The 988th Lecture to be given before the Society and the 25th Main Lecture to be held at a Branch of the Society, “ Problems Associated with the Production and Use of Wrought Aluminium Alloys,” by G. Forrest, B.SC, A.M.I.Mech.E., A.F.R.Ae.S., and K. Gunn, B.Sc, A.R.S.M., was held under the auspices of the Belfast Branch on 5th April 1956. Mr. D. Keith-Lucas, F.R.Ae.S., Chairman of the Belfast Branch, opened the proceedings, and Mr. E. T. Jones, C.B., O.B.E, M.Eng., F.R.Ae.S., presided for the rest of the meeting.

Mr. Keith-Lucas (Branch Chairman): This was a great occasion for the Belfast Branch because for the third time they were honoured to be the hosts of the parent Society, the Royal Aeronautical Society. It was with great pleasure that he welcomed their guests. First of all, Mr. E. T. Jones, the President-elect of the Royal Aeronautical Society, Dr. Ballantyne, the Secretary, and Mr. Dunsby and Mr. Simmons, both of the Technical Department, of the Society. The President, Mr. N. E. Rowe, and the Chairman of the Branches Committee, Mr. Handel Davies, had both sent their sincere apologies that they were unable to be present.

He would also like to extend a special welcome to three members of the Preston Branch, Mr. Turner, Mr. Swales and Mr. Dyson. They were rather “ out on a limb” in Belfast, rather far from other Branches and they did appreciate this neighbourly gesture from the Preston Branch. He would also like to welcome their own President of the Belfast Branch, Sir Matthew Slattery, and their Vice-President, Mr. C. P. T. Lipscomb.

But this was essentially a Royal Aeronautical Society function and not a Belfast Branch function. Therefore he would invite Mr. E. T. Jones, the President-elect of the Royal Aeronautical Society, to take the Chair and to conduct the meeting.

Mr. E. T. Jones: It was a great pleasure and honour to be in Belfast that evening deputising for Mr. Rowe. They had already heard from Mr. Keith-Lucas that Mr. Rowe was unable to be present and he had asked him also to express his regrets.

People working in aeronautics were sometimes liable to overlook the fact that materials had played a tremendous part in the advancement that they had achieved. They knew that the aerodynamicist, the structural engineer, the propulsion engineer, had all made their mark on the progress of aviation but they must not forget that materials had forged a very great key towards the progress which had been made. Indeed he recollected that Sir Harry Garner, in his Wilbur Wright Lecture in 1952, made the statement that he doubted whether the Aircraft Industry today could make a much more forward aeroplane than the Wright Brothers did in 1903 if they were confined to the use of the same materials and to the same stalling speed. He thought that statement would have been a very profound one even if stalling speed had been left out. If one considered the materials that people in those days had to work on it was wonderful that they flew at all. Thus he thought it was fitting that they should have a lecture of the kind Mr. Forrest and Mr. Gunn were to give.

He had a pleasant duty to introduce the lecturers. Mr. Forrest was educated at London University and joined the National Physical Laboratory in 1925, or thereabouts, in the Engineering Division. In 1936 he joined the Northern Aluminium Company and he later transferred to the Aluminium Laboratories Ltd. He was now an Associate Director of Research in the Aluminium Laboratories Ltd. at Banbury. Mr. Forrest had impressed upon him that he should make a point of saying Banbury because there were three Laboratories of the firm. Mr. Gunn was educated at the Royal School of Mines. He joined the Northern Aluminium Company in 1944 and he too transferred to the Aluminium Laboratories in 1946. He did not know quite how they proposed to deal with the Lecture, but he thought that Mr. Forrest would read it and both would be available to reply to the questions.

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.

Supersonic speeds of flight have brought thermal problems due to the kinetic heating of skin materials. These materials, generally metallic, suffer loss of strength and stiffness with increase in temperature and a knowledge of changes in value of these properties at elevated temperatures is a pre-requisite to a design study. More particularly for stress offices the compressive stress-strain curves are required from which are derived tangent- and secant-moduli used to predict buckling in components. A fixture has therefore been developed for testing under edgewise compression sheet materials up to temperatures of 400 °C.

A new proof is given of a method whereby records of the transient vibrations of linear systems can be analysed to give the damping factor and frequency of each mode of vibration associated with the motion. The method is applicable to acceleration, velocity or displacement records, and as the amplitude of each mode can be found, by using a suitable number of pickups, the normal modes of continuous systems may also be determined. Obvious applications lie in the analysis of flight flutter test data, and of the transient responses of servomechanisms.

During the past hundred years much data on the fatigue behaviour of a wide range of materials has been accumulated and it is now well known, as a result of service failures and laboratory tests, that stress concentrators whether mechanically formed or inherent in the material, can cause serious reductions in endurance.

The work described in this note forms part of a project being conducted at the Aeronautical Research Laboratories, Melbourne, Australia on the effect of stress concentrations on the fatigue properties of materials. The primary aim of the project is to establish a series of fatigue curves for different materials under a wide range of theoretical stress concentration factors and to attempt to find a basis on which to assess the notch sensitivity of different materials. The first investigation was carried out on 24S-T aluminium alloy and tests on two additional aluminium alloys, annealed copper and an alloy steel are in progress.

Simple means of checking contractants has been devised which is considered essential to a computor.

In a recent paper Macmillan describes the method of contractants as applied to the evaluation of determinants. The method is essentially based on the extensional identity

Now, any determinant of order n may be expressed as a determinant of order n - 1, all of whose elements are third order determinants. This process is now repeated (n - 2) times until the value of the original determinant is obtained.