The past has been interesting, but what of the future? As Fig. 1 shows, extrapolation is an attractive tool, with pitfalls for the incautious - most often exemplified in aerospace by the prediction that by 2015 the entire US defence budget would fund one aeroplane, or more recently by the belief that avionics will expand into infallibility and reduce costs to invisibility. The first extrapolation is premature, and the latter two as near as makes no difference wrong.

In the case of the single affordable US defence aircraft the extrapolation probably correctly estimated the 2015 US defence budget, but erred in expressing the US Department of Defence requirement in terms of aircraft rather than damage-effects on target. The subsequent step change in avionics miniaturisation undermined the extrapolation and now looks likely to enable the DoD’s damage-effect requirements to be attained using products that lie on a different cost-effectiveness trend line.