carb ice?

[FORANE]

So, who has experienced carb ice? How did it present? What were the symptoms? How long did it take to recognize? How long did it take to resolve?

EGT increase? Rough running motor? Decreasing RPM's? Throttle stops working? Plane a little quieter?

Full carb heat or none at all? Don't touch the throttle before pulling heat? Lean mixture with carb heat or leave it alone? Don't use carb heat below x degrees?

Sure, some motors are more known to be associated with the formation of carb ice than others - ie continental over lycoming. Some POH recommend carb ice under certain conditions or at certain periods of flight while others only recommend carb heat when carb ice is suspected. I do not intend to make this a thread about one plane or another; rather a thread about what carb ice does, how to recognize it and insure it is does not become a big problem.

I ask as I (almost) never use carb heat. Never had a problem with it in my little o-320 lancair in the 800 or so hours I have put on it (sure, sure the o-320 is not prone to ice...). One time while climbing out she started running a little rough I used carb heat. Ambient temp was 70 or so on the ground, did run slightly more roughly for 10-15 minutes or so and eventually resolved. Maybe that was carb ice, just dont know.

 

[benb172]

I know a pilot who lost his plane on takeoff due to carb ice. It was a 60 degree day with extremely high humidity. The ice built up and the engine quit. The pilot was able to pancake it in the trees.

The first indication is usually a drop in RPM (fixed pitch), Engine roughness and possible fuel starvation. The Throttle would technically not stop working, but when increased, only a fraction of forward thrust would result. In the event of ice, it is best to use carb heat. At first there would be a slight drop in RPM, but then it would gradually increase back to a normal power setting as the water vapor (that was the ice) passes through the cylinders.

 

[Dan Thomas]

I know a pilot who lost his plane on takeoff due to carb ice. It was a 60 degree day with extremely high humidity. The ice built up and the engine quit. The pilot was able to pancake it in the trees.

That can happen while on a longer taxi. Ice builds up and full power isn't available for safe takeoff. The pilot should notice the poor acceleration and abort. Just because it's running doesn't mean it's running right.

Too many students are never taught properly about carb ice, its causes, the conditions that raise the likelihood of it, and the right way to deal with it. AOPA says that carb ice is responsible for way too many engine-failure accidents.

A pilot should ALWAYS check the temp-dewpoint spread before flying a carbureted airplane, and know what that spread means.

www.aopa.org/asf/publications/SB09.pdf

http://www.fly13.co.uk/Tug/Carb Ice/Carb Icing.htm

Dan

 

[poadeleted20]

So, who has experienced carb ice?

Me.

How did it present? What were the symptoms?

Generally a decline in RPM with some roughness.

How long did it take to recognize?

About two seconds after I noticed the symptoms.

How long did it take to resolve?

Usually about two to five seconds after pulling the carb heat.

Full carb heat or none at all?

I've not flown many planes with Carb Air Temp gauges, so it's pretty much always been full carb heat for me.

Don't tough the throttle before pulling heat?

If you meant "touch," then yes. If I'm in carb ice conducive conditions (clouds or high humidity and I get an RPM drop with roughness, my first reaction is "carb heat ON". (Unless I'm in a fuel injected plane). Of course, if I have a full engine analyzer, I'll probably also look at that for signs of a fouled plug (one cylinder EGT up 150 or so) or a dead mag (all EGT's up 150 or so).

Lean mixture with carb heat or leave it alone?

No reason to lean the mixture for the few seconds it takes to melt the ice, but if you're going to leave it on as a prophylactic measure, then yes, an appropriate mixture adjustment would be a good idea.

Don't use carb heat below x degrees?

If OAT is much below freezing, it ain't carb ice, and application of carb heat can only make things worse unless structural icing is blocking the air inlet (like on a 172 where the air filter is on the front face, but not a Tiger where the air filter is buried deep in the engine compartment).

 

[MAKG1]

I had a carb ice incident once as a student, intending to fly solo to LVK for landing practice. It was a busy day, and I sat in line for departure after run-up. It was cool and morning fog had just burned off (so it was humid as well). The engine built up a little carb ice while idling. On takeoff, I didn't notice much performance loss (I don't think there was a lot of ice here), but the carb ate a piece at 400 AGL. The engine missed. It recovered right away, and I was still climbing, so I called Tower and turned back, made a normal landing, reran the mag check (I thought it was an ignition miss), passed it, then parked the plane.

