High temperatures affect buckling because the properties of the materials change and because thermal stresses and creep develop. A survey is given of the known solutions of problems arising in consequence of these phenomena and new theories of the creep buckling of columns and of thin circular cylindrical shells are presented.

The formation of shock waves as a limitation in aircraft design has been considered only, as far as the author knows, in the cases of wing sections at low operating lift coefficients and of the airscrew efficiency. There is, however, a further limitation for high flying aircraft in that the small air density causes the aircraft, even at the stall, to travel at a value of Mach number (V/a) which will cause a shock stall to form on the wing. In some cases the aircraft will be able to prevent this shock stall at high C L by flying faster, but in others, due to high wing loading, the wing sections will be shock stalled at all C L values and the only remedy will be to decrease the wing loading.

It is indeed a privilege to be asked to deliver this, the Second Lecture inaugurated by the Royal Aeronautical Society as “ The British Commonwealth and Empire Lecture.” I feel particularly gratified at being asked to follow in the wake of so distinguished a pioneer in Commonwealth Civil Aviation as Mr. Hudson Fysh, who delivered the Lecture last year. I am, however, at the same time distressed by the sequence, because after reading the outline of experience and achievement which was presented in such graphic form by Mr. Hudson Fysh, I realise acutely that I cannot offer you anything comparable. There can be from myself no first-hand account of pioneering or achievement, neither am I a competent spokesman for any of the organisations which have played so great a part in building up the British contribution to world aviation.

In speaking to you to-night on the Economics of Air Line Operation, I propose to speak primarily from the viewpoint of the operator of an internal air line. I do not mean, by that, that I shall confine my remarks strictly to the various problems encountered by my own particular company, nor do I mean that any opinions which I may express will, of necessity, be of interest only to operators of internal services. On the other hand, I do not intend to venture into the realms of very long distance air routes, such as Empire routes, many of the problems connected with which have already been dealt with in considerable detail by Mr. Woods Humphrey in his interesting series of articles in The Times in May of this year. Such small experience as I have had so far with international flying has convinced me that the political difficulties, which are undoubtedly encountered by many of the national air transport companies, must force upon them policies other than those dictated by strictly economic requirements, and in consequence, must render a true comparison between their operation and purely European flying almost impossible.

When tip–mounted engines are employed on a helicopter rotor, such as lightweight turbines, ram-jets or pulse-jets, the action of the fuel flowing along the blade gives rise to a power loss. For a ramjet helicopter this is of the order of 6 per cent, of the total power requirement of the rotor system. In addition, if the fuel injection nozzles in the combustion chamber face upstream this leads to an additional power loss of 1-6 per cent, of the total power, and it is evident that these effects should be allowed for in helicopter performance calculations. It is shown for a ramjet helicopter that the total spraying and centrifugal pumping loss is of the same order as the total transmission and tail–rotor power loss for a conventional shaft-driven helicopter. The same effect can be demonstrated for pressure-jet rotors, where it has an even greater magnitude.