Tailsitting biplane aircraft having a coaxial rotor system

1. An aircraft operable to transition between thrust-borne lift in a VTOL orientation and wing-borne lift in a biplane orientation, the aircraft comprising:

an airframe including a first wing, a second wing and a fuselage that extends between the first and second wings;

a propulsion assembly coupled to the fuselage, the propulsion assembly including a counter-rotating coaxial rotor system that is tiltable relative to the fuselage to generate a thrust vector;

first and second yaw vanes extending aftwardly from the fuselage, the first and second yaw vanes configured to differentially provide yaw authority for the aircraft in the VTOL orientation and collectively provide yaw authority for the aircraft in the biplane orientation; and

a flight control system configured to direct the thrust vector of the counter-rotating coaxial rotor system and control movements of the first and second yaw vanes;

wherein, in the VTOL orientation, the first wing is forward of the fuselage, the second wing is aft of the fuselage and the counter-rotating coaxial rotor system is configured to provide thrust in line with a yaw axis of the aircraft; and

wherein, in the biplane orientation, the first wing is below the fuselage, the second wing is above the fuselage and the counter-rotating coaxial rotor system is configured to provide thrust in line with a roll axis of the aircraft.

2. The aircraft as recited in claim 1 wherein, in the biplane orientation, the first wing has an anhedral configuration and the second wing has a dihedral configuration.

3. The aircraft as recited in claim 1 wherein the first and second wings are swept wings.

4. The aircraft as recited in claim 1 wherein the fuselage has a length in a longitudinal direction and each of the first and second wings has a wingspan; and

wherein, the ratio of the length to the wingspan is between 1 to 2 and 1 to 3.

5. The aircraft as recited in claim 1 wherein the counter-rotating coaxial rotor system further comprises first and second rotor assemblies each having at least four rotor blades.

6. The aircraft as recited in claim 5 wherein the at least four rotor blades of the first rotor assembly and the at least four rotor blades of the second rotor assembly each has a root to tip twist between forty degrees and fifty degrees.

7. The aircraft as recited in claim 5 wherein each of the first and second rotor assemblies has a diameter and each of the first and second wings has a wingspan; and

wherein, the ratio of the diameter to the wingspan is between 1 to 1 and 1 to 3.

8. The aircraft as recited in claim 1 wherein the propulsion assembly further comprises a motor assembly including at least one electric motor.

9. The aircraft as recited in claim 1 further comprising a gimbal assembly coupled between the counter-rotating coaxial rotor system to the fuselage, the gimbal assembly having first and second pivot axes configured for tilting the counter-rotating coaxial rotor system relative to the fuselage.

10. The aircraft as recited in claim 9 wherein the first and second pivot axes further comprise orthogonal pivot axes.

11. The aircraft as recited in claim 9 wherein the first and second pivot axes further comprise a pitch pivot axis and a lateral pivot axis.

12. The aircraft as recited in claim 9 wherein the gimbal assembly includes an inner gimbal ring coupled to the counter-rotating coaxial rotor system, an outer gimbal ring coupled to the inner gimbal ring, an inner gimbal ring actuator configured to tilt the inner gimbal ring about the first pivot axis and an outer gimbal ring actuator configured to tilt the outer gimbal ring about the second pivot axis; and

wherein, the flight control system is configured to control the inner and outer gimbal ring actuators.

13. The aircraft as recited in claim 1 wherein, in the VTOL orientation, the aircraft has translation authority responsive to the thrust vector.

14. The aircraft as recited in claim 1 wherein the aircraft is configured to convert from the VTOL orientation to the biplane orientation responsive to the thrust vector having a pitch forward component during a climb.

15. The aircraft as recited in claim 1 wherein the aircraft is configured to convert from the VTOL orientation to the biplane orientation responsive to the thrust vector having a pitch forward component during forward translation above a predetermined airspeed.

16. The aircraft as recited in claim 1 wherein each of the first and second wings further comprises wingtips; and

wherein, the aircraft further comprises a plurality of tail assemblies, each of which is coupled to one of the wingtips and includes a vertical stabilizer and an elevon, the elevons forming a distributed array of elevons that is configured to collectively provide pitch authority and differentially provide roll authority for the aircraft in the biplane orientation.

17. The aircraft as recited in claim 16 further comprising a plurality of batteries and wherein, each of the batteries is coupled to one of the plurality of tail assemblies.

18. The aircraft as recited in claim 16 wherein the counter-rotating coaxial rotor system defines a rotor disk that is positioned inboard of the plurality of tail assemblies.

19. An aircraft operable to transition between thrust-borne lift in a VTOL orientation and wing-borne lift in a biplane orientation, the aircraft comprising:

an airframe including a first wing having wingtips, a second wing having wingtips and a fuselage that extends between the first and second wings;

a propulsion assembly gimbal mounted relative to the fuselage, the propulsion assembly including a counter-rotating coaxial rotor system that is tiltable relative to the fuselage about first and second pivot axes to generate a thrust vector;

first and second yaw vanes extending aftwardly from the fuselage, the first and second yaw vanes configured to differentially provide yaw authority for the aircraft in the VTOL orientation and collectively provide yaw authority for the aircraft in the biplane orientation;

a plurality of tail assemblies, each of which is coupled to one of the wingtips and includes a vertical stabilizer and an elevon, the elevons forming a distributed array of elevons that is configured to collectively provide pitch authority and differentially provide roll authority for the aircraft in the biplane orientation; and

a flight control system configured to direct the thrust vector of the counter-rotating coaxial rotor system and control movements of the first and second yaw vanes and the elevons;

wherein, in the VTOL orientation, the first wing is forward of the fuselage, the second wing is aft of the fuselage and the counter-rotating coaxial rotor system is configured to provide thrust in line with a yaw axis of the aircraft; and

wherein, in the biplane orientation, the first wing is below the fuselage, the second wing is above the fuselage and the counter-rotating coaxial rotor system is configured to provide thrust in line with a roll axis of the aircraft.