Carb Ice Frequency for Mooneys

[aajones5]

So I've never had an experience of carb ice so far in my 100 or so hours of flying my Mooney. In the first about 50 hours of flying it I never ran the carb ice because the engine always ran rough when I used it and never had a problem with carb ice, but once I figured out I just had to lean the mixture very excessively to get the engine back to normal, I now run it just on my descents until I get to pattern alt. and haven't had any problems. However I flew a friend's 172 a few times in the past month and it seemed to get carb ice almost every time I flew it. My question is, how often have y'all had carb ice in your mooneys and do you think mooneys are just less susceptible to it or have I just been lucky.

[Hank]

I've been flying my C for almost ten years. Other than just after cranking the engine, I've pulled carb heat only when entering clouds that were near freezing a few times. Carb ice? None yet . . . But here in the South, it's certainly possible. My first seven years of ownership were along the Ohio River on the OH/WV border, no ice trouble there either, summer or winter. But Lord have mercy, the climb rate in the winter there, solo with half tanks! 

[aajones5]

I mainly use the carb heat to help reduce power and slow down on the descents, I've also started toying around with reducing prop rpms down to 2200 to help slow down. Off Topic but I've thought about going down to 1950, but would you go that low as long as the MP are below that it should be good.

[Mooneymite]

Lycoming O-360's are not terribly prone to icing.  The cowling tends to keep the up-draft carb warm.  However, my 74 POH is pretty specific if you don't have a carb temp gauge like Hank does:  Use it for reduced power (descent) operations.  Here's the key:  it doesn't cost you a thing.  As you've found on your own, all you have to do is lean the engine a bit more and it runs smooth.  Above a couple thousand feet, unfiltered air is no factor.

If you wait until you need carb heat, the engine has probably quit and you can't get carb heat.  Why take the chance?

 

 

[aajones5]

Very true I use it for my descents but once I get down I turn it off because the chances of it developing from downwind to final are low and once I go full rich for the GUMPS check the engine runs very rough with it on

[Hank]

I descend  power on, simply pushing the yoke for 500 fpm and trimming it hands off. As I descend, MP and EGT both increase, so I occasionally reduce throttle to whatever my cruise setting was, and enrichening the mixture to also regain my cruise setting. Speed generally increases to ~170 mph, just below the yellow zone, which helps make up for that long, slow climb to altitude at takeoff.

If it gets too bumpy, then I pull back the throttle more, but that's not a common experience for me.

And yes, I really like having the carb temp gage!

[aajones5]

That's just below the yellow for you? I descent the same way reducing about one inch MP per thousand feet as I go with carb heat full on and sometimes rpms reduced but if I don't I end up about 170 too buts that's right in the middle of the yellow arc for me so if it gets bumpy I have to pull power way back. Once I got this EDM finally put in I'll have carb temp as well which will be very nice

[Raptor05121]

I have the carb temp gauge. I also use mine proactively if there is visible moisture out. I also use it to get the power down on final. As noted, it runs excessively rich, so I keep the mixture leaned until I'm short final and need reserve for go-around power, and both go in.

I've got 250 hours in Florida and I've never experienced carb ice.

[DXB]

I've never had conclusive evidence of carb ice on my M20C.  However on my digital gauge, it's not at all uncommon to see carb temps in the high 20s/ low 30s F in cruise and descent.  If combined with the right amount of atmospheric moisture, I could imagine this becoming an issue, so I pull partial carb heat in cruise to bump temp into the mid-high 40s.  Supposedly this can help mixture distribution too though I've never seen any evidence of it on my plane.  I pull carb heat full on for descents and turn it off at last gumps check on final to prevent running rough at full mixture when I pull throttle to idle before the flare. Doing so also leaves one less thing to worry about in case of a go around.  

Unless I'm mistaken there have been a few Mooneys brought down by carb ice?  It seems like one of those areas that really could catch you by surprise since it is uncommon overall for the carb/engine setup on these planes.  

[kortopates]

25 minutes ago, aajones5 said:

Very true I use it for my descents but once I get down I turn it off because the chances of it developing from downwind to final are low and once I go full rich for the GUMPS check the engine runs very rough with it on

If you had the carb_temp sensor info in your engine analyzer that would help a lot to keep you out of trouble. But not using carb heat it in the pattern could put you in risk on a balked landing/go around when you discover you have only partial power trying to climb and going no where fast due to some ice. You don't have to go totally full rich either, as required to keep it smooth, but enough you'll make full power on the go and can then add full mixture before the temps climb rapidly - cause they will.

You already know, that if the worst did happen like that, having a partial power loss on the go from carb heat, the NTSB is going to fault the pilot for not following the carb heat guidance in the POH. The risk is likely small but real.

