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 http://www.torque-online.co.uk/news/?p=3631
    --

    Paul Lamar

 Paul,

 Did this kart have ceramic bearings and if not when (if ever) will
 the AIXRO folks add them?

 I have not seen any reference to it, but do they have the liquid cooled
 shaft per the paper you have linked to i.e., the "LCCR" ?

 Also,
 I see the Cubewano UAV Wankel is using Ceramic Coatings on the Rotor
 and the epitrochoid surface, as well as claims of lower BSFC.

 Any comments?

 My best,
 Anthony

 Those questions are above my pay grade :) Send your questions
 directly to:

 Poul Henrik Woelfle AIXRO <ph.woelfle@woelfle-engineering.com

 I will say IMHO ceramic coatings on the rotor are not worth the risk
 of damaging your rotor housings when it comes off.

 BTW they have a new very nice web site.

 http://www.woelfle-engineering.com/index.html

 Paul Lamar
 --

 Hi there,

 First, thanks to Paul for publishing the links.

 Now to the questions:
 The engine may have had ceramic apex seals, but there is not so much
 of a difference to standard seals. The biggest difference is above
 8000rpm, where the ceramic seals produce less friction and allow for
 some more top-end power. Even if it's about 3hp (that's 6% on a
 45hp engine), the average karter will not really notice the
 difference though. On a side note: We hardly ever see any wear, but
 we do see some "running in" with the standard seals. Therefore
 changing from standard to ceramic on a used engine is no good unless
 the trochoid housing is exchanged as well.

 We have tried ceramic rotor needle bearings, which were good for
 lower bearing temperatures. These things are very sensitive though.
 If anything manages to get into the bearing (dirt, etc.), the
 needles will dissolve and destroy the e-shaft, rotor, seals and
 housing, i.e. the complete core engine. The apex seals are much less
 sensitive to such occasions, because they can wipe potential dirt or
 the like out the p-port exhaust. For this reason we don't use
 ceramic bearings. Ceramic coating of the rotor and housing is surely
 interesting, and when it works it's great. But I agree with Paul
 that getting it right is a difficult exercise, especially in aircraft.

 Our trochoid housing and side plates are from aluminium and water cooled.
 The E-shaft is charge cooled. Of course a liquid cooled shaft (or a
 completely different rotor cooling/lubrication system) would allow
 for more power, but it would also add to the cost, weight and
 complexity of the system. The charge cooling system we are using
 works fine in the intended power range.

 Best Regards,
 Poul

 Let me put on my devil's advocate hat here for a few minutes with
 some assumptions and questions. The devil is always in the
 details... especially with a rotary engine.

 Since the kart engine is limited to 10 seconds at full power for max
 HP, what percentage of max HP can it run at full power for 5 minutes?

 A certified aircraft engine must run at full power for 5 minutes at
 a time according to the FAA.

 I assume this is due to the rotor bearing temperature in the charge
 cooled rotary engine.

 Lets also assume for the moment that the dirt particle capable of
 shattering a ceramic needle bearing is made from diamond, being the
 hardest particle I can think of right at the moment.

 What diameter of diamond particle relative to the diameter of a
 ceramic needle causes the needle to shatter?

 Can we come up with a filter that will remove particles that size
 and above in the premixed oil/fuel mixture before it is added to the
 fuel tank?

 Can we come up with a filter that will remove particles that size
 and above in a filter on the engine located in the fuel/oil feed system?

 What is the best place to put a thermal couple to measure the temperature
 of the rotor bearing if that is in fact possible?

 Paul Lamar

 Paul,

 My experience with WOT running problem was self ignition, once on an
 air cooled engine motorcycle I switched the ignition off and rode a
 full lap to make the point to our Chief Engineer, I tossed the keys
 to him as I passed, we switched to water cooled shortly after. Even
 on water cooled we had the problem but this was plug orientated, a
 nodule would build up on the plug and this acted like a glow plug,
scraping
 the nodule off gave a further say 100 odd mile of High speed WOT running.

 On Rotor bearings we had special ones with low skew grade, and in
 fact we used to use a skew test rig, this consisted of a ground
 shaft spinning at a set RPM with a loaded bearing the axial thrust
 being measured. On WOT work we had the Eccentric shaft grow by
 0.0001" per 1000 miles, and the new build clearance did not help the
 noise emitted by a air cooled engine, we Cryogenically treated the
 Shafts to stabilize and speed up the Growth prior to final grinding
 and in so doing we was able to reduce the new build clearances and noise.