I squawked the problem because I really wasn't sure what happened, though I strongly suspected carb ice because of the lack of reproduceability. Mx concurred and put the aircraft back on the line. Aside from some wasted adrenaline, there was no damage to anything. But it sure is scary to have an engine burp at that kind of altitude.

 

[steingar]

Had a bout in some light mist in my Cessna 150. Lowering RPMs, and being the noob I was I actually let the engine quit before I knew what was going on. Headed for a nearby airport, put on the carb heat and got my RPMs back. Headed on my way with a leaned mixture until I got out of the mist.

 

[GauzeGuy]

So, who has experienced carb ice? How did it present? What were the symptoms? How long did it take to recognize? How long did it take to resolve?

BTDT.

I noticed an unexplained RPM drop in straight and level flight. I immediately knew what it was and applied carb heat. I'm glad a very experienced pilot let me know what I expect, because right after full carb heat the engine started running rougher for a few seconds. I decided to descend to get away from visible moisture -- I wasn't in clouds but was close enough where the moisture content was higher and the cold temps didn't help either.

 

[FORANE]

Great responses guys!

Dan, your first link did not work. Second link informative.

Ron, I did mean touch, sorry. A few seconds to melt the ice huh? My carb heat must be as efficient as my cabin heat...which I do not even bother to turn on as it is so miserably ineffective. I try applying it on the ground and just do not see hardy any RPM drop as they say to expect (I do not remember the requisite RPM drop of certified stuff). The one time I did suspect carb ice it literally took about 15 minutes before it started running better.

Visible moisture...my flying is somewhat like an airline in that I am on a schedule. Add to that my tremendous dislike for driving. This results in my flying in some miserable conditions. Before I decided to get XM WX, I flew through a horrendous downpour with water coming in the plane from where I have never seen water. No rough running then...

Thanks for the replies.

 

[Bill Watson]

Sure, some motors are more known to be associated with the formation of carb ice than others - ie continental over lycoming. Some POH recommend carb ice under certain conditions or at certain periods of flight while others only recommend carb heat when carb ice is suspected. I do not intend to make this a thread about one plane or another; rather a thread about what carb ice does, how to recognize it and insure it is does not become a big problem.

I ask as I (almost) never use carb heat. Never had a problem with it in my little o-320 lancair in the 800 or so hours I have put on it (sure, sure the o-320 is not prone to ice...). One time while climbing out she started running a little rough I used carb heat. Ambient temp was 70 or so on the ground, did run slightly more roughly for 10-15 minutes or so and eventually resolved. Maybe that was carb ice, just dont know.

The difference between Continentals and Lycomings is significant and fact based. The difference is generally reflected in the operations manuals for the aircraft. Given that operating procedures, over time, reflect the accident record it's good to pay attention and follow them.

One potential trap lies in flying an aircraft like you are flying where carb ice may be a near impossibility. Then extrapolating that to another aircraft where carb ice is relatively common occurrence. The other trap is believing it will never happen in a certain aircraft, finding it will happen on the rare occassion, and then missing diagnosis. I've fallen in both traps (without incident).

Otherwise, it's just like everyone says.

 

[bobmrg]

Me too. First symptom, as mentioned by others, is a decrease in RPM (fixed pitch). Anyone who is paying attention and scanning the tach regularly will not get an unpleasant surprise. If the situation gets so bad that the engine runs rough before you wake up, bad on you. Next step is FULL carb heat unless you have instrumentation that shows you in a safe range. The NTSB recommends that FULL carb heat be used, no matter what kind of engine you have.

If you caught it right away, the amount of ice should be relatively negligible and it will melt away in a few seconds....causing rough running because the engine does not burn water very well. When it smooths out the carb heat knob goes back in; no partial heat unless you have instrumentation (is there an echo in here?).

A nice July day without a cloud in the sky combined with a long taxi may result in carb ice formation, so it is a good idea to pull FULL carb heat as you taxi into position...and then COLD as you add power for takeoff.

