With the continuing advances in aerospace technology, the “spin-off” benefits increase, too. Although man has now set foot upon the moon, sent unmanned probes to Mars and Venus and placed a series of satellites into earth orbit, we have only touched upon the fringe of celestial and interplanetary venture. Yet from these early and what will one day seem to be clumsy attempts, we have, as individuals, gained many assets which affect our daily lives.

It is indeed regrettable that the enumerable persons who denounce the space-programmes as “a waste of money” “an absolute waste of time”, “unfortunate in that the money could be used to improve the living standards of so many people”, etc., do not give a little more thought to the space programme as a whole, including the “spin-off” benefits.

The need for the testing of aircraft is of course very obvious. New types of aircraft must be flight tested to check the performance predictions, define operational flight envelopes, or set safe-life limits for various components etc. Other flight tests are directed towards the investigation of particular problems, but much of this type of study is best done by model tests; especially when information is required in those areas where theories are known to be poor or even non-existent.

During recent years a major research programme has been undertaken at the National Gas Turbine Establishment into the subject of circulation control and its application to lifting rotors. In the case of rotors intended to be used on helicopters and stowed rotor aircraft, a very important part of the research work is the examination of rotor behaviour in forward flight. Traditionally, this has been investigated mainly on full-scale aircraft but more recently model scale experiments have been done in wind tunnels, particularly in the USA where there are a number of suitably large tunnels.

The high cost of new weapon systems and the loss of tactical capability when vehicles are out of operation for unscheduled repairs are forcing the military services to require a higher order of structural reliability. Fleets are being kept in operation for many years beyond the time originally anticipated during design, resulting in many cases, in the need for costly structural repairs and modification to cure fatigue problems. Consequently, new weapon system procurement contracts are being written with a “fatigue-life” guarantee as a contractual requirement. This situation calls for careful attention to details during the design phase. More testing, both exploratory to aid in detail design decisions, and confirmatory to validate the design and demonstrate compliance with the contractual requirements, is required. Better test methods and more meaningful test results are demanded from the test laboratory. Methods for more accurate predictions of the loads experience during the entire service usage are required of the structural analysts.

This paper is intended to provide a summary of the present role of the flight recorder in relation to the investigation of aircraft accidents and to refer briefly to its future role in this field, together with its potential for flight safety monitoring.

The paper deals principally with the philosophy of data recording for these purposes and with the general needs of the associated data recording, recovery and analysis systems. It also describes the predominant problems encountered up to the present time in the use of such systems for accident investigation purposes in the United Kingdom. The technical problems relating to system design, information recovery and analysis are, however, of a specialised nature and can only be referred to in brief terms within the scope of this paper.

Over the subsonic speed range, the pressure field attached to a ducted rotor decays rapidly with distance away from the rotor. This exponential decay, coupled with the low radiation efficiency of a subsonically rotating pressure pattern, is generally sufficient to bring the radiated sound power well below that produced by interaction of the rotor with disturbances in the flow. This is particularly true for multibladed rotors as used in aircraft-engine fans and compressors, and accounts for the importance of rotor-stator interaction as a source of noise at subsonic tip speeds.

For some years now an increasing amount of experimental and theoretical work has been done to obtain a deeper understanding of separated vortex flow associated with slender wings. Most of it has been concerned with flat plates or thin wings.

Slender thin wings with leading-edge separation have high lift-dependent or vortex drags, and lift-dependent drag factors are usually well above unity. Thick symmetrical wings also have high values of lift-dependent drag factor. On a slender wing with leading edge separation, no leading edge thrust is obtained but by suitable! addition of thickness, the high suction peak underneath the main vortex can be made to act on a forward facing surface to give a reduction in drag.

To save weight, designers of aircraft gas turbines aim to produce axial compressors with fewer rows of blades and greater mass flows per unit of frontal area. These improvements often consist of increases in blade tip speeds and reductions in the ratio of the hub to tip diameters. As the efficiency of transonic blading is partly dependent upon a low value of blade pitch/chord it is now frequently necessary to design a blade with a greater actual chord at the tip than at the hub.

In the theory of the incompressible laminar boundary layer, Stratford's method is widely regarded as one of the best practical methods for the prediction of separation. The method may also be used in conjunction with the Illingworth-Stewartson transformation (described below) for the prediction of the separation positions of certain compressible boundary-layer flows. For one such case, for which an “exact” solution has been computed, it has been suggested, in ref. 4, that the method, in its simplified form at any rate, is not quite as accurate as had been anticipated. It is the point of this note to show that the full Stratford method does in fact give an excellent prediction of the separation position for this flow.