Before detailing the value of non-destructive testing in the aircraft industry, it seems best to explain aircraft structural design philosophies as they affect NDT.

Airworthiness and weight-saving are two over-riding factors in aircraft design. The important parameter from an economic standpoint is the weight. Fig. 1 shows the value of weight saving for a civil aircraft operator in £ per lb with typical values going up to £100 per lb per aircraft per year. (This figure shows the actual financial saving associated with the reduction in operating economics due to the lower weight.) But the vulnerability of an aeroplane in any failure case makes safety a paramount consideration. To save weight, design factors on aircraft are very low.

Present aerospace development work is done in an environment which demands success. This has stimulated interest in methods of planning and controlling project development and costs more positively.

While some developers continue to hold the view that planning other than in the broadest terms is not compatible with high novelty development, the importance of new planning attitudes has been recognised. However, the very magnitude of a major aerospace project is such that the application of new planning and control procedures may in itself constitute a significant development programme, and it is not surprising that the industry has shown caution in introducing major changes of method.

According to the Plowden report, the American worker has weekly earnings of 2 to 2 times those of the British worker. The report also stated that, for the same production run (of 100 aircraft), the average cost in the USA would be between 105 and 115 per cent of the British cost for the same aircraft. This means that the number of man-hours expended in Britain is of the order of 2 to 2 times the number of man-hours taken in the USA for the same job. Or, it means that, if we could make an aircraft in Britain for the same man-hours as in the USA, it could sell at only 40 to 50 per cent of the American equivalent. But bear in mind that the man-hours I refer to are for all employees, not just those usually charged direct.

Early in 1965 the Graduates’ and Students’ Section made a survey of its members to determine the effect on them of the cancellations of several major projects and, in particular, what proportion of members were likely to emigrate to continue their careers in aeronautics as opposed to taking non-aeronautical appointments in this country. Following the publication and debate of the Plowden Report, and the return of the industry to a slightly more stable atmosphere, the Section has made a further survey of its members to sample their opinions of aeronautics as a career, to find to what extent their careers were planned, and what these plans were where they existed. It is hoped that from this, suggestions of value to employers will emerge, particularly on making the careers of young engineers more interesting and worthwhile.

In the note “Aerodynamically induced vibration in coolers”, by D. G. Mabey (pp 876-7, December 1965 Journal), the results of Grotz and Arnold concerning the frequency of the Karman vortex streets in tube banks, such as in heat exchangers, are mentioned, as is also the law of the linear relation between f(T—d)/V and (2T-L)/d, as found by Putnam, where

f frequency of vortex shedding

T transverse distance

L longitudinal distance between tubes

d outer diameter of tube

V mean stream velocity based on minimum flow area between the tubes

This linear relation has no theoretical justification and cannot be accurate, as is admitted by the author cited. A further investigation on a theoretical basis seems to be necessary.

The direct problem of aerodynamics (profile of the aerofoil is given—calculate the aerodynamic characteristics) has been studied for thin aerofoils with small camber. Given the undisturbed stream function

V, ω, α being the constant velocity, vorticity and angle of incidence respectively, the pressure distribution, lift coefficient and pitching moment have been calculated for a general profile.

In recent years there has been considerable interest in the possibility of providing high speed aircraft with the capability of vertical or short take-off and landing (V/STOL). One method for achieving V/STOL is to use lifting engines or fans, the aerodynamic interference effects of which are not yet fully understood. Experimental work on this problem has been done by Jordinson, Otis, Vogler and research workers at the British Aircraft Cor-poration, but no satisfactory theoretical analysis is known. The object of this paper is to put forward a semi-empirical method for predicting the aerodynamic interference of an exhausting jet on a uniform mainstream flow past a wing.

Axi-symmetric buckling of a circular plate having different material properties in the radial and circumferential directions was analysed in ref. 1. A plate with constant thickness and subjected to a uniform edge compression was considered. The plate edge was assumed clamped or simply-supported. The analysis of ref. 1 is extended to include plates with thickness variation in the radial direction.

The solution of the general heat transfer problem for typical aircraft-type structures usually involves a finite element approach involving the solution of a large number of simultaneous equations. This may be performed by calculation using a digital computer or with an analogue simulator. For calculations involving both spatial and time intervals considerable care must be exercised to obtain solutions which are not divergent or oscillatory and this usually involves very small time increments and a large total computation time.