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.

Wind tunnel data from a tanker wing and receiver aircraft model at varying vertical separation have been compared with theoretical results. In the aerodynamic model the tanker wing is represented by a horseshoe vortex while the aerodynamic loads on the receiver are determined by the vortex lattice method and lifting-line theory, although an approximate method is used to determine the side force on the fin. In the longitudinal case data were obtained for low, mid and high tailplane positions and, with the exception of the pitching moment results, fairly good agreement is obtained between theory and experiment. The relatively small differences are due mainly to the wind tunnel boundary interference effect which could not be quantified for the pitching moment measurements. The lateral aerodynamic interference was determined by banking the tanker wing and displacing it sideways and by yawing the receiver model. Fairly good agreement is obtained between the theory and experiment for the most significant terms which are the rolling moments due to bank and sideways displacement. The effect of the sidewash due to the tanker wake on the receiver in yaw is found to be relatively insignificant. Over the range of bank, yaw and sideways displacements tested the results are almost linear.

In 1989, more than 29 million passengers were flown across the North Atlantic Ocean in 167 000 scheduled and non-scheduled flights. At peak times during the Summer months, a trans-Atlantic flight was crossing the Shanwick Oceanic Control boundary every minute and more than 200 flights were reporting between 10 and 50 degrees West. Traffic counts exceeded 750 flights a day.

The following account describes the more recent improvements to North Atlantic air traffic control, the early introduction of computers to the task, with their on-line data interchange between Oceanic Control Centres and the current computer supported services provided by the Shanwick and Gander Oceanic Area Control Centres.

Holography is a very powerful tool for studying compressible flows. It is a non-intrusive technique capable of both qualitative and quantitative assessment. This paper describes a number of applications to both two-dimensional and three-dimensional flow fields.

Passive control experiments were made on an 18% thick biconvex aerofoil model in Mach number range giving shock oscillations and at a Reynolds number of 0.7 x 106 with fixed boundary layer transition. The control methods studied included a passive control of shock wave boundary layer interaction by a porous surface and a cavity, and a buffet breather made of holes connecting upper and lower surfaces of the aerofoil. The experiments show that the shock oscillations can be virtually eliminated by these methods. A physical explanation is given for the success of these passive controls.

Stress intensity factors for centre and edge cracks in finite elastic sheets are calculated from potential energy and complementary energy release rates by dual analysis with simple compatible and equilibrium finite elements. Comparison with very accurate results of other authors who employ special singular functions to model a crack tip provides compelling numerical evidence that the calculated stress intensity factors behave respectively like lower and upper bounds to the exact values. The bound-like character of such results has been reported before in another context, though there are no known bounding principles which strictly apply to finite bodies.

A general dynamic model of the hang glider is applied to the analysis of response to control. The transfer functions of the glider to the longitudinal and lateral controls are formulated and some significant results, in terms of frequency response are presented and discussed. The relevant effects of the unsteady aerodynamics on the dynamics of the system are shown and the characteristics of poor lateral control are confirmed as observed in flight.

The design of guided missile systems presents a wide spectrum of problems to engineers in numerous disciplines which range through aerodynamics, electronics and signal processing. Of all the tasks involved in the design process, perhaps the most difficult is the integration of the various technologies into a complete, harmonised system. IMPACT is a computer program which was developed to address the system design aspects of homing guidance missile systems. The aim of this paper is to describe the engineering philosophy and theoretical background to the IMPACT program.

Kites are currently used in a number of applications (anemometry, aerial platform, traction), but very little information is available for the systematic design of kite systems. An experimental technique based on an instrumented tether for single-line kites is described. This was used to measure the performance of a variety of single-line kites. The analysis techniques are briefly outlined, and incorporate allowances for kite unsteadiness, the displacement of the kite from the anemometers, extrapolation of the line tension from the tether to the kite, and the kite’s velocity relative to the ground. The results are correlated with aspects of kite design, and specific recommendations for kite applications are made.

The scope of the air-ground data links, which have been developed over the last ten years to meet the airlines' operational requirements, will be extended in future years.

Air traffic control is one of the fields which will certainly make extensive use of this type of link. Indeed, it appears to be necessary to deal with the problem of traffic saturation globally by taking account of the navigation capabilities of modern aircraft as regards precision and the considerable automated flight/ground exchange possibilities which will be provided by future telecommunication networks.

