Lab
Library
Journal
Shop
Sign in
to keep
Share image
1
165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
64
I
=
Angle
of
Incidence.
This
angle
is
generally
defined
as
the
angle
the
chord
makes
with
the
direction
of
motion,
but
that
is
a
bad
definition,
as
it
leads
to
misconception.
The
angle
of
incidence
is
best
described
as
the
angle
the
neutral
lift
line
makes
with
the
direction
of
motion
relative
to
the
air.
You
will,
however,
find
that
in
nearly
all
rigging
specifications
the
angle
of
incidence
is
taken
to
mean
the
angle
the
chord
makes
with
a
line
parallel
to
the
propeller
thrust.
This
is
necessary
from
the
point
of
view
of
the
practical
mechanic
who
has
to
rig
the
aeroplane,
for
he
could
not
find
the
neutral
lift
line,
whereas
he
can
easily
find
the
chord.
Again,
he
would
certainly
be
in
doubt
as
to
"the
direction
of
motion
relative
to
the
air,"
whereas
he
can
easily
find
a
line
parallel
to
the
propeller
thrust.
It
is
a
pity,
however,
that
these
practical
considerations
have
resulted
in
a
bad
definition
of
the
angle
of
incidence
becoming
prevalent,
a
consequence
of
which
has
been
the
widespread
fallacy
that
flight
may
be
secured
with
a
negative
inclination
of
the
surface.
Flight
may
conceivably
be
secured
with
a
negative
angle
of
chord,
but
never
with
a
negative
inclination
of
the
surface,
if,
as
seems
reasonable,
we
regard
the
surface
from
the
point
of
view
of
the
neutral
lift
line.
All
this
is
only
applicable
to
cambered
surfaces.
In
the
case
of
flat
surfaces
the
neutral
lift
line
coincides
with
the
chord
and
the
definition
I
have
criticized
adversely
is
then
applicable.
Flat
lifting
surfaces
are,
however,
never
used.
Marker
Marker
Fine marker
White-out
Fine white-out
Circle
Paint
Unmarker
Hand
Scalpel
Dice
Sieve
Purify
Undo
Redo
Start over
