AIRCRAFT CIRCULARS

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

No. 196

AVRO C.30 DIRECT-CONTROL AUTOGIRO (BRITISH)

By C. N. Colson

Washington
September 1934
 , NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

AIRCRAFT CIRCULAR NO. 196

AVRO 0.30 DIRECT-CONTROL AUTOIRO (BRITISH)*

By C. N. Colson

Now that the Avro 0.30 type autogiro has reached the
production stage, we are able to publish the first author-
itative description of its construction (figs. 1, 2, and
3).

Like all Avro airplanes the fuselage is built up of

welded steel tubes. The front and rear halves are made
up separately, the division being at the bulkhead behind
the-rear, or pilot's cockpit (figs. 4 and 5). In both
cases the sides of the fuselage are welded up on flat,
table-like jigs, and subsequently the two sides are placed
in their correct relation to one another in a vertical jig
and the cross struts welded in. In the rear half the di-
agonal bracing between the two longerons in a horizontal
plane is by the Avro method of forming a continuous loop
of piano wire by passing it through small curved pieces
of steel-tube welded into each corner, and joining the
ends with a wire strainer. The diagonal bracing in the
vertical plane is rigidly built up with tubes. The front
half is entire1' tube-braced. Wherever possible, jigs are
used both in order to insure accuracy and to cheapen pro-
duction. Consequently, there are not only jigs for weld-
ing, but also for drilling, as, for example, at the four
attachment points where the legs of the rotor pylon join
the top longerons.

After the main part of the fuselage has been erected,

the sternpost and tins are welded on and the whole is
stove-enameled. The fins, although in reality, continu-
ous, may be considered as three in number: The fin on top
of the fuselage; the tail fin which, like the others, is
fixed and occupies the same position as the rudder in a
normal airplane; and the fin underneath the fuselage. All
are built up of small-diameter steel tubes welded together.

The fuselage, from the front of the front cockpit to

the tail, is encircled with plywood formers (fig. 6) car-
rying numerous thin spruce stringers running fore and aft

*prom Plight, August 2, and 9, 1934.

2 N.A.C.A. Aircraft Circular No. 196-

and forming a framework over which a doped fabric covering

is secured. This fabric is..on].y carried up to the top
longerons in the front half of the fuselage, as the deck-
ing over the two cockpits is a separate structure of ply-
wood. The engine bay, and the sides and top of the fuse-
lage in the bay behind the fireproof bulkhead, are covered
with detachable aluminum panels secured with Avro cowling
clips.

The 'ngine mounting consists of steel tubes bolted to

fittings at the ends of the four longerons, carrying at
the front a ring which registers with the back plate of the
engine. The 7-cylinder Armstrong-Siddeley Genet Major en-
gine, developing 140 horsepower at 2,200 r.p.m., is there-
by mounted outside the line of the cowling in a very ac-
cessible position, but the drag is kept low by the smooth
curve of the cowling behind. it. A collector ring with a
single downward-facing outlet carries away the exhaust.
Fuel is carried in a 23-gallon welded aluminum tank,
strapped in position abo .ve .the top longerons in the bay
directly behind the fireproof bulkhead., which is of the
normal sheet aluminum and asbestos construction. Mounted
on the front of this bulkhead is the oil tank, of 3-gallon
capacity, and also of welded aluminum. The throttle con-
trols are the push-and-pull type with d.uralumin rods.

Wooden construction is used in the tail plane, which

has spindled spruce spars, plywood ribs, and spruce strut
drag bracing, the whole being covered with doped. fabric.
This unit is interesting as the camber on the port side
is reversed to counteract the engine torque reaction (fig.
9).'At each end of the tail plane there are upturned.tips
of fairly large dimensions which serve to keep the auto-
giro on a straight course and also to give it the neces-
sary Stability in turns. The trailing edges of these tips
and those of tin tail plane are in the form of flaps which
maybe adjusted by means of a small screw for the purpose
of trimming the aircraft.

A tail wheel is carried in a compression strut and

fork'andhas a 270 by 100 mm (10.63 by 3.94 in.) tire. It
is very neat and yet at the same time amply sprung for the
heavy loads imposed upon it during typical autogiro land.-
ings. It is steerable by cables from a cross foot-bar in
the pilot's cockpit.

The two cockpits are well fitted with the usual in-
struments, map cases, and so on, and the sheet aluminum
 N.A.C.A. Aircraft Circular No. 196 3

seats are dished to take service type parachutes. A ply-

wood floor extends the length of both cockpits and is
bolted to small corner pieces of steel plate welded on to
thefuselage between the cross bracing and the longerons.
The front cockpit has a sliding door on the port side.

'Vide outriggers of pyramid form, which carry the top

ends of the Avro oil-and-spring landing gear compression
legs, appear rather massive, but it must be remembered that
autogiro landings impose greater stresses on this particu-
lar Dart of the structure than do the less vertical land-
ings of the normal airplane. The upper pyramids are built
of streamline-section steel tube, and the axle radius rods,
as wall as the compression legs, are faired to streamline
shape with balsa-wood fairings; consequently, the drag.
should not be unduly high. The assembly in detail is given
in figure.?.

