What is the purpose of the Carb heat

Fuel injected planes don't have carbs, therefore don't have venturis, therefore don't make carb ice, therefore don't need carb heat. That said, FI planes do need an alternate source of air in the event the air filter gets plugged with snow/ice/dirt/schmutz. There is a spring loaded door in the intake tract of the Mooney, if vacuum in the intake rises sufficiently the door will be sucked open to admit air into the engine.
 
Allison Riccardi said:
I am very much a woman. Now, back to to topic at hand. How were newer planes designed to not need carb heat? What changed.
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Since a large part (not all) of the temperature drop is from changing the fuel from liquid to gas (that state change takes lots of energy-it's how most air conditioners work) in the carb throat, fuel injection. Fuel injection removes one of the largest contributors.
 
Here is a great graph of what conditions are ripe for carb ice. It's pretty sobering to think you could encounter carb ice on an 80 degree day, if you have carb ice you should use it, opposite the numbers in the pattern before I pull the throttle is where it comes on for me if it is there on the airplane I am flying. Once again, if the engine starts running rough, it's the first thing you should pull (fully) in my opinion and if the engine gets worse after you pull you've probably found the problem, leave it pulled until it clears up.

http://www.boldmethod.com/learn-to-fly/systems/carb-ice/

carb-ice-potential-chart.jpg
 
jsstevens said:
Since a large part (not all) of the temperature drop is from changing the fuel from liquid to gas (that state change takes lots of energy-it's how most air conditioners work) in the carb throat, fuel injection. Fuel injection removes one of the largest contributors.
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AIr conditioning, like other refrigeration systems, uses both evaporation and pressure drop. That's what the compressor is all about.
 
Dan Thomas said:
AIr conditioning, like other refrigeration systems, uses both evaporation and pressure drop. That's what the compressor is all about.
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Indeed. And the state change is a major part of the energy absorption.
 
Clark1961 said:
Carb heat is avoided during warm up and taxi because the intake air is not filtered. Check card heat as part of the run-up. Ice should be cleared at that point.
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The plane I fly, carb heat is filtered, with the plumbing and mounting of the carb (not up-draft) POH says only use when ice is detected.
 
1RTK1 said:
The plane I fly, carb heat is filtered, with the plumbing and mounting of the carb (not up-draft) POH says only use when ice is detected.
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Brings the question, how is the ice detected in that aircraft?
 
Guess I should have said suspected.
To answer the question, drop in rpm, roughness, etc.
To date, hasn't ever been suspected or detected;)
 
Carb heat is something that I am very interested and it is something that worries me. I find it even more interesting that there are still, after all the discussions and history, appears to be many different options about it and when to use carb heat. Frankly, scares the hell out me. So, I mostly fly an archer iii and so piper says only use carb heat if suspected.... but FAA says to ignore that advice and use it during glide descent and traffic pattern. Now you all say may during long taxi, but be careful not to fowl the plugs and make sure you lean right. Too much to freakin stuff to remember for something that seems as important as this. Okay so, fine, here are my questions which I am afraid will only cause more questions that answers:

1) During taxi, should apply carb heat prior to take off just to be sure? Also I lean during taxi, should I go fuel rich before applying carb heat?

2) if you suspect carb ice during the climb out, should you apply carb heat even though you give up some power?

3) during cruise, and after leaning, so you just switch on carb heat or should you change the mixture to full first?

I think I got descent and traffic pattern down...

Whew..this stuff is confusing.
 
1) I wouldn't bother
2) Unless you ain't making it over the trees (And if you do really have ice, be prepared for a sputter). But carb ice is less likely at wide open throttle.
3) Heat will rich a bit for you anyhow, so just pull the heat.
4) I ain't no CFI and/or A&P so listening to me will probably cause you to die.
 
1) This is the confusing one to me too. You hear of carb ice being a cause of engine failures on takeoff. That means it was most likely making ice down on the ground. None of the older POH's seem to really address this. I think your questions really comes down to certain atmospheric conditions with close temp/dewpoints, higher humidity and temperatures right in that ugly zone. Good luck getting a "official" answer on this one.

2) If you know your engine isn't making full power on take off and you're airborne I think many POH's are going to call to rapidly check for mixture rich, carb heat on and verify fuel selection while picking a landing spot ahead. @Capt. Geoffrey Thorpe had to use his sage advice and throw in a tree line!!!

3) Carb heat should make the engine run rich so I don't see why going full mixture rich prior to carb heat during cruise would be of any benefit? I know during cruise (mixture leaned), when I pull the carb heat the engine continues to runs just fine - just make less power. With my first instructor we tried something interesting about 3500agl. We slowed way down, mixture full rich and then carb heat on full. We then slightly leaned the mixture and it purred like a tiger! He was just demonstrating how carb heat does make the engine run rich. And we also did the same in cruise, carb heat on full and then re-leaned the mixture to the full carb heat setting to make the most power. Both were for demonstration purposes. The later (re-leaning with continuous partial/full carb heat) is in the POH.
 
Capt. Geoffrey Thorpe said:
1) I wouldn't bother
2) Unless you ain't making it over the trees (And if you do really have ice, be prepared for a sputter). But carb ice is less likely at wide open throttle.
3) Heat will rich a bit for you anyhow, so just pull the heat.
4) I ain't no CFI and/or A&P so listening to me will probably cause you to die.
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Number 4 I paid a lot of attention! Thanks. I wasn't expecting anything official here. I am just amazed of there isn't a singular "best practice" for the common single engine planes we all fly. Seems odd to me.
 
So most if not all ac with carb heat have you check that it works as part of the run up, this should also tell you if you have carb ice. The thing about carb ice is that you can get it at 75 degrees if the relative humidity is high enough.
 
Capt. Geoffrey Thorpe said:
1) I wouldn't bother
2) Unless you ain't .making it over the trees (And if you do really have ice, be prepared for a sputter). But carb ice is less likely at wide open throttle.
3) Heat will rich a bit for you anyhow, so just pull the heat.
4) I ain't no CFI and/or A&P so listening to me will probably cause you to die.
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My experience has been pretty much the above FWIW.
 
PaulS said:
So most if not all ac with carb heat have you check that it works as part of the run up, this should also tell you if you have carb ice. The thing about carb ice is that you can get it at 75 degrees if the relative humidity is high enough.
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I think what's got @steviedeviant freaked is cases like when you've landed, taxi back for another and get stuck waiting #6 in line for another departure and it happens to be on that day "you can get it at 75 degrees if the relative humidity is high enough".
 
Bill Jennings said:
Fuel injected planes don't have carbs, therefore don't have venturis, therefore don't make ice
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Throttle body fuel injection can still have a venturi. The primary reason for fuel injection having less danger of induction icing is because fuel vaporization takes place in or nearer the cylinder than engines with carburetors.
 
I like my carbs heated. They taste much better that way.
 
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