Convertiplane

A convertiplane in popular usage is an aircraft that converts in flight to change its method of obtaining lift. The FAI define it more narrowly as an aircraft which uses rotor power for vertical takeoff and landing (VTOL) and converts to fixed-wing lift in normal flight. This is the definition used here.

Convertiplanes may be divided into two broad classes, based on whether the rotor is fixed as in a helicopter or tilts to provide thrust in forward flight, as a proprotor.

A proprotor may be in a tilt rotor or tilt wing configuration in which case a fairly complicated tilt mechanism is required. An engine failure could be disastrous even in the case of twin rotor configuration, similarly to helicopters.

In most cases gyroplanes and compound helicopters use the same primary method of lift throughout flight without any conversion needed, so they are generally not regarded as convertiplanes. However, at least two aircraft did achieve a winglift higher than their rotorlift :

Convertiplanes have appeared only occasionally in the course of aviation history.

In 1920 Frank Vogelzang filed a patent for a convertiplane, but the design was never constructed. Between 1937 and 1939 the British designer L.E. Baynes developed a proposal for his Heliplane, a tiltrotor convertiplane having two tilting wingtip-mounted nacelles containing the engines, proprotor mounting and main undercarriage. The wheels did not retract but were partially covered and protruded from the rear of the nacelles when in forward flight. The proposed engines were of an unusual hybrid gas turbine design, in which the proprotor was driven off a gas turbine supplied in turn by a free-piston hot gas generator. Baynes was refused official backing and the type was never built. The basic design would not be revisited for some 20 years or so, and would eventually become the basis of the successful Bell-Boeing V-22 Osprey.

In 1950s the concept gained brief attention in United States as an intended improvement of helicopters, but the experimental McDonnell XV-1 and Bell XV-3 did not enter production.

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