SILENT AEROPLANES.

Ellesmere Guardian, Volume LII, Issue 37, 8 May 1931, Page 2

SILENT AEROPLANES.

MACHINES OF THE FUTURE

Early motor cars were so noisy that pedestrians were almost deafened when they passed. To-day the motor car has been made so quiet that the main sound heard is that made by the tyres on the road. The aeroplane still remains the noisest form of transport. A single aeroplane passing over a large town makes people look up, even if it is at a great height. Those who live near aerodromes find the noise rather troublesome at times. It is good news, therefore, to learn that the problem of silencing the aeroplane is likely to be solved. Aeroplanes produce noises in two ways. There is first of all that of the engine exhaust, which is like the ordinary machine-gun rattle of a mo-tor-cycle—only more so. Secondly, there is the droning or whining of the propeller as it whirls in the air. All sound is caused by waves in the air, and one can bring about complete silence if matters can be so arranged that the crest of one wave coincides with the trough of another. In this way the waves cancel each other. A wopderful new silencer working on this principle may render aeroplane engines completely quiet at their cruising speed. It has been found, too, that by altering the shape of the propeller its

sound waves can also be made to cani eel. The aeroplane of the future may well be as quiet as the motor car of to-day.