light twins?

Rusty,

I don't want to beat this issue to death, and I'm not a power transmission
expert either, but this is the first time I've heard of "amplitude" as an
issue in redrive design.

Usually the redrive designer is concerned with handling the maximum torque
and will devise a load model that will encompass the worst-case operating
scenarios.

I think the guy is referring to amplitude of power pulses because the torque
coming from an internal combustion engine is not linear like in an electric
motor, or turbine -- it has torsional spikes.

Still, compared to a piston engine, the rotary is a pussy cat when it comes
to torsional issues, because it does not have the lever-arm effect of the
crankshaft throws to worry about -- which creates the bulk of the torsional
flex in a piston engine.

When it comes to belt drives, the manufacturers have two ways of rating
them: one for smooth, continuous power like electric motors, and another for
combustion engines.

They also rate them for max continuous torque, so I feel pretty safe in
saying that with a single rotor engine making half the torque, you will need
less belt. With a gearbox, the dynamic gear tooth leads will likewise be
less.

Regards,

Gordon.




"Gordon Arnaut" wrote in message
...
Rusty,

Yes, I meant exactly what you said: three power pulses per single rev of
the rotor, and one pulse per rev of the e-shaft.

Regards,

Gordon.

PS: I like that you are using a turbo as a muffler -- not much more
weight, similar or even better noise reduction, not to mention the power.




"Russell Duffy" wrote in message
...
As far as I can see, this cannot be valid. If I'm thinking this through
correctly, each rotor will make three power pulses for each revolution
of
the rotor, or one revolution of the e-shaft.

My recollection from my mechanicking days is that the eccentric shaft
rotates at three times the speed of the rotor.

Abolutely right Corky. Gordon got it right in the rest of his post, so I
just figured he left out a word above, and it should have read "one PER
revolution of the e-shaft".

Cheers,
Rusty

On Thu, 28 Jul 2005 16:08:46 -0400, "Gordon Arnaut"
wrote:

Still, compared to a piston engine, the rotary is a pussy cat when it comes
to torsional issues, because it does not have the lever-arm effect of the
crankshaft throws to worry about -- which creates the bulk of the torsional
flex in a piston engine.

This may not be accurate Gordon. There was a company based up in
Washington State that produced a planetary gear box as a PSRU for the
Mazda rotory and they had a HORRENDOUS developmental period with many,
repeat many broken boxes.

They finally got something that was extremely professional looking as
machined aluminum can be, and robust and long lived. They had it on
the front of an RX4 and flew it to various air shows. One of the
developmental partners was killed in an airplane crash and for a while
the psru was still available but I don't know if it still is.

The big issue, the one that was busting props and tearing their boxes
apart was torsional vibration. I remember reading that they claimed
there was something about the rotory engine that gave it a really
powerful torque spike.

I think they eventually solved the problem with some kind of cushion
drive. But for a while it was busting one attempt after another on
the test stand, and a bunch of dead stick landings.

Corky Scott

Thanks Corky,

My assumptions about the rotary were not based on experience, so it's good
to learn something new.

I would have expected the rotary to have less spiky torque output than a
piston, but perhaps the wobble of the rotor along its ellipsoidal path
creates enough inertia to cause some sizable spikes.

I may post a question about this to the Mazda newsletter -- once Paul gets
back from Osh. I'm sure there will be some people there with good insight on
this.

I still have to think though that maximum torque is the limiting factor in
both gear and belt design. Even if torsional vibration is an issue (with the
rotary or any engine), the way to address that is to dampen the spikes and
prevent harmonics from causing destructive resonance. Just using bigger
stronger gears is one approach, but not really the most elegant -- or
lightweight.

I notice that Tracy uses rubber doughnuts between the flywheel and the
gearbox coupling, just for that reason I would assume.

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.

I was hoping the rotary was less of a problem in this area. Darn.

Regards,

Gordon.




"Corky Scott" wrote in message
...
On Thu, 28 Jul 2005 16:08:46 -0400, "Gordon Arnaut"
wrote:

Still, compared to a piston engine, the rotary is a pussy cat when it
comes
to torsional issues, because it does not have the lever-arm effect of the
crankshaft throws to worry about -- which creates the bulk of the
torsional
flex in a piston engine.

This may not be accurate Gordon. There was a company based up in
Washington State that produced a planetary gear box as a PSRU for the
Mazda rotory and they had a HORRENDOUS developmental period with many,
repeat many broken boxes.

They finally got something that was extremely professional looking as
machined aluminum can be, and robust and long lived. They had it on
the front of an RX4 and flew it to various air shows. One of the
developmental partners was killed in an airplane crash and for a while
the psru was still available but I don't know if it still is.

The big issue, the one that was busting props and tearing their boxes
apart was torsional vibration. I remember reading that they claimed
there was something about the rotory engine that gave it a really
powerful torque spike.

I think they eventually solved the problem with some kind of cushion
drive. But for a while it was busting one attempt after another on
the test stand, and a bunch of dead stick landings.

Corky Scott

I notice that Tracy uses rubber doughnuts between the flywheel and the
gearbox coupling, just for that reason I would assume.

As I understand it, there are two ways to avoid the resonance issue. One is
to make the drive coupling tighter, and the other is to make it looser.
Powersports chose tighter I believe, and the precision they need could be
why their drive costs $6000. Tracy chose the looser path. Both work fine.
The biggest unknown I face with the single rotor is the resonance frequency,
and how it works with the rubber dampeners that Tracy chose for the two
rotor engine. I may very well have to change the durometer of the rubber
dampeners, but I won't know until I try it.

Cheers,
Rusty

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

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

All this talk about the rotary engine.

If they were this great, would there not be at least a couple cars
running them ?
--
Mark Smith
Tri-State Kite Sales
1121 N Locust St
Mt Vernon, IN 47620
1-812-838-6351
http://www.trikite.com
[/quote]

This begs the question, if Connies and Lycs were so great, would there not be at least a couple cars running them? - LOL

jetdesigner wrote:
All this talk about the rotary engine.

If they were this great, would there not be at least a couple cars
running them ?
--

This begs the question, if Connies and Lycs were so great, would there
not be at least a couple cars running them? - LOL

Now THAT is funny (LOL too)

jetdesigner wrote:

This begs the question, if Connies and Lycs were so great, would there
not be at least a couple cars running them? - LOL



The answer to the question is that the rotaries power curve does not
lend itself well to automobile applications. If you drove around town
at 120mph, it would be another story. In real life, you want to punch
the gas and have your vehicle jump out ahead of oncoming traffic. The
rotary doesn't have that power down low.

Mazda has gone through hell and back to make the rotary work in a car,
but it is an overly complicated mess to deal with. Turbos...adjustable
intake...a ridiculously complicated exhaust system. It's a work of art,
but still barely a decent auto engine.

In the airplane, build an intake tuned to 6000rpm (give or take), build
a stainless steel muffler and your ready to go.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

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)