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Thread: Dew point, temp and carb ice.

  1. #1
    Join Date
    Jul 2006
    Location
    Toronto, Ontario, Canada.
    Posts
    105

    Default Dew point, temp and carb ice.

    The other night my instructor (in class) says - when the dew point is close to the temperature (you hear on the ATIS), then you have a high potential for carb ice. When there is a large differential, you don't have to worry about it as much.

    Question: is there a rule of thumb for a spread between the dew point and the outside temp. where you don't have to worry about carb ice?

  2. #2
    Join Date
    Mar 2005
    Location
    Westminster, CO
    Posts
    5,414

    Default RE: Dew point, temp and carb ice.

    That's a new one on me, although he's really just saying that high humidity makes carb ice more likely, which is certainly true. Dew point is just an indication of humidity, and anytime there's a 5º spread or less you should be watching for fog, meaning that you're closing in on 100% humidity. You can have carb icing even at 90º, if there's much humidity, since under certain conditions (especially at low throttle settings) there can be 60º or more drop in temp in the carburetor.

    The best way to avoid carb ice is to have a carb temp gauge, and keep it well above freezing. Cessna recommends (in their carbureted aircraft) pulling carb heat on anytime you make a major throttle reduction, while other manufacturers may have different recommendations -- the aircraft handbook is the place to look.

    [HR]
    http://home.comcast.net/~lfn3/Cub_Pix/LarryCub03_s.jpg http://home.comcast.net/~lfn3/Peg_Ab...590Mklfn_s.jpg
    Larry N.

  3. Default RE: Dew point, temp and carb ice.

    Well your instructor is gernalizing a important subject. Carb ice can occur anywere below approximately 75 degrees and is most likely to accure when the relitive humidity is between 70-100%. So yes, if the temp and dew point are close, it is more likely. But, it must be below, 75ish degrees. As far as being concerned about it. I have never heard of anyone having an engine failure due to carb ice. Just remember to pull the heat when appropriate. Referece the Pilots Handbook of Aeronautical Knowlege.

  4. #4

    Default RE: Dew point, temp and carb ice.

    Re.....>>>I have never heard of anyone having an engine failure due to carb ice.

    Don't kid yourself.....it CAN happen.

  5. #5

    Default RE: Dew point, temp and carb ice.

    <<I have never heard of anyone having an engine failure due to carb ice>>

    Writing your own epitaph?

  6. Default RE: Dew point, temp and carb ice.

    http://ibis.experimentals.de/images/...omcaassl14.gif

    CARBURETOR ICE
    The Cessna 182 Skylane is prone to developing carburetor ice. The reason for this is because the design of the induction system has the carburetor positioned well below the engine in the cowling and away from the warm air around the engine. Because of this tendency towards carburetor ice many Cessna 182 Skylanes were delivered with a carburetor temperature gauge. The Cessna Pilots Association has strongly recommended to its members that they utilize carburetor heat in such a manner as to keep the carburetor temperature indication out of the yellow zone of the gauge. This may only require the use of partial carburetor heat, a practice that in standardized flight training is considered a poor procedure, being taught that carburetor heat should be all or nothing. The carburetor icing characteristics of the Cessna 182 Skylane make partial carburetor heat an acceptable practice for this aircraft.

    http://www.cessna.org/store/buyers_g..._excerpts.html

    Best and Warm Regards
    Adrian Wainer

  7. #7

    Default RE: Dew point, temp and carb ice.


    >
    CARBURETOR ICE
    >The Cessna 182 Skylane is prone to developing carburetor ice.
    >The reason for this is because the design of the induction
    >system has the carburetor positioned well below the engine in
    >the cowling and away from the warm air around the engine.
    >Because of this tendency towards carburetor ice many Cessna
    >182 Skylanes were delivered with a carburetor temperature
    >gauge. The Cessna Pilots Association has strongly recommended
    >to its members that they utilize carburetor heat in such a
    >manner as to keep the carburetor temperature indication out of
    >the yellow zone of the gauge. This may only require the use of
    >partial carburetor heat, a practice that in standardized
    >flight training is considered a poor procedure, being taught
    >that carburetor heat should be all or nothing. The carburetor
    >icing characteristics of the Cessna 182 Skylane make partial
    >carburetor heat an acceptable practice for this
    >aircraft.
    >

    And my Lyc has "more" tolarance to icing because the carb is mounted directly to an oil sump on the bottom of the engine, which in turn, somewhat preheats the carb & air.

    The downside, is technically a bit less rated power per cubic inch, than the Cessna's Continental engine, because warmer air isn't as efficient as cooler air.

    This is a reason, that you'll see many Cessna POH's having carb heat applied on the landing checklist, while many Pipers (Lycomings) just say "as required" or don't say it at all.

    And to make matters more confusing, many Cessna "drivers" will insist on always using carb heat (unless fuel injected) for nearly every aircraft during the landing phase, while prior Piper pilots like me, would rather skip the process at high altitude airports, such as those I fly around. To me, leaving carb heat accidently applied during a go-around at a high altitude airport, is worse than using carb heat---- just in case. But like, what causes "lift", and leaning past peak, this subject will always be debated! :)


    Ladamson

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