Snips... Variable
Ideal for our use would be a Lemans type variable length set
up
where we would have one length for take off RPMs and another
for
top speed and a third for cruise RPM for best BSFC. Not all
that
hard to do as we are only talking about a four or five inch
change in length. This will become more important as the
2.85:1
and 3.12:1 gear box and the higher max RPM RX8 engine come
into
use.
I think Mazda has already found that out with the RX8
engine.
Basically the poor torque characteristics of the rotary
engine
make it a better aircraft engine than a car engine.
IMHO Mazda will eventually address that issue with e
super charger to enhance the torque down low.
BTW Ed how far down your airstrip do the RPMs finally peak
if at all? What are the RPMs that you use to climb out
after you break ground?
Paul Lamar
It would be nice to try some different configuration on a dyno
for
comparison. My current sliding tube manifold was fabricated
with
the
idea
of trying different manifold lengths (can vary length by 2
1/2").
Its
currently set for the long position (21") but could be
shortened
to 18
1/2"
by simply opening a tube clamp and lowering the top part. I
had
envisioned
a high torque dc motor driving a screw to run the tubes in and
out
with
a
two position swithc "Take-Off" and "Cruise". Had too many
other
variables
early on to play with changing its length, but now might be
the
time to
do
so.
snips...
Ed
I have been thinking about it too. If you apply a point load on
telescopic tubing it tends to cock and jam. I am thinking about
a light weight integral annular hydraulic cylinder on each
runner to
serves as actuators. I'll draw something up.
Paul Lamar
Yes, the tubes can be adjusted by tapping on the plate welded to
all
four
(up or down), but had to keep the fit tight between outer and
inner
tubes to
stop air leaks and that does not lend itself to easily running
them up
and
down. Be interested in your drawing.
more snips...
Ed Anderson
OK here it is. The control in it's simplest form would be a hydraulic
cylinder
on the instrument panel with a knob on the ram. Move the knob in and
the
runner elongates. Move the knob out and the runner contracts.
All done with low pressure fluid piping. Mazda should make this
instead of
all that Mickey Mouse three stage dynamic chamber mess. This should be
fairly
cheap to build in large quantities.
Since the runner would have to move in and out inside the plenum a
gadget
in the plenum could limit runner extension travel.
To answer those that will ask: "How come the bell is 180 degrees
instead
of only 90 degrees as in my other designs? The answer is: a 180 bell
works
better when it is not attached to a wall. In other words in the middle
of
a plenum.
If the bell is attached to the plenum wall 90 degrees is sufficient.
The trick to keeping the runner wall thickness down is the trick with
the off set O rings shown in the second jpg. Teflon encapsulated
silicone
O-rings would work well hear as they would reduce the friction forces.
Paul Lamar
Interesting arrangement on the"O" rings to seal the tubes and permit
movement.
I'll file that for future reference.
Ed
So what do you think of the hydraulic drive itself? :)
Paul Lamar
Hydraulic drive is peachy, however, adapting my hydraulic jack and pumping
the handle like mad just before takeoff just might make any passenger
nervous {:>).
Ed
Real funny Ed. You even look a little bit like Red Skelton :)
You don't have to pump the handle. The runner displacement
is 6.28 x .1 x the length of travel of the runner.
Or 3.14 cubic inches for a five inch travel.
Total displacement required for all four is 12.56 cubic inches.
With a knob that sticks out of the panel four inches
the area of the control cylinder is then 3.14 or
a radius of one inch. Check my arithmetic.
The control cylinder can be lightly constructed out of thin
wall 2 inch tubing as the pressure is minimal.
It is not like we are lifting the whole airplane.
Each runner gets 25% of the force applied to the knob.
If you apply 20 pounds to the knob the runners would see
5 pounds of moving force each. Way more than enough
and the pressure in the system would be 20/3.14 or
ONLY 7 PSI!!!!
Think of it as a low cost controllable
pitch prop. In for low pitch out for high pitch.
Paul Lamar
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