AH-64 Cheyenne

Written by: Matthew J. Seelinger

In the early years of the Vietnam War, the Army experienced a high level of success by adapting Bell Helicopter’s UH-1 Iroquois–better known as the Huey–into an aerial gunship. This success convinced leaders that the Army needed a specially designed close air support attack helicopter. The quest for the attack helicopter began on 1 August 1964 with the Request for Proposal (RFP) for the Advanced Aerial Fire Support System (AAFSS). The vague name was used to keep the project low key so as not to anger the Air Force and its political supporters, who were already unhappy over the direction the Army was taking with helicopters. The AAFSS was to be an all-weather aircraft with a top speed of 220 knots, a hover ability of 6,000 feet at 95°F, and a ferry range of 2,415 miles. The weapons array would include a 40mm grenade launcher, 30mm cannon, and six missiles such as the BGM-71 Tube-launched, Optically tracked, Wire-guided (TOW) or MGM-51 Shillelagh. It would be able to operate at night and have an advanced all-weather fire control system, something new for a helicopter.

The Army set 24 November 1964 as the deadline for proposal submission and expected to determine a winner and award a contract by 1 November 1965. Twelve companies submitted proposals for the AAFSS, but the Army realized that it would need an interim measure to fill the immediate need for an attack helicopter while the AAFSS was fully developed.

In 1965 the Army considered several provisional alternatives. These included versions of the CH-47 Chinook, UH-2A Seasprite, and SH-3 Sea King. Bell Helicopter’s entry was a proof of concept vehicle called the Model 209 HueyCobra. It combined the engine, transmission, and tail structure of the Huey with a new fuselage and some unique weapons systems. On 13 April 1966, the Army ordered 112 Cobras; in the next five years Bell would build over 1,000 Cobras.

Of the twelve proposals, the Army accepted the Lockheed CL-840. This unique aircraft had several innovations, not the least of which was a patented hingeless rotor that dramatically decreased weight, and increased speed and maneuverability. This feature, also called a rigid rotor, had been under development for decades but had always been too unreliable and unstable for flight. The CL-840 had a crew of two, a downward pointing rear tail, a left side anti-torque rotor, and a pusher propeller at the extreme rear of the tail.

It promised to exceed the standards specified in RFP. A single General Electric T64-GE-16 turboshaft engine could crank out 3,425 horsepower to accelerate the aircraft from zero to 200 knots in thirty-eight seconds and back to zero in seventeen seconds. Lockheed promised a top speed of 220 knots at sea level, a ceiling of 26,000 feet, cruising distance of 872 miles, and ferry distance of 2,870 miles. Lockheed submitted a technical proposal on 11 August 1965 and a cost proposal a few weeks later.

Barbed wire and observation posts are common features of the Demilitarized Zone separating North and South Korea, as shown in Chester Jezierski’s 1970 watercolor on paper, Bayonet Tower. (Army Art Collection)

The Army announced on 3 November 1965 a desire to purchase 200 CL-840s at a unit cost of $500,000 each. Under procurement rules at the time, called Total Package Production (TPP), purchase of these helicopters would happen in three phases: program definition; engineering development; and production. LTC Emil E. “Jack” Kluever was designated as the Army program manager. On 23 March 1966 the Army signed a contract for ten prototype CL-840s at a cost of $12.75 million. These would include one static ground test vehicle, one flyable prototype without weapons, and eight flying prototypes. The Army designated the helicopter the AH-56A.

Production began immediately in Lockheed’s Building 901 of Plant A, in Van Nuys, California. When the first aircraft rolled off the line on 16 April 1967, the Chief of the U. S. Army Research and Development Command, LTGeneral Austin Betts, christened the helicopter the Cheyenne. By that time the Army hoped that an accelerated production run would result in 1,500 Cheyenne in service by the end of 1972. But by that time cost projections were up to a hefty $1 million each. Five months later, on 21 September, one day earlier than the contract called for, the Cheyenne took to the skies for the first time at Van Nuys Airport. Test pilot Don Segner was at the controls for a twenty-six minute test flight with LTC Kluever riding in the front seat.

This flight was followed by increasingly ambitious flights, all within the confines of the airport. On 15 November, the Cheyenne made its first cross-country flight to an airport Oxnard, California making a speed of 115 knots at 2,000 feet. The Cheyenne’s public debut occurred on 12 December with a thirteen minute flight. Pilot Don Segner impressed observers by gaining 170 knots and a 30° bank angle. He held the aircraft in a steady hover during a thirty knot crosswind and moved it forward and backward using the just the pusher propeller, keeping the fuselage level.

The show was concluded when Segner landed the Cheyenne, holding the rear wheel about five feet off the ground as it taxied to the tarmac. He then lowered the helicopter’s nose for the onlookers in what became known as the “Cheyenne bob.” The Cheyenne was impressive and expensive. Flight tests were going well but there was limited money available for developmental projects. The war in Vietnam exposed the need for an attack helicopter, but diverted funds from such programs as the Cheyenne, as well as the Air Force’s F-111 and the C-5 Galaxy. The Cheyenne contract obligated the Army to make a production commitment by the end of 1967 or face an inevitable increase in per unit costs.

The Army asked the Department of Defense for Fiscal Year (FY) 1968 procurement funds but was told to wait until FY69. The only option for the Army was to find funds internally. Even though the deadline lapsed Lockheed granted a grace period while the Army scrapped together the cash. On 8 January 1969, the Army reallocated $21.4 million to keep the project going. With the program saved, production of the first operational AH-56A was planned for September 1968 with delivery one year later. Lockheed produced subassemblies in Van Nuys and Burbank, with final assembly in Palmdale, California. The Army hoped to order 600 Cheyennes but settled for 375 even though the smaller order resulted in a higher unit cost. At the same time the Army was squeezing other programs for cash they were fighting Air Force claims that the AH-56A incurred on the development of their A-X close support aircraft that eventually became the A-10 Thunderbolt II.

Throughout 1968, flight tests continued to push the Cheyenne’s envelop. Flight characteristics and weapons capability continued to impress Army leaders with the Cheyenne’s potential not only in close support, but also as a direct support aircraft. Whatever its ultimate, use the Cheyenne would easily outperform the AH-1 Cobra. Its firepower was especially adaptable not only to the jungles of Southeast Asia, but also to the plains of Europe. The AH-56A’s advanced weapons system with magnifying sight, laser range finder, and moving map would allow the Cheyenne to standoff at a safe distance and relay targeting information to artillery. The development of passive infra-red night equipment (PINE) by Hughes Aircraft gave it night and all-weather capability. The AH-56A could also work as a team with one aircraft tracking and others shooting at targets, all the while maneuvering in a superior manner than that of the Cobra.

The implementation in the cockpit was a collection of old and new. Conventional round gauges, tape-style instruments, and for the first time in helicopters, electronic displays (CRT), provided pilots with the information they needed to keep the craft aloft. The cockpit itself was unique with the pilot in the rear elevated position and gunner in the forward depressed position. The gunner’s seat was designated the XM-112 stabilized gunner station (SGS) designed by General Electric Avionics Controls Division. The seat rotated as much as 210° to either side of centerline giving the gunner visibility of targets all around the aircraft. The gunner also had duplicate flight control so he could fly the aircraft if necessary.
The pilot had Honeywell’s state of the art twenty-two ounce visual precision fire control equipment (VIPRE) that attached to his APH-5 helmet by nylon screws. The effective system broke away in any serious impact to avoid head and neck injury.

