AH-56 Cheyenne

AH-56 Cheyenne
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AH-56 Cheyenne during testing
Type	Attack helicopter
Manufacturer	Lockheed
Maiden flight	21 September 1967
Status	Canceled
Number built	10
Developed from	XH-51

The Lockheed AH-56 Cheyenne was a two-seat, single-engine, rigid-rotor, compound helicopter with low-mounted, fixed wings and retractable main landing gear. The AH-56A was the design winner of the United States Army's Advanced Aerial Fire Support System program in 1965 to establish a technologically advanced, dedicated attack helicopter. It was armed with a 30 mm cannon in a belly turret and either a 7.62 mm minigun or a 40 mm grenade launcher in a nose turret. It was also capable of being armed with 2.75 inch rockets and TOW missiles. The Cheyenne's compound helicopter design was intended to provide a 212 knot dash capability in order to serve as an armed escort to the Army's transport helicopters.

Lockheed was awarded a production contract in 1967 but was unable to deliver production aircraft by 1968, and the production contract was subsequently canceled in 1969. Development continued in the hopes that eventually the Army would be able to field the Cheyenne. A 1972 congressional report from the Senate which recommended funding of the United States Air Force's A-10 and the United States Navy's Harrier programs sounded the end for the AH-56, and the program was canceled by the Secretary of the Army in August 1972.

Development

In the mid-1960s the U.S. Army concluded that a purpose-built gunship with more speed and firepower was required in the face of increasingly intense ground fire (often using heavy machine guns and anti-tank rockets) from Viet Cong and NVA troops. Based on this realization, and with the growing involvement in Vietnam, the U.S. Army developed the requirements for a dedicated attack helicopter, the "Advanced Aerial Fire Support System" (AAFSS). The aircraft would be able to cruise at 195 knots with dash speed of 220 kt. It would be able hover-out-of-ground effect (OGE) at 6,000 feet (PA) and 95 °F (35 °C), and carry a much larger payload of weapons.

In August 1964, the Army released its request for proposals for the AAFSS. In February 1965, Lockheed and Sikorsky were selected as finalists. In the end, Lockheed's design was announced the winner in November 1965 on the basis of the design being less expensive, available earlier, and having less technical risk. The quantitative requirements for the AAFSS were finally released by the Army on 17 December 1965, which included several changes including adding an aerial rocket subsystem. In all, fourteen requirements were added to what was in Lockheed's proposal.

An engineering development contract was signed by the Army and Lockheed in March 1966. Later in 1966, options for production were finalized and added to the contract. In January 1967, the Army ordered 375 aircraft for $31.4 million with an option for further aircraft provided validation of the AH-56's need.

A rigid rotor helicopter had been built by Lockheed as the XH-51 and the AH-56 followed in its path. Its 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 canceled in 1969 as a result of budget cuts, and further development was halted in 1972.

In the end ten Cheyenne prototypes were built with one destroyed during wind tunnel testing along with the in-flight loss.

After cancellation

The development of the new technologies on the AH-56 led to many cost and time overruns. This, coupled with Vietnam war experience and an adjustment in the Army's specification, along with heavy campaigning by the Air Force which was in the midst of trying to get the A-10 authorized, 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 in the specification which would lead to the AH-64 Apache.

Design

File:Ah56aam.jpg

AH-56A Cheyenne at U.S. Army Aviation Museum, Ft. Rucker, AL, displaying the stub-wing, and both tail rotors.

The AH-56 Cheyenne was a compound helicopter with a two-seat tandem cockpit, fixed low wings and retractable landing gear.

The Cheyenne had a short but substantial wing on each side of the airframe and a rigid main rotor. Thrust was 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 was able to reach high speeds - in excess of 200 kts. The design is classed as a compound helicopter, or gyrodyne, and was unable to qualify for speed records in helicopter categories. The Cheyenne also featured an advanced navigation and fire control suite which became the basis for the fire control suite in the AH-64 Apache.

File:Ah-56 side.jpg

Front/Side view of AH-56

An unusual feature of the AH-56 was the gunner's station. Like the AH-1 Cobra, the AH-56 has two crew members, 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 afforded the gunner direct viewing from the turret.

Specifications (AH-56A)

Data from Jane's Aircraft

General characteristics

• Crew: 2 pilots: 1 pilot, 1 copilot/gunner (front seat)
• Length: 54 ft 8 in (16.66 m)
• Rotor diameter: 51 ft 3 in (15.62 m)
• Height: 13 ft 8.5 in (4.18 m)
• Empty weight: 12,215 lb (45,540 kg)
• Loaded weight: 18,300 lb (8,300 kg)
• Max takeoff weight: 25,880 lb (11,739 kg)
• Powerplant: 1× General Electric T64-GE-16 turboshaft, 3,925 shp (2,930 kW)

Performance

• Maximum speed: 212 knots (244 mph, 393 km/h)
• Cruise speed: 195 knots (225 mph, 362 km/h)
• Range: 1,063 nmi (1,225 mi, 1,971 km)
• Service ceiling: 20,000 ft (6,100 m)
• Rate of climb: 3,000 ft/min (15.23 m/s)

Armament

nose turret with either an M129 40 mm grenade launcher or an XM196 7.62x51 mm machine gun

• A belly turret with an XM140 30 mm cannon

See also

Related development

• Lockheed XH-51

Comparable aircraft

• AH-1 Cobra
• AH-64 Apache
• Sikorsky S-67

Related lists

• List of active military aircraft of the United States
• List of helicopters
• List of military aircraft of the United States
• List of Lockheed aircraft

See also

• Attack helicopter
• U.S. Helicopter Armament Subsystems

References

Notes

Bibliography

• Robb, Raymond L. "Hybrid helicopters: Compounding the quest for speed", Vertiflite. Summer 2006. American Helicopter Society.
• Shrader, Cecil L., COL (Ret.), USA. "Attack Helicopter Transformation". Letter to the editor. ARMY Magazine. January 2003. Association of the United States Army.

External links

Wikimedia Commons has media related to:

AH-56 Cheyenne

• Evolution of the Armed Helicopters into Air Maneuver units in Vietnam, US Army, 1986 (1.5 MB).
• The Abridged history of the Army Attack Helicopter program, US Army, 1973.
• AH-56 page on GlobalSecurity.org
• Assault Helicopters on U.S. Centennial of Flight Commission web site.
• Lockheed AH-56 "Cheyenne" on avia.russian.ee
• AH-56A pictures and specs
• TOW Missile System Chronology, Redstone Arsenal historical information

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "AH-56 Cheyenne".