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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
21
"But,"
objected
Efficiency,
"the
Lift
varies
with
the
Angle
of
Incidence,
and
surely
such
a
condition
will
result
in
one
side
of
the
Aeroplane
lifting
more
than
the
other
side?"
"That's
all
right,"
said
the
Propeller,
"it's
meant
to
off-set
the
tendency
of
the
Aeroplane
to
turn
over
sideways
in
the
opposite
direction
to
which
I
revolve."
"That's
quite
clear,
though
rather
unexpected;
but
how
do
you
counteract
the
effect
of
the
gusts
when
they
try
to
overturn
the
Aeroplane
sideways?"
said
she,
turning
to
Lateral
Stability
again.
"Well,"
he
replied,
rather
miserably,
"I'm
not
nearly
so
perfect
as
the
Longitudinal
and
Directional
Stabilities.
The
Dihedral
Angle--that
is,
the
upward
inclination
of
the
Surfaces
towards
their
wing-tips--does
what
it
can
for
me,
but,
in
my
opinion,
it's
a
more
or
less
futile
effort.
The
Blackboard
will
show
you
the
argument."
And
he
at
once
showed
them
two
Surfaces,
each
set
at
a
Dihedral
Angle
like
this:
"Please
imagine,"
said
the
Blackboard,
"that
the
top
=V=
is
the
front
view
of
a
Surface
flying
towards
you.
Now
if
a
gust
blows
it
into
the
position
of
the
lower
=V=
you
see
that
the
horizontal
equivalent
of
the
Surface
on
one
side
becomes
larger,
and
on
the
other
side
it
becomes
smaller.
That
results
in
more
lift
on
the
lower
side
and
less
on
the
higher
side,
and
if
the
=V=
is
large
enough
it
should
produce
such
a
difference
in
the
lift
of
one
side
to
the
other
as
to
quickly
turn
the
Aeroplane
back
to
its
former
and
normal
position."
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