Carb Heat IMC?

[DXB]

On 5/5/2017 at 10:12 AM, orionflt said:

the carbs in the C are very resistant to icing especially if you are WOT or close to it, use carb heat when you need it, and a carb temp gauge is very inexpensive for the benefits if you are going to be flying a lot of IMC. I ran across a story several years ago written by a gentleman who was flying the plane I currently own, he was flying IMC in weather and lost the engine because of too much water being ingested. nice to say it was a good outcome. here is a link to the story.

Brian

http://www.airspacemag.com/daily-planet/it-was-a-dark-and-stormy-night-1-66741228/

This is a fascinating account of how our engines may fail in a heavy downpour.  Unfortunately it will make me unsettled now if I fly in rain of lesser intensity, and the seasoned author here also did not take a position on whether carb heat is wise under these conditions.   I'm wondering if carb heat may even be a liability in heavy rain.  That unfiltered air intake at the back of a doghouse, which catches air coming through a big guppy mouth cowl, doesn't look particularly resistant to ingesting water either.  I suppose a lot of that water would turn to steam when it hits the muffler shroud. That could be an advantage over a possibly lesser amount of water getting sucked past a soaked filter but not rising to above ambient temp before getting to the carb. In that case, full carb heat, which also closes off the regular intake entirely, might be advantageous.  I'm just thinking out loud here and have no real expertise or notion of what the right answer is.  

What do the experts here think?  

Is there a case to use full carb to limit liquid H2O ingestion, even if carb temps are well above freezing??

Do more modern cowl designs (e.g. Sabremech's cowl) let less H20 reach the carb heat air intake?

[carusoam]

Carb heat is also known as the Alternate air source for the M20C.

Air intake systems and alternate air doors improved with the J.  Water gets separated and drained using intake plumbing. An actual alternate air door is opened using a control wire.

The cowl mounted air filter is a hint to the type of intake system that is used on a plane.  If a bunch of snow and ice is encountered while flying, the filter may get glazed over. Carb heat won't clear the glazing off the filter, but it will allow air to enter the carb through the alternate route...

PP thoughts only, not a CFI...

Best regards,

-a-

[cliffy]

Just a random thought-

Enough snow and ice to clog the air filter so Alt Air is needed or enough rain in IMC to snuff the fire out with cloud tops 40,000' and 200/ 1/2 over mountainous terrain in a small, single engine airplane? I wouldn't want to be there in a Boeing let alone my Mooney.

Just because we have an IR are we invincible? 

What in the H E double L would any one want to be there for?  Why would anyone be there in a Mooney? 

Let's get real folks, We don't have a FIKI, all weather interceptor here. There are limitations that any prudent pilot should be aware of and acknowledge. Even after 55 years in this business I sometimes walk away shaking my head in disbelief. 

Sorry, I'm off my soap box now. 

[RLCarter]

6 hours ago, DXB said:

I ran across a story several years ago written by a gentleman who was flying the plane I currently own, he was flying IMC in weather and lost the engine because of too much water being ingested. nice to say it was a good outcome. here is a link to the story.

11-4 M20C N78959 McCollum – Statesville NC 2.0 hrs
Gloomy forecast. Heaviest rain ever!! Engine out @7000’ over Barrett’s Mt due to showers

11-4 M20C N78959 Statesville – LYH 1.3 hrs
Emergency landing @ Statesville, MVFR (thank God!) Try to push on. More showers; Precautionary landing LYH. Stayed @ Holiday Inn

11-5 M20C N78959 LYH-W09 1.3 hrs
Mostly IFR, little rain. Good to be home!!

