The field of viscosity forces in fluid currents of low viscosity—i.e., high Reynolds number—is frequently confined to a narrow zone in the vicinity of the surface; consequently, calculation can be simplified by the following assumptions :—

1. In the friction zone, customarily called the “ boundary layer,” only the most effective components of the viscosity force μΔω, are considered—e.g., for the x component of this force, μΔu (calling the direction of main flow parallel to the surface, the x direction, and that perpendicular thereto the y direction) the expressions μ (∂2u/∂x2) and μ (∂2u/∂z2) can be neglected for μ (∂2u/∂y2).

In 1954, Preston introduced a new concept of skin friction measurement in turbulent flows by using a surface pitot tube. Since then considerable controversy has risen in the use of Preston tubes for skin friction measurements. However, Head and Rechenberg investigated Preston tubes extensively and confirmed the validity of the Preston tube method. Recently Rajaratnam has given a theoretical calibration curve for the Preston tube using logarithmic velocity distribution for the boundary layer velocity profile.

Unshrouded impellers of centrifugal compressors and centripetal turbines manifest an increase of the flow losses in comparison with the shrouded ones. Assuming that the controlling factor in such increase of loss is the leakage through the gap between wheel and casing, the author develops a simple theory leading to a formula for the volumetric efficiency. Only one experimental quantity is required for applying the formula; and tentative values, based on some experimental evidence, are presented.

The wind channel and the whirling arm have been devised and perfected over a period of a number of years with a view to providing reliable aerodynamic data for aircraft designers. Of late years the wind channel has been used considerably more than the whirling arm.

In the two pieces of apparatus distinct methods are used. In the whirling arm the model is carried through the air, which is stationary, in a circular path by a long arm. In the wind channel, on the other hand, the model is stationary and a current of air is caused to flow past it.

Various types of wind channel have been evolved, but I intend to describe fully the English wind channel in its present form, as perfected by the National Physical Laboratory and the Royal Aircraft Establishment, Farnborough.

Experiments are reported of the self-preserving turbulent corner wall jet formed by directing a jet of air parallel to the line of intersection of two walls abutting at right angles. Self preserving profiles of the mean and turbulent flow are established by approximately 50 jet diameters downstream. Like the three-dimensional wall jet on a plane-wall surface there is evidence of a significant secondary flow induced by vortex line bending, though its magnitude is smaller than in the plane-wall case.

A probe is described which will detect contamination, by driver gas, of the test section flow in a shock tunnel. It is a continuously sampling device, which responds to the difference between the ambient speed of sound in the driver gas and the test gas. The probe is compact, easy to construct, and can be used for detection of driver gas in routine testing. The theory of the probe is explained, and experiments are reported which confirm its effectiveness.

The fatigue properties of unmachined extrusions of high-strength aluminium-copper alloys are known to be lower than those of conventional fully-machined test pieces. Work described in this note has shown that the removal of a layer of metal 0·025 in. thick from the surface of B.S. L65-type extrusions results in an increase in fatigue properties to values approaching those obtained from the conventional laboratory test pieces. Because the removal of material from the surface is not always a practical proposition, other methods of improving strength have been examined and the effect of surface compressive stresses has been shown to be beneficial. Sufficient compressive stress can be induced by surface-rolling to increase the fatigue properties to those of conventional specimens, but this method can only be easily applied to round sections and it is suggested that shot-peening or vapour-blasting could be used for more complicated sections.

Curves are presented which, together with a knowledge of the intake performance, enable ram-jet thrust coefficients and specific consumption figures to be obtained quickly and accurately in the range M = 1·0 to 3·0.

Fuel consumption in flight is dependent on three main factors—the aerodynamic efficiency of the aeroplane, the thermal efficiency of the engine, and the efficiency of navigation, which entails a study of the most advantageous height, speed and direction of flight under any conditions of wind. Fuel consumption is therefore the ultimate measure of the overall efficiency of the complete aeroplane, the pilot, and the organisation ; its complete study would require far more time than can be given to it in a single lecture. I propose, therefore, to confine myself to fairly general considerations, with particular reference to the commercial aeroplane. There have been distinct advances in the direction of fuel economy in flight since the war period, but even now the weight of fuel carried in a commercial machine operating over the comparatively short London-Paris route of 230 miles and capable of a cruising speed of 100 miles per hour is approximately half the full paying load carried, so that a reduction of the fuel load by 40 per cent., which is by no means outside the range of possibilities, would increase the paying load by 20 per cent., other things being equal.

It would seem that Mr. Heughan (Journal, March 1954) has missed the basic design criterion of drag exerted for a given weight (and bulk) penalty. No mention is made of this fundamental point in the choice of a device for the reduction of the landing run of an aircraft. The choice of comparison of the “Wake brake” with a 7 ft. brake parachute has therefore been made somewhat arbitrarily. Brown does not state that “the usual size of a parachute used for braking an aeroplane is 7 ft.”; on page 271 of the reference concerned (“Parachutes,” Sir Isaac Pitman, 1951), a case for “a particular aircraft” was quoted as “ using a 7 ft. parachute.”