Carb heat, while enroute

AggieMike88

AggieMike88

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The original "I don't know it all" of aviation.
Whats the word on using carb heat while enroute?

During today's flight, we observed the carb heat guage showing a carb temp between 32°F and 35°F.

When I observe this during lower power phases (such as entering the approach), I pull the carb heat out to half, and then full when on final approach.

Should it be used enroute when I'm at my planned cruise power settings?
 
I personally would not use it in cruise unless there was noticeable power loss. The air temp may be sufficient for carb icing at cruise altitude but you may or may not have enough moisture to make it happen. Why rob your engine of power when you don't need to? Others I am sure will have varying opinions.

David
 
flhrci said:
I personally would not use it in cruise unless there was noticeable power loss. The air temp may be sufficient for carb icing at cruise altitude but you may or may not have enough moisture to make it happen. Why rob your engine of power when you don't need to? Others I am sure will have varying opinions.

David
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Since I'm getting into IFR style flying, and eventually will be in the clouds, the "moisture" part of your response is the part I'm curious about.
 
I had an engine shut down during cruise due to, I suspect, carb ice. Of course we were flying at several hundred feet AGL at the time and carb heat brought it back before there was any necessity to put it into the trees.
 
Get a carb temp gauge, and use it. keep it in the yellow or above even it requires all the heat you can't.
 
Tom-D said:
Get a carb temp gauge, and use it. keep it in the yellow or above even it requires all the heat you can't.
Click to expand...

Such a gauge is on the aircraft. Which is what started my search for more knowledge.
 
AggieMike88 said:
Whats the word on using carb heat while enroute?

During today's flight, we observed the carb heat guage showing a carb temp between 32°F and 35°F.

When I observe this during lower power phases (such as entering the approach), I pull the carb heat out to half, and then full when on final approach.

Should it be used enroute when I'm at my planned cruise power settings?
Click to expand...

If I'm IMC, I use carb heat to stay above the orange stripe. If there's visible moisture out (precip, bad haze, etc.), I'll add enough carb heat to stay out of the orange stripe. Going half or full "just because" when you have a Carb Heat gage is counterproductive.
 
I've never developed carb ice enroute. That said, it is possible.

Never use partial carb heat though. That's a no-no. It's either full on or off!
 
I had to use carb heat in a 150 (O-200) going into Osh years ago in order to keep the engine running.
It would wind down gradually then stumble until I put the heat on whereupon it would return to full function, except a bit rich.
After several of these events I left it on full for the last 20 miles and leaned it out.
It was a 75°F day, below a low overcast, with plenty of haze.
 
Let'sgoflying! said:
I had to use carb heat in a 150 (O-200) going into Osh years ago in order to keep the engine running.
It would wind down gradually then stumble until I put the heat on whereupon it would return to full function, except a bit rich.
After several of these events I left it on full for the last 20 miles and leaned it out.
It was a 75°F day, below a low overcast, with plenty of haze.
Click to expand...

With a Carb Temp gage, you'd have known when to add it, and just how much was needed. Without it, you just have to go Full Heat and relean.
 
I'm not well-versed in carb. aircraft. Why can't you use partial heat?

I'd hope it's more than, "my CFI said so..."
 
Cpt_Kirk said:
I'm not well-versed in carb. aircraft. Why can't you use partial heat?
Click to expand...

If you don't have a Carb Temp gage, you don't know how much to add. Partial heat may not be enough to melt the forming ice and prevent additional accumulation.

With a Carb Temp gage, it's only necessary to add enough carb heat to get the temp out of the "danger zone," which is an orange stripe on mine.
 
Hank S said:
If you don't have a Carb Temp gage, you don't know how much to add. Partial heat may not be enough to melt the forming ice and prevent additional accumulation.

With a Carb Temp gage, it's only necessary to add enough carb heat to get the temp out of the "danger zone," which is an orange stripe on mine.
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So, sort of like leaning with no engine gauges. Do it all the way or don't do it at all. I just didn't know if there was possibly something wonky about only using partial heat.
 
I've read some old geezer's who say they run with carb heat in cruise and lean into it. Anything else is flooding your engine aka wasting gas.

I don't subscribe to this, as I was taught that carb heat robs power.

I'll pull carb heat on a long high letdown then go back to off for pattern work. Never have had any problems. I don't pull heat to remain out of the yellow (I have a guage). Only on letdown or occasionally just to clear any ice then it's back off.
 
txflyer said:
I don't subscribe to this, as I was taught that carb heat robs power.
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The reason the power goes down is carb heat richens the mixture. If you adjust the mixture afterwards, you're not really loosing anything.

The argument really is whether you should use prophylactic carb heat, if you have a carb temp gauge, or you've got a long low power period of operation, perhaps.

If you do get signs of apparent carb ice, then no you don't want partial heat. Add both heat and all the power you can until it clears.

