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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
131
FLUTTER.--Propeller
"flutter,"
or
vibration,
may
be
due
to
faulty
pitch
angle,
balance,
camber,
surface
area,
or
to
bad
mounting.
It
causes
a
condition
sometimes
mistaken
for
engine
trouble,
and
one
which
may
easily
lead
to
the
collapse
of
the
propeller.
CARE
OF
PROPELLERS.--The
care
of
propellers
is
of
the
greatest
importance,
as
they
become
distorted
very
easily.
1.
Do
not
store
them
in
a
very
damp
or
a
very
dry
place.
2.
Do
not
store
them
where
the
sun
will
shine
upon
them.
3.
Never
leave
them
long
in
a
horizontal
position
or
leaning
up
against
a
wall.
4.
They
should
be
hung
on
horizontal
pegs,
and
the
position
of
the
propellers
should
be
vertical.
If
the
points
I
have
impressed
upon
you
in
these
notes
are
not
attended
to,
you
may
be
sure
of
the
following
results:
1.
Lack
of
efficiency,
resulting
in
less
aeroplane
speed
and
climb
than
would
otherwise
be
the
case.
2.
Propeller
"flutter"
and
possible
collapse.
3.
A
bad
stress
upon
the
propeller
shaft
and
its
bearings.
TRACTOR.--A
propeller
mounted
in
front
of
the
main
surface.
PUSHER.--A
propeller
mounted
behind
the
main
surface.
FOUR-BLADED
PROPELLERS.--Four-bladed
propellers
are
suitable
only
when
the
pitch
is
comparatively
large.
For
a
given
pitch,
and
having
regard
to
"interference,"
they
are
not
so
efficient
as
two-bladed
propellers.
The
smaller
the
pitch,
the
less
the
"gap,"
i.e.,
the
distance,
measured
in
the
direction
of
the
thrust,
between
the
spiral
courses
of
the
blades
(see
illustration
on
preceding
page).
If
the
gap
is
too
small,
then
the
following
blade
will
engage
air
which
the
preceding
blade
has
put
into
motion,
with
the
result
that
the
following
blade
will
not
secure
as
good
a
reaction
as
would
otherwise
be
the
case.
It
is
very
much
the
same
as
in
the
case
of
the
aeroplane
gap.
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