HL-10 Limit Cycle Tests

The limit cycle tests were used on pitch, roll, and yaw transfer functions simplified by a gain and integrator.
$$G(s)=k\frac{1}{s}$$
The integrator added 90 deg of phase lag to simulate filters, actuators, and linkages. The maximum peak-to-peak limit cycle for safe flight was 0.5 degrees. Flight tests revealed a limit cycle caused by contaminated actuator hydraulic fluid which gave a nonlinear behavior. This caused PIO tendencies during approach and landing.

Pitch Limit Cycle

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