66
DOC.
93
MARCH
1908
The rudder
has this
shape
because
it
is
the easiest
one.
I have
chosen
a
floor
made
of small ash
boards.
You
can see
that the
thing
is
very rigid.
In
my
calculations
I
never
exceeded the
limits
considered
permissible
in machine construction,
thus
I could
make
many things
up to
1/3 lighter,
but
I
don't
want
to,
because
precisely
the
things
that
one
could
alter[15] may
become stressed
by
accidental
loads
and
so
I
am on
the
safe side.
Now
the
whole
thing
is
so simple
that
not much
more
will be
changed.
It's
now more
than
a
week that
I have
had
the
thing
in this
form,
and
I
have
nothing
more
to do
on
it,
whereas
previously
the
thing
used
to
change
from
day
to
day.
How do
you
like it?
This
is
how it flies:
The
pilgrim (whom
I have
provided
with
a
staff
for
the
sake
of
safety)
moves
to
the indicated
place
for
the
take-off.
Then vertical
ascension,
and
now
the
man
goes
still
a
little
farther
away
from
the
motor, turns
around and
sits down
there
on a
bench. Now he flies
upwards,
with
the
motor out
in
front.
In
order
to
fly
forward-downward,
the
man
releases
the
clutch,
brakes the
rotors and
moves
(preferably
on a
(wheeled bench?)
close to the
motor. (The
motor
then
has
the
greater
moment)
so
it
goes
ahead.
Backward
flying can
also be
managed.
For the
most part,
weight
was
saved
by
the idea of
having
the rotors
run on
rollers
and
by
using a
thin
ascending
shaft.
Another
difficulty
has
been
the
driving
of the
motor.
The
outer
rims
of the
rotors
are
of aluminum-the
rest is
steel tube
and wire.
The
pretty
accompanying
picture
depicts
the beast.
The
propellers
have
an
aluminum
hub. This
hub
is
a
tube
with
a
diameter of
45
cm
and
height
of
60
cm.
On
its
inside,
the hub carries
2
ring gears,
each
4
cm
wide,
with ribs
on
the
ring gears.
Each
ring
gear is
engaged
by
two
gears
on
the
shaft
running
at 1500
rpm (rawhide
rotors).
The hub
has
no
inner
supports, instead,
it
runs
on
rollers that
are
carried
by
4
fixed
supports.
These
fixed
supports
are
fastened
to
the
central
tube. I
made
this
construction
in
order
to
get by
with
the
1500
rpm
ascending
shaft.
The further
advantage is
that
by
means
of
the wires
that
connect
the
supports,
one can
make
the
whole
thing rigid.
These
wires also
absorb
part
of the
bending
of
the
supports,
so
that
the latter
too
become weaker than
they
would otherwise be.
In
order
to
keep
the
torque
in the central
shaft and
the transmission ratio
in
the
gears small,
I
had
to
have
the
rotors
turn
faster than
originally
intended.
This
is
no
advantage
with
regard
to
efficiency,
but
I
have to do
it. Therefore,
I
increased the
efficiency by
making
the
propellers low,
because
the air
then
stays
in
the
rotor
for
only
an
extremely
short
time,
it
is
not
severely
stressed
by friction,
and
owing
to
friction,
gyration
etc.
Of
course,
the
number of blades
is
then
correspondingly
large.
In the
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