A theoretical investigation of short-scale inviscid instability in boundary-layer flow past an obstacle on a surface is described, with the application to trip-wire transition and wall roughness effects in mind. An analytical model and computational results show that the occurrence of an inflexion point in a local velocity profile is necessary but not sufficient for the instability to arise.

A simple modification is described to the integral method of P. D. Smith for calculating turbulent boundary layers on infinite yawed wings to allow for wing planform taper. A comparison has been made between the modified and general methods for calculating three-dimensional boundary layers. This suggests that the modified method is useful for obtaining a rapid indication of the separate effects on the boundary layer of wing sweep and planform taper.

An exact expression for the flow variables through a viscous shock wave is obtained from the Navier-Stokes equations. The Prandtl number is taken to be ¾, which is close to the value for air, and the viscosity is assumed to be given by Sutherland's formula.

By considering the limit as the viscosity tends to zero, it is shown that the solution to the Euler equations has an entropy spike at the shock wave. This explains certain, hitherto considered spurious, features of shock waves captured by numerical solutions of the Euler equations.

Pressure fluctuation measurements were made on an 18% thick biconvex aerofoil in the region of shock boundary layer interaction at various levels of free stream flow unsteadiness. Experiments were performed with free transition and transition fixed models at a shock Mach number of 1.44 and blade chord Reynolds number of 1.6 x 105. The transition free model with a laminar boundary layer showed the presence of periodic flows at low turbulence levels which disappeared with the increase in turbulence levels. The general effect of free stream turbulence on transition fixed model is one of broad band amplification of pressure fluctuation levels in the region of shock interactions.

This note attempts to clarify some basic ideas, and correct some common misunderstandings, on wing flexure-torsion flutter. Topics include:

• (i) an understanding of the physics of wing flexure-torsion flutter through a number of specific examples,

• (ii) an examination of the energy interpretation of the physics of flutter, indicating its limited usefulness,

• (iii) a discussion of the significant differences between wing flexure-torsion flutter and the Duncan flutter engine,

• (iv) a graphical representation to assess the contribution of various parameter to flutter onset,

• (v) subcritical response below the critical flutter speed,

• (vi) some practical wing flutter considerations.

This paper describes the results of an investigation of the flow over two cylinders in which the diameter of the upstream cylinder is half that of the downstream cylinder. Measurements were made of the surface pressure distribution around the downstream cylinder, and of the base pressures and Strouhal numbers of the two cylinders for separations between 1·32 D and 3·88 D, where D is the diameter of the downstream cylinder, and for angles of stagger between 0° and 45°.

With the cylinders in tandem two different flows were found, and it is suggested that there is a step change between the flows at a critical separation.

The behaviour of the measured quantities with a change of the angle of stagger is found, in general, to depend on whether the separation is less or greater than the critical separation. For each separation an angle of stagger is found at which the pressure distribution has a strong asymmetry over the rear of die cylinder. These pressure distributions are similar to each other, and they indicate the presence of an enhanced flow over the upper half of the cylinder. Also the lift force, for a given separation, then has its maximum value.

It is found that for separations greater than the critical separation the Strouhal numbers of the vortex shedding from the two cylinders are identical over a considerable range in the angle of stagger.

Ghosh’s large-deflection hypersonic similitude and consequent plane and conico-annular piston theories have been applied to obtain unsteady pressure and the pitching moment derivatives for oscillating non-slender wedges, cones and ogives. The plane piston theory for a wedge is extended from a quasi-steady analysis, which gives the moment derivative due to pitch rate Cmq, to an unsteady analysis; the two analyses combine to give the moment derivative due to incidence rate , which is shown here to be the same for wedges and quasi-wedges. The present theory can separately give Cmq and for a quasiwedge of arbitrary shape; this principle is illustrated for a particular quasi-wedge namely the parabolic arc plane ogive. In comparison, a previous theory by Hui gave only the sum of Cmq and , only for wedges. The conico-annular piston theory is employed to obtain Cmθ, which is the moment derivative due to a steady pitch angle, and Cmq for non-slender cones and axisymmetric ogives in closed form for the first time.

Experiments are reported of the self-preserving turbulent corner wall jet formed by directing a jet of air parallel to the line of intersection of two walls abutting at right angles. Self preserving profiles of the mean and turbulent flow are established by approximately 50 jet diameters downstream. Like the three-dimensional wall jet on a plane-wall surface there is evidence of a significant secondary flow induced by vortex line bending, though its magnitude is smaller than in the plane-wall case.

A flow surveying technique is described which provides a direct and quick output of either flow speed or direction. The computer based system enables ‘contour plots’ of these quantities to be obtained for fixed offset distances from a surface, using a series of surface contacting cylindrical probes. Pre-set values of the signal from the flow sensing system are used to switch a tri-coloured light source which traverses in unison with the probe, while a time exposure photograph is taken. For flow direction measurement, the signal activating the lights is computed from the pressure difference between yaw meter tappings on the cylinder in conjunction with the cylinder base pressure. Flow velocity is obtained from the base pressure alone, or alternatively from a hot wire probe.

Results are presented to show that the method can provide useful and detailed data. It is seen mainly as a complement to other methods available for visualising complex flows.

