carb ice w/ carb heat on

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jesse

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Jesse
Conditions: KRST 022254Z 09004KT 10SM BKN100 OVC120 M11/M16 A3010 RMK AO2 SLP225 T11061156

Went for a quick flight today after work just to get it out of my system.

The airplane: Cessna 150M

It's the airplane I've done all my primary training in and received my PPL in. I haven't flown it.. for quite a few months, But it's cheap.. and I didn't have any passengers..so I went with it.

I departed RST to the west and climbed to about 2100 AGL. I did some clearing turns, followed by steep turns.

I then went ahead and did a power off stall.. Carb heat on, throttle back, airspeed in white arc, flaps, pull power...maintain / stall / break. ... Power / Carb heat / Flaps... It was textbook, No issues.

I went ahead and did another one. Same deal .. carb heat was ON. When it broke from the stall this time I applied full throttle, But there was nothing. No power.. Nothing.. Zip.. Pulled the throttle back, nothing.. back in.. nothing. I glanced around quick and picked a field under me that looked acceptable. Time at this point: about 10 seconds into it. I then circled for this field while playing with the engine.. Right mag, nothing.. left mag, nothing.. I keyed the mic and got out "Approach Cessna Seven Zero" I was playing with the engine still at this point and pulled the mixture from full rich to idle cutoff. The engine coughed. I released the mic and moved it back and forth a few times. Approach then called me.. I told them to standby.. I continuted to play with the throttle and mixture and finally...full power. Total time: 30 seconds. Altitude loss: about 1000 feet.. I then told them I had a rough engine and was returning to the airport. I didn't feel the need to declare the emergency this time. Oil temp: no indication / cold

I returned and landed.. when I pulled the power to idle on short final it died again. I was able to get it started and taxied back to the ramp.
Oil temp: no indication / cold

I talked to a mechanic who told me it was carb ice. I told him the carb heat was on. I also asked him why there used to be plugs in the cowling i nthe winter and there isn't now... He said it wasn't cold enough yet.....I'm not sure but 12 degrees should be cold enough?... He then said he'd take a look but it had to be carb ice...


Lessons learned:

I'll probably go higher now, It'd give me more time in this type of situation.


I'm pretty sure the mechanic just didn't put the plugs in the cowling in and was just BSing me about it not being cold enough.

Also the RPM was varying up and down 100 RPM about every second on the way back to RST


.....How common is carb ice with carb heat ON .. ?
 
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Dave Krall CFII said:
What type of conveyor belt would the airplane be on ???
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Black with pink stripes.
 
The air was alread cold enough that any moisture in the air was frozen. You added carb heat, raising the temperature of the air, causing the moisture to melt, it then hit the venturi and froze.

There are times NOT to apply carb heat just because the book says. This is one of them. Carb heat = carb ice at those temps and dewpoints.
 
The C-150 has hanlon and Wilson mufflers, these are made from sheet stainless steel. and they will cool very quickly.

When you do POWER OFF stalls, you are in a closed throttle no heat producing situtation. and the muffler will cool until it can not produce hot air to melt the ice.

You got lucky, you did finally get some hot air to clear the ice.
 
I was taught to apply carb heat only when the engine starts running rough because in certain conditions the carb heat can actually cause icing.
 
Well I'm not sure.

I did all of my training this time last year, and into Jan. where it was sometimes much colder.

I'm pretty sure it had something to do with the fact that they didn't have the plugs in the cowling. Which would cause the muffler / etc to cool very quickly.
 
Dave Krall CFII said:
I was taught to apply carb heat only when the engine starts running rough because in certain conditions the carb heat can actually cause icing.
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Using the old flat pancake style mufflers on the C-120/140/ and the early C-170 and several other aircraft, this was true. They just didn't produce very much heat..carb temps with heat applied was near 60-70degrees.

With the newer Hanlon & Wilson round tube style, the carb temps will rise to around 90-100 degrees.

