The force on a plane wire screen at right angles to the axis of a fully-developed, turbulent and effectively two-dimensional and incompressible jet has been determined. This study was suggested by the use of perforated surfaces in the operation of aircraft. Perforated landing and takeoff pads are used to reduce adverse ground effect, and the re-ingestion of burnt gases, on VTOL aircraft with centrally-located, downward-pointing jets. Perforated baffles are occasionally used to attenuate jet speeds during ground testing of conventional jet aircraft. The study is also relevant to a process in the making of paper. The pulp and water mixture is deposited on a moving screen (Fourdrinier wire), and the jet approaches the screen at an oblique angle.

The purpose of this paper is to attempt a broad review of some of the factors that influence the economic development of a country and to illustrate in general terms the importance and the application of airborne survey techniques, as a means of collecting the information on which any sound development must be based.

The industrial and agricultural revolution that is now taking place on a world-wide scale demands a completely new approach to the problem of economic development. When economic development was slow and confined to small areas it was sufficient perhaps to base that development on limited information. Today, however, the pace is quickening every year, but the speed with which we are obtaining the information, on which such development must be based, is lagging behind.

Why is the present position different from any other epoch in world history? The main cause is the industrial revolution, which has produced rapid means of communication, by air and by radio. The Twentieth Century now lives literally as neighbour to the Stone Age.

The special structural problems of VTOL aircraft are examined, taking the Do 31 as a basis and it is shown how these problems can be solved without significant weight penalties.

After a short description of the aircraft and the systems associated with aircraft testing, the structural design of the Do 31 is described.

The effect of special VTOL load cases on the individual aircraft components are illustrated and it is shown where these are critical. The methods used in the calculations are explained briefly and theoretical results are compared with tests.

Special emphasis is given to the lift pod structure and its structural analysis.

There are special problems with VTOL aircraft which must be considered during the structural design phase. The effects of temperature on the engine pods, wing and fuselage are shown and the solution of the associated design problems are indicated. The results obtained are compared with a number of Do 31 test results.

If conventional British or US fire requirements are applied to the design of lift pods, there is a possibility of some weight penalties. Fire problems and fire requirements for lift pods are discussed with reference to test results. Recommendations for minimising the danger of explosions and for the use of fire detecting devices are also made.

A great advantage of VTOL aircraft is their ability to use unprepared sites. Debris may be thrown up by the downward deflected jet exhausts and strike the aircraft. Calculations and test results show the effect of impact velocities, stone shape, etc. Structural optimisation for withstanding debris impact is considered.

Noise problems have to be investigated during the aircraft design phase because of the high engine thrust installed in a VTOL aircraft. Results of the Do 31 tor near field noise levels are given. Particular attention is given to the proportion of overall noise level which affects the airframe.

It is my very great honour to be asked as an operator to cover the Bell 212s part in the story of IFR operation of medium helicopters.

None of us should forget that two great British companies have for years been blazing a trail in the IFR operation of two helicopters, the S-61 and the Wessex 60, and I can only assume that it was because Irish Helicopters was, I understand, the first operator to put the CAA approved Bell 212/IFR into operation that the privilege of giving this talk has come my way, and I speak humbly and mindful of the invaluable efforts of others before us.

The continuation of mass travel over long distances, is inconceivable if the world really runs short of energy. Thus, looking at the year 2000 we have two alternatives:

either: fuel will be strictly rationed and reserved for essential purposes, which certainly would not include long-distance mass-travel,

or: fuel will continue to be freely available to the airlines at some price.

In the first scenario, there is no future for civil aviation as we know it and the aerospace industries must turn to new fields of endeavour.

In the second scenario, we have to answer the question: ‘what fuel at what price?'. This has to be answered because, if the price were to rise sufficiently, then the result would be similar to that of the first scenario as the present travelling public could no longer afford to buy airline tickets.

