Gust loads alleviation using special control surfaces

Control laws are designed for the alleviation of dynamic gust loads on a wind-tunnel model of a transport aircraft using wing-mounted control surfaces. Three different control surfaces are used: the symmetrically actuated main ailerons, special underwing forward-positioned control surfaces at about 0.8 of the wingspan, and special wing-tip forward-positioned control surfaces. The 5.3-m-span cable-mounted wind-tunnel model was constructed at the TsAGI laboratories and is being tested as there part of the 3AS 5th Framework European Commission research project. The length of a one-minus-cosine vertical gust velocity profile is tuned to yield maximal wing-root bending moment. All the control laws are based on simple low-pass filters for easy and robust application in the wind tunnel. Each is based on single input of a wing-tip accelerometer, which is shown to react sufficiently before the peak of the wing-root bending moment. All the three control means are shown to alleviate the extreme wing-root moments at intermediate design flight velocities by 9-16% and the wing-tip accelerations by 26-33%. The wing-tip control surface is found to be most effective, whereas the existing aileron least effective at these speeds. The existing ailerons become even less effective at higher speeds due to reduction in their aeroelastic effectiveness. They are also shown to be most problematic in creating aeroservoelastic instability when the gust-alleviation loop is closed. The effects of the designed control laws on the statistical response of the wing loads to continuous gusts are shown to be similar to their effects on discrete gusts.