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jeff(at)rmmm.net
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 Posted: Fri Jan 23, 2009 7:17 pm Post subject: Exhaust Question |
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Exhaust question from a non technical Europa builder flyer. I remember
my flight instructor 15 or 20 years back always said a stupid question
is the one not ask so here it goes...
As I'm doing my annual and looking at this large muffler pushed into a
small place I can't help wondering why it has to be this large. It
would seem something smaller wouldn't have such a heat buildup and
allow cooling air from above to move down thru easier. I understand the
noise requirements across the pond but here in the states has anyone
gone with something smaller? Would it not be good for the 912 to go
with straight pips?
Just curious...
Jeff R.
A258 - N128LJ / Gold Rush 170 hours and climbing slowly.
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Sat Jan 24, 2009 6:23 am Post subject: Re: Exhaust Question |
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Internal combustion engines are very sensitive to exhaust gas pressure.
In operation, the cylinders put out large pulses of pressure and want to clear
the contents of the exhausting cylinder as quickly and easily as possible.
Quality exhaust systems and mufflers are designed to minimize the
oscillations in back pressure which would interfere with emptying a
cylinder.
See: http://cafefoundation.org/v2/research_reports.php
for some specific aircraft exhaust system information
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_________________
Ira N224XS |
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topglock(at)cox.net
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| Posted: Sat Jan 24, 2009 7:49 am Post subject: Exhaust Question |
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Jeff,
The new cowl design, I'm working on, will require a new exhaust system.
I'm currently looking at a split system with two collectors for two
pipes, each. I want to incorporate a small baffle in each side to help
with the noise, but haven't gotten that far, yet. Just something to
ponder when you're not flying... 
Jeff - Baby Blue
JEFF ROBERTS wrote:
| Quote: | Exhaust question from a non technical Europa builder flyer. I remember
my flight instructor 15 or 20 years back always said a stupid question
is the one not ask so here it goes...
As I'm doing my annual and looking at this large muffler pushed into a
small place I can't help wondering why it has to be this large. It would
seem something smaller wouldn't have such a heat buildup and allow
cooling air from above to move down thru easier. I understand the noise
requirements across the pond but here in the states has anyone gone with
something smaller? Would it not be good for the 912 to go with straight
pips?
Just curious...
Jeff R.
A258 - N128LJ / Gold Rush 170 hours and climbing slowly.
size color="#000000" face="courier new,courier">
href="http://www.matronics.com/Navigator?Europa-List">http://www.matronics.com/Navigator?Europa-List
href="http://www.matronics.com/contribution">http://www.matronics.com/contribution
------------------------------------------------------------------------
Checked by AVG - http://www.avg.com
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jeff(at)rmmm.net
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| Posted: Sat Jan 24, 2009 7:49 am Post subject: Exhaust Question |
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Okay I get and understand this. However on some other light planes I've
seen the 912-S with smaller or different looking mufflers. My question
is... Is there another type of smaller muffler that could be an option?
Or could straight pips be tuned in some way for the right amount of
back pressure for this engine? Has anyone heard of this being done for
the rotax?
Always curious.
Jeff R.
A258 - N128LJ / Gold Rush 176 hours and climbing slowly.
On Jan 24, 2009, at 8:23 AM, rampil wrote:
| Quote: |
Internal combustion engines are very sensitive to exhaust gas pressure.
In operation, the cylinders put out large pulses of pressure and want
to clear
the contents of the exhausting cylinder as quickly and easily as
possible.
Quality exhaust systems and mufflers are designed to minimize the
oscillations in back pressure which would interfere with emptying a
cylinder.
