b), and (c) indicate some differences in the L/D depending on whether the

3
parachute was flown in a horizontal or vertical plane. However, these
differences are within the repeatability of the data on a given parachute as
shown in figures 5(b) and (c).

It is apparent from the results of figure 5 that of the single canopy

configurations investigated, the rectangular canopies (configurations 9 to 11)
achieved the highest values of L/D. The maxi" value was about 2.1. The
maxi" L/D achieved by all of the configurations investigated was limited
by collapse of the.canopyleading edge. To delay or prevent this collapse
the effects of modifications to the shape of the canopy leading edge and the
effects of leading-edge support devices (see figs. 2(a) and 2(e)) on the
aerodynamic characteristics of the basic single circular canopy ( configura-
tion 4) were investigated. The results are shown in figures 6 and 7. It can
be inferred from these results that reshaping the leading edge or employing
stiffening devices generally delayed collapse of the leading edge of the
canopy. The inflated torus was the most effective device; it increased the
L/D from about 1.1 to about 1.9 and, hence, appears to be a promising method
of increasing the L/D capability of gliding parachutes.

Data from clusters of three parachutes and single canopy shapes resem-
bling clusters (fig. 2(f)) are presented in figures 8 and 9. The three-lobe
canopy (configuration 7) achieved a maximum L/D of 2.1.

Although the maximum L/D capability of the parachutes could be

P
increased by varying canopy shape or adding Leading-edge sup ort devices
(figs. 5 through 9 ) , it was not possible to achieve zero L D correspond-
ing to a vertical descent. At control settings intended to produce low L/D,
the parachutes oscillated violently in pitch and yaw. Analysis of the data
in reference 2 indicated that parachute oscillations are primarily due to a
static instability resulting from insufficient canopy porosity. The porosity
of the sailcloth was essentially zero and there was very little geometric
porosity.

Effect of Geometric Porosity

The geometric porosity of the three-lobe canopy (fig. 2(f)) was varied
by increasing the vent opening on each lobe. The parachute with a porosity
of 6 percent achieved a minimum L/D of 0.3. At low L/D the parachute
was operating near or in the wake of the sup ort strut; hence its stability
could be affected by this wake. Maximum I$ and the corresponding resultant
force coefficient decreased with increasing porosity (figs. 10 and 11).
Similar porosity studies were not performed on the other configurations
investigated. However, these results are considered to be generally appli-
cable for gliding parachutes employing sailcloth which is essentially
nonporous.

4
 Drag in Reefed Configuration

In addition to glide performance, the drag of parachutes 5 and 7 with

the skirt reefed to various diameters was determined. The effect of reefed
diameter on parachute drag is shown in figure 12. With the parachutes reefed
at the diameters investigated (up to 60 percent Do for configuration 5 ) the
parachute oscillations were reasonably small and the parachute did not produce
a significant amount of lift.

CONCLUDING REMARKS

Maxi" L/D was limited by collapse of the canopy leading edge and
m i n i m u m L/D was limited by the uncontrollable oscillation of the canopy.
When the canopy leading edge was sup orted with an inflatable torus, the
collapse was delayed and maximum L$ achieved was about 1.9. This was
nearly double the value without the torus. The glide capability of the
parachutes investigated was affected by canopy configuration. Three-lobe
and rectangular shaped canopies attained the highest L/D, about 2.1. Gen-
erally, the canopies investigated had essentially zero porosity which is
necessary for high maximum L/D. The use of centrally located geometric
porosity reduced the maximum LID but greatly increased the range of L/D
which was not accompanied by oscillation of the canopy.

Ames Research Center

National Aeronautics and Space Administration
Moffett Field, Calif., Jan. 31, 1967
124-07-03-07-00-21

REFERENCES

1. Gamse, Berl; and Yaggy, Paul F.: Wind-Tunnel Tests of a Series of

18-Foot-Diameter Parachutes With Extendable Flaps. NASA TN D-1334,
1962.
2. Heinrich, Helmut G.; and Haak, Eugene L.: Stability and Drag of
Parachutes With Varying Effective Porosity. ASD-TDR-62-100, Sept . 1962.

5
 (a) Configuration 1.

Figure 1.-The parachutes mounted in the tunnel.

7
 (b) Configuration 2.

Figure 1.-Continued.

a
(c) Configuration'3.

Figure 1.- Continued.

9
 (a) Configuration 3 .

Figure 1.- Continued .

10
( e ) Configuration 6.
Figure 1.- Continued.

11
 (f) Configuration 7.

Figure 1.- Continued.

12
 ( g ) Configuration 9.

P
Figure 1.- Conthued .
w
( h) Configuration 10.

