Carb Ice Frequency for Mooneys

[jlunseth]

1 hour ago, peevee said:

I've never had carb ice in a mooney. It might have something to do with not having a carb

I looked under the cowling and I couldn't find mine either.  Have there been a rash of thefts?

[peevee]

Just now, jlunseth said:

I looked under the cowling and I couldn't find mine either.  Have there been a rash of thefts?

I haven't had induction icing either.

[smwash02]

2 minutes ago, Andy95W said:

So then you can lean even more aggressively in the descent. 

You can't get something from nothing. You're effectively simulating a higher altitude giving you a lower power setting, which you could achieve by pulling out a little throttle.

[Hank]

3 minutes ago, Andy95W said:

So then you can lean even more aggressively in the descent. 

 I always thought carb heat was recommended on descent for those who make significant throttle reductions to descend at cruise speed. Personally, I leave the power in for a faster descent, to make up time for the slow climb.

[Andy95W]

14 minutes ago, smwash02 said:

You can't get something from nothing. You're effectively simulating a higher altitude giving you a lower power setting, which you could achieve by pulling out a little throttle.

Yup. 

Referring to your comment about the engine running cooler due to lower density air entering the induction system- this can be offset by leaning more aggressively in the descent. Referring to Hank's post above- because the POH recommends it. Referring to Gus's comment above (Mooneymite)- because it doesn't cost anything to pull the knob. 

Use it, don't use it, to each their own. 

[jlunseth]

28 minutes ago, peevee said:

I haven't had induction icing either.

Well, that's kind of a personal subject, but I am proud of you.  

[Hector]

In 6 years of C ownership in Florida flying in all kinds of conditions I think I may have had carb icing once, but I'm not sure. It ran a little rough so I pulled carb heat and it seemed to help. It could have been something else. I don't use carb heat in my C except during run up to make sure it works in case I need it.


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[Raptor05121]

While we're on the subject- what is the little round inlet on the LEFT side of the airbox? has a butterfly valve in it? Mine isnt hooked to anything

[Skates97]

1 hour ago, Raptor05121 said:

While we're on the subject- what is the little round inlet on the LEFT side of the airbox? has a butterfly valve in it? Mine isnt hooked to anything

I think you are talking about the bypass for the carb heat. With carb heat off it should be open and carb heat on it should be closed. It doesn't need anything hooked up to it but if you wanted to put a piece of scat tubing on to route it out your cowl flap you could. 

[gsxrpilot]

400 hours in a C and never once used carb heat, other than to check its function during run-up.

The only change needed for the descent is to adjust the trim.

[rdav]

I've only experienced carb ice once in my Mooney, flying near Kelowna, British Columbia.  It was a very humid day, with temps at freezing.  Definitely ran rough with carb heat on, but that was better than how rough she ran without the carb heat on!

[aajones5]

5 hours ago, smwash02 said:

When you apply carb heat the air into the carb is hotter, which is even thinner resulting in an even richer mixture to the engine, which will cause the engine to cool down even more during the descent, which isn't ideal usually.

What's the rationale behind using carb heat during the descent?

yeah I didn't mention that I lean my mixture too to maintain the same EGT temp I had for cruise and then will start to richen it as needed when I get lower

5 hours ago, Hank said:

Why are you using Carb Heat to descend are cruise power???

Yellow for me is 175-200 mph. If I push speed into the yellow, descent rates get pretty large. Groundspeed is often pretty good even at 170, I've seen 200 knots groundspeed a few times. I seem to reach the same 170 mph regardless of altitude, whether I'm coming down from a long time at 10,000 msl or a 15-minute trip at 3000 msl to pattern at 1600.

I'm still stuck on why your yellow arc is higher than mine is at, mine starts at 150mph and goes to like 195. Yours is a C model?

[carusoam]

1) Older Cs got a larger yellow arc...

2) Newer Cs got less of a yellow arc...

3) carb heat is the alternate airsource for the M20C. Age / wear of the wire and butterfly valve can make the carb heat system not work.

4) It is easy to block the airfilter with snow and ice.  If ice is showing up on the windshield it is probably doing the same on the air filter

5) In 10 years of C flying I only got carb ice on one flight. Going to SnF with three people on board. Engineered to the max, not a pound over weight. Not a pound under either....

