The superposition of the flexural instability of the plane form of a cantilever wing in its own plane, over that of the torsional elastic equilibrium, gives rise to a special phenomenon of mixed instability which has been translated analytically by Prof. C. Minelli into the problem of determining the first positive characteristic value of a certain system of two ordinary, linear and homogeneous equations, in two unknown functions, with given limiting conditions. The methods of calculation, both analytical and numerical, for the solution of this problem are described. The results confirm the intuitive inferences according to which, other conditions being equal, the backward displacement of the elastic axis worsens conditions by lowering the critical speed.

The mean flow of an incompressible fluid in a straight suction duct with porous walls is considered and relations between the inflow and the pressure difference required to produce it are established on the basis of an elementary momentum analysis. It is assumed that bom the velocity and the pressure across planes normal to the direction of the mean flow inside the duct are distributed uniformly everywhere and that the effect of obstructions, which do not alter significantly the area of the duct cross section at any position, can be described in terms of losses of total pressure which are proportional to the square of the local speed within the duct. A variety of cases is discussed and it is shown that calculation of the internal pressure is straightforward and in agreement with experiment, at least for the case of a pipe having uniform porosity.

In many internal flow problems, the velocity profile of the flow in a duct of a given cross section is of major importance. In combustion chamber flow, for example, the entry velocity profile is a critical factor in determining the relative amounts of primary and secondary combustion air. Further, in the flow in an axial compressor, the peaked velocity profile between the root and the tip of the rotor blades has a marked effect upon the design of the blading. Recent work by Zanker has shown the effect of variation in velocity profile upon the accuracy of orifice-plate flowmeters.

The paper discusses recent work in the Theoretical Division at the Aircraft Research Association Limited (ARA) on the modelling of complex configurations, rotors, propulsion and viscous flows. The general features of the ARA multiblock system, which provides a grid generation and Euler flow solution capability for complex configurations, are discussed. Although very successful, the system has various limitations, in particular the tendency for the grid quality to depend on configuration complexity and type. A new multiblock system is being developed which allows regions of unstructured grid to be included, giving increased flexibility in dealing with complex geometries and other improvements. Work on rotors has included the development of a new Euler code for propellers, as a replacement for the code in current use. Improvements in flow solution offered by the new code are illustrated. In the propulsion field, the extension of a viscous-coupled Euler code for afterbody flows to a complete cowl unit is described briefly. The code is particularly relevant to the new generation of large civil turbofans. Work on Navier-Stokes methods for afterbody/nozzle flows is also discussed. Other work on viscous flows includes a 2-D investigation into viscous modelling with hybrid grids, and the further development of an established transonic flow aerofoil code.

For the calculation of the climbing speeds of aeroplanes several methods are in use, which, as is well known, do not yield quite accurate results when applied to machines with great climbing capacities, and give rise to inaccuracies which become of greater importance with increasing climbing capacity of the plane. The climbing speed, up to the present, has not been great in respect to the forward speed used when climbing, so that for the calculation of the climbing speeds the method fairly generally used and described in the “Handbook of Instructions for Airplane Designers, ”from the U.S. Army Air Service, could be used without serious objections. It has, however, been found desirable to look for a better method for calculating the climbing speeds, owing to increasing engine powers accompanied by decreasing drag coefficients of the aeroplanes, as well as to the introduction of variable pitch airscrews.

An incompressible method is presented to predict the upwash corrections associated with vortical flow as a result of wind-tunnel side wall effects. An image system is used to simulate the tunnel side walls which are assumed to be solid. An integral expression is formulated, representing the average upwash induced over the wing by the image system. Wall effects may be determined for flows with and without vortex breakdown. Comparisons of the results with upwash predictions from a Navier-Stokes study show close accord. The upwash expression also displayed the ability to successfully predict corrections for flows involving vortex breakdown.

