Applied aeronautics; the airplane - Beeldbibliotheek

—96 APPLIED AERONAUTICSThere is a fourth form of error which is mechanical and is due tothe lag of the instrument. It occurs especiall}' in connection with thenose dive, and may be the cause \)f a very serious accident. The aviatorin dropping from an altitude of 10,000 ft. to 1,000 ft., for instance, willreach the lower elevation before his instrument can record the change.The danger lies in the fact that if he depends entirely upon his altimeter,he may not realize until too late that he is much closer to the groundthan the altimeter indicated. This error will probably' never be entirelyeliminated, but it gradually is being reduced with increasing perfectionin construction.This practically covers the main errors of the instrument, all ofwhich are due to external influences. Mechanical errors can be detectedeither by comparing the instrument with a standard barometer or bytapping it to discover slack. In fact, the instrument frequently shouldbe compared with a standard mercurial barometer, merely as a checkon its accuracy.It should be added that since hot air weighs less than cold air, thereadings of an altimeter for the same height will vary with the temperatureof the air. Obviously it is impossible to obtain this temperature atall times, hence this factor must be neglected, thus introducing an errorwhich may reach as high as ten per cent.Banking MeterAs its name indicates the banking meter, or banking indicator as itis sometimes called, is used to show the amount of bank which the pilotis making and guard him against skidding or side-slipping.There are two forms in use at the present time. One form of thismeter is constructed on the same principle as the ordinary spirit levelsuch as is in use on carpenter's levels, transits, etc. It consists essentiallyof a small glass tube nearly filled with liquid, leaving a smallbubble. When the tube and its mounting are horizontal the bubble willcome to rest in the center of the length of the tube. Any slight inequalityin the surface beino; tested issufficient to send the bubble to the end ofFig. 56A form of hanking meter patterned after the spirit level