Carb heat on Warrior (LYCOMING O-320-D3G)?
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They are not reasons, they are bullet points of what happens when carb heat is on!
This first 4 are EXACTLY what happens with carb heat, which may lend itself to the 5th point of "possible detonation"
To say any are incorrect, shows a basic lack of understanding on the recip powerplant.
This first 4 are EXACTLY what happens with carb heat, which may lend itself to the 5th point of "possible detonation"
To say any are incorrect, shows a basic lack of understanding on the recip powerplant.
crossed swords with him a couple of times but quite like the guy 
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To say any are incorrect, shows a basic lack of understanding on the recip powerplant.
Why don't you go ahead and provide a basic understanding of the "recip powerplant," then. This ought to be good.
First, explain why applying carburetor heat will "increase in cylinder temps/pressures for same output (no heat)."
Next, why don't you explain how enrichening the mixture, or "increasing the fuel air ratio" will cause detonation, "higher cylinder temps," or "higher pressures." That should really be interesting.
Perhaps you can explain how all this happens in a normally aspirated engine with a fixed pitch prop, to keep it simple. I'm looking forward to a good education.
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Originally Posted by barrow
4, increase in cylinder temps/pressures for same output (no heat)
When one applies carb heat the power goes down and the mixture is slightly richer; so do the cylinders really get hotter or do they actually get colder?
So flying a C150/152 or PA28, is pulling the carb heat every 10 minutes or so while doing a FREDA check wrong (in the UK?)
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One hears this a lot.....but is it true?
When one applies carb heat the power goes down and the mixture is slightly richer; so do the cylinders really get hotter or do they actually get colder?
When one applies carb heat the power goes down and the mixture is slightly richer; so do the cylinders really get hotter or do they actually get colder?
Again...what happens when the mixture is enriched? Unless you are already operating lean of peak...where most pilots do NOT operate, when you increase the richness of the mixture, you're going to cause a decrease in the engine temperature.
Not an increase.
The only time that making the mixture richer will cause the engine to get warmer is if one is operating lean of peak. In that case, increasing the mixture towards rich moves the mixture closer to peak EGT and peak cylinder temperatures...and you're going to see an increase in CHT and EGT.
If you're operating with a lean mixture, which is lean of peak, and you lean the mixture, you'll see a temperature decrease. If you're operating rich of peak and lean the mixture, you'll see a temperature increase.
If you're rich of peak and apply carburetor heat, you're making the mixture richer...and cooling the engine.
I know it seems to make sense that increasing the temperature of the air entering the engine might make it run hotter, but that's not the case, and it's a minor thing with respect to the internal operating temperatures. Remember that there's already a fire inside making that engine warm, and that fire is what's determining the CHT and EGT...not the induction air temp. Changing the temperature of the fire inside the engine, the combustion temperature, by changing the mixture ratio, has a far greater effect, because after all, that's what's making the engine hot in the first place. Cool the mixture by moving it farther to the rich side of peak (enrichening a mixture that's already operating rich of peak), and you cool the engine...which is what occurs when you apply carburetor heat.
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REALLY??
Why don't you go ahead and provide a basic understanding of the "recip powerplant," then. This ought to be good.
First, explain why applying carburetor heat will "increase in cylinder temps/pressures for same output (no heat)."
Next, why don't you explain how enrichening the mixture, or "increasing the fuel air ratio" will cause detonation, "higher cylinder temps," or "higher pressures." That should really be interesting.
Perhaps you can explain how all this happens in a normally aspirated engine with a fixed pitch prop, to keep it simple. I'm looking forward to a good education.
Why don't you go ahead and provide a basic understanding of the "recip powerplant," then. This ought to be good.
First, explain why applying carburetor heat will "increase in cylinder temps/pressures for same output (no heat)."
Next, why don't you explain how enrichening the mixture, or "increasing the fuel air ratio" will cause detonation, "higher cylinder temps," or "higher pressures." That should really be interesting.
Perhaps you can explain how all this happens in a normally aspirated engine with a fixed pitch prop, to keep it simple. I'm looking forward to a good education.
What happens to EGT when only one plug fires?
What happens to CHT when only one plug fires?
Does Engine speed have an effect on timing?
Does the mixture have an effect on timing?
Does the angle of the valve placement have an effect on CHT + EGT?
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We get it. You're an automotive genius.
