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jeanphilippeneel(at)yahoo
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 Posted: Sat Dec 11, 2010 12:40 pm Post subject: Icing: 912S versus 912 |
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Hi all,
I flown my europa with a 912 80hp during 1200h/11years.It's a mark one but with XS engine mounting and cowlings.Majority of flights took place here in the French Alps as well in summer as in winter. I never had icing issue although I had no carb preheater .The only caution I had ,when descending ,was to keep 4500/4800 rpm . Never in idle position.
In the beggining of that year I change my 912 for a new 912S 100hp. That new engine has now about 125h. Yesterday I had for the first time a rough running during few seconds.Outer Air Temp was negative at every level and the issue occurs at the end of a descent 4500/4800rpm from 8000ft to 1500ft. There was about 8°C of difference at ground level betwen OAT and dew point.
Several time I read on Rotax and Europa web site discussions about icing issues and I kept in mind that 912S should be more sensitive to icing than 912.
As I know:
- Carbs are the same ,except needle diam (2.72 versus 2.70 on S) and ,may be, main fuel jet and diffuser (in accordance with needle) .Does those difference could explain more sensitivity to icing?
- Compression ratio and bore are increased on S but stroke is the same . In my opinion these difference have not thing to do with icing issue.
So here is my question : Could some body explain why a 912S should be more exposed to icing than a 912?
Jean-Philippe Neel
F-PSLH Kit N°273
Grenoble France
[quote][b]
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rob(at)hyperion-ef.com
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| Posted: Sat Dec 11, 2010 3:36 pm Post subject: Icing: 912S versus 912 |
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The cooling (isentropic throttling) that makes carb icing happen is a function of the amount of fuel vaporized so with all other things being equal (same atmospheric conditions, engine manifold, carbs, RPM, etc.) you can expect the somewhat greater fuel flow (more power requires more fuel) to cause more cooling and hence a greater propensity to make ice. Obviously the 912 and 912S are “different” engines but those differences are internal and downstream from the carbs. The 914 is less prone to carb ice because the air compressed by the turbo is warmer than the intake air. Thermodynamics rules!
Best regards,
Rob Housman
Irvine, California
Europa XS
S/N A070
Rotax 914
Airframe complete
Avionics soon
From: owner-rotaxengines-list-server(at)matronics.com [mailto:owner-rotaxengines-list-server(at)matronics.com] On Behalf Of NEEL Jean Philippe
Sent: Saturday, December 11, 2010 12:35 PM
To: rotaxengines-list(at)matronics.com; europa-list(at)matronics.com
Subject: Icing: 912S versus 912
Hi all,
I flown my europa with a 912 80hp during 1200h/11years.It's a mark one but with XS engine mounting and cowlings.Majority of flights took place here in the French Alps as well in summer as in winter. I never had icing issue although I had no carb preheater .The only caution I had ,when descending ,was to keep 4500/4800 rpm . Never in idle position.
In the beggining of that year I change my 912 for a new 912S 100hp. That new engine has now about 125h. Yesterday I had for the first time a rough running during few seconds.Outer Air Temp was negative at every level and the issue occurs at the end of a descent 4500/4800rpm from 8000ft to 1500ft. There was about 8°C of difference at ground level betwen OAT and dew point.
Several time I read on Rotax and Europa web site discussions about icing issues and I kept in mind that 912S should be more sensitive to icing than 912.
As I know:
- Carbs are the same ,except needle diam (2.72 versus 2.70 on S) and ,may be, main fuel jet and diffuser (in accordance with needle) .Does those difference could explain more sensitivity to icing?
- Compression ratio and bore are increased on S but stroke is the same . In my opinion these difference have not thing to do with icing issue.
So here is my question : Could some body explain why a 912S should be more exposed to icing than a 912?
Jean-Philippe Neel
F-PSLH Kit N°273
Grenoble France
01234567890123456
[quote][b]
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flyadive(at)gmail.com
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| Posted: Mon Dec 13, 2010 6:09 am Post subject: Icing: 912S versus 912 |
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Excellent point Rob:
But I think you have taken it one step further than the Gaggle need to
disseminate.
Everything said is true but there is one ingredient missing....WATER.
No mater how great the isentropic action is ice will not form unless the
temperature drops to and below the freezing point of the liquid. The
freezing point of Gas is around -95 Deg F (-70 C) and water is +32 F (0 C).
So the isentropic action upon gas is not an issue. You did say it but I
do not know how well it was received. Ice forms from WATER. The
temperature in the carb drops due to a drop in temperature due to the
venturi action. Simply put: The speed of the mass of air going through the
carb is increased by the carb's venturi. This increase in speed reduces the
pressure in the air flow. The reduction in pressure lowers the temperature
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