6) carb ice event.... April in NJ. Low ceilings, precipitation, improving west of philly. Plan to fly VFR beneath the clouds until clear. Power kept becoming noticeably less. Carb heat would restore the power. After a few cycles of carb heat, power restoration, carb ice...select an emergency landing field, carb heat, power restoration, carb ice...select a field...

7) flying like that isn't much fun.  Full carb heat lowers the power. No carb temp indicator eliminates the safety of running partial carb heat.

- Get the butterfly and its control up to working properly

- Get a carb temp gauge

- know how this stuff is supposed to work.  If it doesn't work, it won't be much help when you need it.

 

Alex, I can only guess what you mean when you say it isn't connected to anything....

- if the butterfly isn't connected, that is bad.

- if the outlet from the butterfly valve doesn't have a hose on it... This is normal.

 

How the carb heat works is a full discussion....something like this....but not exactly (fuzzy aged memories....)

- Air is heated by the heater muff

- warm air is routed towards the carb

- this warm air stream is dumped by the butterfly valve

- warm air dumped by the butterfly valve joins the air that was warmed by cooling the cylinders.

- all this warm air gets dumped overboard out the cowl flaps.

- segregating the warm carb air from the warm air from the cylinders won't be of any help.

- in the event that the filter gets completely blocked, all the air for the induction system will have to come from the heater muff route..?

Aged fuzzy memories. Enough to get a pilot started on the route to finding out more about carb and filter ice, what the effects are,  and how to avoid it.

The plane Being fully loaded isn't the time to figure out how much power you have vs. how much power you need...

Don't run partial carb heat without a carb temp indicator.  This is the recipe for cooling heater muff, while building carb ice, snuffing out the engine with no way to use full carb heat again...

Yes, one carb ice experience is enough, like one stuck valve is enough. It is great to have an engine monitor for this stuff.

Best regards,

-a-

Edited April 22, 2017 by carusoam

[Raptor05121]

Butterfly isnt connected and is rusted away.

[carusoam]

Get on it...  

Lasar probably has some details to know about...

Of all the things, this one is probably not measured in AMUs....

carburetor parts like the valve and bits are probably available through A. spruce.

Also check to see where the warm air is coming from, just in case somebody removed it along the way...(?)

Best regards,

-a-

[WilliamR]

I've encountered carb ice once in an M20C in about 400-500 hours of "C" time.  Engine had significant roughness, but did not get bad enough to lose any material amount of manifold pressure.  Conditions were over the Gulf between Cedar Key and St Pete. 7000', WOT, outside temps low 50 degrees F, dew point probably within a degree or two.  VMC at the time, but I was intermittently IMC and there was a low undercast (read lots of moisture in the air).  BTW, the plane had been running for at least 2 hours at cruise power.  If you remember back to your Private Pilot days, there is a chart that shows likelihood of icing based on temp and dew point.  I was in the heart of icing even with cruise power.  I wish I had a carb temp gauge that day.  For the next hour until landing, anytime I would try to reduce or shut off carb heat, the engine ran rough.

Question, why is it recommended to have carb heat all the way on or all the way off, but never in between? 

BTW, I swear the C-150 I used to instruct in would get carb ice if there was a cloud anywhere within the Continental US.   

William

[aajones5]

I've encountered carb ice once in an M20C in about 400-500 hours of "C" time.  Engine had significant roughness, but did not get bad enough to lose any material amount of manifold pressure.  Conditions were over the Gulf between Cedar Key and St Pete. 7000', WOT, outside temps low 50 degrees F, dew point probably within a degree or two.  VMC at the time, but I was intermittently IMC and there was a low undercast (read lots of moisture in the air).  BTW, the plane had been running for at least 2 hours at cruise power.  If you remember back to your Private Pilot days, there is a chart that shows likelihood of icing based on temp and dew point.  I was in the heart of icing even with cruise power.  I wish I had a carb temp gauge that day.  For the next hour until landing, anytime I would try to reduce or shut off carb heat, the engine ran rough.
Question, why is it recommended to have carb heat all the way on or all the way off, but never in between? 
BTW, I swear the C-150 I used to instruct in would get carb ice if there was a cloud anywhere within the Continental US.   
William

