The AMCS corrected the problem where a blade moment stall could cause the loss of an aircraft.[3] After the accident and wind-tunnel failures, the gyro behavior was better understood and upgraded.[1] It was moved below the transmission.[1] It was smaller, lighter, and turned faster.[1] The feedback path to the gyro could only sense the blade-root flapwise bending moments.[1] Irreversible servos controlled the blade cyclic.[1] It transmitted the gyroscope precession to irreversible hydraulic servos, these caused an angular displacement of the sliding lever, which then changes the pitch of the blades.[3] The servos eliminate feedback from the rotor to the gyro through the pitch change linkage.[3] A flapping feedback system is incorporated as the flapping feedback is stabilizing.[3] This system reduced the trim shifts during transition and eliminated any pilot-coupled roll oscillations.[3] The lateral-directional stability characteristics reduce the visibility conditions for low-level low-speed mission tasks when flying under 120 KCAS.[3] The pedal breakout forces were reduced by 5 lb/in.[3]
This system was tested over 20 flights for a total of 18 hours.[2] Below is a table of breakout forces and gradients in the control system.[2]
| Test | AMCS Result |
|---|---|
| Longitudinal Breakout (lb) | 0.0 aft, 1.0 forward |
| Longitudinal Gradient (lb/in) | 3.5 aft, 3.0 forward |
| Lateral Breakout (lb) | 2.0 |
| Lateral Gradient (lb/in) | 2.1 right, 2.5 left |
| Pedal Breakout (lb) | 8.0 right |
| Pedal Gradient (lb/in) | 7.0 left |
| Collective Breakout Friction Off (lb) | 8.5 |
| Collective Breakout Friction On (lb) | 27 |
There was no tendency to overcontrol in any axis.[2] The graph below shows static longitudinal stability.[2]
Sources
- [1] R. PROUTY and A. YACKLE, “The Lockheed AH-56 Cheyenne – Lessons learned,” in Guidance, Navigation and Control Conference, American Institute of Aeronautics and Astronautics. doi: 10.2514/6.1992-4278.
- [2] J. N. Johnson and G. L. Bender, “ENGINEERING EVALUATION AH-56A COMPOUND HELICOPTER 44WITH ADVANCED MECHANICAL CONTROL SYSTEM”.
Backlinks
[[AH-56 Control System]]
[[Calibrated Airspeed]]
[[CL-840 Gyro Dynamics]]
[[Flapping Hinge]]
[[Irreversible Hydraulic Servoactuator]]
Pilot-Induced Oscillations