Abstract: An aircraft comprises at least one jet engine having a surrounding, open-ended duct coaxial with the engine and spaced therefrom radially to define a passage of annular cross-section. The casing or duct extends upstream and downstream of the jet engine and tapers internally in the forward direction over a region, in which a leading edge of a casing of the jet engine is disposed. Upstream of the tapering region, the interior of the duct forms a cylindrical entry section of the passage through the duct, in which an axially displayable open-ended tube is disposed, spaced radially from the wall of the entry section of the duct passage.

Abstract: A jet propulsion engine such as a gas turbine engine has an air compressor for supplying compressed air to the engine compressor stages. The air compressor is controllably and selectively driven by way of a disconnectable drive connection between the air compressor and a freely rotatable fan which is arranged in front of the air compressor and which in operation is rotated by the flow of intake air into the engine. A by-pass duct permits a part of the intake air to be by-passed around the air compressor and passed in variable proportions either to the engine compressor stages or directly out of a by-pass duct outlet.