The value of 1 lb. of weight saved in an air liner has been given as equal to 1 lb. of gold in an American paper. This figure has been calculated in a more complete way, and on the assumptions made is reduced to £16 10s. or near enough to one guinea per oz. saved.

1. (1) It is almost always possible to reduce the weight of any component of an aircraft or engine by refining the design. This can be done in many ways, but chiefly by improved material, by reducing dimensional tolerances, by more accurate stressing and by development by mechanical testing. These processes increase the cost and time of manufacture, and as the value of an air liner starts only when it is put into service, and its useful life is settled by obsolescence rather than by wearing out, there is always a practical limit to the time that can be spent on design, development and manufacture. During wartime the resources of the country are pushed to their limit and it is often impossible to get a big enough production of the best materials, o r i o work to fine tolerances; hence we accept an aircraft a good deal short of the ideal. The life of the aircraft is comparatively short and is governed largely by factors outside our control, so that an assessment of the value of weight saving is nearly impossible.