Computational Procedures for the Aeroelastic Simulation of Maneuvering Rotorcraft Vehicles

We propose a methodology for extending the applicability of comprehensive analysis rotorcraft codes to the maneuvering flight regime. Our approach can be interpreted as a generalization of the classical steady flight trim procedures, implemented in all rotorcraft codes, to the problem of time dependent trim in unsteady flight. Rotorcraft maneuvers are here mathematically described in a concise yet completely general form as optimal control problems, each maneuver being defined by a specific form of the cost function and by suitable constraints on the vehicle states and controls. The solution of the maneuver optimal control problem determines the flight trajectory and the control time histories that fly the vehicle model along it, while minimizing the cost and satisfying the constraints. Since optimal control problem are prohibitively expensive to solve for detailed aeroelastic models of rotorcraft with a large number of degrees of freedom, our formulation makes use of two models of the same vehicle. A coarse level flight mechanics model is used for solving the optimal control problem. The controls computed at the coarse flight mechanics level are then used for governing a fine scale aeroelastic model which is here based on finite element non-linear multibody dynamics. Parameter identification of the flight mechanics model is used in an iterative fashion for ensuring close matching of the trajectories flown by the two models. We demonstrate the proposed approach studying the take-off of a helicopter in the one-engine failure case under Category-A certification requirements.