In July, 1935, I had the honour of reading a paper before a joint conference of the Royal Aeronautical Society and the Society of British Aircraft Constructors, entitled, “ Future Research on Air-Cooled Aero Engines.” Much water has flowed under the bridges since that date, and we have entered on a period of intensive activity and development in aeronautical matters not fully envisaged 18 months ago.

A number of the suggestions put forward in my previous paper, as being suitable subject matter for research or investigation, have been, or are in course of being, investigated by various Government departments, or interested firms in this country, so that, when I received an invitation from the Royal Aeronautical Society to read another paper during the present Session, I thought it might prove useful to endeavour to write an addendum to the original paper, and try to outline the trend of a future air-cooled power plant for aircraft which would be built during the next five years, it being presumed that these engines would be designed as a result of the experimental work which had already been completed, or is being carried out at the present time, and with the object of meeting the more searching requirements demanded by this increased activity.

Almost the first thing anyone thinks of, when confronted with a type of aeroplane which he has not seen before, is its performance. He thinks, “ What will she do?” This paper is an attempt to set out the methods by which the performance is estimated for a new design.

The subject has considerable scope, and only a certain portion of it will be covered here: Level speed and climb, range (at constant r.p.m.) and the take-off run.

Before anything can be done at all, something must be known about lift and drag, and something about airscrews. These will therefore be considered first.

The fact that attention must be given to stiffness as well as strength in aeroplane design is now generally recognised. The provision of adequate strength alone is not sufficient to ensure that an aeroplane is immune from such troubles as flutter, loss of lateral control due to twisting of the wing and wing divergence. This is illustrated by the case of the Puss Moth. As shown in R. and M. 1645 this machine was examined in detail by the Aeronautical Research Committee and found to be completely satisfactory as far as the existing official airworthiness requirements were concerned, and yet it experienced failures which were attributed to flutter, an instability involving the stiffness of the wings and tail.

In the earlier stages of the investigations into these stiffness problems it appeared to many practical people that the work. was of academic interest only. As a matter of fact it was of subsidiary importance while operational speeds of aeroplanes were relatively low, but the higher speeds of the modern aeroplane make such problems of direct practical interest.