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Thread: 912S - Carb Heat or Not??

  1. #21

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    Smile Re: 912S - Carb Heat or Not??

    I have 750 hr on my Fox 912S and never had carb heat. I fly all winter in upstate NY and never had a prob. If you have it use it !!

  2. #22
    Senior Member HighWing's Avatar
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    Default Re: 912S - Carb Heat or Not??

    John,

    A suggestion for a homework assignment. When you are not busy flying or building, check the accident database for Kitfox accidents flying behind Rotax 912 series airplanes and see if you can come up with any carb ice issues in carb heat free airplanes. I have been monitering several Kitfox list/forums for over 15 years and the only occasion I remember is the Alaska group in the mid 90s that reported burps in their engines while cruising that they postulated was ingested ice, and that it was ice was just a guess. None of them had a carb heat system. The comments on this thread that the only reported instances of carb ice in a Kitfox with a 912 has been in airplanes with the carb heat induction system with forward air intake is spot on.

    Then again if you really are a belt and suspenders guy, go for it, but you will be a member of a tiny minority of Kitfox owners.

  3. #23
    Senior Member jtpitkin06's Avatar
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    Default Re: 912S - Carb Heat or Not??

    Quote Originally Posted by HighWing View Post
    John,

    A suggestion for a homework assignment. When you are not busy flying or building, check the accident database for Kitfox accidents flying behind Rotax 912 series airplanes and see if you can come up with any carb ice issues in carb heat free airplanes......
    Thanks for the homework assignment.
    I’d love to provide you with an accurate report of the number of carb icing incidents in Kitfoxes with Rotax 912 engines. But here’s the problem... When someone does have an icing problem and the engine quits, chances are they don’t get on the phone and call the FAA to report they had icing. If they landed on the airport dead stick (as is usually the case) they restart the engine and press on. Sometimes they check out the fuel system thinking it was contamination, alcohol from mogas, bad plugs, lead in the gas, or a dozen other suspected problems. But most refuse to believe it was ice. Even if ice is suspected, the pilot is not about to report it.That makes it hard to get accurate figures.


    Am I a belt and suspenders kind of guy? I suppose so. Having carb heat is a pretty simple decision for me.


    The FAA requires it on all carbureted engines for certified aircraft.
    Canada requires it on all carbureted engines, certified or experimental


    Now, Just because you or several others have flown without detecting carb ice doesn’t make me all warm and fuzzy. If I told you I’ve flown over 18,000 hours without an ignition failure, would you be willing to remove one of your ignition systems? Probably not.


    There is a Canadian company that makes heaters for the Rotax 912 with Bing carburetors.It is noteworthy that this web page:
    http://www.lightsportaircraft.ca/912...carb_heat.html
    has a picture of an unheated carburetor installed on a Rotax 912 engine with ice forming in the throat. I’ll take that as pretty solid evidence that 912s can get ice under certain conditions. [It is not stated if this picture was from an engine with intakes inside the cowling] I do admit, however, it appears that a 912 with the Bing carburetors installed in a Kitfox with intakes under the cowing is resistant to icing. The point is, resistant does not mean it is immune.


    For me, having carb heat is safer than not having it available. If I’m in the minority, I’m happy with that.


    Now, I was just looking at some pictures of the factory built Kitfox SLSA. Is that a carb heat knob next to the throttle?
    JP

  4. #24
    Senior Member Dorsal's Avatar
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    Default Re: 912S - Carb Heat or Not??

    John,
    Yes, I believe the LSA rules require Carbheat. Your reasoning seems solid to me, if I had it I would keep it however I am not terribly concerned flying without it. I think your ignition analogy is a good one, I have never had one fail and certainly would not take one out. Maybe someday I will put in one of those electric carb warmers.
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  5. #25
    RIVERFOX's Avatar
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    Default Re: 912S - Carb Heat or Not??

    JP, give us a little more info on your switch to the AREOINJECTOR and what is needed for the conversion.
    Kurt
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  6. #26
    Senior Member Dorsal's Avatar
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    Default Re: 912S - Carb Heat or Not??

    I believe JP is talking about his Corvair conversion engine not a Rotax.
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  7. #27
    Senior Member jtpitkin06's Avatar
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    Default Re: 912S - Carb Heat or Not??

    Yes, I’m installing a Corvair engine and using a Aeroinjector for fuel delivery. This is not a Rotax conversion. Carburetor conversions can be difficult. I don’t recommend carburetor swaps unless you have a really big problem with getting your fuel mixture correct. To my knowledge, most Rotax engines run just fine with the Bing carbs. I mentioned the Aeroinjector as it is less prone to icing than almost any carburetor, and even so, I will install a heat source.

