Since the driving torque exerted by the engine is a periodic function of the time, the speed of rotation must also be periodic, which implies that the airscrew must be subjected to inertia stresses as well as to the stresses due to air forces and centrifugal forces. In the case of engines having six or more cylinders these inertia stresses will not in general be important as the cyclic variations of torque will be comparatively small. But with engines having two or three cylinders these stresses must be considered, for.it will readily be seen that the bending moment due to inertia forces is such as to increase the stresses due to the air load.

If the thought of another war troubles you, then don't read this article. If you would rather say to yourself as the Secretary of State said to the Air Conference, “ There won't be another war for ten years, so why worry? ” then no doubt you will think with him that it is better to let other nations have alk the bother and expense of trying to advance; after all, we are jolly fine fellows and can soon pick up. If, on the other hand, you have imagination which gives you a nasty queasy sensation when you think of what might be, then perhaps the following notes, albeit disjointed and mostly stale, may at least conjure up in you thoughts of your own on the subject. This is all that is needed to help, our advancement in the air–the stimulation of spoken and written thoughts by the British nation, for if every taxpayer in the British Empire says “ Air Force,” then the Press and Parliament will say it too.

The power plant of an aeroplane is usually designed by a different person situated in a different works from the aeroplane designer, yet it is essential that both should understand something of each other's work, if the best result is to be attained. It is of the first importance that the engine designer should have a clear idea of the value to the aeroplane designer attaching to low weight per b.h.p. and low fuel consumption per b.h.p., when considering a new design or comparing the merits of existing ones.