Aeroplane – June 2018

92 http://www.aeroplanemonthly.com AEROPLANE JULY 2018

TECHNICAL DETAILS FAIREY ROTODYNE

A

n innovative design it

may have been, but

in terms of its main

structure the Fairey

Rotodyne was essentially

conventional. The basis of the

prototype was a rectangular

metal box 8ft (2.46m) wide

and 6ft (1.85m) high. At the

rear of the fuselage were large

clamshell doors which enabled

the aircraft to carry a variety of

loads ranging from passengers

to cars.

It was intended that the

cabin layout could be changed

with relatively little disturbance

to the powerplant, control and

rotor systems. As Flight

remarked in 1956, 3,000

unobstructed cubic feet (85

cubic metres) of capacity,

capable of ascending and

descending vertically and of

fl ying at 200mph (320km/h), “is

surely a unique attraction”.

Apart from the controls running

from the pilots’ cabin to the

engines, rotor head and tail,

there was no element of the

powerplant or control system in

the fuselage itself.

The wing was a stressed

skin-covered structure with two

main spars. It was attached to

the fuselage at four points. Of

constant section from root to

tip, it carried the forward

propulsion engines and

supported the one-piece rotor

pylon, which was fastened to

the fuselage by four bolts. The

pylon itself was constructed of

17swg steel tubing, narrowing

at either end to 22swg. The

tubes were up to 8ft (2.46m)

long and carefully butt-jointed

to a very high fi nish. This

structure transmitted all loads

between the airframe and the

rotor head.

The key aspect of the

Rotodyne’s design and

construction was the all-steel,

power-operated rotor head

and head mechanism.

Construction involved

machining large steel forgings

weighing up to 14cwt (711kg)

with complex light alloy

castings and a wide variety of

light alloy and rolled steel

components. Fairey had

installed new machine tools in

its factory specifi cally for

machining these components.

The rotor blades were

essentially stainless steel

envelopes including internal

ducting for the air supply to the

tip units. They contained a

solid forward spar and leading-

edge ballast weight. The

limitations of contemporary

heat-treatment equipment

meant that diffi culties were

initially encountered in the

supply of the 35ft (10.77m)-

long leading-edge spars but

the English Steel Corporation

was able to develop a suitable

process. Stainless steel tubing

was also used for the internal

air ducting.

Initial Rotodyne studies had

featured a variety of engine

options. It was not until BEA

issued its detailed specifi cation

for a 40-seat helicopter that

Fairey decided the Napier

Eland best met its needs and

was far enough advanced in

development. But in the

Rotodyne installation the

Elands featured two key

changes. A purpose-designed

auxiliary axial-fl ow compressor

mounted at the rear of each

engine and driven by a shaft

supplied air for the tip-jets at a

combined rate of 45lb (20kg)

per second. The fl ow rate was

controlled by an umbrella valve

arrangement of fl aps in the air

intake and operated by the

collective pitch lever. There was

a hydraulic clutch between the

turbine shaft and the

compressor.

Further changes involved

bifurcating the engine jet pipe

to enable it to pass air around

the auxiliary compressor, and

fi tting a gear-tooth coupling to

A remarkable creation

The fi rst prototype aircraft under construction at Fairey’s Hayes, Middlesex, plant in January 1956. AEROPLANE

It was not until BEA issued its detailed

specifi cation for a 40-seat helicopter that Fairey

decided the Eland engine best met its needs

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