Then
the fast walker must travel a farther distance than the slow
one, and his angle of path (pitch angle) must be smaller
than the angle of path taken by the slow walker. Their
pitch angles are different, but their pitch (in this case altitude
reached in a given time) is the same.
In order to test the pitch angle, the propeller must be
mounted upon a shaft at right angles to a beam the face of
which must be perfectly level, thus:
First select a point on the blade at some distance (say
about 2 feet) from the centre of the propeller. At that
point find, by means of a protractor, the angle a projection
of the chord makes with the face of the beam. That angle
is the pitch angle of the blade at that point.
Now lay out the angle on paper, thus:
The line above and parallel to the circumference line must
be placed in a position making the distance between the
two lines equal to the specified pitch, which is, or should be,
marked upon the boss of the propeller.
Now find the circumference of the propeller where the
pitch angle is being tested. For example, if that place is
2 feet radius from the centre, then the circumference will
be 2 feet X 2 = 4 feet diameter, which, if multiplied by
3.1416 = 15.56 feet circumference.
Now mark off the circumference distance, which is
represented above by A-B, and reduce it in scale for convenience.
The distance a vertical line makes between B and the
chord dine is the pitch at the point where the angle is being
tested, and it should coincide with the specified pitch.
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