[kortopates]

3 minutes ago, DXB said:

Supposedly this can help mixture distribution too though I've never seen any evidence of it on my plane.

It really works, but you need to try a range of carb-temp values (temps) and perform some GAMI sweeps WOT. I've seen it make a big difference but what you really want is a decent spread below 1.5 GPH where the carb heat reduces it by half and you can now run lower power LOP successfully  - and that is still pretty rare. 

[peevee]

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

[aajones5]

What does WOT stand for?


Sent from my iPhone using Tapatalk

[DonMuncy]

Wide open throttle

[kortopates]

My apologies - WOT is Wide Open Throttle. I said this because that when good mixture distribution is most practical  importantance

25 minutes ago, DXB said:

Unless I'm mistaken there have been a few Mooneys brought down by carb ice?  

I can't say for sure, but there have been many downed vintage Moony's due to induction icing and at least one early 231 close call. The downed planes I recall where from flying in visible snow - and not necessarily IFR as you might think.

[smwash02]

I've had it two or three times in my M20C.

One time you could feel the engine really miss a beat. The other time the engine actually died. My reflexes had me immediately swap tanks, carb heat on, and aim for the road. In couple seconds it took me to do that it roared back to life. I attribute it to waiting on the ground for a long time before take off on a day very conducive to carb icing. Event happened climbing through 2-3k.

[M20F]

Carb ice is very dependent upon atmospheric conditions thus why some people never see it and others do.  

[DXB]

52 minutes ago, kortopates said:

It really works, but you need to try a range of carb-temp values (temps) and perform some GAMI sweeps WOT. I've seen it make a big difference but what you really want is a decent spread below 1.5 GPH where the carb heat reduces it by half and you can now run lower power LOP successfully  - and that is still pretty rare. 

Interesting - thanks.

[Andy95W]

In nearly 1,000 hours of M20C time, I have had carburetor ice exactly one time- about 25 years ago at 10,000 feet, IFR, in the tops of a stratus cloud layer. OAT was probably about 35° F, so prime icing conditions. 

[DXB]

27 minutes ago, smwash02 said:

I've had it two or three times in my M20C.

One time you could feel the engine really miss a beat. The other time the engine actually died. My reflexes had me immediately swap tanks, carb heat on, and aim for the road. In couple seconds it took me to do that it roared back to life. I attribute it to waiting on the ground for a long time before take off on a day very conducive to carb icing. Event happened climbing through 2-3k.

That's a pretty chilling story.  Does anyone here routinely keep running carb heat after run-up if you have to wait? I don't although I've heard this issue come up before.  I wonder if that should go on the checklist. I turn boost pump off and re-lean mixture if I'm waiting and have made it a hard-wired reflex to check both right before entering the runway.  I wonder if carb heat should be added to this short list.

Also I imagine carb heat effectiveness rapidly drops to nil in the moments after the engine fully quits as EGT plummets, so it's best not to delay if there is the slightest concern.

[Hank]

My C would never run smoothly LOP. Then I spent two annuals resurrecting my doghouse and rebuilding the carb heat flapper, and viola'!! Now I can run smoothly about 25°LOP. I'm now shopping for an engine monitor (although I have no remaining panel space), which will allow me the option of cruising at LOP.

I lean enough on the ground that I need to enrichen slightly to taxi uphill, and the engine nearly died pulling from grass parking up onto the taxiway until I pushed the mixture forward a lot. So no, I don't worry about carb ice on the ground. I've only had long waits to depart two or three times, though--once for an airliner on approach (too many minutes in 100° heat in Savannah), and one ten-minute hold to depart into IMC from my uncontrolled field because of traffic into/out of the nearby Class D when I called for clearance. 

[Hank]

1 hour ago, aajones5 said:

That's just below the yellow for you? I descent the same way reducing about one inch MP per thousand feet as I go with carb heat full on and sometimes rpms reduced but if I don't I end up about 170 too buts that's right in the middle of the yellow arc for me so if it gets bumpy I have to pull power way back. Once I got this EDM finally put in I'll have carb temp as well which will be very nice

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.

[smwash02]

Just now, Hank said:

I lean enough on the ground that I need to enrichen slightly to taxi uphill, and the engine nearly died pulling from grass parking up onto the taxiway until I pushed the mixture forward a lot. So no, I don't worry about carb ice on the ground.

For what it's worth, I lean just as aggressively on the ground. Coming from a 150 with an O-200, it was pretty much mandatory (aside from a little MMO) to keep the stuck valves at bay so it's a long ingrained habit.

[smwash02]

1 hour ago, aajones5 said:

I descent the same way reducing about one inch MP per thousand feet as I go with carb heat full on

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?

[Andy95W]

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