Carb heat on Warrior (LYCOMING O-320-D3G)?
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Carb heat on Warrior (LYCOMING O-320-D3G)?
I just can't seem to get a straight answer on this one....
I've always been taught apply carb heat on any carb engine as part of pre-take off, FREDA and downwind checks. This is how I've always operated and continue to operate.
I have the CAA AIC on carb icing and from time to time consult to remind myself of the most dangerous conditions for ice formation.
But I have heard different stories (this has been covered before on here) about the use of the carb heat on the carbed PA28s....
Considering the above imagine my shock at being told by my IR instructor in Florida upon seeing me reach for the carb heat during a FREDA check "nah it's too hot for carb heat" mentally I just said to myself WTF?!! (Temp about 30 dew point about 25). He also seemed to think that oil temperature had a bearing on whether ice would form or not....again something that really surprised me.
Reading the POH however revealed this:
Still not convinced I asked the examiner during my checkride "would you use carb heat now" when we where descending with about 1900RPM set and in close proximity to yet not actually in clouds. "No I would not" came to reply; he had asked the factory and in there opinion during normal descents the use of carb heat was not recommended.
This left me with the impression that Piper are pretty confident that the O-320 engine doesn't really suffer carb icing in normal conditions. How do they know this though? I've never seen a graph that describes ice forming conditions for the PA28....does one exist and what do other people think of this?
I've always been taught apply carb heat on any carb engine as part of pre-take off, FREDA and downwind checks. This is how I've always operated and continue to operate.
I have the CAA AIC on carb icing and from time to time consult to remind myself of the most dangerous conditions for ice formation.
But I have heard different stories (this has been covered before on here) about the use of the carb heat on the carbed PA28s....
Considering the above imagine my shock at being told by my IR instructor in Florida upon seeing me reach for the carb heat during a FREDA check "nah it's too hot for carb heat" mentally I just said to myself WTF?!! (Temp about 30 dew point about 25). He also seemed to think that oil temperature had a bearing on whether ice would form or not....again something that really surprised me.
Reading the POH however revealed this:
The mixture control should be kept in full "RICH" position to ensure maximum acceleration if it should be necessary to open the throttle again. Carburetor heat should not be applied unless there is an indication of carburetor icing, since the use of carburettor heat causes a reduction in power which may be critical in the case of a go-around. Full throttle operation with carburetor heat can cause detonation.
This left me with the impression that Piper are pretty confident that the O-320 engine doesn't really suffer carb icing in normal conditions. How do they know this though? I've never seen a graph that describes ice forming conditions for the PA28....does one exist and what do other people think of this?
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There is a somewhaht different perception of carb icing in the US to the UK. I suspect some of that is the difference in temperatures, or rather the difference between ambient and dew point.
But there is also a big difference between a Lycoming and the Continental ice making machines. i've mainly flown behind the ice making machines - Continental and Gypsy. So your technique is largely the one I have used. But I have also had the same sort of comment in the US about the need for cab heat. Or rather the lack of need of carb heat. Given a good gap between ambient and dew point and a Lycoming then probably carb heat is largely not needed.
But there is also a big difference between a Lycoming and the Continental ice making machines. i've mainly flown behind the ice making machines - Continental and Gypsy. So your technique is largely the one I have used. But I have also had the same sort of comment in the US about the need for cab heat. Or rather the lack of need of carb heat. Given a good gap between ambient and dew point and a Lycoming then probably carb heat is largely not needed.
I've got an FAA diagram of temp, dew point, and carb icing probability. In the U.K. usually only in the coldest air am I outside the carb icing range. There is also high temp at which, regardless of humidity, carb icing cannot occur. The instructors is likely to be right.
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Carburetor heat should not be applied unless there is an indication of carburetor icing, ...
The POH is right: it only makes sense to apply carb heat if there is an indication of carb ice, and it may actually be dangerous to apply carb heat unnecessarily - detonation comes to mind.
But in the absence of carb ice detectors and students who can make perfect judgement calls about whether the situation is conducive to carb ice forming, flying schools have developed some general guidelines which are not damaging to the aircraft and will prevent carb ice from becoming a problem if the conditions happen to be right.
So you and I have been taught to apply carb heat briefly during the runup checks (to melt the ice that may have formed during taxi, and to test the mechanism), to apply carb heat during FREDA in the cruise (to detect formation of carb ice during cruise settings), to apply carb heat on downwind (probably actually as part of the RPM reduction to 2000 or below), and to turn off carb heat just before or after landing so that a go-around is flown without carb heat.