    Yesterday morning I was reading the NTSB accident reports and there was another carb ice dual fatality accident. The student and instructor were doing simulated emergency landings. Interviews with other students reported the instructor never used carb heat during emergency landing practice because the RPM was “in the green”. The engine was a Lycoming O-235. I mention this report because I hear far too often that Lycoming engines don’t need carb heat even though the operating manual says to use it.

    Certainly, if you have heat on an engine, use it. It’s free. If you don’t have heat on your engine, you may wish to do the following test:


    Take you aircraft up about 2000 feet over the airport on a cool humid day and pull the throttle to idle. Spiral down for a power off landing. When you get on short final add power to go around. If you get full power, then your engine installation is ice resistant, but not ice proof. If you don’t get full power, then you probably need to install carb heat.


    If you elect to do this test, please be prepared for a total power loss.


    Be safe... JP

  8. #28
    Super Moderator Av8r3400's Avatar
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    Default Re: 912S - Carb Heat or Not??

    I have done just that on several occasions, JP. From as high as 5000 agl, power off decent to an aborted landing. I did this after the needle adjustments, to test it's placement. I have never experienced a "total power loss" in any of these tests. Ever.

    Does anyone here know the physics of how a constant velocity carburetor works? Why it is less prone to icing? Why there aren't iced up motorcycles laying on the side of the road all the time?

    Every one seems to love to bash the Rotax 9xx engines. (It's almost an Olympic sport around here.) Yet, they are still the best performing and maybe the safest engine to install in this design aircraft. C'mon guys.


    If you doubt me. please find an example (NTSB report) of a KITFOX, with a 912 properly installed, that crashed due to carburetor icing. As has been said, nothing is ICE PROOF. However this setup is very ice resistant.
    Last edited by Av8r3400; 04-20-2011 at 06:52 AM.
    Av8r3400
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  9. #29
    Senior Member Dorsal's Avatar
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    Default Re: 912S - Carb Heat or Not??

    I can't say if anyone is missing a point or not though I do expect that most on this board are familiar with the fundamentals of carb ice (never hurts to review it ). I believe the question at hand is; does the specific installation of a Rotax in a Kitfox drawing air from behind the engine and inside the cowl provide enough pre-heat as to prevent our Bing carbs from icing. That would be difficult to answer definitively so the questions becomes has anyone with this setup experienced carb ice. Mostly what I read here are the experiences of others and the choices they have made which I value highly. In the end, of course, my choices are mine alone and I try not to assume anything
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  10. #30
    Senior Member jtpitkin06's Avatar
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    Default Re: 912S - Carb Heat or Not??

    I don’t think we are bashing Rotax engines on this thread, at all. This is experimental aviation and discussions on anything affecting safety is probably a good thing. I’m very happy to hear av8r3400’s installation provides an adequate level of protection for icing. As previously discussed, the combination of the intake inside the cowling and the Bing carburetors appears to be quite resistant to icing. That’s good.

    The Rotax 912 has enjoyed a pretty good record of dependability. Even the two strokes have done quite well installed in the Kitfox over the years.

    Because I am installing a Corvair engine, I’m in unknown territory. I must use extra caution as the engine and airframe combination is extremely limited. So if I tout installing carb heat, it is a rally for anyone installing anything other than the Rotax 912 in the factory configuration. Doing the power off descent test should be part of anyone’s initial flight testing.

    I did take the suggestion of av8r3400 to look at crash reports. While looking through the NTSB files I did find one report of a Kitfox with a Rotax 582 that crashed due to carburetor ice. But none with a 912.

    http://dms.ntsb.gov/aviation/AccidentReports/o0robt455jfawr3patqw2jjq/I04202011120000.pdf


    In addition, there are several reports of partial engine power loss due to unknown reasons in the 2 strokes, the 912’s and engines other than the Rotax. Many of them would indicate carb ice, but it can’t be proved.


    What I did find alarming was the number of fuel system problems. From contamination to improper plumbing; one thing kept popping up… Fuel starvation due to plugging of the filters seems to be the number one cause of power loss in the Kitfox.



    Please folks, check those fuel filters and increase the inspection frequency no matter what engine you have installed. Also inspect the tank screens for blockage.


    There’s a lot of information to be gained by plowing through the NTSB files. The search function makes it pretty easy to look for just Kitfox or Rotax. I recommend it for anyone looking to improve their aircraft.



    It’s unfortunate that others had to crash for us to get the information.


    Enjoy the build and fly safe.


    John Pitkin
    Greenville, TX

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