Used to have a Pressure Carb on the Gopher. Was always told those were immune to carb ice but Margy managed to ice up on a short hop (2W5 back to VKX) where she kept the power low so she'd not climb or get too much faster than the gear speed. The engine sputtered about the time she hit downwind. Since we've had problems with the engine she just pointed it at the numbers. I figured out what it was after we rolled out and applied the heat and a little power.

Of course the Gopher was replaced with an IO-550 so I've not had to worry about carb ice in a long time.
 
Friends don't let friends fly family around in a cessna installed carbed engine. :no:

Joking aside, I sold my warrior and got an Arrow in part due to my desire to get away from the whole proposition of flying behind a carburetor. The Warrior never gave me much hassle but on one late night in Oklahoma City going back to Shreveport, where it gave me a scary stumble 10 seconds after liftoff, behavior compatible with a chunk of ice dislodging from the carb and being ingested as the engine's rising oil temperature heated the carb by conduction. Carb check on the ground (long idling taxi on KOKC obviously, though I taxi leaned aggressively) was normal and yet not good enough to clear formation of engine-disrupting ice a mere 2 minutes later. The rest of the flight was uneventful and required no carb heat use. I'm still an avid believer Lyco-Piper installations are the most ice-resistant of the carbed lot, but as I added my kid into the mission profile, I decided it was enough finicky stupidity to entertain the whole carb business. It's 2015, fuel injection for me from here on out.
 
This carb ice syndrome is why the 210 is a good alternative.
 
flhrci said:
I personally would not use it in cruise unless there was noticeable power loss. The air temp may be sufficient for carb icing at cruise altitude but you may or may not have enough moisture to make it happen. Why rob your engine of power when you don't need to? Others I am sure will have varying opinions.

David
Click to expand...

Well, because it can help you atomize fuel in carbureted systems more efficiently and allow smoother LOP operations. If you are only going to cruise 65% power anyway, no need to be able to make 80%.
 
When in doubt check it, ain't that big of a deal.

..or just go fuel injected
 
Henning said:
Well, because it can help you atomize fuel in carbureted systems more efficiently and allow smoother LOP operations. If you are only going to cruise 65% power anyway, no need to be able to make 80%.
Click to expand...

My understanding is that this is applicable on the O-470 due to the inherent lousy distribution in the intake. The heat allows better atomization and thus more even mixture between cylinders.

The main reason I heard against partial is that if your temps are just below the danger zone for ice and conditions are right, partial can heat it up just enough to place you in the zone but not hot enough to be over it. Again just something I heard.
 
Mike,

In 1350 hours of flying my 182 I've experienced carb ice exactly once. A PnP trip on a humid fall day. I cleared ice three times before deciding to just leave the heat on for the rest of the fligt. Some claim O-470s are ice machines. Mine's not. And I would not advocate using carb heat until your engine tells you that you need it unless you find that your engine is a constant ice maker.


flyingron said:
The reason the power goes down is carb heat richens the mixture. If you adjust the mixture afterwards, you're not really loosing anything.
Click to expand...

Yes you are. Thinner air requires less fuel to obtain the same mixture ratio. Thus you're making less power when properly leaned with carb heat on than you would be with it off.

Henning said:
Well, because it can help you atomize fuel in carbureted systems more efficiently and allow smoother LOP operations. If you are only going to cruise 65% power anyway, no need to be able to make 80%.
Click to expand...

Anyone who cruises at 65% or less power (at altitudes affording more) behind an O-470 in a 182 is wasting a lot of time quite unnecessarily. Run it WOT...lean until rough, enriched 'till smooth, you'll never hurt the engine.

I used to drink the "warm the air in the winter" tea but I got tired of losing 5 kts or more in cruise. So unless it's really frakin' cold out, like single digits or below, homie don't play no carb heat game.

I do, however, keep my induction crossover tube insulated.

http://www.aircraftspruce.com/search/search.php?s=FIRE+SLEEVE+HOSE&x=0&y=0
 
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flyingron said:
The reason the power goes down is carb heat richens the mixture. If you adjust the mixture afterwards, you're not really loosing anything.
Click to expand...

I agree with Muttley, you're not understanding the physics at play.
Carb heat heats the air before it goes into the engine. Hot air is less dense and therefore has less oxygen per unit volume. The mixture becomes rich because of a reduction of oxygen, not because of an increase in fuel. You lean to correct the mixture for a more complete burn, but you have now reduced power as you are ingesting less oxygen and less fuel for every intake stroke.

You can see this if you dyno an engine on a cold day versus a hot day. The engine will put out more peak power on the cold day, which is why dyno runs are corrected for temperature, pressure, and humidity.
 
Omalley1537 said:
My understanding is that this is applicable on the O-470 due to the inherent lousy distribution in the intake. The heat allows better atomization and thus more even mixture between cylinders.

The main reason I heard against partial is that if your temps are just below the danger zone for ice and conditions are right, partial can heat it up just enough to place you in the zone but not hot enough to be over it. Again just something I heard.
Click to expand...

