The 773rd Lecture was read before the Society on the 17th March 1949 at the Institution of Civil engineers, Great George Street, S.W.I. Dr. H. Roxbee Cox, B.Sc., D.I.C., F.R.Ae.S., F.I.Ae.S., President of the Society, introduced the lecturers, Mr. G. C. I. Gardiner, A.F.R.Ae.S., Chief Engineer and Mr. J. Mullin, B.Sc., A.F.R.Ae.S., Chief Aerodynamicist of de Havilland Propellers Ltd.

The 776th Lecture was read before the Society on the 31st March 1949 at the Institution of Civil Engineers, Great George Street, London, S.W.I. Dr. H. Roxbee Cox, B.Sc, D.I.C., F.R.Ae.S., F.I.Ae.S., President of the Society, introduced the lecturer, Dr. P. B. Walker, M.A., F.R.Ae.S., Head of the Structures Department at the Royal Aircraft Establishment.

The paper discusses the application of wind tunnels to aircraft design and consideration is given to the potentialities and limitations of types designed specifically for industrial use. Arguments affecting the choice of type, size and speed are stated and a detailed description is given of a particular tunnel which has very steady and even flow with a reasonable turbulence level. This description covers the aerodynamic and engineering design, the electrical driving arrangements and the six-component automatic balance.

A description is also given of a new type of high speed tunnel which has recently been put into operation. This is of the simple straight-through type and is driven by a jet engine acting as an ejector pump; the exhaust heat is used to control humidity and prevent condensation in the working section. This tunnel reaches a Mach No. of 0.9 when empty, and over 0.85 with a model in place. The Reynolds No. is 1.6 x 106 for a three-dimensional half model and 5 x 106 for two-dimensional wings.