Load alleviation for a tilt-rotor aircraft in airplane mode

Results from research into active structural load alleviation are presented for a tilt-rotor aircraft. The work formed part of the European Commission's Fifth Framework "critical technology" Rotorcraft Handling, Interactions, and Loads Prediction project. Results are presented from an analysis of the structural loads of a tilt-rotor aircraft maneuvering in airplane mode. The potential for suppression of structural loads through active control is assessed. The study has addressed modeling aspects, particularly the nature of the buildup of dynamic loads during maneuvers. The Eurocopter EUROTILT configuration has been used as the test aircraft and a model is developed within the FLIGHTLAB simulation environment. Mathematical analysis and simulation of the rotor in-plane moments and gimbal flapping during longitudinal and lateral maneuvers are presented. The problem also addressed the torque split on the interconnect drive shaft in airplane mode for maneuvers involving large roll and yaw rates. Attempts were made to design an "ideal" controller that minimizes the gimbal flap excursions and the loads using a linear quadratic Gaussian formulation. In this preliminary conceptual study, robustness, actuator requirements, or the availability of measurements were not considered. The main objective of the controller design study was to investigate the effectiveness of cyclic controls to achieve simultaneous suppression of the loads and flapping. Evaluations performed using the controller show that use of cyclic controls is very effective in suppressing the buildup of in-plane loads, gimbal flapping, and interconnect drive shaft torque split.