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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
85
Do
not
fall
into
the
widespread
error
that
the
angle
of
incidence
varies
as
the
angle
of
the
aeroplane
to
the
horizontal.
It
varies
with
such
angle,
but
not
as
anything
approaching
it.
Remember
that
the
stabilizing
effect
of
the
longitudinal
dihedral
lasts
only
as
long
as
there
is
momentum
in
the
direction
of
the
first
course.
These
stabilizing
movements
are
taking
place
all
the
time,
even
though
imperceptible
to
the
pilot.
Aeroplanes
have,
in
the
past,
been
built
with
a
stabilizing
surface
in
front
of
the
main
surface
instead
of
at
the
rear
of
it.
In
such
design
the
main
surface
(which
is
then
the
tail
surface
as
well
as
the
principal
lifting
surface)
must
be
set
at
a
less
angle
than
the
forward
stabilizing
surface,
in
order
to
secure
a
longitudinal
dihedral.
The
defect
of
such
design
lies
in
the
fact
that
the
main
surface
must
have
a
certain
angle
to
lift
the
weight--say
5°.
Then,
in
order
to
secure
a
sufficiency
of
longitudinal
stability,
it
is
necessary
to
set
the
forward
stabilizer
at
about
15°.
Such
a
large
angle
of
incidence
results
in
a
very
poor
lift-drift
ratio
(and
consequently
great
loss
of
efficiency),
except
at
very
low
velocities
compared
with
the
speed
of
modern
aeroplanes.
At
the
time
such
aeroplanes
were
built
velocities
were
comparatively
low,
and
this
defect
was,
for
that
reason,
not
sufficiently
appreciated.
In
the
end
it
killed
the
"canard"
or
"tail-first"
design.
Aeroplanes
of
the
Dunne
and
similar
types
possess
no
stabilizing
surface
distinct
from
the
main
surface,
but
they
have
a
longitudinal
dihedral
which
renders
them
stable.
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