Advanced gust load alleviation system for large flexible aircraft

Abstract

The effects of gusts and turbulence do not only affect adversely the passenger comfort but also create significant aircraft loads. That´s why gust load alleviation plays an important role for the development of load control strategies. DLR has a comprehensive know-how in the field of control systems design for aerospace applications especially the design of gust load alleviation systems, their demonstration and assessment. Based on this experience a gust load alleviation system (GLAS) was designed within the frame of the European AWIATOR project based on a feed-forward disturbance compensation. To follow this concept the determination of the disturbances respective the gusts/turbulence is essential. Assuming to have direct lift control surfaces available the reduction of vertical accelerations and alleviation of loads can be envisaged. Thus, it is not necessary to determine the complete three dimensional air mass motion but to compute precisely its vertical fluctuation. This can be done by usingsimplified flight mechanics relations. The computed vertical gust component is used to trigger the GLAS. The principle design of the GLAS is focused on reduction of vertical accelerations (nz) caused by turbulence. This design in mainly related to the improvement of passenger comfort. Simulation results have shown that this design yields an overcompensation of structural loads caused by turbulance. To avoid this overcompensation, we performed an optimization based tuning of the GLAS. The simulation results for this advanced GLAS show very good performance for load alleviation and also improvement of passenger comfort. However, depending on the flight case it may be interesting to choose between parameterizations of the GLAS, e.g. focus on passenger comfort improvement in cruise condition and focus on load alleviation on points of the flight envelope where already high loads arise (sizing cases). In addition, Pareto-bounds were calculated to allow a choise between compromise solutions for wing load and HTP load reduction. The advanced GLAS also contains dynamics filters to consider the structural modes and to avoid the unintentional excitations of the aircraft structure stimulated by the gust and turbulance or by GLAS itself.