In presenting this paper an attempt has been made to examine the development of current propeller theory and practice to cover the range of aircraft speeds between 450 and 550 m.p.h., which at 36,000 ft. represents a flight Mach number range of about 0.68 to 0.83. Inevitably in such a discussion it has been necessary to peep over the wall into the realms of higher speeds, but no serious attempt has been made to cover such a controversial region because of the lack of experimental data.

The 773rd Lecture was read before the Society on the 17th March 1949 at the Institution of Civil engineers, Great George Street, S.W.I. Dr. H. Roxbee Cox, B.Sc., D.I.C., F.R.Ae.S., F.I.Ae.S., President of the Society, introduced the lecturers, Mr. G. C. I. Gardiner, A.F.R.Ae.S., Chief Engineer and Mr. J. Mullin, B.Sc., A.F.R.Ae.S., Chief Aerodynamicist of de Havilland Propellers Ltd.

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