WATCH-BEATING SPEED

Evening Post, Volume CVII, Issue 10, 12 January 1929, Page 21

WATCH-BEATING SPEED

THE TIMING OF AEROPLANES

The speed of racing aei'oplancs has reached a figure which makes it difficult if not impossible to time them accurately with'■stop-watches. . With the 'plane travelling at 300 m.p.U. over a throe-kilometre course, an error of oven one-fifth of a second, an error which can easily bo made, would make a difference of three miles an hour in calculating the speed; but errors of six miles an hour are not unknown. In fact tlie stop-watch for speeds such as these has become unreliable even in the hands of the most skilful observer. The officials at tho Royal aircraft establishment, Parnborough, use a camera gun which photographs at the same time the machine as it passes tho sighting posts and a stop-watch. They endeavour to avoid any possible error in synchronisation by photographing at half-hourly intervals the four watches used before and after tho test; but this does not really prove whether thero has been any variation (luring the speed runs. The Federation ■ Aeronautiquo Internationale, the governing body for all aircraft speed records, has decreed that after July all high-speed tests must lie made "by means of an automatic chronometric machine or by any other machine officially proved by tho 1\A..1."