Multi-Body Analysis of an Active Control for a Tiltrotor

The design of advanced rotorcrafts requires the ability to analyse sophisticated, interdisciplinar systems to a degree of re nement that only recently has become achievable at a low price, thanks to the improvements in computer power. Multi-body analysis allows the detailed modeling of the kinematics as well as of the structural properties of rather sophisticated mechanical systems, such as helicopter rotors. When integrated with aeroservoelastic analysis, it represents a powerful tool for both the analysis and the design of aircrafts, with particular regard to rotorcrafts. An original multi-body formulation is presented, based on the direct writing of a system of di erential-algebraic equations (DAE) that describe the equilibrium and the kinematic constraints of a structural system. The nite rotations, during the time-step integration of the initial value problem, are handled in an efcient manner by means of a technique called \Updated-Updated Rotations", an Updated Lagrangian approach that uses as reference the predicted con guration of the system. This allows to neglect the rotation perturbations in the computation of the Jacobian matrix, with considerable computational savings, while preserving the accuracy by consistently computing the residual. Control equations and the related unknowns are added, to model the control system to the desired level of re nement, from idealised control input/output signals, to each servosystem component. The numerical analysis of a tiltrotor con guration is proposed, based on an analytical model of the WRATS wind tunnel model. This is a 1/5 scale model of the V{22 tiltrotor aircraft, currently tested in the Transonic Dynamic Tunnel (TDT) at NASA Langley. The control strategy is based on the Generalized Predictive Control (GPC) technique, with a Recursive Least Mean Squares (RLMS) on-line identication of an equivalent discrete linear system, that is used to design the adaptive controller. The rotor pitch controls are used as actuators. Di erent combinations of strain gages and accelerometers are used as sensor devices.