Carb Heat during Cruise

Chilito

Chilito

Pre-Flight
Joined
Aug 8, 2019
Messages
55
Location
MN
Display Name
Display name:
Chilito
Hi, everyone. My C150 has a Westach Carb Temp gauge (yellow "danger" zone indicated as -10c to +10c). Today while flying here in MN (temp 8c dewpoint 2c), the gauge indicated between 2-5c for majority of the flight, into the "danger" zone. Various 'ice probability charts' showed significant icing possible during cruise and glide power, so I wasn't totally surprised.

I am constantly scanning, particularly RPMs, and did not notice any significant drops. My question is: Is it safe to fly with the gauge in the danger zone? If I wanted to fly outside of it, I would have had to keep partial carb heat on for the duration of the flight - which I know has been discussed on other threads. I did bump it on for a little bit every now and then as a precaution. Thoughts are appreciated - and yes, I realize that the C150's primary function is an ice maker!
 
Without visible moisture or high humidity I have never seen anything RPM wise that would bother me but we are high and dry in Colorado. I have used carb heat above 16,000 and the engine actually ran better, something about better atomization of the fuel.
 
As a precaution, every half hour or so, put carb heat on for a couple of minutes, then normal. If no change in RPM from before to after, fine, no ice. If the RPM drops, and goes down some more after heat is applied, you are clearing ice, and give the heat a good long time to be sure that it is all gone. Continental engine intake manifolds are notorious for ice melting loose, and moving, then hanging up .

For others reading here, if you are in conditions that do produce some ice, put carb heat on and leave it on, leaning to max RPM. At mos altitudes, the performance reduction is not noticeable, and the possibility of ice is gone.
 
I run partial heat in my carbureted 182 when it is cold. Keeps the gauge out on the yellow and helps vaporize the fuel
 
Pilots are not supposed to use partial carb heat because there is a danger that the heat will just barely melt the ice, and the resulting water will flow further up the induction plumbing and re-freeze. This refrozen ice may not be meltable by the carb heat even on full.

This problem is eliminated with the proper use of the carb temperature gauge. If you keep the carb temp out of the danger zone you will be fine. In this case using partial carb heat to keep the needle out of the zone is good engine management. Do it! Avoid the Danger Zone!

-Skip
 
pull it one in a while, doesnt hurt
 
Bear in mind when carb heat is on you are bypassing your air filter. Use only as necessary. By all means check it occasionally if concerned about icing conditions. Icing is more likely in partial throttle conditions, but of course can occur any time if conditions are right. Those of us without carb temp gauges do just fine by monitoring engine performance and being aware to check carb heat if justified by atmospheric conditions.
 
chemgeek said:
Bear in mind when carb heat is on you are bypassing your air filter. Use only as necessary. By all means check it occasionally if concerned about icing conditions. Icing is more likely in partial throttle conditions, but of course can occur any time if conditions are right. Those of us without carb temp gauges do just fine by monitoring engine performance and being aware to check carb heat if justified by atmospheric conditions.
Click to expand...

for that reason i liked shutting it off before landing
 
James331 said:
for that reason i liked shutting it off before landing
Click to expand...

Before landing checklists: engage carb heat

After landing checklist: close carb heat

Every single carbed plane is the same that I’ve seen.

At what point during landing do you close it? Just asking because you have much more experience than
me. When do you close it? I can see the potential advantage on a go around.
 
woodchucker said:
Before landing checklists: engage carb heat

After landing checklist: close carb heat

Every single carbed plane is the same that I’ve seen.

At what point during landing do you close it? Just asking because you have much more experience than
me. When do you close it? I can see the potential advantage on a go around.
Click to expand...

Been a while since I flew a carb, but short final, extra power for GA if needed and also as I get closer to the dirty dirty terra firma I now have filtered air.
 
woodchucker said:
Before landing checklists: engage carb heat

After landing checklist: close carb heat

Every single carbed plane is the same that I’ve seen.

At what point during landing do you close it? Just asking because you have much more experience than
me. When do you close it? I can see the potential advantage on a go around.
Click to expand...
I started removing carb heat on short final, but I too have a C150 and go arounds are tough if you forget to remove carb heat.
 
geezer said:
... At mos altitudes, the performance reduction is not noticeable....
Click to expand...
Take a ride in my Warrior and I'll show you "noticeable". 800 fpm climb drops to near 0 with carb heat at full throttle.
 
woodchucker said:
Before landing checklists: engage carb heat

After landing checklist: close carb heat

Every single carbed plane is the same that I’ve seen.

