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The Bell X-22 was an experimental aircraft designed to test out the potential of a ducted-fan powered VTOL aircraft.
The X-22 emerged from quite a lengthy development process. In 1953 the US Navy sponsored a one year design study for a ducted-fan assault transport. This produced the Bell Design D-190, for a sea-air- rescue aircraft. This reached the full scale mock-up process but no further.
In 1959 work began on design D-2205, for a US Marine assault transport. This developed into the D-2022, which would have carried up to 30 armed troops, but never got beyond the design project.
In 1961 Bell produced the D-2064 in response to a Tri-Service Transport Aircraft Specification. Once again this wasn't chosen for development, but on 30 November 1962 they were given a contract to produce two research aircraft to test out the duct-fan configuration. This produced the Bell D-2127/ X-22.
Bell focused on three elements during the design process. First, the aircraft had to be able to cope with large shifts in its centre of gravity when hovering. Second, the control forces had to be capable of providing precise movements when hovering and changing to horizontal flight. Third, the aircraft had to have a light empty weight to free up as much space as possible for cargo.
A series of wind tunnel tests began in February 1963, using eight different models of the aircraft or part of the aircraft.
The X-22 had a chunky fuselage. A short, deep, almost rectangular wing was mounted above the back of the fuselage. There was a tall vertical tail. The four engines were carried in nacelles mounted in the front of the wing, two on each side of the fuselage.
Lift, drive and all controls were provided by the four ducted propellers. Two were mounted at the end of the wing and another two close to the fuselage, just behind the nose-mounted cockpit. Each could rotate between vertical and horizontal positions. Control forces were created by altering the blade pitch of each propeller individually.
Each pair of engines was connected to a gearbox, which was in turn connected to a transmission shaft that drove the rear propellers. This shaft also powered a 'T' gearbox which powered the forward propellers. All four engines thus provided power to all four propellers, and the aircraft could fly on three engines. The controls were set up so that the pilot had conventional aircraft controls, even though the X-22 had no conventional control surfaces.
The first prototype rolled out on 25 May 1965 and the second on 30 October 1965. A year and a half of static tests followed, before the first prototype made its maiden flight, a ten minute hover test, on 17 March 1966. This aircraft was damaged beyond repair after a hard landing on 8 August 1966, caused by a failure in the hydraulic system.
The second prototype made its maiden flight on 26 January 1967. It made its first transition from vertical to horizontal flight on 3 March. This was followed by a two year long test programme at Bell and NASA, which involved 220 flights and 110 flight hours.
In January 1968 the X-22A began its first military evaluation, undergoing fourteen flights for the Air Force, Navy and Army. A second military evaluation followed in April 1968. On 19 May 1968 the aircraft was officially taken over by the US Navy, which then passed it to Calspan Corp for the test programme. This involved another 273 flights, with 130 VTOL take offs, 236 VTOL landings, and 279.9 hours of flight. The test programme lasted until the autumn of 1984!
A number of alternative models of the aircraft were considered, but none were built. This included the X-22A-1 with a new forward fuselage and weapons, a general purpose X-22B and the X-22C cargo version
X-22A
Engine: Four General Electric YT-58-GE-8D shaft-drive turbines
Power: 1,250hp each
Crew: 2
Span: 39ft 3in (rear wing); 23ft (forward ducts)
Length: 39ft 7in
Height: 19ft 8in
Empty Weight: 11,458lb
Loaded Weight for VTOL with three engines: 14,600lb
Loaded Weight for VTOL with all engines: 18,016lb
Maximum Speed: 255mph
Ceiling: 27,800ft
Range: 445 miles