Using Carb Heat on C-150

[wbfsinc]

The 150 I'm taking lessons in has a carb temp. gauge that rarely gets out of the caution zone. As a result I pull full carb heat from time to time to avoid ice build up.Question, can I pull just enough carb heat to get the temp gauge out of the caution zone and then compensate for loss of rpm thru increase of throttle?

[skid]

The venturi in the carburetor cools the air passing through it, which is why temps above freezing are the most likely time to get carb ice. Your carb air temp gauge will probably spend a great deal of time in the "ice zone", because these temp conditions are encounterd often. You can occationaly check for ice by useing full heat for a short time. If you do have ice it will probably run worse as it melts and water is ingested by the motor, then gradually smoothing out. If you use partial heat you are giving the engine warmer air which is not as dense and thus leaning the engine by reducing the amount of air for the same amount of gas being fed to it. I think it is preferable to run cold air and if you want to check occaisionaly, use full heat for a short time. I wouldn't worry a great deal about the gauge reading; I've had carb ice outside of the "ice zone" on the gauge just as often as when conditions were favorable. I would pay more attention on a 55 degree day when the air is heavy and damp.

[HighFLyer]

Like Skid say's I wouldn't use just a small amount of carb heat. The gauge is just and indication, and will not really give you a good estimate. I would just check for ice by using full heat whenever you suspect a problem.
Another problem with carb heat, is that the air comes from a muff around the exhaust. I beleve that when you use carb heat, the air coming into the carb skips the air filter. That is why when you land on gravel or dusty runways you should always push the carb heat in right away. Then you lower the risk of ingesting dirt and particles in the engine.

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The sky's not the limit, its a Playground!

[sideslip]

Highflyer is right about the carb heat bypassing the airfilter. Another use of the carb heat is if the airfilter should become clogged. On fuel injected engines they have alternate air in case of a clogged filter.

A slight loss of RPM is the first indication of carb ice. If you notice an RPM drop then try the carb heat. If ice is present then the engine will run rough shortly after applying the heat. As soon as the ice is melted, the engine will smooth out again.

Most icing will occur between 20 and 70 degrees F. But it can occur as low as 0 degrees F or as high as 100 F. After you have flown in a certain plane awhile you will be able to detect even slight changes in the engine.

Of course as soon as the sun goes down or you are over water and out of sight of land the engine always sounds rough.

Mike S.

[wbfsinc]

Thanks to all for the advice.