Place the propeller in a horizontal
position, and it should remain in that position. If a weight
of a trifle over an ounce placed in a bolt-hole on one side of
the boss fails to disturb the balance, then the propeller is
usually regarded as unfit for use.
The above method is rather futile, as it does not test for
the balance of centrifugal force, which comes into play as
soon as the propeller revolves. It can be tested as follows:
The propeller must be in a horizontal position, and then
weighed at fixed points, such as A, B, C, D, E, and F, and
the weights noted. The points A, B, and C must, of course,
be at the same fixed distances from the centre of the propeller
as the points D, E, and F. Now reverse the propeller and
weigh at each point again. Note the results. The first
series of weights should correspond to the second series,
thus:
Weight A should equal weight F.
`` B `` `` `` E.
`` C `` `` `` D.
There is no standard practice as to the degree of error
permissible, but if there are any appreciable differences the
propeller is unfit for use.
5. SURFACE AREA.--The surface area of the blades should
be equal. Test with callipers thus:
The points between which the distances are taken must,
of course, be at the same distance from the centre in the
case of each blade.
There is no standard practice as to the degree of error
permissible. If, however, there is an error of over 1/8 inch,
the propeller is really unfit for use.
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