The association of gas turbines with aircraft designed to make effective use of the special characteristics of jet propulsion has brought the trend of development into a state of transition and uneasy experiment. Already speeds equivalent to a low level Mach number of 0.80 have been recorded under observed conditions.

The purpose of this paper is to present the case that can be made for the tailless aircraft on the grounds of improved performance and operational suitability.

The whole field of possible investigation is not treated here with uniform thoroughness and the main reason for this is that I have only quoted detailed results for those cases which I have actually considered myself, so that in some instances the general qualitative arguments can be backed up by actual figures, whereas in others the argument has had to be confined to generalities.

A large number of individuals took part in the development and application of the methods of accident investigation and prevention outlined in the following paper. Commodore G. d'Erlanger, C.B.E., O.C. Air Transport Auxiliary, took a major part in the general evolution of the procedure; Air Vice-Marshal Sir Lawrence A. Pattinson, C.B., D.S.O., M.C., D.F.C., with his great knowledge of R.A.F. procedure, was responsible for the production of the A.T.A. manual “Instructions for Reporting Flying Accidents, Forced Landings, Aircraft Defects and Casualties”; and starting from scratch, a very competent Secretariat, consisting of Flt/Capt. G. Merton, F/O D. G. Brinjes and F/O J. W. Gibbs, were responsible for the great amount of work involved in working the machine and in the eventual production of the data and information summarised herein. The Chief Medical Officer, A.T.A., Cmdr. A. Buchanan Barbour, is in general responsible for those paragraphs of this paper covering the field of aviation medicine.

Consider the growth of the boundary layer over an aerofoil placed at high incidence, the potential flow pressure distribution of which is shown in Fig. 1. In the region AB, the flow will normally remain laminar because of the large favourable gradient, but after reaching the peak B, instability will begin. Depending on the Reynold's number and the actual adverse gradient, the boundary layer will do one of three things:

1. 1. It will separate from the surface while still remaining laminar;

2. 2. It will become turbulent (transition) and will remain on the surface, or;

3. 3. It will become turbulent and will separate from the surface a little later.

It is a great honour to have been asked by The Royal Aeronautical Society to give the foundation British Commonwealth and Empire Lecture, and I have accepted, having in mind the Australian pioneers of the air from whose past has sprung the beginning of our Australian part in the common effort of to-day.

I would like to congratulate the Society on founding this lecture, which it takes little prediction to forecast will grow into one of the most important annual aviation events in the Empire–as well as facilitating the assembling together in the Journal of information, opinion and suggestion from the four corners of the Empire. This, in itself, is only made possible by air travel, and as an illustration of what can be done, you should know that this is my third visit to this country from Australia in this year of 1945.

An analytical study of the flutter of stalled and unstalled propeller blades is recorded. The flutter of unstalled propeller blades investigated is unstable coupled flexural-torsional oscillation, while the flutter of stalled blades is assumed to be unstable torsional oscillation due to aerodynamical hysteresis, which is Studer's theory of stalled flutter.

A method of estimating critical speeds, which is within the scope of Stress Office work, is proposed and examples given.

The observed and calculated flutter speeds of propeller blades are tabulated.

(All statements made and opinions expressed represent the author's own views.)

In the design of gas turbines, the most important limitation is imposed by the materials of which the combustion chambers, guide vanes, and, most important, the turbine blading are made. Any improvement in the heat resisting properties of the materials used in the construction of these parts will immediately show as an increase in power output.

As Major Halford stated before the Royal Society of Arts in a recent lecture on the gas turbine, a gas temperature of 850°C. at the turbine blade will allow a maximum take-off thrust of 15,000 lb. for one unit, running at 6,200 r.p.m.

The present temperature reached is around 750°C, this being attained after six years of war-time development. From this it will be seen that unless the metallurgist produces a new alloy, the limit with metal blades will soon be reached. Of course, cooling of the blades could be resorted to, but this brings with it the attendant difficulties.