Two types of intermittent wind tunnel drives, the pressure storage drive(with atmospheric exhaust) and the vacuum storage drive (with atmospheric inlet), are examined and found to match well the tunnel pressure ratio-mass flow characteristics over a wide Mach number range (0 to 4). The design of components of intermittent wind tunnel installations, their operation and instrumentation are then considered in some detail. In order to increase the output of intermittent wind tunnels to a level comparable to that of continuously running tunnels, it is proposed to drive the models during each tunnel run through a range of incidence. This technique is at present under development in the National Aeronautical Establishment's High Speed Aerodynamics Laboratory and results so far obtained are discussed. Two tunnels are considered as examples of large intermittent installations: a 4 ft. square pressure-driven tunnel and a 6 ft. square vacuum-driven tunnel. The former is found to be a more compact and economical installation. Relative merits of continuous and intermittent installations are discussed.

The distortion of straight wings is simple and familiar; upward bending causes slight changes in dihedral angle and loads offset either fore or aft of the flexural axis cause twisting, which involves changes in incidence. When wings are heavily swept back, bending causes change of incidence as well as change of dihedral angle, while the changes of incidence due to twisting are no longer equal to the angles through which the wing structure twists.

In no branch of structural engineering is there a rigorous definition of the term “secondary stress.”

If the primary stresses in a structure are determined, that is, the stresses in the members due to an external load system, assuming that all the members are joined together by perfect pin- or ball-joints, then the secondary stresses are in general taken to be the additional stresses due to the rigidity of the actual joints used in practice.

In such a highly redundant structure as an airship hull the labour involved, in determining even the primary stresses, precludes the use of the normal methods of stressing. It is usual to make use of generalised methods which give approximate results. These generalised methods imply that the external loads are applied to the structure in a certain distribution. Though this is rarely achieved, yet the results obtained are in most cases sufficiently accurate if suitable bracing is supplied to redistribute the external loads over the cross-section; the effect of the initial wrong distribution being then merely local.

Range in any given vehicle of transport is generally understood to be the distance that it could travel without requiring to stop for any supplies necessary to maintain its normal performance.

It is, moreover, at least one quality in the aeroplane to which the designer may set a limit to his ambitions. With regard to speed, load carried, and so forth, he faces an endless task, but when range has reached a distance of just over 12,000 miles, equivalent to the greatest distance between any two points on the planet, his task in this respect is presumably at an end and in practice probably much earlier as the distance between which aeroplanes will need to operate will certainly be less than this.

The object of this paper is to contribute one step toward the knowledge of the stresses in the neighbourhood of openings in monocoque aircraft fuselages by developing a procedure for the calculation of the stresses in spaced-curved rings used for reinforcing the edges of openings. The general appearance of such an opening is shown in the perspective view of Fig. 1. The procedure presented here presupposes a knowledge of the forces which act upon the ring. These forces depend upon the relative distortions of the reinforcing ring and of the rest of the fuselage, and the exact determination of their magnitude under different conditions of loading of the fuselage presents great difficulties.