Over the years I have written a lot on this subject, but a couple of test stand photos can do wonders to illustrate a point that flight instructors rarely teach correctly anymore. For a much deeper look at the subject, follow this link: Critical Understanding #10 – Carb Ice.
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Mike Loevin’s Corvair, running on my stand at Corvair College #43. The white section of the intake manifold above the carb is solid white ice, and it is 48F outside.
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The digital Thermometer shows the temp has dropped 30F going through the carb. There is identical ice on the inside of the manifold also. This is simple physics in action, and this is why planes have carb heat. Contrary to popular myth, injected engines do this also, they are jest less prone to quitting when the throttle is advanced when the pilot notices the rpm drop. No carb should be assumed to be immune to this. Popular hangar talk says Elison’s are not vulnerable, but cast right into the Elison body is the phrase “CARB HEAT REQUIRED”.
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Another look at the engine. Look at the prop blade and the balancer; its running. the power setting is 2,000 rpm and 20″ MAP, to break in the cam. This is about 50% power. If anyone tells you to wait until the engine is reduced to idle to use carb heat, they don’t know what they are speaking of.
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The picture above addresses one more myth, that it somehow need to be cloudy or rainy to get carb ice. Look at the sky in the picture, understand that anyone who claims you have to see dense clouds, fog or rain for ice to form is clearly mistaken.
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Just to reiterate it one more time, this isn’t a Corvair issue. Rotax and to some extent, Lycoming, avoid this somewhat by having full time carb heat, but every competent pilot should understand the fact it can happen to any plane, and they should take the engine manufacturers recommendations very seriously and ignore they hangar myths.
