Recently Professor Black showed a photograph of a baby seal swimming in a shallow pool at a speed greater than the speed of the surface waves. In terms of the hydraulic analogy the seal may be said to be a “supersonic” swimmer.

In lighter vein, it may be wondered whether supersonic flow extends to the insect world! The attached Schlieren photograph shows, for example, a blowfly in a flow at a Mach number of 1·4. The blowfly, suitably stiffened by a film of clear plastic to prevent it from shattering, was sting mounted in a shock tube containing freon as the working fluid.

Transatlantic travel has entered a new era, the era of mass tourism. Low cost, newly available air charter services have made it possible. Their far-reaching benefits, economic, cultural, and educational, are now widely recognised and enjoyed on both sides of the Atlantic.

For more and more people lower travel costs are awakening a latent demand. For those who have tasted the benefits of low cost travel there can be no turning back. Low cost charter availability is taking on the character of a right which governments are increasingly being expected to protect and promote.

In a paper by Parsons and Cook, a theoretical solution to the initial buckling under shear stress of a long clamped plate with parallel edges, reinforced by a stiffener mesh was obtained. In the particular case when only diagonal stiffeners are present (having flexural rigidity only) one numerical solution was obtained for a particular value 1·5 of the aspect ratio of the panels of the plate associated with various values of θ, for which a partial check on the accuracy of the computational work could be carried out by comparison with results obtained by Southwell and Skan.

In this paper the numerical work is extended to cover a range of values of θ and a range of values of the aspect ratio in order to determine the optimum arrangement of stiffeners in resisting shear stress applied to the plate, that is to say the arrangement which maximises the onset of buckling.

As in Ref. 1, the cross-sectional area of the stiffeners is neglected, (he effect of a finite area of cross section being discussed in a subsequent paper.

From tests on tunnel cascades one of the sources of loss in axial compressors could be corner stall, i.e. local separation of the flow in and near the corners between the annulus walls and the convex surfaces of the blades.

Tests on a tunnel cascade at entry Mach numbers of 0·5 and 0·6 show that, at least in a tunnel, the stalling may be cured by boundary layer control. The present tests obtain control by suction through a corner slot. The tests show that removal through the slot of 1·3% of the flow decreases the total losses of the cascade by about 25%.

A more detailed examination of the losses in the tunnel cascade without suction suggests that about three-quarters of the end losses are due to the separation and reverse flow. Much of the remaining end loss appears to result from the fact that the low energy stream tubes in the entry boundary layer would experience a disproportionately large increase in cross-sectional area during diffusion, even in attached two-dimensional flow. The suction corner control can eliminate the greater part of the end losses, by eliminating the separation.

Excitation of subharmonic resonances is one of the serious vibration problems which often have to be overcome in the development of high speed machinery. Such resonances have been observed, for example, in gas turbines(3), in rotor systems(4) and in the geared drive of a rotating kiln(5).

The subharmonic resonance of order 1/2, of a single degree of freedom system with viscous damping, is investigated for the case of a centrifugal disturbing force. The restoring force characteristic is of the non-odd form and its asymmetry is expressed in terms of the static deflection parameter. The Ritz averaging method, with a five term approximation, is used for the theoretical analysis. Numerical results are presented for the undamped case and are compared with analogue computer solutions.

The choice of the Ritz averaging method is determined mainly by its adequate accuracy at larger magnitudes of non-linearity. It is also more versatile than other methods and in a previous application(6) to a system with an asymmetrical restoring force it produced satisfactory results.

GEOS-C will be the third of a series of spacecraft designed for the National Geodetic Satellite Programme. The two earlier and successful spacecraft were designated GEOS-I and II. In these, geocentric stabilisation was acheived to optimise the usage of the radiated and reflected radio and optical power of the geodetic observations. It was the atmospheric attenuation of the optical beacons, by which the spacecraft could be photographed against a star background, which imposed the accuracy requirement of earth pointing to within 5°. Descriptions as well as performance analyses of these attitude control systems have been published. In each, the proper mass distribution was obtained through an end mass on a de Havilland extendible boom. Since initial misorientation and perturbing torques induce motion about the equilibrium orientation in a gravity-gradient system, a mechanism for energy dissipation is necessary. A Magnetically Anchored Eddy Current Damper was used for this purpose. It consists of a magnet assembly that is free to lock onto the geomagnetic field and rotate freely within a conducting spherical shell. Relative motion of the two produces eddy currents in the conductor which in turn impede the relative motion.

While my own views are the product of long association with the airline industry, I would not wish to ask the airlines—or any one of them—to assume responsibility for such personal views and conclusions as may be put forward in this paper. Having added this caveat, I am hopeful that what I have to say reflects at least the opinion of some within the airline industry.