The 1346th Lecture to be delivered before the Society, “Structural Design of the X-15”, by Dr. R. L. Schleicher, was given on 18th April 1963 in the Society's Lecture Theatre with Mr. B. S. Shenstone, M.A.Sc, F.R.Ae.S., F.A.I.A.A., F.C.A.S.L, in the Chair. Introducing the lecturer, Mr. Shenstone said that Dr. Schleicher was Manager, Structures Engineering, at the Los Angeles Division of North American Aviation, Inc., and he had been with the firm since its inception in 1934. Dr. Schleicher was a graduate of Villanova University and held a degree of B.S. in M.E., and his D.Sc. had been conferred on him in 1957. He had nearly 34 years experience in aircraft structures engineering beginning in 1929. He had been Chief Structures Engineer at North American Aviation, Inc. on all the aircraft designed and built by the Los Angeles Division of that company and that included the X-15. He was a member of the Society for Experimental Stress Analysis and an Associate Fellow of the A.I.A.A. From 1943 to 1958 he had been a member of a number of NACA (now NASA) Committees and Sub-committees and had written a number of technical papers. He was currently serving on an Advisory Committee on Aircraft Structures for the U.S. Air Forces.

They were indeed grateful to Dr. Schleicher for coming all this way to lecture.

The 55th Main Lecture to be given at a Branch centre, “Light and Executive Aircraft and Their Future Prospects in the United Kingdom,” by F. H. Robertson, A.F.R.Ae.S., Chief of Preliminary Design, Short Bros, and Harland Ltd., was held under the auspices of the Christchurch Branch on 12th December 1962. Mr. E. W. J. Gray, F.R.Ae.S., President of the Christchurch Branch, opened the proceedings by welcoming the President and Secretary of the Society and visitors from the Society's branches at Luton, Bristol and Cheltenham as well as visitors from Shoreham. Mr. Gray then asked the President, Mr. B. S. Shenstone, M.A.Sc, F.R.Ae.S., F.A.I.A.A., F.C.A.S.I., to preside for the rest of the meeting.

Introducing the lecturer, the President said that Mr. Robertson had spent five years with Vickers-Armstrongs Ltd., three in the works and two in the D.O., and then joined Hawker Aircraft in 1934 as a junior draughtsman; in 1936 he had gone to Aeronca Aircraft Ltd. for a year and in 1937 had joined Miles Aircraft Ltd. as senior draughtsman, becoming Chief of Experimental Design. From 1946-1952 he had been with Saunders-Roe Ltd., where he became Chief Project Engineer, and in 1952 had joined Short Bros, and Harland Ltd. After several years as Chief Project Designer, he became the Company's Chief Designer, Light Aircraft in 1959. He was now Chief of Preliminary Design. He was sure that Mr. Robertson was known to many of them, either personally or from things he had written, and they would know that he rarely said anything with which they could all agree. He thought that what Mr. Robertson would say in his lecture would be of the same order.

For many years, studies of various light aircraft designs have been carried on by the Lockheed-California Company in search of a vehicle that had the potential of truly generating the “air age”—a vehicle which would perform a useful service to many people, in many jobs. Shortly after the Second World War, these studies were directed along the lines of present-day light aeroplanes, but were eventually discarded upon recognition of the limited utility of these vehicles when related to general public acceptance. However, in 1959, spurred by recent developments in VTOL craft, the Lockheed research team again raised the question, “Is it possible today to develop a vehicle of low cost and with sufficient utility to reach the mass market?”

The basis of the procedure described in the paper is the replacement of the stiffeners by an approximately equivalent system of line springs. One of two methods may then be used to determine the natural frequencies. A rectangular plate with edge stiffeners, point-supported at the four corners, is used to demonstrate the application of the Rayleigh-Ritz method. Numerical results obtained are compared with known approximate solutions based on finite difference equations. A Holzer-type iteration is employed in the case of a plate with parallel stiffeners, where the two edges perpendicular to the stiffeners are simply supported, the other two edges having any combination of conditions.

In most aerodynamic problems the speed of sound, a, is naturally taken as or where p, ρ and T are static values, γ is the specific heat ratio and R is the gas constant. This particular speed, however, is specifically that of plane waves advancing uniformly into an infinite expanse of a homogeneous medium. There are many other situations where the medium is bounded or inhomogeneous, for instance, in which small pressure waves do not propagate at this speed relative to the medium. Phenomena such as choking can then be shown to occur, not when the flow velocity is exactly equal to but when it reaches the new wave speed appropriate to the local circumstances.

In a technical note in the January 1963 Journal J. Dunham shows a method to determine the choked condition in a cylindrical ejector nozzle which in a simpler way leads to the same expression that has been derived by H. Pearson et al. of Rolls-Royce Ltd. Although Mr. Dunham states it is unnecessary to use the “maximum-discharge” principle, his derivation in the case of two streams in a common passage is, by the assumptions he makes, based on just this principle.

The problem considered is that of a circular plate which is supported along an internal concentric circle and subjected to uniform pressure over the area bounded by the support line; the outer edge of the plate is free. This form of loading and support is used in the testing of glass panels, where the rigidity of the panel is determined from a measurement of the central deflexion. However, the formula in current use does not allow for the stiffening effect of the overhanging outer annulus.

It is shown that by combining the dependence of boundary layer heating on local flow conditions with the lifting characteristics of hypersonic wings a simple relationship between wing loading and surface temperature can be derived. This replaces the common concept of an altitude/Mach number flight corridor through which hypersonic flight appears possible without exceeding an acceptable surface temperature, and indicates that flight beyond Mach 6 will in fact require considerable material or cooling developments.

A method of improving pressure distributions predicted by inviscid theory over two-dimensional aerofoils at transonic speeds taking into account shock-wave turbulent boundary layer interaction as obtained in the case of the flat plate is described.

The method was applied to a non-lifting circular arc aerofoil of eight per cent relative thickness. The shock wave location, pressure distribution and drag coefficient were calculated and compared with experimental and inviscid theoretical results.

It has been found that the method gives results which are consistent with experimental results in various aspects.