Lateral PIO Criteria

Due to augmentation of roll control, some low-frequency oscillations in roll could be possible. This could be mainly due to coupled roll-spiral modes and control surface rate saturation. too high or too low roll response could lead to lateral PIO tendencies.

TABLE 10.13

Pilot-Induced Oscillation Conditions for Bandwidth Criteria Condition Remarks

Theta BW >1 and phase delay <0.14 s Theta BW >1, phase delay <0.14, and pitch rate overshoot (in frequency domain) >9 dB Theta BW <1 and pitch overshoot >12 dB If phase delay >0.14

If phase delay >0.14 and flight path BW <0.55 rad/s If phase delay >0.2

10.7.2.1 Ralph-Smith

Ralph-Smith criterion can be used for prediction of roll attitude PIO [33]. If the phase of the roll angle to roll control force TF (at the crossover frequency) is less than —180°, then the aircraft is prone to roll PIO.

10.7.2.2 Phase Rate

Phase rate criterion is used as a guide in control-law design [46]. The requirement is the same as for the APhR for the longitudinal PIO.