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Further Reading

AH-56A Cheyenne Advanced Aerial Fire Support System (AAFSS)

The AH-56 Cheyenne Advanced Aerial Fire Support System (AAFSS) was a prototype attack helicopter developed to replace the AH-1 Cobra. It never went into production. The Army -- in cooperation with industry -- began developing the AH-56 Cheyenne and the AH-64 Apache during the final years of the Vietnam conflict. The Army's development of specifically designed attack helicopters during the 1970s again raised the question of Army and Air Force aerial missions. By this time, the Air Force was content to permit the Army to continue developing helicopters.

The experience of Vietnam showed that the existing attack helicopter, the AH-1 Cobra, was vulnerable even to light antiaircraft fire and lacked the agility to fly close to the ground for long periods of time. The AH-56A Cheyenne helicopter was intended to correct those deficiencies. The Lockheed AH-56A Cheyenne attack helicopter was designed to meet the US Army's requirement for the Advance Aerial Fire Support System (AAFSS). The helicopter's mission would eventually be assumed by the Boeing (formerly McDonnell Douglas) AH-64 Series Apache attack helicopter.

The Army had long realized that the Huey-gun-rocket combination was a make-shift, albeit, quite ingenious, system that should be replaced by a new aircraft specifically designed for the armed mission. In the early 1960's, industry asserted that advance was within the state of the art. Experts in research and development urged the Army planners to go for a compound helicopter with an integrated armament system as soon as possible. They argued that it was technically feasible and procurement of any "interim" system would mean the Army would be stuck with an inferior capability for years to come. Moreover, it appeared that an advanced system could be procured almost as soon as an interim aircraft.

There were other pressures too. The Office of the Secretary of Defense had been critical of all the Services in their efforts to procure expensive weapon systems that appeared to offer only marginal improvements over the system they were to replace-aircraft that flew a little higher or faster, tanks that had only slightly better performance, ships that cruised but a few knots faster. Ever since the Howze Board, the Army was sensitive to any criticism that it was striving for less than the best in airmobility. Also, the Air Force maintained that much of Army aviation duplicated an Air Force capability rather than, as the Army claimed, complemented Air Force support. The Army decided that its best option was to hold a design competition for a totally new system that would offer unique capabilities.

The Advance Aerial Fire Support System (AAFSS), which began in 1964, was won by the Lockheed AH-56A Cheyenne. Bell entered a scaled-down version of it's Iroquois Warrior. The other competitor was the Sikorsky (S-66) (1964) which looked similar to the AH-56A Cheyenne, but had a Rotorprop tail rotor which could rotate on it's axis throught 90° to act both as an anti-torque rotor or as a pusher, thereby transforming the S-66 into a compound aircraft in cruising flight.

Termed a compound helicopter, the Cheyenne had rotor blades as well as stub wings and a pusher propeller. The rotors provide conventional helicopter performance, and in conjunction with the stub wings and pusher prop permit level flight at speeds of more than 250 miles per hour. The Cheyenne was the first Army aircraft to be designed and built as an integrated aerial vehicle / armament / avionics / fire control gun ship and coincidentally the first compound helicopter to be developed by any of the US military forces. The versatile craft, when fully equipped, will be capable of firing machine guns, grenades, rockets and missiles. The swiveling belly turrent mounts a 30-mm automatic gun. Both the pilot and gunner are protected by armor plate.

The AH-56 was essentially a flying tank built around rigid rotor system. This remarkable compound helicopter relied on a pusher propeller and a set of wings to achieve speeds greater than 322 kph (200 mph). The AH-56A is a compound helicopter designed to perform the advanced aerial fire support mission. The Cheyenne had a single rigid four-bladed main rotor and anti-torque tail rotor, and a three-bladed pusher. In addition to a single four-bladed "rigid" main rotor and a teetering four-bladed antitorque tail rotor, a three-bladed pusher propeller is located at the aft end of the fuselage, and a low wing is located on the fuselage midsection. During high-speed forward flight, the main rotor is partially unloaded with the lift provided by the wing and thrust supplied by the pusher propeller. The cockpit has tandem seals. Normally, the forward seat is for the copilot/gunner, and the aft seat is for the pilot. The conventional wheel-type landing gear is retractable.

Provisions for wide variety of armament systems are available in two turrets and on six external stores stations. The rigid-rotor Cheyenne featured a XM112 swiveling gunner's station linked to rotating belly and nose turrets, and a laser range-finder tied to a fire control computer. It was armed with an XM52 30mm automatic gun in the belly turret and a XM51 40mm grenade launcher or a XM53 7.62mm Gatling machine gun in the chin-turret, TOWs, and XM200 2.75 inch rocket launchers.

The Cheyenne, powered by one General Electric T64-GE-16 3435 shp turbine engine, was designed to fly at nearly twice the speed of combat helicopters used in Vietnam. The AH-56A had a maximum speed of 214 knots, cruise speed of 197 knots, a service ceiling of 26,000 feet, maximum range of 547 nautical miles, and could climb 3,420 feet per minute. Designed for quick turn-around capability, an AH-56A returning from a combat flight could be readied and rearmed for a new mission within ten minutes. A complete engine change could be accomplished in 30 minutes.

Lockheed rolled-out the first prototype on May 3, 1967. The Army's newest and most advanced combat helicopter, the AH-56A Cheyenne, demonstrated its speed, versatility, and maneuverability in December 1967 during its first public flight at Van Nuys, California. Observers at the demonstration included ranking military and U. S. Government officials, representatives of the prime contractor, Lockheed-California Company, and some 800 sub-contractors who helped build the technologically advanced rotocraft.

