The theoretical aerodynamic properties of supersonic aerofoils of polygonal section are well known. This note describes the results obtained by applying supersonic aerofoil theory to a simple curved aerofoil of arbitrary maximum thickness position, the leading and trailing edges of which are pointed.

The results for a symmetrical curved section are compared with the theoretical properties of a symmetrical double-wedge section.

The ubiquity of aircraft in being and yet to be, whether civil or military, manned or unmanned, makes them liable to exposure to wide extremes of atmospheric conditions. The range of temperature to which they may be subjected may possibly be from +90° to –90°C. (+194° to –130°F.), that of pressure, from one atmosphere to something approximating to one-tenth of this amount, while the water content (aqueous vapour plus water in suspension; for example, in a very dense tropical cloud), can, on occasion, be as high as 2.5 per cent. by weight and, at stratospheric heights, at least as low as 0.001 per cent. Such variations in ambient conditions are not without chemical and physical repercussions. The engineering problems which arise will be examined, therefore, from both these view points, and attention will be drawn to potential dangers and means suggested for their avoidance.

The spinning nose dive has confronted the aeroplane designer with two main problems. The first is to evolve an unspinnable aeroplane, and the second to provide controls of sufficient power to ensure an immediate recovery from any spin into which an aeroplane can be forced. At the present time there seems little prospect of achieving a general solution of the first class of problem, although interesting particular solutions have been evolved from time to time. It seems now to be generally accepted that the unspinnable aeroplane would be desirable for every purpose, but it is evident that it must be achieved without sacrifice of performance or manoeuvrability. Moreover, it must be remembered that an imperfect solution of the first class of problem, such as can sometimes be achieved by limiting the power of the control surfaces, may be worse than useless; for the pilot may be deprived of the power to regain normal flight quickly if his aeroplane falls into a spin in unusual circumstances. It is, in fact, very unfortunate that many devices which point the way to the evolution of the unspinnable aeroplane also add to the difficulty of recovery from a spin. It is not my purpose to consider the methods which have been devised to prevent the incipient spin, which occurs when a conventional aeroplane is stalled, but to confine my attention to the problems of ensuring recovery from established spins. For the views expressed I must, of course, accept personal responsibility.

The author has described elsewhere (reference 1) the general principles of the dynamic stiffness method of analysing torsional vibration problems. Amongst the systems treated were those involving simple spur or helical gear-steps. The method can also be applied, however, to deal with epicyclic gearing, making proper allowance for the effect of flexibility in the gear-housing. The present paper outlines this extension.

A similar method may be used to allow for housing flexibility in normal spur gearing.

Before making an appreciation of present knowledge about a single metal, it is not inappropriate to say something of all metals, for the ever-increasing tempo of material civilisation has largely depended on man's increasing knowledge of these constituents of his World. His first discovery in this field was copper. To it and to its alloys he gave an exclusive allegiance for some 100 generations, then about 3,000 years ago iron became, and still continues to be, the predominant metal of his needs.

In the eighteenth century, when alchemy finally gave way to the logic of scientific thought, the metals employed by man for purposes other than currency and decoration were practically confined to iron, copper, tin, zinc, mercury and lead. Today, when over seventy metallic elements are known, only a small number of these are used by the engineer.

In the earlier days of flying, when aircraft speeds were low, it was a relatively easy matter to resort to a parachute to escape from an aircraft in trouble but, as aircraft speeds increased, escape by means of a parachute was more a matter of good fortune than of personal effort. Early in 1944, with the introduction of jet aircraft into the Royal Air Force, it became apparent that some assisted means of escape would have to be provided to enable air crews to escape from fast jet aircraft in an emergency. It was early in 1944, therefore, that I was invited by the Ministry of Aircraft Production to investigate the practicability of providing, in fighter aircraft, a means of safe escape for the pilot in abandoning the aircraft.