By Nathan Pfau, Army Flier Staff WriterMay 31, 2018
FORT RUCKER, Ala. -- The RAH-66 Comanche that currently sits in the U.S. Army Aviation Museum is an eye-catching aircraft that many considered ahead of its time, but there was another that came before it that shared the same rigid-rotor design concept, as well as the fate of simply being born too soon.
The AH-56 Cheyenne was the culmination of Lockheed's foray into helicopter development that utilized the rigid rotor system seen on the aircraft's predecessors, the CL-475 and the XH-51, said Bob Mitchell, U.S. Army Aviation Museum curator.
In 1966, Lockheed was awarded a contract by the U.S. Army for 10 prototypes using this revolutionary design, and because of it the Cheyenne was capable of speeds still considered impressive by today's standards, he added.
"It's an enormous aircraft and it was capable of great speeds -- that was one of the main reasons (the Army) wanted the program," said Mitchell. "(The Cheyenne) had a set of aerodynamic wings on it, so the faster the aircraft went, the more the rotor loads were reduced."
At a length of more than 54 feet, the aircraft was very sizeable for its time, and with a cruising speed of 195 knots and a maximum speed of 212 knots, the aircraft blew past the competition. Comparatively, today's AH-64 Apache helicopters have a cruising speed of 158 knots and a top speed of 197 knots.
"It was a spectacular concept, and it's an aircraft that still to this day is way ahead of its time," said the museum curator.
The aircraft also featured a pusher propeller in addition to the tail rotor that was able to be manipulated by the pilot, which gave the operator more control in high-risk situations, such as diving fire, said Mitchell.
"One of the key factors in gunship operations -- certainly when conducting diving fire -- is that your speed builds exponentially, so you only have a couple of seconds to acquire, engage then start your recovery," he said. "On the Cheyenne, the pilot could enter his dive, then reverse thrust on the pusher to slow the aircraft down considerably, allowing him to fixate on the target, fire and then start his recovery. For that reason alone it was a beautiful gunship."
The aircraft was ahead of its time not only in design, but in its fire controls systems, as well, said the museum curator.
The Cheyenne program wasn't without its faults, though, and early on in the program there were issues with the rotor system that resulted in a few accidents, including one fatal accident where the rotor system made contact with the fuselage.
There are three different types of rotor systems that were tested on the Cheyenne, and the museum currently houses two of the versions in its collection.
Despite early setbacks, Lockheed continued with the program to provide the Army with a gunship that could also serve as close air support, something that typically fell under the Air Force's purview, said Mitchell. Although the Cheyenne was shaping up to be a very capable aircraft, not unlike many programs before it, cost led to the ultimate demise of the program.
"This was the late 1960s and the cost per aircraft (was in the millions), so when (Bell) came out with the Cobra, which was a fraction of the cost, they couldn't justify it," said the curator. "The Army also looked at the commonality because they already had the Huey, and the Cobra was essentially a repackaged Huey, so the parts were interchangeable. That was probably the biggest factor that killed the program."
Although the Cheyenne program never found its place in Army Aviation, that doesn't mean that the program was a failure, said Mitchell.
"Those technologies that were tested back in the 60s and sat on a shelf are now being taken off the shelf, dusted off and being applied to new designs," he said. "With every bold idea --whether it survives or fails -- comes bold technologies that are applied on other airframes. For that reason, it was a good program."
Additionally, it's because of the Cheyenne program that the A-10 Thunderbolt was developed, said Mitchell.
"I like to refer to the Cheyenne as the father of the A-10 program, because after that, the next aircraft the Air Force would design would be the A-10 Thunderbolt for close air support," he said. "Now, because of the Cheyenne, we finally got a dedicated aircraft for close air support."