On Thu, 08 Jul 2010 18:42:13 -0500, cavelamb
wrote:

My friend Chuck and I built a (roughly) 3/4 scale SE-5A (many years ago)
that had a 3 cylinder Geo on it.

Chuck adapted a Rotax "B" box for it. That involved making a mount plate
that fit the motor on one side and bossed in the box on the other.
I recall a spacer on the box side to get the gears to mate up right,
but no details now.


But he also turned down the flywheel to reduce weight.
That's a common task on VWs and Subarus and can really help.
But the Geo flywheel weight is directly proportional to engine life.
It HAS to have the whole flywheel or the crank shaft breaks in 10 to 12 hours.
It's a resonance issue related to 3 hole motors.
And, yes, it broke in flight! Of course.

On a couple of other (2 and 4 cylinder) projects we used belts.

Don't bother with multiple V belts - it's not possible to get several
close enough to the same size to work reliably. And when one goes, the
rest are immediately overloaded and let go as well.

We never found a single V belt arrangement that worked well or was at all
reliable. This on motors in the 50 to 80 hp range.

The best belt solution was the Gates PolyChain set up.

Home made wheels of aluminum worked ok, but hard anodizing is recommended.
Chuck made a cutter for that odd rounded tooth pattern, and with a bit of
practice, made some serviceable wheels.

One of the problem areas is the bottom (engine side) drive pulley.
It needs to be as small as possible to keep the driven wheel from being too
large, but small wheels cause higher tooth loads and wear rapidly.

Harmonic resonance issues require staying away from even numbered ratios.
IE: 2:1 is horrible for resonance. 2.58:1 is much better!
(Guitar players can explain this real well)

Hard learned lesson - don't loose your count on the gear cutter,
and never EVER try to back up!


I've seen the Raven belt setup and was impressed.
http://www.raven-rotor.com/html/redrive.html

Might want to explore the planetary gear boxes as the parts are
smaller and generally available off the shelf.
http://www.rotorcraft.com/ads/nhc.html
http://www.wingsforum.com/viewtopic.php?p=22031
http://www.rotaryaviation.com/Aviation_Prod.htm

Excess weight on the nose of a very light airplane is a real killer.
The airplane MUST balance properly to be at all controllable.
Ballast on the tail may be necessary.
Call it Static Stability Augmentation if anybody objects to "ballast".


But my heart-felt bottom-line advice would be to politely RUN (not walk)
away
from this kind of project.

Beyond the research and development (R&D = ReDo)
is the legal liability in the event of a catastrophic failure.

As we have found out over the years, it's a no win situation...

Build your own if you want.

But be careful of the ramifications of building for others...


Respects,

Richard Lamb




Hold the presses, we've got a great come back.

One of the first things I asked this guy was how big the back main
journal is. I have ground aircraft cranks in a past life time.

Oh well thanks

Sounds like very good advice all around.









Sunworshipper wrote:
Well, got myself in a pickle this time. I answered an ad with some guy
wanting lathe work done, he said it was a couple of groves in pulleys.
Come to find out he wants me to design, engineer, and build a speed
reducer for a Geo Metro engine powered hmmm plane. I'm not sure, but
I'm starting to think that my Atlas lathe won't be able to turn 8"
dia. V groves.

Anyhow, I've been searching the net to the point of getting a
headache. Seems this kind of stuff is hush hush. I assume they run
off a spindle somehow bolted to the block and then an extension is
bolted on to get the prop past the distributor.

The cheapest I can find is $269.38 for the 5 belt 8" pulley and
$123.70 for the 5 belt 3" pulley.

Has anyone done this kind of thing before? The more I think about it
the more I should decline. I'm afraid I might miss something
important, like the vibration between the engine and air turbulence
affecting the triple prop. with aluminum between. Maybe it is just me,
I grew up around aircraft that were build by companies from J-3's to
DC-3's

While searching I see something that looks a lot more safe, an
Airtrike gear box for $2G. The cog ones seem safer than multiple belts
to me cause if ya loose one belt it's gonna take out the distributor
or the coil wire, what's the difference? The other names I have are
J bird and Raven. I see they use cog drives on super chargers, but
nothing 8" dia.

Anybody have any ideas I can help this guy out with? BTW, he's
computer illiterate, I tought I could help at least in that area, but
running into brick walls.

SW wishing he was making his own plane. 31 years since solo.