At what point during landing do you close it? Just asking because you have much more experience than
me. When do you close it? I can see the potential advantage on a go around.
Click to expand...

You must not have seen many airplanes. The Piper Warrior/Archer, Gruman Tiger/Chetah and Cessna 182RG are carbureted models that do not tell you to open prior to landing and close after landing. They tell you to use carb heat if required. I am sure there are plenty more.
 
Last edited:
woodchucker said:
Before landing checklists: engage carb heat

After landing checklist: close carb heat

Every single carbed plane is the same that I’ve seen.

At what point during landing do you close it? Just asking because you have much more experience than
me. When do you close it? I can see the potential advantage on a go around.
Click to expand...
Every single carbed plane I've seen except for the entire Cherokee fleet.
 
Flew my 150 for years in Ohio. Got carb ice once, and there was visible moisture accompanying it. If there isn't any visible water you're probably OK. If there is, you'll find out about it quick, turnoff the carb heat, and all will be well.
 
The use of carb heat at pattern altitude can lead to some excitement if you do have ice. The engine going silent on downwind isn’t a fun way to end a flight. Carb heat toward the end of a low power descent makes sense, but any time you pull heat you need to be prepared to have the engine quit. In cold weather with low power you may not have enough heat to melt ice, either, depending on your heat source.

I had a yellow range carb heat instrument for about 15 years until I added an engine monitor. Because of the persistent myth that big Continentals may have more balanced cylinder temps with partial carb heat I included carb temp in the engine monitor package. I used it once for a few minutes. Long enough to dispel the better cylinder temp myth. I’ve never used it since.
 
In the Cub, it's a normal occurrence on hazy, humid days to have the carb heat on to some degree during the flight.
One of the Cubs I fly is so bad it will ice up taxiing down the runway to do the engine run-up.
For landing, I pull carb heat as I pass 2,000 rpm, and 1,700 ft AGL.
 
If you are flying in conditions where carb ice is likely to form, and you have a panel instrument for carburetor temperature, then use carb heat. Please. I’d suggest using full heat initially, in case there’s already some ice needing cleared. Then back it off as necessary to keep carb temperature in the safe zone, and re-lean the engine. Simple.

There are some in-carb videos of actual carb ice. It’s surprising how much ice has to develop before engine roughness occurs.

I wouldn’t spend much time thinking of filtered versus not-filtered air, either. Once you’re at pattern altitude or so, the amount of particulate in the air is considerably reduced. Besides, carbureted engines choked with ice seldom make it to TBO, but neither do their pilots.

Just shut it off as soon as you can after landing. And abruptly killing the heat when you do a go-around should just be routine muscle memory.
 
Does the C150 have a green band on the tachometer? For Cessnas I was taught that when the RPMs were in the green, no carb heat needed unless indicated by symptoms. When the RPMs were not in the green, carb heat was to be ON.
 
It's not just Piper vs Cessna for the carb heat differences in POH.

It's Continental vs Lycoming. RV's tend to have lycosaurs up front and are more "Cherokee like" than "Cessna like."

Can we overgeneralize to: High Wings, lots of carb heat, Low Wings, not so much? <- that wasn't a serious question
 
RVs use carburetors? Old school!

Lots of Lycoming-powered Cubs make ice. Mine didn't. Cessna 180s are know to be good ice makers. Mine doesn't make ice but a guy I know has an essentially identical airplane. Same year, same mods, and his is a big time ice maker. Guys need to get to know their own planes and manage them for what they are.

Personally I think how airplanes make ice has as much to do with the operator as the airplane.
 
chemgeek said:
Bear in mind when carb heat is on you are bypassing your air filter. Use only as necessary. By all means check it occasionally if concerned about icing conditions. Icing is more likely in partial throttle conditions, but of course can occur any time if conditions are right. Those of us without carb temp gauges do just fine by monitoring engine performance and being aware to check carb heat if justified by atmospheric conditions.
Click to expand...

At altitude that air filter is doing nothing unless there's a volcano belching somewhere nearby. If you can't see dust in the air, as in reduced visibility, it isn't a factor. I once owned a British type-certified airplane that had no air cleaner at all. None. It should have, as I found wear in the cylinders that was caused by dust during off-airport operations. Boats have no air cleaners at all.

One of the things the regs require a pilot to do before flight is a check of the weather. And two of the METAR items are the temp and dewpoint. If one is savvy enough to understand carb ice and the conditions that are favorable to it, the temp-dewpoint spread says it all. Fine today, maybe. Tomorrow might have a three-degree spread, and carb ice is very possible in a lot of airplanes. It should come as no surprise when a carb ices up.
 
