US Patent 9731820 Vertical take-off and landing aircraft

A VTOL aircraft includes at least one puller rotor and at least one pusher rotor. The VTOL aircraft, for example, may include three puller rotors and one pusher rotor. The combination of static puller and pusher rotors allows the rotors to remain in a fixed orientation (i.e., no moving mechanical axes are required) relative to the wings and fuselage of the VTOL aircraft, while being able to transition the aircraft from a substantially vertical flight path to a substantially horizontal flight path.