Hi Remi,
As I recall, we installed the Green Sky HACman mixture control system,
see their URL at;
http://www.greenskyadventures.com/bing/HACmandetails.htm
Since we already had manifold pressure (vacuum) behind our panel (for
the MP pressure transducer) it was only one additional line back to the
carb bowl vents to implement.
My partner in the plane, Dave DeFord, is the one who did most of the
installation and testing, so he knows it better than I do. We use the
mixture control on longer trips at altitude. You would want to use the
EGT on a front cylinder to set lean-of-peak mixture (since the front
cylinders run leaner the the rear), although just leaning until the
engine gets rough and then richening up a little also works just fine
(like I used to do with the Cessna 152). It does work better with the
throttle closed just a little, but may work some even at full throttle,
I don't quite remember that part. The engine can be expected to run
rough if you close the throttle and/or descend, but I don't ever
remember it actually dying. Any aircraft will run rough if you descend
without readjusting the leaned mixture, so this is really not all that
different, and you are unlikely to close the throttle for any other
reason than descending, are you?
I am not sure the leaning mechanism has enough 'authority' to actually
kill the engine, I will check with Dave later tonight to see if he
recalls testing for that.
regards,
Terry Seaver
________________________________
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Remi
Guerner
Sent: Tuesday, January 06, 2009 2:58 AM
Subject: Europa-List: Mixture control
Hi Terry,
That interesting information. I am not surprised to learn that the
engine is running lean of peak at sea level, even at full power, as this
is consistent with the specific fuel consumptions advertised by Rotax.
I am interested in knowing more about your mixture control system.
My concern is about the reliability of this system as you are adding
piping from the engine to the cockpit and a sort of tap to control the
leak I suppose. What happens if one of the pipe connections leaks or
breaks? What are the effect of advancing or retarding the throttle if
you forget to enrichen first? Does that kill the engine?
Regards
Remi
>>>>> We are members of the Experimental Aircraft Association who have
built an 'experimental aircraft'. As such, among other things not
included in our standard kit, we have installed a mixture control on our
912S which bleeds manifold pressure back into the carb bowl vents.
Testing has shown that the standard rotax carb settings are actually
lean-of-peak at sea level on the front two cylinders and that it (of
course) gets richer with altitude, passing thru peak and on down the
richer side of peak EGT with increasing altitude. It is our assumption
that it is acceptable for them to run the engines this way (lean of peak
at take off) because the heads are liquid cooled.
We believe it is then a fair assumption that we can run the engine
lean-of-peak at altitude and <75% power, given that the factory settings
run the engine lean-of-peak at full power/sea level. Of course we
monitor our exhaust, head, water, and oil temps just to make sure
everything is happy while leaning at altitude
regards,
Terry Seaver<<<<<<<<<<<
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