Fairey Rotodyne

https://en.wikipedia.org/wiki/Fairey_Rotodyne

The Fairey Rotodyne was a 1950s British compound gyroplane designed and built by
Fairey Aviation and intended for commercial and military uses. A development of
the earlier Gyrodyne, which had established a world helicopter speed record, the
Rotodyne featured a tip-jet-powered rotor that burned a mixture of fuel and
compressed air bled from two wing-mounted Napier Eland turboprops. The rotor was
driven for vertical takeoffs, landings and hovering, as well as low-speed
translational flight and autorotated during cruise flight with all engine power
applied to two propellers.

One prototype was built. Although the Rotodyne was promising in concept and
successful in trials, the programme was eventually cancelled. The termination
has been attributed to the type failing to attract any commercial orders; this
was in part due to concerns over the high levels of rotor tip jet noise
generated in flight. Politics had also played a role in the lack of orders (the
project was government funded) which ultimately doomed the project.

Due to Army and RAF interest, development of the Rotodyne had been funded out of
the defence budget for a time. During 1956, the Defence Research Policy
Committee had declared that there was no military interest in the type, which
quickly led to the Rotodyne becoming solely reliant upon civil budgets as a
research/civil prototype aircraft instead. After a series of political
arguments, proposals, and bargaining; in December 1956, HM Treasury authorised
work on both the Rotodyne and Eland engine to be continued until the end of
September 1957. Amongst the demands exerted by the Treasury were that the
aircraft had to be both a technical success and would need to acquire a firm
order from BEA; both Fairey and English Electric (Napier's parent company) also
had to take on a portion of the costs for its development as well.

Analysis

The one great criticism of the Rotodyne was the noise the tip jets made;
however, the jets were only run at full power for a matter of minutes during
departure and landing and, indeed, the test pilot Ron Gellatly made two flights
over central London and several landings and departures at Battersea Heliport
with no complaints being registered, though John Farley, chief test pilot of the
Hawker Siddeley Harrier later commented:

"From two miles away it would stop a conversation. I mean, the noise of those
little jets on the tips of the rotor was just indescribable. So what have we
got? The noisiest hovering vehicle the world has yet come up with and you're
going to stick it in the middle of a city?

There had been a noise-reduction programme in process which had managed to
reduce the noise level from 113 dB to the desired level of 96 dB from 600 ft
(180 m) away, less than the noise made by a London Underground train, and at the
time of cancellation, silencers were under development, which would have reduced
the noise even further — with 95 dB at 200 ft "foreseen", the limitation being
the noise created by the rotor itself. This effort, however, was insufficient
for BEA who, as expressed by Chairman Sholto Douglas, "would not purchase an
aircraft that could not be operated due to noise", and the airline refused to
order the Rotodyne, which in turn led to the collapse of the project.

Design

The Fairey Rotodyne was a large hybrid rotorcraft, known as a compound gyroplane
or Gyrodyne. According to Wood, it held the distinction of being "the largest
transport helicopter of its day". It featured an unobstructed rectangular
fuselage, capable of seating between 40 and 50 passengers; a pair of
double-clamshell doors were placed to the rear of the main cabin so that freight
and even vehicles could be loaded and unloaded.

The Rotodyne had a large, four-bladed rotor and two Napier Eland N.E.L.3
turboprops, one mounted under each of the fixed wings. The rotor blades were a
symmetrical aerofoil around a load-bearing spar. The aerofoil was made of steel
and light alloy because of centre of gravity concerns. Equally, the spar was
formed from a thick machined steel block to the fore and a lighter thinner
section formed from folded and riveted steel to the rear. The compressed air was
channelled through three steel tubes within the blade. The tip-jet combustion
chambers were composed of Nimonic 80, complete with liners that were made from
Nimonic 75.

For takeoff and landing, the rotor was driven by tip-jets. The air was produced
by compressors driven through a clutch off the main engines. This was fed
through ducting in the leading edge of the wings and up to the rotor head. Each
engine supplied air for a pair of opposite rotors; the compressed air was mixed
with fuel and burned. As a torqueless rotor system, no anti-torque correction
system was required, though propeller pitch was controlled by the rudder pedals
for low-speed yaw control. The propellers provided thrust for translational
flight while the rotor autorotated. The cockpit controls included a cyclic and
collective pitch lever, as in a conventional helicopter.

The transition between helicopter and autogyro modes of flight would have taken
place around 60 mph, (other sources state that this would have occurred around
110 knots); the transition would have been accomplished by extinguishing the
tip-jets. During autogyro flight, up to half of the rotocraft's aerodynamic lift
was provided by the wings, which also enabled it to attain higher speed.

Specifications (Rotodyne "Y")

General characteristics
Crew: two
Capacity: 40-48 passengers
Length: 58 ft 8 in (17.88 m) of fuselage
Wingspan: 46 ft 6 in (14.17 m) fixed wings
Height: 22 ft 2 in (6.76 m) to top of rotor pylon
Wing area: 475 sq ft (44.1 m2)
Airfoil: NACA 23015
Empty weight: 22,000 lb (9,979 kg)
Gross weight: 33,000 lb (14,969 kg)
Fuel capacity: 7,500 lb (3,402 kg)
Powerplant: 2 × Napier Eland N.El.7 turboprops, 2,800 shp (2,100 kW) each
Powerplant: 4 × rotor tip jet , 1,000 lbf (4.4 kN) thrust each
Main rotor diameter: 90 ft 0 in (27.43 m)
Main rotor area: 6,362 sq ft (591.0 m2) Rotor aerofoil: NACA 0015
Blade tip speed: 720 ft/s (219 m/s)
Disc loading: 6.14 lb/ft2 (30 kg/m2)
Propellers: 4-bladed, 13 ft (4.0 m) diameter

Performance
Maximum speed: 190.9 mph (307.2 km/h, 165.9 kn) speed record
Cruise speed: 185 mph (298 km/h, 161 kn)
Range: 450 mi (720 km, 390 nmi)
Service ceiling: 13,000 ft (4,000 m)




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