There is a ton of information online....Google carburetor ice or carburetor heat.

Bob Gardner

 

[poadeleted20]

Ron, I did mean touch, sorry. A few seconds to melt the ice huh? My carb heat must be as efficient as my cabin heat...which I do not even bother to turn on as it is so miserably ineffective. I try applying it on the ground and just do not see hardy any RPM drop as they say to expect (I do not remember the requisite RPM drop of certified stuff). The one time I did suspect carb ice it literally took about 15 minutes before it started running better.

If so, your aircraft's induction air box needs immediate attention -- before further flight.

 

[Dan Thomas]

Great responses guys!

Dan, your first link did not work. Second link informative.

Something wrong with the way that first link works. Try this page and scroll down to the Combating Carb Ice article and click on it:

http://www.aopa.org/asf/publications/safety_briefs.html

Dan

 

[FORANE]

If so, your aircraft's induction air box needs immediate attention -- before further flight.

Suppose I could be running lean during checks and if so, RPM's would not decrease with application of carb heat.

 

[MAKG1]

Suppose I could be running lean during checks and if so, RPM's would not decrease with application of carb heat.

While that's true, if you're doing that, you need some time with an instructor about checklist use and proper preflight activities. That's contrary to every run-up checklist I've seen. Effectively, you're not testing the carb heat.

And you should KNOW when you're lean and when you aren't.

 

[FORANE]

While that's true, if you're doing that, you need some time with an instructor about checklist use and proper preflight activities. That's contrary to every run-up checklist I've seen. Effectively, you're not testing the carb heat.

And you should KNOW when you're lean and when you aren't.

Most instructors I have had in the plane know far less about it than I do. The "checklist" I have is pretty sparse being an experimental.
I would like to say I know when I am lean and when I am not but honestly cannot say I am very good at it. I have individual digital EGT's on all cylinders and know to lean till peak to identify lean or rich but despite hundreds of hours in the plane I just never felt entirely comfortable knowing exactly where peak was.

 

[poadeleted20]

Suppose I could be running lean during checks and if so, RPM's would not decrease with application of carb heat.

If it's running that lean, then there's a major problem with the carb adjustments. Again -- fix before next flight.

 

[FORANE]

So what's considered a minimum RPM drop with carb heat? 50? 75?

 

[rottydaddy]

Only once for me- 70s-era C172, very cold but not unusually humid day. No clouds or fog in my vicinity. I was running full rich, at about 2000 feet, cruising with 60-70% power. It was the end of the last leg of my long solo XC for my PPASEL; I'd already made two approaches that morning with no problems during initial power reduction prior to the normal application of carb heat abeam the numbers. So it was a bit of a surprise.
First noticed a change in the engine note, and noticed as I checked the tach that the VSI was already showing a descent. I don't recall the amount of rpm drop, but it was enough to make the plane dip its nose to try to maintain the airspeed I'd trimmed for. I was over the Palisades, just north of the GWB, almost exactly where a Piper ditched in the Hudson recently. Had the engine quit, I'd have been forced to do the same... there's no better choice when you are that low in that area.
Hit the carb heat even before I was sure,and immediately checked throttle position... the vernier hadn't slipped or anything, and moving it to the stop confirmed, with a small increase in rpm, that everything was still OK, linkage-wise. Same with the mixture control. So it was probably ice, I reckoned. Being as low as I was, I decided not to try a mag check until I gave the carb heat a chance... for all I knew, I'd switch to the bad one and konk the engine.
I re-trimmed for a lower speed and stopped the descent, and was about to turn anyway for KTEB, just a few minutes away.The heat did the trick- a further drop in rpm due to the heated air, then a disturbing moment when the engine had a shot of water, then all was well again. Took a minute or so, but man, did it seem to take a long time for the heat to take effect. Not fun, as it was way too cold for a swim in the river that day.

 

[FORANE]

So what's considered a minimum RPM drop with carb heat? 50? 75?

I researched it and did not find any numbers for experimentals. AC 90-89A states there should be:
"a positive reductionin rpm each time ‘‘carb heat’’ is applied."

