The evolution of bigger, better and faster aircraft of all classes received a great impetus during the War period. Now, when Peace has come and the Air Age is upon us, the development of more modern aircraft both for military defensive purposes and for civil transport uses, remains a matter of urgency if Great Britain is to retain her position as a great transport power. The tempo of development reached during the War must not be slowed down if we are to keep pace with, let alone excel, the United States.

I have been invited to-day to put forward the case for,the compounding of a piston engine with a turbine, and this I propose to do in very general terms.

This is a scheme which we investigated fairly fully, both theoretically and experimentally, some ten years ago, and with which we would have proceeded actively had not the war, and consequent pressure on more immediate problems compelled us, temporarily, to lay it aside.

The development of the gas turbine is so rapid and the thermo-dynamic ingenuity which is being lavished upon it at the present time is so imaginative and varied that the words “ in its forms ” which appear in the title to this paper can mean as much or as little as you please. Partly because I want to limit the scope of this paper to developments which might be expected to be in service within the next five years, and partly because I am frankly not sufficiently acquainted with the characteristics of many of its more advanced forms, I am going to confine myself to a discussion of the effects upon the speed and economy of commercial aviation of the two simplest and immediate variants of the gas turbine— the simple jet-producing turbine and the simple propeller-driving turbine.

The association of gas turbines with aircraft designed to make effective use of the special characteristics of jet propulsion has brought the trend of development into a state of transition and uneasy experiment. Already speeds equivalent to a low level Mach number of 0.80 have been recorded under observed conditions.