Lockheed AH-56 Cheyenne

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AH-56 Cheyenne during testing

The Lockheed AH-56A Cheyenne was a sophisticated but unsuccessful military attack helicopter. The AH-56 is a compound helicopter: the normal helicopter rotors are augmented by small wings and a propeller, giving it some of the characteristics of both helicopter and a fixed-wing aircraft.

A fixed rotor helicopter had been built by Lockheed as the XH-51 and the AH-56 followed in its path. It first flight was on 21 September 1967. The project suffered a setback on 12 March 1969 when the rotor on one prototype hit the fuselage and killed the pilot. An order for 375 had been approved in 1968 but was cancelled in 1969 as a result of budget cuts and development was halted in 1972.

The AH-56 has a short but substantial wing on each side of the airframe and a rigid main rotor. Thrust is provided by a pusher-prop at the rear of the aircraft. Since the main rotor is not relied on for the full amount of lift (provided by the wings) or thrust (from the pusher prop), the Cheyenne is able to reach high speeds - in excess of 200 kts. The design is classed as a compound aircraft and so is unable to qualify for speed records in helicopter categories. The Cheyenne also featured an advanced navigation and fire control suite. The development of these new technologies led to many cost and time overruns, and an adjustment in the Army's specification led to the Cheyenne's demise in favor of the AH-64 Apache, and continued production of AH-1 Cobra which was quite successful in Vietnam, and would serve in USMC use beyond 2000. The Army would trade speed for survivability and ability to hover in the specification which would lead to the AH-64.

The oddest feature of the AH-56 is the gunner's station. Like the AH-1 Cobra, the AH-56 has two crewmembers, seated in tandem—a pilot and a gunner. A turret with a 360° firing arc is located in the middle of aircraft underbelly, in contrast to the limited forward arc of the AH-1's chin turret. The AH-56 gunner's station, seat and consoles rotate along with the turret to keep the gunner facing the same direction as the guns, although the aircraft's design obscures approximately 120° of the gunner's rear view. The gun-sight affords the gunner direct viewing from the turret. A similar, but opposite arrangement was found in the MBT-70 tank prototype: the driver sits in a counter-rotating seat in the gun turret, so that the driver always faces the front of the tank regardless of turret rotation.