AC 90-89A also states:
"It is strongly recommended that allamateur-builders install a carburetor heat system that
complies with the engine manufacturer’s rec-
ommendation. If no recommendation is available, the
FAA suggests a carburetor heat system for a sea-
level engine and a conventional venturi should be
designed so that it will provide a 90 degrees F
increase in the venturi at 75 percent power. For alti-
tude engines using a conventional venturi carburetor,
120 degrees F increase in venturi temperature at 75
percent power will prevent or eliminate icing.
Remember: Too little carburetor heat will have no
effect on carburetor icing, and too much carburetor
heat will cause a overly rich mixture which will
reduce power and may shut down the engine."

I seem to remember hearing about a specified 75 degree temp rise in the Cessna 1xx series Lycomings but cannot find it. I also seem to remember a specified 100 minimum RPM drop on the Cessna 1xx series lycomings checklist but do not have those checklist anymore. Am I mistaken to recall the Cessna 1xx series lycomings recommended carb heat just when carb ice suspected?

My POH just states to use carb heat when carb ice suspected. I believe the combination of motor design not prone to develop ice (lycoming 320 as I have) along with a tight cowl like many experimentals have (mine is ridiculously tight) yield an environment where ice is very unlikely. I have read where other small experimental guys also see very little to none carb ice, use very little to none carb heat and see very little to none drop in RPM with carb heat.

 

[dell30rb]

I researched it and did not find any numbers for experimentals. AC 90-89A states there should be:
"a positive reductionin rpm each time ‘‘carb heat’’ is applied."

AC 90-89A also states:
"It is strongly recommended that allamateur-builders install a carburetor heat system that
complies with the engine manufacturer’s rec-
ommendation. If no recommendation is available, the
FAA suggests a carburetor heat system for a sea-
level engine and a conventional venturi should be
designed so that it will provide a 90 degrees F
increase in the venturi at 75 percent power. For alti-
tude engines using a conventional venturi carburetor,
120 degrees F increase in venturi temperature at 75
percent power will prevent or eliminate icing.
Remember: Too little carburetor heat will have no
effect on carburetor icing, and too much carburetor
heat will cause a overly rich mixture which will
reduce power and may shut down the engine."

I seem to remember hearing about a specified 75 degree temp rise in the Cessna 1xx series Lycomings but cannot find it. I also seem to remember a specified 100 minimum RPM drop on the Cessna 1xx series lycomings checklist but do not have those checklist anymore. Am I mistaken to recall the Cessna 1xx series lycomings recommended carb heat just when carb ice suspected?

My POH just states to use carb heat when carb ice suspected. I believe the combination of motor design not prone to develop ice (lycoming 320 as I have) along with a tight cowl like many experimentals have (mine is ridiculously tight) yield an environment where ice is very unlikely. I have read where other small experimental guys also see very little to none carb ice, use very little to none carb heat and see very little to none drop in RPM with carb heat.

Are you flying a PA-28?

Yes that is one of the airplanes that is not susceptible to carb ice and you do not need to put on carb heat in normal operations. However it should be applied at the first sign of any engine distress...


I have picked up carb ice several times in 152's. Usually on taxi if the conditions are right. Only once in flight, skimming the tops of a cloud deck at a low cruise power setting.

Reduction in power and a slight roughness is what I noticed when in flight. Applying carb heat solved the problem in about 10 seconds.

In an airplane susceptible to carb ice (152) if I don't run up immediately before takeoff, i'll apply carb heat from the hold short line until i'm lined up on the runway. Firewall it for takeoff and then reach over and turn off the carb heat.

 

[FORANE]

Are you flying a PA-28?

Yes that is one of the airplanes that is not susceptible to carb ice and you do not need to put on carb heat in normal operations. However it should be applied at the first sign of any engine distress...


I have picked up carb ice several times in 152's. Usually on taxi if the conditions are right. Only once in flight, skimming the tops of a cloud deck at a low cruise power setting.

Reduction in power and a slight roughness is what I noticed when in flight. Applying carb heat solved the problem in about 10 seconds.

In an airplane susceptible to carb ice (152) if I don't run up immediately before takeoff, i'll apply carb heat from the hold short line until i'm lined up on the runway. Firewall it for takeoff and then reach over and turn off the carb heat.

