Aircraft, having a pair of counter rotating rotors

An aircraft for hovering and horizontal forward flight, having a housing with a flight axis defining a forward flight direction, at least a pair of rotatively driven, coaxial rotors located within said housing for generating a rotor air stream and a multiplicity of adjustable air guiding means arranged in said rotor air stream, said housing along said flight axis being shaped as an airfoil section with an upper surface and a lower surface, said upper surface comprising a circular air inlet coaxial with said pair of rotors and said lower surface comprising a circular air outlet coaxial with said pair of rotors, said circular air outlet being divided into a plurality of blade array sections, each comprising a plurality of elongate blade members having a longitudinal swivelling axis and forming air guiding surfaces, wherein for each blade array section the blade members are collectively adjustable in their angular position relative to said air stream about their swivelling axis and wherein in a part of said blade array sections, adjacent blade members are adjustable in opposite sense to assume complementary angular positions between an opened and a closed position for controlling the lifting forces without generating a substantial horizontal component of the air stream passing said part of blade array sections.