1961 West Side Drive, Rochester, New York 14624.
Retired Project Engineer in charge of air flow and pressure
standards for the Taylor Instrument Cos. and author of 'The
Engine Wasn't There', 'Of Engines, Governors and
Nomenclature', and other articles.
THE BAKER FAN
The Baker Fan was developed by the Baker Co. as a load for
running-in new engines and not as there seems to be a tendency to
expound at the Reunions, as a device for the measurement of
horsepower. There are two reasons why these fans are inadequate for
such use. First, their performance is air density dependent, and
second, the speed is relatively insensitive to the power input.
At higher elevations, the air is rarefied (less dense) and the
fan spins more easily. Therefore, the power input to the fan would
be less for the same rate of turning.
The normal air pressures at different altitudes are well known.
From those values, I have calculated the change in air density with
altitude and, in turn, the change in the amount of power required
to drive the same fan at the same speed at three specific
locations. If 50 horsepower were required to drive a fan at a
particular speed at Rochester, N. Y. altitude (510 ft.), then only
48 horsepower would be needed drive the same fan at the same speed
at Olean, N. Y. altitude (1438 ft.) and 40 horsepower would suffice
at Denver, Col. altitude (5219 ft.).
Minor biasing of the performance of such fans is also caused by
day-to-day fluctuations in barometric. These changes would
generally be of the order of less than 3 percent either plus or
minus from the norm.
That the fan is subject to the biasing effect of air density
changes is only one of the shortcomings as an indicator of power
input. The power consumption of such a fan varies (at least as a
first approximation) as the cube of the rotational velocity.
Expressed in non-mathematical terms, as a more powerful engine
tends to turn the fan faster, the resistance of the fan to being
turned increases sharply and the more powerful engine fails to turn
it very much faster than a less powerful one.