Here's the highlights as I see them, In 1985 you can bet he had no weather radar on-board and launched with T-Storms probably forecast along his route (Not Wise), then he gets an engine out due to a water soaked air filter and made it safely on the ground, (Damn Lucky), Next he "pushes on" (Just upgraded to Dumb Ass Status) luckily he made it back on the ground and managed to keep his head out of his ass and got a motel. I've seen a A36 Bo that was spit out the bottom of a T-Storm, Vert. Stab. had a 10~15 lean to it, and one wing tip was a good 12" higher than the other, very few skins on the plane that were not wrinkled, he did manage to land the now insurances airplane safely and walk away, soiled shorts and all. I just don't get why if Carb Heat is recommended in these conditions you wouldn't use it, Change the mixture if it makes it run rough, Lycomings or Mooneys for that matter are not immune from carb ice and under the right conditions it will happen. As a pilot you have the responsibility of a safe flight, neglecting the manufactures suggestions because you feel it isn't needed  isn't a good idea, but telling another pilot that something isn't needed that could cause an issue is just flat out wrong....I mean no disrespect to boilermonkey but his question isn't clear, "Carb Heat IMC?" would depend on what is causing the IMC, clouds and visible moisture, "Yes", dark night and no ground reference "No", visible moisture during VMC "Yes". I have forgotten the Carb Heat was "On" and flew 70 miles in a C-150 (Conti 0-200) and never noticed until it was time to land, and that included taking off some 50 minutes earlier. 

 

 

[Boilermonkey]

To be clear, the 1962 POH only calls for carb heat in a decent or landing, whereas more modern advice from the FAA and community dictate carb heat in various humidity+temperature conditions.  IMC (always has visible moisture), so do people use carb heat or not?  I raise the question because of the ambiguity of the original POH and my recent flying experience being in a fuel injected airplane.   Just looking for advice, not a debate ;-)

[midlifeflyer]

3 minutes ago, Boilermonkey said:

To be clear, the 1962 POH only calls for carb heat in a decent or landing, whereas more modern advice from the FAA and community dictate carb heat in various humidity+temperature conditions.  IMC (always has visible moisture), so do people use carb heat or not?  I raise the question because of the ambiguity of the original POH and my recent flying experience being in a fuel injected airplane.   Just looking for advice, not a debate ;-)

Specific type designs and configurations aside, the general recommendation is to use carb heat in two situations. One is when power is low. That's SOP in a Cessna but, as an example, Piper recommends against it (because of the location of the control, not because it would be bad for the engine). That said, the NTSB made a recommendation some years ago that all carbureted aircraft use carb heat when power is low.

Aside from that, the recommendation is to use it when there are signs of carb ice and some will run periodic testsen route. 

My practice? No, I would not use carb heat all the time enroute. I don't see a reason so long as one gears themselves to recognize the symptoms. That's even though I had a serious carb ice encounter.

[Hank]

I've pulled partial carb heat in IMC when the Carb Temp Gage was in the orange stripe, enough to get out of the orange. But  not very often  . . .

Safety Edit:  if you don't have a Carb Temp gage, Do Not Use Partial Carb Heat!! It should be all the way when you use it.

Edited May 7, 2017 by Hank

[carusoam]

Knowledge has increased over the years.  So has equipment.

1) partial carb heat is out of the question without having a carb temp indicator.

2) High RH is the cause of carb ice in Mooneys.

3) visible moisture is one way to know what the RH is.

4) Logic dictates that if you are going to fly a carb'd Mooney in IMC, you want to get a carb temp indicator.

5) use partial carb heat to stay out of the carb ice range using the carb temp indicator is an acceptable practice.

6) flying an M20C around in IMC often? Get a carb temp indicator.  The carb is most likely already set up for the sensor.

7) Adding the sensor makes sense. If you have an engine monitor already, adding the extra thermocouple to the display isn't that expensive, if possible.

8) the mechanical carb temp indicator that Hank described comes complete with a colored range to be avoided. that makes it easy to interpret.

9) Don't be drawn in to using partial carb heat without a gauge.

10) Carb temp: too hot is good, too cold is good.  That middle range from just below freezing to many degrees above freezing, is bad.

PP thoughts only.  Not an instrument sales guy...

Best regards,

-a-

Edited May 7, 2017 by carusoam

[RLCarter]

1 hour ago, Boilermonkey said:

IMC (always has visible moisture), 

IMC exist during times of rain, low clouds, or reduced visibility. IMC generally exist whenever visibility falls below 3 statute miles (SM) or the ceiling drops below 1,000 feet above ground level (AGL).

i personally use carb heat according to the POH and or anytime there is visible moisture

As for your POH, check with Mooney to verify you have the latest edition 

[cliffy]

I'm in a quandary- 

Are you folks saying that any time you are IMC you pull the carb heat on and leave it on the entire time you are in the clouds? No matter what power setting or phase of flight?

