Quite often, those whose honour it has been to deliver the Wilbur Wright Memorial Lecture have used the occasion to present a survey of progress along a fairly broad front and thence to predict what the future holds in store.

It may be that the courage, insight in experiment, and skill in craftsmanship, which culminated in that successful demonstration of fifty years ago last December, have excited those whose privilege it has been to commemorate that achievement to undertake flights in the realm of prophesy. A time so near the fiftieth anniversary might be considered unusually appropriate to historical review and philosophic speculation, but since Sir Harry Garner's 1952 Lecture “Prophesy and Achievement in Aviation,” the Royal Aeronautical Society has been busily converting crystal balls into models of the Montgolfiere balloon.

In recent years interest has been revived in an apparatus which was first developed more than fifty years ago. This apparatus, which is known today as a shock tube, is a very useful research tool, the versatility of which is not generally appreciated in this country. In this paper the author attempts to give a clear physical description of the flow in a shock tube and a review of the problems which may be investigated by means of this apparatus.

Basically, a shock tube consists of a simple fabricated duct which may be closed or open at one end, and closed at the other end. A diaphragm divides this duct into two compartments which initially contain gases at different pressures. In a conventional shock tube the cross-section is constant, the ends are closed, and air is used on both sides of the diaphragm (Fig. 1).

Mathematical and experimental methods for estimating the relative eddy velocity in a radial bladed impeller channel have been determined to replace the empirical velocity so far used in designing and predetermining the performance. The effect of this relative eddy velocity on rotor performance has been experimentally determined on a specially designed compressor and compared with mathematical calculation.

It is only in very recent years that the helicopter has begun to find a place in the pattern of Aviation. Although its development has not been so intensive nor so widespread as that of the more conventional fixed wing aircraft it has remained a positive and progressive force running on a parallel course.

The idea of the screw, as a method of propulsion or lifting, is not new, yet at the beginning of the 20th century its use was still restricted to propelling ships. It is therefore not surprising to find that the development of an early helicopter was carried on in a shipyard.

In treating the compressible subsonic flow by the Prandtl-Glauert method as extended by Göthert, the velocity increment v in the direction of the main stream is found to be 1/β2 times the corresponding velocity increment va on the analogous body in incompressible flow; the analogous body being obtained by reducing the lateral dimensions of the real body in the ratio β:1.

Measurements were made of the pressure in a blunt-nosed pitot tube, in an air stream at Reynolds numbers from about 15 to 1,000. The results are expressed in terms of a pressure coefficient , where P is the pressure in the pitot tube, ρ is the density of the fluid, and p and V are the static pressure and velocity in the undisturbed stream. As found in previous investigations, Cp becomes greater than 1 at low Reynolds numbers, the increase being about per cent, at a Reynolds number of 50 (based on external tube radius). In disagreement with the work of Hurd, Chesky, and Shapiro, no decrease of Cp below 1 was found at any Reynolds number.

One of the routine ground tests carried out on pressurised aircraft is the measurement of the leakage rate and this is often expressed in the form of a time for the cabin excess pressure to fall from a given value to half that value. The technician, however, is usually concerned with the functioning of the pressurised cabin at high altitude and it is the purpose of this note to establish a means of forecasting the high altitude performance from the sea level test. The first part of the note describes the basic theory and provides a unique relationship connecting leakage times at any height with that pertaining to the sea level test. The latter part of the note gives an example of the use of this information in predicting the fall off of cabin pressure after pressurisation failure and with the aircraft descending.