The Melvill Jones equation for the profile drag of a single aerofoil is adapted to the case of an aerofoil in cascade, where the static pressure may be permanently raised (compressor), or lowered (turbine). A simplified procedure for measuring the drag is then described, assuming that the total pressure wake has the form of an error curve. A table of multiplying factors is given, for compressible flow up to an outlet Mach number of 0·9. Many published measurements of cascade drag have ignored this factor, with a consequent error of up to 25 per cent.

The following problem constitutes a minor delay in ultimate production, yet considerable time and effort and manpower are duplicated at present in finding a practical solution to what is really a repetition of Drawing Office calculations.

The problem is that drawings calling up various machined fittings often lack any reference to “practical” measurements by which the operator, the toolmaker and the Inspection Department may ”set-out ” and check the work concerned.

The coriolis effect is a change in the motion of a body passing over the surface of the Earth due to the motion of the Earth itself. The effect may be manifested either as a horizontal acceleration, or, in the absence of the acceleration, as a deflection of the course. The acceleration, which appears in controlled courses such as those of aircraft, usually appears and is significant as a deflection of the vertical. This acceleration appears whenever a body, such as an aircraft, is forced to follow a great circle path over the Earth. The deflection of the course of a moving body appears alternatively whenever the body moves freely in its inertial path above the surface of the moving Earth.

Never before in the history of aviation has the test pilot been so important as he is today. Now that military aircraft are travelling faster than the speed of sound and climbing to over 50,000 ft. in a matter of seconds, with powered controls, pressurised cabins, ejector seats, special oxygen equipment and such like being the order of the day, it is little wonder that the human being whose job it is to fly in these modern high-speed missiles requires more than ordinary Service flying experience if he is to take his place successfully in the team with today's technicians and designers. The day has long since passed when any good pilot could set himself up as a test pilot. The term “test pilot” covers a large field of work, testing aircraft and the complicated equipment fitted in the new revolutionary designs being produced.

This note describes apparatus which has been used for remote measurements of forces and moments on models on the Whirling Arm at the National Physical Laboratory. Good short-term stability, independent of mains frequency and voltage variations, has been obtained with simple apparatus. Descriptions are included of the differential inductance bridge, a stable 1 kc./sec. oscillator used therewith, and a regulated power supply for the oscillator. General comments are made on problems involved in the force and moment measurements.

It is often supposed that the flow of gas from a compressor is, or should be, stable if the pressure-flow characteristic has a negative slope. It is shown here that this is only true if the Mach number is zero, i.e. if the machine is pumping a liquid. As the Mach number is increased towards one, a third regime becomes more and more important, wherein disturbances give rise to damped oscillations. The flow in this regime is stable in the mathematical, but not in the physical sense, since disturbances can occur all the time.

Two conclusions can be drawn. First, although compressors with “flat” pressure-flow characteristics have a wide range of stable flow at low speeds, they are poor at high Mach numbers, where the flat part cannot be used. Next, the actual points on the characteristics at which the flow becomes unstable are not fixed, but depend to a large extent on the steadiness of the entry flow.

Vortices are not usually treated by potential theory, but the latter is so well known and of such general application that there seem to be advantages in doing so.

Consider first the potential function

i.e. distance from O.

There is already in existence a fair volume of work on the subject of bending beyond the limit of proportionality, most of which requires the use of actual material stress-strain curves. This note aims to examine the problem in a more general way by using an accurate mathematical form for the stress-strain curve, strain and bending moments being expressed as functions of the ratios of various properties of the material.

The value of maximum permissible fibre stress is considered in relation to current requirements for military aircraft stressing and a guide is presented for the maximum permissible bending moment in some of the more familiar beam cross sections bending about an axis of symmetry.

The Conventional method of assessing the direct costs or the aircraft type costs on a passenger mile or ton mile basis does not necessarily give a sufficient indication of the economic merit of a particular type of transport aircraft. It can be misleading when comparing aircraft of widely different design, and it does not indicate the best routes for effective airline exploitation.

The profit margin in relation to the fundamental cost or investment unit of the individual airline must be the ultimate yardstick of transport aircraft selection and this is here analysed with a view to providing further insight into the optimum conditions for potential profits. This study of the subject draws attention to the primary factors involved and suggests a criterion which can be simplified into a form valid for most airline economies.

Compressor stages are usually designed on the assumption that the gas velocity is nowhere affected by the friction at the walls. The only way in which viscosity is taken into account is in the assumed efficiency, and in a guessed “work-done factor,” which ensures that by aiming high the required work is actually attained.

It is known that the radial profile of the axial velocity component becomes more and more peaked through successive stages of a compressor, so that the assumptions just quoted become very inaccurate. It is possible that the efficiency of a stage could be raised considerably if the axial velocity profile were controlled; moreover up to 20 per cent. more work could be done if a “ work-done factor ” did not have to be applied.

The minimum comfortable cruising speed of an aeroplane depends on the complexity of characteristics for the design in question, which may be broadly grouped under the headings of stability and control, drag and propulsion.

The store of knowledge relating to such speed is composed, in the main, from experience with aeroplanes powered by supercharged reciprocating engines, for which, at the low powers appropriate to the conditions considered, the brake horsepower and drag horsepower both increase with height at roughly the same rate (constant aeroplane weight and equivalent air speed being assumed). For a turbine-engined aeroplane the brake horsepower (or thrust) decreases with altitude and it might be supposed that this difference would result in a difference between the minimum comfortable speeds of similar aeroplanes driven by turbine engines (either jet or propeller) and by reciprocating engines.

The normal functions of beam vibration may be used in series to solve statical problems of beam flexure and the recent appearance of tables of these functions has rendered this method practicable. An outline is given of the procedure.

The simple equation of free flexural vibration of beams is

1

where v is the displacement, EI the flexural rigidity andAp the mass per unit length. The separation of variables and the application of appropriate boundary conditions at the ends x = 0 and x = l, gives the following normal functions ϕ(x).

In his technical note on “Dimensions required for Inspection” (July Journal), Mr. G. A. G. Saywell stated that drawings calling up various machined fittings often lack any reference to “practical” measurement by which the operator, toolmaker and inspection department may “set out” and check the work concerned. This statement does not really do justice to the draughtsman who, in preparing the detail drawing for manufacture, has to give attention to all aspects of manufacturing.

Tests were made at the request of the Royal Aeronautical Society Structures Committee to extend the information on Data Sheet 02.09.02 from a value of the parameter.

This paper reviews work on the flexural centre of elastic cantilever beams and contains a number of hitherto unpublished results, including a formula giving the position of the flexural centre in terms of the Prandtl torsional stress function.

The appearance of the note by Jacobs has prompted the preparation of a review of this subject which is all the more desirable as several of the investigations made shortly before the 1939-45 War were never published and others, although published, seem to be in danger of being overlooked. The present paper contains a number of hitherto unpublished results. The question of nomenclature is worthy of mention since general agreement is lacking. Some of the names used are flexural centre, centre of flexure, elastic centrum and centre of shear but a complete search of the literature would probably lead to the discovery of yet other names. The terms “centre of shear” and “elastic centrum” seem vague and fail to indicate that the point referred to has any special relation to flexure. We shall here use the name “flexural centre” exclusively.