I have a Lancair with an O-320A model out of a 1940's vintage piper - I think it had an initial date of 1948 in the engine log if I remember correctly (or maybe it was a 1952 apache). It came complete with the Loch Haven PA reference of the small town in PA where Piper started. I visited there once; very interesting and modest beginnings.
Thanks for the post.

 

[Dan Thomas]

I researched it and did not find any numbers for experimentals. AC 90-89A states there should be:
"a positive reductionin rpm each time ‘‘carb heat’’ is applied."



My POH just states to use carb heat when carb ice suspected. I believe the combination of motor design not prone to develop ice (lycoming 320 as I have) along with a tight cowl like many experimentals have (mine is ridiculously tight) yield an environment where ice is very unlikely. I have read where other small experimental guys also see very little to none carb ice, use very little to none carb heat and see very little to none drop in RPM with carb heat.

The Lycomings in 172s have a tiny, wide-open carb heat muff on one of the RH exhaust stacks, and it doesn't raise the air temp very much. The RPM drop is then rather small, maybe 50 or 75 RPM. On the older Continental-powered Cessnas, the carb heat comes via a huge muff around the muffler, and it gets really hot and drops the RPM much more. In some old 180s it makes the engine run really rough once it's applied in the circuit and one needs to lean the thing somewhat.

Every airplane model differs somewhat, or a lot, from other airplane models. Pay attention to the POH. If one doesn't get an RPM drop on runup, he shouldn't go flying. Poorly-maintained systems often have great gaping holes in the SCAT hoses, and the heat valve might be misrigged.

Dan

 

[FORANE]

The Lycomings in 172s have a tiny, wide-open carb heat muff on one of the RH exhaust stacks, and it doesn't raise the air temp very much. The RPM drop is then rather small, maybe 50 or 75 RPM. On the older Continental-powered Cessnas, the carb heat comes via a huge muff around the muffler, and it gets really hot and drops the RPM much more. In some old 180s it makes the engine run really rough once it's applied in the circuit and one needs to lean the thing somewhat.

Every airplane model differs somewhat, or a lot, from other airplane models. Pay attention to the POH. If one doesn't get an RPM drop on runup, he shouldn't go flying. Poorly-maintained systems often have great gaping holes in the SCAT hoses, and the heat valve might be misrigged.

Dan

Thanks for the background info Dan. I remember from the 150 I once owned the RPM drop was something like 200 or so - quite significant. I was not familiar with the 172's or 180's.

My alternate air / carb heat system is not poorly maintained (I do not mean to suggest you implied mine was). I know the scat hose is intact. The shield is a square piece of aluminum bent into a U shape over the exhaust crossover tubes in front of the oil pan. It is open on both sides. It has a 2 inch hole in the bottom for scat tube opening downward into the airbox. Thus, there is little containment of the air.

My cabin heat valve very well may be misrigged. I can say though the heat muff is tiny as there just isn't room in the cowling. It is on the front #2 cylinder only. It is only around 4 inches long. It is only about 1/2 inch wider than the pipe. The intake and outlet are on the same side. The scat into and out of is just 1 inch diameter. I do not know if it has stainless steel inside the muff or not. I do know it is so ineffective that I do not even bother to turn it on no matter how cold it is outside.

 

[bobmrg]

Are you flying a PA-28?

Yes that is one of the airplanes that is not susceptible to carb ice and you do not need to put on carb heat in normal operations. However it should be applied at the first sign of any engine distress...


I have picked up carb ice several times in 152's. Usually on taxi if the conditions are right. Only once in flight, skimming the tops of a cloud deck at a low cruise power setting.

Reduction in power and a slight roughness is what I noticed when in flight. Applying carb heat solved the problem in about 10 seconds.

In an airplane susceptible to carb ice (152) if I don't run up immediately before takeoff, i'll apply carb heat from the hold short line until i'm lined up on the runway. Firewall it for takeoff and then reach over and turn off the carb heat.

I'll go with the NTSB recommendation to use FULL carb heat whenever power is reduced below cruise power, regardless of who made the engine.

Bob Gardner

 

[JohnAJohnson]

Has anyone ever experienced carb icing on anything other than an airplane engine (lawn mower, car, boat, etc.)? I haven't, and am wondering what the difference is.

