Fairey Rotodyne - Design and Development

Design and Development

Fairey developed the Fairey FB-1 Gyrodyne, a unique aircraft in its own right that defined a third type of rotorcraft, including autogyro and helicopter. Having little in common with the later Rotodyne, it was characterised by its inventor, Dr. J.A.J. Bennett, formerly Chief Technical Officer of the pre-Second World War Cierva Autogiro Company as an intermediate aircraft designed to combine the safety and simplicity of the autogyro with hovering performance. Its rotor was driven in all phases of flight with collective pitch being an automatic function of shaft torque, with a side-mounted propeller providing both thrust for forward flight and rotor torque correction. The FB-1 set a world airspeed record in 1948, but a fatal accident due to poor machining of a rotor blade flapping link retaining nut terminated development of the pure gyrodyne. The second FB-1 was modified to investigate a tip-jet driven rotor with propulsion provided by propellers mounted at the tip of each stub wing. This was renamed the Jet Gyrodyne, which despite its name, was a compound autogyro.

Fairey put forward their various designs for the proposed BEA Bus, which were revised over the years, and received government funding. However, getting access to engines proved to be difficult, with first Rolls-Royce then Armstrong Siddeley claiming lack of resources. The Ministry of Supply contracted in 1953 for the building of the prototype (serial number XE521).

With a view to an aircraft that would meet regulatory approval in the shortest time, Fairey's designers worked to meet the Civil Airworthiness requirements for both helicopters and similar sized twin engined aircraft. A one-sixth scale rotorless model was extensively wind-tunnel tested for fixed-wing performance. A smaller (1/15th-scale) model with powered rotor was used for downwash investigations.

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.

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 from helicopter to autogiro took place around 60 mph by extinguishing the tip jets, and up to half the lift was provided by the wings, enabling higher speed.

The rotor blades were a symmetrical aerofoil around a load-bearing spar. The aerofoil was made of steel and light alloy to 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 rivetted steel to the rear. The compressed air was channeled through three steel tubes within the blade. The tip jet combustion chambers were made from Nimonic 80 with liners made from Nimonic 75.

While the prototype was being built, funding for the programme reached a crisis. Cuts in defence spending led the Ministry of Defence to withdraw support, pushing the burden of the costs onto any possible civilian customer. The Government agreed to continued funding only if, among other qualifications, Fairey and Napier (through their parent English Electric) contributed to development costs of the Rotodyne and the Eland engine respectively.