Hybrid Controller for Gust Load Alleviation and Ride Comfort Improvement Using Direct Lift Control Flaps

In this paper two robust H∞ feedback control laws are designed, one for active wing bending damping, and one for active damping of the wing and hull bending modes. For the latter, not only symmetrically commanded ailerons are used, but also the elevator and direct lift control (DLC) flaps. The control objective of these feedback laws is the reduction of fatigue of the wing roots, as well as the improvement of ride comfort. Two different H∞ control design methods, DK iteration and HIFOO, are applied and compared. For the additional compensation of turbulence excited peak loads, the active wing bending damper is augmented by an adaptive feed-forward controller which uses the modified output of an alpha probe mounted at the front fuselage as reference signal. Numeric simulations with a state-space model of the symmetric dynamics of a large airliner are performed for validation of the controllers’ performances.