To: tacks
The whole thing really didn't really work out nicely, the helicopter had rotor instabilities at high speed that caused at least one crew to be lost during development. It was scrapped because these problems were never really solved.
What Nick stated is true and mirrors what I had stated previously however the problems with the rotor instability were solved and according to test pilot reports the Cheyenne was the smoothest helicopter they had ever flown. It was that the solution to the problem was extremely complex and prone to catastrophic failure. The Army had made up their mind that they had already expended too much money for so little return. Also they had shifted their thinking relative to where the AAH would be deployed and also its’ mission. This evolved into the Apache.
The Lynx had a similar problem and the problem with correcting the phase shift was purely electronic where the system employed on the Cheyenne was mainly mechanical driving electrical sensors. The way it worked was when the pilot made a cyclic input the system would monitor which way the disc was moving relative to cyclic input and sent corrective signals to the primary servo which corrected the direction of flap.
The rotor used a unique control system that worked with a stabilizer bar type system, where picth changes were fed thru the gyro bar and then to the blade
This explanation is a bit simplistic. It is true that the system was unique and it was completely different from any other helicopter flight control system. Mounted on top of the main rotor was a gyroscope that was driven by a constant velocity joint attached to both the rotorhead and the gyroscope. The gyroscope was made of four tubes in a cruciform shape. Attached to the end of each tube was a heavy weight that looked like a large tin can. A stout cable connected the four arms and kept them rigid and restricted any in plane movement. The gyroscope was installed so that each arm extended between the blades so that they were 45-degrees from the two blades. The gyroscope arms also had a pitch horn the led the control arm by 45-degrees and attached to the blade
The gyroscope under rotation had the capability to exert a very high degree of force if it were nutated by control input. Being a gyroscope it would respond 90-degrees in the direction of rotation when a force had been applied to it. The control inputs to the gyro were pitch rods that ran through the main rotor mast. These rods were in turn attached to the swash plate which was mounted to the underside of the transmission. Pitch links ran from the stationary part of the swashplate to a servomechanism. The collective stick and cyclic stick drove the servomechanism via a mixing unit. The output of each servomechanism was connected to a horseshoe shaped spring, which was connected to the swashplate by the previously mentioned pitch link. The gyroscope had rigidity in space so when the pilot displaced the servomechanism it compressed the spring, which was resisted by the rigid gyro. This applied force causes the gyro to precess inputting a control force on the blades changing their pitch. With rigidity in space the gyro would hold the position causing the rotor system to align itself with the plane of rotation of the gyro. This allowed the Cheyenne to fly like a fixed wing aircraft and not like a helicopter.
Even though the gyro had a 90-degree phase angle the blades did not. Therein lay the problem.
