ASAPP: a polymorphing wing capable of Active Span extension And Passive Pitch

This paper presents the development of a novel multi-objective polymorphing wing capable of Active Span morphing And Passive Pitching (ASAPP) for small UAVs. The wingspan can be actively extended by up to 25% to enhance aerodynamic efficiency whilst the passive pitch is utilized to alleviate gust and maneuver loads at off-design conditions and shift the lift distribution during 1-g flight. To integrate the two degrees of freedom into a single wing design, each side of the wing is split into an inboard segment and an outboard segment. The inboard segment is used for span extension whilst the outboard segment is used for passive pitch. The inboard segment consists of a main spar that can translate in the spanwise direction. Flexible skin is used to cover the inboard segment and maintain the aerodynamic shape. The skin passes the aerodynamic loads to the main spar through a number of ribs that can slide on the spar, using bearings, to maintain uniform strain in the skin. A linear actuator located along the fuselage length is used to drive the starboard and port spars. The inboard and outboard segments are connected by an overlapping spar surrounded by a torsional spring. The overlapping spar is located ahead of the aerodynamic center of the outboard segment to facilitate passive pitch. The entire outboard segment rotates around the overlapping spar where the maximum pitch angle is determined by the stiffness of the torsional spring and the magnitude of the aerodynamic loads. The aero-structural design, analysis, and sizing of the ASAPP wing are detailed here.