carburetor heat

[pembquist]

I was reading about this accident: http://www.ntsb.gov/about/employment/_layouts/ntsb.aviation/brief2.aspx?ev_id=20001208X09356&ntsbno=NYC98FA047&akey=1 Which was tragic, (the passenger was the pilots 8 years old son,) and it got me thinking about how much you learn in informal ways or only if you pursue what you don't know on your own. Often it seems like it is what you don't know you don't know that is the most dangerous. I learned to fly first in a J3 with a Continental that liked to demonstrate carb icing on beautiful sunny days with the slightest throttle reduction so the idea of carb ice and sunshine was never counter intuitive, very early on I came across a chart like this one: https://www.atsb.gov.au/media/47763/carb_icing.pdf which made me feel smug with understanding. I don't know where I found the chart but it wasn't part of any written and my instructor didn't tell me about it. The poor guy in the accident thought he knew what he was doing, thought he knew when he had to worry about carb ice but he was wrong, he was ignorant and to me that seems unacceptable, not that he made the mistake but that in his flying education and in the mish mash of flight manuals he had been led to a dangerous understanding of something that in a way I only know better about because of chance. It makes me think of the things, the bits of knowledge that are locked up in pilots brains, acquired through experience and chance, that you only learn by osmosis or chance conversation or diligent pursuit of the obscure.

[colmbo]

I didn't read this report, but a huge problem with carb icing is we are taught BS about it.  All the training is if you reduce power you put carb heat on to prevent icing.  I have on many, many occasions gotten carb ice while at full power on takeoff (one of which caused a complete loss of power and emergency landing) or at cruise power.  I don't know of a single instance where I developed carb ice at a reduced power setting such as in the pattern for landing.  I'm not saying you can't get carb ice at low power just that I haven't experienced it.

My carb ice problems were generally just in Cessna 182s with the Continental O-470 which is a champion at making carb ice.  The complete power loss occurred in a 152 with the Lycoming O-235.

[Wolfala]

I had a student doing his long cross country.  This was in a Cessna 182 with the Katmai conversion.  A bit of an oddball.  So just for kicks I decided to shadow him in my plane as he went through his motions.  Not once, not twice, but three times:  The fella got carburetor ice. The first time he had to be reminded to put it on when he started complaining of engine roughness.  He did not need a reminder the second and third.

 Life is funny that way

[Vraciu]

I didn't read this report, but a huge problem with carb icing is we are taught BS about it.  All the training is if you reduce power you put carb heat on to prevent icing.  I have on many, many occasions gotten carb ice while at full power on takeoff (one of which caused a complete loss of power and emergency landing) or at cruise power.  I don't know of a single instance where I developed carb ice at a reduced power setting such as in the pattern for landing.  I'm not saying you can't get carb ice at low power just that I haven't experienced it.

My carb ice problems were generally just in Cessna 182s with the Continental O-470 which is a champion at making carb ice.  The complete power loss occurred in a 152 with the Lycoming O-235.

I seem to think that updraft carbs were worse.   I believe the 152 has that style carb.   The Tomahawk did not, IIRC.   Been awhile I admit so don't quote me.

I always taught my students to turn in a Carb Heat at midfield downwind...    That way hot air is still being produced in large amounts from midfield to abeam the numbers and will melt anything in there.   (It also confirms that the air inlet is not blocked.)   

I have seen people put CH on then immediately reduce power.   On a humid day that can give you carb ice even when relatively warm.  If anyone did that to me I immediately gave them an engine failure to bring the point home.

[colmbo]

A big eye opener for me regarding carb ice was after I put the new engine in the airplane.  Since I was going broke anyway I opted to spend some extra for toys and had a digital engine analyzer installed which gave me carb air temp.  Watching the temps in the carb I would see that the lowest temps occurred at the highest power settings  ---- makes sense, more air/higher velocity thru the venturi the greater the pressure change lowering the temp.  On a warm day with ambient temp in the high 60s or 70s I would see carb temps down into the high 20sF when at takeoff power.  A reduction to climb power would bring carb temps up into the mid 30s and then a further reduction to cruise would see carb temps rise well above freezing.

However the carb temp isn't the whole story, even with carb temps above freezing I would pick up carb ice when flying in precip.

My procedure was carb heat on as I taxi onto the runway and start advancing power.  As throttle gets near full I would push the heat off.   I normally had power on during descent so I would just monitor carb temp and occasionally pull the heat on prophylactically.  Once on down-wind I would pull carb heat on then heat off again as I turn base.

