Advanced Modeling and Active Control Techniques for Aircraft Load Alleviation

Abstract

In order to allow for a more economic and environmentally friendly aircraft operation and to fulfill the greener imperative demanded by today's society, fuel savings and cost reduction play a key role in the development of modern aircraft. Besides the efficiency of engines and aerodynamics, the aircraft weight has a major impact on fuel consumption. Reducing structural wing loads caused by atmospheric disturbances (such as gusts, turbulence and wake vortices) thereby became a main research interest of today's aircraft industry. Reducing such loads will allow the aircraft manufacturer building and certifying aircraft to smaller load envelopes, inherently reducing the airframe structural weight and thus reduce fuel, emissions and cost. In this contribution we discuss latest research and development trends in the field of modelling and control for load alleviation on modern, fly-by-wire aircraft. Covering a broad range of relevant topics, the paper is divided into four main subtopics as follows: (i) For analyzing loads on the aircraft in an early design stage with high fidelity simulation techniques, detailed models of the structure and the aerodynamics are generated. Here, we discuss the latest developments on how these complex aeroelastic models (generated by CFD methods, e.g.) are derived and can be approximated by lower order models for facilitating the subsequent controller design. (ii) Directly linked to the modelling in (i) is the feedback control design task. The use of available local measurements as well as virtual sensors for incoming gusts provides a profound basis for alleviating the associated structural loads. This subsection discusses the current trends in control development such as estimator design and robust control techniques to feed back the gust estimates. (iii) Also, in direct link to the modelling (i) but also to the lidar sensors (iv) feedforward control allows for an enhanced load alleviation performance than a pure feedback due to its anticipative behavior (control actions can be taken earlier). In contrast to the feedback approaches (ii), it requires additional forward sensing capabilities, such as lidar for the gust anticipation. Detailed models of these sensors are needed to allow for a dedicated feedforward control design: these lidar sensor models are investigated in great depth within a dedicated activity (iv) and in surrogate models – derived from them – are considered in the feedforward design tool. In this subtopic the surrogate models of the lidar sensors, the wind reconstruction algorithms as well as the feedforward load alleviation design workflow are presented. (iv) The feedforward control approaches in (iii) require measurements of the incoming gust, which shall be provided by advanced lidar measurement systems. The latest development directions for adapting the lidar technology to fulfil the needs of feedforward gust load alleviation applications are discussed in this subtopic. These progresses represent a key enabling technology for viable anticipation of incoming gusts and winds, paving the way for improving the gust load alleviation capabilities for future aircraft generations.