Carb Heat: What's the deal?
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With both the C90 and O-200 engine aircraft I had taxiing on damp grass almost required carb heat - otherwise the engines would go all 'lumpy' and die. Carb ice at near idle.
I've had a similar 'conversation' with a friend whilst flying my Terrier (Gypsy powered) - when he commented I should have removed the carb heat on short finals. So I did as we taxied back to the hangar - and luckily(?) it then went all lumpy - until I re-applied carb heat.
Granted the humidity on the ground close to grass will always be higher but it does illustrate the point quite well. But my friends O-320 never suffered from these issues.....
I've had a similar 'conversation' with a friend whilst flying my Terrier (Gypsy powered) - when he commented I should have removed the carb heat on short finals. So I did as we taxied back to the hangar - and luckily(?) it then went all lumpy - until I re-applied carb heat.
Granted the humidity on the ground close to grass will always be higher but it does illustrate the point quite well. But my friends O-320 never suffered from these issues.....
Only times I've experienced carb ice was in a 172, taxiing out in cool or cold, and very humid conditions. (Dew on the ground, no wind.)
Carb heat remedied it in a few seconds.
Carb icing is more likely at a reduced throttle setting, because there is a greater resulting pressure difference between upstream and downstream of the butterfly.
Carb icing is slightly more likely if, in addition to the above, the mixture is left fully rich when it needn't be, because more gasoline is forced to evaporate, thus producing a greater cooling effect. It is not suggested that other than full rich is used on the ground when taxiing, nor during takeoff, when the enrichment also provides an important engine cooling function.
Dust/grit is the biggest enemy of piston engines. It can be too fine to see, but still get in and scratch things. Even melt on things, if silica based. avoid using carb heat on the ground any more than absolutely necessary when on a dusty surface.
Fortunately, around the parts I've usually flown, weather conditions conducive to dust blowing around are usually not those that lend themselves to carb ice.
Carb heat remedied it in a few seconds.
Carb icing is more likely at a reduced throttle setting, because there is a greater resulting pressure difference between upstream and downstream of the butterfly.
Carb icing is slightly more likely if, in addition to the above, the mixture is left fully rich when it needn't be, because more gasoline is forced to evaporate, thus producing a greater cooling effect. It is not suggested that other than full rich is used on the ground when taxiing, nor during takeoff, when the enrichment also provides an important engine cooling function.
Dust/grit is the biggest enemy of piston engines. It can be too fine to see, but still get in and scratch things. Even melt on things, if silica based. avoid using carb heat on the ground any more than absolutely necessary when on a dusty surface.
Fortunately, around the parts I've usually flown, weather conditions conducive to dust blowing around are usually not those that lend themselves to carb ice.
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Intake design !
Intake design also is a factor, I have had very little carb ice in a PA28 be it 140, 160 or 180 HP but. DR400's with the same engines fitted are very prone to carb ice.
Saying that having the carb attached to the engine sump will prevent most of the carb ice is tricking yourself into a false sense of security that is likely to end in tears.
Saying that having the carb attached to the engine sump will prevent most of the carb ice is tricking yourself into a false sense of security that is likely to end in tears.
I tried going to Cold on very short final - until I had severe carb ice on opening the throttle to turn after landing. I'm back to Hot until on the ground. In some conditions, I start the take-off run with Hot selected, and go to cold on the run. I've had carb ice stop the engine on a Konsin deiced runway on several occasions. (DR1050/O200 in Scotland.)
I seldom or never have touched carb heat in W. Colorado-Utah-Arizona.
I seldom or never have touched carb heat in W. Colorado-Utah-Arizona.
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http://www.lycoming.com/support/publ...fs/SI1148C.pdf
Lycoming, at least, are pretty clear on their use of carb heat. If you use it on the approach, it should only be selected cold after full power has been selected for a go around. Other than that, it can be selected cold once on the ground.
The whole putting it cold at 3-500' is a UK flying school nonesense and can simply act as a distraction at a rather critical phase of flight. The only exeption I would include is landing on rough grass when you wouldn't want unfiltered air going into the carb, so would select cold as soon as practical.
In the case that full power needs to be applied under these conditions, as for an aborted landing, return the carburetor heat to “Full Cold” after full power application.
The whole putting it cold at 3-500' is a UK flying school nonesense and can simply act as a distraction at a rather critical phase of flight. The only exeption I would include is landing on rough grass when you wouldn't want unfiltered air going into the carb, so would select cold as soon as practical.