That's all fine. Those practices won't damage the engine and in case the conditions are right for carb ice, they are really effective - provided that your FREDA checks are not too far apart. The fact that a carb heat check as part of FREDA at 30 degree ambient doesn't really makes sense, doesn't really matter.
There are other things that you may have learned to do by rote which do not make sense right now. Some schools insist that the pre-landing checks include a "gear down" check, even in aircraft that have fixed gear. It's nonsense right now, but may save your life (or at least prevent an expensive repair) eventually, some day, in a situation where your mental capacity just fell that tiny bit short.
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There are other things that you may have learned to do by rote which do not make sense right now. Some schools insist that the pre-landing checks include a "gear down" check, even in aircraft that have fixed gear. It's nonsense right now, but may save your life (or at least prevent an expensive repair) eventually, some day, in a situation where your mental capacity just fell that tiny bit short.
I'd just like to know more about the actual testing done on that particular engine to determine when and when it won't suffer carb icing. I know because of the location of the venturi the O-320 doesn't suffer like some Continentals do at 'normal' UK temps/dew points but surely at some temperatures (for example when one might think it is too cold for icing) this may actually make carb icing more likely.....just when you aren't expecting it.
What would be nice is an engine specific version of the CAA AIC on the issue.
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It is a very cheap mode to add an optical icing sensor to a Marvel Schriber carb. One of my friends has done it to his last two aircraft.
Flying beind a B2B 0-320 he very rarely sees any sign of icing. But it does happen - especially when dew point and ambient are close.
My flying behind a C90 and O-200 and Gypsy - I've have significant carb icing many times. With the Gypsy continuous warm air is othen the only way to keep it at bay - but there is no way to fit one of those sensors.............
Flying beind a B2B 0-320 he very rarely sees any sign of icing. But it does happen - especially when dew point and ambient are close.
My flying behind a C90 and O-200 and Gypsy - I've have significant carb icing many times. With the Gypsy continuous warm air is othen the only way to keep it at bay - but there is no way to fit one of those sensors.............
http://www.caa.co.uk/docs/33/ga_srg_07webSSL14.pdf
It's the same. I just got the FAA one years ago, before the CAA one. Link above to CAA site explains the lot.
It's the same. I just got the FAA one years ago, before the CAA one. Link above to CAA site explains the lot.
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I have been taugh that the application of carb heat cannot be of any danger with the throttle open at 75% or less so I would say, WHEN in DOUBT of icing formation, just apply.
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Lycoming states that carburetor ice will occur in the 20 to 90 degrees F. temperature range but it also depends on the humidity. I've been suffering quite bad carb ice with my 0320 on the Northwest coast of the USA over the last week or so. It's been approximately 80+% humidity, 70 degrees F, dewpoint 64 degree F.
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Surely the point in applying carb heat during the runup is to ensure that the carb heat selection is functioning, *should* you need it in flight...
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Mark 1234 and Skyhawk N are both correct; it's to check that it's working, it's also to ensure the carb ice is removed prior to beginning the takeoff roll.
Don't assume that the procedures for one airplane apply to all airplanes, or more specifically, simply because this or that is the way you've done it before, you should do it that way all the time.
Apply carb heat where you need it, when you need it.
Simply because you're not normally recommended as needing it during a go-around, for example doesn't mean you won't need it. I've had engines quit as I or a student executed a go-around, with power restored by the application of carburetor heat.
Use it when you need it.
Don't assume that the procedures for one airplane apply to all airplanes, or more specifically, simply because this or that is the way you've done it before, you should do it that way all the time.
Apply carb heat where you need it, when you need it.
Simply because you're not normally recommended as needing it during a go-around, for example doesn't mean you won't need it. I've had engines quit as I or a student executed a go-around, with power restored by the application of carburetor heat.
Use it when you need it.
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Carb ice can certainly occur when not expected, taxiing included. The comments suggesting a reference to the POH are obviously the best to follow. Do remember that not only does the use of carb heat cause a slight loss of power, but to be the most effective, it is vital to lean/relean the engine after application, the obtain the greatest effect. If you actually need the carb heat to deice the carb, the engine may already be running a little more rich than is intended, due to restricted airflow. When you select carb heat, you introduce hooter air, which is less dense (similar to a higher altitude), so less power. Less power equals less exhaust gass temperature, which is the source of heat for the carb heat in the first place. So, to get the heat back, lean the engine. That will increase the EGT again, and you'll get much hotter air, and thus more effective carb heat.
