The lateral buckling of thin deep beams when subjected to a transverse loading system inducing bending initially in the plane of maximum flexural stiffness has been analysed on the assumption that the direction of application of the loads remains unchanged during small deformations of the beam (see, for example, treatments in Refs. 1 and 2). A typical case of a beam so loaded is illustrated in Fig. 1.

The use of primary pulsed radar as a surveillance instrument in Air Traffic Control is familiar to most, and is a direct development of the various ground radars current in the last war. The wavelengths generally employed are 10 cms. for more local control, and 50 cms. for long range and high coverage. The primary radar depends for its information on reflection from the target aircraft of sequences of pulses of electromagnetic energy radiated by the aerial, and displays this information as a “paint” on a P.P.I. (Plan-Position Indicator) cathode ray tube giving range and bearing relative to the radar site. The radar beam is fan-shaped, narrow in the horizontal plane to a few degrees, and wide in the vertical plane to provide adequate vertical cover. The beam is made to scan through the target by a rotation of the aerial about a vertical axis up to a rate of 14 r.p.m. The beam width in the horizontal plane is necessarily kept narrow to provide adequate discrimination between targets at the same range but different bearings. The primary radar is frequently associated with a height-finding radar in which the beam shape is reversed, having a narrow angular cross section in the vertical plane. In this case the aerial is made to nod up and down along an appropriate azimuth selected by the controller, and the height of an aircraft is displayed on a height-range cathode ray tube.

A great deal has been said and written about the necessity to launch into a completely new standard plateau of systems engineering for supersonic, as distinct from subsonic, aircraft. So far as I have been able to gather, one reason for all this could be the argument that, as the supersonic aircraft will be so costly to operate, i.e. so uneconomical, it must be operated at a very high utilisation with very short turn-rounds and that therefore all the systems must be very much more durable than has previously been the case. Another reason could well be that the flight régimes are such that there will have to be much more dependence on certain systems, e.g. pressurisation at 70,000 ft., cabin cooling at very high speed and so on.

In presenting this paper I shall take but a brief look at a rather interesting subject, the impact of which, on our business in aviation, has doubtlessly touched each and everyone of us. I refer to the subject of Cabotage—an old term which like so many others in human affairs has taken on a new meaning in a world shrunken by our own specialised activity of aviation.

Cabotage in its original maritime usage referred to carriage between two places within a geographical unit by earthbound vehicles. The essence of this cabotage however, was its parochial as opposed to international application and this was based on the recognised right of a State to reserve such carriage to its own ships. This restrictive nature of cabotage in maritime law is an exception to the general rule of the freedom of the seas.

The first paper read at the 1876 meeting was by D. S. Brown, his fifth paper to the Society, entitled “ The Advantages of employing power for aerial propulsion in an intermittent manner, and on the soaring of birds.”

Brown was silent on the advantages of intermittent application of power for flight, and was not much impressed by Sir George Cayley's ideas about birds soaring in upward currents of air reflected from cliffs, hills, and so on. But he spoke with obvious knowledge of the effects of increased size on a weight-strength ratio in the light of the cube/square law.

James Armour, whose paper, “ Wings for Men,” filled fifty pages of small type in the 1873 Annual Report, presented a further paper on the subject, read this time by Brearey in the absence of the author, entitled “ Air Compression under Wingplanes.” James Armour was a good engineer, and had to confess that though he argued on general principles about the supporting forces of an aeroplane in full flight, there were many unknown parameters.

Thomas Moy's declaration at the 1873 Meeting of the Society, that he and his partner Shill were constructing a large-scale model of a flying machine, roused considerable interest. Twelve months later, at the Meeting held on 15th May 1874, he said:

“We have not got on so fast as we had hoped. Various difficulties had arisen which had to be mastered one by one as they cropped up. As their machine was only a working model, the aeroplane required to be made of some light material. Some time ago I was trying to get thin steel rolled and corrugated but I was unable to get anything suitable. I next tried a fine kind of brown holland for our wing sails, but found this would not take the curves kindly, but got into wrinkles. I am now making use of thin pine lathes nicely planed and fitted so as to form a sectional screw surface, and I think they would answer very well, and would form the nearest approach to a perfect screw that can be obtained.”

The purpose of this contribution is to draw attention to some of the major areas in A.T.C. where there are difficulties and to outline the steps that are being taken to surmount them.

Before looking quickly at some of the technical problems I think it might be worth taking a brief look at two important aspects which surmount the whole scene: namely the Civil/Military situation and the birth of Eurocontrol.

The relationship between service and civil authorities on A.T.C. matters springs directly from the differing requirements of the two sides for air space. The increasing use of jets by civil operators has made this problem more acute because now the Service aircraft not only have to be shepherded up through the commercial traffic, but also protected from them in the upper levels. The requirements of research aircraft are also stringent and yet again, different.

In many internal flow problems, the velocity profile of the flow in a duct of a given cross section is of major importance. In combustion chamber flow, for example, the entry velocity profile is a critical factor in determining the relative amounts of primary and secondary combustion air. Further, in the flow in an axial compressor, the peaked velocity profile between the root and the tip of the rotor blades has a marked effect upon the design of the blading. Recent work by Zanker has shown the effect of variation in velocity profile upon the accuracy of orifice-plate flowmeters.

The Rayleigh-Ritz method for approximate solution of equilibrium or stability problems in elasticity is based on the theorem of the minimum of the total potential. Hence the assumed displacements have to satisfy only the geometrical boundary conditions of the problem in order to be admissible. The displacements are expressed as a series of suitable chosen functions, called co-ordinate functions, multiplied by parameters which are determined by the minimisation procedure of the method. Except for the essential requirement that these co-ordinate functions have to satisfy the geometrical boundary conditions of the problem, no general rule for their choice can be given, and experience and physical considerations have to be relied upon.

The argument for the supersonic transport seems to run as follows: it offers a new and faster way to go places; it might not cost more to do so; it ought to create new wealth, and its influence on human affairs, although not clearly foreseeable, surely will be beneficial. There is a certain amount of evidence to warrant optimism; there are issues of national prestige and well-being; the technical challenge is exciting; so “ Let us somehow find finance and proceed.”

Operators agree that the design and operational problems of supersonic aircraft, one of the possible great advances in transport, are complex and interesting; they might also speculate on its likely social implications, though this is an unrewarding pastime. The operators accept that the aircraft probably will be developed, for it is as much a challenge of the times as have been all the great innovations of routes and vehicles from Columbus right through to our day; but as has always been the case, before any commitment, they must seek assurance of ultimate economic soundness.