A tailsitting biplane aircraft operable to transition between a thrust-borne lift orientation and a wing-borne lift orientation, the aircraft comprising: an airframe including a first wing, a second wing and a fuselage that extends between the first and second wings, the fuselage including an aft door; 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 (34a, 34b) symmetrically disposed and pivotably coupled to an aft end of the aft door; first and second yaw vane actuators (94a, 94b) respectively configured to tilt the first and second yaw vanes (34a, 34b) about a common axis via first and second linkages (98a, 98b); and a flight control system configured to direct the thrust vector of the coaxial rotor system and to independently control operation of the first and second yaw vane actuators (94a, 94b); wherein, in the thrust-borne lift orientation, a yaw axis of the aircraft extends through the fuselage and the propulsion assembly and wherein the coaxial rotor system is configured to provide thrust in line with the yaw axis; wherein, in the wing-borne lift orientation, the first wing is below the fuselage, the second wing is above the fuselage, the yaw axis extends through the fuselage and the wings (14, 16) and the coaxial rotor system is configured to provide thrust in line with a roll axis of the aircraft; and wherein, the yaw vanes (34a, 34b) are configured to differentially provide yaw authority for the aircraft in the thrust-borne lift orientation and collectively provide yaw authority for the aircraft in the wing-borne lift orientation. an airframe including a first wing, a second wing and a fuselage that extends between the first and second wings, the fuselage including an aft door; 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 (34a, 34b) symmetrically disposed and pivotably coupled to an aft end of the aft door; first and second yaw vane actuators (94a, 94b) respectively configured to tilt the first and second yaw vanes (34a, 34b) about a common axis via first and second linkages (98a, 98b); and a flight control system configured to direct the thrust vector of the coaxial rotor system and to independently control operation of the first and second yaw vane actuators (94a, 94b); wherein, in the thrust-borne lift orientation, a yaw axis of the aircraft extends through the fuselage and the propulsion assembly and wherein the coaxial rotor system is configured to provide thrust in line with the yaw axis; wherein, in the wing-borne lift orientation, the first wing is below the fuselage, the second wing is above the fuselage, the yaw axis extends through the fuselage and the wings (14, 16) and the coaxial rotor system is configured to provide thrust in line with a roll axis of the aircraft; and wherein, the yaw vanes (34a, 34b) are configured to differentially provide yaw authority for the aircraft in the thrust-borne lift orientation and collectively provide yaw authority for the aircraft in the wing-borne lift orientation.