Lockheed AH-56 Cheyenne
Two-Seat Dedicated Attack Helicopter Prototype
Lockheeds first - and last - foray into the helicopter market, the AH-56 Cheyenne, failed to materialize as a viable attack helicopter for the U.S. Army.
Authored By: Staff Writer | Last Edited:
The AH-56 Cheyenne was Lockheed's first and only foray into development of a production helicopter. In many respects, however, the Cheyenne was neither a true helicopter nor was it a true airplane - in many ways that today's tilt-rotor V-22 Osprey defies conventional categorization as a helicopter. The performance specifications inherent in the design allowed for the Cheyenne system to reach unheard speeds for any helicopter type before it - or today for that matter. The system was initially conceived of as an escort for the fast-moving helicopter transports ferrying troops into combat hot zones. As the AH-56 program developed, senior US Army personnel began envisioning more roles for the already impressive AH-56 to undertake. In the end, however, the dream was unfulfilled for many-an-obstacle stood in the way of the Cheyenne eventually leading up to its cancellation.
In the mid-1950s, the concept of armed helicopters was taking hold with the army leaders of the world. Over a decade before, the German Luftwaffe was able to field the first real operational fleet of helicopters but this occurred only in limited numbers. What this did, however, was begin to pave the way for other like-designs to take hold and the US Army was no exception to such thinking. Early attempts by the US Army were made by simply adding machine guns as self-defense measures to existing transport helicopters though this by no means was the solution it sought. The arrival of the turbine-powered Bell UH-1 "Huey" and the Vietnam War allowed for even greater thinking in the area, for this capable systems could be armed well enough and provide performance to keep up with the transports she was charged with protecting. UH-1's were ultimately trialled and fitted with various arrangements of rocket pods, missiles, automatic grenade launchers, miniguns and machine guns. The first UH-1's arrived in Southeast Asia in 1962.
While the UH-1 was capable of keeping up with its older transport counterparts, the arrival of the twin-engine Boeing-Vertol CH-47 Chinook transport series once again changed everything. Chinooks could easily outpace their UH-1 brethren, making their armed escort partners seemingly useless where pure speed over contested areas was the call of the day. As such, the US Army started penciling out plans for a new dedicated helicopter escort capable of saturating the area ahead with strike fighter-like firepower while being able to survive in a low-altitude environment.
Strike fighters of the day proved adequate suppressive components, but this up to a point. Since they operated under the banner of the US Air Force (unlike in World War 2), the US Army was at the mercy of their limitations. Jets still relied on their thirsty engines limiting their loitering times and were built for speed, essentially restricting many of these hotrods to single passes over a given target or target area while their targeting and munitions capabilities were more reserved for annihilating large target areas - not the confined target areas of assisting friendly troops on the ground as close-support aircraft. Many strike fighters had to wait on the ground for the call to help, wasting precious minutes in take-off and journey time to the target. A capable helicopter, at least one armed and dedicated for the role for the job, could be waiting just outside of the hot zone to participate in action at a moment's notice.
The US Army began looking into acquiring their own solution apart from the US Air Force. This included testing out other implements such as the Douglas A-4 Skyhawk and an early form of the AV-8 Harrier jump jet. The US Air Force, long holding to the belief that the fixed-wing realm was theirs and theirs alone, lobbied hard against the US Army acquiring their own fixed-wing strike aircraft - an argument that the US Air Force ultimately won. As such, the US Air Force would continue to supply the airpower for the US Army's needs, though a new set of requirements were written for the Air Force to accomplish this. Some of the more outstanding byproducts of this new initiative would become the twin-engine Rockwell OV-10 Bronco and the single-engine Douglas A-1 Skyraider, each implement proving adequate in the close-support role, but not the solution that the US Army was envisioning. The ever-changing tactics of a resilient enemy in Vietnam would prove that. While the US Army could not field their own fixed-wing aircraft, they were allowed to keep their own contingent of armed helicopters. To that, the US Army presented the Advanced Aerial Fire Support System program in search for their first dedicated attack helicopter platform.