[RLCarter]

1 hour ago, cliffy said:

I'm in a quandary- 

Are you folks saying that any time you are IMC you pull the carb heat on and leave it on the entire time you are in the clouds? No matter what power setting or phase of flight?

IMC is confusing some, visible moisture does not mean you are in IMC, you can be in VMC under VFR and still be flying in the rain, just as you can have visible moisture on the windscreen or leading edges and it not be raining. You can also be in the clouds and not have any signs of visible moisture, 

So what I have have been harping on is go by the POH and if you have visible moisture regardless of being VMC or IMC use carb heat at any power setting. like I said earlier, I have always used carb heat when there was visible moisture and during landing and never had an issue, I have had carb ice 3 times, all 3 times I was in VMC at cruise power with NO visible moisture, all 3 times were in Conti powered aircraft in S. Tx with OAT's greater than 75*F. My thought is if the Manufacturer, FAA and my CFII says use it(carb heat), then why not.

[Hank]

9 hours ago, cliffy said:

I'm in a quandary- 

Are you folks saying that any time you are IMC you pull the carb heat on and leave it on the entire time you are in the clouds? No matter what power setting or phase of flight?

Fly all the time in the clouds with Full Carb Heat?? Never heard such an idea! 

This is what my Owners Manual has to say about it. What does yours say?

[bonal]

My understanding of how carb ice can also form is also due to the low pressure created as air accelerates thru the Venturi. It's important to be aware of humidity and the temp dew point spread. You can be in clear air and still develop ice if these conditions exist. Not likely with our O360 but has happened with my continental 200

[Hank]

10 hours ago, cliffy said:

I'm in a quandary- 

Are you folks saying that any time you are IMC you pull the carb heat on and leave it on the entire time you are in the clouds? No matter what power setting or phase of flight?

But I do switch on pitot heat just before entering clouds. Carb Heat goes on only when needed, see your Owners Manual for details.

[Mooneymite]

16 hours ago, Boilermonkey said:

 Just looking for advice, not a debate ;-)

Uh.....this is Mooneyspace, not the confessional.  

[carusoam]

1) When you get 'Unaccountable loss of MP...' - Hank's POH

Use Carb Heat.

2) If you have a Carb Temp Indicator...

You are free to use partial Carb Heat.

3) If you don't have a Carb Temp Indicator...

You are only going to want to use full Carb Heat.  

4) inappropriate use of partial carb heat (aka: without a carb heat indicator) can strangle the engine in an unrecoverable fashion.

5) Being familiar with what is going on in the carburetor helps...

- moisture falls out of solution as air chills and pressure drops.

- moisture freezes in the carburetor blocking the air passage.

- carb heat melts the moisture and this water causes some roughness temporarily as it passes through the engine.

- inappropriate partial carb heat can partially melt some ice to have it re-freeze further up inside the carb, further blocking the airflow.  

- Blocked airflow limits power.  Limited power is challenged to generate heat. Less heat equates to less carb heat being available.

- recognize the effects of mixture on heat as well

- recognize the effects of blocked airflow on mixture

6) air beneath the clouds in VMC is a great place to identify high RH.  As the air ascends to that level, the moisture falls out of solution causing water droplets, clouds...

7) It really helps to have an engine monitor for all the accurate EGT data it can provide and the carb temp indicator... 

 

There is a lot going on.  Recognizing the unaccountable MP drop is key.

PP ideas only, not a CFI...

Best regards,

-a-

 

 

Edited May 7, 2017 by carusoam

[hoot777]

Merry Christmas and happy holidays. I have a 1968 M20G with a carb temp gauge. I flew ifr yesterday at 2200msl on approach in the soup at abour 3C oat and had a reduction in power of about three inches of mp till heat applied. First time of using carb heat for real in about six hundred hours of Mooney flying. Use it when you need it.

 

[Hank]

1 hour ago, hoot777 said:

Merry Christmas and happy holidays. I have a 1968 M20G with a carb temp gauge. I flew ifr yesterday at 2200msl on approach in the soup at abour 3C oat and had a reduction in power of about three inches of mp till heat applied. First time of using carb heat for real in about six hundred hours of Mooney flying. Use it when you need it.

