Fail-operational vtol aircraft

1. An aircraft capable of carrying at least 400 pounds of payload, comprising:

a main body;

a forward wing mechanically coupled to the main body;

an aft wing mechanically coupled to the main body;

a first variable pitch rotor, a second variable pitch rotor, a third variable pitch rotor, and a fourth variable pitch rotor, with each of the rotors being independently driven by at least one torque-producing source;

each of the first, second, third, and fourth variable pitch rotors are variable speed rotors;

the first and second variable pitch rotors are carried by the forward wing;

the third and fourth variable pitch rotors are carried by the aft wing; and

wherein the first variable pitch rotor, the second variable pitch rotor, the third variable pitch rotor, and the fourth variable pitch rotor are each primary rotors, providing sufficient thrust such that the aircraft is capable of controlled vertical takeoff and landing, even if only any three of the variable pitch rotors are operational.

2. The aircraft of claim 1 , wherein at least a portion of the forward wing is configured to pivot relative to the main body.

3. The aircraft of claim 1 , wherein the first and second variable pitch rotors are opposite each other across an envelope containing a center of gravity and wherein the first and second variable pitch rotors are collectively capable of providing all the thrust required to enable the aircraft to accomplish controlled vertical takeoff and landing.

4. The aircraft of claim 1 , further comprising a tilt mechanism configured to tilt the first variable pitch rotor by at least 80 degrees.

5. The aircraft of claim 1 wherein the first and the second variable pitch rotors are to the port side and the third and the fourth variable pitch rotors are to the starboard side of the main body, and wherein the first and second variable pitch rotors are configured to rotate a first direction.

6. The aircraft of claim 5 , wherein the third and fourth variable pitch rotors are configured to rotate in a second direction, and wherein the second direction is opposite the first direction.

7. The aircraft of claim 1 , wherein the first variable pitch rotor is configured to provide rotor cyclic control.

8. The aircraft of claim 7 , wherein the first variable pitch rotor comprises rigid blades and a hub configured to apply a mast moment to the aircraft.

9. The aircraft of claim 8 , wherein the first variable pitch rotor comprises rotor blades with individual blade control.

10. The aircraft of claim 1 , wherein the aircraft comprises no more than four variable pitch rotors.

11. The aircraft of claim 1 , wherein the first torque-producing source is a first electric motor.

12. The aircraft of claim 11 , further comprising a gear reduction system operationally coupling the first variable pitch rotor and the first electric motor.

13. The aircraft of claim 12 , wherein the first variable pitch rotor is driven by each of the first electric motor and at least a second electric motor through the gear reduction system.

14. The aircraft of claim 1 , wherein the first variable pitch rotor is configured to operate at an RPM level less than 60% of a maximum rotor RPM level.

15. The aircraft of claim 1 wherein electronic flight control system is configured to command controlled flight of the aircraft even if only three of the rotors are operational using vehicle attitude data.

16. The aircraft of claim 1 wherein a electronics flight control system is configured to command controlled flight of the aircraft even if only three of the rotors are operational using vehicle attitude data and without using discrete switching of states.

17. The aircraft of claim 1 , wherein left and right outboard portions of the forward wing are configured to rotate with the first and second variable pitch rotors, respectively.

18. The aircraft of claim 1 , wherein the aircraft has only four lifting rotors, the first, second, third, and fourth rotors.