Experiments have been performed to study the influence of multiple surface static pressure tappings on transition of the boundary layer on a circular cylinder in cross-flow. A wide range of tapping and cylinder dimensions have been examined to demonstrate that the tappings can act in the same way as trip wires or other surface roughness to reduce the Reynolds number at which transition occurs. Hence, the pressure distribution around the cylinder may be influenced by the presence of the tappings, leading to incorrect measurements. Examination of the data has resulted in a correlation which should make it possible to avoid this tapping/boundary layer interaction in future experiments involving similar cylindrical bodies.

The paper traces the evolution of Sir Sydney Camm's Kingston Design Office through an examination of internal practices and external technical and other pressures at three Jubilee points in its history from 1935 to 1985. Some personal observations are given on the achievements of Camm and his team and an account offered of their continued success over a period of half a century.

The high level of vibration experienced on the helicopter has been an unfortunate feature of the vehicle throughout its existence, and considerable efforts have been expended over many years in attempts to reduce vibration to levels typical of other forms of transport. Much has been achieved, but as the forward speed increases some components of rotor generated vibration increase very rapidly and consequently, at the increased cruise speed of modern helicopters, vibration can still be high. Also, the requirements have become more stringent, due partly to what the passengers or crew are prepared to tolerate, and partly to the complexity of the tasks required of the crews, especially on military machines.

Some observers believe that there will be such growth in the travelling public and such constraint on airport and airspace usage that, by early in the 2000s. very large passenger carrying aircraft will be required. By ‘very large’ is meant anything from 1,000 to 2,000 seaters. Whilst the problems which come to mind when musing on this possibility are mostly those of ‘passenger flow’ in the widest sense and rather less related to the vehicle itself, there are some issues related to the vehicle which suggest themselves. One is the choice of fuselage cross section.

Because cabins have to be pressurised (10 psi is a typical figure for cruise altitudes up to say 40,000 ft), it has been the norm to utilise circular cross sections (or double-bubble type) since the pressure forces are contained by hoop loads only, without frame bending, which affords a light and fatigue-insensitive structure (Fig. 1).

A review is given of some recent research, mainly at low speeds, into the development of dynamic lift. Sudden movement of aerodynamic surfaces can generate dynamic lift due to the transient development of separated flow. These dynamic effects are large and well established for aerofoils. They are considered likely to be small for highly swept wings and negligible for slender wings, but there is little experimental evidence to support this inference. The dynamic lift might be increased if conventional sinusoidal motions can be replaced by appropriate periodic saw-tooth motions.

The control of large-scale flow separations by rapid movements of aerodynamic surfaces requires further investigation to resolve some of the controversial issues raised in the review.

First essentials of classical flutter are demonstrated by a comprehensive study of the behaviour of a lifting surface with two degrees of freedom under the action of airforces limited to those in phase with displacement. Structural coupling between the coordinates is eliminated by taking the normal modes to be the deflection coordinates, and this results in conditions for stability with particularly concise forms. It is shown that the flutter stability can be seen to be very much a matter of the relative amplitudes of heave and pitch in the normal modes.

In-quadrature airforces are then introduced and it is shown that they have little effect when the flutter is severe. They are of more importance in the milder forms of flutter, the extreme of which are shown to be little different from instabilities in a single degree of freedom.

For all who are specialists of one kind or another, it is a very healthy exercise to read books written by scientists or engineers of the calibre and breadth of F. W. Lanchester. He was at the same time truly a pioneer of flight, an expert in fluid mechanics, in flight mechanics, in the practical, and (well ahead of his time) in the military applications of flight, in the novel use of materials, and an inventor of devices and mechanisms. However, it was with particular surprise that I found, on studying the literature under the name F. W. Lanchester, a book published in 1935 entitled Relativity and two earlier papers on the subject published in 1921. Lanchester had met Minkowski in 1908 at the house of his friend Carl Runge, the applied mathematician, at Göttingen, and following a discussion with Minkowski had taken such an interest in the field that he was able to make these early English contributions.

Perhaps the most important property that makes such pioneers is the courage to think truly new thoughts. His fascination with the new philosophy in physics may be easily understood in terms of this bold style of thought.

Experimental and analytical techniques are presented for the determination of the response characteristics of a scale-model aircraft wheel to changes in runway friction. Results obtained from tests using these techniques are given. The wheel spin-up acceleration is shown to be proportional to wheel load and to the magnitude of the surface friction coefficient after surface change. It is also found to be inversely proportional to brake torque, but is largely independent of speed. An increase of speed is shown to increase the distance required for spin-up of a locked wheel as it encounters surfaces of higher friction coefficient. Good correlation of these trends is obtained analytically.

The effects of tyre flexibility are indicated by the results of both the experimental tests and the analytical simulations. These effects may degrade the performance of aircraft antiskid braking systems. It is recommended, therefore, that simulations used in the development of such systems take proper account of tyre flexibility when modelling the dynamics of the wheel and tyre.

Fractal geometry provides a method for modelling the scale dependence of fluctuations in atmospheric-turbulence velocity. In this paper the basic concepts are outlined and illustrated by a method of data analysis which, for a fractal process, displays measured probability distributions in scale-invariant form. To a first approximation the data exhibit statistical self-similarity, consistent with the classical theory of Kolmogorov. However, on more detailed analysis, the more intense fluctuations show systematic departures from self-similarity, consistent with recent theoretical estimates of the fractal dimension of the support of turbulence. Implications for aircraft gust response are discussed.