Civil aviation has instilled new perceptions of a smaller world, creating new opportunities for trade, exchange of cultures and travelling for leisure. However, it also brought with it an unforeseen impact on the environment. Aviation currently contributes to about 3·5% of the global warming attributed from human activities. With the forecasted rate of growth, this is expected to rise to about 15% over the next 50 years. Although it is projected that the annual improvements in aircraft fuel efficiency are of the order of 1-2%, it is suggested that the current gas turbine design is fully exploited and further improvements are difficult to achieve. A new generation of aero engine core concepts that can operate at higher thermal efficiencies and lower emissions is required. One possibility of achieving higher core efficiencies is through the use of an inter-cooled (IC) core at high overall pressure ratios (OPR). The concept engine, expected to enter into service around 2020, will make use of a conventional heat exchanger (HEX) for the intercooler. This paper seeks to introduce a heat pipe heat exchanger (HPHEX) as an alternative design of the intercooler. The proposed HPHEX design takes advantage of the convenience of the geometry of miniature heat pipes to provide a reduction in pressure losses and weight when compared to conventional HEX. The HPHEX will be made of a number of stages, each stage being made of a large number of miniature heat pipes in radial configuration, that will extend from the inter-compressor duct to the bypass split, thus eliminating any ducting to and from the intercooler. This design offers up to 32% reduction in hot pressure losses, 34% reduction in cold pressure losses and over 41% reduction in weight.

The idea of using the reaction of a jet of water pumped sternwards from a ship is endowed with a respectable antiquity, but tests on the efficiency of such propellers, whether model or full-scale, have not been extensive. Perhaps the most thorough tests were those of S. W. Barnaby (Thornycroft and Co.) in 1880, described by him in the Proceedings of the Institute of Civil Engineers, Vol. LXXVII, page 1, 1883. This investigator measured the reaction on a nozzle delivering water under pressure into still water by a force balance connected to the nozzle itself. As a result, the “ Waterwitch,” a vessel of 1,160 tons, was constructed to work on this principle, the jet being supplied by a centrifugal pump which took water from a scoop amidships. The efficiency of the jet itself worked out at .71, but with the pump the combined efficiency was only .38.

A submersible is defined as a neutrally buoyant submarine which relies largely on the buoyancy of the hull rather than gas or liquid filled floats at ambient water pressure. 29 different kinds of submersible have been built in USA and 15 in other countries. One has been built in England. Half of these do not go below 2000 ft and one third do not go below 1000 ft. The minimum safe weight for a vehicle is 5 tons at 1000 ft and 10 tons at 20 000 ft. A useful research or light work vehicle must be twice the minimum weight, and a heavy work vehicle in the 30-100 ton range.

High utilisation factor can only be obtained with special handling and support equipment, underwater navigation aids, high manoeuvrability, and a reserve of speed, life support, payload, and endurance. Principle applications of submersibles are in scientific research, geological mapping, prospecting, the oil industry, dredging, pipe-laying, and search and salvage.

Reference 1 describes a numerical procedure for calculating the roll-up of the wake behind a wing of finite span, when the wake vorticity is assumed to occur within a layer of finite thickness with thin elliptic cross-section normal to the stream. The vorticity is assumed to be a function of spanwise position only (corresponding to a linear transverse velocity profile when the wake is thin), the process is treated as a two-dimensional unsteady one, as in the work of Westwater, Moore and others, and viscous and turbulence effects are ignored.

In Ref. 1 the technique was applied to the classical elliptic loading, to calculate the very early stages of the roll-up. In the present paper these calculations are extended to larger values of the dimensionless time t* and the results are seen to tally fairly well with those of Moore, which were obtained by using a point-vortex model. Similar calculations have also been carried out for a particular non-elliptic loading which was dealt with by Clements and Maull by a two-dimensional, point-vortex method. They gave this loading as an example of a distribution which produces two roll-up cores on each half span, with an induced drag only 10% greater than that of the elliptic loading having the same Ch. The results of the new calculations are presented here, and are seen to be similar to those of Ref. 4 in a general way, both qualitatively and quantitatively.

Although an interest in electric propulsion has existed in the UK for a considerable time, it is only in the past few years that it has been considered worthwhile to undertake the development of hardware and produce detailed systems studies. The practical developments can be divided into two categories: —

1. 1. The development of comparatively large thrusters (in the region of ½ kW power, giving 10-20 milli Newtons of thrust), for producing major movements in a satellite's position.

2. 2. The development of micro-thruster systems for the maintenance of a satellite's attitude and position against the small disturbing forces and torques it normally experiences in orbit.

A generalised conical flow theory is used to deduce an integral equation relating the velocity potential on a delta wing (with subsonic leading edges) to the given downwash distribution over the wing. The complete solution of this integral equation is derived. This complete solution is composed of two parts, one being symmetric and the other anti-symmetric with respect to the span wise co-ordinate; each part represents a velocity potential. For example, if y is the spanwise co-ordinate and x is measured in the free stream direction, then a downwash of the form w= - α11 Ux|y| is symmetric and will give rise to a symmetric potential, whereas w= - α11 Ux|y| sgn y is anti-symmetric and gives rise to an anti-symmetric potential. The velocity potentials of such flows are given in the form of Tables for all downwashes up to and including homogenous cubics in the spanwise and streamwise co-ordinates. Table III gives similar formulae in the limiting case when the leading edges become transonic; these are compared with results given elsewhere and serve as a check on the results of Tables I and II.

