In the 1960s, the Army tested the AH-56A Cheyenne, an attack helicopter that might have revolutionized warfare. Had a civilian version existed, it might have changed aviation.

Instead, the Cheyenne became a “might have been.” It was costly and technologically challenging. It may have been too advanced for its time. Its performance in flight was sometimes “spectacular,” as one pilot put it, but there were minor kinks that were never quite ironed out.

During vertical and hovering flight all power was applied to the main and anti-torque rotors, while during forward flight all but about 700shp was shafted to the pusher propeller. In forward flight lift was generated by the stub wings and windmilling main rotor. In “clean” configuration the AH-56A was capable of sea-level speeds in excess of 275 miles per hour.

The AH-56A was also called the Advanced Aerial Fire Support System (AAFSS). During the period when the United States was building up its troop strength in Vietnam, the AH-56 became a bold attempt to compete with the Air Force for a key role in air-to-ground support. The Cheyenne was a highly sophisticated compound rotorcraft incorporating design features pioneered in Lockheed’s earlier XH-51A test ship.

It was a long, slim helicopter with retractable landing gear, small wings that spanned almost 27 feet, and a General Electric T64-GE-16 shaft turbine engine with a four-bladed rotor. The power rating of the engine was increased to 3,922 horsepower as the test program evolved.

The Cheyenne used an innovative propulsion system built around the T64. The powerplant drove a rigid, four-bladed, gyro-stabilized main rotor, the tail-mounted anti-torque rotor, and the pusher propeller at the extreme end of the tail boom.

During vertical and hovering flight all power was applied to the main and anti-torque rotors, while during forward flight all but about 700shp was shafted to the pusher propeller. In forward flight lift was generated by the stub wings and windmilling main rotor. In “clean” configuration the AH-56A was capable of sea-level speeds in excess of 275 miles per hour.

Raymond L. Robb, a Fairborn, Ohio, author of an unpublished history of the AH-56, said in a 2003 interview that the fast, powerful helicopter “could have given the Army a new capability to support its combat troops.”

Giant Leap

The Army was looking for a truly giant leap with the AH-56. The service established exceedingly ambitious goals. It said it wanted an aircraft with a top speed of 220 knots, able to hover out of ground effect at 6,000 feet, with a ferry range of 2,100 nautical miles. A little noticed feature of the Cheyenne, according to Arthur Moss, who wrote the AH-56 flight manual, was its ability to self-deploy over long distances, including the 2,200-mile flight from California to Hawaii.

Although Lockheed had little experience building helicopters, the Army chose its design in 1966.

But in tests the AH-56 had difficulty maintaining stability close to the ground and at high speed. Various design changes seemed to help, but no certain fix had been found when the third Cheyenne built was lost in a crash on March 12, 1969.

The crew of two, pilot and gunner/co-pilot, sat in tandem in an enclosed cockpit. The impressive armament of the Cheyenne included a 30-mm XM140 cannon in a belly turret, and a 40-mm XM129 grenade launcher or 7.62-mm Minigun in a nose turret. Under the wing were six hardpoints for ordnance, consisting of Hughes TOW anti-tank missiles or 2.75-inch folding fin aircraft rockets. The AH-56 had an advanced weapon sighting system that included night vision equipment and a helmet gun sight.

“It was a helicopter carrying the kind of weapons you typically found on an Air Force fighter-bomber,” said Donald F. Segner, the Lockheed test pilot in a 2003 interview.

The Army was enthusiastic enough that in January 1968, it placed an initial production order for 375 aircraft.

As it turned out, only 10 Cheyennes were built.

With Army Lt. Col. Emil “Jack” Kluever on board, Segner took the prototype AH-56 for its first flight at Van Nuys, Calif. on Sept. 21, 1967.

But in tests the AH-56 had difficulty maintaining stability close to the ground and at high speed. Various design changes seemed to help, but no certain fix had been found when the third Cheyenne built was lost in a crash on March 12, 1969.

