Trends in Aeronautical Science and Engineering: SynopsisAuthor(s): Arnold HallSource: Notes and Records of the Royal Society of London, Vol. 16, No. 1, The TercentenaryCelebrations (Apr., 1961), pp. 49-50Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/530761 .

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49

TRENDS IN AERONAUTICAL SCIENCE AND ENGINEERING

Tercentenary lecture delivered by Sir Arnold Hall, F.R.S., at 10.15 a.m. on Monday 25 July 1960 at the Royal Institution

SYNOPSIS T HE Lecture reviewed some of the advances in scientific understanding

which had influenced aeronautical engineering in the past ten years, and are likely to influence it in the coming decade.

The shape of aircraft had changed from the traditional straight wing and tail configuration to the swept-back wing, and delta-wing form. These

changes were guided by understanding of the influence of compressibility in the air, and of the effects due to the presence of shock waves at speeds near and above that of sound. Particularly significant among these effects is the inter- action between shock waves and the boundary layer, which has strong influence on the lift and drag forces in steady flow, and introduces unsteady flow effects which in some circumstances can be self-exciting. Several of these effects were illustrated, and discussed and the design procedures to bring them under control outlined.

The development of both first and second order theories dealing with the ratio of lift to drag attainable in complete aircraft configurations were outlined, and their effect on design-and particularly that of the procedure known as 'the area rule'-were considered. The inter-relation between these theories and the shapes necessary to secure aerodynamically efficient aircraft were considered.

The development of aerodynamic theories concerned with flows at speeds large compared with that of sound was discussed. In these circumstances, the generation of high temperatures leads to dissociation of the gas, which can therefore no longer be considered as a continuous medium. There are large interactions between the boundary layer and the external flow, and magneto- aerodynamic effects become of some significance due to ionization of the gas. The state of the science was reviewed, and the likely impact on engineering considered.

The demands of aerodynamics for shapes providing stable and efficient

flight have themselves presented new problems in structural design and in the use of materials. This, and the need to derive strength at lighter structure

weight, have led to many advances both in structural theory and in the tech-

nology of manufacture. These points were illustrated by a brief review of the

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50

technological progress in the use, for example, of large forgings, large area milling and glueing.

Whilst there has recently been much advance in the field of metal physics, so that the simpler mechanical properties of materials were now understood, the more complex properties such as fatigue and creep were less well grasped. Recent work in these fields was discussed and the likely implications in aero- nautical engineering considered. The advances made in design techniques to permit control of fatigue were outlined, and in particular an outline given of the means used in design to ensure either a minimum safe fatigue life, or the ability, if failure occurred, to fail in a safe way.

The means used in the design of power plant, and particularly turbine and rocket engines, to achieve greater power output at lower plant weight and bulk were considered in relation to advances in high temperature materials, and in the understanding of the aerodynamic and thermodynamic problems of rotating machinery. It is now possible to achieve power to weight ratios wlhich permit the use of engine thrust to lift, as well as to propel, aircraft. The probable influence of these matters on aircraft performance and particu- larly on the ability to rise vertically, or use short runways, was analysed. There are new possibilities for amending the airflow around the wings of aircraft to advantage. These derive from a growing ability to provide large masses of gas from relatively light weight power plant.

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