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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
67
Those
factors
are
as
follows:
1.
Velocity.--The
greater
the
velocity
the
greater
the
proportion
of
drift
to
lift,
and
consequently
the
less
the
efficiency.
Considering
the
lifting
surfaces
alone,
both
the
lift
and
the
(active)
drift,
being
component
parts
of
the
reaction,
increase
as
the
square
of
the
velocity,
and
the
efficiency
remains
the
same
at
all
speeds.
But,
considering
the
whole
aeroplane,
we
must
remember
the
passive
drift.
It
also
increases
as
the
square
of
the
velocity
(with
no
attendant
lift),
and,
adding
itself
to
the
active
drift,
results
in
increasing
the
proportion
of
total
drift
(active
+
passive)
to
lift.
But
for
the
increase
in
passive
drift
the
efficiency
of
the
aeroplane
would
not
fall
with
increasing
velocity,
and
it
would
be
possible,
by
doubling
the
thrust,
to
approximately
double
the
speed
or
lift--a
happy
state
of
affairs
which
can
never
be,
but
which
we
may,
in
a
measure,
approach
by
doing
everything
possible
to
diminish
the
passive
drift.
Every
effort
is
then
made
to
decrease
it
by
"stream-lining,"
i.e.,
by
giving
all
"detrimental"
parts
of
the
aeroplane
a
form
by
which
they
will
pass
through
the
air
with
the
least
possible
drift.
Even
the
wires
bracing
the
aeroplane
together
are,
in
many
cases,
stream-lined,
and
with
a
markedly
good
effect
upon
the
lift-drift
ratio.
In
the
case
of
a
certain
well-known
type
of
aeroplane
the
replacing
of
the
ordinary
wires
by
stream-lined
wires
added
over
five
miles
an
hour
to
the
flight
speed.
Head-resistance
is
a
term
often
applied
to
passive
drift,
but
it
is
apt
to
convey
a
wrong
impression,
as
the
drift
is
not
nearly
so
much
the
result
of
the
head
or
forward
part
of
struts,
wires,
etc.,
as
it
is
of
the
rarefied
area
behind.
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