623,049. Reducing surface friction on aircraft. SVENSKA TURBINFABRIKS AKTIEBOLAGET LJUNGSTROM. Oct. 1, 1946, No. 29266. Convention date, Oct. 10, 1945. [Class 4] In an aircraft having an internal-combustion turbine or turbines 1 fed by a compressor 4, the boundary layer of air is removed through slots 11 and ducts 10 in the wing 2 and other surfaces and through an aperture 8 in the air intake 7 of the compressor, the area of the air intake 7 being adjustable manually or automatically to ensure that the static pressure thereat is less than that at any part of the aircraft surface. The aperture 8 is preferably near the narrowest section of the air intake. The area of the aperture 8, which may comprise an annular set of small apertures, may also be variable and non-return valves may be provided in the ducts 10. As shown, a non-rotary member 52 is mounted at the front of a rotary member 5<SP>1</SP> carrying the moving blades of the axial-flow compressor 4 and the fixed blades 3 are carried by the casing. The boundary layer air may be removed in part from the fuselage and ailerons, and some of the slots employed for this purpose may be adapted to be closed by flap valves.