The Fifty-First Wilbur Wright Memorial Lecture, “Man in Military Space”, was given by Professor C. D. Perkins, Chairman of the Department of Aeronautical Engineering at Princeton University, on 23rd May 1963. Professor A. R. Collar, M.A., D.Sc, F.R.Ae.S., F.A.I.A.A., F.C.A.S.I., President of the Society, was in the Chair. Professor Collar presented the Lawrence Hargrave Memorial Lecture Medallion to Professor A. V. Stephens on behalf of the Melbourne Branch of the Australian Division. He explained that Professor Stephens had delivered the first Lawrence Hargrave Memorial Lecture in 1956 when he was the Lawrence Hargrave Professor of Aeronautical Engineering at Sydney University, but the Australian Division had not then had the Medallion struck. Professor Stephens was now Professor of Aeronautical Engineering at Queen's University, Belfast.

A review of the various means of producing vertical take-off is made and the salient advantages and disadvantages of each type discussed. The place of the vertical take-off aircraft in the air transport picture is considered and the optimum type of aircraft for each role suggested.

I have approached this topic from the point of view of an airline, but the conclusions may be of value over a number of industries. In order to make the approach clear, it is worth defining some terms and also giving a simplified map of the subject.

I have referred in a number of places to “operational” engineering as opposed to “design and manufacture”; the term operational used in this sense should be understood to cover any activity based primarily on the use of machines to produce a service or material of some kind, rather than the design and creation of machines themselves. For example, transport as a whole would come in this category, as would the distribution of goods, the distribution of power in the form of electricity, and possibly mining operations and the production and distribution of crude petroleum.

The invitation to read this, the Ninth Barnwell Memorial Lecture, gives me the opportunity of acknowledging publicly the friendship and encouragement I used to receive from that great and kind gentleman. For several years before his death, he accorded me the privilege of a weekly meeting, and although I was in every way very junior, he invariably treated me as a friend as well as a colleague, thereby adding affection to the deep respect I felt for him.

I do not recall any details of our discussions of gas turbines, although I am certain we did review their possible advent on more than one occasion. Had he lived to see them, I am sure our efforts would have received his encouragement and support.

Incompressible turbulent flow in smooth pipe bends of circular-arc curvature and constant cross section is discussed. The effects of bend angle, radius ratio, duct cross-sectional shape and Reynolds number are considered. Particular attention is paid to the influence of the tangents on the flow and losses in a bend. In addition consideration is given to the definition and measurement of the bend loss.

A correlation of experimental pressure loss data is made. It is shown that large variations in experimental results, which cannot be ascribed to the effects of geometrical parameters or Reynolds number, are accounted for by the effects of the downstream tangent and position at which the pressure measurements were made. The inadequacy of existing experimental information is an obstacle to the presentation of comprehensive data on the effect of geometrical parameters on bend losses.

Graphical and experimental methods exist for the determination of the local shearing stress and heat flux on the boundary of a duct of constant cross section in a fully developed turbulent flow. While the graphical method (see for example Ref. 1) is simple to effect, the premise on which it is based is questionable and even so a high order of drawing accuracy is necessary for reliable results. In the graphical method, it is assumed that there is no turbulent stress on surfaces which are perpendicular to the w-velocity contours (see Fig. 1). The shearing forces on the elemental area which is subtended at the boundary are then equated to the difference between the pressure forces acting over the elemental area of the duct cross section. This is a clever technique, but the use of surfaces across which the w-velocity gradient is zero for the calculation of the boundary stress needs more justification. Similarly, for heat flux distribution by a graphical method, it is difficult to determine the planes in the duct across which there is no turbulent heat transfer. As for the stress, surfaces across which there is no temperature gradient are not necessarily coincident with surfaces of zero heat flow. For the experimental determination of the wall stress, the ingenious Preston tube is available, but for the heat flux there is no simple counterpart. Heat meters (and their associated instruments) which are sometimes used are difficult to manufacture and their data must be treated with care.

The problem of two identical circular holes in an infinite sheet has been solved by Ling using bipolar co-ordinates and taking advantage of the double symmetry.

The case of any two unequal holes is of interest in that one common situation is that of a small circular hole close to a relatively larger one. In this case it is tempting merely to use the classical single hole solution, first for the larger hole and then for the small hole situated in the “uniform” stress field produced by the larger one. The accuracy of this simple method of superposition is examined.

The notation of Muskhelishvili is followed where the problem consists of finding two functions of the complex variable z=x+iy which are analytic in the region and satisfy the boundary conditions on both holes and at infinity.

For a given plate and loading the optimum supporting ring radius is shown to be approximately 0·677a, there being a slight variation with Poisson’s ratio.

The “edge square” condition, i.e. zero slope at the circumference of the plate, is also investigated. It is satisfied by a ring radius of , a result which is independent of Poisson’s ratio.

Macaulay’s brackets are used in the analysis as an example of their value in circular plate problems.

The toepler schlieren system of wind tunnels is usually designed in such a way that an image of the flow in the test section can be formed in a camera for taking flow pictures. For visual observation, a mirror is inserted in the light beam and the image is projected on a screen. When a photograph or film record of the flow is desired, the mirror is removed by some quick-acting mechanism to allow the light beam to enter the camera. Especially in the case of non-steady flows, the time lag involved in removing the mirror can prove to be a drawback. An interesting pattern observed upon the screen may have vanished by the time the light beam is switched over to the camera. At the same time the image disappears from the screen, leaving the operator in doubt whether or not the pattern lasted long enough to be recorded by the camera. In this note a very simple arrangement of the schlieren system is described, which gives simultaneously an image on the viewing screen and in the camera. So far as the author knows, it is not applied elsewhere. The method consists of the use of a mirror knife edge instead of the usual knife edge.