6. CAMBER.--The camber (curvature) of the blades should
be (1) equal, (2) decrease evenly towards the tips of the blades,
and (3) the greatest depth of the curve should, at any point
of the blade, be approximately at the same percentage of
the chord from the leading edge as at other points.
It is difficult to test the top camber without a set of
templates, but a fairly accurate idea of the concave camber
can be secured by slowly passing a straight-edge along the
blade, thus:
The camber can now be easily seen, and as the straight-
edge is passed along the blade, the observer should look for
any irregularities of the curvature, which should gradually
and evenly decrease towards the tip of the blade.
7. THE JOINTS.--The usual method for testing the glued
joints is by revolving the propeller at greater speed than it
will be called upon to make during flight, and then carefully
examining the joints to see if they have opened. It is not
likely, however, that the reader will have the opportunity
of making this test. He should, however, examine all the
joints very carefully, trying by hand to see if they are quite
sound. Suspect a propeller of which the joints appear to
hold any thickness of glue. Sometimes the joints in the
boss open a little, but this is not dangerous unless they extend
to the blades, as the bolts will hold the laminations together.
8. CONDITION OF SURFACE.--The surface should be very
smooth, especially towards the tips of the blades.
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