Now we conic to what may be termed the "autogiratory

part of this flying machine. The rotor system consists of
• 3-blade rotor revolving about a massive head mounted on
• form of universal joint, so that it can be tilted in any
direction by a control column (fig. a). This control col-
umn is "hanging" as opposed to that in a normal airplane,
where it is mounted on the floor of the cabin, but the ef-
fect is just the same; that is, to say, pushing the column
forward has the effect of pushing the aircraft down, and
Vice versa. A fore-and-aft-bias is fitted, which trims the
autogiro, much in the same way as the shock-absorber cord-
loading device trims some light aircraft, but it does not
have the disadvantage of giving an entirely false feel to
the controls. A lateral bias is also arranged to overcome
any tendency of the aircraft to wander from the straight
path laterally and directionally.

At this stage it is probably as well to explain that

the rotor is not driven by the engine, but once the air-
craft is in the air it rotates of its own accord, hence
its name "autogiro." Before the autogiro can fly, howev-
er, it is necessary to start up the rotor, and for this
purpose there is a shaft drive, operating through a clutch
and gearing, from an extension on the back of the engine
(fig. 7). Immediately the throttle is opened wide for
taking off, the rotor clutch is withdrawn, and from then
on the rotor operates entirely automatically. The blades
have free movement through several degrees in the vertical
plane, and a very much smaller movement in the plane of
rotation. This latter movement is controlled by friction
4 .ircraft Circular No. 196

dampers. Motion in the vertical plane is necessary for

aerodynamical reasons and allows the forward-traveling
blade to rise and the rearward-traveling blade to fall.
This moveniert is also immediately apparent when an auto-
giro at rest is compared with one in the air. When sta-
tionary it will be seen that the blades droop considera-
bly, whereas in movement they assume a very definite con-
ing angle (fig. 9). Two of the blade hinges are arranged
so that the corresponding blades may be folded back when
a release pin is pulled out, and thus the autogiro can,
when necessary, be housed in a very narrow space (fig.
10). The blades themselves have a long steel tube spar,
ply-faced spruce ribs, and plywood covering 0.03937 inch
thick, the extreme tip being shaped from solid balsa wood.
The rotor head itself is a straightforward engineering job,
running on ball bearings and incorporating a Bendix brake
which allows the blades to be locked when not in use.

Briefly, the blades are arranged aerodynamically so

that the resultant of the lift and drag forces acts upon
them in a slightly forward direction. The effect is to
pull the blades around, and the centrifugal force keeps
them extended. One of the great advantages of this sys-
tem is that the speed of the blades through the air is,
within limits, not dependent upon the speed of the whole
aircraft through the air. There can-1 therefore, never be
any sudden loss of lift due to the flying speed dropping
too low, as whatever the rate of progress of the aircraft,
the blades still rotate at their correct speed. Thus, the
air flow over them is unchanged and the lift remains the
same. The reader will appreciate from this explanation
why a vertical descent is possible with the autogiro and
not with the normal aircraft, as the latter is dependent
upon its speed through the air for air speed over its lift-
ing surfaces.
 lc.A.C.A. Aircraft Circular No. 196 5

CHARACTERISTI CS

Dimensions:

Diameter of rotor circle 11.28 m 37 ft. 0 in.

Height, over-all 3.36 11 11 0-3/4 in.

Length, over-all 6.01 19 8-1/2 II

Wheel track 2.74 II

9 0 in.

Span of tail piano 3.10 10 2

Ar e a s:

Tail plane 1.45 m2 15.6 sq.ft.

Upturned tips (both) .84 8.55

Tipper fin 1.20 12.9 I'

Lower fin .38 3.38

Rotor blade (each) 1.45 I' 15.6 II

Weights (458.66 km =
285 miles range):

Tare weight 553.38 kg 1220 lb.

Crew (two) 149.69 330

Fuel (23 gallons) 80.28 I' 177

Oil ( 3 gallons) 14.51 32

Baggage 18.60 41 I

Gross weight (maximum

permissible) 816.46 1800

Performance:

Speed at sea level (max.) 177.03 km/h 110 m.p.h.

Cruising speed 152.89 It

95 U
6 1.A.C.A. Aircraft Circular No. 196

Performance (continued):

Minimum flying speed,

about 24.14 km/h 15 m.p.h.

Landing speed 0

Take-off run 10.9? in 12 yd.

Landing run 0

Rate of climb (initial) 3.56 m/s 700 ft./min.

Ceiling 3657.6 rn 12000 ft.

N.A.C.A. Aircraft Circular No. 196 iig.1

AREAS INSQ.FT
TAIL PLANE .156
UPTURNED TIPS (roral).. 855
UPPER FIN ..............
..............
129
338
$40 W. ARMSTRONG SIDDELLY
GENET MAJOR ENGINE
LOWER FIN
ROTOR BLASE ... ........ 156
ROT BLADES (Thral). .468 FEET
0 , 2 3 4
0 05 I
METRES

Figure 1.- General arrangement drawing of the

C. 30 autogiro.
N.A.C.A. Aircraft Circular No. 196 Figs, 23

Figure 3.- The first of the Avro C 30a autogiros ready roi' O.e.L1YSI7
to the Royal Air Force for army co-operation work.
N.A.C.A. Aircraft Circular No. 198 Figs. 4,5

PETROL
TMU(

Figure 4.- Fuselage details of the 0 30 autogiro.

The letters show the position of the
enlarged details on the fuselage.

P.

Figure b.-
Welded
construction.
The rear of
the fuselage
with the
tail wheel
mounting
N.A.0.A. Aircraft Circular No. 198 Pigs. 6,7,8,9,10

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