You can't adjust the valve "angle of placement" from the cockpit. Neither can you turn on or off one plug, nor does the firing of one or two plugs have anything to do with adjusting the mixture. Engine timing and speed are equally irrelevant to the use of carburetor heat, or mixture setting in the cockpit. Timing of magnetos is fixed in relation to the engine on reciprocating aircraft engines, and the use of the carburetor heat and the mixture controls is likewise unrelated to timing.
You made some very incorrect assertions...so instead of attempting to introduce even more and tap dance around, why don't you back up about what you said in the first place, instead of defending it.
Show us how application of carburetor heat increases "cylinder temperatures and pressures." Can you do this? You were just very adamant that this is a true statement and that you were not incorrect. Show us how.
You can't adjust the valve "angle of placement" from the cockpit. Neither can you turn on or off one plug, nor does the firing of one or two plugs have anything to do with adjusting the mixture. Engine timing and speed are equally irrelevant to the use of carburetor heat, or mixture setting in the cockpit. Timing of magnetos is fixed in relation to the engine on reciprocating aircraft engines, and the use of the carburetor heat and the mixture controls is likewise unrelated to timing.
You made some very incorrect assertions...so instead of attempting to introduce even more and tap dance around, why don't you back up about what you said in the first place, instead of defending it.
Show us how application of carburetor heat increases "cylinder temperatures and pressures." Can you do this? You were just very adamant that this is a true statement and that you were not incorrect. Show us how.
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Can you answer a few simple questions for me?
What happens to EGT when only one plug fires?
That would depend on whether the EGT is fitted to all exhaust pipes; it's usually only one at the rear of block. The probe is mounted a few inches from the exhaust outlet. And don't forget that there are two plugs per cylinder so there would only be a minuscule amount of change to performance and temperature of any particular cylinder.
What happens to CHT when cylinder only one plug fires?
The CHT is a thermocouple usually attached to the spark-plug copper washer and I doubt whether losing one plug would make any difference; again it's usually only fitted to one cylinder. I believe cylinders would be cracking on a regular basis if there was a real difference between different parts of the cylinder head temperature. And the whole purpose of the fins on the cylinders is for cooling and even dissipation of the temperature.
Does Engine speed have an effect on timing?
No, not if using magnetos, although with electronic ignition it would be possible. However, there are not many aircraft using this as mags are pretty reliable and don't require a battery. Most aircraft engines only rev at a max of 2700 rpm so there is little need for messing about with the timing. If you are considering diesel engines like the Thielert then they rev higher and have a reduction gear to keep propellor speed from going supersonic and they do have electronic ignition with separate emergency battery.
Does the mixture have an effect on timing?
None at all.
Does the angle of the valve placement have an effect on CHT + EGT?
Not sure which valve you mean. If you mean the butterfly valve in the carb/fuel injection system then 'yes' because you are changing the amount of fuel going into the engine.
I'm only considering the general case here but of course there are many exceptions.
What happens to EGT when only one plug fires?
That would depend on whether the EGT is fitted to all exhaust pipes; it's usually only one at the rear of block. The probe is mounted a few inches from the exhaust outlet. And don't forget that there are two plugs per cylinder so there would only be a minuscule amount of change to performance and temperature of any particular cylinder.
What happens to CHT when cylinder only one plug fires?
The CHT is a thermocouple usually attached to the spark-plug copper washer and I doubt whether losing one plug would make any difference; again it's usually only fitted to one cylinder. I believe cylinders would be cracking on a regular basis if there was a real difference between different parts of the cylinder head temperature. And the whole purpose of the fins on the cylinders is for cooling and even dissipation of the temperature.
Does Engine speed have an effect on timing?
No, not if using magnetos, although with electronic ignition it would be possible. However, there are not many aircraft using this as mags are pretty reliable and don't require a battery. Most aircraft engines only rev at a max of 2700 rpm so there is little need for messing about with the timing. If you are considering diesel engines like the Thielert then they rev higher and have a reduction gear to keep propellor speed from going supersonic and they do have electronic ignition with separate emergency battery.
Does the mixture have an effect on timing?
None at all.
Does the angle of the valve placement have an effect on CHT + EGT?
Not sure which valve you mean. If you mean the butterfly valve in the carb/fuel injection system then 'yes' because you are changing the amount of fuel going into the engine.
