Carb Heat: What's the deal?
So, when the engine sounds like it is going to die on you after pulling carb heat on, don't immediately go to back to cold power - keep carb heat on while turning towards a suitable field, just in case.
This is the first time (that I can remember) that I have seen this aspect of carb icing mentioned.
I had been flying for about six years (~500 hours) before I experienced carb icing. I was flying a 172 in the summer time, about 4000' AGL near the Canadian Rockies, with cloud base not much higher (i.e. about 4000' lower than normal), with virga coming out of most of the clouds. Passing near one of these clouds, I thought it would be prudent to check for icing. I pulled on the carb heat and got the symptoms you described. The point of this long-winded preamble is that it scared me so much that I instinctively put the carb heat back to cold!
It was only after thinking about it for a minute that I realized what was happening and put the carb heat on again and let the engine cough and splutter as the ice melted.
I wish one of my instructors had mentioned this issue during my training. Not one ever did.
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I found this explained carb ice very well.
I fly a C152 and a Rotax powered C42. I prefer the Rotax engine for a number of reasons, one is not having the worry of carb ice. Biggest worry when going back to the 152 is forgetting to use the carb heat!
I fly a C152 and a Rotax powered C42. I prefer the Rotax engine for a number of reasons, one is not having the worry of carb ice. Biggest worry when going back to the 152 is forgetting to use the carb heat!
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I wish one of my instructors had mentioned this issue during my training. Not one ever did.
Last edited by thing; 14th May 2012 at 17:37.
I'm currently sitting my ATPL exams...and i can tell you, there not easy
@peter... I have the best of both worlds, a carburetted engine whose carb is tucked up at the back of the engine where it never gets cold (and a carb temp gauge too just in case). I've flown injected aircraft and hot starts can be a nightmare. Never a problem with a carb.
I've flown with quite a few instructors (in the US and for that matter the UK too) and never come across this idea of turning off carb heat on short final. Sounds nuts to me, a distraction just when you don't need it (especially for low time pilots but also for everyone else too). On everything I've flown, carb heat can be reset in the same movement as applying throttle for a go-around, and indeed that's what I've always been taught to do.
It does however seem to do a splendid job at encouraging a usually undeserved "God of the Skies" mentality in many of the pilots who undertake the ludicrously long and complicated process required to prepare for the exams
Last edited by Big Pistons Forever; 14th May 2012 at 23:32.
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I think it is important to note that the first indication of carb ice in cruise flight should be the pilot noticing an uncommanded reduction in RPM (or MP in an aircraft with a constant speed prop). At that point the first action should be to suspect carb ice and apply full carb heat.
A lot of instructors when teaching PFLs start the initial actions by waffling about speed for height, selecting a field planning, a circuit, making a call and by the time they get round to finding out why the engine might have stopped, guess what the engine is much colder. Is that going to help if it stopped due to carb icing?
Engine roughness partial power loss or failure on SE a/c with a carburettor should be immediately:
CARB AIR HOT, SELECT FULL POWER
Dont wait till the engine has cooled down!
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Select Full Power ?
Do you mean full power the instant you realize there is icing or after the heat has been engaged and the icing cleared? Also if icing occurs while in cruise configuration and heat is engaged then full power either simultaneously or after ice clearing would the mixture not have to be enriched prior to full power, I recall reading about potentially harmful effects on the engine of going to full power while running lean, any thoughts?
Do you mean full power the instant you realize there is icing or after the heat has been engaged and the icing cleared? Also if icing occurs while in cruise configuration and heat is engaged then full power either simultaneously or after ice clearing would the mixture not have to be enriched prior to full power, I recall reading about potentially harmful effects on the engine of going to full power while running lean, any thoughts?
Last edited by piperboy84; 15th May 2012 at 23:59.
If you let the engine actually stop due to carb ice then full throttle won't do you a lot of good. However I heartily agree with your point about taking early action to try to rectify a faltering engine. The best way to deal with an engine failure is not to do the perfect forced approach it is to restore engine power. In the case of a carb ice induced engine failure there is a point of no return where you can't get the engine back with carb heat. If the first thing you do when the engine starts fading is spend a lot of time on some elaborate flight school forced appraoch ritual by the time you get to the carb heat you may have created your own totally preventable engine failure.
