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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
130
It
is
difficult
to
test
the
top
camber
without
a
set
of
templates,[18]
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.
Some
propeller
tips
have
a
speed
of
over
30,000
feet
a
minute,
and
any
roughness
will
produce
a
bad
drift
or
resistance
and
lower
the
efficiency.
9.
MOUNTING.--Great
care
should
be
taken
to
see
that
the
propeller
is
mounted
quite
straight
on
its
shaft.
Test
in
the
same
way
as
for
straightness.
If
it
is
not
straight,
it
is
possibly
due
to
some
of
the
propeller
bolts
being
too
slack
or
to
others
having
been
pulled
up
too
tightly.
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