Ahead of its time in performance and design, the Lockheed AH-56 seemed like a promising attack helicopter for the United States Army during the Vietnam War, but instead ended up on the chopping block.
Gunship Success
During America’s involvement in Vietnam, it was discovered that adding firepower to a Bell UH-1 Iroquois or “Huey” helicopter, creating an aerial gunship, became a very effective weapon on the battlefield. The United States Army decided they needed a dedicated gunship attack helicopter for CAS (Close Air Support). In 1964 the Army presented a Request for Proposal for a vague weapon known as Advanced Aerial Fire Support System (AAFSS). The ambiguity was intended to keep the United States Air Force in the dark on the intentions of the Army, as the Air Force was already concerned about the Army’s helicopter infatuation for use in CAS. Requirements included a hover ability of 6,000 ft at 95 degrees Fahrenheit, important in the hot and humid climate of Southeast Asia. Speed was to be 224 mph cruise and 250 mph maximum speed. The ability to operate in darkness and have all-weather fire control capabilities was included as requirements. Weapons would consist of a 40 mm grenade launcher, a 30 mm cannon and missiles and rockets.
Lockheed’s entry, known as CL-840, was accepted out of twelve proposals, along with a proposal from Sikorsky. The Army also continued to pursue an interim attack helicopter, and Bell developed the AH-1 Cobra two-seat attack helicopter, using the Huey’s transmission, engine, rotor system, and tail structure.
Lockheed’s Entry
The Lockheed CL-840 was declared the winner over the Sikorsky model on Nov. 3, 1965. On Mar. 23, 1966, the Army awarded a contract for 10 prototypes to Lockheed, designating the helicopter the AH-56A “Cheyenne”, continuing the practice of using Native American names for helicopters. The AH-56A would incorporate several innovations, including a hingeless rotor system also known as a rigid rotor. This system decreased weight and increased speed and maneuverability and was controlled through gyroscopic means. A downward pointing tail, left side anti-torque rotor and a pusher propeller at the extreme rear of the tail gave the helicopter a unique appearance.
A crew of two included a gunner sitting forward in a seat that swiveled to follow the gun turret with fire control and periscope sighting systems moving with him and a pilot behind and elevated above the gunner. The gunner also had duel flight controls. The pilot had a helmet mounted sight system developed by Honeywell for aiming weapons as well. CRT (cathode ray tube) electronic displays were also used along with conventional gauges in the cockpit.
The compound helicopter also had two low-mounted stub wings that during high speeds provided lift as increased trust was produced by the pusher propeller reducing the lift needed by the main rotor. Power came from a General Electric T64 turboshaft engine producing over 3,400 horsepower and providing a maximum speed of around 244 mph. Service ceiling was 21,000 ft.
Armament included a Philco Ford XM-140 30 mm cannon mounted on the belly mid-fuselage in a turret that allowed the gun to rotate 360 degrees, elevate 26 degrees, and depress 60 degrees. Under the nose of the aircraft was another turret housing a Philco Ford XM129 40 mm grenade launcher that rotated 200 degrees. Both turrets were connected electronically to rotate as the gunner rotated. The forward turret could have a XM196 7.62 mm minigun installed in place of the grenade launcher. Four hardpoints under the wings could carry 2.75 in unguided rockets in pods or BGM-71 TOW missiles (Tube-launched Optically-tracked, Wire-guided) anti-tank missiles. A pair of fuselage mounts was usually reserved for external fuel tanks, as well as wingtip hardpoints that could carry fuel tanks.
The Cheyenne was 54 ft 8 in long, 13 ft 8.5 in high, and had a maximum take-off weight of 25,880 lb. Main rotor diameter was 51 ft 3 in, while wingspan was 26 ft 8.4 in. The helicopter incorporated lengthy retractable landing gear to allow clearance for the belly turret.
Test Flight Tragedy
The first flight of the AH-56 was Sept. 21, 1967. Tests demonstrated the helicopter had promise, with high speeds and advanced weapon aiming capabilities, as well as good maneuverability and hovering capabilities. However on Mar. 12, 1969, tragedy struck. Piloted by test pilot David A. Beil, serial number 66-8828 began to suffer severe rotor oscillation up to three feet vertically, and the rotors struck the tail boom and the cockpit, separating the tail section and also striking Beil in the cockpit, killing him. Investigation revealed safety controls had been turned off, and the rotor and control systems were modified in the aftermath of the incident to prevent such an accident. Another prototype, 66-8835, was destroyed in a similar manner in September of 1969 during wind tunnel testing, however the aircraft was attached to fixed mounts preventing it from moving relative to the rotor.
Cheyenne Cancelled
While showing impressive abilities, advances, and potential, the AH-56 was cancelled on Aug. 9, 1972 by the Secretary of the Army. While it’s somewhat difficult to pinpoint one specific issue leading to the demise of such an advanced helicopter, several factors can be considered.
Costs of the project had continued to climb since the onset of the project. The helicopter went from an initial purchase price of $500,000 each in 1965 to over one million dollars each by 1967 when the Army had hopes of a fleet of 1,500 Cheyennes in service by 1972. With cost issues, the Army adjusted the number to 600, then eventually down to 375 AH-56s. By 1972 the cost per unit was over $3 million.
In April of 1969 the Army had demanded Lockheed fix a list of issues within 15 days on the aircraft, and on May 19 the Army cancelled further production claiming Lockheed had failed to perform and was in violation of their contract. However, the contract remained in place and testing and development continued, but the wind tunnel accident in September aided in the demise of the project. Vibration issues, problems with directional control during sideways flight, and other control issues seemed to plague the project.
In 1972 it seemed most of the kinks had been worked out and it was hoped the helicopter was ready for service. However during a demonstration of the AH-56 to the Senate Armed Services Committee at the Yuma Proving Grounds, the first firing of a TOW missile failed upon launch as it dropped to the ground. While a missile issue and not a failure of the Cheyenne, many of the onlookers were less than impressed. Unit cost was now over $4 million per helicopter.
Perhaps the largest dagger plunged into the heart of the AH-56 was the constant feuding with the Air Force over which service was responsible for CAS duties. The Air Force was in development of the AX project which eventually produced the fixed-wing A-10 attack aircraft, and insisted CAS missions belonged to them and the Army’s AH-56 infringed upon mandates of the Key West Agreement of 1948. The Key West Agreement outlined the functions of the Air Force in conjunction with the other service branches.
When the program was cancelled in 1972, reasons stated included the inadequate night and all-weather capabilities as well as the aircraft being too large. The smaller AH-1 Cobra was now a proven alternative and much more affordable, though with inferior performance in many areas. By now most of the systems and avionics on the Cheyenne were becoming rapidly obsolete, and further improvements only meant ballooning costs once again. The Army initiated the AHH (Advanced Attack Helicopter) program just days after cancellation of the AH-56, the program eventually resulting in the AH-64 Apache attack helicopter.
There are four surviving examples of the original ten Cheyenne helicopters produced: one on display and one in storage at Fort Novosel, Alabama at the United States Army Aviation Museum, one at Fort Johnson, Louisiana, and one at Fort Campbell, Kentucky.
