Aeroelastic Flight Control for Subscale UAVs

Abstract

This paper describes a new type of aeroelastic wing panel which relies on a sweeping movement of the main spar to alter its ∞exural axis and consequently change the amount of wash-out in the wing induced by the aerodynamic forces. A 1.8m (6ft) electrically powered glider was fltted with two aeroelastically active panels at either side of the wing, each spanning 450mm (17.7in.). By hinging the main spar at the root of each panel it could sweep over an angle of 14 ‐ peak-to-peak, covering 60% of the local chord at the wing tip. The wing structure was entirely composed of balsa wood members and the front and rear spars were intentionally left ∞exible to increase the dependency of the local elastic center on the main spar position. Furthermore, a composite skin was used, which provided enough torsional ∞exibility to allow for active wing twisting. The application of the modifled wing panels added 3% to both the operational empty weight and planform area, leaving the wing loading unchanged. To model the aeroelastic behavior, a flnite element model of the wing was made using MSC.PATRAN/MSC.NASTRAN and coupled to a three dimensional aeroelastic model (ZAERO). Dynamic bench tests demonstrated a change of 40% in elastic center position at the tip of the aeroelastic wing panel and showed good agreement in bending natural frequencies with the flnite element model. Furthermore, an increase of 28% in the flrst coupled natural frequency was demonstrated between the most forward and most rearward position of the main spar. Wind tunnel tests were carried out to show wing twist dependency on main spar position and angle of attack. At cruise conditions, when sweeping the main spar over its maximum range, a change in lift coe‐cient of 35% and a change in twist of 3.7 ‐ were shown. At increased angle of attack, the range of twist even increased to 9.1 ‐ peak-to-peak. Static aeroelastic modeling showed to be accurate in predicting the twist at spar sweep angles ranging from -4.5 to +2.5 degrees. Flight test proved the efiectiveness of aeroelastic roll control without any weight penalties.