Also, my certification testing of several carb heat systems, including my Cessna 150, indicates that if you really have to get rid of ice in the carb in flight, the very best result will be attained with a power setting much less than full power. I attribute this to the lower mass airflow through the exhaust heat exchanger and carb, which allows the air to heat up more, and carry more of that heat to the offending carb ice. This reduced power setting also allows many engines to be operated at, or beyond peak lean without damage (consult you engine's manual please). Therefore, without an exhaust gas temperature gauge, you can lean for heating effect simply by bringing the mixture toward lean until the engine stumbles, then richening it a little (with carb heat already hot).
In my 150, an RPM of about 2100 and peak lean with carb heat hot gives the best result (I have a carb air temperature gauge). Incresing power fromthis setting will result in coller carb air temperatures, thus, one would presume, less effective carb deicing.
Also be cautious that the use of carb heat as a preventative measure, can create a different problem. If the moisture in the air is just below freezing (yes, you can have water drops in air which is jut below freezing), and the carb air temperature is also less than freezing, there is a chance that the water will go right through the carb without interfering with the way the engine ran. If you apply carb heat, you can warm the moisture, which then may refreeze in the carb. I have been able to produce this effect at times. In this case, carb heat cold would have been safer.
Also remember that the use of carb heat on the ground removes the air filter from the induction air circuit (on purpose), thus if it is dusty, that's wht's going through your engine. It is agreed though that dusty and moist do not usually occur at the same time in air.
For what it's worth, I (while using a carb air temperature gauge) never use carb heat, inless it's use is indicated by the conditions. I check it's working, and that's it. Only in moist conditions, when the carb air is right around freezing do I apply carb heat, and then only enough to bring the carb air up out of the freezing range.
The application of carb heat will not cause harmful detonation in the engine, if it is otherwise being run properly (correct octane gasoline and not over square for normaly aspirated engines)
Pilot DAR
Also, my certification testing of several carb heat systems, including my Cessna 150, indicates that if you really have to get rid of ice in the carb in flight, the very best result will be attained with a power setting much less than full power. I attribute this to the lower mass airflow through the exhaust heat exchanger and carb, which allows the air to heat up more, and carry more of that heat to the offending carb ice. This reduced power setting also allows many engines to be operated at, or beyond peak lean without damage (consult you engine's manual please). Therefore, without an exhaust gas temperature gauge, you can lean for heating effect simply by bringing the mixture toward lean until the engine stumbles, then richening it a little (with carb heat already hot).
In my 150, an RPM of about 2100 and peak lean with carb heat hot gives the best result (I have a carb air temperature gauge). Incresing power fromthis setting will result in coller carb air temperatures, thus, one would presume, less effective carb deicing.
Also be cautious that the use of carb heat as a preventative measure, can create a different problem. If the moisture in the air is just below freezing (yes, you can have water drops in air which is jut below freezing), and the carb air temperature is also less than freezing, there is a chance that the water will go right through the carb without interfering with the way the engine ran. If you apply carb heat, you can warm the moisture, which then may refreeze in the carb. I have been able to produce this effect at times. In this case, carb heat cold would have been safer.
Also remember that the use of carb heat on the ground removes the air filter from the induction air circuit (on purpose), thus if it is dusty, that's wht's going through your engine. It is agreed though that dusty and moist do not usually occur at the same time in air.
For what it's worth, I (while using a carb air temperature gauge) never use carb heat, inless it's use is indicated by the conditions. I check it's working, and that's it. Only in moist conditions, when the carb air is right around freezing do I apply carb heat, and then only enough to bring the carb air up out of the freezing range.
The application of carb heat will not cause harmful detonation in the engine, if it is otherwise being run properly (correct octane gasoline and not over square for normaly aspirated engines)
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Ok, I should have worded that more precisely 
What I meant to communicate was: Even if icing is unlikely, one should still test the carb heat during the runup to ensure it is functioning, in case you should for some reason need it later!
I confess I do mindlessly apply carb heat once I throttle back on base then knock it off turning final; I was taught not-above 2000rpm unless dictated by icing. I guess that's attempting to mitigate people feeding the engine excessively hot air at flat chat.
What I meant to communicate was: Even if icing is unlikely, one should still test the carb heat during the runup to ensure it is functioning, in case you should for some reason need it later!I confess I do mindlessly apply carb heat once I throttle back on base then knock it off turning final; I was taught not-above 2000rpm unless dictated by icing. I guess that's attempting to mitigate people feeding the engine excessively hot air at flat chat.
Carb heat also depends on the model of aircraft. In the PA28 series, the carb inlet is in a position in the cowling where warm air is drawn in so an element of carb heat already exists. The POH reflects this is it's advice already mentioned here.
