The X-22A was built by Bell Aerospace Textron for research into the applications of ducted propellers for VTOL flight. It was designed under the direction of Bell engineer Vincent Praxhia at the company’s Wheatfield, Niagara Falls plant, and two aircraft were built.
The X-22A was a bulky aircraft, constructed mainly of aluminum and powered by four turboshaft engines, rated each at 1,250 shp. The two engines drove four propellers housed in barrel-like nacelles (ducts) which could rotate from zero to 90 degrees. Two of the nacelles were mounted on the short stubby wing aft of the fuselage, while the other two were hinged to the forward fuselage, immediately after the cockpit.
The X-22A had no conventional flaps, ailerons or rudder, and relied on propeller blade pitch and duct angle for attitude control. It was equipped with a fixed landing gear.
Bell test pilots Stanley Kakol and Paul Miller completed the maiden flight of the first aircraft on 17 March 1966, making four successful take-offs and landings and some limited maneuvers. Several additional flights followed, but the aircraft was written off on 8 August 1966 in an accident. Both crewmen were unhurt.
It was left to the second aircraft to resume the flight test program, starting with a successful first flight by Kakol and Richard Carlin on 26 January 1967. The first transition from vertical to horizontal flight was carried out on 3 March.
Bell and NASA pilots made extensive investigations of the aircraft’s performance in the following two years, with more than 200 flights and almost as many transitions from vertical to horizontal flight and back. Service pilots also evaluated the aircraft early in 1968, before the contractor test program was concluded and the aircraft formally delivered to the US Navy in May, for further research work.
A second military preliminary evaluation of the X-22A was carried out in April 1969. Eleven flights were conducted during 12 hours of flying time. Five pilots participated in the tests, including one Marine, one Navy, two Army and one Air Force pilot from the AFETC.
After that, Calspan Corporation at Buffalo Airport was given control of the X-22A for investigation of short take-off and landing approaches (visually and by instruments), transitions, flight dynamics and control, operational requirements and performance. When the program ended in October 1984, both prototypes had totalled 501 flights and more than 1,300 transitions, and proved the feasibility of the ducted propeller concept. Moreover, the aircraft had effectively served as testbed for various VSTOL systems and instruments.
© Henry Matthews 2012