In the early stages of preliminary design, it is essential to have a method for the comparison of aircraft on an operating cost basis. The standard S.B.A.C. method is too lengthy and, in any case, demands a greater amount of data than is usually available in the early design stages.
The formulae presented in this note were evolved by the author some years ago and the general method was quoted in a paper entitled “The helicopter—has it a future?” which was read to the Belfast Branch in January 1955. (See Journal, November 1955.)