Also, WRTo cooling in the carb, the venturi effect will cool about 15 degrees and evaporation about another 15. There is a school of thought that carb icing is not possible over 30 degrees OAT. (Not likely in the UK!).
Having said that, caution is the best policy.
Also, WRTo cooling in the carb, the venturi effect will cool about 15 degrees and evaporation about another 15. There is a school of thought that carb icing is not possible over 30 degrees OAT. (Not likely in the UK!).
Having said that, caution is the best policy.
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I've about 200 hours on PA28s with O320s and O360s, so not a huge amount compared to some of the other posters.
Having "gone through the motions" for over a 100 hours of carb ice free flying on PA28s, I was doing a few night circuits with an instructor on a lovely moonlit early November night.
Having started up and taxied to the hold, apparently all normal, I appplied the carb heat during the power checks.
There was coughing and misfiring as I'd never heard before
The instructor turned to me and said word to the effect that it was a surprise we'd picked up carb ice on a nice night like this, but it just goes to show how it can happen and why the checks exist.
ILAFT.
Having "gone through the motions" for over a 100 hours of carb ice free flying on PA28s, I was doing a few night circuits with an instructor on a lovely moonlit early November night.
Having started up and taxied to the hold, apparently all normal, I appplied the carb heat during the power checks.
There was coughing and misfiring as I'd never heard before
The instructor turned to me and said word to the effect that it was a surprise we'd picked up carb ice on a nice night like this, but it just goes to show how it can happen and why the checks exist.
ILAFT.
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Reading the POH is usually the key - with a Gypsy it is recommended that you use hot air on the ground in dusty conditions! (the induction route has a sharp 90 deg bend which much reduces the dust ingested!).
Taxiing on wet grass is a classic location for severe carb icing, my C90 would require hot air if idling for any time.
Taxiing on wet grass is a classic location for severe carb icing, my C90 would require hot air if idling for any time.
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Carbu Heat should be used when the OAT is between +20 and -5ºC with visible moisture present. Visible moisture would be in the clouds, rain or bad visibilty. If you have 20 Km visibility there would not be a lot of moisture in the air.
If you use it to prevent ice forming AND you have a Carburetor temperature indicator you should apply just enough heat to get the temperature 5 degrees C above the yellow arc.
If you use it to get rid of icing that has accumulated allready you should use full heat, then when icing has disipated adjust heat to 5º above the yellow arc.
If you have no carbu temp indicator I would use full heat.
You should not use carbu heat on the ground for a prolonged time unless absolutely necessary. Because as you may or may not know, when using carbu heat the air going to the carburator does no longer pass through the air filter and therefore you can suck dust, sand or other particles in the engine.
If you use carbu heat (certainly full and with high powersetting) it may be necessary to lean because otherwise the mixture becomes too rich.
However it all depends on the engine type. In my experience with the SF260 (Lycoming O-540-E4 A5) it is very prone to get carbu icing. A symptom of carbu icing in that aircraft is that when you change power from about 75% power to full power the engine would start running rough and hesitating while changing the throttle.
Using full heat in this aircraft results in a huge loss of power and a very rough running engine so leaning is then absolutely necessary.
On the other hand, the C152 is in my opinion less likely to build up carbu ice and if you use full carbu heat you do not notice a lot of diference in how the engine runs.
If have no experience in the PA28
Hope this helps.
Bart
If you use it to prevent ice forming AND you have a Carburetor temperature indicator you should apply just enough heat to get the temperature 5 degrees C above the yellow arc.
If you use it to get rid of icing that has accumulated allready you should use full heat, then when icing has disipated adjust heat to 5º above the yellow arc.
If you have no carbu temp indicator I would use full heat.
You should not use carbu heat on the ground for a prolonged time unless absolutely necessary. Because as you may or may not know, when using carbu heat the air going to the carburator does no longer pass through the air filter and therefore you can suck dust, sand or other particles in the engine.
If you use carbu heat (certainly full and with high powersetting) it may be necessary to lean because otherwise the mixture becomes too rich.
However it all depends on the engine type. In my experience with the SF260 (Lycoming O-540-E4 A5) it is very prone to get carbu icing. A symptom of carbu icing in that aircraft is that when you change power from about 75% power to full power the engine would start running rough and hesitating while changing the throttle.
Using full heat in this aircraft results in a huge loss of power and a very rough running engine so leaning is then absolutely necessary.
On the other hand, the C152 is in my opinion less likely to build up carbu ice and if you use full carbu heat you do not notice a lot of diference in how the engine runs.
If have no experience in the PA28
Hope this helps.
Bart