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IN a series of articles entitled “Tailless Aircraft and Flying Wings”, concluded last month, the evolution of the tailless aeroplane and the flying wing was treated. The different trends of the development were classified, and a short discussion of the difficulties which had been experienced during experimental work given.

WITH tailless aeroplanes, all known aerodynamic control devices possess the peculiarity of not only producing moments about one axis, but of also causing secondary moments about one or both of the other axes. Horizontal controllers forming part of the wing near the tips in wings having sweep‐back or sweep‐forward, for instance, do not produce rolling moments alone, when differ‐entially deflected; they also cause yawing and pitching moments. Similarly, wing‐tip disk rudders operated on such wings not only produce yawing moments, but may cause rolling and even pitching moments.

Assisted high‐lift devices which are based on the removal or the addition of air jets from the flow over the wings may be classified as follows, in accordance with their method of operation:

IN wooden aeroplane manufacture, the technique to be adopted in the workshop is more or less a matter of the engineering experience gained by mistakes and disappointments.

THE present conception of the air flow over aeroplane wings assumes that, in general, the flow pattern conforms closely to that of potential flow (i.e. the inviscid, incompressible flow of hydrodynamic theory) with the exception of a very thin layer of air which is in contact with the wing surface. This layer of fluid, the boundary layer, is characterized by the fact that all phenomena of viscosity (shear forces within the fluid) are restricted to it. Further, it is established that the lift is generated by a circulation about the aerofoil, and that stalling is a result of separation of the boundary layer from the wing surface at or near to the leading edge, with resulting vorticity over the dorsal wing surface, instead of an ordered flow with circulation. Thus at the stall, the circulation suffers a more or less complete breakdown.

COMPRESSED laminated (“ improved ”) wood is generally counted among the hardening laminated plastics; it is built up from a large number of very thin veneers (0.0–1.005 in.) which are arranged with parallel grain directions. With the use of thermosetting synthetic resins, the veneers are highly compressed between hot platens. The adhesive, normally of the Bakelite type, is also a strengthening agent, or, with material of high resin content and high density, the wood may be considered as more or less a carrier for the resin, the latter being in this case the main strength‐producing agent.

IN the tailless aeroplane, side‐slip motions during take‐off and landing manoeuvres are specially undesirable, since it tends to be deficient in lateral stability, as we have seen. Hence, arrangements which provide for early compensation of unintentional side‐slipping may have some justification.

THE study of the flight of birds has provided and will still provide much valuable information for tiie progress of human flight. Many suggestions for the improvements of wings by the use of special wing tips owe their existence to the observation of nature. In spite of such suggestions, free‐flight experimentation—as far as published work goes—is still rather rare and restricted in scope. This reluctance may be due to practical design considerations (handling) as well as to the necessity of making the conventional aileron as efficient as possible; it may also be caused by the impression that experiment in this direction is not worth the effort.

Adhesives of this kind have in recent years become increasingly important for aeronautical purposes. This has been a consequence of the gluing processes adopted in German aircraft manufacture about 10 years ago. Although the application of phenole formaldehyde (bakelite) adhesives for plywood manufacture had already been investigated during 1916–1918 in this country, and although these adhesives were highly recommended by the Adhesive Research Committee in its Report of 1922, every further research and any intended use of adhesives of this kind was discontinued shortly after the war. This is a good example of the slowness in adopting progressive methods in wooden construction.

As the most common aeronautical timber is SITKA or silver spruce, its main deficiencies will be of special interest. The essential properties and defects appearing in converted timber, i.e., at planed surfaces (rough portions are unsuitable for timber selection) are as follows: