In 1931 Peters showed that flow entry conditions had a marked effect on diffuser performance. Later, Winternitz and Ramsay indicated that the pressure recovery coefficient Cp of a conical diffuser might be regarded as a linear function of β(θ/d)i for values of β(θ/d)i up to 0·1. This note draws attention to the fact that diffusers with much larger values of this parameter are of interest and presents some experimental and theoretical results. Work is continuing along the lines indicated.

We are at the moment at what is probably the most interesting phase of the battle between man and gravity. This battle has been waged since the days of the ancient Greeks when men dreamed of emulating the birds, and using various “stick and string” devices tried without success to fly under their own power.

In the present day we have much more sophisticated machines into which a great deal of careful thought and design work has gone. Much publicity and speculation is at present centred around the Southampton and Hatfield fixed-wing machines which are enjoying a certain amount of initial success. Whether either machine will ultimately be successful remains to be seen and I am sure that all of us are following their progress with interest and wish them all the best in their endeavours. These are not by any means the only two projects being pursued at present, although there is a definite preference for a fixed-wing machine.

In this note a brief description is given of some interesting results obtained in smooth pipes of circular cross section during an investigation of the steady flow losses in a 90° mitre bend at the Endicott Product Development Laboratory of I.B.M. The tests indicated that in a certain Reynolds number range the presence of a mitre bend was sufficient to cause flows of different types to exist in the upstream and downstream tangents of the bend. The definition of the bend loss in the light of this phenomenon is considered.

It is hoped that this paper will stimulate comment on similar occurrences, which would lead to a better understanding of flow behaviour in this rather neglected area of fluid mechanics.

When estimating the skin friction drag on bodies of revolution at the project design stage, it is normal practice to use an “equivalent flat-plate” method. This calculation is simple and requires little time to perform. However, in the final design stage, when more accurate estimates of the skin friction drag should be made the “equivalent flat-plate” method is still used. More exact methods, which include pressure gradient effects, are very laborious if they are evaluated by hand calculators. Even if a digital computor is used to evaluate the more exact methods, the time required to perform the calculations is considerably longer than that taken to calculate the other forms of drag. For these reasons, the simple “flat-plate” method has long held favour with designers.

The Belvedere, previously known as the Bristol 192 helicopter, was designed and developed to an Air Staff Requirement for a General Purpose helicopter for the Royal Air Force.

While the design embodied certain principles which had been well proved in the Bristol Sycamore and, while useful information had been learned about the tandem configuration from the research 173 helicopter, the design of the Belvedere was new in all its engineering aspects. The machine was to be powered by turbine engines with more than twice the installed power of the 173; it was to be approaching twice the weight of the 173. The choice was the Napier Gazelle engine—the first turbine designed primarily for helicopter use. Hence, the helicopter was of new and larger design than that which had preceded it, and the engine was also of new design and type.

There is a considerable body of literature which is concerned with plates having straightforward plan forms, for example circular and rectangular plates have been studied extensively. When the edges are irregular relatively little work seems to have been done, although plates having single notches have been studied and a useful bibliography is found in reference . As far as the present author is aware, the problem of plates built into irregular boundaries has not been tackled.

In the “Peak Amplitude” method of resonance testing the total amplitude of vibration is plotted against frequency or (frequency). The method is unreliable for systems which are heavily damped and for systems with close natural frequencies (for both of which a vector plot such as that suggested by Kennedy and Pancu should be used) but for many systems it provides a rough guide to the resonance properties. One of the principal difficulties attending the analysis of the amplitude plots is to find which part of a given peak is due to the resonant mode and which to the off-resonant vibration. In the note a method is described for analysing a peak assuming that:—

• (i) only a single resonant mode is involved

• (ii) the contribution to the amplitude from the off-resonant vibration is constant in the neighbourhood of the peak.

Using the Argyris matrix formulation a concise and definite justification for the correctness of the use of groups of unknowns in the analysis of redundant structures is given. It is shown also that to consider groups of unknowns is equivalent to changing the basic system. These two intimately related concepts are applied to the force as well as to the displacement method.

This paper presents a numerical method, derived directly from the basic differential equations of motion and expressed in the form of recurrence-matrix of finite differences, that can be generally applied to all multi-degree-of-freedom structures subjected to dynamic forces or forced displacements on any masses at any instants of time. The movements of the system may be described by any form of generalised co-ordinates.

