It has been found that the addition of a whirl velocity component to an otherwise axial flow in a conical diffuser can lead to improvements in static pressure recovery and in efficiency, according to a restricted definition. Diffusers of total conical angle 10, 20 and 30 deg. were tested in detail; improvements were evident only in the last two, which would otherwise have suffered from flow separation problems caused by their relatively large divergence angles. The agency for improvement seems to be a beneficial redistribution of axial velocities.

This paper reports experimental results for the performance of a freely hinged door between two incompressible air flows of different total pressures and different velocities. The apparatus used is a laboratory idealisation of the tertiary door system for an aircraft propulsion nozzle. The governing parameters are identified and the performance is presented in terms of the equilibrium door angle and the relative magnitude of the mass flow admitted. Three doors of different shapes were used and results are also presented for a plain opening. The main aerodynamic parameters are shown to be the velocity ratio and a non-dimensional pressure difference across the door. The shape of the downstream door jamb is found to have a considerable influence on the operation of the door at low angles. Removal of the door results in a lower entry mass flow over most of the operating range. It is shown that the mass flow ratio can be predicted quite well from the measured door angles by means of a simple theory.

A double Fourier series solution is presented for the buckling of simply supported orthotropic and isotropic skew plates, subjected to in-plane compressive and shear edge loads. All the boundary conditions, including the vanishing of the normal bending moment along the edges, are satisfied. Numerical results, suitable for design purposes, are presented graphically for a number of independent parameters such as skew angle, ratio of flexural rigidities and aspect ratio. The results show that the buckling strength is substantially effected by the skew angle, and to a lesser extent, by the ratio of the flexural rigidities and aspect ratio. In contrast with positive shear edge loads, which tend to decrease the skew angle, negative shear edge loads appear to reduce the buckling strength of orthotropic and isotropic skew plates.

Many aspects of parachute behaviour are dominated by the permeability of the canopy cloth. Techniques employing kinematic principles to predict parachute opening behaviour, for example, must first be able to predict the air flow through the canopy material. This paper is concerned with the development of such a predictive capability.

The flow of air through cloth of gauze has been studied by many workers; since the 1850’s, in connection with filters; and since the early twenties, in connection with parachutes. Workers in each of these disciplines seemed unaware of the work being done in the other.

In the case of parachute cloth permeability we find the foundations being laid down by such eminent workers as Glauert in 1932 and Taylor in 1944. Yet most subsequent writers seem not to be aware of this, and since World War II, there have been many papers “rediscovering” basic principles; often with errors which could have been corrected by reference to the earlier authorities.

In this paper we attempt to bring together all the work which has been done in this field, and to rationalize the data by simple mathematical modelling. Individual elements of the model have been proposed before, of course.

We then examine the effect of tension on the geometric porosity of fabric, and hence the pressure loss Ap. A theoretical analysis shows that tension is likely to be a major factor. For cloths which have low porosity when unloaded our simple mathematical model shows that, for a given Ap, a stress equal to 50% of ultimate can increase the air volume flow Q by an order of magnitude. In general, the increase in permeability is greatest at the lower values of Ap, indicating that the viscous term is more influenced by tension than the dynamic term. This theoretical result is confirmed by some rather limited experiments carried out by Lashbrook and Marby. But their data also shows that a cloth made from relatively stiff glass fibers can experience a reduction in permeability when loaded, due to a “closing up” of the weave. The reasons for this are discussed.

Although the Cebeci-Smith method of calculating turbulent boundary layers is widely used and generally gives acceptably accurate results, highly inaccurate skin-friction values are obtained for relaxing flows and equilibrium layers in strong adverse pressure gradient. In the present paper, these anomalies are removed by suitable modifications to the basic eddy-viscosity model.