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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
81
What
I
have
described
is
continually
going
on
during
flight,
but
in
a
well-designed
aeroplane
such
stabilizing
movements
are,
most
of
the
time,
so
slight
as
to
be
imperceptible
to
the
pilot.
If
an
aeroplane
was
not
stabilized
in
this
way,
it
would
not
only
be
continually
trying
to
leave
its
course,
but
it
would
also
possess
a
dangerous
tendency
to
"nose
away"
from
the
direction
of
the
side
gusts.
In
such
case
the
gust
shown
in
the
above
illustration
would
turn
the
aeroplane
round
the
opposite
way
a
very
considerable
distance;
and
the
right
wing,
being
on
the
outside
of
the
turn,
would
travel
with
greater
velocity
than
the
left
wing.
Increased
velocity
means
increased
lift;
and
so,
the
right
wing
lifting,
the
aeroplane
would
turn
over
sideways
very
quickly.
LONGITUDINAL
STABILITY.--Flat
surfaces
are
longitudinally
stable
owing
to
the
fact
that
with
decreasing
angles
of
incidence
the
centre
line
of
pressure
(C.P.)
moves
forward.
The
C.P.
is
a
line
taken
across
the
surface,
transverse
to
the
direction
of
motion,
and
about
which
all
the
air
forces
may
be
said
to
balance,
or
through
which
they
may
be
said
to
act.
Imagine
A
to
be
a
flat
surface,
attitude
vertical,
travelling
through
the
air
in
the
direction
of
motion
M.
Its
C.P.
is
then
obviously
along
the
exact
centre
line
of
the
surface
as
illustrated.
In
B,
C,
and
D
the
surfaces
are
shown
with
angles
of
incidence
decreasing
to
nothing,
and
you
will
note
that
the
C.P.
moves
forward
with
the
decreasing
angle.[17]
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