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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
74
THE
BEST
CLIMBING
ANGLE
is
approximately
half-way
between
the
maximum
and
the
optimum
angles.
All
present-day
aeroplanes
are
a
compromise
between
Climb
and
horizontal
Velocity.
We
will
compare
the
essentials
for
two
aeroplanes,
one
designed
for
maximum
climb,
and
the
other
for
maximum
velocity.
ESSENTIALS
FOR
MAXIMUM
CLIMB:
1.
Low
velocity,
in
order
to
secure
the
best
lift-drift
ratio.
2.
Having
a
low
velocity,
a
large
surface
will
be
necessary
in
order
to
engage
the
necessary
mass
of
air
to
secure
the
requisite
lift.
3.
Since
(1)
such
a
climbing
machine
will
move
along
an
upward
sloping
path,
and
(2)
will
climb
with
its
propeller
thrust
horizontal,
then
a
large
angle
relative
to
the
direction
of
the
thrust
will
be
necessary
in
order
to
secure
the
requisite
angle
relative
to
the
direction
of
motion.
The
propeller
thrust
should
be
always
horizontal,
because
the
most
efficient
flying-machine
(having
regard
to
climb
or
velocity)
has,
so
far,
been
found
to
be
an
arrangement
of
an
inclined
surface
driven
by
a
horizontal
thrust--the
surface
lifting
the
weight,
and
the
thrust
overcoming
the
drift.
This
is,
in
practice,
a
far
more
efficient
arrangement
than
the
helicopter,
i.e.,
the
air-screw
revolving
about
a
vertical
axis
and
producing
a
thrust
opposed
to
gravity.
If,
when
climbing,
the
propeller
thrust
is
at
such
an
angle
as
to
tend
to
haul
the
aeroplane
upwards,
then
it
is,
in
a
measure,
acting
as
a
helicopter,
and
that
means
inefficiency.
The
reason
of
a
helicopter
being
inefficient
in
practice
is
due
to
the
fact
that,
owing
to
mechanical
difficulties,
it
is
impossible
to
construct
within
a
reasonable
weight
an
air-screw
of
the
requisite
dimensions.
That
being
so,
it
would
be
necessary,
in
order
to
absorb
the
power
of
the
engine,
to
revolve
the
comparatively
small-surfaced
air
screw
at
an
immensely
greater
velocity
than
that
of
the
aeroplane's
surface.
As
already
explained,
the
lift-drift
ratio
falls
with
velocity
on
account
of
the
increase
in
passive
drift.
This
applies
to
a
blade
of
a
propeller
or
air-screw
which
is
nothing
but
a
revolving
surface
set
at
angle
of
incidence,
and
which
it
is
impossible
to
construct
without
a
good
deal
of
detrimental
surface
near
the
central
boss.
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