Concurrent Optimization of a Feed-Forward Gust Loads Controller and Minimization of Wing Box Structural Mass on an Aircraft with Active Winglets

摘要

This paper discusses the multidisciplinary preliminary design optimization of an aircraft equipped with active winglets for loads alleviation. Winglets are intended to improve the aircraft's aerodynamic efficiency but at the same time they introduce significant loads to the outer wing. In general, these additional loads lead to a heavier wing structure which can jeopardize the initial benefit. Especially when it comes to retrofitting an already operational aircraft type with large winglets, the necessity to redesign the outer wing structure would be a very costly downside. Equipping such large winglets with active control surfaces for loads alleviation however can avoid the necessity of modifications on the wing structure. This paper summarizes the design optimization of a full-scale active winglet, discusses the flight system dynamics modelling of the flexible aircraft equipped with these winglets, and provides an optimization of a feed-forward gust loads alleviation controller for minimization of wing box structural mass based on beam modelling. As the inner wing is sized by manoeuvers, the minimization of structural weight of the wing box by active gust loads alleviation primarily affects the outer wing. Ultimate loads for several failure cases of the proposed feedforward gust load alleviation system are assessed in order to prove that none of the failure cases constitute a show-stopper for the application of active winglets for loads control. In order to verify the flightworthiness of the wing box seized for loads alleviation, a subsequent aero-elastic assessment is performed. For this exercise the original beam model with reduced structural weight is translated to an equivalent shell element model. The critical flutter speed after resizing is slightly reduced, but still by far sufficient for the investigated aircraft. It is concluded that the proposed active control system is an enabler to equip an aircraft with large winglets without having to strengthen the outer wing structure.