Never, at any time since the Wright Brothers made their first flight have the means of propulsion exercised a more dominant influence over the shape of aircraft or the shape of things to come, nor can it have been so difficult to forecast the form resulting from that influence. It has been a platitude for some time past to say that aircraft and engine design are mutually interdependent: now it is more than a platitude, it is a fact, and one to which we have not yet grown accustomed.

That power installations can no longer be procured “off the peg” is to-day an article of faith which is generally professed: what is rarer is an appreciation of the implications of this state of affairs. Pursued to its logical conclusion, the implication is that a new aircraft and its means of propulsion should originate in the same brain, and be designed, developed and manufactured under the guidance of that brain.

A few of the outstanding problems connected with the design of tailless aircraft are discussed. The paper does not set out to be in any way a comprehensive dissertation of the whole field of tailless design, as it was considered that it would be more useful to concentrate on some of the recent problems which are exercising the minds of designers at the present moment.

Since the problems discussed are those which are currently causing some degree of speculation, it follows that in the majority of cases only possible means of solution may be suggested and only tentative conclusions drawn.

This paper was requested to deal with (1) the future relations between designers and production; (2) the special problems to be faced by the production people and the assistance to be expected from the designers; and (3) how such design problems as pressurisation, silencing and the fitment of turbine engines were being tackled.

These terms of reference are very broad and probably can only be touched upon in a general way. I, personally, have been engaged entirely on the design side for the past thirty years and therefore it might have been more fitting if a member of the production organisation had been asked to give this paper.

The scope of this paper is necessarily restricted. A large aeroplane, within the new definition, has not yet flown in this country. This event, however, is not very far off and the preparatory work that makes it possible has brought to light many novel problems. In some cases these could be predicted with normal anticipation, whereas others have only emerged as analysis progressed. These latter are frequently good examples of the dangers of too facile extrapolation.

Some of the reasons for having large aeroplanes are examined and subsequently, the chief technical problems arising are described. These descriptions avoid mathematics, as in many cases this approach is extremely long and involved and merits individual publication.

Much difficulty has been experienced in the past by those who have to apply aerodynamic data to aircraft design problems, in visualising the standard sign convention for controls, movements along and moments about the X, Y and Z axes. This difficulty has been specially pronounced with the staffs of wind tunnels where often, for mechanical reasons, the tunnel model has to be tested in an inverted position.

This paper presents a rational method of stressing single or many cell tubes particularly of the type encountered in wing structures. The theory has been developed for conical or cylindrical tubes of arbitrary cross-section the shape of which is maintained by a closely spaced system of diaphragms rigid in their own planes and parallel to the root section. Within the limits of the assumptions the theory is exact for right cylindrical tubes, and is applicable with adequate accuracy to cylindrical or conical tubes in which the inclination of any generator to the normal to the root plane does not exceed 10°.

The analysis given unifies the theories of bending and torsion and shows that the commonly used method of separating the bending and torsion loads by means of a shear centre is in general incorrect.

The formulae have been developed in such forms that attention is concentrated on the necessary corrections to the stresses as indicated by the ordinary engineers' theory. These correction terms include all effects of shear lag, diffusion, and end effects hitherto taken into account only in some very special cases.

Particularly important for practical applications is the structure consisting of a number of direct stress carrying members (booms) connected by walls effective only in shear. The simplest structure of the latter type is the four-boom tube with or without nose and trailing cells, and in this case explicit formulae are given which are immediately applicable to practical calculations. Formulae are also given for the more complex case of a six-boom tube in which the two extra booms are introduced to represent more accurately the direct stress carrying capacity of the top and bottom panels between the two spars.