I wish to give you to-night some idea of the computing work necessary between the receipt of the performance figures from the pilots and the issue of the complete report.

The term Aircraft Instrumentation is used to describe the special instruments which in a variety of circumstances are needed to determine aerodynamic, structural and power plant characteristics. Such circumstances may be flight tests of prototype aircraft, tests in the air or on the ground of the aeroplane, its structure or power plant, or the acquisition of statistical data on the conditions to which aircraft are subjected in civil or military operation. These special instruments therefore are additional to, and usually different from, the instruments needed in an aeroplane to enable it to fulfil its military or civil role.

It is demonstrated how, with increase in speed, the diameter of optimum efficiency and the maximum possible value of efficiency of an airscrew diminish. The efficiency of a system of two counter-revolving airscrews with different angular velocities is then determined, and the variation of efficiency with variation in the relation between the angular velocities of the two airscrews.

With increase in the height and speed of flight, airscrew performance inevitably falls off, frequently in a marked degree; this being mainly due to the decrease in aerodynamic efficiency of the blade sections at high Mach numbers.

The object of the present article is to analyse the influence exerted upon the performance of an airscrew by the various parameters that determine it, wit-h special reference to those connected with the speed and height of flight.

A similar study has also been made of systems constituted of two counter-rotating airscrews, with a view to comparing them with isolated airscrews designed to absorb the same power under identical conditions.

By the methods here described, an approximate numerical evaluation of the performance can be made, utilising the experimental results which are already to hand.

The method generally used in England for calculating the aerodynamic characteristics of wings is that suggested by Glauert (1), in which the circulation across the span of the wing is represented by a Fourier series. On account of the form of the series, certain difficulties arise which make the calculation very tedious when more than about four points along the semi-span are considered.

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.

That synthetic glues for wood were used extensively for making Mosquito and Hornet aircraft during the 1939-45 War, and are now used for making Vampires in many European countries, is well known to aeronautical engineers, but not so well known is the fact that, since 1944, synthetic glues for metals have been used in the production of many hundreds of military and civil aircraft. A glue for metals, which gives joints stronger than can be obtained by riveting and which is also resistant to the severe conditions to which aircraft are exposed in service, offers the possibilities of savings in structure weight and of aerodynamically cleaner wing and fuselage surfaces. Such a glue may also be expected to be of value in the manufacture of pressurised fuselages, because it will avoid the large number of small leaks occurring at the rivet heads and may also help to solve the difficult problem of making integral fuel tanks in aircraft wings.

The 909th Lecture to be given before the Society and the 16th Main Lecture at a Branch, was held under the auspices of the Chester Branch of the Society on 8th April 1954. Mr. K. G. Hancock, Chairman of the Chester Branch, expressed the pleasure of the Branch at having a Main Meeting of the Society at Chester and welcomed the visitors, particularly the officers of the Main Society. He then asked the President, Sir William Farren, to preside for the rest of the Meeting.