It is unnecessary to enlarge on the importance of the fuels used in aviation in a paper before this Society. Not only is fuel quality the most important individual factor to be considered in the economics of civil aviation, but engine development, aircraft design and performance depend upon it.

An apology is offered, in view of the title of the paper, that as it is barely possible in the confines of a single paper to deal adequately with the volatile fuels (known as petrols and gasolines) used in the normal carburettor or homogeneous charge engines, other types of fuels have necessarily been omitted.

The present stage in the evolution of commercial aeroplanes brings questions of speed and load into prominence, and it is hoped that an attempt to look at these things from a designer's point of view may be justified.

An aeroplane at first glance might appear to be an uneconomical vehicle. It may have over 100 h.p. installed per passenger, and this gives an expensive impression. The other side of the picture is that aeroplanes can achieve over 60 passenger miles per gallon of petrol at a higher speed than any other form of transport.