There has recently been evidence of an upsurge of activity in general aviation in the United Kingdom, particularly in small scheduled operations which are frequently referred to as ‘third level’. Much of the non-scheduled activity has been generated by North Sea exploration and the tendency for stronger ties with the European Economic Community (EEC). The recent growth in third level operations owes some of its impetus to each of these reasons, but there have also been moves to operate domestic links on routes which are not well served by the ground transport infrastructure. These include the Newquay-Gatwick and Norwich-Birmingham-Swansea-Newquay routes, the helicopter service between Fort William and Glasgow, the formation of Air Wales and Air Westward and the intention of British Caledonian to set up its own network of third level feeders for its international services at Gatwick.

The discovery of the essential logic of engineering design through the development of the ‘procedure for analysing the design of interactive solutions’ (PADIS) has made it possible to prepare authoritative flowcharts for the design process. This deeper understanding has revealed that, for the design task overall, there is no unique flowchart but many. Each project study is inspired by a combination of up to five types of inspiration, and by appropriately combining the flowcharts given here, an individual flowchart can be determined for each design task undertaken.

At subordinate levels of design, it is true, the design process is normally stereotyped, but if invention or new knowledge encourages redesign there may be need to adopt different procedures.

‘Active Control Technology’ (ACT) is a jargon of the last few years describing the technological requirements which permit the earlier concept of the Control Configured Vehicle (CCV). The CCV idea was that by suitably driving specially arranged controls, various desirable aircraft characteristics, notaby stability and good handling, could be provided synthetically and as a result the tail and fin sizes could be reduced and the wing mounted in a more advantageous position on the fuselage: more freedom of choice was thus given the designer in settling his configuration. The technology to do this was barely ready at the time but meanwhile has been progressing apace in the form of minicomputers, electrical signalling, digital control systems and a deeper analysis of what is involved in a total system.

The present note is concerned with the flexural vibrations of a thin elastic plate with variable rigidity and having the form of a sector of a circular ring. Plates of this shape have been rather sparsely treated in the literature.

The problem of free vibration of sectorial plates with radial edges simply supported has been investigated by Ramiah and Vijaykumar and by Ramakrishnan and Kunnukkasseril. For the case of a plate having clamped radial edges and the circumferential edges having any combination of boundary conditions, an approximate solution has been obtained by Bhattacharya. The free vibration of annular plates for various boundary conditions are summarised by Leissa. All these are for plates of constant thickness only.

Vortices are of interest in many situations in fluid mechanics. One type of vortex with which the gas turbine designer is concerned is the line vortex springing like a miniature tornado from a point on the ground (or from a nearby aircraft surface) and entering the engine intake. It is possible for these vortices to suck stones up into the engine (Refs. 1, 2) and also to reduce the compressor surge margin (Refs. 3, 4). They are unsteady, in that their point of origin wanders about and so does their point of entry into the intake. This unsteadiness makes it very difficult to measure them, and so far no one known to the author has reported measurements of ground vortex strength, in the course of several investigations of the phenomenon (Refs. 1-3, 5-8).