Segmented-Freewing Concept for Gust Alleviation

Abstract

A promising technology for gust alleviation is the free wing. A free-wing design allows the wing to adjust itself in pitch about a spanwise axis in response to aerodynamic loads rather than being rigidly attached to the aircraft fuselage. The extension of the concept proposed here is called a segmented free wing and differs from a conventional free wing by sectioning the wing into multiple independent segments. This allows the wing to adjust to not only time-varying gust fields but also to gust fields that vary across the span. Initial wind-tunnel results showed an almost 40% reduction in rolling moment for a segmented free wing when subjected to an asymmetric velocity field, when compared with a traditional free-wing design. A 13.3-ft-span model was constructed, and experimental tests of this model showed a divergent oscillatory roll mode that appears with increasing velocity. An analytical model of the experimental test was developed that successfully predicts the instability. Comparison of the analytical model with the experimental results shows an overprediction of the stability of the system by the analytical model, and causes for the overestimation were investigated. Using the analytical model and experimental model, a successful solution to the roll instability was devised and tested.