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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
86
The
main
surface
towards
the
wing-tips
is
given
a
decreasing
angle
of
incidence
and
corresponding
camber.
The
wing-tips
then
act
as
longitudinal
stabilizers.
This
design
of
aeroplane,
while
very
interesting,
has
not
proved
very
practicable,
owing
to
the
following
disadvantages:
(1)
The
plan
design
is
not,
from
a
mechanical
point
of
view,
so
sound
as
that
of
the
ordinary
aeroplane
surface,
which
is,
in
plan,
a
parallelogram.
It
is,
then,
necessary
to
make
the
strength
of
construction
greater
than
would
otherwise
be
the
case.
That
means
extra
weight.
(2)
The
plan
of
the
surface
area
is
such
that
the
aspect
ratio
is
not
so
high
as
if
the
surface
was
arranged
with
its
leading
edges
at
right
angles
to
the
direction
of
motion.
The
lower
the
aspect
ratio,
then,
the
less
the
lift.
This
design,
then,
produces
less
lift
for
weight
of
surface
than
would
the
same
surface
if
arranged
as
a
parallelogram.
(3)
In
order
to
secure
the
longitudinal
dihedral,
the
angle
of
incidence
has
to
be
very
much
decreased
towards
the
wing-tips.
Then,
in
order
that
the
lift-drift
ratio
may
be
preserved,
there
must
be
a
corresponding
decrease
in
the
camber.
That
calls
for
surface
ribs
of
varying
cambers,
and
results
in
an
expensive
and
lengthy
job
for
the
builder.
(4)
In
order
to
secure
directional
stability,
the
surface
is,
in
the
centre,
arranged
to
dip
down
in
the
form
of
a
V,
pointing
towards
the
direction
of
motion.
Should
the
aeroplane
turn
off
its
course,
then
its
momentum
in
the
direction
of
its
first
course
causes
it
to
move
in
a
direction
the
resultant
of
the
thrust
and
the
momentum.
It
then
moves
in
a
more
or
less
sideways
attitude,
which
results
in
an
air
pressure
upon
one
side
of
the
V,
and
which
tends
to
turn
the
aeroplane
back
to
its
first
course.
This
arrangement
of
the
surface
results
in
a
bad
drift.
Vertical
surfaces
at
the
wing-tips
may
also
be
set
at
an
angle
producing
the
same
stabilizing
effect,
but
they
also
increase
the
drift.
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