EARLY aircraft relied for propulsion and for speed upon small, low‐powered internal‐combustion engines. During the course of the last fifteen years the technique of aircraft production and of transport aviation has advanced so rapidly that to‐day we are beginning to think in terms of aircraft with total horse‐powers in some cases not far short of 3,000 and 3,500. There is every indication too, that higher powers may be anticipated within the next few years.