Today's Message Index:
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1. 08:25 AM - Baffling for cylinder cooling (carl bertrand)
2. 08:38 AM - 912 engine cases needed (ricklach)
3. 04:09 PM - Re: Baffling for cylinder cooling (Roger Lee)
Message 1
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| Subject: | Baffling for cylinder cooling |
I built my 701 from plans in 1994/95. It is powered by a Rotax 912 covered
with a Zenair cowl without any internal baffling as per the Zenair
demonstrator and recommendations at the time.
The engine now has 490 hrs and is still running smooth and strong; I see no
difference in static RPM since first flight. I am concerned about two things
however:
1. Front Cylinders head temp is much cooler than the rear;
2. Compression on the front cylinder is 20 lbs less than the rear. 115 vs.
135. This has existed and remained steady since first annual in Nov 1995.
I suspect a cause and affect between these to parameters.
My questions to the list is:
I know of two other 701s that have the same cowl set-up and have never
seen a 701/912 with baffles. Is this the norm?
I'm considering investigating the reason for the lower compression in
the front (vales or cylinders) and designing some baffling to equalize the
cooling. If I just correct the cooling could this destabilize an engine that
is running well?
Any comments appreciated.
Carl
Message 2
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| Subject: | 912 engine cases needed |
I am looking for a pair of 912 engine cases that are JUNK. I need them for a mock-up.
They can be crashed, cracked or what ever. The only part that needs to
be there is all the mounting bosses on the bottom and the rear of the cases.
80HP, 100HP or 914 for that matter, it doesnt matter to me. I can be reached at:
rick@ravengear.us
Rick
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=184871#184871
Message 3
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| Subject: | Re: Baffling for cylinder cooling |
Hi Carl,
I wouldn't play with the air flow. Zenair spent good money to make sure you had
decent airflow under the cowling. I don't personally know of a 701 that has and
special cowl for cooling for the engine. If you start to play with it you better
have an extremely good working knowledge of baffling and air flow patterns
under your cowling. Many people have done this only to cause worse problems.
Thinking they are redirecting flow for the better and only hinder it. A CHT
difference from the front to the back is normal under a cowling for the 912. You
did not say what the difference was? 20-30F is quite normal depending on the
installation and maybe even bigger differences in some applications. I see about
12F on my CT CHT's between front and back.
I take it 155-135psi is static compression test. What is the differential pressures.
This would be more informative.
The static compression should be between 174-130 and no more than a 29psi difference
between cyl.
The differential should be between 87 to 65 psi. Make sure the engine is at operating
temps or your readings will be wrong.
--------
Roger Lee
Tucson, Az.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=184938#184938
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