See: http://cafefoundation.org/v2/research_reports.php
for some specific aircraft exhaust system information
--------
Ira N224XS
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p 26524#226524
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rparigor(at)suffolk.lib.n
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| Posted: Sat Jan 24, 2009 8:38 am Post subject: Exhaust Question |
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Hi JeffMy friend had a 912 powered pusher seaplane that kept breaking exhaust parts and threatened to lop off tail boom in the process. He finally hacked off everything and just left fairly short straight pipes. I don't think most anything you do that will allow reasonable flow will make much of a noticeable difference in performance, some but not tremendous. I am much more concerned with mixture with a modified exhaust, MAKE SURE YOU ARE PREPARED TO CHECK AND TUNE WHERE YOU ARE NOT RUNNING LEAN. Too rich is not too nice, but far better than too lean. Taint towards a little rich at high power settings.Of course you could buy 914 header pipes and turbo (along with 914 airbox, carbs, enrichment solenoid and fuel pressure regulator (perhaps ask Paul pretty please to sell you if he has)) and set up a system to give you 100% rated power until the turbo can't keep up. The turbo acts as a muffler when it is pressurizing, you could fabricate a simple non restricting exhaust from turbo out, but you would probably be best to stick with the beautiful 309SS muffler Rotax currently provides. 309SS is OK to wrap with header wrap BTW. Sticking with turbo normalized mission will greatly simplify compared to the hocus pocus the TCU goes through on a 914 to make the decision to make 115HP or 80HP. Even if your mission was to turbo normalize, I would incorporate the enrichment solenoid when the go fast lever is above 80% (could install a simple reed or mechanical micro switch). Plumbing from turbo downwind is not as critical as a 912/S, just restrict as little as you can and keep with an acceptable noise level.I talked to a friend who has an older style Rotax exhaust on his 914 Xamango, he said it is susceptible to breakage. He said if you get a good break in a header pipe f, the motor will quit. I don't fully understand, but it is worth mentioning if you are designing an exhaust.Good luckRon Parigoris [quote][b]
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jeff(at)rmmm.net
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| Posted: Sat Jan 24, 2009 9:04 am Post subject: Exhaust Question |
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Interesting Jeff!! Keep us all posted and if you have any pictures of
your cowl yet send em over direct to me. I've got the clay out and
working on some new intake holes right now.
I'm also going to make a shroud to go over the 912 like the one I saw
on the RV-12 at KOSH. This will allow me with a flap to control CHT's
better. Plus I'm doing Buds heater mod as well. Looks like I'm down for
a while but now is the time with the weather and all.
Regards,
Jeff R.
A258 - N128LJ / Gold Rush 176 hours and climbing slowly.
On Jan 24, 2009, at 9:48 AM, Jeff B wrote:
| Quote: |
Jeff,
The new cowl design, I'm working on, will require a new exhaust
system. I'm currently looking at a split system with two collectors
for two pipes, each. I want to incorporate a small baffle in each
side to help with the noise, but haven't gotten that far, yet. Just
something to ponder when you're not flying...
Jeff - Baby Blue
JEFF ROBERTS wrote:
> Exhaust question from a non technical Europa builder flyer. I
> remember my flight instructor 15 or 20 years back always said a
> stupid question is the one not ask so here it goes...
> As I'm doing my annual and looking at this large muffler pushed into
> a small place I can't help wondering why it has to be this large. It
> would seem something smaller wouldn't have such a heat buildup and
> allow cooling air from above to move down thru easier. I understand
> the noise requirements across the pond but here in the states has
> anyone gone with something smaller? Would it not be good for the 912
> to go with straight pips?
> Just curious...
> Jeff R.
> A258 - N128LJ / Gold Rush 170 hours and climbing slowly.
> size color="#000000" face="courier new,courier">
> href="http://www.matronics.com/Navigator?Europa-List">http://
> www.matronics.com/Navigator?Europa-List
> href="http://www.matronics.com/contribution">http://
> www.matronics.com/contribution
> ----------------------------------------------------------------------
> --
> Checked by AVG - http://www.avg.com
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garrys(at)tampabay.rr.com
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| Posted: Sat Jan 24, 2009 3:34 pm Post subject: Exhaust Question |
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You might try "Vettermans". They make all the custom exhaust systems for RV
planes. Perhaps they've experimented with Rotax engines, but I don't have
any direct knowledge of that. I do have personal experience with them for
my RV, and they're good people to work with.
Garry Stout
914 Trigear, & RV7A
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budyerly(at)msn.com
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| Posted: Sat Jan 24, 2009 4:06 pm Post subject: Exhaust Question |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Jeff/Jeff,
Keep in mind the muffler is for noise concerns in Europe. In the US we do not have these limitations as of yet. Check with Rotax on exhaust backpressure requirements (tuning the exhaust pipe length) and you can modify away. Each of the new SLSA aircraft have a different exhaust shape and size. I am tempted to take my bore-scope to Sun N Fun to have a peek at some different 912 exhausts. Personally, I will keep my 914 stock. I don't have cooling problems on my engine cowl arrangements I build in the shop. I have done Jabiru's with straight pipes, why not the Rotax. Jason Parker and I have a 914 doing well without a muffler, but the turbo gives us the the same backpressure of the stock engine.
A lot of the cowl design concerns on the 912S/914 Rotax powered Europas are a compromise between maintenance, plumbing and production. Custom cowl changes create a number of challenges. I am now doing another Lopresti style cowl for a 914/Airmaster customer who wants a belt driven hi output alternator. I have a slick through the shaft brush assembly which allows it all to work. Sorta-kind-maybe-hopefully with numerous front mods it will cool better than stock. It just takes time, money, and experimentation.
Keep us posted,
Bud Yerly
Custom Flight Creations
[quote] ---
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