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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
90
This
tendency
is
offset
by
increasing
the
angle
of
incidence
(and
consequently
the
lift)
of
the
side
tending
to
fall;
and
it
is
always
advisable,
if
practical
considerations
allow
it,
to
also
decrease
the
angle
upon
the
other
side.
In
that
way
it
is
not
necessary
to
depart
so
far
from
the
normal
angle
of
incidence
at
which
the
lift-drift
ratio
is
highest.
Wash-in
is
the
term
applied
to
the
increased
angle.
Wash-out
is
the
term
applied
to
the
decreased
angle.
Both
lateral
and
directional
stability
may
be
improved
by
washing
out
the
angle
of
incidence
on
both
sides
of
the
surface,
thus:
The
decreased
angle
decreases
the
drift
and
therefore
the
effect
of
gusts
upon
the
wing-tips,
which
is
just
where
they
have
the
most
effect
upon
the
aeroplane,
owing
to
the
distance
from
the
turning
axis.
The
wash-out
also
renders
the
ailerons
(lateral
controlling
services)
more
effective,
as,
in
order
to
operate
them,
it
is
not
then
necessary
to
give
them
such
a
large
angle
of
incidence
as
would
otherwise
be
required.
The
less
the
angle
of
incidence
of
the
ailerons,
the
better
their
lift-drift
ratio,
i.e.,
their
efficiency.
You
will
note
that,
while
the
aileron
attached
to
the
surface
with
washed-out
angle
is
operated
to
the
same
extent
as
the
aileron
illustrated
above
it,
its
angle
of
incidence
is
considerably
less.
Its
efficiency
is
therefore
greater.
The
advantages
of
the
wash-in
must,
of
course,
be
paid
for
in
some
loss
of
lift,
as
the
lift
decreases
with
the
decreased
angle.
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