Dr. Stratford (p. 133, February 1965 Journal) is to be supported in his endeavour to apply boundary layer theory to the prediction of optimum loading requirements in flow through blades in cascade. Inevitably some simplification of the general flow system in a blade passage is necessary if undue complexity is to be avoided. In the simplified flow model, however, care must be taken to avoid over-simplification, and the limitations imposed by legitimate approximations must be appreciated.

When a long unreinforced flat elastic strip with free edges is bent to a uniform curvature about transverse axes in its own plane, anticlastic curvature is produced due to the influence of Poisson's ratio. Provided that the applied curvature is sufficiently small, the anticlastic curvature is constant across the strip and is proportional to the applied curvature. A finite deflection analysis shows, however, that the anticlastic deformation is reduced by the action of middle surface stresses, and the deformed strip approaches asymptotically a cylindrical form as the applied curvature is increased. Nevertheless, in some engineering applications it is necessary to limit the anticlastic deformation when the applied curvature is small, and for this purpose transverse ribs can be attached to the strip. In this note a small deflection analysis is given of the effect of uniformly spaced rigid ribs on the deformation of such a strip.

Ample evidence(1, 2, 3) exists to indicate that, in the presence of contaminated water and microbiological growths, the present widely used nitrile rubber compositions for lining integral fuel tanks of aircraft do not always offer satisfactory protection against corrosion. Failure of the lining sometimes occurs, which leads subsequently to pitting and inter-crystalline corrosion of the underlying aluminium alloy, resulting in structural weakening of the affected members, and in some instances actual perforation of the aircraft skin. In the majority of observed instances, the corrosion occurs beneath a section of the lining which has become deteriorated. This deterioration occurs in areas where water lies in contact with the nitrile rubber lining, especially where micro-biological slimes have developed at the interface of water, fuel and tank lining. Our evidence in kerosine systems indicates that these slimes are essentially fungal in nature, the predominant fungus being Cladosporium resinae (Lindau) de Vries, and that the associated water may range from low levels of electrolyte contamination to about 3500 ppm of salinity. We are not unmindful of the fact that numerous bacterial species have been found in such slimes, and may well contribute to the mechanism of deterioration of the lining, and the subsequent corrosion of the metal.

An analysis of experimental results shows that the maximum pressure rise attainable in a two-dimensional subsonic diffuser of length L correlates with the parameter L/δ0*, δ0* being the displacement thickness of the boundary layer at entry. The results agree well with boundary layer theory.

When fluid flows in a tube which rotates about an arbitrary axis, the presence of centripetal and Coriolis acceleration components modify the velocity and pressure fields which exist in the absence of rotation. Barua considered the case of an incompressible fluid flowing in laminar motion through a cylindrical tube which was rotating about an axis perpendicular to itself with uniform angular velocity. For distances well away from the tube entrance Barua illustrated that secondary flow in the r-θ plane occurred and that the axial velocity profile was distorted towards the leading edge of the tube. Since the pressure gradient along the tube is proportional to the gradient of the axial velocity profile at the tube wall the rotation thus has a consequential influence on the resistance to flow offered by the tube.

—The experience from several environmental trials on helicopters is reviewed to show how the life of main and tail rotor blades was reduced by erosion and how effective various modifications have been in protecting these blades. The compressors of the gas turbine power units were also affected by sand ingestion and intake filters were used on later trials to protect the engines. The engine erosion problem is discussed with reference to the position of the intake, the degree and type of filtration and the design of the compressor itself. The design features of the helicopter which affect its ability to operate in dust and salt-laden atmospheres are also considered, along with suggestions for further research and development.

In the Introduction to the second paper in this series (September 1965 IOURNAL), a simple flow diagram illustrates the relationship between demand and supply for aircraft and air transport which is shown in Fig. 1.

Manufacturers supply airlines with aircraft from which a fleet is built. The airlines are thus faced with problems of capital investment and procurement programmes, which were discussed under the heading of fixed costs in the second paper.

The discussion of problems of fleet effectiveness and optimal utilisation begun in the second paper, and elaborated in the third (October 1965 JOURNAL), is continued in Section A of the present one.

Attention is then switched in Section B to the demand for air transport. On the basis of demand for transport of passengers and freight, airlines must determine routes, allocate frequencies to these routes, and prepare time-tables.

The paper concludes the discussion of Operational Research applied to airlines by summarising the models used in the series in the light of the aims specified in the first paper (August .1965 JOURNAL).

In the establishment of a fluid circuit's behaviour, it has been shown that the condition of the entry flow into each component of the circuit is of significance. This note indicatesthe problems encountered by a designer using diffusers at the present state of knowledge, and outlines a hopeful method of reducing diffuser pressure losses.

In the design of cascade blading for compressors and turbines it is often assumed that the maximum efficiency will be attained at the maximum loading that just avoids separation and critical Mach number effects. In a turbine, the overall pressure gradient is favourable so that it should be possible to achieve very high loadings and yet avoid separation. The question then arises as to whether or not such high loadings would produce a high efficiency. The present note suggests that in fact there is an optimum loading, beyond which there would be no improvement in efficiency even though separation and critical Mach number effects were avoided.

Vortices shed from cooler tubes can excite standing pressure waves in coolers if the vortex shedding frequency coincides with the standing wave frequency(1, 2, 3, 4). If resonant conditions are encountered in a particular cooler the single vortex shedding frequency may be suppressed by fitting in-clined splitter plates into the coolers. These splitter plates also “detune” the coolers by raising the resonant frequencies.

Splitter plates of this type were used recently to eliminate severe noise and structural vibration in a new cooler for the 3 ft wind tunnel at the Royal Aircraft Establishment, Bedford.

This Note is concerned with the axisymmetric buckling of orthotropic circular plates. A circular plate fabricated with radial and/or circumferential reinforcements may be idealised as an orthotropic plate of uniform thickness h having different material properties in the radial and circumferential directions.

A simplified approximate solution for clamped skewed plates under uniform pressure is presented. Variations in maximum edge and centre moments with skew angle and sides ratio are shown plotted. The convergency of the solution is checked and results compared with the limited available data. Results were verified by an experimental investigation.