The pay-off, in the final analysis needs to be a better air transport system for the traveller. This will, in turn, generate more traffic for the airline and hence more business for the aircraft manufacturer. To achieve a substantial and profitable share of the available market for new aircraft the manufacturer's product must be produced at the right time, meet the requirements of the airlines, and be competitive in terms of price and capability with the products, both new and existing, of his competitors. Advanced technology, applied in a cost effective manner, can be one of the ways of achieving this competitiveness and of improving the air transport system.

In the past thirty years the exploration and exploitation of space has been one of the few new eras into which man has penetrated and opened a new frontier. Naturally, this drive was made by the two world powers which possess the resources and which are pushed by their competitive fight for public prestige and world-wide admiration. Once again Europe supplied many of the ideas and many of the leading people. And what did we do for ourselves?

In the beginning of post Second World War space activities we missed the start. The first satellites were already in orbit when the first space activities in Europe were proposed. But when we began to move in 1961 we began to move in the right direction. For our purpose the essential factor was the creation of the European agencies—ELDO and ESRO at that time—in which the national efforts of the member states were combined and co-ordinated towards the common goal.

Airline efficiency is not a simple concept which can be measured by a single parameter. It is an amalgam of complex relationships which are in turn the results of many different activities. Probably because of this, efficiency criteria are mostly looked at in isolation which results in the overall concept of airline efficiency remaining nebulous. In fact the airline efficiency concept possesses a number of different but inter-related aspects. Figure 1 is a diagrammatic representation of the airline efficiency concept and depicts the various aspects and relationships which go to form it. This diagram portrays, in basic form, the major forces involved.

At the Symposium in April last year the Society met to consider how design and operation of quiet aircraft related to the often conflicting economic and environmental pressures. The prospects for quieter aircraft and engines were discussed from many technical points of view. The message emerging from the discussion was that, compared to the improvements made in the past 10 years, and which would be available now at the cost of replacing existing noisy, older generation installations, further reductions in noise at source would be very much harder to win. Moreover, they would be made against a steeply-rising trend of overall detriment to performance and direct operating cost.

So far as the possibilities are concerned for further reductions in the noise of subsonic propulsion engines, if we are to have more than modest, evolutionary improvements in levels, there will need to be radical changes affecting engine design, such as a definite move towards lower jet velocities.

As one means of achieving the required movement of a flying control the simple skew-hinge mechanism appears attractive because it has a significant range of approximately linear operation and because all of its mechanical components can be accommodated easily within the sort of shallow depth available in some wings. The mechanism is kinematically similar to that of the well-known Z-crank and Fig. 1 shows one possible arrangement of it inside a wing. For this particular case an axial translation of the control push-pull rod AA causes rotation of the flying control H about its hinge axis BB and the mechanical connection between these driving and driven members consists of the skew-hinge itself, which is attached to the flying control H and which has an axis CC which intersects the axis BB at an angle α, together with the other components of the mechanism. These are the hinge driving-block F, the driving-link G, and the drive transmission-collar I.

There are several well developed theories reported in literature for evaluating performance of a hot wire anemometer. On the other hand, although hot film probes play a rather useful role in the experimental liquid flow studies, no well developed theory systematically accounting for conduction and free convection losses is available, particularly, in the Reynolds number range of 2-350 (based on average flow rate and film width). This is indeed surprising since the fact that in this range of Rn viscous effects are of the same order as those due to inertia, was first recognised by Barker as early as in 1922. Thus it has been necessary to resort to careful calibration for each shape of the probe. The theory presented here represents a modest step towards minimising dependence on such tedious experimentation with reference to widely used wedged film probes.