Abstract: An aircraft, particularly a solar powered, high altitude, long endurance, unmanned aerial vehicle, is equipped with a combination of canted down, raked back wing tips and trailing “tip tails” carried on booms from the tip regions of the mainplane. Each tip tail is positioned to be subject to the upwash field of the respective wing tip vortex, at least in the cruise condition of the aircraft. The wing tip form can achieve a reduction in induced drag and help to relieve wing root bending moment while the tip tails can act through their connections to the mainplane to provide torsional relief to the latter, particularly under lower incidence/higher speed conditions. In the higher incidence/lower speed cruise condition, however, the presence of the tip tails in the upwash fields of the wing tip vortices means that they can generate lift with a component in the forward direction of flight and hence contribute to the thrust requirements of the aircraft.

Abstract: An aircraft, particularly a solar powered, high altitude, long endurance, unmanned aerial vehicle, is equipped with a combination of canted down, raked back wing tips and trailing “tip tails” carried on booms from the tip regions of the mainplane. Each tip tail is positioned to be subject to the upwash field of the respective wing tip vortex, at least in the cruise condition of the aircraft. The wing tip form can achieve a reduction in induced drag and help to relieve wing root bending moment while the tip tails can act through their connections to the mainplane to provide torsional relief to the latter, particularly under lower incidence/higher speed conditions. In the higher incidence/lower speed cruise condition, however, the presence of the tip tails in the upwash fields of the wing tip vortices means that they can generate lift with a component in the forward direction of flight and hence contribute to the thrust requirements of the aircraft.

Abstract: A heavier-than-air air vehicle, particularly a long endurance, solar powered, unmanned aerial vehicle (UAV) intended for “perpetual” flight within the stratosphere, is carried to its operational altitude suspended on a tether from a helium balloon. The tether is attached at or towards a tip of the UAV's wing so that it is carried in effectively a 90° banked attitude. At the desired altitude the UAV's powerplant is started and it flies on its tether in an upwardly-spiralling path relative to the balloon until a level or near level attitude is attained, when the tether is released and the UAV is permitted to assume free flight.