Aerodynamics is the foundation on which we build aircraft, as did the Wright Brothers. In their day, it was something of a mystery. It has become a profession in itself—a Science and an Art.

Its parent science—the mechanics of fluids—is one of the most difficult branches of the general science of mechanics, which is itself possibly not one of the easier departments of science. The simplest of our flying machines is aerodynamically excessively complex. We have always been prepared to design and build aircraft to meet extraordinarily severe conditions. There is only one yardstick by which we can expect to be judged—results. We need all our skill—and skill is art, though not the whole of it.

From the earliest days, it has been an accepted article of faith that every aircraft flying outside its own country should carry some guarantee of its safety, conforming to an international standard, if not controlled internationally. No aim has been more assiduously pursued. But, after nearly forty years of the international regulation of aviation, there is no international standard of airworthiness with which aircraft are compelled to comply. The questions that now arise are whether the objective is ever likely to be achieved, and whether, in fact, international standards are necessary to safety.

A review is given of developments in the field of aeroelasticity during the past ten years. The effect of steadily increasing Mach number has been two-fold: on the one hand the aerodynamic derivatives have changed, and in some cases brought new problems, and on the other hand the design for higher Mach numbers has led to thinner aerofoils and more slender fuselages for which the required stiffness is more difficult to provide. Both these aspects are discussed, and various methods of attack on the problems are considered. The relative merits of stiffness, damping and massbalance for the prevention of control surface flutter are discussed. A brief mention is made of the recent problems of damage from jet efflux and of the possible aeroelastic effects of kinetic heating.

Strong plastics consist of two-phase arrangements of pairs of brittle solids which in combination may be very tough. Improvement now depends upon an understanding of brittle solid theory. The strength of brittle solids is generally very low but may occasionally approach the very high theoretical values. This is due to the high inherent strength being generally marred by tiny defects. When these defects are removed or contained high strength may be achieved. The various mechanisms by which this may be done are exemplified in mica, common salt, glass, metal whiskers and so on. The relevance of these substances and mechanisms to the manufacture of plastics is discussed.

Assuming the formation of plastic hinges at the quarter points of a ring subject to a diametral compressive force, a comparison is made between experimental collapse loads and those predicted by use of a simple expression based on the use of plastic rectangular stress blocks, for some common materials; good correlation is obtained with aluminium.

A member may be said to fail when it yields completely at several positions and so allows collapse as a mechanism to occur. The smallest load at which this happens marks the end of useful life of the member. In the case of very thin rings loaded at the ends of a diameter in compression, as shown in Fig. 1, it is obvious that the sections of greatest bending moment are at A, B, C and D. These moments will continue to increase with increasing diametral load.

The elastic stability of rectangular plates compressed in two perpendicular directions by forces uniformly distributed along the edges is considered. Edges x = 0 and x = a are simply supported, edge y = 0 is free and edge y = b is rigidly built-in (Fig. 1). Using the method described in a previous paper, after satisfying the boundary conditions at the edges of plate, the following transcendental equation is obtained:

In a recent note Professor Duncan gives a method for finding the reciprocal of a matrix which is triply partitioned both horizontally and vertically. In spite of the apparent complication of the formulae, such a procedure may shorten the calculations in the case when the submatrices involved are especially simple (e.g. null or diagonal), or when their arrangement exhibits some symmetry. In Ref. 1, the submatrices a to j of the desired reciprocal are obtained by a series of operations summarised in equations (3) to (19); these operations consist altogether of 5 inversions of submatrices, 29 matrix multiplications of various orders and 15 matrix additions.