Although V/STOL had its true origins in Germany during the Second World War – the rocket-powered Bachem Ba 349 Natter (Adder) had made its first piloted flight in February 1945 – practical progress had to wait until the 1950s, when jet engines were far more advanced and there was a stronger operational motivation.
The successful development of jet engines was, by the 1950s, producing powerplants with a thrust that was very much greater. This offered the possibility of aircraft that could take off vertically, thereby not requiring long, expensive and vulnerable runways.
Rolls-Royce developed the Thrust Measuring Rig (TMR), popularly known as the ‘Flying Bedstead’ in 1953 to test this principle with two Nene turbojets, at that time one of the most powerful in the world. This was to discover whether jet-borne flight could be safely controlled by the pilot. A control system, devised in association with RAE Farnborough, used jet reaction from ‘puffer jets’ carried on long outriggers and fed with high-pressure air bled from the engine compressors.
Tests with the Flying Bedstead, culminated in its first untethered flight on 3 August 1954, piloted by R.T. Shepherd. This showed that pilots could achieve stable hovering flight and paved the way for the development of the control system still used today on the Harrier. The machine is now preserved in the Science Museum, South Kensington.
One of the driving forces behind V/STOL development came from the USA, where the US Navy funded the Lockheed XFV-1 and Convair XFY-1 turboprop ‘tailsitters’, but these tests ceased in 1956. A third US tailsitter was the single-seat Ryan X-13 Vertijet. Powered by a 10,000lb (44.5kN) Rolls-Royce Avon turbojet it became the world’s first jet-powered VTOL research aircraft when it was flown on 10 December 1955. It featured a hook mounted beneath the forward fuselage from which it was suspended for take-off, and was launched from and recovered to a tilting platform. But the tailsitter was very limited, and attention increasingly turned to the flat-riser, which required less mental gymnastics from the pilot.
With a high-set delta-wing, the X-13 had no landing gear and was designed to take off vertically. Two prototypes were built and the first complete transition from vertical take-off to horizontal flight – and a vertical landing – was accomplished on 11 April 1957. The Vertijet proved to be successful and was at one time thought likely to form the basis for the projected XF-109 VTOL fighter for the USAF.
What made possible a comparatively simple V/STOL combat aircraft was the invention of a new type of powerplant. The thrust from this new engine could be turned through more than 90°, rotating about a point very close to the engine’s centre of gravity. This vectored-thrust engine was fitted to the Bell X-14, which made its first conventional flight and hovers in 1957, and achieved the transition from horizontal to vertical flight on 24 May 1958. This is regarded as the world’s first successful vectored-thrust V/STOL demonstrator.