U.S. Patent Specifications

An aircraft includes a body, an air compressor located within the body and having a discharge duct directed downwardly to develop a lift reaction, and a second air compressor located within the body and having a discharge duct directed downwardly for developing a lift reaction, both of the ducts having their outlets located adjacent to one another and the centre of area of the outlets of all of the ducts being substantially under the fore‐and‐aft centre line of the aircraft so that the centre of lift of the reaction is affected very little whether one or both compressors are in operation.