The W.9 helicopter pioneered the NOTAR principle, using coolant air from its DH Gipsy Queen piston engine for torque reaction control. The sole example, PX203, first flew in 1945. It was demonstrated in an air pageant at Southampton on 22 June 1946 too but we believe this is Radlett. It seems to have flown well but work stopped after it crashed. This happened in 1946 according to most sources, though the German Wikipedia gives 20 January 1948. Photo from: Nationaal Archief (Netherlands)