This paper considers two-dimensional flow past flexible membranes whose supports are aligned at right angles to the flow. Unlike a previous study of bluff impervious membranes, the present membranes are slightly porous having a porosity similar to that of parachutes. The drag and base pressure have been measured for various lengths and for a variety of fabrics. The results have been correlated by two theories which are extensions of those already published. When the porosity is not too small the results are shown to depend only on the total volume flow through the membrane. The tendency for the membrane to oscillate in harmony with regular vortex shedding is reduced by the porosity and increased by the length of the membrane. Above a certain porosity oscillation is inhibited for all membrane lengths.

An experimental investigation has been performed to study the formation and development of spiral vortex flow over a swept-back wing. An aerofoil section with three alternative leading edge shapes was tested at sweep angles ranging from 0° to 56° for unit Reynolds numbers of 1 × 106/m and 2 × 106/m. The principal diagnostic tool was the surface oil-flow visualisation technique supplemented by pressure distribution measurements in certain cases. No spiral vortex flow was observed for sweep angles of 0° and 15° but at higher sweep angles the oil-flows indicated that there were three different mechanisms for the formation of spiral vortices. The angle of incidence at the onset of vortex flow, and the mechanism responsible for its formation, were found to depend upon the sweep angle, the leading edge shape and the Reynolds number. It was also noted that the larger the leading edge radius the greater the dependence upon Reynolds number. However, comparison with other work suggests that Reynolds number, incidence and sweep angle alone are insufficient to determine the type of spiral vortex flow occurring on a given wing.

The development and use of a ‘minituft’ surface flow visualisation technique in the RAE 5m Pressurised Low-Speed Wind Tunnel is described.

The method, due to Crowder, uses very fine nylon monofilaments to show surface flow direction. These tufts are made visible by coating them in a fluorescent dye and then illuminating them with a powerful ultra-violet light source.

Because of their small size, a large number of tufts may be used without interfering with the flow to a great extent. However, it is shown that if accurate force measurements are required, then it is advisable to test the model in the absence of tufts.

Seven composite laminates, three carbon, one Kevlar and three hybrid as supplied by an aircraft manufacturer were assessed for damage tolerance. Rectangular coupons were subjected to low velocity impact in the range 0-4 Joules by a swinging pendulum. The coupons were ultrasonically C-scanned to measure delamination area and visually inspected for damage. Residual strength tests in tension, compression, flexure and shear were then carried out on the damaged coupons. Visual damage, delamination damage and strength reduction thresholds were determined from the data and compared. Of the three thresholds, delamination damage and strength reduction tended to coincide. For the various lay-ups these were in the range of 1·5 to 2·0 J for the longer (tensile) specimens or in the case of the smaller (shear) specimens between 0·2-0·3 J. In all cases onset of visible damage occurred at slightly higher values of impact energy. The significance of specimen stiffness was noted.

The lateral dynamic stability and control of a large receiver aircraft was considered during air-to-air refuelling. A simple aerodynamic model was developed in order to determine the aerodynamic forces and moments acting on the receiver aircraft due to the tanker aircraft's vortex field. These forces and moments were then expressed in derivative form and included in the linearised equations of motion. Solution of these equations revealed a divergent oscillation, characteristic of air-to-air refuelling and consisting mainly of bank and sideways displacements. An approximation to this mode, which highlights two important aerodynamic derivatives was made. The values of these derivatives depend mainly on the vertical separation between the tanker and receiver aircraft and the ratio of the tanker-to-receiver aircraft wing spans. In flight, it appears that the pilot controls the divergent mode by frequent alternate movements of the ailerons.

A numerical method for calculating transonic flow around general inlet configurations is presented. The method is based on a finite volume potential flow algorithm with enhancements to reduce truncation errors. An approximate factorisation iterative scheme is employed and the computer code is written to take advantage of the architecture of a vector computer. The method has also been coupled with an integral boundary layer method to take into account viscous effects on the inlet surface. Results are presented for a number of configurations which are representative of current design trends, at both take-off and cruise conditions. Comparison with experimental data shows favourable agreement. The method is shown to be accurate, reliable and cheap to run.

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.

