The Dynamic Relaxation method is used to analyse the post-buckling of flat rectangular plates. Extensive results are obtained for two types of problem in which the transverse edges are unloaded; in one case the transverse edges remain straight, in the other they are free to wave. Comparisons are made with alternative experimental and theoretical results. The potentiality of this approach to post-buckling problems is demonstrated by considering a variable thickness plate with mixed boundary conditions.

An experimental study of supersonic flow over wall mounted cavities with different aft wall angles is carried out. Unsteady pressure measurements were made on the walls and floor of the cavity. Data analysis was performed on the experimental results using statistical methods. In the case of higher angled cavities, the presence of an upstream traveling acoustic wave could be confirmed. For lower angled cavities (60 degrees and less) where the acoustic wave could not be identified, the flow inside the cavity was more or less stable. Mode switching occurring in higher angled cavities was confirmed by spectrogram studies.

Accurate stress and strain analysis in bolted joints is of considerable interest in order to design more efficient and safer aerospace structural elements. In this paper, a finite element modelling of aluminium alloy 7075-T6 bolted plates, which are extensively used in aircraft structures, is discussed. The ANSYS Finite Element (FE) package was used for modelling the joint and estimating the stresses and strains created in the joint due to initial clamping forces and subsequent longitudinal tensile loadings. A double-lap bolted joint with a single bolt and nut was considered in the study. A three-dimensional (3D) finite element model of the joint was generated, and then subjected to three different simulated clamping forces followed by different levels of longitudinal tensile load. 3D surface-to-surface contact elements were employed to model the contact between the various components of the bolted joint. Friction effects were considered in the numerical analysis; and moreover, the clearance between the bolt and the plates was simulated in the model. FE results revealed beneficial compressive stresses near the hole edge as a result of applying the clamping. It was found that a higher clamping force can significantly decrease the magnitude of the resultant tensile stress at the hole edge and also bearing stress in the joint when subjected to the longitudinal tensile load.

Operation of vehicles over dusty terrains and unprepared airstrips has highlighted the erosion problems incurred by ingestion of dusty air. Hibbert summarised the experience from British helicopter trials up to that date and drew attention to some of the factors that influenced the extent of erosion damage and to methods of minimising it. He cited a trial during 1963 in which a twin-engine Wessex Mk 2 helicopter having one intake protected by felt filters was tested in North Africa. Some idea of the severity of the problem may be gained from the fact that the unprotected engine surged after 3h 40 min while the other was found to have lost half its surge margin. However, operation can usually be arranged so that time spent in the dusty environment is minimised and service lives under desert conditions may be typically around 100h. In attempts to improve lives to a more acceptable level, different types of filtration have been investigated and the mechanism of erosion studied in some detail. This note describes some laboratory experiments to determine the influence of particle size on the erosion and attempts to relate this to filtration and engine life.

The cycloidal propeller for a Micro-Aerial Vehicle (MAV)-scale cyclogyro in hover was studied using a 2D Reynolds-averaged Navier-Stokes equations solver. The effects of the blade dynamic stall, parallel Blade Vortex Interaction (BVI), inflow variation and flow curvature were discussed, based on the results of numerical simulation. The results from the 2D Computational Fluid Dynamics simulation indicated that the blade of the cycloidal rotor is actually performing a pitching oscillation, if observed in a moving reference frame. The dynamic stall vortices shed from the upstream blade cause intense parallel BVI on the downstream blade. The interaction will induce upwash and downwash on the downstream blade. This changes the effective reduced frequency and actually delays the stall of the blade, which is beneficial to the thrust generation. There is also strong downwash in the rotor cage and it changes the inflow velocity experienced by the blade. The downwash and flow curvature can either be beneficial or harmful to the thrust generation. The combined effects of dynamic stall, parallel BVI, inflow variation and flow curvature cause large aerodynamic force peaks and ensure the cycloidal rotors work at very low rotation speeds with high thrust. This guarantees that the cycloidal rotors possess at least the same level of hover efficiency as screw propellers.

When a vibrating structure encloses a volume of fluid, the acoustic effects within this volume modify considerably the response characteristics of the structure, provided that the cylinder is vibrating in radial modes only. Measurements made of the displacement caused by a particular sound wave are of the same order as the values predicted. The calculation of the response of the cylinder to an acoustic wave also yields the sound field inside the cylinder and, again, the results are in general agreement with practical experience.

