Aeroplane – June 2018

FLIGHT-TESTING FAIREY ROTODYNE

Into the unknown

Once the tail fins had been

revised and a new retractable

undercarriage fitted, the

Rotodyne could realise more of

its performance potential.

AEROPLANE

Development

Technical Details

Flight Testing

Cancellation

Insights

AEROPLANE JULY 2018 http://www.aeroplanemonthly.com 89

T

he Rotodyne wasn’t

looking its best when

it made its maiden

flight because some of

the engine panels had been

removed to aid cooling. The

aircraft was in a bare metal

finish devoid of markings,

apart from the military serial

number XE521. It never

received a civilian registration.

In the course of the ground

test programme the retractable

undercarriage had been

replaced by a fixed and braced

unit limited to 4in (10cm) of

travel. This was to eliminate the

risk of ground resonance while

a new unit with revised

dampers was designed and

manufactured, this flying

during 1958. To increase

airframe stiffness the impressive

tail assembly was removed and

temporarily replaced by a

metal strut running from the

top of the rotor pylon to the

aircraft’s tail.

The first untethered flight on

6 November 1957, plus two

others that day, were

completed in helicopter mode.

It had originally been planned

to keep within the ground

cushion during these early

sorties but a circuit of White

Waltham well above cushion

height was made on the same

day as well.

As flight testing proceeded

the wind tunnel test data was,

in general, confirmed. The first

phase was conducted with

tip-jets lit and at altitudes up to

5,000ft (1,540m). At speeds

below 70mph (112km/h) the

propellers were maintained at

fairly low thrust to avoid

sudden yaw in the event of

engine failure.

The first transition was

approached in easy stages.

Apart from the need to confirm

Ron Gellatly makes the Rotodyne’s maiden untethered flight at White

Waltham on 6 November 1957. ZUMA PRESS/ALAMY

the tip-jets’ relight performance

it was necessary to assess the

airframe trim changes involved

and avoid large rotor blade

flapping angles. The first step

was to cut fuel supply to each

pair of blades in turn. The

compressor was declutched,

the compressor re-engaged

and the jets relit.

Once the technique was

established, full transitions

both ways in level or gentle

climbing flight quickly became

what Gellatly called, “fairly

simple manoeuvres”. Air speed

in autorotative flight was then

quickly increased to 160mph

(250km/h).

The next stage was to

progress beyond manual

control of collective propeller

pitch to interconnected

control of pitch and engine

speed through normal

propeller governors. “This was

entirely satisfactory and

immediately allowed much

more latitude in thrust

handling”, Gellatly reported.

Up to this point the

Rotodyne was limited to

160mph (256km/h) but even

then, he pointed out, the

aircraft was nearly twice as fast

as conventional helicopters.

“Already we have cleared the

worst of the handling hurdles

and with reasonable

confidence it looks as if this

revolutionary aircraft is going

to fulfil all its design

expectations”, he observed.

During this period, it was

discovered that the sloping

upper tail fins, which had been

designed to fold outwards to

avoid contact with the rotor

blades on the ground, were

introducing an unacceptable

level of cross-coupling in lateral

and directional control. Making

them vertical helped cure

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