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The Lockheed AH-56A Cheyenne attack helicopter
In the 1960s, the Army tested the Lockheed AH-56A Cheyenne, an attack helicopter that might have revolutionized warfare. Had a civilian version existed, it might have changed aviation. Instead, as explained by James C. Goodall in his book 75 years of the Lockheed Martin Skunk Works, the Cheyenne became a “might have been.” It was costly and technologically challenging. It may have been too advanced for its time. Its performance in flight was sometimes “spectacular,” as one pilot put it, but there were minor kinks that were never quite ironed out.
The AH-56A was also called the Advanced Aerial Fire Support System (AAFSS). During the period when the United States was building up its troop strength in Vietnam, the AH-56 became a bold attempt to compete with the Air Force for a key role in air-to-ground support. The Cheyenne was a highly sophisticated compound rotorcraft incorporating design features pioneered in Lockheed’s earlier XH-51A test ship.
A long, slim helicopter
It was a long, slim helicopter with retractable landing gear, small wings that spanned almost 27ft, and a General Electric T64-GE-16 shaft turbine engine with a four-bladed rotor. The power rating of the engine was increased to 3,922hp as the test program evolved. The Cheyenne used an innovative propulsion system built around the T64. The power plant 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 tail boom. 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 the stub wings and wind milling main rotor generated lift. In “clean” configuration the AH-56A was capable of sea-level speeds in excess of 275mph.
The Army was looking for a truly giant leap with the AH-56. The service established exceedingly ambitious goals. It said it wanted an aircraft with a top speed of 220kt, able to hover out of ground effect at 6,000ft, with a ferry range of 2,100 nautical miles. A little noticed feature of the Cheyenne was its ability to self-deploy over long distances, including the 2,200-mile flight from California to Hawaii. Although Lockheed had little experience building helicopters, the Army chose its design in 1966.
Advanced weapon sighting system
The crew of two, pilot and gunner/co-pilot, sat in tandem in an enclosed cockpit. The impressive armament of the Cheyenne included a 30mm XM140 cannon in a belly turret, and a 40mm XM129 grenade launcher or 7.62-mm minigun in a nose turret. Under the wing were six hard points for ordnance, consisting of Hughes TOW anti-tank missiles or 2.75in folding fin aircraft rockets. The AH-56 had an advanced weapon sighting system that included night vision equipment and a helmet gun sight. The Army was enthusiastic enough that in January 1968, it placed an initial production order for 375 aircraft. As it turned out, only ten Cheyennes were built.
With Army Lt Col Emil “Jack” Kluever on board, test pilot Donald R. Segner took the prototype AH-56 for its first flight at Van Nuys Airport on Sep. 21, 1967. But in tests the AH-56 had difficulty maintaining stability close to the ground and at high speed. Various design changes seemed to help, but no certain fix had been found when the third Cheyenne built was lost in a crash on Mar. 12, 1969.
Following the grounding of the AH-56s, tests resumed in July 1969. By then the Army had abandoned its production order – prematurely, many observers said. The Cheyenne program had also suffered from cost increases. Meanwhile, the Army was getting good results with a less advanced, less ambitious helicopter, the AH-1G Huey Cobra, which went into combat in South Vietnam in October 1967.
More advanced than today’s AH-64 Apache
Had its technical difficulties been overcome and had politics not intervened, the Cheyenne would have been a formidable weapon. In some ways, it was more advanced than today’s AH-64D Longbow Apache, which offers some of the capabilities the Cheyenne had but is not as effective at high altitude. The Cheyenne “was an incredible aircraft,” said Richard Berch, who piloted the AH-56A at the Yuma Proving Ground in Arizona. “It would have changed military aviation. A passenger carrying version would have changed short-haul commercial aviation.”
75 years of the Lockheed Martin Skunk Works is published by Osprey Publishing and is available to order here.
Photo credit: William Pretrina via Wikipedia and U.S. Army