The result derived in a previous paper for the primary effect of the jet mixing on the thrust is confirmed, both by an investigation using momentum principles and by a quantitative examination of the sink effect. Boundary layer behaviour still cannot be predicted with accuracy, but it is suggested that, even under cruising conditions, a jet flapped aerofoil may exhibit unconventional properties.

Kinetic heating associated with supersonic flight presents new problems to the aircraft structural engineer. Some of these can be resolved by the use of the theorems of thermo-elasticity. This paper outlines the foundations of this subject and derives generalisations of the usual variational theorems, which are so often used in structural analysis.

The mathematical theory of nosewheel shimmy is given, with particular reference to twin nosewheel assemblies. It is shown that a sovereign remedy for shimmy is to make the castor length greater than what is here called the “ creep distance,” which in practice is found to be approximately equal to the tyre radius. Lateral flexibility of the oleo leg is disadvantageous but elastic constraint at the pivot is a good feature. The one necessitates an increased castor for stability while the other allows a smaller castor. It is also shown how, by the use of a compact linkage mechanism, the effective castor length can be made independent of the wheel-leg offset and can have any desired value. Model experiments that confirm the theoretical conclusions are described.

Approximate solutions are given for the lowest natural frequency of flexural vibration of isosceles triangular plates which have the equal edges simply-supported and the base clamped. The results are presented graphically to allow rapid determination of a desired fundamental frequency.

The class of incompressible axially-symmetric laminar viscous flows considered are exact invariant (similarity) solutions of the Navier- Stokes equations. The functional forms of the velocity components are deduced by group-theoretic arguments. The system of governing partial differential equations is reduced to a system of ordinary differential equations and these in turn are reduced to a single first order non-linear ordinary differential equation for the dimensionless tangential velocity component. The general solution of this equation is obtained in terms of hypergeometric functions.

The classes of laminar viscous flows bounded by a right conical surface or by right inner and outer conical surfaces with a common apex obtainable from the previously mentioned (similar) solutions of the Navier-Stokes equation are studied. Suction/injection velocities (inversely proportional to the distance from the apex) normal/parallel to the conical boundaries are admissible for the classes of flows considered. If the flow is bounded by impermeable conical surfaces, then it is shown that these solutions of the Navier-Stokes equation imply that it must be identically quiescent.

When the bounding cones are not impermeable, closed solutions for the single-cone case are found in terms of elementary functions. A numerical example of such a flow, with fluid injected normal to the conical boundary, is given. Such a simplification of the hypergeometric functions entering into the problem, however, cannot be achieved in the two-cone case.

Detailed calculations based on linearised supersonic flow theory have demonstrated in a number of cases the equivalence between the wave drags of yawed or swept wings of constant section and zero lift and the corresponding values in two-dimensional flow. These results and others are shown to follow readily from a general theorem for which a simple proof is given. Some interesting deductions are illustrated in Fig. 3.