Lidar-based Gust Load Alleviation - Results Obtained on a Generic Long Range Aircraft Configuration

In this paper a lidar-based preview gust load alleviation controller is synthesised via modern robust control methods in discrete time and optimised for an industrial long-range aircraft configuration. The synthesis and load analysis is performed using a set of 54 linear-time-invariant state-space models corresponding to a wide range of mass distributions and flight conditions. The controller performance is tested in a realistic hybrid and multi-rate simulation environment in which, in addition to the aeroelastic aircraft model (continuous time) and the various control functions in discrete time, the lidar measurement chain (sensor, wind estimation) as well as speed and position-limited actuators are simulated. The load alleviation performance is evaluated for a wide range of mass distributions, altitudes, airspeeds and gust lengths, leading to results based on over 4000 analysed gust load cases. The paper concludes with a discussion of the impact of the GLA control function on the structural loads, the load hierarchy and the general aircraft behaviour. The gust load alleviation controller achieves a reduction in peak bending moment between 17 % and 18 % at the important wing root, about 20 % in the middle of the wing and still over 10 % near the wing tip. It barely reaches the rate and position limits even on the extreme gusts defined in the certification specifications for large aeroplanes and only moderate increases of peak gust loads are observed on other load types or stations. Directly outside of the engine position a few percent increase in torsional moment is found. The controller yields an increase of about 50 % of the HTP gust loads, which is not critical as the HTP is usually, by far, not sized by gust loads but rather by manoeuvre loads. If needed, this figure could drastically be reduced by reducing the aggressiveness of the pitching behaviour and tolerating slight higher loads on the wing