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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:

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Committee, Reports and Technical Notes of the U.S. National Advisory Committee for Aeronautics, and publications of other similar research bodies as issued

THE task of building a wind tunnel for the requirements of Switzerland was somewhat complicated by the fact that the grant available for the purpose was strictly limited, a still greater difficulty being the need to be as economical as possible as regards space. It was, of course, desired to have a flow cross‐section as large as possible, but it is inadvisable to compress to excess the other dimensions of a tunnel owing to the possible detrimental effect on the steadiness of the flow and the consequent errors in the measurements. We would certainly be faced with a difficulty if we were asked to arrange for a material decrease in the total length of the tunnel while maintaining the present jet unchanged, without reducing the speed or the steadiness. Comparison with the wind tunnel at Warsaw shows clearly that our design for Zurich has gone through a very thorough process of compression. Having regard to the noise factor, a fairly massive type of construction is necessary; the precedent laid down by Prandtl was followed and concrete used. The question of cost interfered here and required the simplest possible inlays, which meant only simple curved surfaces. Excessively sharp angles being unfavourable, however, the solution was right angles with well bevelled corners. The quality of the air stream, as also the power requirements, were determined by careful measurements conducted in a model of the whole tunnel built accurately to a scale of 1 : 10. The test chamber is a rectangle, in section 3 by 2·1 metres, with bevelled corners. Tests can be conducted either with an open jet or with the chamber totally enclosed or half enclosed, the latter arrangement being a new departure. The jet is caught in a collector and deflected through a right angle downwards by baffles of strongly reinforced concrete. After a second deflection the stream is drawn through two fans set side by side. Each fan has a diameter of 2·5 metres with a maximum rate of revolution of 1,500 r.p.m., six blades (elektron castings) and a diffusor in front of the impeller, comprising a large number of welded blades which impart to the air a counter twist smoothing out all rotation of the stream so that after the fan parallel flow is ensured. The hub is well faired off. The blades are mounted on pivots, and their angle can be adjusted when the fan is at a standstill. The fans are driven by D.C. motors, with an output of 275 h.p./hr., mounted outside the tunnel. Their sense of rotation is the same, and they are synchronised by a continuous silk belt running over the couplings. This type of belt is the invention of the well‐known steam turbine expert, Dr. H. Zoelly. Their pliability ensures elimination of flapping even at very high peripheral velocities, and they are capable of transmitting very high powers.

ONE of tin: most important causes of low efficiency in duel systems is tin; large loss which accompanies a transformation from kinetic energy to pressure. The exit cones of wind tunnels and turbines and the expanding entries to cooling duets and air‐intakes on aircraft are some of the duct systems which lvcpiirc ellicient expansions of the flow.

OVER A QUARTER of a century ago, in September 1938, we published a review of diffuser behaviour by G. N. Patterson which, together with one of its main information sources by Gibson, has formed the accepted guide to diffuser design. Patterson's paper was broad in scope and made clear reference to the effect of parameters which were not fully investigated until much later. It is the purpose of this paper to review experimental work, much of it being along the lines formulated by Patterson, and to indicate the improved analytical understanding of diffusers.

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.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Notes of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued.

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.

THE development of modern aeroplanes designed for high speeds, with their thin, almost symmetrical wing sections, has led inevitably to high landing speeds and small gliding angles with the normal wing arrangement.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Committee, Reports and Technical Notes of the U.S. National Advisory Committee for Aeronautics and publications of other similar research bodies as issued