Accompanied by a chase plane, the Cheyenne was flying at 2,500 feet off the Pacific coast of California. The AH-56 was in the hands of Lockheed test pilot David Beil. As the chase pilot looked on, the Cheyenne’s main rotor oscillated out of control and the blades sliced into the pilot’s canopy and then chopped off the tail boom. Beil was killed instantly. All Cheyennes were grounded temporarily.

Chasing the Cheyenne

The mere task of finding a “chase” aircraft was needed to shadow the Cheyenne on test flights was, in itself, a difficult undertaking. No helicopter could keep up. In fact, none came close.

The Army acquired three F-51D Mustang fighters of World War II vintage, built by North American Aviation, Inc., and later modified by Cavalier Aircraft Corp.

The Army’s Mustangs differed from World War II versions in having additional fuel, a second cockpit station for a cameraman, and a gyro-stabilized camera mount for the second crewman. Cavalier removed the six .50-caliber Browning M2 machine guns built into the Mustangs. The Army flew them without armament.

According to retired Army Col. Alexander J. Rankin, who led the “chase” effort and uttered the “spectacular” quote about the Cheyenne, about half a dozen Army pilots flew the Mustangs.

According to Roby, the final test report issued just after termination of the program identified the Cheyenne as “the finest aircraft” ever tested at Edwards Air Force Base, Calif.

Following the grounding of the AH-56s, tests resumed in July 1969. By then the Army had abandoned its production order – prematurely, many observers said. The Cheyenne program also suffered from cost increases. Meanwhile, the Army was getting good results with a less advanced, less ambitious helicopter, the AH-1G Huey Cobra, which went into combat in South Vietnam in 1969.

In an Internet posting, David Roby, an engineer on the Cheyenne program, describes himself as one of the “six Cheyenne biased bastards” in a statement attributed to Army Secretary Stanley Resor. Roby lists the following reasons why the Cheyenne didn’t succeed: “Air Force concerns with its A-10 Thunderbolt II program; Bell Helicopter and Sikorsky business practices; Lockheed’s own “failures” on UH-1 Huey depot maintenance contracts, shipbuilding schedule problems; a ‘Golden Handshake Clause’ in the C-5A Galaxy contract, with which Congress took issue, that allowed Lockheed to recoup any financial loss on the contract for the first 25 on any subsequent reorder … and finally the various development problems with the most advanced helicopter ever conceived.”

According to Roby, the final test report issued just after termination of the program identified the Cheyenne as “the finest aircraft” ever tested at Edwards Air Force Base, Calif.

The nation has seen several efforts by the Army to introduce advanced, high-tech helicopters. The RAH-66 Comanche, which was also canceled, began as the LHX project of the late 1980s, which would have pushed technology to the limit. Today, the Army is interested in the X2 demonstrator and the proposed S-97 Raider from Sikorsky, both of which would have cutting-edge features. In a poignant reminder of just how far ahead of its time the Cheyenne was, the X2 has a tail propeller that looks almost like a carbon copy of the Cheyenne’s.

Had its technical difficulties been overcome and had politics not intervened, the Cheyenne would have been a formidable weapon. In some ways, it was more advanced than today’s AH-64D Longbow Apache, which offers some of the capabilities the Cheyenne had but is not as effective at high altitude. The Cheyenne “was an incredible aircraft,” said Richard Berch, who piloted the AH-56A at the Yuma, Arizona Proving Ground in Arizona. “It would have changed military aviation. A passenger carrying version would have changed short-haul commercial aviation.”

Today, all that remains of the Cheyenne program is an AH-56 at the Army Aviation Museum, Fort Rucker, Ala., another on outdoor display at Fort Polk, L.,a and a third at Fort Campbell, Ky., at the outdoor display of the 101st Airborne Division (Donald F. Pratt Memorial) Museum.