Modeling the Effects of Underwing Missile Canards on F-16 Limit Cycle Oscillations

Abstract

This research evaluated various methods using ZONA’s Euler Unsteady Aerodynamic Solver against flight tests previously flown at USAF Test Pilot School, using underwing air-to-air missiles with removable canards, which allows the aerodynamics of the store configuration to be changed while maintaining identical mass properties. ZONA’s Euler Unsteady Aerodynamic Solver was employed with various linear flutter and nonlinear time-domain analyses. ZONA’s Euler Unsteady Aerodynamic Solver correctly predicted that removing the canards would delay limit cycle oscillation onset. However, all of the methods generally predicted onset earlier than flight test. Consistent with the results found by previous researchers, the nonlinear simulation still predicted divergent classical flutter rather than limit cycle oscillation until nonlinear structural damping was added and tuned to produce limit cycle oscillation. Without known structural damping characteristics, the nonlinear structural damping model needed to be arbitrarily tuned to match flight-test data. This research demonstrated a different tuning method from that had been used by previous researchers. Nonlinear structural damping plays an important role in limit cycle oscillation, but a better understanding of the actual nonlinear aerodynamic and structural effects is needed before reliable limit cycle oscillation predictions can be made for all configurations and throughout the flight envelope.