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Aviation History
1967
1967 - 0453.PDF
IS5Q The Bell Aerosystems X-22A, one of two prototypes, begins its transition from the hover to forward flight BELL X-22A Analysis of a VTOL research vehicle FOR MANY YEARS the United States Department of Defencehas supported programmes for investigating possible usesof V/STOL aircraft and assessing the technical feasibility of a number of different configurations. Neither in the USA nor in other countries, however, have military advantages, economics, and a number of other aspects of V/STOL operation been fully determined: only one country—Great Britain—has so far placed production orders for an aircraft of this type. Nevertheless, the United States is doing the lion's share of the work over a broad front in establishing operational criteria, particularly in the field of air transport. The Bell X-22A dual-tandem ducted-propeller aircraft represents one of three programmes sponsored by the DoD for this purpose, the other two being for the tilt-wing Ling-Temco- Vought/Ryan/Hiller XC-142 and the unducted, tilting-propeller Curtiss-Wright X-19A (since cancelled). The X-22A was the most recent of the three to fly (the first-flight date was March 17, 1966), and has a number of unusual features. The pro- gramme, which is under US Navy guidance, called for the construction of two aircraft. The first of these was badly damaged during an emergency landing near Niagara Falls Airport on August 8, 1966, as a result of failures affecting both hydraulic systems simultaneously (see Flight, September 1, 1966). It had made about 40 flights and was undergoing a programme to extend the flight envelope. The second aircraft made its first flight on January 26 this year. The loss of the first aircraft is not expected to have any significant effect on the planned flight programme apart from lengthening its duration. The description which follows is based largely on an American Institute of Aeronautics and Astronautics paper by R- S. Postle and C. Henderson of Bell Aerosystems, X-22A * ISTOL Aircraft Research Capabilities. Design Requirements The Bell X-22A is designed and built under a tri-Service contract to explore the mechanical and aerodynamic characteristics of the dual-tandem, ducted- Propeller V/STOL concept and^to assess its military potential. The US Navy will, in addition, use it to investigate the suitability of the configuration for shipboard operation, over- water missions and operation from confined areas on land. The Aircraft The general arrangement drawing on page 448 illustrates the layout with the ducts horizontal. The two pilots have zero-zero ejection seats, which eject through the trans- parencies, while in the cabin area aft of the front ducts there is room for 1,2001b of payload (usually flight instru- mentation) or six passengers. The airframe is generally of conventional aluminium-alloy construction, with great emphasis being placed on weight saving. The configuration was developed with the aid of a number of wind tunnel programmes. An unpowered model was tested in the David Taylor Model Basin 8ft X 10ft wind tunnel to provide conventional flight data. This work was followed by tests of a powered model in the 17ft section of the 7ft X 10ft tunnel at NASA Langley Research Centre to assess the effects of power on the force and moment characteristics, particularly under transitional flight conditions. A spin model has been evaluated by NASA with satisfactory results, and a free-flight model has been tested in the Langley Research Centre full- scale wind tunnel. Additionally, a powered aero-elastic model of the aircraft has been evaluated at the David Taylor Model Basin. The dual engine nacelles each house two General Electric engines which exhaust at 65° to the horizontal, thus providing additional take-off thrust. The engine driveshafts extend from the rear of the engines to the transmission system which inter- connects and drives all propellers, while overrunning clutches automatically allow a dead engine to disengage. The acces- sory drive and oil cooling systems are attached to the aft "T" gearbox and occupy the fuselage volume under the wing. Because of the V/STOL research objective, design of the propellers and ducts has been biased towards good static and low-speed operation. The Hamilton Standard three-blade glass-fibre propellers are of 7ft diameter with a maximum rotational speed of 2,590 r.p.m., and the fore-and-aft ducts are identical internally except for the differently-sized elevon surfaces installed in the duct diffuser sections. The ducted units have been evaluated in wind tunnel tests of a one-third- scale model at David Taylor Model Basin and of a full-scale model in the NASA Ames Research Centre 40ft X 80ft tunnel. Performance of the X-22A is adequate for any anticipated research work. On a standard day, and at the design gross
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