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Side view of the AH-56 (source: Wikimedia Commons)
The Lockheed AH-56 Cheyenne was an attack helicopter developed for the US Army. It was designed to fly high-speed escort missions for transports and provide direct fire support for front-line troops. It was one of the fastest helicopters, capable of reaching almost 400 km/h. It also carried a diverse set of armaments consisting of TOW missiles, FFAR rockets, and two gun turrets. It pioneered many avionics now common on military aircraft, including the first thermal sight used on aircraft. Extremely advanced for its time, it was unfortunately abandoned due to protracted development, rising costs, and shifts in executive opinions.
History
In the early years of the Vietnam War, the US Army had already begun placing additional armaments on their UH-1 Iroquois helicopters, including rockets, grenade launchers, and machine guns. However, as the new CH-47 Chinook began arriving on the scene, the Army realized that the Iroquois were too slow to keep up with the Chinook. Therefore, a new purpose-built attack helicopter was needed.
The US Army decided that they needed an attack helicopter capable of cruising at 361 km/h and capable of short dashes of 410 km/h, based on the speed of the Chinooks they were expected to escort. Note that this is faster than the Chinook’s top speed, as the escorts were also expected to dash ahead of the transports as they approached the landing zone to soften up enemy resistance so that troops could land safely. These requirements practically meant that only compound helicopters would be considered. The Army opened the Fire-support Aerial System (FAS) project, which was later reorganized into the Advanced Aerial Fire Support System (AAFSS) project on 26 March 1964, for procuring such a helicopter.
Bell, Convair, Sikorsky and Lockheed all submitted proposals. Sikorsky and Lockheed’s proposals were selected to enter the second stage. On 3 November 1965, Lockheed was declared the winner, as their proposal was judged to be less expensive and risky and required less development time. The helicopter was designated the AH-56A on 23 March 1966 and a contract for 10 prototypes was issued. The first prototype was rolled out on 3 May 1967, and the helicopter was given the nickname “Cheyenne”. The first flight of the AH-56 occurred on 21 September 1967. Funding was approved for 375 pre-production aircraft on 8 January 1968, and by 1969 all 10 prototypes were completed. Everything seemed to be going swimmingly.
However, things soon started going downhill. Lockheed struggled to fix the various issues on the Cheyenne in time, and on 10 April 1969, the US Army issued a cure notice to Lockheed, stating that 11 serious issues persisted in the AH-56 and the program was falling behind schedule. The production contract was cancelled on 19 May 1969, but development continued in the hope that the issues would eventually be fixed. However, further flight testing only revealed more issues with stability, vibrations and control. Additionally, the Air Force was also upset about the program, viewing it as a violation of the Key West Agreement and the Johnson-McConnell Agreement of 1966. Congress was also becoming opposed to the AH-56 after their investigations and seeing some failed flight and weapons tests. Finally, the Cheyenne program was cancelled by the Secretary of the Army on 9 August 1972, as the Cheyenne started becoming outdated, and incorporating newer systems would increase the unit cost far too much.
Specifications
Where secondary sources give differing values, an approximate average is given.
Crew: 2
Physical characteristics and flight performance:
Empty weight: approx. 5,400 kg
Gross weight: between approx. 8,000 kg to approx. 10,000 kg
MTOW: approx. 12,000 kg
Max speed: approx. 400 km/h
Climb rate: approx. 17 m/s
Engine: 1x General Electric T64-GE-716 at 4,275 hp, earlier models used 1x General Electric T64-GE-16 at 3,925 hp, very early models had T64-GE-16 derated to 3,425 hp due to gearbox issues
Armour: unclear, but stated to have armour plating around the crew compartment.
Avionics and weaponry:
Avionics:
- Gyro-stabilized sight: 1.5x, 4.2x, and 12x magnification
- Hughes Passive Infra-red Night Equipment (PINE, also described as the AAS-25 infrared sensor), probably an early thermal sight
- Laser rangefinder
- Computer Central Complex (CCC), described to provide “ballistic corrections and prediction calculations”, probably equivalent to CCIP for all weapons (guns and rockets). Also provides automatic tracking of designated targets
- Pilot Helmet Sight and Direct Sight
Weaponry:
- 1x nose turret, ±100˚ horizontal traverse, +18˚/-70˚ vertical traverse
- XM-51 system with XM-129 40 mm grenade launcher, 350 rpm, 780 rounds
- XM-53 system with XM196 7.62 mm minigun, 750, 1,500, 3,000, or 6,000 rpm, 11,750 rounds (not used on later aircraft, perhaps due to compatibility issues)
- 1x belly turret, ±200˚ horizontal traverse, +26˚/-70˚ vertical traverse
- XM-52 system with XM-140 30 mm autocannon, 450 rpm, 2,010 rounds
- 6x hardpoints
- 2x fuselage hardpoints, can carry 300-gallon external fuel tanks
- 4x underwing hardpoints, inner 2 can carry triple-TOW launcher, outer 2 can carry triple FFAR rocket pod, all 4 can carry single FFAR rocket pods or 450-gallon external fuel tanks (max loads, 6 TOW missiles in two pods, or 152 FFAR rockets in eight pods)
- N.B. Due to weight restrictions, ferry missions could only carry four 450-gallon tanks and one 300-gallon tank
More pictures
AH-56 with all available armaments (source: Landis)
AH-56 with fuel tanks and rocket pods (source: Landis)
Loadout diagram (source: Landis)
Sensor systems (source: Landis)
Sources
- “Lockheed AH-56A Cheyenne” by Tony Landis
- “The Illustrated Encyclopedia of Helicopters” by Giorgio Apostolo
- ENGINEERING EVALUATION AH-56A COMPOUND HELICOPTER WITH ADVANCED MECHANICAL CONTROL SYSTEM (AD910262)
- “Interservice Rivalry and Airpower in the Vietnam War” by Dr Ian Horwood (ADA460480)
- HISTORY OF ARMY ATTACK HELICOPTER PROGRAM (AD1121533)
- “AH-56 Cheyenne” by Edgar E. Ulsamer in the Air Force magazine v.51 Jan-June 1968
- United States Army aviation digest v.14 1968
- https://www.aviastar.org/helicopters_eng/lok_cheyenne.php
- https://armyhistory.org/ah-56-cheyenne/
