In this paper the many aspects of tyre performance criteria are discussed, as they have developed over the last decade. The corresponding tyre developments that have been effected to date are set out in considerable detail, together with the forward developments which are currently engaging the skills of modern tyre designers.

For the most part the paper deals with the present standard aircraft tyre, of conventional or cross-ply construction (Fig. 1), but the future role of the radial ply tyre (Fig. 2) is treated in some detail.

Probably the most significant happening in 1971 was the formation of Engineering Sciences Data Unit Limited, which began to function on the 1st April. This is important in two ways; in the first case it enlarges the capacity of the Unit in the production of Items both in the aeronautical field and in other branches of engineering, and secondly it may well set a pattern for other organisations wholly owned by the Society. During the nine months of the year during which the Company has been in operation, the Unit has made satisfactory progress, progress which augurs well for the future, and the Council wish to record its appreciation of the work done by both ESDU Ltd, and the subsidiary of the Thomson Organisation, Engineering Data Sales Limited, which is responsible for marketing the Data Items produced by the Unit.

There is little published work on the flow past a sphere. Some experiments were carried out in the 1930s (see Fage), and other measurements have been made more recently (Cometta and Kendall). Much of the work has been restricted to flow visualisation and to measurements of drag and surface pressure distribution. Very few measurements have been made in the near wake.

In the present paper, measurements of vortex shedding frequency, wake dimensions and static pressure up to three diameters downstream are reported. The experiments were carried out in the Aerodynamics Laboratory of the Cambridge University Engineering Department, under the supervision of Professor W. A. Mair.

Smoothing screens are frequently used in wind tunnels and other ducts to minimise irregularities in velocity profiles and reduce turbulence.

There is an optimum value for the screen pressure drop coefficient which, for wire gauzes, corresponds to an open area ratio less than 0·5 if only one screen is used. However, screens with open area ratios of about 0·5 or lower, produce lateral non-uniformities in the downstream flow due to jet coalescence. To avoid coalescence, two or more relatively open screens may be used in succession, either so close as to behave more or less as a single screen or more spaced out with each screen operating independently. It is the latter situation which is considered in detail in this note.

Because of inevitable manufacturing tolerances there will always be errors in the characteristic screen parameters, which will make the screen impose its own irregularities on the downstream flow.

Demand forecasting is a hazardous business, particularly in civil aviation. Any technique which can improve the accuracy of forecasts will aid the development of the industry, for demand fluctuations are a prime source of aviation's instability. If these fluctuations could be predicted accurately the consequences of wide demand fluctuations could be minimised, but this rarely happens. Many of the causes of the fluctuations are outside the control of the forecaster. Otherwise, ignorance of the relationship between cause and effect is the source of inaccurate predictions. An approach to forecasting, which is designed to overcome the latter, is the application of econometric models. Many of the econometric models in civil aviation are still primitive, yet, much has been expected of them.

The concept of manoeuvrable re-entry vehicles capable of controlled re-entry from earth orbit to tangential landing is attractive to a number of military and civilian space missions. One of the several manoeuvrable re-entry techniques that has been proposed is the lifting body concept. Early studies on lifting body configurations indicated that unpowered horizontal landings would be feasible since subsonic lift/drag ratios of four or better were consistently obtained from model tests in wind tunnels. In 1962 the NASA Flight Research Center initiated a programme to investigate the capability of a pilot to control, manoeuvre, and land a lifting body vehicle. I would like to compare the philosophies and procedures used in the lifting body flight test programme at Edwards Air Force Base with those more commonly used in the flight testing of high performance aircraft. Also I would like to discuss limited results of the M2/F2 flight programme and give one pilot's opinion of the requirements for operational lifting bodies.

One of the severest operational limitations of a fighter is high angle of attack. I would like to discuss a philosophy of requirements on approach to testing and aircraft improvement. I will also summarise the results of the recent USAF, F-4E Stall/Near Stall Investigation.

For review, consider the classic approach used to testing at high angle of attack. All fighters are stall tested, i.e. a determination of handling qualities is made up to maximum usable lift. This, of course, also involves determination of natural stall warning, stall speeds and stall recovery techniques. Testing at angles of attack above maximum usable lift is generally delayed until a spin test programme is accomplished.