Then there's the TO-360. I always found it funny they happen to come with carb heat. I always thought that orange glow turbine in the oven hot compartment would be enough for the intake manifold. Even the Lycoming manual for it essentially says "yeah, this thing won't ice up in cruise, so don't worry about it...". LOL :D My kind of carb installation. :rofl:
 
I was told in no uncertain terms by all the instructors I've ever had to either have a carb heat fully on or fully off never in between


the logic being that you'll heat the air up just enough that ice will form further downstream and you will be screwed


*in my experience, granted I haven't flown a carbureted aircraft in probably three years, but in my experience if you lean you can gain back the RPM loss...



**mini rant: this whole full rich thing is also somewhat moronic, I really don't understand why more effort isn't given in primary training on educating how an internal combustion engine actually works and the stoichiometric air fuel ratio.. granted many 1970 relic aircraft have the bare minimum of engine instruments, but if you've got a JPI or some kind of half capable engine monitor and you've read the poh then you should know for giving atmospheric conditions what your best power fuel flow and manifold pressure settings should be..
 
mryan75 said:
Every single carbed plane I've seen except for the entire Cherokee fleet.
Click to expand...
The difference has many reasons, the first is the Lycoming vs Continental engine, second is the location of the carb on Pipers v Cessnas. There are others, don’t remember but please chime in.
 
Dan Thomas said:
At altitude that air filter is doing nothing unless there's a volcano belching somewhere nearby. If you can't see dust in the air, as in reduced visibility, it isn't a factor. I once owned a British type-certified airplane that had no air cleaner at all. None. It should have, as I found wear in the cylinders that was caused by dust during off-airport operations. Boats have no air cleaners at all.

One of the things the regs require a pilot to do before flight is a check of the weather. And two of the METAR items are the temp and dewpoint. If one is savvy enough to understand carb ice and the conditions that are favorable to it, the temp-dewpoint spread says it all. Fine today, maybe. Tomorrow might have a three-degree spread, and carb ice is very possible in a lot of airplanes. It should come as no surprise when a carb ices up.
Click to expand...

What about flying a carbed plane in IMC?
 
murphey said:
The difference has many reasons, the first is the Lycoming vs Continental engine, second is the location of the carb on Pipers v Cessnas.
Click to expand...

The location of the carb thing is really more properly how the carb is mounted. On the Lycs the carb is bolted to the bottom of the oil pan, and it gets some heat from the hot oil in the pan. On the Conti the carb is bolted to a bracket near, but not touching the oil pan.

-Skip
 
Skip Miller said:
The location of the carb thing is really more properly how the carb is mounted. On the Lycs the carb is bolted to the bottom of the oil pan, and it gets some heat from the hot oil in the pan. On the Conti the carb is bolted to a bracket near, but not touching the oil pan.

-Skip
Click to expand...

Do you have any evidence to back that up? I've heard it for years but given how Lycoming powered Cubs make ice I don't buy it. Does anyone use a carb temp gauge on a Lycoming? I'm guessing the air flowing through the carb is the same temp as with a Continental.
 
Skip Miller said:
The location of the carb thing is really more properly how the carb is mounted. On the Lycs the carb is bolted to the bottom of the oil pan, and it gets some heat from the hot oil in the pan. On the Conti the carb is bolted to a bracket near, but not touching the oil pan.

-Skip
Click to expand...
True for many Continentals, but the O-300 has its carb bolted to the oil sump just like Lycoming.
 
Stewartb said:
Do you have any evidence to back that up? I've heard it for years but given how Lycoming powered Cubs make ice I don't buy it. Does anyone use a carb temp gauge on a Lycoming? I'm guessing the air flowing through the carb is the same temp as with a Continental.
Click to expand...
We had a Citabria 7GCBC that had Lyc O-320A2B in it. It was a real bad ice-maker. The O-320-E2A's in the 172s weren't a tenth as bad. The carb mountings and locations were the same. The airbox shape and size was different, and maybe the cooling airflow off the cylinders and heads flows around the Cessna box and carb more than in the Citabria. One could spend a lot of time figuring out why, but one would still have to deal with carb ice. It's likely along the same lines with the difference in POH carb heat use between the 172 and Cherokee.

We had 172's ice up their carbs on beautiful summer mornings on the first start of the day. The oil sump is cold and if the temp and dewpoint are close enough you can get a boatload of ice before you take off.
 
You must log in or register to reply here.
Back
Top