That's where the carb heat temp gauge comes in, so you KNOW the conditions, not guess at them.
 
My stock cerb temp gauge, which was replaced by a UBG-16, has a yellow arc from -15c to +5c and is placarded "keep needle out of yellow arc during possible carburetor icing conditions."

Emphasis mine.
 
saddletramp said:
I've never developed carb ice enroute. That said, it is possible.
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I have. 250 HP Comanche at full throttle. Almost classic. 70° at my altitude in the clouds. Carb ice serious enough to freeze my throttle in place and require an emergency descent through the clouds and a diversion for an emergency landing.

More generally on the topic, I subscribe to the blurb about use of carb heat en route in the FAA's Winter Flying Tips - P-8740-24
In general, carburetor ice will form in temperatures between 32° and 80° F when the relative humidity is 50% or more. If visible moisture is present, it will form at temperatures between 15 and 32° F. A carburetor air temperature gauge is extremely helpful to keep the temperatures within the carburetor in the proper range. Partial carburetor heat is not recommended if a C.A.T. gauge is not installed.
​
I think Hank gave the reason for the difference: without carb temp, you don't know how much is enough. With one, you do.

If I missed the temperature indications and saw the signs of icing, I'd go full and then use the gauge to maintain.
 
AggieMike88 said:
Since I'm getting into IFR style flying, and eventually will be in the clouds, the "moisture" part of your response is the part I'm curious about.
Click to expand...
What makes you curious? :dunno:

Yes, of course, in the clouds, you have moisture but the moisture doesn't need to be visible, which is why carb ice can be an issue even for VFR flight.

Is that all you meant?
 
midlifeflyer said:
I have. 250 HP Comanche at full throttle. Almost classic. 70° at my altitude in the clouds. Carb ice serious enough to freeze my throttle in place and require an emergency descent through the clouds and a diversion for an emergency landing.

More generally on the topic, I subscribe to the blurb about use of carb heat en route in the FAA's Winter Flying Tips - P-8740-24
In general, carburetor ice will form in temperatures between 32° and 80° F when the relative humidity is 50% or more. If visible moisture is present, it will form at temperatures between 15 and 32° F. A carburetor air temperature gauge is extremely helpful to keep the temperatures within the carburetor in the proper range. Partial carburetor heat is not recommended if a C.A.T. gauge is not installed.
​
I think Hank gave the reason for the difference: without carb temp, you don't know how much is enough. With one, you do.

If I missed the temperature indications and saw the signs of icing, I'd go full and then use the gauge to maintain.
Click to expand...

Just to clarify...they're talking in terms of ambient air temperatures above, and not carb air temps.
 
I use full carb heat in the 152 when the engine tells me so. Sputters etc and conditions are right. No gauge.
 
Here's some nifty little chart I found. Not sure how useful it would really be..

6836376-4x3-940x705.jpg
 
Nice chart, Ted, but °Friday would be better. I've seen one somewhere with air temperature and humidity, requiring no calculations. I check the Carb Temp periodically, especially in high humidity, haze and when IMC. Fortunately my carb is mounted above the oil pan. I can count on my fingers the times I've used carb heat.
 
AggieMike88 said:
Whats the word on using carb heat while enroute?

During today's flight, we observed the carb heat guage showing a carb temp between 32°F and 35°F.

When I observe this during lower power phases (such as entering the approach), I pull the carb heat out to half, and then full when on final approach.

Should it be used enroute when I'm at my planned cruise power settings?
Click to expand...


My understanding is that this has been common/standard practice -- especially for coastal people --- flying O-470's for decades.

If so, than it shouldn't be a problem
 
ollopa said:
I agree with Muttley, you're not understanding the physics at play.
Carb heat heats the air before it goes into the engine. Hot air is less dense and therefore has less oxygen per unit volume. The mixture becomes rich because of a reduction of oxygen, not because of an increase in fuel. You lean to correct the mixture for a more complete burn, but you have now reduced power as you are ingesting less oxygen and less fuel for every intake stroke.

You can see this if you dyno an engine on a cold day versus a hot day. The engine will put out more peak power on the cold day, which is why dyno runs are corrected for temperature, pressure, and humidity.
Click to expand...

And if you are at wide open throttle, this makes a difference. If not, you just push the black knob half an inch and get your power back.
 
Capt. Geoffrey Thorpe said:
And if you are at wide open throttle, this makes a difference. If not, you just push the black knob half an inch and get your power back.
Click to expand...

But if you're on any kind of a XC you'll likely be at an altitude that affords, if not dictates, WOT...at least I am.

Maybe that's where the difference lies. Unless headwinds dictate otherwise, I don't fly a XC lower than 5500' because my plane is fastest from there up to 8500' or 9500' on the very outside...depending on temps...pressures...etc. And at those altitudes it's WOT.

And if I'm not on a XC and down lower then I couldn't care less about exactly how fast I'm going.
 
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