A Nonlinear Pre-Filter to Prevent Departure and/or Pilot-Induced Oscillations (PIO) Due to Actuator Rate Limiting
AIR FORCE INST OF TECH WRIGHT-PATTERSONAFB OH SCHOOL OF ENGINEERING
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Closed loop instability caused by excess phase lag induced by actuator rate limiting has been suspected in many aircraft departures from controlled flight and pilot-induced oscillations PIO. As part of the joint Air Force Institute of Technology Test Pilot School AFITITPS program, a nonlinear rate limiter pre-filter RLPF was developed to minimize the phase lag induced by rate limiting. RLFF performance was evaluated inside the feedback path, but primary emphasis was on the pilot command path. Closed loop computer and motion-based flight simulation were conducted to prepare for the flight test. The HAVE FILTER flight test project was flown using the NF-16D Variable Stability in-flight Simulator Test Aircraft VISTA aircraft and evaluated using a software rate limit SWRL with and without an RLPF on the pilot command path. A programmable heads-up-display HUD was used to generate a fighter tracking task. Flight test results showed the SWRL was useful in preventing departure andor PIO. However, with low SWRL settings 40 degsec handling qualities deficiencies were uncovered due to sluggish initial pitch response. The RLPF plus SWRL combination resulted in more departure andor PIO protection than the SWRL alone. But with low SWRL settings 40 degsec significant handling qualities deficiencies were sometimes found.
- Flight Control and Instrumentation