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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
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craigb(at)onthenet.com.au
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| Posted: Sat Dec 11, 2010 9:12 pm Post subject: Icing: 912S versus 912 |
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perhaps the increased displacement of the 912s has a higher vacuum and thus greater temp drop through the carb for any given throttle opening
below 100%, just a theory
[quote] --
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jpg12305
Joined: 16 Jul 2008
Posts: 23
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| Posted: Fri Dec 17, 2010 2:13 pm Post subject: Re: Icing: 912S versus 912 |
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Bonjour Jean-Philippe,
This could be a good bar discussion, fueled by liters of beer...
What is strange here is that flight conditions were apparently not suited for a significant risk of icing.
Negative OAT and 8C difference with DP makes a quite dry atmosphere. There could have been anyway a layer close to saturation in altitude, but I am pretty sure that in the 125h flight hours life of the engine, real potential carb icing conditions have been encountered apparently without issue.
The rough running could have been related to something else.
I share your question about why 912S may be more prone to carb icing. One reason of temperature drop in the carb is fuel vaporisation. The higher fuel flow of the 912S may let think about more risk of icing? And to my level of knowledge of CV carburettors, this means a higher depression around the diffuser lowering temperature there as well. Open discussion.....
Anyway I stopped worrying about all that two months ago by installing the Skydrive carb heat kit. My peace of mind increased a bit.....
Jean-Paul
Europa 332
LFEF
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