This paper concerns the boundaries between flow regimes for sharp-edged delta wings in supersonic flow and the relation of some predictions of thin-shock-layer theory to these boundaries. In particular, it is shown that the theory predicts that the attachment lines on the lower surface of a thin delta wing at supersonic speeds suddenly jump from just inboard of the leading edges to the centre line in certain flight conditions. In general there is close agreement between the conditions for this jump and the flight conditions corresponding to the change-over from attached flow to the leading-edge separation on the upper surface. Since the movement of the attachment lines on the lower surface must change the position of the sonic line and the nature of the expansion around the edge, it is suggested that the two phenomena are directly related. Thus thin-shock-layer theory can be used to establish the boundaries of the various flow regimes for a wide range of Mach number, incidence and wing sweep. The theory can also be used to predict the effects of wing thickness on leading-edge separation, but here the experimental data is very sparse and somewhat contradictory, so the value of the prediction in the case of thickness requires further investigation.

Free vibration characteristics of stiffened plates possessing symmetrical stiffeners have been investigated by the finite element method. The main elegance of the element used lies in that the formulation takes into account the arbitrary orientation of a stiffener inside the plate element. The element being isoparametric in nature caters effectively for the irregular edges of the boundary as well as the transverse shear deformation of the plate and the stiffeners. Rectangular and skew stiffened plates having various boundary conditions and with stiffeners varying in number and in spacing, have been analysed. The correlation of the natural frequencies obtained by the present approach with the published results have been found to be very good.

The prediction of blade deflections and vibratory hub loads concerning helicopter main rotors in forward flight is the objective of this work. They are determined by using an aeroelastic model derived through the coupling between a nonlinear blade structural model and a boundary integral equation solver for three-dimensional, unsteady, potential aerodynamics. The Galerkin method is used for the spatial integration, whereas the periodic blade response is determined by a harmonic balance approach. This aeroelastic model yields a unified approach for aeroelastic response and blade pressure prediction that may be used for aeroacoustic purposes, with the possibility of including effects from both blade-vortex interaction and multiple-body aerodynamic interaction. Quasi-steady aerodynamic models with wake-inflow from the three-dimensional aerodynamic solver are also applied, in order to perform a comparative study. Numerical results show the capability of the aeroelastic tool to evaluate blade response and vibratory hub loads for a helicopter main rotor in level flight conditions, and examine the sensitivity of the predictions on the aerodynamics model used.

It is becoming recognised that before civil aircraft can operate at high density, the most important problem to be solved is that of traffic control. Methods exist by which a single aircraft can navigate from a distant point to an airport and let down to a safe landing under bad weather conditions. Difficulties arise when several aircraft are involved at once and long delays can occur in the neighbourhood of airports carrying high density traffic. In this paper an analysis is made of the traffic problem in an attempt to clarify some of the factors involved.

The separation or breakaway of over-expanded gas from a nozzle wall plays an important role in the estimation of the thrust from a rocket engine when run at altitudes considerably less than the design. A number of reports have been written on the subject but the agreement of test results has not appeared to be good.

In an effort to clarify the position, the Rocket Department of Bristol Siddeley Engines Ltd. has carried out tests on experimental combustion chambers having static pressure tappings in the nozzle divergent section. These tests have shown that, contrary to some previous suggestions, the pressure at which the gas separates is neither constant nor independent of the nozzle length. The paper, which includes results from other workers, divides the field into separation adjacent to the nozzle exit and also at positions where the area ratio is less than 80 per cent of the exit area ratio.

For the most part, consideration is given to conical nozzles having divergence half angles of 15° to 17°, but comment is made on the effects of divergence and other variables. A tentative suggestion as to the mechanism of separation is also made.

Finally, the effect of separation on the sea-level thrust of a nozzle designed for high altitude Is shown.

A problem of some practical importance concerns the interference between a wing surface in a free stream and a nearby streamwise vortex. This situation can arise for example, either in a helicopter rotor system, or when concentrated vortices, which are shed from a fuselage nose or from forward canard controls, interfere with an aft lifting surface.

An approximate non-linear analytical study is described in Ref. 1 in which the three-dimensional loading on a two-dimensional non-swept wing underneath a streamwise line vortex in low speed flow (as shown in Fig. 1) is deduced. Since publication of Ref. 1 a number of linearised theoretical studies have come to light.

The paper presents an experimental study of vortex systems generated in the region where an incompressible flow with spanwise varying velocity moves about a circular cylinder connected to a flat plate. The role that the various flow and geometric parameters play in the generation of the horseshoe vortex at the front of the cylinder is discussed and the dimensionless similarity numbers which describe the flow are derived.

Circumstances can arise in which a rectangular panel, forming part of a structure, is subject to non-uniform in-plane compression, and in which it is important that instability of the panel should not occur. Problems of this nature occur, for example, in the structure of modern highspeed aircraft subject to the transient thermal stresses that can arise from rapid changes of speed or altitude.

