The problem of determining the type of engine which best suits a particular application is not new to the engine designer, but the supersonic transport is perhaps unique in that a number of design criteria have been introduced which cannot easily be taken account of in the usual terms of engine weight, fuel consumption or even aircraft direct operating cost.

However, an examination of the effect of these standard criteria on different types of engines is a starting point in determining what engine will best match the supersonic transport requirement. A survey of a series of thermodynamic cycles both at Mach numbers in the region of 2.0 and at subsonic speeds typical of standoff or diversion suggests that two types of engine merit further study.