One of the outstanding questions of the hour is the form of power plant which is likely to prove most satisfactory for various classes of transport aircraft for various stage lengths.

“Most satisfactory” can, of course, cover a multitude of desirable features. But there is one pre-eminent requirement which should always Jbe kept in view. That is that the combination of airframe and engine considered should be capable, first of covering its direct operating costs plus overheads and, having done that, of flying as fast as possible.