A survey is presented of results obtained from experiments in the RAE 5m low-speed pressurised wind tunnel. The tunnel is capable of operation over a range of pressures (from one to three atmospheres) so that the effects of Mach and Reynolds number may be separated. This decoupling of scale and compressibility effects has made possible reliable extrapolation of test results to full-scale conditions (where this is necessary) as well as giving greater insight into the underlying flow mechanisms. The large size of the tunnel, combined with pressurisation to three atmospheres, has enabled some tests, on small combat/trainer aircraft and on bomb-like stores, to be carried out at full scale.

Three facets of the work of the 5m tunnel are described — work aimed at predicting or improving the high-lift performance of specific aircraft, work of a more fundamental nature concerned particularly with the optimisation of high-lift devices on generalised research models, and work on the drag of stores carried externally on combat aircraft.

Buckling equations for stiffened cylinders under the specified loading are formulated and solved by means of double Fourier series using the Galerkin process to reduce the solution to the standard algebraic eigen-value problem. Matrices of order 80 by 80 are required for convergence reflecting the complexity of the mode shape describing the buckling patterns.

Simple design curves are developed for determining buckling loads of monocoque cantilever loaded cylinders.

Excellent agreement with test values is demonstrated, indicating that the cylinders are not highly sensitive to imperfections, as is the case of the uniform, axially loaded cylinder. This also follows from the fact that considerable post buckling strength exists for the cantilever loading condition.

After I had described the flight theory and practical ornithopter of Carl Friedrich Meerwein, my attention was drawn to a relevant passage in Joachim Heinrich Campe’s Sammlung interessanter und durchgängig zweckmässig abgefasster Reisebeschreibungen für die Jugend. Translator of Robinson Crusoe, traveller, and populariser of high culture, Campe included in his improving collection of travel decriptions an account of a journey from Hamburg to Switzerland which he himself had undertaken in 1785. Having reached Giessen on his way south, he was about to press on to Frankfurt when some acquaintances urged him to stay a day or two longer to watch something curious: Carl Meerwein was about to attempt to fly.

Currently there is renewed interest in the evaluation and reduction of steady wind tunnel wall interference, especially for large models.

Evaluation of previous predictions for perforated and slotted tunnels suggests that a hybrid slotted tunnel, ie a slotted tunnel with closed slats and perforated slots) should offer minimum corrections for upwash, flow curvature and solid blockage. This suggestion is confirmed by the present computer studies of a range of rectangular hybrid slotted tunnels.

The computer studies are for tunnel working section height to breadth ratios of 0·835 and 0·600 over the Mach number range from 0 to 0·85. Wings swept at 28° and 50°, with ratios of model span to tunnel breadth varying from 0 to 0·7, are considered. An idealised fuselage shape is used to predict solid and wake blockage corrections for the wall configurations selected on the basis of minimum upwash and curvature interference.

The mixing of single or multiple jets is relevant in several engineering applications ranging from flame stabilisation in combustion to high lift devices for V/STOL aircraft. In some of these applications, expeditious manufacturing and ease of installation may dictate the use of sharp-edged slots in preference to nozzles with contoured upstream shaping.

It has been suggested that cruciform nozzle exit shapes may be suitable for improving mixing and thus thrust augmentation in STOL aircraft. The effects of nozzle geometry on the performance of an axisymmetric thrust augmentor have been investigated experimentally and a very slight improvement in the performance of the axisymmetric thrust augmentor was observed when cruciform nozzles were used after the tests had been performed with circular nozzles.

The conversion of the Hercules aircraft for flight refuelling necessitated the installation of a small drogue box on the lower surface of the rear fuselage. This produced a long flow separation and unacceptable rear fuselage and elevator buffeting at the drogue towing speeds required.

The flow separation was stabilised, and the buffeting eliminated, by the installation of strakes and the provision of a small bleed flow through the drogue box.

The synthesis of discrete-time tracking systems incorporating Lur’e plants with multiple non-linearities is illustrated by the design of a fast-sampling digital controller and associated transducers for the automatic control of the longitudinal motions of the CH-47 helicopter with both gang-collective and differential-collective non-linearities. In particular, it is demonstrated that non-interacting control of the vertical velocity and pitch attitude of the helicopter is readily achievable for large classes of non-linear actuator characteristics such as ‘deadzone’ provided that the controller and transducer parameters are chosen so as to ensure that state-bounded absolutely stable tracking occurs.

A general formulation based on a variational approach is used to study the static bending, vibration and stability of circular plates having mixed elastic rotational constraints at the boundary. A single displacement function suitable for these three classes of problems is used in a Ritz scheme to obtain static bending solutions and eigenvalues for various combinations of boundary parameters that exhibit symmetry about two axes. Results obtained are generally in good agreement with those available in the literature and in some cases represent an improvement on those previously reported. The lowest eigenvalues for the stability problem are presented for the first time.

Analytical and experimental studies of the effect of geometric and aerodynamic variables on the performance of the Wells self-rectifying air turbine are presented in this paper. Two approaches to the prediction of the Wells turbine performance are described, both of which are based on the two dimensional cascade theory and isolated aerofoil data. Experimental results are based on the investigations in Unidirectional and oscillating airflow rigs.

Comparisons are made on the analytical and experimental results.

This paper presents a new finite element model for the dynamic analysis of thick rotating blades with flexible roots. The new model is based on the fast convergent element developed by Abbas and Thomas which can satisfy all the geometric and natural boundary conditions of a thick non-rotating blade. It is the only element developed so far which can distinguish between roots of blades that are rigidly clamped and are elastically supported.