A convenient method is pointed out for calculating the response of a damped linear system with one degree of freedom to harmonic excitation. Results of such calculations are usually represented by the familiar “ resonance curves ”—one curve being plotted for each intensity of damping. These curves are not particularly convenient to use and Yates has overcome several of their defects by throwing them into a nomographic form. Yates' nomogram is based upon the concept of viscous damping and it does not give the information of a conventional set of resonance curves in that it relates to the velocity of vibration. By changing over to hysteretic damping, a nomogram of somewhat similar form may be constructed such that it gives amplitudes and phase angles of displacements while retaining the advantages, over resonance curves, of this form of representation.

There is at present no thoroughly satisfactory method of measuring accurately the true air speed of an aircraft, particularly at high speeds.

Ground radar can accurately follow a high-speed aircraft but, without the development described here, can only measure the speed of the aircraft relative to the ground. The method developed by the authors makes immediate allowance for wind speed and is capable of giving the true air speed of an aircraft to within one per cent. There is no apparent reason why the method should not be applicable even at very high speeds and there is no limit in aircraft altitude at which the measurement may be made.

This note describes brief tests made to check a proposed extension to the Royal Aeronautical Society Stressed Skin Data Sheets on stresses and deflections in flat panels subjected to normal pressure. Simple modifications to the test rig, which greatly improved the edge fixing, are also included.

This paper investigates the effect of the torsional stiffness of the ribs on the buckling strength of stiffened plates compressed in the direction of the ribs. For the case of plates simply-supported on all sides, a closed form formula is derived for calculating the buckling load.

As is well known, standard lifting-line theory cannot be applied to a wing with sweepback in order to determine the amount and distribution of the lift. Various methods, all fairly laborious, are available, and while they give results which agree fairly well with experiment, they do not show in detail the source of the various differences due to sweep. It is with the object of separating the several effects involved, which can be regarded as distinct for practical purposes, that the present method has been developed. Since one of the items, finite-chord loss, is shared with the straight wing, although not included in simple lifting-line theory, it is calculated first for the straight wing. The wing is represented by its median or camber surface and is assumed nearly flat.

The imposition of swirl on co-axial jets exhausting into confined space, akin to a combustor model, has far reaching effects on their mixing and flow development. In the present paper, the influence of swirl on both the jets has been determined in terms of velocity and pressure distributions in the confined space. It has been shown that swirl in the central jet leads to faster mixing whereas higher swirl in the annular jet improves both mixing and development.

In a recent note, Allen has investigated the use of Preston tubes and Clauser charts for determining the skin friction in supersonic, boundary-layer flows. He concluded that the Preston tube was best used in conjunction with the law of the wall of Fenter and Stalmach but that the Baronti and Libby wall law was most suitable for determining local skin friction from velocity profiles; both methods are complex and do not permit the direct use of Clauser charts. The present note presents a simple transformation which permits incompressible Clauser charts to be used for the evaluation of skin friction in supersonic flows; the method is applicable to both adiabatic and nonadiabatic situations. Some conclusions, based on experimental experience, are drawn regarding the determination of skin friction by sub-layer methods.

This paper is concerned especially with the reliability of inspection in the nondestructive testing of military aircraft structures. The first part considers design philosophies, examines how the requirements for inspection arise and highlights the difference between the approaches being adopted in the USA and in the UK.

The second part examines what data are already available on the reliability of inspection and discusses the UK programmes that are aimed at gathering more data.

The usual method of load measurement with strain gauge load cells in a bridge circuit involves the measurement of the out of balance voltage either by the height of a trace displayed on a cathode ray oscilloscope, or the width of a band produced by a tuned galvanometer. Both involve careful regulation of the input voltage or calibration during use. The method described provides for a null balance of the bridge at any instant in the cycle of a uniformly repeated cyclic load up to 10,000 cycles per minute. An accuracy of ±½ per cent, of the capacity of the load cell is obtainable.

A theory is presented for the airflow and power requirements of a compressible hovercraft jet operating under equilibrium conditions. It is shown that, even for a partially sonic jet, these requirements may not differ markedly from those of an incompressible peripheral jet.

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.