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Big_Pistons_Forever
You have said some really important errors in BASIC aircraft operation and also in airmanship. Now you seem like a pretty opnionated person, so i will leave you to discover and note your shortfall.
You have said some really important errors in BASIC aircraft operation and also in airmanship. Now you seem like a pretty opnionated person, so i will leave you to discover and note your shortfall.
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ABGD
The best advice i can offer is to consult official sources. Dont listen to bods on here (including me)
If in doubt, there is NO doubt. And if in doubt, chicken out !
Ice is a problem - get rid of it! Carb heat induces a loss of power (recall carb heat check on run up) so lose it !..especially on final !
Inbox me dude, i'm from around your area :-p
The best advice i can offer is to consult official sources. Dont listen to bods on here (including me)
If in doubt, there is NO doubt. And if in doubt, chicken out !
Ice is a problem - get rid of it! Carb heat induces a loss of power (recall carb heat check on run up) so lose it !..especially on final !
Inbox me dude, i'm from around your area :-p
Could you be more specific as to which "official sources" advocate turning off the carb heat on final ? I am asking because I am not aware of any aircraft manufacturer supporting this practice. Is the CAA the ones who are pushing this ?
I tend to listen to lots of people and also check with the official sources.
My view is that conditions and aircraft vary, so there can be no one true checklist to cover all situations. You get the basic protocol nailed, then occasionally adjust it on the basis of principles and experience. Hence my interest in what people here have to say. It would never have occurred to me that you could get carb icing as quickly as some here have experienced, for example, as the only carb icing I've ever encountered has been relatively insidious.
My view is that conditions and aircraft vary, so there can be no one true checklist to cover all situations. You get the basic protocol nailed, then occasionally adjust it on the basis of principles and experience. Hence my interest in what people here have to say. It would never have occurred to me that you could get carb icing as quickly as some here have experienced, for example, as the only carb icing I've ever encountered has been relatively insidious.
Last edited by abgd; 5th May 2012 at 02:12.
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but before touch down (approx 100 feet) carb heat MUST be set to COLD. The reason for this is simples = if you are forced to do a go around, full engine output will be required to ascend,
If, the pilot decides to overshoot, the carb heat can be moved to the cold position quickly - in many aircraft, without removing one's hand from the throttle. Certainly easily in any aircraft, and without detracting from the ability of the pilot to safely control the aircraft on climbout. A pilot who's workload is too high when having to select carb heat cold at the time of the decision to overshoot, is perhaps flying beyond their skill. It gets a lot more busy when you're flying a multi, and having to reconfigure flaps, cowl flaps, trim, and get the gear up after positive rate - carb heat is nothing compared to all of that!
The aircraft will safely climb with the carb heat hot, if all other things as they should be. Certainly at least enough climb to begin the overshoot, and get the aircraft reconfigured. If you think about it, the application of carb heat generally reduces the RPM (for fixed pitch prop engines) about 100 or so. Can you takeoff and climb away a C 150 at 2400RPM instead of 2500+? Of course you can. It's going to take more space, but is safely possible in most normal dimension runways. For the C 150, takeoff and climb away is possible at engine speeds as slow as 2100 RPM - though it's going to take a lot more runway and clearway. If you're going into a runway from which you cannot safely overshoot carb heat hot, you have already committed yourself to a landing from which a safe overshoot is not possible - and there are some, so it happens.
BTW I note you have listed your age as 28. I started my commercial flying career when I was 27, I am now 52
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Love/Hate
I always find these threads useful as they make me think about my own current knowledge/skill and what should I brush up on.... 
What makes me despair however is the constant 'dick-measuring' which adds absolutely nothing to the debate...
As for the Trolls and armchair pilots on PPRuNe!
What makes me despair however is the constant 'dick-measuring' which adds absolutely nothing to the debate...
As for the Trolls and armchair pilots on PPRuNe!
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I'm delighted that I don't have to worry about selecting and deselecting carb heat.
I fly a Rotax 4 stroke engined aircraft. The carb bodies are permanently heated by the engine coolant but there is no power loss because the air entering the carbs is at ambient temperature.
I fly a Rotax 4 stroke engined aircraft. The carb bodies are permanently heated by the engine coolant but there is no power loss because the air entering the carbs is at ambient temperature.
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I was always taught to select carb heat downwind and leave it on until you land. I can't see the problem on a go round, you just shove the carb heat and throttle forward at the same time. You might have to take another half second to do it on a 28. I suppose a minor advantage as well is that if your idle setting is slightly high you would have less residual thrust when on the landing roll.
