page_title: Lockheed AH-56 Cheyenne
section_title: Design
hierarchical_section_title: Lockheed AH-56 Cheyenne / Design
caption_attribution_description: English: Design of the AH-56 "Cheyenne" began during the Vietnam War to replace the AH-1 Cobra, which was vulnerable to light antiaircraft fire and lacked agility. Because of cost overruns, delays, and changing Army requirements, the AH-56 never went into production. The AH-64 "Apache" eventually was chosen to fill the role for which the "Cheyenne" was developed. This is one of the ten prototypes built after Lockheed won the design for the Army's Advance Aerial Fire Support System (AAFSS)
context_page_description: The Lockheed AH-56 Cheyenne was an attack helicopter developed by Lockheed for the United States Army. It rose from the Army's Advanced Aerial Fire Support System program to field the service's first dedicated attack helicopter. Lockheed designed the Cheyenne using a four-blade rigid-rotor system and configured the aircraft as a compound helicopter with low-mounted wings and a tail-mounted thrusting propeller driven by a General Electric T64 turboshaft engine. The Cheyenne was to have a high-speed dash capability to provide armed escort for the Army's transport helicopters, such as the Bell UH-1 Iroquois.
  In 1966, the Army awarded Lockheed a contract for ten AH-56 prototypes, but as a stopgap also ordered the less complex Bell AH-1G Cobra as an interim attack aircraft for combat in Vietnam War. The AH-56's maiden flight took place on 21 September 1967. In January 1968, the Army awarded Lockheed a production contract, based on flight testing progress. A fatal crash and technical problems affecting performance put Cheyenne development behind schedule, resulting in the cancellation of the production contract on 19 May 1969.
context_section_description: Lockheed designed the Cheyenne as a compound helicopter, which combines a helicopter with fixed-wing features for increased performance, usually speed. The design included features such as a rigid main rotor, low-mounted wings, and a pusher propeller. The Cheyenne was powered by a General Electric T64 turboshaft engine. Thrust was provided by a pusher propeller at the rear of the aircraft. At high speeds, the amount of lift provided by the wings, along with thrust from the pusher prop, reduced the aerodynamic loading of the rotor. At such speeds, the rotor produced up to 20% of the lift, which could be adjusted by collective pitch control changes. Rotor tilt was controlled through gyroscopic precession. The Cheyenne achieved speeds over 200 knots (230 mph, 370 km/h), but as a compound helicopter was unable to qualify for speed records in helicopter categories.
  The Cheyenne had a two-seat tandem cockpit featuring an advanced navigation and fire control suite. The tandem seating placed the pilot in the rear seat, and the gunner in the front seat. An unusual feature of the gunner's station was that the entire seat, sighting system, and firing controls rotated to keep the gunner facing the same direction as the gun turret being controlled. The gun-sight afforded the gunner direct viewing from the turret by way of a periscope sight. The pilot had a helmet mounted sight system for aiming weapons.
  Weapon turrets were mounted at the nose and the middle of aircraft underbelly. The nose turret could rotate +/- 100° from the aircraft's centerline and could mount either a 40 mm (1.57 in) grenade launcher, or a 7.62 mm (0.308 in) minigun. The belly turret included a 30 mm (1.18 in) automatic cannon with 360° of rotation. Mechanical stops prevented the belly turret from aiming at any part of the helicopter.
  Six external hardpoints were located along the bottom of the helicopter, with two under each wing and two on the fuselage under the sponsons. The two inner wing hardpoints could carry pods of three BGM-71 TOW anti-tank missiles. 2.75-inch (70 mm) rockets in 7-rocket or 19-rocket launchers could be carried on the four wing hardpoints. The two fuselage mounts were dedicated to carrying external fuel tanks. The wing hardpoints were also plumbed to allow the carriage of additional fuel tanks if required.
caption: View of AH-56 nose and canopy
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