[Vraciu]

You guys in the big recips always have ice issues. 

I seem to recall Ernest Gann discussing this phenomenon and trying to unplug them by backfiring the engines.   Wow. 

Some engines have their carbs aft of the engine which reduces this phenomenon.   Of course it also reduces air volume and thus power to some extent. 

[cpxxx]

Like so many other inexperienced pilots the first time I experienced carb icing. I had no idea what was happening. I was cruising along on one of those misty summer days in a Cessna 150 when the engine began to lose power and run rough with the whole airframe vibrating. I opened the throttle but it got worse. However I surmised that the rough running seeming to indicate an over rich mixture. Leaning a bit cured the rough running. Genius that I am I never made the connection between over rich and carb icing. Heading hastily back to the airport the engine once again ran rough as I descended over some less than friendly terrain. This time I realised that the cause was due to the engine running lean. Full rich cured it. So at least half a brain was working. Somewhat relieved back on the ground I found a more experienced pilot and told him I thought the fuel might be contaminated. It was of course with ice! He ran the engine and found nothing wrong. I went home none the wiser but somewhat shaken.

Later that night I had my eureka moment. It was of course carb icing. Doh! In my defence nothing in training told me what the actual symptons of carb icing were.

But it can happen to anyone. Two pilots I know were killed when they experienced carb icing in a Cessna 150 on a normal summer's day. While practising a forced landing the carb iced up and when they attempted to recover the engine cut and they spun in from low level. One was an experienced Instructor and the other was training to be an Instructor. In the confusion of the moment they let it get too slow.

[ariansworld]

On a sa200 welding machine with the continental f162 and f163 engine, the carbs ice up. They have a hose that runs from the aircleaner to a pipe with holes in it that lays on top of the exhaust manifold allowing it to draw warm air. Do they have something similar for aircraft engines?

[Zimme83]

Yes but it has to be activated manually by the pilot.

[Vraciu]

Like so many other inexperienced pilots the first time I experienced carb icing. I had no idea what was happening. I was cruising along on one of those misty summer days in a Cessna 150 when the engine began to lose power and run rough with the whole airframe vibrating. I opened the throttle but it got worse. However I surmised that the rough running seeming to indicate an over rich mixture. Leaning a bit cured the rough running. Genius that I am I never made the connection between over rich and carb icing. Heading hastily back to the airport the engine once again ran rough as I descended over some less than friendly terrain. This time I realised that the cause was due to the engine running lean. Full rich cured it. So at least half a brain was working. Somewhat relieved back on the ground I found a more experienced pilot and told him I thought the fuel might be contaminated. It was of course with ice! He ran the engine and found nothing wrong. I went home none the wiser but somewhat shaken.

Later that night I had my eureka moment. It was of course carb icing. Doh! In my defence nothing in training told me what the actual symptons of carb icing were.

But it can happen to anyone. Two pilots I know were killed when they experienced carb icing in a Cessna 150 on a normal summer's day. While practising a forced landing the carb iced up and when they attempted to recover the engine cut and they spun in from low level. One was an experienced Instructor and the other was training to be an Instructor. In the confusion of the moment they let it get too slow.

All Cessna 150/152/172 pilots should learn the "L" flow.  Use that for engine failures.

The manufacturer checklist is garbage.   Glad it ended well for you.  That's scary stuff.

 

[pembquist]

On a sa200 welding machine with the continental f162 and f163 engine, the carbs ice up. They have a hose that runs from the aircleaner to a pipe with holes in it that lays on top of the exhaust manifold allowing it to draw warm air. Do they have something similar for aircraft engines?

Yes, it is controlled by a lever in the cockpit, using it reduces the power the engine can develop and it bypasses the air filter so it is only used to prevent or cure icing when conditions demand it. Unfortunately operating manuals and flight instruction are inconsistent as to when that is. The pilot of the accident airplane did not know that given the dew point-air temperature differential on the day of the accident a carburetor would be likely to develop ice, his understanding of the use of carb heat seemed to be that it should be "used as necessary" which while maybe accurate is terribly incomplete, further he was under the misconception that there has to be visible moisture to get carburetor ice. It appeared from the narrative that he had had an earlier instance of engine failure due to carb ice that was misconstrued as an idle stop set too low. The problem with engine failure with ice is that once the engine quits, adding carb heat might or most likely will not work as the engine is making less heat and the flow of air drawn into the carburetor is insufficient to melt out the ice and allow the engine to gargle. When you do have ice in cruise it is kind of cool to pull on carb heat and feel/see the engine digest the ice. I wouldn't be surprised if a fair number of pilots believe that it is power reduction that causes icing, I believe that power reduction is when you discover that your carb is iced up and that the occlusion of ice has a more pronounced effect when the throttle is closed than when it is open, (possibly causing you to suspect a mal adjusted idle stop.)

