An aircraft has at least one drive motor coupled to first and second propellers for forward thrust of the aircraft. The first propeller is dimensioned for takeoff and landing conditions and for flight conditions below a predetermined first flight altitude. The second propeller has a radius which is larger than a radius of the first propeller and is dimensioned for a second flight altitude which is substantially greater than the first flight altitude. The two propellers are alternatingly coupled with the at least one drive motor so that the two propellers are respectively individually adapted to the power of the at least one drive motor for a full utilization of the power of the at least one drive motor for forward thrust.

A boundary layer control device including a rotating cylinder mounted on a shaft disposed along the trailing edge of the wing of an aircraft and a flap structure secured to the shaft on which the rotating cylinder is mounted. In the preferred embodiment, the flap structure is coupled to the shaft by brackets, each of which having one end pivoted about the shaft and an opposite end to which the flap is pivotally supported. This arrangement facilitates rotation of the flap structure between a first "cruise" position in which the flap structure is disposed substantially horizontally at the trailing edge of the wing, and a second "VTOL" position in which the flap is disposed either above or below the wing in a "stowed" or aerodynamically hidden position. Various other embodiments are disclosed.

In the invention, the speeds of both propellers in a counterrotating aircraft propeller pair are measured. Each speed is compared, using a feedback loop, with a demanded speed and, if actual speed does not equal demanded speed for either propeller, pitch of the proper propeller is changed in order to attain the demanded speed. A proportional/integral controller is used in the feedback loop. Further, phase of the propellers is measured and, if the phase does not equal a demanded phase, the speed of one propeller is changed, by changing pitch, until the proper phase is attained.

This invention is directed to stopped rotor Flipped Airfoil X-wing (FAX-WING.sup..TM.) aircraft which comprises: (a) A rotary wing flight mode which operates similar to a helicopter, wherein all main rotor airfoils rotate with leading edges into the oncoming airstream (neglecting forward motion) to provide lift, and utilize an anti-torque rotor to cancel main rotor torque. The fixed wing flight mode, including supersonic flight, utilizes all stationary main rotor airfoils for primary lift, such that all airfoil leading edges are positioned forward, meeting the oncoming airstream generated by forward aircraft motion. Two airfoils are forward swept 45 degrees, and the other two airfoils are aft swept 45 degrees. The transition mode for converting from rotary wing to fixed wing flight, and vise-versa, causes two adjacent airfoils to flip 180 degrees (in approximately 1/16 second) about their pitch axis, such that all airfoils have leading edges in the correct orientation for a particular flight mode. (b) Rotating flywheel inertia mass(es) capable of being coupled to the main rotor airfoils, via a flywheel clutch, for the purpose of rapidly starting or stopping airfoil angular rotation (in approximately 1 second) without applying adverse torque to the aircraft fuselage, and a spin up/spin down mechanism for applying angular momentum to the flywheel inertia mass(es) at gradual rates such that the anti-torque rotor and/or rudder can cancel torque. (c) Computer based flight control system capable of directing rotary wing, fixed wing, and transition therebetween. (d) Variable pitch ducted fan to provide forward thrust, coupled to common turboshaft engine(s), that also provide power to the main rotor.