About this time, Bell produced their private venture Bell 209 model which ultimately became the successful AH-1 HueyCobra (or simply "Cobra"), fulfilling the gunship role of the Cheyenne. These systems held some inherent benefits such as their successful Bell pedigree (ala the UH-1), a slim forward profile and adequate survival capabilities for the crew. Their limitations - when compared to the Cheyenne - was their lack of an advanced fire control system, limited armament capabilities and limited endurance. Despite this, the inevitable faltering of the Cheyenne project would give rise to the Cobra gunship and decades of faithful service thereafter before being replaced by the Hughes AH-64 Apache gunship.
While Bell was working through their Model 209, Sikorsky, Convair and Lockheed submitted proposals to fulfill the Army need. Sikorsky showcased a promising design while Convair's approach was seemingly out of this world. Convair put forth their Model 49, a VTOL-capable system built around a protected cylindrical engine shroud, armed to the teeth and - perhaps most distinctly -with a positional cockpit containing pilot and co-pilot. The cockpit could be set to a horizontal position when in flight and similarly leveled in hover, this while the rest of the fuselage stayed vertical.
Lockheed unveiled its CL-840 model idea, an ambitious and highly-advanced single-engine design that seated two in tandem. The aircraft would feature a sophisticated fire-control system and performance promises surpassing anything in the world by helicopter terms. The Lockheed design also featured a "rigid rotor system", which in itself was quite a different approach to the more flexible systems of conventional and previous helicopter designs. The rigid rotor system promised unparallel handling and performance more akin to that of a fighter than a helicopter. Previous attempts as a rigid rotor met in failure or produced such complexities beyond the realm of full-scale production within a budget. Lockheed felt it had found an answer to these issues and then some.
Lockheed produced, at first, a small radio-controlled model to test out their rigid rotor system concept, ultimately proving the idea sound. This was followed by Model CL-475, a full-scale, multi-seat helicopter with an initial two-bladed main rotor. This graduated to become a three-bladed main rotor made of aluminum and further live tests followed. The XH-51 was a further light helicopter design that proved successful in testing but - much to Lockheed's misfortune - was never produced. The CL-475 and the XH-51 both survived their development histories to become museum showpieces. The final competition now fell between Lockheed and Sikorsky to which Lockheed was officially announced the winner. The US Army contract ($12,750,000) was signed on March 23rd, 1966 and called for ten aircraft to be produced under the AH-56 designation.
Secretary of Defense Robert McNamara put forth a new initiative to help ease along the development and procurement of future defense systems. This essentially involved contractors and defense branches committing to a product regardless of it living up to expectations. Essentially, this new procurement policy covered a weapon system from design and development to testing and purchase. Contractors hated the idea as they would have to commit to a fixed price assessment of the product while it was still in development, a period when costs almost certainly tend to rise especially when dealing with new-fangled technologies. The defensive branches were equally negative on the idea for it forced them to commit to an unproven product before the system was properly tested and cleared for operational duty. In a number of ways, McNamara's initiative would only add to the demise of the Cheyenne's potential and promising legacy yet to be written.
The first prototype AH-56 was presented to the US Army on May 3rd, 1967. First flight of the AH-56 was completed on September 22nd, 1967 using the second Cheyenne prototype with test pilot Don Segner at the controls. The flight lasted 26 minutes and was successful on the whole, proving the design sound, responsive and reliable. The first public flight of the Cheyenne occurred on December 12th of that year, again with Segner at the controls. By this time, the AH-56 was already clocked just under 200 miles per hour while other abilities were clearly distinguishing her from anything that had flown before. She showcased the uncanny ability to hover forward and in reverse without so much as tilting her fuselage - a feat made wholly possible by her pusher propeller system.
