In projecting future turboshaft engines for helicopter appUcations the engine designer is faced with the problem of selecting the size of engine to meet the likely size, configuration, performance and economic requirements of future helicopters. It is also desirable to meet as many different helicopter applications as possible with the same basic engine design. The helicopter designer is, likewise, faced with the problem of which engines could be available for the future and how they could best be tailored to his requirements. This is the perennial problem of the “chicken and the egg.”

This paper summarises the results of a preliminary study of the problem, based on some assumed airworthiness requirements and simple engine assumptions and, while it makes no claim to be a method in itself of assessing the problem, it does show the sort of trend which could be expected.