The variation of the Crack Stress Intensity Factor (SIF), for two cracks growing from one hole only in an array of holes in an isotropic material under uni-axial tension has been studied. The effect of the fastener hole ahead of the growing crack was found to give an increase in the SIF only when the crack was within about one and a half diameters of the approached hole edge, compared with the level predicted by considering a single central hole in a plate. An equation suitable for inclusion in a crack growth program has been derived from the research results.

Details of a visual method for indicating boundary layer transition are given, with particular reference to tests at high Reynolds number in the RAE 5 metre pressurised low-speed wind tunnel on a slender-body model. The method is compared with other techniques on the basis of ease of use and quality of the indication.

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.

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.

A simplified output error method based on the Gauss-Newton minimisation technique is formulated in the frequency-domain and its application demonstrated for extraction of aircraft longitudinal parameters from simulated flight data. A study is carried out to show the effects on the accuracy of estimated parameters due to use of different input forms to generate the flight data, using different initial values to start the algorithm, presence of measurment noise in the flight data and fixing some weak parameters at a priori values. It is shown that the use of Packing Theorem to increase the sparsely sampled frequency data does not lead to better accuracy by the proposed method, as has been reported for the maximum likelihood method in the literature. Finally, relative advantages of the frequency-domain approach as against the time-domain approach are pointed out by analysing the same flight data in these two domains. It is shown that frequency-domain approach is better equipped to analyse noisy-data and can yield better estimates at reduced computational time.