A technique for calculating the dispersion of unguided missiles due to strong turbulent wind is presented. The three components of turbulent wind velocity are simulated along a trajectory by means of a moving average process according to Box and Jenkins. Variations of the statistics of turbulent wind with height are taken into account. A six degree of freedom program is used to calculate a trajectory. The effect of turbulent wind on both powered and unpowered flight is considered. The results of the calculation for two types of missiles are presented.

This paper describes a novel flow tracing technique which has been developed to obtain data on mixing and dispersion processes in gaseous flow systems. Tracer gas is injected at low flow rates into an air stream. Choice of tracer gas — primary fluid combination in relation to gas properties and detection techniques is discussed. The mode of operation of the mass spectrometer is described together with the sampling system. Analysis of samples drawn from the flow field provides tracer gas concentration profiles throughout the flow and these may be used to yield information on mixing rates. Two examples are given which illustrate the use of the method.

A rig for measurement of forces and moments due to continuous rate of roll has been commissioned at RAE Bedford. Tests have been made on a High Incidence Research Model (HIRM) in two wind tunnels at M = 0·2, 0·4 and 0·7. At present models can be tested up to 40° angle of attack at rotational speeds up to 350 rpm.

Tests on HIRM included an investigation of configuration and Reynolds number effects. Results are compared with similar data from tests with another rolling rig and from small amplitude oscillatory tests.

An unsteady lifting line theory for a general motion of a wing of high aspect ratio is presented. Our analysis parallels that of Van Dyke (1964) in his solution for the steady lifting line by the method of matched asymptotic expansions but is complicated by the shedding of transverse vortices associated with variation of circulation with time. We find expressions for the downwash due to three-dimensional (finite span) effects and the lift on the wing. Calculations are presented for a wing of elliptic planform following a curved path.

Attention is focused on the installation aerodynamic aspects, rather than ejector design itself, of ejector augmentors installed in combat aircraft as part of the lift and propulsion system.

It is indicated that in the case of the combat aircraft required to perform vertical land but not VTO, the installed thrust is such that only a small level of augmentation is required. The reason for installing an ejector is that it is capable of providing this augmentation together with a benign ground footprint. The design problems are seen to be those of relatively large volume and ensuring satisfactory aerodynamic performance in all relevant flight regimes.

The installation aerodynamic problems focus on the inlet and exhaust. Performance is very sensitive to intake pressure recovery with the critical area being at the start of the landing transition. In the second case, the problem is that of providing a degree of thrust vectoring for the large low pressure exhaust to provide adequate transition performance in the face of considerable intake momentum drag.

The object of this paper is to uncover the nature of the destabilising coupling that is the major cause of body-freedom flutter and to see whether a simple cure for the flutter can be found. To do this frequency-coalesence theory is applied to a simple aircraft. It is shown that the aircraft is liable to flutter if it has a sweptforward wing and a positive ‘tail-off’ cg margin or a sweptback wing and a negative cg margin but a simple cure for the flutter does not appear to exist.

An analysis of an extensive series of unsteady and steady pressure measurements at transonic speeds on a rigid 12% thick NACA 16 series aerofoil reveals a useful classification of the type of excitation characteristics of particular flow regions.

The pressure fluctuation measurements suggest that when the shock from the aerofoil reaches the tunnel roof, serious interference (both dynamic and static) occurs.

The RAE 2 ft × 1½ ft Transonic Tunnel used for the tests has low levels of flow unsteadiness at low frequencies, making it a useful facility for basic research in time-dependent aerodynamics.

The Two-Sting Rig system provides captive trajectory and grid survey testing in the ARA 2·74 m × 2·44 m transonic wind tunnel, on models of the order of 10% scale. The system has been in productive operation since 1979, having been used primarily in the captive trajectory mode to predict release characteristics for a wide range of stores/aircraft.

The paper describes the improvements to and developments of the system that have arisen from experiences gained during the last two years of its operational use. A brief description only is given of the general arrangement of the rig. Improvements to performance, simulation capabilities and to wind tunnel productivity are described together with current design studies for new applications.

An appraisal of the overall performance of the method against three other ground based techniques is used to illustrate its merits and defects, using results from recent Two-Sting Rig wind tunnel tests and flight.