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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
89
It
is
now,
I
hope,
clear
to
the
reader
that
the
lateral
dihedral
is
not
quite
so
effective
as
would
appear
at
first
sight.
Some
designers,
indeed,
prefer
not
to
use
it,
since
its
effect
is
not
very
great,
and
since
it
must
be
paid
for
in
loss
of
H.E.
and
consequently
loss
of
lift,
thus
decreasing
the
lift-drift
ratio,
i.e.,
the
efficiency.
Also,
it
is
sometimes
advanced
that
the
lateral
dihedral
increases
the
"spill"
of
air
from
the
wing-tips
and
that
this
adversely
affects
the
lift-drift
ratio.
The
disposition
of
the
keel-surface
affects
the
lateral
stability.
It
should
be,
in
effect,
equally
divided
by
the
longitudinal
turning
axis
of
the
aeroplane.
If
there
is
an
excess
of
keel-surface
above
or
below
such
axis,
then
a
side
gust
striking
it
will
tend
to
turn
the
aeroplane
over
sideways.
The
position
of
the
centre
of
gravity
affects
lateral
stability.
If
too
low,
it
produces
a
pendulum
effect
and
causes
the
aeroplane
to
roll
sideways.
If
too
high,
it
acts
as
a
stick
balanced
vertically
would
act.
If
disturbed,
it
tends
to
travel
to
a
position
as
far
as
possible
from
its
original
position.
It
would
then
tend,
when
moved,
to
turn
the
aeroplane
over
sideways
and
into
an
upside-down
position.
From
the
point
of
view
of
lateral
stability,
the
best
position
for
the
centre
of
gravity
is
one
a
little
below
the
centre
of
drift.
This
produces
a
little
lateral
stability
without
any
marked
pendulum
effect.
Propeller
torque
affects
lateral
stability.
An
aeroplane
tends
to
turn
over
sideways
in
the
opposite
direction
to
which
the
propeller
revolves.
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