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 (AAFSS) 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 the helicopter’s development behind schedule, resulting in the cancellation of the production contract on 19 May 1969.
Development of the Cheyenne continued in the hope that the helicopter would eventually enter service.
As American involvement in the Vietnam War was winding down, the Army cancelled the Cheyenne program on 9 August 1972.
By this time, the AH-1 Cobra was widely deployed by the Army in South Vietnam and equipped with the TOW anti-tank missile.
Controversy with the United States Air Force over the Cheyenne’s role in combat as well as the political climate regarding military acquisition programs had caused the Army to amend the service’s attack helicopter requirements in favour of a twin-engine conventional helicopter, viewed as less technical and more survivable.
The Army announced a new program for an Advanced Attack Helicopter (AAH) on 17 August 1972, which led to the development of the Hughes AH-64 Apache.
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 gunsight 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 centreline 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.
Specifications
Crew
2
Length
54 ft 8 in (16.66 m)
Height
13 ft 8.5 in (4.178 m)
Empty weight
12,215 lb (5,541 kg)
Gross weight
18,300 lb (8,301 kg)
Max take-off weight
25,880 lb (11,739 kg)
Powerplant
1 × General Electric T64-GE-16 turboshaft engine,
3,925 shp (2,927 kW)
Main rotor diameter
51 ft 3 in (15.62 m)
Main rotor area
2,063.2 sq ft (191.68 m2)
Blade section
Root
NACA (4.6)3012 mod
Tip
NACA (0.6)3006 mod
Rotor systems
4-bladed main rotor, 4-bladed tail rotor
Propellers
3-bladed constant-speed pusher propeller
Performance
Maximum speed
212 kn (244 mph, 393 km/h)
Cruise speed
195 kn (224 mph, 361 km/h)
Range
1,063 nmi (1,223 mi, 1,969 km)
Service ceiling
20,000 ft (6,100 m)
Rate of climb
3,000 ft/min (15 m/s)
Armament
Guns
1 × nose turret with either a 40 mm (1.575 in) M129 grenade launcher
Or
0.308 in (7.62×51 mm) NATO XM196 mini gun
+
1 × belly turret with an XM140 30 mm (1.181 in) cannon
