A Variable Speed Fan Dynamometer Page: 2 of 11
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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
TECHNICAL NOT3 NO. 26.
A VARIABLE SPEED FAN DYNAMOMET R.
By
Karl D. Wood,
Bureau of Standards.
The following Technical Note descriptive of a Variable Speed Fan
Dynamometer, was prepared under the supervision of the Automotive Power
Plant Section of the Bureau of Standards, and submitted through the
Subconmittee on Power Plants for Aircraft to the National Advisory Cnm-
mittee for Aeronautics for publication.
Fan brakes are widely used as absorption dynanometers in testing
internal combustion engines because they are comparatively simple, in-
expensive, and flexible. They have, however, the disadvantage that a
given fan will run at only one speed when the engine is delivering
full power, that speed being determined by the sise, proportions, and
environment of the fan, and the density of the air. In order to be
able to vary the speed at which a given power will be absorbed, English
manufacturers have for some time been using a cylindrical housing around
the fan with one or two variable openings in the periphery. The tests
here reported were undertaken by the Automotive Power Plant Section of
the Bureau of Standards to determine how great -a range of speed can be
obtained with such a device. The tests made show that a power ratio of
5 to 1 can be obtained, power ratio being defined as the ratio of the
power absorbed by the fan at a given speed with the outlet open to the
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Wood, Karl D. A Variable Speed Fan Dynamometer, report, December 1920; (https://digital.library.unt.edu/ark:/67531/metadc53722/m1/2/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.