de Havilland Cierva C.24 Autogiro
An autogyro differs from a helicopter in that its lifting rotor is unpowered and so has no need of a tail anti-torque rotor. Instead, the backwards-tilted rotor auto rotates in the airstream, giving lift as the aircraft is pulled forward by the nose tractor engine and propeller. Intended for private owners operating from small fields, the Cierva C.24 tandem two-seat autogiro was detailed and built in some secrecy by de Havilland at Stag Lane, to a design by Sr Juan de la Cierva, the Spanish inventor of the autogyro. It was first flown, by de la Cierva himself, at Stag Lane in 1931. The C.24 was unusual in having an enclosed cabin, the first in the world for any form of rotorcraft; and a tricycle undercarriage, very rare in 1931. It was based on a DH Puss Moth fuselage, with a C.19-type 3-bladed rotor assembly supplied by the Cierva Company. A streamlined triangular pylon over the cabin contains a gravity-feed fuel tank and supports the rotor high enough for the blades to clear the truncated tail. Initial rotor spin-up used a direct drive (now missing) and clutch from the engine. Serious ground resonance (lateral shaking from rotor unbalance) during spin-up was cured with redesigned blades. Flight control down to very low speed was provided by aeroplane-type control surfaces in the propeller slipstream, including ailerons extending right inboard. The upturned wing tips aided lateral stability. The C.24 could maintain level flight at speeds down to 24 mph and would not stall or spin. But take-off run, climb rate and cruise speed were all worse than on the Puss Moth.
Power Unit: One 120 hp de Havilland Gipsy 3 in-line engine
Rotor Diameter: 34 ft (10.36 m)
All-up Weight (A.U.W): 1,800 lb (816 kg)
Max Speed: 115 mph (185 kph)
Rotor Speed: 200 rpm
Range: 350 miles (563 km)
On display at the Museum:
The C.24 was the only rotorcraft built by de Havilland, and only this one example was built. It was acquired by the Science Museum in 1974, and is now on permanent loan to this museum. The engine is the original, but the twisted slab propeller is not.