Extended range quad tiltrotor aircraft

1. A quad tiltrotor aircraft having a vertical takeoff and landing flight mode and a forward flight mode, the aircraft comprising:

a longitudinally extending fuselage having forward and aft stations;

a forward wing extending laterally from the forward station having first and second outboard ends;

an aft wing extending laterally from the aft station having first and second outboard ends;

first and second forward rotors respectively coupled proximate the first and second outboard ends of the forward wing, the first and second forward rotors reversibly tiltable relative to the forward wing between a vertical lift orientation and a forward thrust orientation; and

first and second aft rotors respectively coupled proximate the first and second outboard ends of the aft wing, the first and second aft rotors reversibly tiltable relative to the aft wing between a vertical lift orientation and a forward thrust orientation;

wherein, the forward rotors are rigid rotors having collective pitch control;

wherein, the aft rotors are gimbaled rotors having collective pitch control and cyclic pitch control;

wherein, the forward rotors are higher disk-loading rotors than the aft rotors;

wherein, a rotor speed of the forward rotors is greater than a rotor speed of the aft rotors in the vertical takeoff and landing flight mode; and

wherein, the aft rotors are foldable in the forward flight mode.

2. The quad tiltrotor aircraft as recited in claim 1 wherein the aft wing has a greater span than the forward wing.

3. The quad tiltrotor aircraft as recited in claim 1 wherein the aft wing has a higher elevation than the forward wing in level flight.

4. The quad tiltrotor aircraft as recited in claim 1 wherein the aft rotors have a larger diameter than the forward rotors.

5. The quad tiltrotor aircraft as recited in claim 1 wherein the forward rotors co-rotate.

6. The quad tiltrotor aircraft as recited in claim 1 wherein the forward rotors counter rotate.

7. The quad tiltrotor aircraft as recited in claim 1 wherein the aft rotors counter rotate.

8. The quad tiltrotor aircraft as recited in claim 1 wherein the aft rotors have a larger diameter than the forward rotors and wherein a ratio of the diameters of the forward rotors to the aft rotors is between 1 to 3 and 2 to 3.

9. The quad tiltrotor aircraft as recited in claim 1 wherein, in the vertical takeoff and landing flight mode, a ratio of rotor speeds of the forward rotors to the aft rotors is between 2 to 1 and 3 to 1.

10. The quad tiltrotor aircraft as recited in claim 1 further comprising at least one engine operable to drive the forward and aft rotors.

11. The quad tiltrotor aircraft as recited in claim 10 wherein the at least one engine further comprises first and second forward engines operable to respectively drive the first and second forward rotors and first and second aft engines operable to respectively drive the first and second aft rotors.

12. The quad tiltrotor aircraft as recited in claim 10 wherein the aft rotors are operable to disengage from the at least one engine during forward flight mode.

13. The quad tiltrotor aircraft as recited in claim 10 wherein the aft rotors are coupled together with a cross shaft such that either of the aft engines is operable to drive the first and second aft rotors.

14. The quad tiltrotor aircraft as recited in claim 10 wherein the forward rotors are not coupled together.

15. The quad tiltrotor aircraft as recited in claim 1 wherein the aft rotors are operable to autorotate.

16. The quad tiltrotor aircraft as recited in claim 1 wherein the forward and aft rotors further comprise differential collective control.

17. The quad tiltrotor aircraft as recited in claim 1 further comprising a first short takeoff and landing mode wherein the forward rotors are in the forward thrust orientation and the aft rotors are in the vertical lift orientation and a second short takeoff and landing mode wherein the forward rotors are between the vertical lift and forward thrust orientations and the aft rotors are between the vertical lift and forward thrust orientations.

18. A tiltrotor aircraft having a vertical takeoff and landing flight mode and a forward flight mode, the aircraft comprising:

a longitudinally extending fuselage having forward, mid and aft stations;

a forward wing extending laterally from the forward station having first and second outboard ends;

a mid wing extending laterally from the mid station having first and second outboard ends;

an aft wing extending laterally from the aft station having first and second outboard ends;

first and second forward rotors respectively coupled proximate the first and second outboard ends of the forward wing, the first and second forward rotors reversibly tiltable relative to the forward wing between a vertical lift orientation and a forward thrust orientation;

first and second mid rotors respectively coupled proximate the first and second outboard ends of the mid wing, the first and second mid rotors reversibly tiltable relative to the mid wing between a vertical lift orientation and a forward thrust orientation; and

first and second aft rotors respectively coupled proximate the first and second outboard ends of the aft wing, the first and second aft rotors reversibly tiltable relative to the aft wing between a vertical lift orientation and a forward thrust orientation;

wherein, the forward rotors are rigid rotors having collective pitch control;

wherein, the mid and aft rotors are gimbaled rotors having collective pitch control and cyclic pitch control;

wherein, the forward rotors are higher disk-loading rotors than the mid and aft rotors;

wherein, a rotor speed of the forward rotors is greater than a rotor speed of the mid rotors and the aft rotors in the vertical takeoff and landing flight mode; and

wherein, the mid and aft rotors are foldable in the forward flight mode.

19. The quad tiltrotor aircraft as recited in claim 18 wherein, in the vertical takeoff and landing flight mode, a ratio of rotor speeds of the forward rotors to the mid rotors and the aft rotors is between 2 to 1 and 3 to 1.

20. The quad tiltrotor aircraft as recited in claim 18 wherein each of the mid rotors and the aft rotors has a larger diameter than the forward rotors and wherein a ratio of the diameters of the forward rotors to the mid rotors and the aft rotors is between 1 to 3 and 2 to 3.