A Technique for Performing Closed Loop Flutter Evaluation on a Joined Wing UAV 2013-01-2197
The present paper is focused on techniques aimed at including control law dynamics into linear flutter equations.
An UAV in an unconventional joined wing configuration has been taken as test case for setting up the methodology. For this test case the pitch control law is included in the flutter equations, obtaining a model to perform closed loop flutter calculations.
The extra degrees of freedom of control surfaces and additional terms due to the control law have been modeled by means of dynamic sub-structuring approach. The equations governing the dynamics of the control law are added to the aeroelastic stability equations after a suitable manipulation based on a derivative approach.
The interesting aspect of the work is that the control law can be modeled as six external matrices to be properly assembled into the aeroelastic system. This is advantageous when already written codes for flutter evaluation are available since the requested modifications are minimal.
For the test case two models of the control law have been prepared: a detailed representation and a “reduced” representation, with less degrees of freedom for the control law. To verify consistency of the approach the impulsive response of the closed-loop system with both the control law formulations has been performed. The displacements on the wing, the fuselage and the elevator balancing mass have been picked before and after flutter occurrence. The results obtained show consistency in terms of aeroelastic behavior and flutter speed.