Some wind tunnel experiments have been made on a variable pitch airscrew which shall change its pitch automatically as V/nD changes. The change in pitch is operated by the resultant effect of centrifugal and aerodynamic forces.

Reduction in air density, e.g., due to increase in height, causes an increase in pitch.

In the event of engine failure the blades assume the position of minimum drag.

A tentative design for a model screw, together with tests thereon, are described, and it appears that if the friction in the bearings about which the change in pitch occurs can be made reasonably small, it should be possible to construct a satisfactory full-scale screw.

There has been a great advancement in recent years in the technique and production of suitable fuels for both aircraft and automobile engines and the author hopes that a few notes on the fuel problem with particular reference to aircraft work may be of help to those engaged on aero engine design and operation.

In the author's opinion it is somewhat surprising that, with the information and data at present available on the subject of fuels, greater use is not made of this when considering the design and operation of an aero engine.