A nose mounted turret contained a Philco Ford Aeronutronic XM-129 40mm grenade launcher. The gun elevated 18°, depressed 70°, and rotated 200° to either side. An interchangeable XM-196 7.62mm minigun was planned but later eliminated. At mid-fuselage another turret, the XM-52, housed the Philco Ford XM-140 30mm cannon. This weapon elevated 26°, depressed 60°, and also rotated 200°. Both turrets were connected electronically to the SGS to rotate along with the gunner. The Cheyenne had great promise but like all new equipment it was not without problems. On 12 March 1969 it suffered its only flight loss.

Test pilot David Beill took ship number 1003 on a solo flight up to 2,500 feet. A chase pilot noticed the rotors oscillating wildly just before it sliced into the cockpit and tail boom, killing Beill instantly. The Cheyenne fleet was immediately grounded pending an investigation. That investigation by the Army, the Federal Aviation Administration, and Stanford Research Institute accused the company and test pilot of several failures. Lockheed disputed most of these as false or claimed that problems had been cleared up before the fatal flight. The accident did bring about some changes including stiffening of the main rotor blades, improvements of the gyro, and changes in the rotor geometry. A policy change also dictated that future test flights would be conducted from the gunner’s cockpit. The SGS in ship number 1009 was replaced with a downward-firing ejection seat from an F-104 to give the test pilot a chance of escape in an emergency.

On 10 April 1969, the Army issued a formal “cure-notice” to Lockheed demanding certain fixes within fifteen days. At the same time the Army denounced the Cheyenne as unstable even though Lockheed had already developed improvements. On 19 May the Army cancelled Cheyenne production due to nonperformance by Lockheed. By claiming that Lockheed was in default of its contract the Army expected to recoup $54 million. However, under TPP, the development contract remained in place with $17 million allocated for FY 70 and FY 71. More testing followed until another catastrophic accident on 17 September 1969 at the NASA Ames Research Center wind tunnel. One Cheyenne was destroyed but this time no one was injured. Even though the conditions that resulted in the accident were artificial and could not have happened in flight, this went a long way toward its ultimate cancellation of the Cheyenne.

Barbed wire and observation posts are common features of the Demilitarized Zone separating North and South Korea, as shown in Chester Jezierski’s 1970 watercolor on paper, Bayonet Tower. (Army Art Collection)

Further testing that continued until 1972 revealed other deficiencies that were corrected in turn until it finally appeared that the Cheyenne may yet be fielded. But by that time the Air Force A-10 Thunderbolt II program was progressing nicely and the unit cost of the Cheyenne had increased to over $3 million. Congress was beginning to question the need for two similar projects. Hoping to impress the Senate Armed Services Committee a firepower demonstration was held at the Yuma Proving Grounds. Despite previously firing 130 TOW missiles successfully, the first fired this day grounded itself. Even though this was a missile failure the AH-56 was doomed. After an expenditure of over $400 million, with a unit cost now over $4 million the Cheyenne was finally cancelled on 9 August 1972.

Immediately after cancellation of the Cheyenne the Army opened the Advanced Attack Helicopter competition. This helicopter would incorporate many of the advances of the Cheyenne but not be as fast. Lockheed proposed a twin engine version of the Cheyenne without a pusher propeller. Hughes (later McDonnell Douglas, ultimately Boeing) won the competition with the AH-64 Apache, arguably the best offensive helicopter in history.

Even though the Cheyenne was never fielded, it and test pilot Don Segner won awards for engineering achievement and piloting from both the Society of Experimental Test Pilots and the American Institute of Aeronautics and Astronautics. Today one can get a close up look at the Cheyenne at the U.S. Army Aviation Museum at Fort Rucker, Alabama, the Don F. Pratt Museum at Fort Campbell, Kentucky, and at Fort Polk, Louisiana. For further reading Jim recommends AH-56A Cheyenne, Volume 27 of the Warbird Tech Series by Tony Lnadis and Dennis R. Jenkins. For more information regarding the development of the helicopter as a close air support weapon see Interservice Rivalry and Airpower in the Vietnam by Dr. Ian Horwood (http://usacac.leavenworth.army.mil/CAC/csi/RandP/airpower.pdf)