AIRCRAFT PROGRESS.

New Zealand Herald, Volume LXVII, Issue 20722, 15 November 1930, Page 12

AIRCRAFT PROGRESS.

EFFORTS TO LESSEN NOISE. USEFUL RESEARCH WORK. [FROM OCR OWN CORRESPONDENT.] LONDON, Oct. 9. Tho aircraft designer has yet much to do before he produces the silent aeroplano. But research of the past ten years has not been done in vain. Many points have emerged from the research work. Much of the noise is caused by the engine. A great deal comes from the airscrew. The flapping of the sides in a fabriccovered aeroplane may bo a serious source of noise and vibration of the entire craft, set up in a variety of ways, adds to tho turmoil. Increase of speed introduces fresh difficulties'; it has been found that a speed rise of 100 ft. per second—abojit 70 miles an hour—multiplies airscrew noise ten times.

An airscrew with four blades is quieter than a two-bladed screw; thin blades make less noise than thick ones. Here is an indication of a partial cure for the important airscrew noise. In the design of erigines, in spito of the difficulty of producing an efficient oxhaust silencer, much can bo done by enclosing valve gear and other moving parts. Vibration is lessened in modern British practice by the employment of rubber shock absorbers in the engine bearers. The British aircraft and engine builder is thus endeavouring to quieten his production in many ingenious ways. In the later big commercial crafts-land machines and flying boats—the size of the structure enables the desigrjer to place the power plant at a considerable distance from the passenger quarters. This is noticeable at once in the lay-out of tho large fourengiried air liners which Imperial Airways are planning to place in commission next year on the European and Imperial routes. The motors are carried in nacelles streamlined into the structure at points distant from tho saloons; unlike most three-engined craft, these new flying machines have no central engine in the nose to transmit incessant vibratory shocks through tho passenger-carrvinc fuselage.

Recent progress in aerodynamical knowledge, resulting in the' building of "cleaner" aeroplanes has markedly reduced noise The modern air liner is not braced with a multitude of wires, which hum and thrum as the craft moves through tho air; exterior wire bracing is reduced to a minimum nowadays and there is a considerable gain in quietness from this advance alone.