Production was penciled to begin on September 20th, 1968 with deliveries beginning a year later. It was to take place at Lockheed assembly plants in Van Nuys, Burbank then finally completed systems would be handled at Palmdale, California. Due to budgetary constraints, an initial US Army order for 600 Cheyennes was curtailed to 375. The contract was given to Lockheed in January of 1968 though by the middle of 1969, the whole production contract was cancelled after delays and an in-air accident killed a test pilot.
Just 11 total Cheyennes were ultimately produced (including the static test airframe) before the projects final cancellation. Each AH-56 model was intended to handle a different part of the rigorous development schedule. The first AH-56 (no serial number) was the aforementioned static test airframe and never became airborne. The second Cheyenne (first prototype and assigned serial number 66-8826) was another flightless derivative, this time charged as a ground test airframe for proving the rotors and engine. The third AH-56 (second prototype s/n 66-8827) became a flight test vehicle sans its weapons components. This was the first AH-56 to achieve flight.
The fourth AH-56 (s/n 66-8828) was another similar Cheyenne used for in-flight testing. This aircraft was involved in a fatal crash, killing test pilot Dave Beil, on March 12th, 1969. Number four's loss was attributed to an uncontrollable oscillation of the main rotor that had dropped down into Biel's cockpit as well as the tail rotor, dooming the aircraft. AH-56 number five (s/n 66-8829) was used as a weapons test vehicle and was ultimately scrapped. Number six (s/n 66-8830) was an avionics development vehicle and survived. Number seven (s/n 66-8831) was an armaments test platform and survived as a museum piece. It was noted historically for its emergency landing at Yuma on April 22, 1970. Cheyenne number eight (prototype seven with serial number 66-8832) was used to test out various missile and night vision systems. Number nine (s/n 66-8833) was used as a flightless avionics test bed. Cheyenne ten (s/n 66-8834) replaced Cheyenne number four and was ultimately scrapped herself. Number eleven (s/n 66-8835) was the real deal with the avionics systems installed. This final Cheyenne form was ultimately lost to an accident while undergoing wind tunnel testing at the Ames Wind Tunnel on September 17th, 1969.
Many factors played a role in the demise of the Cheyenne. Monetarily, funding for such an advanced project proved a huge undertaking and worsened by the fact that technologically advanced systems of today were yesterday's relics tomorrow. Originally, it was estimated that each individual Cheyenne would cost tax payers just $500,000 USD. This later ballooned to a projected $5,000,000 USD per unit by project's end. An advanced system like this was also open to many-a-project delay but in many ways this was an accepted part of the program considering its reach - though under McNamara's initiative, there was little room for delay. The US Army used its worry about the main rotor oscillation deficiency to begin distancing itself from the project. They also noted issues with the Cheyenne's performance as a due to rising weights. The US Air Force also tried have the AH-56 cancelled outright when fulfilling the requirements to its A-X Close-Support Program (this eventually producing the fantastic Fairchild A-10 Thunderbolt II). Quite possible throughout the entire project, the US Army was essentially way in over its head in uncharted territory, not knowing how to deal with the political angle of procurement with the Pentagon. For Lockheed's part, their early promises for the AH-56 to the US Army did them no favors in curtailing the level of expectancy for the AH-56 program.
The program in whole was cancelled on August 9th, 1972. Despite this, the US Army continued evaluating the seventh Cheyenne up until March of 1973. Number seven was unceremoniously shipped back to Lockheed on the top of a flatbed semi truck. Only seven of the 11 Cheyennes survived the programs development.