 

I use carb heat prophylacticly before entering IMC if carb temp is in thr orange stripe. Just remember to re-lean the mixture after adding carb heat. And don't use partial carb heat unless you have a carb temp gage!

[carusoam]

+1 for having a carb temp gauge...

For that 1 in 600 hours...

The one time I was fighting carb ice, my C didn’t have the fancy gauge...

My plane was loaded with precision to MGTW...

The small amount of power lost due to warm air, made it difficult to sustain altitude....

Running WOT, below a cloud deck, was still allowing carb ice to form....

It would have been great to have a carb temp gauge for that one hour!   

An IR would have been really good too!

The RH just below the clouds is pretty high... a set-up for strong carb ice build-up...

It was an interesting battle of forces....

1) carb heat on.... no carb ice. Not enough power to maintain altitude...

2) carb heat off... maintaining altitude. Not enough capability to avoid carb ice...

3) with a carb temp gauge... the PIC can modulate the carb heat to produce the most power without the danger of accidentally packing in carb ice...

4) Once the carb ices up for real... there is no way to restart the fire to melt it out...

5) Always test the carb heat system to make sure it is working... which is even more complicated without the carb temp gauge...

PP thoughts only, not a weatherman....

Best regards,

-a-

[0TreeLemur]

When flying through visible moisture and my carb temp is in the danger range on my engine monitor, I apply enough carb heat to raise the carb temp just above the danger range.

I learned to do this from my first experience with carb ice in IMC that caused a power reduction.  Boy was that an attention getter.  In a full power climb in West Texas, August 2019, I said something like "were losing power".   My co-pilot said "look at that temperature" pointing to the carb indication on the engine monitor.   I applied carb heat, and the engine came back to full power in about 10 sec. Smiles all around.

She's not a pilot.  Sometimes she's smarter than me!

[carusoam]

On 12/20/2020 at 10:45 AM, 0TreeLemur said:

 

She's not a pilot.  Sometimes she's smarter than me!

Smart team building idea...

Always surround yourself with smarter people...

Hmmmmmmm.... that’s why I hang out on MS... I’m fully surrounded.

Best regards,

-a-

[David Lloyd]

Only 500 hours or so with M20Cs, have only experienced carb ice a couple, maybe three times.  Each was in cloud and moderate rain.  A little roughness, a drop in manifold pressure, apply carb heat and within 30 seconds everything is back to normal.  Never had carb ice in cloud only.  Rime yes, carb no.

[Shiny moose]

My early flying in the midwest taught me alot about Icing, both carb icing and airframe icing.  Carb icing can sneak up on you, a slow loss of power during cruise,  or on take off or climb out when your just not perfoming as well as you should. Dont hesitate to apply carb heat when you think icing is possible, you can aways turn it off.  During initial climb out When your engine swallows that first chunk of water in bad carb icing, it will get your attention, you will think the carb heat is the problem when the engine shutters for which seems to last for several min ( really only a second). Now continuing your initial climb out with reduced perfomance is another thought process. 

Make sure your carb heat works properly. 

dont ever say it wont happen to you.

know the indications of carb icing beyond the carb temp guage

should have more focus during primary/ IFR  training

dont hesitate to use your carb heat

[hoot777]

On 12/18/2020 at 12:34 PM, Hank said:

I use carb heat prophylacticly before entering IMC if carb temp is in thr orange stripe. Just remember to re-lean the mixture after adding carb heat. And don't use partial carb heat unless you have a carb temp gage!

Thanks

[AIREMATT]

I’ve seen carb ice in my C a few times. On the ground taxiing and inflight. Usually lots of humidity (clouds) and temps above 32F. Watch the MP in flight and when an inch or so loss of MP is indicated, Carb heat on-when ice is removed, Carb heat off. Repeat through out the flight. During a 1 hour flight in light rain and solid imc I had to use it 5-6 times. C models can and do build up ice even at 65-75% power. During taxi out, I didn’t realize it had built up as much as it had until run up when I tested the carb heat and the engine sped up after the ice melted. Had to use it again before takeoff due to same highly humid conditions. Running with carb heat full on at cruise just because you are imc would require leaning the mixture to regain smoothness in the engine. Can’t say if it is bad for the engine but if you monitor MP and use carb heat as needed, you won’t have to worry about it being bad for the engine or not.