I'm only considering the general case here but of course there are many exceptions.
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As an FI, I would expect to see carb heat selected to full ON before closing the throttle. Never takeoff with carb heat on (except on the RAF's Chipmunks, when it was wired ON). IT is better to land with it ON than to end up without response on a go-around (you select COLD as you advance the throttle). 
dbee
dbee
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If you are considering diesel engines like the Thielert then they rev higher and have a reduction gear to keep propellor speed from going supersonic and they do have electronic ignition with separate emergency battery.
I'm only considering the general case here but of course there are many exceptions.
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SNS3Guppy, could you please answer the questions, one by one?
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Can you answer a few simple questions for me?
What happens to EGT when only one plug fires?
What happens to CHT when only one plug fires?
Does Engine speed have an effect on timing?
Does the mixture have an effect on timing?
Does the angle of the valve placement have an effect on CHT + EGT?
What happens to EGT when only one plug fires?
What happens to CHT when only one plug fires?
Does Engine speed have an effect on timing?
Does the mixture have an effect on timing?
Does the angle of the valve placement have an effect on CHT + EGT?
The answers are:
a) Increases
b) Slightly decreases
c) If you mean the crank angle at which the plug sparks, not materially across the range of speeds we operate our engines
d) If you mean the crank angle at which the plug sparks, no
e) Yes
Having got that out of the way, any chance you can answer the one question we've been asking you? If you're operating a cylinder ROP (which is quite likely if you haven't yet selected carb heat on, since carb heat and a reduced throttle setting are both generally required to stand much chance of getting a typical carburetted Lycoming or Continental engine to run LOP
), what is it that leads you to believe the cylinder temperatures and pressures will increase when carb heat is applied, given that power output will reduce significantly (maybe by 15%)?
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since carb heat and a reduced throttle setting are both generally required to stand much chance of getting a typical carburetted Lycoming or Continental engine to run LOP
Hmmm...no; carburetor heat doesn't contribute to moving a rich mixture toward a lean of peak setting, and reducing throttle doesn't either.
Any recip engine can easily be run lean of peak...simply by adjusting the mixture to a lean of peak condition. An engine operated lean of peak runs cooler than an engine run at peak...just as an engine run rich of peak runs cooler.
Lean of peak operation is generally recommended by light airplane engine manufacturers, not because it's harmful to the engine if done properly but because pilots don't tend to do it properly...and there's more potential for pilot error. It's actually a much more efficient way to run an engine, when properly done, under the proper circumstances.
---for the benefit of Barrow, edited to say the above should read "Rich of peak operation is..." A typo.
Last edited by SNS3Guppy; 27th Sep 2008 at 18:26.
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SNS3Guppy
Hmmm...no; carburetor heat doesn't contribute to moving a rich mixture toward a lean of peak setting, and reducing throttle doesn't either.
Any recip engine can easily be run lean of peak...simply by adjusting the mixture to a lean of peak condition. An engine operated lean of peak runs cooler than an engine run at peak...just as an engine run rich of peak runs cooler.
Lean of peak operation is generally recommended by light airplane engine manufacturers, not because it's harmful to the engine if done properly but because pilots don't tend to do it properly...and there's more potential for pilot error. It's actually a much more efficient way to run an engine, when properly done, under the proper circumstances.
Hmmm...no; carburetor heat doesn't contribute to moving a rich mixture toward a lean of peak setting, and reducing throttle doesn't either.
Any recip engine can easily be run lean of peak...simply by adjusting the mixture to a lean of peak condition. An engine operated lean of peak runs cooler than an engine run at peak...just as an engine run rich of peak runs cooler.
Lean of peak operation is generally recommended by light airplane engine manufacturers, not because it's harmful to the engine if done properly but because pilots don't tend to do it properly...and there's more potential for pilot error. It's actually a much more efficient way to run an engine, when properly done, under the proper circumstances.
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That should have said "rich of peak operation is..."
A typo.
But then lean of peak operation has been taught since long before you began flying. It's seldom taught today...probably something you wouldn't know about or understand.
You're still unable to provide an answer, then. Like I said...no credibility for you.
A typo.
But then lean of peak operation has been taught since long before you began flying. It's seldom taught today...probably something you wouldn't know about or understand.
You're still unable to provide an answer, then. Like I said...no credibility for you.