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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
63
CHAPTER
I
FLIGHT
Air
has
weight
(about
13
cubic
feet
=
1
lb.),
inertia,
and
momentum.
It
therefore
obeys
Newton's
laws[14]
and
resists
movement.
It
is
that
resistance
or
reaction
which
makes
flight
possible.
Flight
is
secured
by
driving
through
the
air
a
surface[15]
inclined
upwards
and
towards
the
direction
of
motion.
S
=
Side
view
of
surface.
M
=
Direction
of
motion.
CHORD.--The
Chord
is,
for
practical
purposes,
taken
to
be
a
straight
line
from
the
leading
edge
of
the
surface
to
its
trailing
edge.
N
=
A
line
through
the
surface
starting
from
its
trailing
edge.
The
position
of
this
line,
which
I
call
the
Neutral
Lift
Line,
is
found
by
means
of
wind-tunnel
research,
and
it
varies
with
differences
in
the
camber
(curvature)
of
surfaces.
In
order
to
secure
flight,
the
inclination
of
the
surface
must
be
such
that
the
neutral
lift
line
makes
an
angle
with
and
above
the
line
of
motion.
If
it
is
coincident
with
M,
there
is
no
lift.
If
it
makes
an
angle
with
M
and
below
it,
then
there
is
a
pressure
tending
to
force
the
surface
down.
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