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As the OP of this thread I have found it extremely interesting and educational reading the different viewpoints on carb heat use, I have deduced the following:
1. Re-read and understand what the AFM says, and just as importantly what it DOES NOT say in regards to carb heat.
2. Carry with me the “carb icing danger zone chart” and understand how to relate its calculations to the combination of actual weather conditions before/ during flight and prior to the finals
3. When considering when to engage and disengaging car heat be cognizant of not just the elements (temperature, humidity etc.) but also field conditions such as thin grass with loose dirt, fleshly cut grass and wet grass both on TO and landing that can bypass air filtration when crab heat is on and cause additional problems. But remembering that if faced with a choice, unfiltered air is better than an iced carb
4. When in doubt whatsoever there is very little downside in any flight configuration to putting the carb heat on to verify there is no icing.
5. If landing in the conditions susceptible to carb icing keeping carb heat on all the way down till reaching ground effect, then only closing the carb heat due to either having to go around or conditions on the ground favouring filtered air such is the case on my airstrip which swings from wet to dusty with a thin cover of grass
6. Expect the unexpected and expect it happening quick and at times of high workload. And carb icing can happen pretty much at the entire normal temperature range for the area I fly in.
Thanks folks
1. Re-read and understand what the AFM says, and just as importantly what it DOES NOT say in regards to carb heat.
2. Carry with me the “carb icing danger zone chart” and understand how to relate its calculations to the combination of actual weather conditions before/ during flight and prior to the finals
3. When considering when to engage and disengaging car heat be cognizant of not just the elements (temperature, humidity etc.) but also field conditions such as thin grass with loose dirt, fleshly cut grass and wet grass both on TO and landing that can bypass air filtration when crab heat is on and cause additional problems. But remembering that if faced with a choice, unfiltered air is better than an iced carb
4. When in doubt whatsoever there is very little downside in any flight configuration to putting the carb heat on to verify there is no icing.
5. If landing in the conditions susceptible to carb icing keeping carb heat on all the way down till reaching ground effect, then only closing the carb heat due to either having to go around or conditions on the ground favouring filtered air such is the case on my airstrip which swings from wet to dusty with a thin cover of grass
6. Expect the unexpected and expect it happening quick and at times of high workload. And carb icing can happen pretty much at the entire normal temperature range for the area I fly in.
Thanks folks
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Big_Pistons_Forever
Unfortunately i am very poor at articulating your errors, so i will leave you to measure how big your pistons are.........although i'm guessing there pretty big :-) Regarding my age....i'm actually a 75 year old ballet dancer..which confirms ???
Unfortunately i am very poor at articulating your errors, so i will leave you to measure how big your pistons are.........although i'm guessing there pretty big :-) Regarding my age....i'm actually a 75 year old ballet dancer..which confirms ???
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Good try at a reasonable thread Piperboy. I'm happy for you that you got some useful responses, before the thread drifted into silliness. I would take Big Piston's advice verbatim any day. You can see that there are varied ways in which carb heat is used by pilots. and some passion about it too.
Keep your eyes open for an opportunity to fly an aircraft equipped with a carb air temperature indicator - watching that while selecting carb heat, and then adjusting the power and mixture to optimize the heat, is an education. What you will see is that the techniques which are taught, are often only a part of the story. The flight manual techniques err to the simple and conservative, as one would expect. Pilots who feel confident that they have assured their security from carb ice simply by selecting carb heat, and then ignoring the other engine controls could be in for disappointment - I have been. Like any control of the aircraft, carb heat should be applied as a part of good, informed pilot decision making.
I applaud your effort to become more informed. Good attitude! Perhaps another will begin to act their age - well, at least one of them.....
Keep your eyes open for an opportunity to fly an aircraft equipped with a carb air temperature indicator - watching that while selecting carb heat, and then adjusting the power and mixture to optimize the heat, is an education. What you will see is that the techniques which are taught, are often only a part of the story. The flight manual techniques err to the simple and conservative, as one would expect. Pilots who feel confident that they have assured their security from carb ice simply by selecting carb heat, and then ignoring the other engine controls could be in for disappointment - I have been. Like any control of the aircraft, carb heat should be applied as a part of good, informed pilot decision making.
I applaud your effort to become more informed. Good attitude! Perhaps another will begin to act their age - well, at least one of them.....