I think it's because if you don't have a carb temp gauge and you're running partial carb heat your carb temps could still be below freezing


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[Hank]

3 hours ago, aajones5 said:

 

I think it's because if you don't have a carb temp gauge and you're running partial carb heat your carb temps could still be below freezing


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The purpose of carb heat is to melt the ice into water, so it can flow into the cylinders (rough running) and go away through the tail pipe. Without a Carb Temp gage, you may not heat it enough to clear the throat and go into the cylinders, but maybe only run a little way and refreeze, since the cold temperatures extends some distance downwind of the carb throat. Then you may have a real problem, as even full carb heat carb heat may not melt it . . .

The more we discuss this, the happier I am that my C was equipped with the (optional) Carb Temp gage when I bought her. It's obviously not the factory gage, as it's in °C, but if I'm worried I'll pull enough Heat to get it out of the orange stripe. There was that one winter day over central WV, between layers, with intermittent light snow showers, where I was concerned and very watchful. A little carb heat really makes a man feel better!

[Jim Peace]

I have had carb ice in my C during initial climb out.  Atmospheric conditions were perfect for it and it happened.  Carb heat on for 10 seconds or so cleared it right up.  I thought you could not get it with WOT, but after a google search it appears that it happens to a fair amount of pilots.

 

 

 

[tigers2007]

That's a pretty chilling story.  Does anyone here routinely keep running carb heat after run-up if you have to wait?

I came close to crunching a C150 due to carb ice becoming dangerous immediately after takeoff. Temp was a few degrees from dewpoint. IIRC, 59F OAT on July 12. I had an unusually long taxi due to me fumbling around in the cockpit for a while after startup. I made it back on the last couple hundred feet or so of the 5500' runway and slid off the end into the grass. That was the end of my relationship with Continental O-200's for life.

My O-360-A1D powered M20D was involved in a full carb icing engine shutdown over New Mexico in the 70's. They landed uneventfully at an airport (per NTSB). I had mine on today during visible moisture with an OAT of 28F.




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[carusoam]

Airflow through the Venturi drops the carb air temp.

the lower air pressure and temp both drop moisture out of solution.

The throttle valve has a way of magnifying the pressure drop.  Open throttle has less risk, but still has some.

The combination of water falling out of solution and temperature falling below freezing are the two required parts of icing...

Best regards,

-a-

Edited May 2, 2017 by carusoam

[M20C_AV8R]

Living in this icebox called the PNW,   I flew the plane down to the avionics shop yesterday, absolute perfect atmospheric conditions for carb icing, high humidity and cold.  Really noticed it in cruise and descent. I have, never used my carb heat so much, albeit not my first rodeo, it was educational to have a flight where managing carb ice was key, and the reminder of how to best manage the plane with it as a constant, increased the workload but, not horribly. I also had my IA put the carb temp :-) sensor in with the JPI install, fantastic investment.

Edited November 9, 2018 by M20C_AV8R
correction

[carusoam]

Carb temp sensor makes a world of difference...

specifically, better than a carb ice sensor. That is better than no sensor at all...

great pirep from the PNW!

Best regards,

-a-

[Boilermonkey]

My partners and I had carb ice THREE times THIS YEAR!  Once at cruise (WOT), once on departure (WOT), and once on approach in IMC (without carb heat applied).

We have changed a few things:

1) Always use carb heat on approach or in the pattern

2) Always leave carb heat on for more than a few seconds at run up.  

3) If holding for release either use card heat or check it again.

4) Make sure you lean when carb heat is on to ensure smooth running engine and no fouling of the plugs

5) We overhauled the carb, since it was way overdue and might be contrbuting to the problem.

6) We added a carb temp gauge so we know what is really happening.  (and we'll adjust the items above as needed based on the carb temp)

7) Just because the carb temp is in the "ice zone" doesn't mean that it will ice...there must be moisture...so we'll be learning because we don't want to have carb heat on all the time.

[Hank]

I ALWAYS turn on carb heat before entering IMC, at least enough to keep the needle above the orange stripe. Pull some heat, punch into the cloud, adjust to stay above the ice zone and re-lean the mixture. When breaking out not on approach, turn off carb heat and re-lean the engine.