Because of the advanced technologies in the AH-56 Cheyenne, the program ran into serious delays and cost overruns. Unfortunately, the Cheyenne experienced developmental difficulties with some of the new technology it employed. Thus, Congress was severely critical of the program. However, advocates of the AH-56 Cheyenne argued that the program was about to succeed, but it would still take several years for this aircraft actually to go into the field and help soldiers on the ground. Eventually, Lockheed had eliminated nearly all of the bugs but the Cheyenne languished under an awkward procurement process put in place by Secretary of Defense Robert McNamara.

Unfortunately, what was a straight forward concept for a new armed helicopter soon became bogged down in a morass of permutations, modifications and additions to its design. The technicians had taken over from the tacticians. The concept grew in complexity and cost. Worse, it was being pushed into a later time frame when it was sorely needed in combat. Such things as a rigid rotor, ground avoidance radar, inertial navigation and computerization were straining the state of the art and pricing the Army out of mass production. A reevaluation was inevitable.

The production contract was canceled during the fiscal year 1969 because of technical problems. The development program was still in effect, however, and an early solution to technical problems was expected. There were no firm plans to enter into another production contract at the time production was cancelled.

Lockheed-California Co. said it has remedied virtually all problems of the AH-56A compound helicopter cited in a cure notice from the Army in 1969. The restructured AH-56A development program identified two Army test programs which were to be conducted by the US Army Aviation Systems Test Activity (USAAS A) on the Improved Control System (ICS) configuration of the AH-56A. These programs were the Army Preliminary Evaluation I (APE I) and a portion of the Research and Development Acceptance Test I (RDAT I).

The Army Preliminary Evaluation I and a portion of the Research and Development Acceptance Test I were conducted periodically on the AH-56A Cheyenne compound helicopter by the US Army Aviation Systems Test Activity between 30 January and 23 December 1971. These engineering tests were divided into five distinct phases to permit Army evaluation of the aircraft at various stages of the contractor development program. Primary test objectives were to gather stability and control data to provide an early assessment of the AH-56A, to assist in determining flight envelopes for future Army tests, and to examine previously identified problem areas.

None of the rotor dynamic instabilities previously encountered in the contractor's development program were noted during these tests. Lateral control migration with airspeed was not objectionable. The capability of the pusher propeller to provide rapid deceleration and to control airspeed independently of dive angle is an excellent feature.

Five deficiencies and 54 shortcomings were identified. The deficiencies are (1) excessive pilot workload due to unacceptable static lateral-directional stability characteristics at low airspeed seriously impairs the capability to operate at minimum altitudes unaffected by conditions of darkness or adverse weather, (2) uncommanded aircraft motion and loss of control during some maneuvering flight conditions, (3) rapid rate of rotor speed decay following simulated engine failures which allows the rotor speed to drop below the present transient limit, (4) inadequate directional control margins in sideward flight, and (5) excessive vibration levels in portions of the flight envelope.

Correction of the deficiencies would be a prerequisite for an airworthiness it release for operational Army aviators, and correction of the shortcomings was desirable. Two deficiencies warranted a reduction of the flight envelope size for future Army tests until correction of those deficiencies is accomplished. Further testing of the AH-56A was recommended.

The US Army Aviation Systems Test Activity (USAASTA) conducted an Attack Helicopter Evaluation of the AH-56A Cheyenne Compound Helicopter during the period 15 April to 15 June 1972. The AH-56A was tested at Yuma Proving Ground, Arizona and Mammoth Lakes, California. This evaluation was conducted to provide data for use in determining Advanced Aerial Fire Support System effectiveness model inputs, validating material need requirements, and validating contractor claims. The forward area concealment evaluation was conducted by the US Army Combat Developments Command Aviation Agency and the maintenance characteristics evaluation was conducted by the US Army Aviation Systems Command. The performance and handling qualities testing consisted of 49 test flights totaling 42.2 flight hours. The pusher propeller was a major contributor to several enhancing performance and handling qualities characteristics.

By the time the aircraft was ready for production in 1972, the Army was becoming interested in a helicopter with night and all-weather attack capability - a requirement that was not included in the Cheyenne contract. Congress then cancelled the program at a significant financial loss to Lockheed. Ten prototypes were completed before the program was terminated August 9, 1972 due to delayed development, rising costs, and the appearance of two competitive company-funded initiatives by Sikorsky and Bell. Most Cheyenne airframes ended up at Aberdeen Proving Grounds.

Bell Helicopter Company had prudently carried on its own research and development program using proven dynamic components of the Huey. Consequently, they were able to offer, at the appropriate moment, an "off-the-shelf" armed helicopter for just slightly more than the modified UH-1 that the Army was then buying to replace Vietnam attrition. The "Cobra" had enough speed to meet the escort mission; tandem seating; better armor; and a better weapons system. With the strong urging of the combat commanders, the Army decided to procure an interim" system for immediate requirements while it sorted out the problems of the "ultimate" system.

The Army wanted a smaller, more agile Advanced Attack Helicopter (AAH) with a less complicated fire control and navigation system. The new attack helicopter program announced in August 1972 drew from the combat experience of the Cobra and the developmental experience of the Cheyenne to specify an aircraft that could absorb battle damage and had the power for rapid movement and heavy loads. The helicopter would have to be able to fly nap of the earth and maneuver with great agility to succeed in a new antitank mission on a high-intensity battlefield. In December 1976 the Army selected the Hughes YAM-64 for production.