Bottom line: If you are flying along and you see a loss of power or the engine starts to run rough, Immediately apply full carb heat
Last edited by Big Pistons Forever; 16th May 2012 at 00:15.
I think this Memphis Bell guy has some fairly serious issues... here's a PM which I just got (and I guess I'm not the only one):
Memphis_bell
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What a boring individual.
Blocked anyway. Hope he doesn't get his ATP - it's a bit frightening that he could be in the right seat of a 737 one day!
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What a boring individual.
Blocked anyway. Hope he doesn't get his ATP - it's a bit frightening that he could be in the right seat of a 737 one day!
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This is such a MASSIVELY over-engineered debate. Geeeeeees !
I've enjoyed it too... Learned a lot + the more you discuss something, the better it gets rubbed into your mind.
Another part of my reasoning is that I see something homebuilt in my future. The POH may not be quite as definitive as it is on a PA-28 and the more I understand about the fundamentals of how everything all works the better.
Another part of my reasoning is that I see something homebuilt in my future. The POH may not be quite as definitive as it is on a PA-28 and the more I understand about the fundamentals of how everything all works the better.
Memphis Bell(e?)
I'm afraid I couldn't see the flaws in Big Piston's post. Based on his explanations and experience, I'm inclined to take his advice over yours, so perhaps you could post an explanation of what he got wrong for my benefit - if not for his.
I'm afraid I couldn't see the flaws in Big Piston's post. Based on his explanations and experience, I'm inclined to take his advice over yours, so perhaps you could post an explanation of what he got wrong for my benefit - if not for his.
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If you are at cruise flight power and you get carb ice, selecting carb heat without adding power will still get more then enough heat into the engine to melt the ice.
I did find that different power settings gave differing card heat rise with the application of carb heat. A greater effect could be had by leaning to peak once the power was reset (and often selecting cabin heat off, to direct all of the hot air to the carb).
A carb air temperature indicator is vital for making these determinations. If you have chosen carb heat because you really mean it, consider peak leaning the engine once it is applied. Choose the power setting you like, and start to lean 'till the engine falters (more), and rich it up just a little. Carb heat hot enrichens the mixture, so leaning it gets you back to the optimum mixture, which will give you the most heat, which you need....
Big Pistons, please allow me to supplement that thought a little. My experience has been that some types have marginal carb heat capability. This is based on my doing quite a bit of testing. One of my early certification projects was to modify, test and approve a Continental IO-520 to be an "O"-520. This meant the installation of a carb, and development of a carb heat system for it. It was surprisingly difficult to achieve the required heat rise for certification.
I did find that different power settings gave differing card heat rise with the application of carb heat. A greater effect could be had by leaning to peak once the power was reset (and often selecting cabin heat off, to direct all of the hot air to the carb).
A carb air temperature indicator is vital for making these determinations. If you have chosen carb heat because you really mean it, consider peak leaning the engine once it is applied. Choose the power setting you like, and start to lean 'till the engine falters (more), and rich it up just a little. Carb heat hot enrichens the mixture, so leaning it gets you back to the optimum mixture, which will give you the most heat, which you need....
I did find that different power settings gave differing card heat rise with the application of carb heat. A greater effect could be had by leaning to peak once the power was reset (and often selecting cabin heat off, to direct all of the hot air to the carb).
A carb air temperature indicator is vital for making these determinations. If you have chosen carb heat because you really mean it, consider peak leaning the engine once it is applied. Choose the power setting you like, and start to lean 'till the engine falters (more), and rich it up just a little. Carb heat hot enrichens the mixture, so leaning it gets you back to the optimum mixture, which will give you the most heat, which you need....
However even without a carb temp gauge the actual effectiveness of the carb heat will be evident during the run up check. You should see a definite drop of at least 150 RPM drop when carb heat is selected on.
Last edited by Big Pistons Forever; 16th May 2012 at 04:03.