[DaveBB]

Can someone explain in simple terms what actually causes ice to form in the carburetor?

[Vraciu]

Can someone explain in simple terms what actually causes ice to form in the carburetor?

Humid air combined with a drop in temp within the Venturi can form ice.  As ice forms the effect can amplify the problem creating more ice until it starves the engine of air.

This even on a relatively warm day one can experience icing.   As standard practice students should be trained to use Carb Heat appropriately even on warm days.

[earl1937]

Can someone explain in simple terms what actually causes ice to form in the carburetor?

There are many situations which can cause carb ice, but mainly its due to condensation! If you will remember the Ventura history of air being forced though a "throat" area, which does two things, it increase the velocity and decreases the temperature. Throw in the right atmosphere conditions and wa la, you have ice!
While most of the post are concerning "opposed" engines, the big "iron" also had carb ice problems. No one seemed to know why, but the B-26 engines were famous for carb icing! I don't think it was "common" to the general line of R-2800's, but I used to hear a lot of complaints about that problem with the 26! Might have had something to do with the "baffling" around the engine!
ON most light aircraft I ever flew, the problem of carb ice seem to be more prevalent in the Southeast and Southwest, as opposed to operating in the Northern area's. When the temperature and dew point get within about 10 degrees of each other, that seem to be the most threatening set up for carb ice!
 

[Vraciu]

I didn't read this report, but a huge problem with carb icing is we are taught BS about it.  All the training is if you reduce power you put carb heat on to prevent icing.  I have on many, many occasions gotten carb ice while at full power on takeoff (one of which caused a complete loss of power and emergency landing) or at cruise power.  I don't know of a single instance where I developed carb ice at a reduced power setting such as in the pattern for landing.  I'm not saying you can't get carb ice at low power just that I haven't experienced it.

My carb ice problems were generally just in Cessna 182s with the Continental O-470 which is a champion at making carb ice.  The complete power loss occurred in a 152 with the Lycoming O-235.

I seem to think that updraft carbs were worse.   I believe the 152 has that style carb.   The Tomahawk did not, IIRC.   Been awhile I admit so don't quote me.

I always taught my students to turn in a Carb Heat at midfield downwind...    That way hot air is still being produced in large amounts from midfield to abeam the numbers and will melt anything in there.   (It also confirms that the air inlet is not blocked.)   

I have seen people put CH on then immediately reduce power.   On a humid day that can give you carb ice even when relatively warm.  If anyone did that to me I immediately gave them an engine failure to bring the point home.

Can someone explain in simple terms what actually causes ice to form in the carburetor?

Humid air combined with a drop in temp within the Venturi can form ice.  As ice forms the effect can amplify the problem creating more ice until it starves the engine of air.

Thus even on a relatively warm day one can experience icing.   As standard practice students should be trained to use Carb Heat appropriately even on warm days.

There are many situations which can cause carb ice, but mainly its due to condensation! If you will remember the Ventura history of air being forced though a "throat" area, which does two things, it increase the velocity and decreases the temperature. Throw in the right atmosphere conditions and wa la, you have ice!
While most of the post are concerning "opposed" engines, the big "iron" also had carb ice problems. No one seemed to know why, but the B-26 engines were famous for carb icing! I don't think it was "common" to the general line of R-2800's, but I used to hear a lot of complaints about that problem with the 26! Might have had something to do with the "baffling" around the engine!
ON most light aircraft I ever flew, the problem of carb ice seem to be more prevalent in the Southeast and Southwest, as opposed to operating in the Northern area's. When the temperature and dew point get within about 10 degrees of each other, that seem to be the most threatening set up for carb ice!
 

    

Yo, bruh.  Merhinks reading the threads before one responds is a sorta' good idea.  Then mayhaps not use ! so much, possibly...

Not hatin' here.  Just trying to help.