|Fig. 18-1 Michel Wibault's ground attack gyropter (concept) 1956|
2. Early in 1941, the late Dr A. A. Griffiths, the then Chief Scientist at Rolls-Royce, envisaged the use of the jet engine as a powered lift system. However, it was not until 1947 that a light weight jet engine, designed by Rolls-Royce for missile propulsion, existed and had a high enough thrust/weight ratio for the first pure lift-jet engine to be developed from it.
3. In 1956 the Bristol Aero-Engine Company was approached by Monsieur Michel Wibault with a proposal to use a turbo-shaft engine and a reduction gearbox to drive four centrifugal compressors which would be situated two on each side of the aircraft. The casing of these compressors could be rotated to change direction of the thrust (fig. 18-1). The concept incorporated two original ideas i.e. the ability to deflect the thrust over the complete range of angles from the position for normal flight to that for vertical lift and a system where the resultant thrust always acted near to the centre of gravity of the aircraft.
|Fig. 18-2 Lift/Propulsion engine.|
5. Subsequent experience with the Pegasus engine in the Harrier V/STOL fighter aircraft (fig. 18-3), lead to the development of the short take-off and vertical landing (STOVL) operational technique. In this way the additional lift generated by the aircraft wing, even after a short take-off run, provided a large increase in the payload/range capability of the aircraft compared to a pure vertical take-off. Vertical landing had several operational advantages compared to a short landing and so was maintained.