A simple formula is presented for the safe life of an aircraft under reasonably good operating conditions from the standpoint of wing fatigue. Gusts are treated as the main factor in determination of fatigue life, though other factors are allowed for as being secondary. Before the formula can be used a simple fatigue test is required on critical components, and is repeated several times to establish variation of nominally identical specimens. The loading cycle for this test corresponds to a sequence of up and down gusts of 8 ft./sec. equivalent velocity. The life obtained is termed the “Standard Life” and corresponds to normal operating conditions on European air lines. Reservations in the use of the formula and correction for other operating conditions are discussed in general terms.

In a previous paper it has been shown that a general method may be developed for calculating the various changes which take place in a flowing gas. The changes considered were the addition and extraction of heat in a subsonic flow, the addition and extraction of heat in a supersonic flow and sudden changes, such as shock waves. The changes were considered to be stationary and to take place in a parallel pipe. It was of interest to see if a similar approach would produce a general treatment for moving waves. The investigation was limited to moving shock waves and detonation waves.

Experiments were made on an aerofoil of 25 per cent, thickness with a suction slot at the rear and a flap that could be withdrawn into the slot. The main object of the work was to investigate the effect of withdrawing the flap when all the air in the boundary layer was sucked into the slot. In particular, as a test of the type of anti-gust device proposed by Thwaites, it was required to observe the change of lift that occurred during withdrawal of the flap and a subsequent change of incidence (with the flap still withdrawn).

The flow was investigated by the use of smoke and tufts, by pressure plotting on the surface of the aerofoil, and by measurements of total and static pressures in the wake. The effects of varying incidence, flap position, and suction velocity were investigated.

It was found that the provision of a flap downstream of the enclosing streamline, so that the rear stagnation point was not in the free fluid, was all important in relation to the behaviour of an aerofoil which had a suction slot at its rounded rear.

With the flap extended beyond the enclosing streamline and with the ratio of suction-slot velocity to free stream velocity higher than the theoretical value, a stable flow was obtained within the theoretical incidence range. A favourable pressure gradient was observed in the slot entry and no measureable wake existed downstream of the flap. Smoke filaments, emitted from a tube projecting from the slot slightly beyond the enclosing streamline, travelled far downstream with apparently little diffusion.

When the flap was placed so that its trailing edge was inside the enclosing streamline, i.e. so that there was in theory a stagnation point in the free fluid, an instability of a three-dimensional character occurred, with a wide wake and a large drag coefficient. The lift curves were unusual and it was found that movement of the flap caused a large change of lift coefficient. There was no evidence that the lift could be maintained constant, independent of incidence, when the flap was withdrawn into the slot.

This paper is primarily concerned with structure weight as related to aircraft shape and size, rather than with the saving in structure weight that may be brought about by improved methods of construction. The difference in weight due to differences in methods of construction is a question of structural efficiency, and this will not be discussed here. Structure weight, even when expressed as an overall percentage, is not in itself a measure of structural efficiency. If the depth of an aircraft wing were doubled, without altering the lift distribution on the wing, the bending loads would be unaltered so that the resultant end loads in the top and bottom surfaces would be halved. If the second wing had the same weight as the first the structural efficiency would be less. Conversely, if they both had the same structural efficiency the deeper wing would have the lower structure weight

There is at present no thoroughly satisfactory method of measuring accurately the true air speed of an aircraft, particularly at high speeds.

Ground radar can accurately follow a high-speed aircraft but, without the development described here, can only measure the speed of the aircraft relative to the ground. The method developed by the authors makes immediate allowance for wind speed and is capable of giving the true air speed of an aircraft to within one per cent. There is no apparent reason why the method should not be applicable even at very high speeds and there is no limit in aircraft altitude at which the measurement may be made.

The coriolis effect is a change in the motion of a body passing over the surface of the Earth due to the motion of the Earth itself. The effect may be manifested either as a horizontal acceleration, or, in the absence of the acceleration, as a deflection of the course. The acceleration, which appears in controlled courses such as those of aircraft, usually appears and is significant as a deflection of the vertical. This acceleration appears whenever a body, such as an aircraft, is forced to follow a great circle path over the Earth. The deflection of the course of a moving body appears alternatively whenever the body moves freely in its inertial path above the surface of the moving Earth.

Symmetrically loaded circular plates of constant thickness are dealt with adequately in several of the standard textbooks on the strength of materials. The problem of non-uniformly thick plates subjected to symmetric loading has been discussed by M. Donath and, more recently, by D. C. Boston. So far very little has been done on the problem of a circular plate of varying thickness subjected to an asymmetric load. A tabular method approximating to the solution is outlined in this note. A typical example of the problem arises in certain manoeuvres of a jet aircraft in flight, the rotor discs of the engine being then subject to gyroscopic moments.