Also, after my mag checks, I pull the carb heat, verify the RPM drop, then cycle the prop twice with the carb heat on. This gives any ice plenty of time to melt before taking off.

 

[FORANE]

Has anyone ever experienced carb icing on anything other than an airplane engine (lawn mower, car, boat, etc.)? I haven't, and am wondering what the difference is.

Also, after my mag checks, I pull the carb heat, verify the RPM drop, then cycle the prop twice with the carb heat on. This gives any ice plenty of time to melt before taking off.

Air cooled are more likely to form ice. I have read the old VW bugs and motorcycles would suffer from it from time to time. Most autos are liquid cooled and have warm water which provide heat. There are also heat risers on cars to warm the air like carb heat. I have not observed it that I know of, but may have had an unrecognized occurrence.

I'll go with the NTSB recommendation to use FULL carb heat whenever power is reduced below cruise power, regardless of who made the engine.

Bob Gardner

Good post Bob. I was not aware of this recommendation.

 

[Dan Thomas]

Has anyone ever experienced carb icing on anything other than an airplane engine (lawn mower, car, boat, etc.)? I haven't, and am wondering what the difference is.

Also, after my mag checks, I pull the carb heat, verify the RPM drop, then cycle the prop twice with the carb heat on. This gives any ice plenty of time to melt before taking off.

All of them will do it if they have carburetors and are given the chance. They are designed to handle or eliminate it without the operator's input. Most small engines have the carb either bolted directly to the engine block and get lots of heat conducted into them, or they have intake air taken from near the block or cooling discharge, or they're located inside a tight cowl (like an outboard) and get warm air from inside. Carbureted cars have the carb mounted on an intake manifold that is usually either bolted to the exhaust manifold (inline fours or sixes) or has exhaust running through smaller channels in it (V engines), and will also have a heat muff around some part of the exhaust manifold that ducts hot air through a hose to a thermostatically-controlled air valve on the air cleaner. That control will keep the carb air at around 75-80°F. The guys that suffer carb ice are those that have replaced the stock air cleaner with some fancy chromed thing that has the filter exposed all the way around "for better breathing," and instead of better breathing it makes better carb ice, since the carb ice control system is tossed out.

I once owned a '74 Ford Courier. A Mazda pickup in Ford's disguise. It had a manual carb heat control on the air cleaner, labelled "cold weather" and "warm weather." It sometimes made ice in the summer, of course, so I installed a carb heat control cable to the panel to deal with it. Better than stopping and getting out and resetting the silly thing all the time.

Dan

 

[Garthur]

I'm fairly confident that I have had carb ice a few times. Cruising at altitude the RPM's slowly start to drop off. I apply carb heat for a few mins and then removed it and the RPM levels returned to their previous levels.

When I do my runups, I check the end of the prop and if I see even a slight indication of water vapor coming off of it, if there is I apply carb heat for a few mins before I depart.

 

[poadeleted20]

So what's considered a minimum RPM drop with carb heat? 50? 75?

Even for an E-AB aircraft, if it's a certified engine like a Lycoming or Continental, the engine manufacturer's Operator's Manual will give that information. Contact Lycoming for the manual for your O-320-A engine -- chock full of other good information, too.

 

[JHW]

Has anyone ever experienced carb icing on anything other than an airplane engine (lawn mower, car, boat, etc.)? I haven't, and am wondering what the difference is.

Also, after my mag checks, I pull the carb heat, verify the RPM drop, then cycle the prop twice with the carb heat on. This gives any ice plenty of time to melt before taking off.

sure. For one example, you can get carb ice on virtually any older dodge pickup with the 318 engine

 

[bobmrg]

Has anyone ever experienced carb icing on anything other than an airplane engine (lawn mower, car, boat, etc.)? I haven't, and am wondering what the difference is.

Also, after my mag checks, I pull the carb heat, verify the RPM drop, then cycle the prop twice with the carb heat on. This gives any ice plenty of time to melt before taking off.

Yes. Sunbeam Alpine.

Bob Gardner

 

[kgruber]

I had carb ice on my old "327" Corvette. Although it could have been impacted snow, it was in the middle of the night in a blizzard going over Loveland Pass.

