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Thread: 912S - Carb Heat or Not??

  1. #11
    Senior Member Dorsal's Avatar
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    Default Re: 912S - Carb Heat or Not??

    While I support John's usually sage advice I would still like to know if anyone has ever experienced carb ice on a Rotax 9xx with the intake inside the cowl?
    Last edited by Dorsal; 01-03-2011 at 12:16 PM.
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  2. #12
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    Default Re: 912S - Carb Heat or Not??

    912s on my fox IV. no carb heat...no icing so far, knock on wood. 84 hours on it with the air intake against the firewall

  3. #13

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

    Up here in the Pacific North Wet, rain and moisture are common every day experiences. It's relatively common to have temp/dew points within 3deg. I have flown in all types of conditions and have never had carb ice on my 912UL, that I know of. My neighbor on the other hand, gets carb ice frequently on his 172.

  4. #14

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

    Quote Originally Posted by sdemeyer View Post
    My neighbor on the other hand, gets carb ice frequently on his 172.
    If your neighbor has an early 172 with an O-300 I feel his pain. The O-300 on my 172 is a great engine but it'll pick up carburetor ice on a Summer's day here in Florida.

  5. #15
    Senior Member jtpitkin06's Avatar
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    Default Re: 912S - Carb Heat or Not??

    I think that’s a valid point that some engines and installations are more prone to ice than others. For example: The Continental O-200 and O-300 have a carb hung from free standing intake manifold with long runners. They have no effective ambient or conductive heating and they ice up like an igloo. The Lycoming O-235 and O-360 have the carb and manifold mounted on the bottom of the oil pan where it gets conductive heating and it is much less likely to get ice.

    With that in mind, there is definitely something about the Rotax with the intakes inside the cowling. It gets some ambient heat and it appears less likely to ice up. Perhaps some of the resistance to icing is also due to higher RPM and higher manifold pressures on approach than a non-geared engine.

    Another factor may be that the Kitfox pilot rarely uses long power off descents. The high drag airframe requires the pilot to “cruise” almost all the way to the airport. That’s quite different from some cleaner aircraft that can descend for ten minutes or more with the throttle closed.

    Certainly, we can look to certified aircraft for guidance on good practices. FAR 23.1093 requires an intake air heating system. The regulation states it must provide a temperature rise of 90°F at 75% power. I have doubts the ambient temperature rise in a Kitfox cowling is enough to meet this requirement.

    One problem I see is most pilots do not know when they have ice on approach. The power is reduced and the pilot typically makes sequential reductions in power, not increases, as one makes an arrival. Unless the pilot needs a large power increase, icing goes unnoticed. Once on the ground the power demands are small and the ice typically dissipates as the throttle is opened for taxi. The net result is, the pilot never realizes there is carb icing until a go around is necessary and full power is suddenly not available.

    In any case, if you have carb heat on your aircraft now, I certainly wouldn’t take it off just to save 2 pounds. It’s cheap insurance and low maintenance.

    As for injection, it’s not always immune to icing. Ellison states carb heat is mandatory with their injectors. I am installing an AeroInjector on my engine and it will also have pilot selectable “carb” heat.

    Check gear down.
    John Pitkin
    Greenville, TX

  6. #16

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

    I've got a Kitfox 4 with the Rotec R2800 Installed, but it uses the Bing 94 for a carb. When I was searching for a carb heat solution, I discovered the Jabiru engines use an easily installed, electrically heated system attached to the Bing carb throat forward of the slide. It has two possible setting. One can be used constantly to preclude carb ice with little to no performance decrease, and a increased setting for known icing conditions. I purchased it from the Jabiru dealer in Shelbyville, TN, but have not used it in flight yet (shortly I hope). It is easily installed, light, takes up hardly any space and really heats up quickly. I turned it on and touched it, and it works! Downside is it was $200.00. Kind of expensive if you've got two carbs. Dave Dean (49LOOPER)

  7. #17
    Ken Birchard's Avatar
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    Default Re: 912S - Carb Heat or Not??

    I put the Bing 64/32 electrodes that screw into the vacuum port on the carbs in my 912uls. Easy to install, hook to a switch on the panel and shouldn't affect HP. Look like they should work. Haven't tied them out yet...Ken

  8. #18
    Bryan's Avatar
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    Default Re: 912S - Carb Heat or Not??

    I will chime in here. I am not going to say which is the best but I will tell you that I visited with Lockwood Aviation at Oshkosh this past year about my 912engine quiting on me shortly after takeoff on my third touch and go. I was wondering about the possibility of carb ice and after talking with them they felt real strong about the 912's not needing carb heat. They told me that the only instance of a 912 icing that they were aware of was on their Aircam, and it was in perfect icing conditions. They told me that with a cowled engine and the carbs located directly above the exhaust, and heat rises, that there was no need to have the carb heat. We came to the conclusion that my problem was vapor lock. Just wanted to let you know what I was told.

  9. #19
    Senior Member jtpitkin06's Avatar
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    Default Re: 912S - Carb Heat or Not??

    I'd like to hear from someone that has a carb temp gauge on their 912 engine.

    JP

  10. #20
    Senior Member Monocock's Avatar
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    Default Re: 912S - Carb Heat or Not??

    I looked into carb heat with my Mk 5 and 912s (smooth cowl) and was basically told that the heaters would make no difference whatsoever to the carb temp on the basis that they already operate in a hot and closely cowled environment. I stand to be corrected, but I took this advice as sound.

    As I understand it, an engine that is mounted in an exposed location (ie back of a pusher ultralight type) is more at risk of carb icing.

    Interesting topic though.

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