In recent years some types of aircraft have shown signs of structural trouble due to repeated loading and exploratory thought has therefore been given to the general problems arising. There are two main aspects to be considered: the nature and magnitude of the loads repeatedly occurring in flight and the behaviour and strength of aircraft structures under such loads. In this country a good deal of attention has already been given to the first side of the question, mainly by V-g recorder work, but also by some strain gauge investigations, but the other side of the matter—the resistance of aircraft structures to repeated loading— has so far received less attention. Direct experiments have not in this country gone much beyond exploratory work on a series of Typhoon tailplanes, described by Oaks and Townshend.

Until recently the gust requirements laid down by the airworthiness authorities had not caused any serious difficulty in design. This was due to the fact that other loading conditions (manœuvring loads imposed by the pilot) had been more severe than the loads produced by gusts. Over the past few years, various factors have altered this position. Increase of aeroplane speeds, increase of operating altitudes, decrease of the manœuvring loads (in the case of large aeroplanes) and increase of size, have each contributed to raise the gust loads until they have become, in many cases, the main design criteria for the flight structure.

A consideration of the factors suggesting that new types of flying instruments are becoming necessary.

To safeguard the aircraft and crew against the danger of excessive speed and normal acceleration loads, until recently it was considered sufficient to provide for the pilot an airspeed indicator and to fix in the aircraft a plate giving the maximum safe speeds permitted for diving, without and with external stores, flaps and undercarriage down and so on. In the case of Service aircraft these limitations are usually published in Pilot's Notes for the type. Based on design data these speeds are those at which, allowing suitable factors of safety, the stresses in the appropriate parts of the aircraft's structure are calculated to reach the maximum safe limits.

A meeting of the Royal Aeronautical Society was held in the Library of the Society at 4 Hamilton Place, London, W.l, on Tuesday 25th September 1945, at which M. L. Malavard, of the Laboratoire des Analogies Electriques, Paris, lectured on “The Use of Rheo-electrical Analogies for the solution of Aerodynamical Problems.” In the chair, Mr. E. F. Relf, C.B.E, F.R.S., F.R.Ae.S. (at that time Superintendent of the Aeronautics Division, National Physical Laboratory).

Part 5 continues the theory given in Parts 1–4 in the February 1947 issue of the Journal (pp. 199–269). The present paper deals with the stresses and deformations of conical and cylindrical tubes under arbitrary loading, thus completing the analysis given in Part 4 which dealt only with pure torque.

A remarkable unification of the theory of bending and torsion is achieved. It is shown that the axial constraint stresses, i.e. the corrections to the engineers' stresses, may in general be calculated as if caused by torque about axes different in each mode. The analysis proves that it is in no circumstances correct to calculate the axial constraint stresses from the torque about the flexural axis.

Functions giving the cross-wise distribution of stress are fully worked out for the n-boom tube of arbitrary cross-section and for the singly symmetrical trapezoidal tube with continuous direct stress-carrying covers. The analysis is a considerable extension of the results given for the four-boom tube in Part 4.