Accelerometer design Page: 4 of 16
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ANNUAL REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS.
period of the fiber is about one-twentieth second, and the damping is solely by air friction.
This instrument gives a continuous record, but its period and damping are low and the deflec-
tion on the record is small, so that it can not be read to better than 0.1 g. Also, as will be
shown later, a rather serious error is introduced by components of acceleration acting at other
than normal to the plane of the fiber. However, the instrument is very compact and simple
to operate, and has been used very successfully to determine the loads on airplanes in flight,
but is unsatisfactory for landing shocks.
RECORD FROAL ZA/LWV
I: I" -ZAM, ACCELEROMTEt. A/74 4CCC'EROA1eTER
A type of accolerometer * designed on the principle of a seismograph has een u,c :sc(l to
determine the properties of automobile springs. This instrument (fig. 4) records displacemrrents
so that the curve must be differentiated twice in order to obtain accelerations. This is an
inaccurate and laborious method of obtaining accelerations, and it could obviously not be used
for anything except short periods. The instrument is of value, however, for obtaining the
period and amplitude of small high frequency vibrations.
The National Advisory Committee for Aeronautics' accelerometer consists of a flat canti-
lever spring, the deflection of whose end rotates a small mirror, thus reflecting a beam of light
on to a moving film, as shown diagrammatically in figure 5. A more complete description of
this instrument will be given later in this report.
F/. . R. A. F. ACCELEROAMTER OF ACCdLERO/7AP ETYPE
DEFLECTIONS AND NATURAL PERIODS OF SPRINGS.
It is obvious that for an accelerometer the greatest deflection with the highest natural
period is desired. Unfortunately the deflection and period of a uniformally loaded flat spring
under static load, are connected by the formula:
where D= deflection
I'= time for complete oscillation
K= a constant varying slightly with the type of spring.
SThe Journal of the Society of Automobile Engineers, January, 1920, p. 17.
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Norton, F. H. & Warner, Edward P. Accelerometer design, report, 1921?~; (digital.library.unt.edu/ark:/67531/metadc65750/m1/4/: accessed January 22, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.