New messages on bottom.


  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 pressure fed
oil system and a planet gear box. What would you have to charge for it ata
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 sets in
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 for five
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 the way
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 use a
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 about that?

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

Devil


Then rather stay with the same displacement and modify an engine for OCR as
new displacement means that one can't even use the existing trochoid housing
and seals.
You're right about the fuel consumption. If an engine is charge cooled, and
it is leaned for better BSFC, this will obviously lead to less cooling.

The devil's advocate probably knew I would come back with those answers, but
I assume he is happy to hear them anyway ;-) And I don't disagree that an
OCR engine is a good option for an aircraft. My point is just that there is
room for CCR as well, and that it's also good for some flying applications.
Maybe not as good as OCR, but way better than anything with a piston,
conrods, valves, etc.

Poul