It should be fairly obvious that, in contemplating the design of a future combat aircraft, it is important at the outset to relate the effort to some forecast definition of what is needed. This may take the form of an official or an unofficial requirement; however, its precise form is immaterial to the central argument. Either way, it is necessary to recognise several limitations to a so-called requirement:

1. i) the chances of it being ‘right’, some 10-20 years before the realisation of its potential wartime application, is fairly remote. This is particularly true with today’s rapid advancement in, for example, weapons and sensor technology. These developments make it doubly difficult to predict the nature and strength of the threat force;

2. ii) the postulated scenarios will change from day to day, and indeed, during the day–according to the course of the main battle; therefore the military commander's requirements of the forces at his disposal can change by the hour;

3. iii) the environment, both militarily and climatically, plays a large part in the definition of a design. The variability of the environment is neglected only with grave risk to the eventual utility of the weapon system.

It is a fact that there were many more sceptics and only a few advocates for the airship in the UK some ten years ago. Few people had given serious thought to the possible return of the airship as a modern transport form, still fewer were prepared to back it financially and it was left to the few to put forward their thoughts and plans for its return. In this they were encouraged by the small fleet of blimps being flown by Goodyear in the USA and by the fact that the US Navy had not phased out airships until 1962.

Prior to 1937, responsibility for civil aviation in the UK, including airworthiness and operation of airships, was vested in the Air Ministry, a Government department, and it was only in 1937 that it was devolved to an independent authority, the Air Registration Board, which is now the Airworthiness Division of the CAA.

The first involvement of the CAA with airships occurred early in the present decade when it was confronted firstly with an extremely unorthodox configuration of airship. The Skyship project (Fig. 1) was 720 ft in diameter, 48 million cu ft in volume, and 400 tons pay-load capacity.

The purpose of this paper is to give a brief introduction to the scope, flexibility and power of the British Aerospace Numerical Master Geometry (NMG) System, which is a computer aid for the design and manufacture of complicated three-dimensional curved surfaces. NMG is currently used at all ex-BAC sites within the Aircraft Group of British Aerospace for the purpose of generating and storing master computer models of the external shapes of aircraft or components. These master models may then be interrogated using a simple command language to derive information about the external shape for such diverse uses as aerodynamic analysis, detail structural design, numerically controlled machining and inspection. The use of such models means that everyone has access to the same basic information, and consistency is assured.

The buckling coefficient for a conventional shear web, reinforced by a series of equally-spaced transverse stiffeners, is practically independent of the flexural rigidity of the stiffeners provided this exceeds a certain critical value. The stiffeners then provide conditions close to simple-support (if they are of negligible torsional stiffness). For stiffeners of less than this critical rigidity, reduced buckling coefficients are plotted in Ref. 1, in terms of a stiffness parameter μ related to the second moment of area of the stiffeners. Reference 1 also shows that the critical value μc referred to above increases rapidly with reducing stiffener pitch, leading in some cases to impractically large stiffeners.