The contents of the messages exchanged between aircraft and air traffic control centres, and the interfaces with the human operators concerned, i.e. pilots and controllers, must form the subject of thorough investigations conducted with all the parties involved: constructors, equipment manufacturers, traffic control organisations, and airlines. Aerospatiale have already taken this problem into account in the various studies being performed within the framework of the PREFACE and FANSTIC programmes.

Numerical methods have been developed to analyse incompressible viscous flows past three dimensional wings with deflected flap using viscous-inviscid interaction techniques. By using a surface transpiration technique, a panel method for external potential flow calculation is combined with a boundary-layer calculation based on an integral method. For the clean wing case, both three dimensional boundary layer corrections and two dimensional boundary layer corrections are applied in a strip theory sense and compared with experimental results in the literature. It is found that for wings with moderate aspect ratio and sweep angle, viscous corrections at low incidences by the two methods are of the same order. Based on this observation, a two dimensional boundary layer correction method (strip theory sense), including the wake-boundary layer interaction, is developed for the case of wings with a deflected flap of similar planform. Experiments have been conducted to assess the accuracy of the calculation methods for wings with deflected flap; comparison between the experimental and predicted results is encouraging.

For conical bodies, at moderate angles of attack, the flow separates from the lee side, forming two vortices. Although the vortex lift contribution is highly desirable, as the angle of attack increases, the vortex system becomes asymmetric, and eventually the vortices breakdown. Thus, some control of the separation process is necessary if the vortex lift is to be exploited at higher angles of attack.

The theoretical model which is used in this analysis has three parts. First, the ‘single line-vortex’ model is used within the framework of ‘slender-body theory’ to compute the outer inviscid field for specified separation lines. Second, the 3-D boundary layer is represented by a momentum equation for the cross-flow, analogous to that for a plane boundary layer and a von Karman/Pohlhausen approximation is applied to solve this equation. The cross-flow separation for both laminar and turbulent layers is determined by matching the pressure at the upper and lower separation points. This iterative procedure yields a unique solution for the separation lines and consequently for the positions of the vortices and the vortex lift on the body. Third, control of separation is achieved by blowing tangentially from slots located symmetrically along cone generators.

In circumstances where a pilot is forced to follow a specified flight path, such as during a landing approach or in nap-of-the-earth conditions, it will be shown that there is an apparent modification of the helicopter's stability characteristics. This effect is identified in helicopter flight data from nap-of-the-earth agility trials where oscillations are observed in the time histories of the pilot's control inputs and the vehicle's response. A technique of predicting the nature of these oscillations using a linearised helicopter mathematical model is developed. The model is inverted to give the response of the unconstrained states in terms of those strongly controlled by the need to remain on a specific flight path. Results are compared with data from flight trials and it is shown that good correlation between the period of the oscillations in the flight data and the predicted values can be obtained.

The solution of sandwich plate problems by the framework method is proposed and the basic elements of the method used are reviewed. The technique is demonstrated by application to a simple framework analog for rectangular sandwich panels with very thin faces and an antiplane core. A number of illustrative examples involving small and large deflections are solved.

To satisfy a user’s request for spaceborne remote sensing data a series of elements in the data chain must come together. The complete data chain has three major elements; orbiting platforms (to collect the data), data reception facilities and data processing facilities. The UK has a wide range of remote sensing users and, to support them, it has a strong presence in all areas of the data chain.

This paper will describe the less well known, but equally important area of data processing and dissemination. The two main UK facilities are the National Remote Sensing Centre (NRSC) and the Earth Observation Data Centre (EODC).

A method is described for predicting the two-dimensional incompressible turbulent boundary layer on a semi-infinite flat plate under small harmonic progressive oscillations of the free-stream volocity for arbitrary frequency and wave speed. The free stream considered consists of a constant mean on which an oscillating amplitude varying with downstream distance is superimposed. The Reynolds shear stress is modelled by a new single-layer eddy viscosity formulation and.a differential-difference technique is used to solve the governing equations numerically. The oscillatory eddy viscosity formulated is complex, allowing a phase difference between the Reynolds stress and the velocity oscillations. Comparisons between the calculated results and those obtained by other existing methods and measurements show that the method and the turbulence model are satisfactory for a full range of frequencies and wave convection speeds. It is also found that a change in the wave speed has a drastic effect on the boundary layer response.