This paper describes the current status of knowledge regarding the impact of aviation on the atmosphere. The growth of the aviation industry is likely to continue in the future and at present there are significant concerns that this will adversely affect climate and local air quality in the vicinity of airports. Indeed, it is possible that air quality may become a constraint to increased capacity of some large hub airports. Currently the radiative forcing impact from aircraft emissions, other than CO2, are not accounted for in the International Civil Aviation Organization emission trading scheme proposals. Taking only this approach, emissions trading could, in theory, increase the radiative forcing, rather than decrease it. The study of improved ‘environmentally friendly’ flight is still in its infancy, however any proposed and actual new developments, in terms of technology and operational practice, should include an environmental assessment.

The first basis for the design of any power-driven mechanism is an exact knowledge of the characteristics and capabilities of the power unit available. Without such information no designer is able to start on the initial sketch of the mechanism. The man powered aircraft is no exception and its designers have suffered in the past by insufficient knowledge about man's power. This may seem remarkable because until about two centuries ago almost all the world's work was done by muscle-power, and much of the muscle was human.

This paper reports on the measurement of aerodynamic forces that act on a square cylinder which was downstream to an identical cylinder. When the two cylinders were in tandem formation, a critical spacing equal to about four times the side length D of the square cylinder, was found to exist. For L/D < (L/D)cri, where L is the streamwise centre to centre spacing between the two cylinders, the boundary layers which separate from the upstream cylinder reattach onto the downstream cylinder. Only the latter sheds vortices and it is subjected to a thrust rather than a drag force. For LID > (L/D)cri, both cylinders shed vortices and both are subjected to drag forces. When the two cylinders were in staggered formation, due to the presence of various lift generating mechanisms, the lift force that acts on the downstream cylinder can be either positive which points away from the wake centre line of the upstream cylinder or negative which points towards the wake centre line of the upstream cylinder. It was found that in the range 4 ⩽ LID ⩽ 12, an unstable regime exists in that the lift force generated pushes the downstream cylinder away from the upstream cylinder’s wake centre line at small dimensionless transverse spacing (Y/D) where Y is the transverse centre to centre spacing between the two cylinders and reverses its direction only at Y/D > 2. At L/D = 29, the largest streamwise spacing that can be investigated in the present study, the influence that the upstream cylinder has on the aerodynamic forces acting on the downstream cylinder was found to be still fairly appreciable.

It is both an honour and a responsibility to deliver a lecture commemorating the names of two scientists who have made unique contributions to fluid dynamics, and whose names perhaps above all others will remain immortal in our subject. The range of topics that would be suitable for such a lecture is very wide, because there is scarcely a branch of fluid dynamics in which the work of Reynolds and Prandtl does not continue to play a significant part. In a lecture of current interest there is, therefore, no problem of relating the subject matter to the names to be commemorated; the influence of Reynolds and Prandtl remains as strong as when they were alive, and many of the problems that engaged their attention are even today only partially solved. The lecturer must, therefore, use other considerations for guidance in the selection of his subject from the limited range on which he is qualified to speak, for few could hope to work over the wide field covered by Reynolds and Prandtl. He must if possible select a, topic in which major contributions have originated from Germany and the United Kingdom, on which research is actively in progress in both countries, and for which progress has relied on the combination of theoretical and experimental work to provide acceptable simplifying assumptions that characterised many of the investigations of Reynolds and Prandtl.

Trailing edge blowing over a Coanda surface has been utilised as a circulation control mechanism for increasing the lift of an aircraft wing. Typically, high energy air is blown from a narrow spanwise slot over the rounded trailing edge of a wing and the air supply is modulated to effect a degree of lift control on the wing. This configuration produces an aerodynamic force in a uni-directional sense only. An alternative novel flow control actuator is described which utilises a simple variable geometry Coanda surface with upper and lower spanwise blowing slots to achieve fully proportional bi-directional control in the manner of a conventional flap. A prototype device has been wind-tunnel tested and is shown to have substantially linear response characteristics and to be as efficient as an equivalent flap surface. The performance of a flow control actuator suitable for small UAV applications is described.

Measurements were made of the pressure in a blunt-nosed pitot tube, in an air stream at Reynolds numbers from about 15 to 1,000. The results are expressed in terms of a pressure coefficient , where P is the pressure in the pitot tube, ρ is the density of the fluid, and p and V are the static pressure and velocity in the undisturbed stream. As found in previous investigations, Cp becomes greater than 1 at low Reynolds numbers, the increase being about per cent, at a Reynolds number of 50 (based on external tube radius). In disagreement with the work of Hurd, Chesky, and Shapiro, no decrease of Cp below 1 was found at any Reynolds number.