AH-56 Cheyenne

AH-56 Cheyenne. The Lockheed AH-56 Cheyenne was an advanced attack helicopter developed for the United States Army during the Vietnam War. Designed by the Lockheed Corporation, it was a compound helicopter featuring a rigid rotor system, a pusher propeller, and small wings, intended to deliver high-speed, long-range fire support. Despite its innovative design and promising performance, the program was cancelled in 1972 after a protracted development plagued by technical challenges, budgetary issues, and interservice rivalry with the newly formed United States Air Force.

Development and design

The program originated from the United States Army's Advanced Aerial Fire Support System (AAFSS) requirement, issued in the early 1960s to field a dedicated, high-performance attack helicopter. The Lockheed Corporation, better known for fixed-wing aircraft like the C-130, won the contract in 1965 against proposals from Sikorsky and Boeing Vertol. The design was radical, centered on a rigid rotor system for stability, a four-blade pusher propeller mounted on the tail for high-speed cruise, and stub wings to provide lift in forward flight, offloading the rotor system. It was powered by a single General Electric T64 turboshaft engine, driving both the main rotor and the pusher propeller via a complex transmission. The Cheyenne's armament suite was formidable, centered on a nose turret housing either a 30mm XM140 cannon or a 40mm XM129 grenade launcher, with six hardpoints on its wings for ordnance like the BGM-71 TOW missile or 2.75-inch rocket pods. The crew of two sat in a tandem cockpit, with the pilot in the rear and the copilot-gunner in the front.

Operational history

The first of ten prototypes, designated YAH-56A, flew on 21 September 1967 at the Lockheed facility in Van Nuys, California. Flight testing soon revealed the aircraft's exceptional potential, achieving speeds over 250 knots, but also exposed significant technical hurdles. The most critical issue was rotor system instability, specifically a phenomenon known as "main rotor pylon whirl mode," which caused severe vibrations. During a test flight on 12 March 1969, this instability led to a fatal crash at Rucker, Alabama, killing Lockheed test pilot David A. Beil. The accident severely set back the program, necessitating a major redesign of the rotor system and drive train. Despite an order for 375 production aircraft from the United States Army, the ongoing technical problems, rising costs, and the evolving battlefield needs from the Vietnam War cast increasing doubt on the program's viability.

Specifications (AH-56A)

* **Crew:** 2 (pilot, copilot-gunner) * **Length:** 54 ft 8 in (16.66 m) * **Height:** 13 ft 8.5 in (4.18 m) * **Empty weight:** 12,215 lb (5,541 kg) * **Max takeoff weight:** 18,300 lb (8,301 kg) * **Powerplant:** 1 × General Electric T64-GE-16 turboshaft, 3,925 shp (2,927 kW) * **Maximum speed:** 244 kn (281 mph, 452 km/h) * **Cruise speed:** 195 kn (224 mph, 361 km/h) * **Range:** 1,063 nmi (1,223 mi, 1,968 km) * **Armament:** * **Nose turret:** 1 × 30mm XM140 cannon or 1 × 40mm XM129 grenade launcher * **Hardpoints:** 6 with provisions for combinations of: * BGM-71 TOW missiles * 2.75-inch FFAR rocket pods * M134 Minigun pods * M18 grenade launcher pods

Cancellation and legacy

The program's demise was the result of a confluence of factors. Persistent technical issues, particularly with the rotor system, led to delays and cost overruns. Concurrently, the United States Air Force vigorously opposed the United States Army operating a high-performance fixed-wing-like aircraft, citing violations of the Key West Agreement which governed roles and missions. This interservice rivalry was a significant political obstacle. Finally, the United States Army began to favor a simpler, more affordable concept for an advanced attack helicopter, which would eventually materialize as the AH-64 Apache. The Cheyenne program was officially terminated by the United States Department of Defense in August 1972. Despite its cancellation, the AH-56 Cheyenne served as a critical technological stepping stone, proving concepts for high-speed compound helicopters and advanced rotor system designs that would influence later projects like the Sikorsky S-97 Raider and the Bell V-280 Valor.

Variants

Only one primary variant was built and tested. * **YAH-56A:** Designation for all ten prototypes constructed for the flight test and evaluation program. No production models were manufactured before cancellation.

Category:Attack helicopters of the United States Category:Lockheed aircraft Category:Cancelled military aircraft projects of the United States Category:1960s United States attack aircraft