Abstract: 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.

Abstract: The invention is directed to a solar thermal propulsion engine which comprises:(a) an ogive solar collection cavity with inner and outer walls having therebetween a heat exchange medium which can pass and heat a propellant fluid, and having its highest temperature deep within the cavity, and (b) a nozzle attached to and communicating with the heat exchange medium through which the heated propellant fluid can be passed to create thrust. In addition, this invention is directed to a solar thermal propulsion engine which comprises. (a) a heat exchanger having a geometry such that it has inner and outer walls having therebetween an open cell foam heat exchange medium through which a propellant can pass with tubulence, wherein solar radiation can heat the inner wall and the open foam heat exchange medium to, in turn, heat the propellant, and (b) a nozzle attached to and communicating with the open cell foam heat exchange medium through which the heated propellant fluid can be passed to creat thrust.