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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
69
From
a
rigging
point
of
view,
one
must
presume
that
every
standard
aeroplane
has
its
lifting
surface
set
at
the
most
efficient
angle,
and
the
practical
application
of
all
this
is
in
taking
the
greatest
possible
care
to
rig
the
surface
at
the
correct
angle
and
to
maintain
it
at
such
angle.
Any
deviation
will
adversely
affect
the
lift-drift
ratio,
i.e.,
the
efficiency.
3.
Camber.--(Refer
to
the
second
illustration
in
this
chapter.)
The
lifting
surfaces
are
cambered,
i.e.,
curved,
in
order
to
decrease
the
horizontal
component
of
the
reaction,
i.e.,
the
drift.
The
bottom
camber:
If
the
bottom
of
the
surface
was
flat,
every
particle
of
air
meeting
it
would
do
so
with
a
shock,
and
such
shock
would
produce
a
very
considerable
horizontal
reaction
or
drift.
By
curving
it
such
shock
is
diminished,
and
the
curve
should
be
such
as
to
produce
a
uniform
(not
necessarily
constant)
acceleration
and
compression
of
the
air
from
the
leading
edge
to
the
trailing
edge.
Any
unevenness
in
the
acceleration
and
compression
of
the
air
produces
drift.
The
top
camber:
If
this
was
flat
it
would
produce
a
rarefied
area
of
irregular
shape.
I
have
already
explained
the
bad
effect
this
has
upon
the
lift-drift
ratio.
The
top
surface
is
then
curved
to
produce
a
rarefied
area
the
shape
of
which
shall
be
as
stream-line
and
free
from
attendant
eddies
as
possible.
The
camber
varies
with
the
angle
of
incidence,
the
velocity,
and
the
thickness
of
the
surface.
Generally
speaking,
the
greater
the
velocity,
the
less
the
camber
and
angle
of
incidence.
With
infinite
velocity
the
surface
would
be
set
at
no
angle
of
incidence
(the
neutral
lift
line
coincident
with
the
direction
of
motion
relative
to
the
air),
and
would
be,
top
and
bottom,
of
pure
stream-line
form--i.e.,
of
infinite
fineness.
This
is,
of
course,
carrying
theory
to
absurdity
as
the
surface
would
then
cease
to
exist.
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