I also use carb heat on my Cherokee 180. There is no downside to using carb heat in low power flight. Once you start gliding without power there may not be enough heat in the exhaust shroud to give good carb heat. So I just leave it on.

In any airplane with carb heat I also use it on the first part on full power on takeoff. Give it a good blast of heat to make sure you didn't pick some ice up taxiing. After a second or two, push it off.

 

[EdFred]

Had a bout in some light mist in my Cessna 150. Lowering RPMs, and being the noob I was I actually let the engine quit before I knew what was going on. Headed for a nearby airport, put on the carb heat and got my RPMs back. Headed on my way with a leaned mixture until I got out of the mist.

The engine quit and the carb heat worked huh? OK.

 

[dell30rb]

The engine quit and the carb heat worked huh? OK.

I'm guessing it was running, but very poorly. If the fire went out completely - he would probably be writing about his off-airport landing.

For those who don't know - the carb heat uses the heat of the exhaust headers. (Different in some models, but all I have seen use the exhaust system in some way for the heat source). When you pull carb heat, a valve is switched that changes the air intake source from the air filter on the front of your plane, to a shroud that directs the air over the hot exhaust pipe before it is pulled into the carburetor.

These headers contain the very hot (1400F) exhaust gases. They are relatively thin and they cool off very quickly if the fire goes out.

 

[EdFred]

I'm guessing it was running, but very poorly. If the fire went out completely - he would probably be writing about his off-airport landing.

For those who don't know - the carb heat uses the heat of the exhaust headers. (Different in some models, but all I have seen use the exhaust system in some way for the heat source). When you pull carb heat, a valve is switched that changes the air intake source from the air filter on the front of your plane, to a shroud that directs the air over the hot exhaust pipe before it is pulled into the carburetor.

These headers contain the very hot (1400F) exhaust gases. They are relatively thin and they cool off very quickly if the fire goes out.

Exactly why I don't believe that the engine quit and restarted if it was carb ice. Now, it could have been a plugged intake filter. No air = no combustion. Switching to an alternate air source via the carb heat gets that air into the mixture for combustion.

That's actually how I found out my right exhaust stack exploded. My carb heat is pulled from the RH exhaust stack, and when I did my run up with the carb heat the engine almost died. Back to the ramp, and opened up the cowl.

"Oh, that's not good."

 

[dell30rb]

. Now, it could have been a plugged intake filter. No air = no combustion. Switching to an alternate air source via the carb heat gets that air into the mixture for combustion.

Headed on my way with a leaned mixture until I got out of the mist.

It was that mist. Strange things hiding in there.

 

[EdFred]

It was that mist. Strange things hiding in there.

 

[MAKG1]

Has anyone ever experienced carb icing on anything other than an airplane engine (lawn mower, car, boat, etc.)? I haven't, and am wondering what the difference is.

Also, after my mag checks, I pull the carb heat, verify the RPM drop, then cycle the prop twice with the carb heat on. This gives any ice plenty of time to melt before taking off.

Absolutely. Most automotive carbs have heat risers to prevent this problem -- that is, there is an automatic carb heat that triggers on intake temperature (actuated by manifold vacuum so it turns off at full throttle). They break or plug with alarming regularity, and owners don't like to maintain "all that smog crap." And then the engine runs like crap after a while in cool weather at low throttle.

I've never had one quit, but I've certainly had problems maintaining idle. Then I fix the riser and it works again....

 

[SkyHog]

I got what I suspected was carb ice in a lawn tractor last year. Engine quit, and wouldn't restart until after some time when it warmed up considerably.

I've also had carb ice in a 182. Easily recognized, after a bit of engine roughness, applying carb heat fixed the problem in just a few seconds. Removing carb heat reintroduced the issue after about 5 minutes.

 

[spinfire]

I've experienced carb ice in a Tecumseh engine in a 4000 watt generator.

I fly a fuel injected plane now but I put the carb heat on plenty preemptively in the 172K I learned in and the Cutlass I flew for a little while but never experienced any carb ice symptoms. SOP was carb heat on when below the green arc and a few times when it was quite humid out I put partial carb heat on in cruise. Never used carb heat on climb out.