The Forty-Ninth Wilbur Wright Memorial Lecture, “Researches in Space Flight Technology,” was given by Dr. Abe Silverstein, B.S., F.R.Ae.S., F.I.A.S., Director of Space Flight Programs, N.A.S.A., before a large and distinguished audience in the Lecture Theatre, 4 Hamilton Place, on 12th September 1961. Air Marshal Sir Owen Jones, K.B.E., C.B., A.F.C, B.A., D.I.C., F.R.Ae.S., M.I.Mech.E., R.A.F.(retd.), President of the Society, presided. The Lecture was given during the Eighth Anglo-American Aeronautical Conference, and the President was accompanied on the platform by Dr. H. Guyford Stever, President of the Institute of the Aerospace Sciences, and Head of the Mechanical Engineering Department at the Massachusetts Institute of Technology, and Air Commodore W. P. Gouin, R.C.A.F., a member of the Directing Staff of the National Defence College, Canada, and President of the Canadian Aeronautical Institute.

As has become the custom, before the Lecture was delivered, the President presented the awards made by the Council for 1961 for outstanding contributions to aeronautics. The list of awards presented on this occasion was published in the June 1961 Journal (p. XXVII).

Introducing the Lecturer, the President reminded the audience that the first Wilbur Wright Memorial Lecture was given in 1913 by Horace Darwin. The list of Lecturers, as they would see in their programmes, contained the names of eminent scientists and engineers from America and from this country. They had with them on this occasion a number of those who had given the lecture, among them their very distinguished visitor, Dr. von Kármán.

This lecture had been given alternately by a lecturer from this country and one from the United States, with one exception. On one occasion it had been given by the late Professor Ludwig Prandtl—a name well-known to them all.

Now Dr. Abe Silverstein was to give the 49th Wilbur Wright Memorial Lecture and had chosen as his subject “Researches in Space Flight Technology.” Dr. Silverstein was Director of Space Flight Programs at the National Aeronautics and Space Administration headquarters in Washington. Before the N.A.S.A. was established on 1st October 1958, Dr. Silverstein had been Associate Director of the Lewis Flight Propulsion Laboratory, Cleveland, a research centre of the National Advisory Committee for Aeronautics, which formed a nucleus of the N.A.S.A. Dr. Silverstein joined the N.A.C.A. in 1929 and spent much time at the Langley Aeronautical Laboratory on wind tunnel design and high speed research until he was transferred to the Lewis Laboratory in 1943 to direct research at the Altitude Wind Tunnel. He had done pioneering work on large scale ram-jet engines and on the supersonic wind tunnels at Lewis.

If man's desire to fly was not totally inspired by the flight of birds at least his early attempts at heavier-than-air flight were a direct imitation of birds. To the earliest known aviators two features seemed indispensable in any flying machine, wings that flapped, and wings covered with feathers. The former at least seems reasonable, but no attempt was made to discover the purpose of feathering a bird's wing and feathers were used simply to give the flying contraption the appearance of a bird. As we shall see later these factors probably delayed the advent of sustained flight—not necessarily powered—by many years.

Imagination has always, in the past, attributed the bird with greater powers than it really possessed. Many early flying machines were designed as chariots borne by as few as six doves—powerful indeed! Its powers to soar so high that it became lost to sight gave it the status of a semi-deity, from which came the mariner's faith in the albatross, perhaps.

The tailless aircraft configuration is relatively rare in the field of aircraft design and for many years was regarded as a “freak” design. It is intended to trace the development of tailless and flying wing aircraft and to outline the major problems in control and stability.

First it is necessary to arrive at an arbitrary definition of the term tailless aircraft. Later an attempt will be made to classify the different tailless types in detail, but for the moment it is sufficient to regard a tailless aircraft as “an aircraft having no auxiliary horizontal stabilising plane, deriving lift and controlling moment solely from the main plane.” This definition, as it stands, includes what are often termed flying wing aircraft.

As at present envisaged the man powered aircraft will more closely resemble the glider than any other type of flying machine. Because of this it was suggested that a paper on the relationship between gliding and man powered flight might be of value.

The papers which have been read to the Group have dealt with the aerodynamic, physiological and engineering aspects of the problem and they show that a man powered aircraft capable of flight just clear of the ground is a possibility.

Before undertaking the detail design a fourth aspect—pilotage—must be considered. It is in this field that the experience which exists in flying gliders is applicable and should be used.

A survey is made in retrospect and prospect of the field of VTOL aircraft. The helicopter and the new VTOL aircraft, although historically separated and differing in appearance, belong to the same family of VTOL aircraft. The dominant parameter in this family is the disc loading, giving the two fundamental types of actuator disc—open disc or rotor and buried disc or fan. Noise and vibration criteria are discussed. The rotor is subject to fundamental aerodynamic limitations, which give speed limits for the pure rotor as well as the rotor compounded with a fixed wing. Rotors are subject to scale effects which limit the economic size of helicopters. Engine requirements for helicopters are discussed. There are three basic types of helicopter. Their characteristics, economics and uses are examined.

Downward deflection of a propulsive jet may be employed to augment aerodynamic lift in an advantageous manner. In each situation there occurs a simple optimisation when the losses due to reduced propulsive efficiency are contrasted with the gains which accrue from jet lifting. Typical cases will be considered here for wing dominant configurations, i.e. cases where the lifting surfaces contribute most of the drag, with the body contributing but a minor effect. Variable geometry of both airframe and engine is implicitly assumed so that results may be applied to preliminary design studies which will determine the relative propulsion system size and wing area.

When a circular plate of constant thickness is simply supported on a concentric ring and is subjected to a uniform normal pressure, there is a radius for the supporting ring giving optimum bending stress conditions in the plate. Assuming the plate deflections are small, it is concluded that the required supporting ring radius varies between 70·1 and 73·0 per cent of the outside radius of the plate, depending on the value of Poisson's Ratio for the plate material.

The lateral buckling of thin deep beams when subjected to a transverse loading system inducing bending initially in the plane of maximum flexural stiffness has been analysed on the assumption that the direction of application of the loads remains unchanged during small deformations of the beam (see, for example, treatments in Refs. 1 and 2). A typical case of a beam so loaded is illustrated in Fig. 1.