Externally, the AH-56 held a distinct and unique appearance to anything that had flown before it. The two crewmen were seated in a tandem cockpit arrangement with the pilot in the rear placement and the gunner in the forward placement. Visibility out of the canopy was excellent and supplied plenty of headroom, with views obstructed by only some thin framing on the canopy glass. The fuselage itself was slender in shape and highly contoured to bring out the most aerodynamic qualities of the design - this would, after all, be a fighter lampooning as a helicopter. Side fuselage sponsons contained the main landing gears, allowing for a semi-retraction of each system. To each side sponsons the swept-back wings sporting some dihefral were added. The engine was fitted behind the cockpit and fed by small intakes to either side of the main rotor mast and the single exhaust system facing aft. An additional set of intakes were also set flush along each side of the fuselage. The pilot had the option of which set of intakes to use based on operating conditions. Cable cutters consisted of one dorsal (behind the pilot's cockpit) and one ventral assembly. The Cheyenne was one of the first aircraft to be fitted with an integrated avionics system consisting of a communications, navigation and weapons suite.
The four-bladed main rotor sat low on the design and provided the primary lift source of the aircraft as well as its cyclic control while the flight control system maintained the rotor's pitch. The main rotor was powered by a Kelsey-Hayes transmission system and rotated via the main rotor mast in a counter-clockwise fashion.
The empennage added to the unique appearance of the AH-56, this made up of a straight fuselage extension component containing the drive shaft for the two tail rotors. The anti-torque four-bladed rotor sat on the extreme edge of the horizontal stabilizer (jutting out to the portside) and rotated clockwise with straight blades. The Hamilton-Standard three-bladed "pusher" rotor faced aft and it was this "pusher" propeller system that afforded the Cheyenne its top-flight performance capabilities - no other helicopter system of the time would have matched it. The pusher rotor received power from the main transmission system and was fed via the running shaft in the empennage to a gearbox located in the tail. This rotor system rotated counter-clockwise. Both the anti-torque and the pusher system were driven by the same drive train and gearbox. The pitch of the pusher system was controlled by either crewmember (pilot controls were redundant in both cockpits) through a twist grip located on the collective lever. The Cheyenne held three internal self-sealing fuel tanks of 300-, 78- and 60-gallons.
Cheyenne sported a downward vertical tail fin to which a single-wheeled semi-retractable tail landing gear was affixed. The undercarriage - including tail wheel - were all retractable to an extent with the main landing gears semi-recessed backwards under each side sponson and the tail wheel disappearing into the vertical tail fin. It is interesting to note that the undercarriage was implemented in such a way that, when fully extended with the aircraft at rest, the Cheyenne's posture was essentially level. In contrast, the AH-65 Apache sits with its forward fuselage angled upwards.
The Cheyenne was powered by a single powerplant, this being from a General Electric family of turboshaft engines. One of the earlier engines was a T64-GE-16 originally rated at 3,425 shaft horsepower. This was later increased to 3,925 shaft horsepower with improvements to the gearbox and rotor components allowing for more power and better efficiency. By the time of the ninth prototype Cheyenne, the T64-GE-716 was in use delivering an impressive 4,275 shaft horsepower.
The gunner was seated in the forward position of the tandem-seat arrangement. His position was dominated by the large pedestal holding the weapons sight and controls. Along with the periscope sight, the pedestal was also home to a right-sided pistol grip. His instrument panel consisted of traditional and conventional dials, tape-style gauges and large map display plotter. To the gunners left was the collective while the cyclic was in a stowed position to his right - this redundancy allowed the gunner to take over piloting duties as necessary. The gunner's seat was integrated into the fire control system - a system that turned his seat horizontally in unison with the direction of the turret. It is interesting to note that early forms of the Cheyenne left this forward cockpit area incomplete as the weapon system had yet to be added. Access to this cockpit was standardized to the starboard side, this via a hinged entry door.
The pilot was afforded a higher position overlooking the gunner's cockpit and the view beyond. In some ways this position was a more "simplified" arrangement in terms of not having the gunner's pedestal system. The a main instrument panel was dotted by various gauges, dials and system readouts. Between the pilots knees were the cyclic control column as well as the map display plotter. Above the map display were the weapon controls. The collective stick was to his left while to his right along the forward panel displayed the Cheyenne's caution light grid. Access to this cockpit was standardized to the starboard side in late Cheyennes, this also via a hinged entry door and in place of the sliding canopy available in early models. In all, the Cheyenne's pilot and gunner were treated to good vision and clean lines from within the cockpit.
