This paper contains nothing new to airline people. It is not an original contribution. For some time I had been under the impression that the ideas we use and the troubles we have in the airline business were clearly understood by technical people outside the airlines. Recently, however, I have been surprised to discover that this is not so and this fact is the excuse for the shape of this lecture. So I am not talking to airline people but for them. If, when you have heard me, you have heard nothing you did not know, I shall be happy.

We all recognise that the aircraft turbine engine has permitted a revolution in aircraft design and performance, opening up avenues of progress which were not practicable with other forms of propulsion. The question that is asked is, what further progress is possible with aircraft turbine engines and what are the major problems which are likely to be encountered on the way?

The title of this paper is to be construed as primarily referring to guided missiles. Some of the principles have possible application to more peaceful purposes, such as aircraft flight, but the primary emphasis is towards weapon systems.

The principal guidance and control methods are discussed on a review basis but certain of them, which are particularly important or of which the author has special experience, are considered more fully. These are, in particular, guidance and control problems relating to homing missiles.

We are now, I believe, at a time of crisis in aeronautics and in Great Britain the sense of crisis is made more acute on account of the issue by the Government of the White Paper on Defence for 1957. This paper announces vitally important changes of Government policy which are intimately concerned with aeronautics. For example, the policy is to make the English Electric P.l Supersonic Fighter the last of the manned fighter aircraft in Britain and to concentrate effort in defensive aircraft upon the unmanned guided weapon.

Around the end of the fifteenth century were written what must have been about the first set of airworthiness requirements ever compiled. These were notebooks of Leonardo da Vinci in which he discussed the physics of flight and the design of flying machines. In one of these notebooks he wrote:—

“ In constructing wings one should make one cord to bear the strain and a looser one in the same position so that if the one breaks under the strain the other is in position to serve the same function.”

Now a Days, the phenomenon is well known of the plane normal shock waves set up in the divergent section of a convergent-divergent nozzle, and the oblique shocks which occur in the resultant jet downstream of the nozzle exit when operating under overall pressure ratios less than the design value. Stodola was among the first to demonstrate experimentally the effect on the flow within the nozzle of increasing the back pressure above the design value, and work by Schmidt, Martin) and others, has been concerned with the theoretical changes in pressure, temperature, density and Mach number across a normal shock wave whose position varies along the nozzle axis. The effect of working substance on these changes, which is taken into account by the ratio of specific heats, has also been investigated.

In a previous note a method was developed for calculating the exhaust port area for two-stroke cycle engines assuming the cylinder length to be constant. It was pointed out by Williams and Pullman that the effect of the variation in cylinder length was important, this was appreciated in the preparation of the note, but it was necessary to assume a constant length in order to obtain an analytical solution. In this note the method given earlier is extended to cover a cylinder discharging direct to atmosphere with a moving piston.