Optimization of tiltrotor conversion manoeuvre using linear parameter-varying models

The conversion manoeuvre is that flight phase in which a tiltrotor changes from a helicopter to an airplane configuration and vice-versa. This work aims to optimize the conversion manoeuvre of a generic tiltrotor on different objectives. Considering conversion manoeuvre data from the XV-15 and from the contemporary V-22 Osprey and AW-609 tiltrotors a “typical conversion manoeuvre” is defined. This manoeuvre is then optimized trying to improve safety, reduce rotor blades flapping, pilot control effort and the conversion required time. The conversion modelling is based on a database of XV-15 Linear-Time-Invariant (LTI) models scheduled on airspeed and nacelles angle parameters. Following the Modified Optimal Control pilot Model (MOCM) guidelines a virtual pilot in the form of an LQI controller is designed for each XV-15 LTI model. To obtain pilot commands that are replicable by a real helicopter pilot the control lever displacement derivatives are considered as control inputs. This allow to restrain the speed with which pilot acts on commands by an adequate choice of LQI input weights. To verify that commands movements respect pilot limitations the command derivative histories and commands spectrum are checked after simulations. Availing of the Linear Parameter-Varying (LPV) technique the XV-15 LTI models database is linearly interpolated in the scheduling parameters and a nonlinear like model is obtained. The LQI gain matrixes are also linearly interpolated in the same scheduling parameters. Finally, the closed-loop system XV-15 LPV model - virtual pilot allows the simulation and study of the conversion manoeuvre on the whole conversion corridor domain.