Kuchemann's weight model as applied in the first Greener by Design Technology Sub Group Report : a correction, adaptation and commentary

In the first report of the Greener by Design Technology Sub Group, the author made an error in deriving modern values for the empirical constants in the weight model, taken from Kuchemann, that was used in the study of fuel efficiency of a range of aircraft designs. In this note the error is corrected and the weight model is also extended to take account of the observed variation with range of the ratio of design payload to maximum payload. This leads to the conclusion that the effect of design range on fuel efficiency is substantially greater than suggested in the Greener by Design report. The conclusion, which is in agreement with a correlation by Nangia of existing aircraft data, indicates that a modem aircraft with a design range of 15,000km burns approximately twice as much fuel per passenger-km as one with a design range of 4,000km. This powerfully reinforces the call made in the Greener by Design reports for in-depth studies to be made of the use of medium-range aircraft for long-distance travel.