|M.Sc Student||Jamchi Ziv|
|Subject||Wing Store Limit Cycle Oscillations Using Increased-|
|Department||Department of Aerospace Engineering||Supervisor||Professor Emeritus Mordechay Karpel|
|Full Thesis text|
Limit cycle oscillations (LCO) have been a persistent problem on several fighter aircraft. The F-16 and F/A-18 encounter LCO at high subsonic and transonic speeds for different store configurations with AIM-9L missiles on the wingtips and heavy stores on the outboard pylons. The LCO response is characterized mainly by anti-symmetric motion of the wing and stores and a lateral motion of the fuselage and aircrew. This limit cycle behavior occurs in both level flight and during elevated aircraft load factor maneuvers.
Increased-Order Modeling (IOM) is a practical and efficient approach to modeling dynamic systems that are mostly linear, but their behavior may be significantly affected by local nonlinearities. The approach is based on augmenting a main linear block with nonlinear feedback loops that represent the important system nonlinearities.
The goal of this research was to develop an efficient tool for predicting wing-store LCO onset velocity and vibration frequency and amplitude in fighter aircrafts at the transonic flight regime. The Increased-Order Modeling (IOM) approach is used to model the LCO simulation for a generic fighter aircraft. The model is based on a linear flutter detection core model augmented by nonlinear feedback signals that correct the unsteady aerodynamics based on static CFD results. The resulting LCO is presented and analyzed.