When, in the course of his visit to Paris in May 1948, Dr. Roxbee Cox invited me to lecture to the Royal Aeronautical Society on our work in the field of turbopropeller and turbo-reaction engines, I was torn between two sentiments; the great honour which was done to me, and the seeming temerity for a French engineer to discourse on aircraft turbines before some of the people who had been responsible for the W2 700, the Nene, Ghost, F2, Theseus, Mamba, and other engines. The first of these sentiments however carried the day, as it could hardly fail to do in view of Dr. Roxbee Cox's extreme kindness.

Therefore I ask for the indulgence of my audience in listening to this, the first account to be given of the modest work done since 1941 by a team of French technicians, who were specialists in steam and industrial gas turbines, who had foreseen the possible development of the latter for aircraft, and who, completely cut off from the engineering world during the Occupation, at first worked literally in complete isolation, unaware even of the existence of the British and German achievements.

The Mamba engine has now been in existence some two–and–a–half years and in that comparatively short period of time it has been developed to the stage of being a type tested engine with over 5,000 hours test bed running and 100 hours flying as a background. The purpose of this paper is to give a brief account of the progress of the development and of the many problems which have been met and overcome during the period. Because of the many aspects of the development work it is not possible to deal in great detail with any particular item but rather to present the over–all picture, from the original design conception to the complete power plant of to–day.

In the course of investigation into the operating economics of transport aircraft, the cruising speed arises as a fundamental variable and a rapid method of correction of speed for variation of power, height and weight is frequently required. Other problems present themselves, such as the estimate of cruising speeds in the course of a new type design study, or the correction of a “one–point” published performance of a new aircraft to a standard operational condition differing in specified weight, altitude or power output for cruising.

In this note no account will be taken of the block speed correction arising because of the modification of true air speed by the various factors, such as wind, climb and glide which distort the optimum flight path. The principle of the method here suggested involves the unique relationship of p, the ratio of thrust power required at any speed (V) to the thrust power at the minimum drag speed (u) at the same altitude, and n the wellknown speed ratio V/u.

The paper “Aircraft Servicing” by Norman and Wilkinson published in the November issue of the Journal demands the close attention of both operators and aircraft manufacturers. The suggestions made can be further developed.

There is little doubt that the attainment of higher utilisation rates is one, if not the ultimate, solution of the economic problems that face air transport. This is even more evident when the present–day capital cost per pound of complete but unladen weight of varying transport vehicles is compared.