One of the main problems in connection with the development of air-cooled engines appears to consist in securing adequate cooling without increasing the head resistance above that of corresponding water-cooled engines.

This problem particularly applies to large air-cooled engines which are limited in size by cooling difficulties. Air-cooled engines for windmill planes and helicopters for alternate slow and fast flying present a further problem, because such aircraft engines will be required to develop maximum horse-power when the speed of translation is lowest.

The airflow over the nose of a bulky body, such as that of an aeroplane, diverges radially in every direction from its axis. Such radial flow tends to overshoot laterally, at its core, the periphery of the engine or other obstruction and so depart from the contour thereof, with the result that a considerable turbulence is set up. Such turbulence has also the undesirable effect of causing a reversal of the pressure gradients, and a corresponding reversed or forward flow of air, in the boundary layer behind the engine, thereby creating a ” dead “ area or areas and so considerably reducing the cooling effect of the general air flow and increasing the turbulence.

The standard method of strength calculation of a framework is based on the assumption that members are freely pinned together and external forces are applied only at nodes. Actually aircraft fuselage members are stiffly joined and transverse forces are often acting on them at considerable distances from nodes, e.g., weights of crew, instruments and oil, reactions of controls, stabiliser adjusting gear, etc.

The safest method of computing stress in such members is to assume both ends pin—jointed. As they actually are stiffly connected to adjacent members, they are not allowed to twist freely, i.e., the truss exerts moments on the loaded member. The effect of these end moments consists in diminishing deflection andfield moments. The decrease of maximum bending moment may attain nearly 50 per cent.

Since framework members are designed to withstand axial forces only, viz., tension or compression, they are comparatively weak against bending and have to be strengthened appreciably if transverse forces are present.

It has been known for many years that the rectangular wing stalls first in the central region, burbling spreading gradually tipwards with further increase of incidence. This phenomenon is useful in connection with lateral control, because this control is retained for a while (though reduced) past the stall. Increased use of the1 tapered wing to-day raises the question of whether this phenomenon holds good with tapered wings. There is already some doubt on this score.

In deep-drawing operations connected with mass production the question of the reduction that can be obtained in a single draw without causing excessive waste is of considerable importance. This drawing capacity (maximum draw) has, as will be obvious from Fig. i, proved capable of very considerable increase in the course of the last decade.