An interactive computer programme, based on linear-elastic laminated plate theory, is used to study the effect of lay-up geometry on first ply failure loads. A maximum allowable strain failure criterion is used and a number of design problems are considered where searches are made for optimum lay-up configurations for typical carbon fibre reinforced plastic properties. The relative weakness of this material in tension across the fibres, is found to have a significant effect on first ply failure loads. An optimisation technique based on principal load directions is introduced and compared with the familiar 0/90/±45 lay-up configuration.

An investigation of the generic vibration of prestressed thick orthotropic cylindrical shells was carried out. A set of Flügge type equations. of motion for orthotropic shells has been reduced to an equivalent set of equations containing only non-dimensionalised geometrical parameters, loadings and generalised global constants of orthotropic materials. The influence and importance of the global constants on the vibration of cylindrical shells are studied. Based on the results, the figures shown in this paper are applicable for a large group of materials, making the understanding of the correlation between composite material properties and vibrational behaviour of the shells very easy. The results of this paper show that an increase in vibrating frequency is brought about by (1) increasing generalised rigidity ratio, (2) increasing transverse shear modular ratios, (3) decreasing generalised Poisson's ratio and (4) decreasing principal rigidity ratio. The key parameters to the problems are generalised rigidity ratio and principal rigidity ratio only.

A displacement-based versatile and effective finite element analysis of sandwich panels is presented. The analysis is applicable to both small and large deflections. Allowance for the local bending stiffness of the faces is made. The procedure described is readily adapted to arbitrary laminated beams and plates. Selected example problems are given to illustrate the applicability of the formulation.

An experimental correlation is presented between the losses and the inlet flow conditions in short dump diffusers for turbojet combustors. Cascades of compressor blades upstream of the diffuser were used to make the flow field at inlet similar to that in a real jet engine. The flow field was altered in two ways — by varying the distance between the cascades and the diffuser inlet plane and by changing the blade aspect ratio. The measurements show clearly that distortions in the radial direction affect the losses to a much larger extent than non-uniformities in the circumferential direction. In consequence, the performance can be correlated to a satisfactory degree of accuracy simply by using the radial blockage factor at inlet.

A numerical method has been developed recently to solve the Navier-Stokes equations for laminar compressible flow around delta wings. A large-scale Navier-Stokes solution on a mesh of 129 × 49 × 65 points for transonic flow Mx = 0·85, α = 10° and Rex = 2·38 × 106 around a 65° swept delta wing with round leading edge is presented and compared with a correspondingly large-scale Euler solution. The viscous results reveal the presence of primary, secondary, and even tertiary vortices. The starting location of the primary vortex is seen to be quite different in the two solutions. In the viscous solution it starts at the wing apex, but in the Euler results it starts about one quarter chord downstream. The secondary reparations are also different, due to the up-lifting of the boundary layer in the viscous results, but to a cross-flow shock in the Euler computation. Comparison with experiment shows that the interaction between the primary and secondary vortices in the Navier-Stokes computation is obtained correctly and that these results are a more realistic simulation than the one given by the Euler equations.

Pseudo-streamwise vortices develop during the transition of a boundary layer from the laminar to the turbulent state. It is suggested that the induced velocities associated with these vortices cause a gross change in the flow, and that the initial uniform flow is no longer tenable. The character of the flow in the boundary layer must change suddenly, and it is believed that this change provides the trigger for flow breakdown to turbulence.

In considering reliability, it is logical to look at sources of uncertainty, variability and inaccuracy. British Civil Airworthiness Requirements - Section D defines the factor of safety in terms of several sources of unreliability, as follows:

Viscous/inviscid interaction techniques for calculating the flow about multiple-element aerofoils have been under development in the UK for the last decade producing such programs as MAVIS and HILDA. These methods give reasonable predictions of the lift for viscous attached flow, but fail to give an estimate of the maximum lift and the associated flow separations on the aerofoils. The methods also fail to give adequate predictions of the drag for both attached and separated flow. The disappointing performance of the methods in predicting maximum lift stems primarily from the use of direct methods to solve the first order boundary-layer equations, whilst the poor drag predictions arise from inadequate methods for predicting the development of the flow over the flap. The assumption of incompressible flow could also be a contributory factor in both cases. Methods of overcoming the first restriction are described by using a more appropriate coupling between the inviscid and viscous flows which properly assigns the correct role to each partner in the coupling: this approach is illustrated by ‘semi-inverse’ and ‘quasi-simultaneous’ couplings of a finite-element method for the compressible inviscid flow with an integral method for the boundary layers and wakes. Some methods for calculating the compressible flow about multiple-element aerofoils are also reviewed. However these improvements do not give an adequate estimate of the drag so possible improvements to the calculation of the flow over the flap are discussed.

The procedures employed for the design of a closed-circuit, boundary layer wind tunnel are described. The tunnel was designed for the generation of relatively large-scale, two-dimensional boundary layers with Reynolds numbers, pressure gradients and free-stream turbulence levels typical of the turbomachinery environment. The results of a series of tests to evaluate the tunnel performance are also described. The flow in the test section is shown to be highly uniform and steady, with very low (natural) free-stream turbulence intensities. Measured boundary layer mean and fluctuating velocity profiles were found to be in good agreement with classical correlations. Test-section free-stream turbulence intensities are presented for grid-generated turbulence: agreement with expectation is again found to be good. Immediate applications to the tunnel include friction drag reduction and boundary layer transition studies, with future possibilities including flow separation and other complex flows typical of those found in gas turbines.

This paper is structured firstly to describe the operational requirements of a modern military aircraft with particular reference to its armament systems, secondly to derive and consider developing architectures for armament control and thirdly to present one of the architectures from an implementation point of view.

The paper concludes that the optimum architecture for safety, availability and control of airborne weapons can be derived logically from the military aircraft operational requirement. It is not necessary to indulge in over duplication to achieve a cost effective, safe and available system.