A large number of far-field jet noise measurements obtained over a considerable period of time are presented, correlated in such a manner that they may be used to provide a complete noise assessment for any jet of which the performance parameters are known. The data are presented in two sections, one dealing with the problem of a static source near ground level, the other dealing with the case of a source in flight.

Much of the data was derived from Avon engine tests, but a wide range of other jet noise sources has also been encompassed. Comparisons are drawn which show good correlation to exist between the overall sound pressure levels produced by jets of all sizes. It appears also that even the spectra quoted, which are based only on Avon measurements, are valid over a fairly wide range of jet sizes and are not peculiar to the Avon engine.

For lifting re-entry there may be advantages in using wings which give as high a lift coefficient as possible at the design value of the lift/drag ratio. This paper presents the results of an experimental and theoretical study of wings with recessed lower surfaces designed to give high values of CL. The calculations show that a wide range of wing shapes can be found that give values of CL which are much larger than those on a flat wing with the same lift/drag ratio.

The slender–body solution for the flow about low aspect–ratio wings of non–zero thickness yields a pressure distribution which is valid in the vicinity of the leading edge and therefore suitable for comparison with measured distributions. In this note an expression is derived for the theoretical pressure distribution, due to small incidence, on a slender elliptic half–cone in uniform motion. It is shown that this distribution is additive to the zero incidence pressure distribution. A comparison with some low speed measurements shows qualitative agreement.

The method can be simply extended to other bodies of elliptic cross section.

The linear vibrating system of two degrees of freedom, see Fig. 1, whose mathematical solution is well known (see for example ref. 1), is nevertheless on the verge of being too awkward for manipulation in the design office. It is of considerable interest as the basis of a vibration absorber and techniques continue to be developed for investigating the effects of changing the design constants on the properties of the system and the more complicated ones derived from it.

Within the present publication, the rotor head of a compound helicopter known as Rapid And Cost-Effective Rotorcraft (RACER) is investigated. In particular, the aerodynamic design optimisation of the RACER blade-sleeve fairings (BSFs) is conducted. For this purpose, an isolated rotor head is generated featuring a full-fairing beanie, the BSF and a truncated rotor blade (RB). Moreover, a single RB is investigated at two different azimuthal rotor positions, which correspond to the advancing and the retreating RB case. For this purpose, an averaged circumferential velocity is determined in the blade-sleeve region and superposed with the RACER cruise speed in order to estimate the prevailing flow conditions. The automated aerodynamic design optimisation is performed by means of a previously developed optimisation tool chain. A global multi-objective genetic optimisation algorithm is applied for the given problem. During preliminary work, a 2D aerodynamic design optimisation of selected blade-sleeve sections was conducted. These optimised aerofoils represent the design variables for the current optimisation problem. The shape modification of the 3D fairing is realised by exchanging specific aerofoils at certain spanwise sections.

The general requirements for the complete air conditioning of aircraft are discussed in the light of the complete system concept. The author takes into consideration safety, differential pressure, weight saving, power and air supply, passenger comfort, cooling and humidity. Particular systems are then described and there is a section on the test equipment required for the laboratory testing of air conditioning equipment. Cooling systems are taken first and divided into the air cycle system embodying bootstrap, turbine fan, and regenerative applications of cold air units–the vapour cycle system employing a boiling tank and that using proprietary refrigerants; properties of liquid refrigerants are discussed. Regulation of cabin temperature, air flow, humidity, pressure and oxygen is done by control systems and the equipment used is described. Four appendices give (1) suggested detailed requirements for air conditioning equipment and user requirements, (2) sample data and calculations for air conditioning a 100-seater civil transport, (3) some notes on the definition of refrigeration terms and (4) data on pressure losses in aircraft ducts.

Although normal flapped and /or slatted wings may be considered as having a variation of camber because of the deflection of such devices, a variable camber airfoil is considered here as a mechanical unit employing flexible leading and/or trailing edges, thus eliminating surface discontinuities, but otherwise operated in the same manner as the more conventional devices they replace and is simply illustrated in Fig. 1 (i.e. flaps and ailerons on the trailing edge and slats or droop on the leading edge). The use of varicam trailing edge systems for lateral control implies that such systems should preferably be capable of both up and down (i.e. differential) movements.