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.
1. An aircraft comprising a mainplane, said mainplane comprising wings with canted down tips; wherein an additional plane is attached to an outboard location on each of said wings, and positioned aft with respect to the wing tips.
2. An aircraft according to claim 1 wherein each said additional plane is positioned to be subject to the upwash field of the respective mainplane tip vortex, at least in the cruise condition of the aircraft.
3. An aircraft according to claim 1 wherein each said additional plane extends outboard with respect to the respective said tip.
4. An aircraft according to claim 1 wherein each said additional plane is carried on a boom extending from the mainplane in the region of the root of the respective said tip.
5. An aircraft according to claim 1 wherein the lift vector of each said additional plane is inclined forwardly in the cruise condition of the aircraft.
6. An aircraft according to claim 1 wherein the downward cant angle of each said tip increases in the outboard direction thereof.
7. An aircraft according to claim 1 wherein in planform the leading and trailing edges of each said tip are swept back in relation to the leading and trailing edges respectively of the mainplane inboard thereof.
8. An aircraft according to claim 7 wherein in planform the sweep angles of the leading and trailing edges of each said tip increase in the outboard direction thereof.
9. An aircraft according to claim 1 wherein the chord of each said tip reduces in the outboard direction thereof.
10. An aircraft according to claim 1 wherein each wing of said mainplane includes an inboard portion having a chord which reduces in the outboard direction thereof, an outboard portion of substantially constant chord, and a said tip.
11. An aircraft according to claim 1 wherein each wing of said mainplane includes an inboard portion having a chord which reduces in the outboard direction thereof, an outboard portion having a positive dihedral angle, and a said tip.
12. An aircraft according to claim 10 wherein the root portion of each wing of said mainplane is of substantially constant chord.
13. An aircraft according to claim 11 wherein the root portion of each wing of said mainplane is of substantially constant chord.
14. An aircraft according to claim 1 wherein roll control is provided by means of spoilers on said tips.
15. An aircraft according to claim 1 wherein roll control is provided by varying the lift produced by said additional planes to vary the twist of said mainplane.
16. An aircraft according to claim 1 comprising sensors for sensing gusts ahead of said mainplane in the regions of the locations from which said additional planes are carried, and a system for controlling the lift produced by said additional planes in response to said sensors to vary the twist of said mainplane such as to alleviate the effect of gusts on said mainplane.
17. An aircraft according to claim 1 being a solar powered, unmanned aerial vehicle.