Gordon Arnaut wrote:
Yes, the Egg redrive has no failures yet, from what I know.

However, he seems to have taken the "build it strong as hell" approach and
doesn't use any kind of damping, such as elastomers, sprag clutch, etc. He
is also using a heavy flywheel that helps to smooth out the torque spikes.

The result is quite a heavy unit. Still his FWF package is competitive with
Lyc on a power-to-weight basis. Not bad at all.


Regards,

Gordon.


"Corky Scott" wrote in message
...

On Thu, 28 Jul 2005 22:08:10 -0400, "Gordon Arnaut"
wrote:


Your story is just another reminder that gearboxes are one of the big
bugaboos of any auto engine conversion -- and torsional vibration (or
resonance) is always the culprit. I know that in the Subaru community
there
is not really a box that I would consider completely trustworthy.

Really? Not even Eggenfellner's? I haven't heard of any failures of
his design yet, but I haven't been actively following Subaru
conversions.

Corky Scott



Sorry for coming in a little late on this; I usually frequent the
Flyrotary list & Rusty mentioned that this thread was alive over here.
The non-existent email address is there because I got tired of a steady
diet of spam.

Several things come to mind about the previous few messages in this
thread, from the stuff I've read in about 10 years of following
Powersport, then Tracy Crook's development trials & tribulations. This
is from memory & I never claim to have a good memory. :-)

Gearbox strength for 1rotor vs 2rotor: The big deal about a 1rotor is
that the torque curve actually reverses (goes negative) with a 1 rotor,
like a 4cyl 4stroke piston engine. With a 2 rotor, the torque curve
never actually reverses so the gear box isn't stressed as much in the
torsional resonance dept. even though there's twice the power. If you
frequent Paul Lamar's list I'm sure he will be happy to show you the
torque curve for the 2rotor. IIRC, the torque curve for a 1rotor looks
like a 4cyl piston engine, going negative between each positive torque
peak. If the system resonates & you continue to excite it without
damping the resonance, no amount of strength will keep it from breaking.

The 1st incarnation of Powersport are the guys in the northwest with the
rotary powered RV-4 that had such horrendous torsional resonance
problems *on a dyno*. Current thinking is that they had a problem with
resonance on that particular dyno with that particular engine/dyno
coupling (it was built to test V-8's) They also had severe problems
getting their P-port engine to idle properly. Others have had no problem
at all getting them to idle smoothly. The developers had racing V-8
backgrounds & some of that stuff doesn't transfer well to the rotary.
Their internal tooth ring gear, designed to keep the gearbox 'tight',
like Rusty mentioned, is very heavy, very expensive, & if it isn't heavy
enough will actually loosen up as rpm comes up & the ring gear tries to
stretch. Kind of self-defeating. The 'tight' vs 'loose' issue is really
an issue of moving resonant frequency above the operating rpm range or
moving it below the operating range. 'Tight' moves it up; 'loose' moves
it down. Manual transmission cars are 'loose', moving resonance below
normal operating rpm. You've probably experienced the automotive version
of torsional resonance if you've put a manual trans car in 2nd or 3rd &
let the idling engine try to pull the car. If the engine continues to
run, the car will move forward in big surges. That's the resonant
frequency of the drive train. I don't remember Powersport ever having a
problem with broken props or gearboxes; my memory is that they went
straight from their dyno problems to the big internal spur gear. They
did have a gearbox failure when competing in time-to-climb at SNF
because they were using nitrous & over stressed a bearing in the
gearbox. I think they were producing somewhere between 350-400hp (13B
without turbo) when that happened.

Damping torque pulses with belt slippage: inefficient & produces a lot
of heat.

I think Corky mentioned the nightmare of an intake manifold on RX-7
13B's; fortunately a much simpler & lighter intake works fine for
aircraft since low rpm torque isn't needed.

Eggenfellner: I believe they've recently had the 1st failure of one of
their gearboxes.

Charlie
(Rusty's 'hangar away from home' for the next hurricane)