Mechanism for Warp-Controlled Twist of a Morphing Wing

A new concept for actively controlling wing twist is described. The concept relied on introducing warping deformation of the wing skin, which was split at the trailing edge to create an open-section airfoil. An internal screw mechanism was introduced near the trailing edge, so that the load-carrying capability of the wing was maintained while allowing the introduction of warping displacement between the lower and upper wing skins at the trailing edge. Simple structural modeling of the warping wing based on generalized thin-walled beam theory was performed. A demonstration wing was built based on a NACA 23012 airfoil section with a span of 0.68 m and a chord length of 0.235 m. A maximum peak-to-peak twist of 27 deg was demonstrated, with excellent correlation between theory and experiment. Wind-tunnel tests showed that warping could change the lift coefficient by as much as 0.7 at maximum peak-to-peak twist. Analytical and vortex-lattice models were demonstrated to give accurate predictions of the lift coefficient at smaller absolute twist angles. Furthermore, analytic modeling of the wing drag was shown to be in close correspondence with the drag measurements and showed that wing warping could be used to influence the lift induced drag. In general, it was demonstrated that at lower angles of attack, a more positive twist resulted in a higher lift-to-drag ratio. This study proved that a twist-active wing can have sufficient gain to control the rolling motion of an aircraft and to ensure that the lift-to-drag ratio is Maximized at various flight conditions.