BUT,,,, it won't do that when you have the throttle closed. When the throttle is closed only idle fuel is being burned and not much heat is created. the mufflers cool, and ice forms on the venturi from the idle fuel being evaporated. This ice forms in the carb throat destroying the venturis abiloity to create a low pressure zone that pulls the fuel from the float bowl.

Now,,, when you open the throttle you will have no fuel flow, the venturi isn't working, and the idle circuit isn't being used, when the throttle is open. nothing to run the engine and create heat to melt the ice.
 
interesting food for thought....


I was taught to always use it with low rpms.

Basically out of the green arc , use carb heat.
 
jangell said:
interesting food for thought....


I was taught to always use it with low rpms.

Basically out of the green arc , use carb heat.
Click to expand...

If it's well below freezing, you don't need carb heat. If it's really cold or if your engine is idling and it's just a little below freezing, you shoun't use heat as you found out. The missing winter baffles may have contributed slightly, but I suspect the bigger factor was the moisture in the air and the cold temps with carb heat.

BTW, a useful trick to coax some power out of the engine in such a situation is to:

1) pump the throttle. This will actially force fuel into the engine if the carb has an acclerator pump (most do, my Porterfield doesn't). In addition, if you have ice, moving the throttle from closed to open and back a few times may physically break off some of the ice.

2) Try the primer. You may be able to get the engine running strong enough to keep you aloft.

Both of these tricks might also get the exhaust hot enough to melt the ice with the carb heat on.
 
Hopefully you learn on the ground.

if not...you learn in the airplane.


Sometimes it pays to be lucky.

You'd be suprised how quick you can take your very loose seatbelt / should harnesses...to very very very tight without even noticing you did it.
 
N2212R said:
The air was alread cold enough that any moisture in the air was frozen. You added carb heat, raising the temperature of the air, causing the moisture to melt, it then hit the venturi and froze.

There are times NOT to apply carb heat just because the book says. This is one of them. Carb heat = carb ice at those temps and dewpoints.
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I dunno about that. Our Robinson POH explicitly calls for full carb heat below 18" MP regardless of what the carb temperature gauge says, and in fact it automatically comes full on when the collective is lowered. The engine is a Lycoming O-360.
 
This is not a new phenomenon. I received an email several years ago from a guy who went in a cloud at -10F OAT (too cold for structural icing). Everything was fine until he decided to preemptively turn on the carb heat, at which point the engine rapidly choked down to not much above idle. He didn't get enough power to maintain altitude until he got down low enough to where the OAT was high enough that the carb heat could warm the intake air enough above freezing that the venturi effect in the carb wouldn't chill it back below freezing.

Keep in mind that air temp drops 30F degrees or so across the carb throat, and carb heat warms the air about 50F degrees. So if the OAT is down below about 0F, and you pull the carb heat, you've raised the inlet air temp to 50F, and it cools to 20F in the carb -- bad news when there was ice in the inlet air because the ice in the 0F outside air melts in the carb heat muff when it warms to 50F and then cools to 20F in the carb throat and ice forms in the carburetor. At that point, you're stuck, because you can't warm the inlet air enough (up to 65F or so) to keep it above freezing after it drops 30F degrees in the throat so it can melt out the ice that formed.
 
Dave Krall CFII said:
I was taught to apply carb heat only when the engine starts running rough because in certain conditions the carb heat can actually cause icing.
Click to expand...

I was assuming in non-routine operations such as an emergency or engine roughness given in the example. Otherwise, we were taught to go by the individual aircraft POH and were additionally informed of the dangerous range that Cap'n Ron outlined in detail.
 
I talked to the mechanic today. He said there was nothing abnormal with the engine that he found.

He said it was impossible to get carb ice with carb heat. Basically said it was water and that I should sump the fuel next time..which I did of course.

Final Conclusion:
Self-Induced carb ice.

