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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
99
The
centre
line
is
still
the
same
length
as
before
being
bent;
but
the
top
line,
being
farther
from
the
centre
of
the
circle,
is
now
longer
than
the
centre
line.
That
can
be
due
only
to
the
strain
of
elongation
produced
by
the
stress
of
tension.
The
wood
between
the
centre
line
and
the
top
line
is
then
in
tension;
and
the
farther
from
the
centre,
the
greater
the
strain,
and
consequently
the
greater
the
tension.
The
bottom
line,
being
nearest
to
the
centre
of
the
circle,
is
now
shorter
than
the
centre
line.
That
can
be
due
only
to
the
strain
of
crushing
produced
by
the
stress
of
compression.
The
wood
between
the
centre
and
bottom
lines
is
then
in
compression;
and
the
nearer
the
centre
of
the
circle,
the
greater
the
strain,
and
consequently
the
greater
the
compression.
It
then
follows
that
there
is
neither
tension
nor
compression,
i.e.,
no
stress,
at
the
centre
line,
and
that
the
wood
immediately
surrounding
it
is
under
considerably
less
stress
than
the
wood
farther
away.
This
being
so,
the
wood
in
the
centre
may
be
hollowed
out
without
unduly
weakening
struts
and
spars.
In
this
way
25
to
33
per
cent.
is
saved
in
the
weight
of
wood
in
an
aeroplane.
The
strength
of
wood
is
in
its
fibres,
which
should,
as
far
as
possible,
run
without
break
from
one
end
of
a
strut
or
spar
to
the
other
end.
A
point
to
remember
is
that
the
outside
fibres,
being
farthest
removed
from
the
centre
line,
are
doing
by
far
the
greatest
work.
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