Figure 1.- Continued .

(i) Configuration 11.

Figure 1.- Concluded.

Flap enclosures

m
--I k l . 1

L't
Do Nominal diameter, f t 12
So Nominal area, ft2 113
D, Vent diameter, ft, .83
D, Suspension line diameter, in .08

AI I dimensions in inches
(a) ,.mfigurations 4.
Figure 2 . - Geometry of t h e parachutes.
 Same basic conopy os configurotion I except for the
addition of the louvers, os shown, and the absence
of flaps

Suspensioi lines to t h e s e A
gores used for control

Leading
edge

(b) Configuration 3.

Figure 2.- Continued.

 ne no
29 40

I
I

!
1
I
Lineno 1 Length
1
Same basic shape as
configuration 2 with
the addition of the
center lines 31, 38
30,39 .897
29,40 .872
6 0 0 0 0

Line location
Lines 2 through 9 and 15 on rear center gore to one link
plus line 29
Lines 22 through I and 16 on rear center gore to one link
plus line 40
These lines grouped together Flap lines I I through 14 one link
for A I , control [Flap lines 17 through 20 one link
Flap lines IO, 15,16 and 21 snap link
These lines grouped together Lines 30,31,38, and 39 one link
for A I i control (Lines 32,33,34,35,36 and 37 one link

( c ) Configuratior, 5 .

Figure 2.- Continued.

18

I
 e e
R",. P
Laodinqsdqe
e Leading edge

mu Rib dimensions

Leodinq c6q. TreClLnq eoqo

35 14 2966 0 2491 0 3916 0 33W 0 2785 0

C' '
Section A-A
for links 1,2,
3,&l0,1l,l2
1-1 AI I dimensions in inches

(a) Configuration 6.

Figure 2.- Continued.

Iu
0

"\\ \\\ \ I I I 'I/Y' I "

Configuration 4 with 6 inch Configuration I with I 1/4 inch Configuration I with triangular
inflatable torus aluminum tube leading edge. leading edge stiffeners fabricated
stiffener from 1/4 inch aluminum tubing

(e) Leading-edge stiffeners.

Figure 2.- Continued.

 Vent cover

Gore 64 1

’ >Flap
B
enclosure

View K-K 8 L-L

e
Nominal diameter 12 f t
Nominal area 113 ft2
36 1 1 I I
IT
Suspension line diam .08 in.
38
10 i * Suspension line length 12 f t

Suspension lines to gores 38 through

42 and 45 through 49 grouped
together for A & control and lines
to gores 7 through 23 grouped
together for AZi control.
Gore detail AI I dimensions in inches
( f) Configurations 7 and 8.

Figure 2 . - Continued.
 Iu
Iu

0 20 40
Front view w
Scale, inches

I
(g) configuration 9.

Figme 2.- Continued.

 Reference area 169.8 ft2
Inflated span 20 f t
Inflated maximum chord 6 f t

( h) Configuration 10.

Iu
w
Figure 2.- Continued.
 Control line attachment
points

Leadidg edge Leadingedge’

- - v u

-Rib-,/ \ tl Control line

Reference area 328 ft2 Rib

Inflated span 24 f t
Inflated maximum chord 9 f t

Front view

(i) Configuration 11.

-
0 40 80

Scale, inches

Figure 2.- Concluded.

Figure 3. - Control mechanism.
 -- v

Top view

Tunnel

Side view

(a) Horizontal flight.

f -v
Top view

(b) Vertical flight.

Figure 4.- The two methods of mounting the parachutes in the wind tunnel.

26
 1.c

CL
.8

.6

I .o

CD
.e

.6

I .4
I I IlrmT
7
Parachute flown:

I .2

LID

1.0

.0
0 .I .2 .I .2 .3
AZ,/D, A2,/D0
h/D,= 1.0 h/Do = I.73
(a) Configuration i, v = 30 fps.
Figure 3 . - Aerodynamic characteristics of basic configurations.

27
 I

I I .

I .o

.8 I
I , : . , I : " '

I I

CD

-
--------

I .2

1.0
L./D :-I .-
..
. . . ..'.
. . .. .
x-----.rz
Parachute flown:
-
:0 Vertically -
-
-
-
I 0 Horizontally -
-
0 Horizontally (repeat) Z
l I I I , I I I I I I l l I / I I /
.-_ _ , I 1 I I I LJ L l l I I I I I

0 .I .2 .3
AZc/D0

Configuration 2; V = 30 fps onfiguration 3; V = Configuration 4; v = 30 fps,

h/Do = 1.0. h/Do = 1.0. flown horizontaIly.
Figure 5. - Continue
 1.2

1.0
,
CL
I I

.a

1.0

.a
CD

.6

1.4
L/D
1.2

1.0
0 .I .2 0 .I .2 .3 0 .I .2 .3
AZc/D0 Zc/Do
D, = 12 f t Do = 16 ft
( e ) Configuration 5 ; V = 30 fps, h/Do = 1.0.

