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National Advisory Committee for Aeronautics, Technical Notes - NACA Langley Field Wind Tunnel Apparatus, The Tilting Manometer

The following is a description of a tilting manometer
designed by the technical staff of the National Advisory
Committee for Aeronautics to meet the requirements of a I
manometer for use in the Wind Tunnel of the Langley Memor—
ial Aeronautical Laboratory.

Taisgauge was designed to meet the requirements of a
manometer for use in connection with a static pressure
plate, to indicate the wind speed in the tunnel. These
requirements are: first, that the sensitivity of the
gauge may be made inversely proportional to the pressure
to be measured; second, that the gauge may be accurately
and quickly set for'any desired pressure; and third,
that when set at the desired pressure the extent of var—
iation between the existing and the desired pressures
may be readily estimated. As the pressure measured be—

tween the static plate in the tunnel wall, and the air
center of rotation. In use the arm is set at an angle,
determined from the calibration chart, corresponding to
the desired air speed. The propeller is then Operated
at a speed such that the alcohol again rises to the ref-
erence mark.

It will be seen by a moment‘s consideration that the
absolute head may be represented by:
h :21 sin (cc + 3&0) ~ 111

where h is head of alcohol, 4L is the distance from the
center of reservoir to center of rotation, and hl is the
vertical distance from the center or the reservoir to
the surface of the contained liquid (hl :46 sin 3%0 = con-
stant); and that the sensitivity, considering a vertical
tube as having unit sensitivity, is Ei%7§§ , thus satis—‘
factorily approaching the sensitivity requirements except
for the very lowest pressures.

In order that the gauge may be set quickly to any
given speed after calibration a number of adjustable steps
are placed along the scale at every ten miles per hour
so that the arm can be easily snapped into the correct
position.