Carb heat question

flyinmomof3

flyinmomof3

Learning to fly....but I ain't got wings.
So I've heard two different stories about carb heat. One of my instructors says that the application of carb heat during run-up will help warm the engine up faster because your putting warmer air into the engine. Another instructor says that the amount of heat that comes in off of the exhaust is insignificant compared to the internal heat in the engine, so that it really doesn't make a difference.

Both arguments have good points to me, and I intend to investigate this the next time I have a carburated engine to play with.
 
Keep in mind that using carb heat in many aircraft completely bypasses the air filter, so extended use of carb heat on the ground is usually a bad idea.

Given the fact that the temperature of the cylinder walls and exhaust gasses is far higher than the carb heat can bring the intake air, I don't see how running carb heat on the ground would warm the engine up enough to be useful, especially given the fact that you're running unfiltered air through the engine while doing so.
 
yeah, that's what i was leaning towards. But 90% of the guys think the other way. Their main argument is that if you bring in air that is hotter than the OAT, then no matter what it has to make a difference. I guess the real question should be if the difference would be significant, and maybe the difference would be greater in cold weather...
 
A bit of digging online turned this nugget from a Lycoming service instruction regarding all of their carbureted engines, although they do say the aircraft manufacturers' recommendations supersede that document.
Use of the carburetor air heat on the ground must be held to an absolute minimum. On some installations the air does not pass through the air filter, and dirt and foreign substances can be taken into the engine with the resultant cylinder and piston ring wear. Only use carburetor air heat on the ground to make certain it is functioning properly.
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That said, I've never seen an aircraft manual that recommends using carb heat on the ground for extended periods.
 
flyinmomof3 said:
90% of the guys think the other way.
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That is the part I can't get over. I am right in line with what everyone wrote in response. I think over the years I've heard every possible opinion on every aviation subject and I've never heard anyone talk about using carb hear to warm an engine. In fact, I would hazard a guess that if a person didn't lean the mixture when they did that, they would actually be delaying the warming of the engine because of the overly rich nature of the fuel air mixture. Again, just taking a guess, if 90% of the people where you are think that way, I wonder if maybe they didn't all have the same flight instructor.
 
I aplologize, I guess i should mention we are flying r-22'S. We don't lean the mixture. The air does come in unfiltered and we have alot of dirt everywhere around the airport. I think the other pilots need to be patient and just let the engine warm up normally. The pilots that think that way did stem from the same flight instructor which is no longer there, so now it's just a way of thinking. I've had many different instructors and that's how this subject came up. I believe because of the unfiltered air, that you should only check it and then leave it be for obvious reasons.
 
flyinmomof3 said:
So I've heard two different stories about carb heat. One of my instructors says that the application of carb heat during run-up will help warm the engine up faster because your putting warmer air into the engine. Another instructor says that the amount of heat that comes in off of the exhaust is insignificant compared to the internal heat in the engine, so that it really doesn't make a difference.

Both arguments have good points to me, and I intend to investigate this the next time I have a carburated engine to play with.
Click to expand...

Carb heat does not "warm" the engine up faster. Were is the heat coming from? The the same engine... There's no free lunch.

However, if you have a carbureted engine that has a hard time with staying running in the cold, what the carb heat CAN do to is have a choke affect. When you apply carb heat you are introducing hotter (less dense) air into the intake. The idle mixture is set at a fixed setting. Less dense air, with the same amount of fuel being introduced will enrich the air:fuel ratio. Don't lean it... Cold engines like rich conditions. After start, carb heat combined with a some off-idle throttle should keep it running long enough to warm up on it's own. If you cant keep the engine running, it'll never warm up....

The "unfiltered air" is a bunch of BS. Only if you're operating in a dust cloud or your alt-air intake is 2 inches from the ground, this would be an issue. Even though your highest manifold vacuum is at idle, the CFM moving through the intake is really nothing. I know quite a few piston airplanes that run NO air filter at all, granted these are all FI engines... I guess on a carbureted engine you could get a big bug stuck in the venturi.
 
I suppose it could warm up faster, since it's unfiltered and you're sucking sand and dust into the engine and increasing the internal friction...

Apply it just long enough to test it ;)
 
flyinmomof3 said:
One of my instructors says that the application of carb heat during run-up will help warm the engine up faster because your putting warmer air into the engine.
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Well he is right, but whether or not is a significant amount I'm not qualified to say. However, I bet all the rocks and debree you grind up intisde the engine with all that unfiltered air will really help you warm it up fast! :rolleyes:
 
In airplanes where it is appropriate I use carbheat on the ground. If you're getting unfiltered air, only use it with float planes where you need your power at an absolute minimum or to test it, or if it seems like you're getting carb-ice on the ground. Unfiltered air isn't exactly good for engines. I could be wrong, but if I recall, the continentals don't have unfiltered carb-heat in the smaller models.
 
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