| Lockheed AH-56 "Cheyenne" 1956 |  |
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| Lockheed AH-56 "Cheyenne" 1956 | |
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The Lockheed AH-56 Cheyenne attack helicopter was created in response to the US Army's need for a fast, armoured and heavily armed helicopter to supplement the escort/attack role. The Cheyenne featured a revolutionary compound helicopter configuration as well as a gyro-controlled rigid-rotor and three-bladed pusher tail propeller as well as a four-bladed anti-torque rotor. It had small wings attached to the side of the fuselage that could off-load the rotor during high speed flight. The helicopter was powered by a 4350shp General Electric T64-GE-16 gas turbine engine derated to 3925shp. The Cheyenne could accommodate a crew of two sitting in tandem in the enclosed cockpit with the gunner co-pilot in front of the pilot on a gun platform which could swivel 360°. A second gun system was housed in a nose turret. Six under-wing attachment points were used for missiles or rocket pods. The sophisticated weapon-sighting system included night-vision equipment and a helmet-gun sight. The Cheyenne at first proved highly capable and in December 1967 the Army ordered a production batch of 375 Cheyennes. During further flight testing however there were three crashes. The helicopter proved unstable at high speeds in excess of 320km/h. After the third crash in 1969, when the main rotor collided with the fuselage, the production order was delayed. Further design modifications took place and by 1972 most of the Cheyennes' faults were cured but the program was cancelled due to budgetary problems. There were ten Cheyennes built. Armed with a nose turret, with either a 7.62mm minigun or 30mm XM140 cannon, or a 40mm XM 129 grenade launcher, wing mounted TOW missiles or 2.75mm rocket pods, the Cheyenne could cruise at 388kmh with a max speed of 407km/h. It had a rate of climb in excess of 1025m/min and a range of 1970km. P.Allen "The Helicopter", 1996
The ambitious AH-56 Cheyenne helicopter, with which Lockheed hoped to establish a foothold in the rotary wing sector, was in fact a resounding failure for the Californian company. It featured a rigid main and tail rotor, which Lockheed had been researching since 1959 — a rigid rotor enables helicopters to perform genuine aerobatic manoeuvres. The AH-56A Cheyenne was driven by a General Electric T64 turbine delivering over 3400shp. It had a stub wing with an 8m span and an area of 24m2, attachment points for six underwing stores weighing 900kg each, a streamlined fuselage with a tandem cabin seating arrangement, retractable front landing gear units, a fixed tailwheel, a rigid four-blade anti-torque tail rotor and three-blade pusher propeller at the tip of the tail boom. However the Cheyenne was technically too complicated and US Army orders were cancelled and development suspended in 1972. G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984
Developed as Lockheed's entry in the Army's Advanced Aerial Fire Support System (AAFSS) competition, the Cheyenne was a highly sophisticated compound rotorcraft whose design incorporated several features pioneered in Lockheed's earlier XH-51A. The Cheyenne was named winner of the AAFSS contest in March 1966, at which time Lockheed was awarded an Army contract for the production of ten YAH-56A prototypes. The first of these made its maiden flight in September 1967, and all ten aircraft (serials 66-8826 through -8835) had been delivered to the Army for flight testing by July 1968. In January of that year the Army had placed an initial order for 375 production machines, and the ten prototypes were subsequently redesignated AH-56A in early 1969. The Cheyenne was, to say the least, a rather exotic-looking aircraft. The forward end of its long and narrow fuselage was dominated by an outsized segmented canopy covering a tandem, two-seat cockpit, while the tailboom supported a large ventral fin, a conventional anti-torque tail rotor, and a decidedly unconventional pusher propeller. A pair of small, low-set stub wings fixed to the fuselage sides contributed to the Cheyenne's hybrid look, as did its retractable, wheeled main landing gear. The AH-56A's ungainly appearance was deceptive, however, for in flight the craft was amazingly agile and extremely fast. The Cheyenne's impressive performance was the product of an innovative propulsion system built around a 3435shp General Electric shaft turbine engine. This powerplant drove a rigid, four-bladed, gyro-stabilized main rotor, the tail-mounted anti-torque rotor, and the pusher propeller at the extreme end of the tailboom. During vertical and hovering flight all power was applied to the main and anti-torque rotors, while during forward flight all but about 700shp was shafted to the pusher propeller. In forward flight lift was generated by the stub wings and windmilling main rotor, and in absolutely 'clean' configuration the AH-56A was capable of sea-level speeds in excess of 400kph. The Army's AAFSS specifications had called for an aircraft capable of undertaking armed escort, long range interdiction, fire support, and anti-tank operations by day or night and in all weathers, and the Cheyenne had been armed and equipped accordingly. The AH-56A's armament consisted of a nose turret housing either an XM129 40mm automatic grenade launcher or XM134 7.62mm multi-barrelled minigun, a 30mm cannon mounted in a revolving belly turret, and an impressive number of TOW anti-tank missiles and/or pods of 2.75 inch unguided rockets carried on underwing hardpoints. The Cheyenne's day and night, all-weather flight capability was based on an extensive avionics suite which included automatic terrain-following radar, Doppler radar, an inertial navigation unit, and an automatic flight control system that allowed high-speed flight at altitudes as low as fifteen feet. Despite its technological sophistication, or perhaps because of it, the AH-56A was fated never to enter regular Army service. The flight test programme revealed several significant problems with the aircraft's innovative propulsion system, problems which ultimately resulted in the fatal crash of one of the ten prototypes. In addition, by March 1979 significant cost overruns had increased the per-unit Cheyenne price by more than $500.000, an increase that was unacceptable in light of the Army's continued high expenditures in support of operations in Vietnam. And, finally, the USAF had become increasingly vocal in its opposition to the Army's acquisition of an aircraft as capable as the Cheyenne, and continued to push for the cancellation of the AH-56 project. The Army ultimately decided to develop a cheaper and less sophisicated helicopter in place of the Cheyenne, and in August 1972 formally terminated the AH-56 programme. S.Harding "U.S.Army Aircraft since 1947", 1990
- Since the Cheyenne project, Lockheed has not put a military or civil helicopter into production. - Power of the T64 engine was increased to 3,922hp during testing. - Cancellation, in May 1969, came just six months before production began. - In common with other US Army helicopters, the Cheyenne was named after a native American tribe. - The highly manoeuvrable AH-56 was found to be a stable weapons platform. - The other short-listed AAFSS prototype was the Sikorsky S-66.
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