e 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.

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 toget