A joint meeting of the Royal Aeronautical Society and the Royal Meteorological Society was held on 14th December 1950 at the Institution of Civil Engineers, Great George Street, London, S.W.I, at which the 814th Lecture to be delivered before the Royal Aeronautical Society was given by Dr. G. S. Hislop. Major G. P. Bulman, C.B.E., F.R.Ae.S., presided at the meeting and after welcoming the members of the Royal Meteorological Society and especially their Secretary, Professor Sheppard, and expressing his regret at the absence in America of the President of the Royal Meteorological Society, Sir Robert Watson Watt, he introduced the Lecturer, G. S. Hislop, Ph.D., B.Sc, A.R.T.C, A.F.R.Ae.S., M.I.Mech.E., Senior Assistant to the Controller of Research and Special Development, British European Airways Corporation.

In this paper the thrust of the turbo-jet engine is rigorously defined, and is divided into the three components front external, internal and rear external. The measurement of thrust in static tests and in flight is discussed. Current methods are critically examined and test methods are proposed. Special attention is given to a method of calculating flight performance from simple static tests with different nozzle areas. A convenient form of engine curves for static tests is shown and a method of flight testing is given.