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Thread: carburetor heat recommendation for 912 ULS?

  1. #1

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    Default carburetor heat recommendation for 912 ULS?

    Does anyone have any recommendations for adding carb heat to a 912 ULS? thanks in advance

  2. #2
    Senior Member jiott's Avatar
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    Default Re: carburetor heat recommendation for 912 ULS?

    If you really think you need it, I think the best and easiest to install is the coolant collar kit that installs on the carb inlets using hot engine coolant to heat the carb throats. It is ON all the time heating only the carb throat, not the air so there is no loss of power. Sold by most of the Rotax parts dealers, ACS, Lockwood, CPS, etc.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  3. #3
    Senior Member Dave S's Avatar
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    Default Re: carburetor heat recommendation for 912 ULS?

    In my opinion, Jim is spot on.

    There is probably a good reason why Rotax providers use that system.

    I am a bit hesitant about the original carb heat on the IV . Aside from unfiltered air, the fabricated heat muff is potentially a source of loose parts/rivets/etc that could potentially mess up the carbs operation or get sucked onto the the engine due to the design/construction of that particular part - you want to inspect it frequently enough to assure that vibration has not worn and dislodged the spacers/rivets between the outer tube and the exhaust pipe.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  4. #4

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    Default Re: carburetor heat recommendation for 912 ULS?

    thanks both of you - Jim, you said "if I think I need it"... so I'm new to the kitfox world and my build is almost complete, but is it the case that many do NOT install carb heat? , I ask because all the other small craft I've flown have had it. I'd rather not install it if its not necessary...?

  5. #5
    Senior Member Dave S's Avatar
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    Default Re: carburetor heat recommendation for 912 ULS?

    HC,

    I don't know how many do vs how may don't; however, I suspect that a lot of 912 operators do not have carb heat.

    I studied the issue quite a bit when our kitfox was built and decided against it. I don't know that the 912 is immune to carb ice, but it certainly is resistant to the problem. A rotax is designed differently compared to traditional aircraft carbureted gasoline engines. A C150 with a continental will find 12 molecules of water within a 5 KM radius, put it in the carb and make ice; but, the carb is under the engine and completely insulated from the engine heat, except for the carb heat. A 912 has the carbs on top and a certain amount of heat will be conducted and radiated upward - then you have two carbs so the temp drop due to fuel vaporization is split between two places with each carb evaporating only half of the fuel and consequently each carb makes only half of the "cold" necessary to make ice. The 912 engine has variable venturi carbs rather than a butterfly system which behaves a bit differently too.

    At any rate, over the time we have flown our kitfox, never a hint of carb ice, admittedly it is not flown through clouds with lots of moisture - but I think each builder needs to figure it out for themselves.

    It would be nice if there was some sort of survey to find out how prevalent the use of carb heat is with the 912 carbureted engines.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  6. #6
    Senior Member jrevens's Avatar
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    Default Re: carburetor heat recommendation for 912 ULS?

    Drawing air from the warmer rear, upper area of the engine compartment, as opposed to your average Lycoming or Continental that draws air directly from outside (when carb heat is "off") is a big difference in my mind. I'd like to instrument that area with a thermocouple some day and measure what the temperature is compared to the outside air temp. It would be useful to do that several different times under various ambient conditions. For the record, I don't have carb heat for my 912 ULS either.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  7. #7
    Senior Member HighWing's Avatar
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    Default Re: carburetor heat recommendation for 912 ULS?

    Much of my flying has been alongside a bunch of Model IVs. My kit came with the carb heat box and like the vast majority of others the carb heat box eventually went into the recycle bin. Lots of talk about in the early e-mail lists and experience resulted in very few installations and virtually no reports if issues. Of course, these were mostly the 912 UL version.
    Lowell Fitt
    Goodyear, AZ


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  8. #8
    Senior Member jiott's Avatar
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    Default Re: carburetor heat recommendation for 912 ULS?

    Hallschuch, you can do a search on this forum for carb heat and find a lot of reading. I, like the other responders to your post do not have carb heat, nor never found a need for it, but like Dave said, I don't fly thru moist clouds for any length of time. Seems to me like most of the folks installing it live in Canada where I think it is required by law.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  9. #9
    Senior Member Dusty's Avatar
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    Default Re: carburetor heat recommendation for 912 ULS?

    I use a temperature guage by the firewall on my 4. The temp is generally 10c above ambient in flight.
    A smooth cowl installation may see a bigger differential. I removed my airbox assembly and use hot water directly to the throttle spindle as there wasn't enough room to use the carb intake heaters. Carb icing is is sometimes a problem in our environment.

  10. #10
    Senior Member jrevens's Avatar
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    Default Re: carburetor heat recommendation for 912 ULS?

    That's good information, Dusty.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

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