Multibody Simulation of Integrated Tiltrotor Flight Mechanics, Aeroelasticity and Control

This work describes the application of an adaptive control algorithm based on the generalized predictive control paradigm to a detailed nonlinear aeroelastic model of a tiltrotor aircraft that includes rigid-body degrees of freedom, restricted to the plane of symmetry. The analysis is based on an original multibody dynamics formulation. The model is augmented by an autopilot and a stability augmentation system; in relevant cases, a model of the passive biomechanics of the pilot is considered as well. The interaction of rigid-body and deformable degrees of freedom alters the aeroelastic behavior of the system compared with that of the clamped wing rotor, discussed in a previous work. The flutter mechanism, originally consisting in whirl flutter, changes after considering rigid-body degrees of freedom; the short-period flight mechanics mode now dominates high-speed stability. This issue is mainly addressed by the stability augmentation system, whereas the generalized predictive control is mainly used to reduce gustinduced wing loads, although its intervention for whirl-flutter suppression is still needed to extend the flight envelope at very high speed. The capability of the adaptive regulator to reduce wing loads is assessed in hover and in highspeed forward flight. In the latter condition, the capability to suppress whirl flutter is assessed as well.