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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
71
Thus,
you
see,
the
front
part
of
the
surface
is
the
most
valuable
from
the
point
of
view
of
securing
an
upwards
reaction
from
the
air;
and
so,
by
increasing
the
proportion
of
front,
or
"span,"
to
chord,
we
increase
the
amount
of
reaction
for
a
given
velocity
and
area
of
surface.
That
means
a
better
proportion
of
reaction
to
weight
of
surface,
though
the
designer
must
not
forget
the
drift
of
struts
and
wires
necessary
to
brace
up
a
surface
of
high
aspect
ratio.
Not
only
that,
but,
provided
the
chord
is
not
decreased
to
an
extent
making
it
impossible
to
secure
the
best
camber
owing
to
the
thickness
of
the
surface,
the
higher
the
aspect
ratio,
the
better
the
lift-drift
ratio.
The
reason
of
this
is
rather
obscure.
It
is
sometimes
advanced
that
it
is
owing
to
the
"spill"
of
air
from
under
the
wing-tips.
With
a
high
aspect
ratio
the
chord
is
less
than
would
otherwise
be
the
case.
Less
chord
results
in
smaller
wing-tips
and
consequently
less
"spill."
This,
however,
appears
to
be
a
rather
inadequate
reason
for
the
high
aspect
ratio
producing
the
high
lift-drift
ratio.
Other
reasons
are
also
advanced,
but
they
are
of
such
a
contentious
nature
I
do
not
think
it
well
to
go
into
them
here.
They
are
of
interest
to
designers,
but
this
is
written
for
the
practical
pilot
and
rigger.
5.
Stagger.--This
is
the
advancement
of
the
top
surface
relative
to
the
bottom
surface,
and
is
not,
of
course,
applicable
to
a
single
surface,
i.e.,
a
monoplane.
In
the
case
of
a
biplane
having
no
stagger,
there
will
be
"interference"
and
consequent
loss
of
efficiency
unless
the
gap
between
the
top
and
bottom
surfaces
is
equal
to
not
less
than
about
1-1/2
times
the
chord.
If
less
than
that,
the
air
engaged
by
the
bottom
of
the
top
surface
will
have
a
tendency
to
be
drawn
into
the
rarefied
area
over
the
top
of
the
bottom
surface,
with
the
result
that
the
surfaces
will
not
secure
as
good
a
reaction
as
would
otherwise
be
the
case.
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