• Version
• 139 Downloads
• 1,021.44 KB File Size
• 1 File Count
• November 25, 2016 Create Date
• November 25, 2016 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - Performance Characteristics of Venturi Tubes Used in Aircraft for Operating Air Driven Gyroscoptic Instruments

Wind~tunnel and flight tests were made to determine
the performance characteristics of two designs of commer~
cially available venturi tubes"used in airplanes to operate
air—driven gyroscopic instruments.

For constant values of the ratio of suction to atmos—
pheric pressure, the air flow is approximately a linear
function, independent of altitude for a double venturi
tube, of the product of the indicated air speed and the
square root of the ratio of standard air pressure to the
atmospheric pressure. Consequentlv data obtained at sea
level may be used to make approximate predictions of per~
formance at higher altitudes. There is some“indicetion
that this may be also done for_single venturi tubes.

For a given installation in which an air—drivonvin~
strument is connected through tubing with a venturi tube,
the volume rate of induced air_flow is approximately pro-
portional to the product of indicated air speed and the
square root of the ratio of standard to ambient air pres—
sure. The off iciency of such a system at a given altitude
is constant.

Rather large variations in suction and efficiency were
found for individual tubes of the same designa Cylindrical
fairing on the external surface resulted in a reduction of
both dre g and suction but little change in efficiency.

The effect of large angles of pitch or yaw was small. Heesé
urements were also made of the pres sure along the wall of
the tune.

Venturi tubes are used in many airplanes to operate
air-driven gyroscopic instruments. The Operating efficien—
cy of venturi tubes is known to be low in comparison with
that of vacuum pumps of the displacement type but their
mechanical simplicity and low first cost have—furthered _
their continued use. Although some data on the performance
of venturi tubes as vacuum pumps have been published (refu
erences l, 2, and 3), it was considered desirable—to under-
take an experimental study of~the performance characteris—
tics pf venturi tubes now being used. As part of this
study, two types of commercially available venturi tubes
were subjected to wind—tunnel and flight tests. The in-
vestigation was made with the cooperation and financial
support of the National Advisory Committee for Aeronautics.