Figure 5 . - Continued.
 1.2

CL
I .o

.0

-. I 0 .I -.I 0
AZ,/D, AZ,/D, AZ,/D,
V = 30 fpS v = 45 fps V = 60 fps

(f) Configuration 6, h/D, = 1.0.

Figure 5 . - Continued.

30
 I .o

CL
.8

.6

.6

CD
.4

.2

I
I I

2.0 I
r
LID 1

I.8

1.4
-.04 -.02
A?.,/b
V = l O O fps
0 20 40
I I 60
v, fps
AZ,/b = -.013
IO0

( g ) Configuration 9.

Figure 5 . - Continued .
 I I 1 I
I I
I! I I
I .o II
TI
I I

II II I
I
11
I I
1 1
I
I
I
CL II I :0
I

II 1 1
.8
wi l tI 1I

I
I
I I I I

.6 II
-
I I l II

I I I I
II
II I
.6 II
rl
I
I
I I II
ii
I I
I+
I
I
I
CD u II
I I
.4 I I
TT
II i
I I
I
I
I:I I I
I I
I I i
1
.2 II
rr I
II 11
[I, I

2.2
J
?
1
I
2.0 I
I
I
L/D I
I
I
I .8 I
I
I
I
I
I
I C
1.V !
-.06 -.04 -.02 -.08 -.06 -.04 -. 02 3
AZC/b AZc/b

(h) Configuration 10. Configuration 11.

Figure 5 . - Concluded.

32
 I.o

.8

CD

.6

.4

1.2

L/D
1.0

'-0 .I .2 .3 0 .I .2 . .3
A2,/Do A2 JD0
w
Lc, Figure 6.- E f f e c t of leading-edge s k i r t extension; flown horizontally, h/Do = 1, V = 30 f p s .
 I .o

.8
CL

.6

.8
CD

.6

.4

2.0

I .8

.6
L/D
4

I .2

I.o

.8
0 .I .2 .3 0 .I .2 .3 0
. .

.I .2 .3
A2,/Do A I ,/Do A2,/Do
Figure 7.- E f f e c t of canopy support devices; flown h o r i z o n t a l l y ,
h/Do = l’,V = 30 f p s .

34
 l . O-p I 1 I I I I I I1 I I I I I I I I I1 I I I I-
I I I
-
1 Parachute
mconfigurotion
.8

CL
.6

tl
.4 I I l l I I I I I I I I I I I I I I I I I I I I I I I I I

I LL

I I

I.4
LID
1.2

I.o
0 .I .2 .3 0 .I .2 .3 0 .I .2 .3
A?.,/D,

Figure 8.- Aerodynamic characteristics of clusters of parachutes; :flown horizontally, h/Do = 1, V = 30 0 s .

 I.o

.8
CL
.6

L
iii
2.2

2.0 I 1% =.028

I .8

0 .I 0 .I 0 0 .I
AZ,/D, AZ,/D, AZ,/D, AZ /Do A2,/Do
V=6OfPS v=30fps v = 45 f ps V = 60 fpS

(a) Configuration 8. (b) Configuration 7.

Figure 9. - Aerodynamic characteristics of shaped parachutes, h/Do = 1.

36
 .6
CL
.4

.6
CD
.4

.1.8

I.6

.4

LID
I.o

.8

.6

.4

.I 0 .I .2 -.I 0 .I .2 0 .I .2
A2 JD0 AZc/Do A2,/D0
Porosity .09percent 3.0 percent 6.0 percent

A1 *
Figure 10. - E f f e c t of p o r o s i t y ; c o n f i g u r a t i o n 7 , V = 40 f p s , 2 = 0.
DO
37

I
 3

L/D

.8
C, at

.6
0 2 4
V e n t porosity, percent

Figure 11.-Effect of porosity on glide capability; configuration 7,

V = 40 fps.
I
P
0
03
CD

I , , , , I , , , / /, , I I , , , , ,,,,,,,,,,,,,,,,/,/,/,,,,,,,,,,,,,J,,
I I I I I I I I I I I I I I I ~ I I I I I ~ I I II I I I I I I I I I I I I ~ I I I I I I I I I I I I I I I I I I I ~

0 IO 20 30 40 50 60
Reefed diameter, percent Do

(a) Configuration 7. (b) Configuration 3.

Figure 12.- Drag of reefed parachute.

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