Aeroelastic Modeling and Control of an Experimental Flexible Wing

Abstract

Structural weight reduction and high aspect ratio wings play a key role in improving the performance of modern transport aircraft. This leads to a highly flexible aircraft structure which is sensitive to external disturbances like gusts. To counteract this undesired effect, active control is a promising technology. In this paper, a gust load alleviation controller is designed for a wind tunnel model of a flexible wing with various trailing edge flaps and acceleration sensors. For a sophisticated model-based controller design, a detailed aeroelastic model is derived describing the coupling of structural dynamics and aerodynamics. Additionally, actuator dynamics and structural modes are identified and used to improve model accuracy. Subsequently, the weakly damped first wing bending mode, which causes high structural loads, is isolated via H 2-optimal blending of control inputs and measurement outputs. In this way, a gain-scheduled single-input single-output controller can be designed to control the desired aeroelastic mode. Eventually, the great potential of the proposed control approach is verified by a wind tunnel test including different gust excitations and varying airspeeds.

$\mathcal{H}_{2}$ -Optimal Blending of Inputs and Outputs for Modal Control

“…Thereby, the numerical values of the model as well as the resulting controller can be provided herein. For realistic physical applications, the reader is referred to [19], [20] and [21], where the proposed blending approach is successfully applied to different aeroelastic systems.…”

Design and Optimization of an Aeroservoelastic Wind Tunnel Model

“…Accordingly, to design the gust load alleviation controllers, state space models of the different flexible wings are derived for a true airspeed of 40 m/s following the aeroelastic modeling procedure described in [41]. To that end, the eleven structural modes of lowest frequency were coupled with an unsteady aerodynamics model generated using the doublet lattice method [42] in combination with a rational function approximation according to Roger [43].…”

“…For more details on gust load alleviation controller design and tuning the reader is referred to [41]. Here, the control inputs are the command signals for the servos driving the three trailing edge flaps and the measurement outputs are eight vertical accelerations measured at the outer part of the wing, as depicted in Figure 13.…”

“…For more details on gust load alleviation controller design and tuning the reader is referred to [41].…”

“…Eventually, in step three the model was closed by adhering upper and lower skin. In a dedicated test setup, several servo drives, for flap actuation, were investigated and compared with respect to their dynamic behavior, eventually resulting in the selection of the "MKS HBL990" brushless digital servo [41].…”