Roll Ratchet describes an abrupt roll response that causes a high frequency PIO.[1] This is common when the primary roll control is a pedestal-mounted sidearm controller.[2] The roll ratchet is observed as damped oscillations at the initiation and recovery of large roll maneuvers.[2] Large roll rate commands require high gradient gains to initiate and recover from the rolls.[2] Roll ratchet predominates during the recovery of a large amplitude roll maneuver.[2] This effect is similar to a bobweight that produces oscillations between 2 and 3 Hz.[2] The magnitude and damping of the roll ratchet are determined by the weight of the arm, the weight of the controller, the wrist interface, and the command roll gradient gain.[2] Roll ratcheting increases as the ungmented roll damping is increased.[2] The closed-loop feedthrough “bobweight” effect reduces the gain margin.[2]
[[FBW Jaguar]] – minor roll ratchet was corrected with viscous damper and lateral bobweight
C-17 PIO – structural coupling with pilot input caused roll-ratcheting effects
[[YF-23 Mass-Induced Oscillation]]
[[F-16XL Roll Ratcheting]]
Sources
- [1] R. Bailey, B. Powers, and M. Shafer, “Interaction of feel system and flight control system dynamics on lateral flying qualities,” in 15th Atmospheric Flight Mechanics Conference, Minneapolis,MN,U.S.A.: American Institute of Aeronautics and Astronautics, Aug. 1988. doi: 10.2514/6.1988-4327.
- [2] W. Smith, “Induced and Controller Coupled Oscillations Experienced on the F-16XL Aircraft During Rolling Maneuvers”.
Backlinks
[[Bobweight]]
[[Gain Margin]]
[[Gain Scheduling]]
[[LATHOS]]
Pilot-Induced Oscillations
Sidestick Controller