 Bob
 UK


 A few years ago it was determined most engine wear was caused by particles
of
5 to 25 microns size. At the time and I suspect even today, that most
filters only removed particles larger than 40 microns.
 With charge cooling, dirt in the intake air will be the culprit. The
fuel/oil should be fairly clean and not be the start of a problem unless
care has not been taken transffering the liquids.

Dale Davies


Poul, Suppose for the moment you built a two rotor with a full pressurefed
oil system and a planet gear box. What would you have to charge for it at a
quantity of one per week for the non certified Light Sport Aircraft market
and the US experimental market.

We need a light weight 2 rotor 100 HP engine for aircraft service.

Take a guess.

Paul Lamar



Hi Paul,

First, it seems that my reply to that guy with the devil's advocate hat
didn't come through, so here it is again:

The XR50 "sprint" karting engine has its suggested redline at 11000 rpm, and
the limiter now sets in at 11500rpm. Peak power of 33kW/45HP is at around
8750rpm.
The XF40 "continuous power" version, which is also used in some aircraft, is
basically the same engine, but with some modifications (side bearings, port
control, ignition and output setup, etc.). The limiter of the XF40 setsin
at 7000rpm, and we suggest to set the engine up to reach max. 6500rpm under
full load. At 6500rpm it will supply 26kW/35HP, and it will do that forfive
minutes.
You are right in that the main bearing temperature is the limiting factor.
That's why we stay below the limit with our engines. We have just recently
got a message from another customer who bought an XR50 karting engine,
didn't read the manual and went flying with up to 10000rpm, and the engine
survived, but I think that was more luck than anything.

I don't think you need a diamond particle to shatter a ceramic needle. They
can carry very high loads, but they are sensitive to punctual loads. If
something gets in the way for a needle and the needle rolls over it, the
needle can crack even if it crunches the particle to pieces. And once one
needle cracks it will cause a "chain reaction", which will stop the engine
instantly. Next thing you do is throw it in the bin and get a new one. Steel
needles may be more temperature sensitive, but if something gets in theway
they will at least fail slowly, so there is some time to react (stop the
engine in a kart, reduce power and find a good spot for landing in an
aircraft). Given this and the cost of the ceramic needles we decided rather
not to use them anymore.

Apart from this the occurrence of such problems is not very high at all, but
we rather want to be on the safe side. We do suggest that customers usea
proper fuel filter, and that does help (also against carburettor failures).
But especially in karting there is often a dusty, dirty environment, and
sometimes dirt also makes its way into the engine through the air filter, or
it even gets dirty inside when people try to clean it...
All this is probably less of an issue in an aircraft, because aviation
people are generally more cautious about their engine for obvious reasons,
and that helps a lot.

A good place for a thermocouple to monitor the bearing is in the transfer
port, i.e. where the charge that has just passed the rotor and main bearing
enters the combustion chamber. All our engines come with an M5 thread in
this area, and it is recommended to use a small (=quick) thermocouple. We
call it the bearing temperature, but of course it's just a relative
indicator. The bearing temperature increases with the engine load, and if
something should be wrong it will also rise.

I hope that answers your questions. If not, put the hat on again :)


I understand that there is a need for a 100hp twin with planetary re-drive,
and that it should be oil cooled (OCR). I know there are some objections to
charge cooled (CCR) engines, and we may be looking at OCR at some point, but
whether a CCR engine works on not depends on how you use it. It has lower
limits than an OCR engine, but if the engine is designed and built properly
and you stay on the right side of the limit it's not a problem at all.

Best Regards,
Poul



Poul Henrik Woelfle

Woelfle Engineering GmbH
Randstraße 109
D - 47804 Krefeld
Tel. +49 2151 151020
Fax +49 2151 151019
www.woelfle-engineering.com


The devil got all that.

Well then how about a larger displacement, 2 rotor, CCR engine so we have 100 HP continuous?
We need 100 HP continuous. I am under the impression that an CCR engine
does not have as good a BSFC as an OCR engine? Is the devil wrong aboutthat?

Now that Mario has an order for production engines perhaps he can builda 100 HP continuous
OCR engine for us. Rotax us charging big bucks for the 912 and 914. Around $20,000.

Devil


Thinking out of the box:  3 AIXRO's mounted together so they each spin a
planet in a planetary reduction.  In other words, the planet carrier is
fixed and the AIXRO's are mounted to it.  This could even be an adaptation
of an automobile differential.

130 hp for takeoff and still under 200 lbs firewall forward.  And still less
than than a Continental.

Chris Cosman