In a Technical Note published in the April 1954 issue of the JOURNAL an approximate equation was presented for calculating the propeller moment of a helicopter rotor at the project stage, the solution to which could be obtained from two graphs.

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.

This note presents in matrix form the equations of motion of a rotating and vibrating beam. The natural frequencies of the system are obtained by plotting an impedance-frequency diagram and noting the frequencies at which the impedance vanishes. Uncoupled bending vibrations are considered but the analysis can easily be extended to include coupled bending-torsion vibrations. The arrangement of the method for solution on a digital computor is quite straight-forward.

Glass Cloth/Polyester resin laminates similar to those described by Irving and Saunders (Journal, February 1954) have been used at the University Engineering Laboratory, Cambridge, in the manufacture of blades for an axial flow compressor. In the first experiments, an existing aluminium stator blade was used as a pattern, and a mould was made by pouring molten type metal round this pattern, held in a steel sided moulding box.

Propeller moment is the name given to a dynamic phenomenon which causes considerable trouble in the design of variable pitch propellers and helicopter rotors. The development of the fundamental equation has not previously been published, to the author's knowledge, and for this reason the steps leading up to it are given. The propeller moment on any section tends to place its major axis in the plane of rotation, and the fundamental equation is equation. Its use to determine the total moment at a blade root results in lengthy calculations, with the possibilities of delays and errors.

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.

Professor koiter, in his note (January 1954 Journal) states that I (April 1953 Journal) was “ apparently unaware” of Weber's two papers on the subject, published in 1924 and 1926. I was aware of the papers, having cited them in the bulletin by Seely, Putnam and Schwalbe on “The Torsional Effect of Transverse Bending Loads on Channel Beams.“

Some references in addition to those already cited may be of interest. The unorthodox behaviour of a channel beam in bending was observed and reported by C. Bach in 1909–1910. A. and L. Foppl wrote a section on the “Schubmittelpunkt” in their book “Drang und Zwang.“

An Experimental study of fluid flow past a symmetrical aerofoil with a rear suction slot and a retractable flap was described by D. M. Heughan in the October 1953 JOURNAL. The present note describes the electric tank method for studying the same problem. The experimental apparatus is shown in Fig. 1. A and B are electric poles along two of the edges of the tank which is filled with water. The poles A and B together with the central pole P are connected to an electric supply via a resistance R in such a way that the potential of P is intermediate between that of A and B. The aerofoil F is represented by a wooden block coated with paraffin wax and the pole P is located in such a way as to represent the sink in the suction slot. A voltmeter V records the potential at a point in the tank.