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Carb heat
#1
I have'nt seen anything about carb ice pertaining to the Mosquito so can anyone tell me if there are any issues or are two strokes less susceptible to icing?
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#2
Haven't heard of any carb ice instances and haven't had any myself.  Some of the operators operate in colder climates with visable moisture.  Any carbureted engine could develop carb ice under low temps and visable moisture.  It could be that the slide and needle type fuel metering used on these and many small engines is less prone than the butterfly type used on Lycoming and Continental engines.  There has been discussion on this subject before.
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#3
I am NOT familiar with icing as it pertains to the MZ/Bing combination. I am familiar with the Rotax/Bing combinations. Carb icing was never an issue in the Rotax powered machines I have flown. Seems like it was because the engine was close enough to the carburetor that enough engine heat warmed the carburetor body to avoid it. Rotax mentions it only briefly in their manuals.
I do feel the need to correct some things that were stated in earlier posts about carb ice in general.

The temperature drop in the throat/venturi of a carburetor can exceed 70°F.
Therefore, carb ice CAN occur in some instances when outside air is as high as 100°F.
The most susceptible temperature for icing is in then 50° +/- range.
Below 32°F, most airborne moisture is already frozen into ice crystals and cannot accumulate in the carburetor.
Carb ice does NOT require moisture to be visible, such as rain, fog, or clouds. Humidity can also FREEZE into carb ice.

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#4
Thanks for that information Bryan, I am being taught a lot of carb heat use in the R22 I'm training in: Apply carb heat whenever there is visible moisture, manifold pressure is 18" or under, and whenever the carb heat temp gauge is in the yellow.
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#5
cjb5591 - 3/9/2011 12:05 PM

Thanks for that information Bryan, I am being taught a lot of carb heat use in the R22 I'm training in: Apply carb heat whenever there is visible moisture, manifold pressure is 18" or under, and whenever the carb heat temp gauge is in the yellow.
That is exactly per POH in the R-22. It's kind of nerve-wracking to take your hand off the collective at the bottom of your approach to turn off the carb heat so you have enough power to hover, since you don't want to be trying to hover with 2 passengers and carb heat ON. Not only does that rob power, it sucks up the dusty air stirred up by your rotor and feeds it, unfiltered, into your $50,000 engine.
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#6
Two stroke engines don't have an issue with carb heat due primarily to the oscillating flow of the intake charge. There is some reverse flow prior to the reed valves closing which prevents ice from forming in the carb.
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#7
My instructor has me shut off the carb heat when we cross the threshhold. I can just barely touch the knob without taking my hand off the collective. You're right, it is a scary procedure. Somebody should come up with a fix for that!!
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#8
Thanks John, that's a very reassuring explanation especially for us cold-weather fliers.
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#9
on the R22 beta2 you have a simple linkage called carb heat assist to automatically reduce carb heat as collective is increased . pilot still has ability to override and control on his own but it works well to help reduce workload at the end of the approach. Also the heated air IS filtered in the r22 helicopter installation, so dont worry about dusty air when carb heat is on.
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#10
Never flown a Beta II but I THOUGHT they were fuel injected??
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