...oh well.. chalk it up as a lesson learned.
 
Ron Levy said:
This is not a new phenomenon. I received an email several years ago from a guy who went in a cloud at -10F OAT (too cold for structural icing). Everything was fine until he decided to preemptively turn on the carb heat, at which point the engine rapidly choked down to not much above idle. He didn't get enough power to maintain altitude until he got down low enough to where the OAT was high enough that the carb heat could warm the intake air enough above freezing that the venturi effect in the carb wouldn't chill it back below freezing.

Keep in mind that air temp drops 30F degrees or so across the carb throat, and carb heat warms the air about 50F degrees. So if the OAT is down below about 0F, and you pull the carb heat, you've raised the inlet air temp to 50F, and it cools to 20F in the carb -- bad news when there was ice in the inlet air because the ice in the 0F outside air melts in the carb heat muff when it warms to 50F and then cools to 20F in the carb throat and ice forms in the carburetor. At that point, you're stuck, because you can't warm the inlet air enough (up to 65F or so) to keep it above freezing after it drops 30F degrees in the throat so it can melt out the ice that formed.
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Ron, with all due respect, I have problems with that. If that were true, Robinson helicopters would be falling out of the sky frequentlty. They don't as it turns out. Every R22 and R44 automatically applies full carb heat when the collective is lowered... And the POH calls for full carb heat below 18" MP...
 
jangell said:
I talked to the mechanic today...He said it was impossible to get carb ice with carb heat.
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Hmmm...your mechanic may need some additional education.

RotaryWingBob said:
Ron, with all due respect, I have problems with that. If that were true, Robinson helicopters would be falling out of the sky frequentlty. They don't as it turns out. Every R22 and R44 automatically applies full carb heat when the collective is lowered... And the POH calls for full carb heat below 18" MP...
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Perhaps the Robinson helicopter induction and carb heat system is different from that of airplanes -- I haven't any idea about its design. But for things like C-172's, it can happen and has happened.
 
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Ron Levy said:
This is not a new phenomenon. I received an email several years ago from a guy who went in a cloud at -10F OAT (too cold for structural icing).
Click to expand...

Another good myth...my cousin STILL gives me crap about telling him that. Sheesh! It's been over 10 years since he got all that airframe ice on his Viking at -20F!

Fly safe!

David
 
Quote:
Originally Posted by jangell
I talked to the mechanic today...He said it was impossible to get carb ice with carb heat.

Hmmm...your mechanic may need some additional education.

end quote


many old wives tales started many years ago, back when carb heaters were not what that are now. any aircraft/engine that is equipped with the Hanlon & Wilson style muffler, you can't hold your hand on the carb airbox when it is selected heat on.

Your later 172s that have the Lycoming 0-320-H2AD have a very poor carb heat system, it takes heat from one cylinder exhaust pipe (right front) and it won't clear ice very well.

When you reduce power the pipe cools, then you select carb heat and there ain't any.
 
MauleSkinner said:
It's been over 10 years since he got all that airframe ice on his Viking at -20F!
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While there is a very, very small chance of structural icing at temperatures below -4F (-20C), it takes an incredibly unusual combination of conditions to produce droplets large enough to remain liquid. At -20F (-28C), it's almost impossible. So I have serious doubts whether your cousin "got all that airframe ice on his Viking at -20F" unless he flew into a SIGMET for severe icing or confused the C and F scales on his OAT gauge.
 
Ron Levy said:
While there is a very, very small chance of structural icing at temperatures below -4F (-20C), it takes an incredibly unusual combination of conditions to produce droplets large enough to remain liquid. At -20F (-28C), it's almost impossible. So I have serious doubts whether your cousin "got all that airframe ice on his Viking at -20F" unless he flew into a SIGMET for severe icing or confused the C and F scales on his OAT gauge.
Click to expand...

Actually, he probably climbed into an inversion. but he still gives me grief ;)
 
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