March 2015

2015 MarchBell Aerosystems X-22A Quad Tilt-Duct
Tri-Service V/STOL Transport Program and Variable Stability Research Aircraft
First flight (1st prototype): March 17, 1966,
First flight (2nd prototype): January 26, 1967

The X-22A was the U.S. Navy-contracted and managed portion of the Tri-Service Assault Transport Program. The Bell X-22A was 39 ft (11.9 m) long, featured side-by-side pilot seats, and had a gross weight of 17,000 lb (7,711 kg), including six passengers or a 1,200 lb (544 kg) payload. It was powered by four 1,250 shp (895 kW) General Electric YT58-GE-8D turboshaft engines that were cross-linked and had 35% excess power in case one of the engines failed in hover. The span across the canards – including the 7 ft [2.1 m] diameter three-bladed ducted propellers – was 23 ft (7.0 m); across the rear wingtip ducts it was 39 ft (11.9 m). The ducts rotated non-differentially from 0° to 95° and had spanwise elevons across the center of the duct. Differential propeller pitch and the elevons were used to control the X-22A in hover. In forward flight, the ducts provided a significant amount of the aerodynamic lift.

The first aircraft was rolled out on May 25, 1965. It made its first hovering flight in March 1966, and was tested to transition angles of up to 30° at speeds of up to 100 kt (185 km/hr). That August, the first prototype was lost in a hard landing after only three hours of flying time due to a hydraulic failure. The second prototype made its first flight in January 1967 and performed hundreds of complete transitions. It reached a maximum speed in forward flight of 273 kt (161 km/hr), and had a range of 190 nm (725 km). In early 1968, the X-22A's variable stability and control system was demonstrated, which allowed for research into hover and transition flight characteristics of other possible V/STOL aircraft. On July 30, 1968, it set a record by hovering at an altitude of over 8,000 ft (2.4 km). Flying until 1980, it accrued about 200 hours in the air.

(Photo by Bell, via AHS Archives; text by Mike Hirschberg)

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