The Weapons Suite
As an attack helicopter, the AH-56 shined in terms of her munitions capabilities. The Cheyenne showcased six total hardpoints - two under each wing and an additional two at under-fuselage positions, just inboard of the sponsons. Each wing held an outboard and inboard pylon position to which mission parameters could allow for the mixing and matching of variable weapons loads. The outboard pylons could be fitted with a 450-gallon drop tank or a 2.75-inch FFAR rocket pod (1 x 7-shot or 1 x 19-shot pod) each. The inboard pylons could also make use of a 450-gallon drop tank, a 2.75-inch FFAR rocket pod ( 1 x 19-shot pod) or 3 x TOW anti-tank missiles (for a total of 6 x TOW launchers). The portside under-fuselage hardpoint could carry an additional 300-gallon drop tank but the starboard side could not. The official US Army flight manual also showed that each hardpoint position could singularly carry up to 2,000 pounds in stores. Outboard wing pylons could also make use of a triple adapter rack for carrying up to 3 x 2.75-inch FFAR 19-shot rocket pods per pylon, giving the Cheyenne a more formidable appearance than she already exhibited.
While external munitions were optional and could be mixed and matched as needed, the Cheyenne maintained standard fixed armament as well. The nose could serve as a platform for mounting the XM-129 40mm air-cooled automatic grenade launcher or the XM-196 7.62mm minigun. For the grenade launcher installation, the Cheyenne could carry up to 780 x 40mm anti-personnel grenades and fire them off at a rate of 350 projectiles per minute. If using the minigun armament, the count topped off at 11,750 rounds of 7.62mm ammunition with a maximum rate-of-fire of 6,000 rounds per minute (though this was adjustable by the gunner in 750, 1,500 and 3,000 intervals as well.
Design of the Cheyenne made interesting use of a powered belly-mounted turret system to compliment the nose armament. The weapon fitted to this system was the XM-140 30mm cannon with 2,010 rounds of ammunition and a rate-of-fire up to 450 rounds-per-minute. This powered turret was fitted under the fuselage. As the Cheyenne featured a retractable undercarriage, it made sense to supply the platform with an under-fuselage turret system like this to take full advantage of the available fire arc against ground-based targets. This turret had access to a 200-degree sideways and +26/-60 degrees up/down fire arc meaning that no potential ground target would have been safe from the AH-56.
Despite the loss of the Cheyenne as a viable US Army weapon, the results garnered from the development and testing of its various systems played a major role in the success of the follow-up Hughes AH-64 Apache tank-killing system. In addition, it was reported that many of the Cheyenne's existing issues were solved - or on the verge of being solved - by the time the axe fell on her. Despite her image of a grand Cold War folly, we can still call upon our imaginations as to what a system like the AH-56 could have done on the battlefields with all of the benefits of a helicopter with the performance an airplane. Even today the Cheyenne would have bested its closest rotary-wing rivals on performance alone. One can only imagine adding the AH-64's tank-killing prowess to the AH-56 design.
As American involvement in the Vietnam War dwindled down and many-a-lesson now learned by the US Army, a new competition emerged under the Advanced Attack Helicopter (AAH) name on August 17th, 1972. This gave birth to the YAH-64 by Hughes, eventually to become the AH-64 Apache. Though not a direct descendant of the Cheyenne (nor a replacement for that matter), she no doubt took into account many of the qualities that made the Cheyenne so breath taking a concept -except her top-flight speed that is. The Apache did, however, essentially replace the Bell AH-1 Cobra proving just how cyclical history can be. And the Apache, unlike the Cheyenne, was a helicopter through and through.