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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
66
1.
The
vertical
component
of
the
reaction,
i.e.,
Lift,
which
is
opposed
to
Gravity,
i.e.,
the
weight
of
the
aeroplane.
2.
The
horizontal
component,
i.e.,
Drift
(sometimes
called
Resistance),
to
which
is
opposed
the
thrust
of
the
propeller.
The
direction
of
the
reaction
is,
of
course,
the
resultant
of
the
forces
Lift
and
Drift.
The
Lift
is
the
useful
part
of
the
reaction,
for
it
lifts
the
weight
of
the
aeroplane.
The
Drift
is
the
villain
of
the
piece,
and
must
be
overcome
by
the
Thrust
in
order
to
secure
the
necessary
velocity
to
produce
the
requisite
lift
for
flight.
DRIFT.--The
drift
of
the
whole
aeroplane
(we
have
considered
only
the
lifting
surface
heretofore)
may
be
conveniently
divided
into
three
parts,
as
follows:
Active
Drift,
which,
is
the
drift
produced
by
the
lifting
surfaces.
Passive
Drift,
which
is
the
drift
produced
by
all
the
rest
of
the
aeroplane--the
struts,
wires,
fuselage,
under-carriage,
etc.,
all
of
which
is
known
as
"detrimental
surface."
Skin
Friction,
which
is
the
drift
produced
by
the
friction
of
the
air
with
roughness
of
surface.
The
latter
is
practically
negligible
having
regard
to
the
smooth
surface
of
the
modern
aeroplane,
and
its
comparatively
slow
velocity
compared
with,
for
instance,
the
velocity
of
a
propeller
blade.
LIFT-DRIFT
RATIO.--The
proportion
of
lift
to
drift
is
known
as
the
lift-drift
ratio,
and
is
of
paramount
importance,
for
it
expresses
the
efficiency
of
the
aeroplane
(as
distinct
from
engine
and
propeller).
A
knowledge
of
the
factors
governing
the
lift-drift
ratio
is,
as
will
be
seen
later,
an
absolute
necessity
to
anyone
responsible
for
the
rigging
of
an
aeroplane,
and
the
maintenance
of
it
in
an
efficient
and
safe
condition.
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