My Company is a small firm, situated near Colchester, Essex, operating only in the United Kingdom. It is entering its sixth year of operation, and owns seven aircraft, all Tiger Moths, five Agricultural and two Club aircraft of which, generally, only four are serviceable, the remainder being on maintenance or repair— of which more later.

Our experience is probably quite different from other operators’ as a season can vary enormously from area to area, and just a few weeks of working to capacity on something that occurs locally can make all the difference between a good year and a bad one. But although differing substantially in detail, the overall pattern is probably similar.

Aircraft have been profitably employed in a multitude of forest operations in many parts of the world. Their usefulness is, of course, greatest where the forest cover is extensive and more or less continuous and where ground access is difficult. In such situations, as, for example, in parts of the American continent and in some tropical areas, aircraft have become indispensable forest tools and are used for such varied duties as the survey and evaluation of the species composition and volume of the standing crop; the detection of outbreaks of fire, disease, and insect pests; the transport of men and materials for fire fighting; the application of chemicals, in either liquid or solid form, for the control of damaging insects, fungal disease, and rodents; the application of herbicides and fertilisers; the re-seeding of cut-over areas; and for surveys of wild life resources.

In many internal flow problems, the velocity profile of the flow in a duct is of major importance. A recent survey has shown that the study of the effect of different velocity profiles on the performance of various components has been hampered because no general means of generating profiles was available.

Livesey, Parker and Jones have described a baffle specially developed in connection with gas turbine combustion chamber work, with which velocity profiles can be generated, having Vmax/Vmean ratios of up to 1·42, for an inlet profile of Vmax/Vmean = 1.15.

Using Glauert's three-dimensional aerofoil theory, an expression for the induced velocity due to the trailing vortices of an infinite cascade of wings of finite span has been derived. The reduction in the average lift coefficient due to these induced velocities has been evaluated for some cases. It is shown that for a cascade of low space-chord ratio, the reduction in lift due to the interference from the trailing vortices is quite considerable.

It is well known that the main purpose of the by-pass principle is to improve the propulsive efficiency of a simple jet engine by removing some of the energy left in the jet gases and using this to compress an extra quantity of air, known as the by-pass air, this air being ejected rearwards with the jet gases. In this way a greater mass of air is ejected rearwards at a lower jet velocity and thus a better propulsive efficiency is obtained. This is an extremely simplified view of the advantages of the by-pass engine, however, since an equivalent result of obtaining a lower jet velocity can be obtained by designing the jet engine for a lower combustion temperature. The by-pass principle is of advantage because it enables a higher propulsive efficiency to be obtained at the same time as employing a high combustion temperature and therefore a high basic cycle efficiency. If the component efficiencies of a gas turbine were 100 per cent, cycle efficiency would not depend upon combustion temperature at all, and there would thus be no advantage in principle in using the by-pass engine. In practice there would probably be some residual advantage left in that for a given thrust a lower engine weight could be obtained.

Recent lunar and planetary return vehicle studies have stimulated interest concerning the effect upon stagnation point heating due to electronic heat conduction associated with re-entry at speeds greater than 30,000 ft./sec. In order to provide experimental data for comparison with theory, a series of experiments was undertaken in which shock tube techniques were utilised for the measurement of the stagnation point heating of a blunt body over a stagnation enthalpy (Hst/RT0) range of 650 to 900, corresponding to velocities between 32,000 ft./sec. and 39,000 ft. /sec. respectively. The tests were performed in a 1·5 inch diameter shock tube with 3 foot length driver and 16 foot length driven section.

Using relations derived by Dixon and Inglis, the values of the elastic stress concentration factor for a fixed length notch in a finite width tensile strip with a varying notch end radius have been obtained in the form:

Photoelastic tests on internally notched tensile strip models showed excellent agreement with the analytical results.

The effect of wall divergence (in excess of the normal value given for compensating the Boundary Layer growth on the tunnel walls), on the simulation of Sonic flows in solid wall wind tunnels is presented in this note which is a condensed version of Ref. 1.

Recently Spreiter showed that flows with free stream Mach number one can be simulated reasonably well in choked solid tunnels. Berndt and Petersohn showed that the thickening of the boundary layer on the walls of solid wall tunnels reduced the interference considerably. Wall divergence θg in excess of the normal one of about one degree (used for Boundary Layer compensation) may lead to favourable conditions for the thickening of the Boundary Layer and this appeared to be an interesting way of reducing the interference.