Quick Question about Carb Heat

[MIR2018]

So, when flying a Cessna Skyhawk, I pretty much pull the Carb Heat anything below 2100 RPM.  What's the normal MP that Carb Heat should be applied?  The POH doesn't say much about it...

 

[Boilermonkey]

We've had carb ice three times this year. Once at cruise, one in an IFR approach, and once on departure. We hadn't been consistently using carb heat, but are now. It does require us to lean a bit otherwise it runs too rich.

Sent from my SM-G960U using Tapatalk

[carusoam]

1) Carb heat procedures are very specific to airframe/engine combination... (skip the Cessna reference)

2) weather phenomena specific... high humidity in the air... near clouds, beneath clouds, in clouds, in rain...

3) High vacuum phenomena...reduced throttle ... (adiabatic cooling, so not directly OAT related...)

 

4) without a carb temp sensor... your choices are limited to carb heat on or off...  without data, you would be guessing... an incorrect guess could block the carb full of ice...

5) by procedure, use in the traffic pattern, remove on the go-around...

 

6) best method is adding the carb temp sensor/gauge...

 

Nothing worse than flying along beneath the clouds and getting carb ice with a plane full of people at max gross... and the engine not producing power for some reason... is it carb ice or is it a land now engine issue?

The carb temp gauge can tell you if you are in the range of having ice, and gives you the ability to modulate the heat to stay out of the icing range, while providing the proper power to continue the flight....

How does that sound?

PP thoughts only, not a CFI...

Best regards,

-a-

[MIR2018]

6 minutes ago, carusoam said:

 

1) Carb heat procedures are very specific to airframe/engine combination... (skip the Cessna reference)

 

I included the Cessna reference because I understand it is airframe specific and that is it for that aircraft.  I was assuming that the Mooney airframe also had a more precise recommendation than what is in the POH...  I was looking for more of a What-do-you-guys-do response...

At this point there is not a carb temp gauge.  So saying I should get one, doesn’t answer the question or help much...

[midlifeflyer]

The C manuals I've seen have carb heat "hot" for landing rather than carb heat "as needed" for landing.

FWIW, some years ago, based on a review of carb ice incidents, the NTSB recommended that , in all cases, with all carbureted airplanes, carb heat should be used as a preventive.  The recommendation went nowhere. 

Edited September 22, 2018 by midlifeflyer

[carusoam]

Sorry...

my writing skills are still improving...

1) I added the Cessna reference because carb ice is so specific to airframe/engine combo, I didn’t know a better way and be less blunt.  The 2100 rpm referenced, is good for that one machine, but is technically, unrelated to the ice making machine... especially when an adjustable pitch prop is used... 

2) To Avoid carb ice, use full carb heat.  (That has a HP cost associated with it)

3) Carb ice requires two things moisture and near freezing temps in the carb Venturi...

4) Avoid these two things.

5) Low throttle settings decreases the temp in the Venturi.  (Hard to avoid when you want to land)

6) Check the latest copy of the M20C POH to see if there is any improvement... (there is one available in the download section)

7) I left out the part that mentioned how good the MS search function works, didn’t I?  

8) I also didn’t reference the engineering steam tables that would give a method of predicting carb ice based on atmospheric pressure, temp and RH, combined with MP setting...

 

 

Mir,

I gave you the three things to know, that MSers use to avoid carb ice.

...And gave you the next step MSers use when a few dollars more they can achieve the next level.  Get a cab temp sensor for your JPI? Or add a thermocouple to your existing JPI...

Or to keep things really simple add the analog carb temp gauge... @Hank has shown a few pictures of his...

...And I may have thrown a jab/dig at brand C planes...

...and intentionally left out how to use the search function...

 

The M20C was delivered as a pretty simple machine, with the ability to stepwise improve it.  The carb has a location to add a thermocouple. The panel has a location to add a gauge...

The level of safety improves by adding less than 1amu of hardware...

I’m only a PP, not a pro writer or a mechanic... or I would copy a few pages out of the AS catalog to point out the parts for you...

Briefly... 

• if you have High RH, expect to use carb heat.  Visible moisture, and some not visible moisture...
• If you reduce throttle, expect the chance of carb ice to increase, unless outside air is below freezing...
• Don’t use partial carb heat without the instrument to guide its use...
• yes, MSers have added instrumentation to their M20Cs...

Is that any clearer?

Other challenges for consideration...

• How well is your carb heat system really working? Have looked recently? (Aged systems have been known to fail)
• Do you test the carb heat system to get an MP drop prior to each flight?
• One MSer recently had a carb heat system get replumbed incorrectly... quirky story, but being knowledgeable about carb heat saved the situation from getting worse... search for carb heat and MSC in the same sentence...

Trying to help, sorry if I am unable... 

Best regards,

-a-

[Jim Peace]

Carb temp gauge is not that expensive....put one in.  I did and now I see the big picture.  Should have done it years ago.

I thought I had carb ice a few times in a climb right after takeoff.  My engine did run a bit rough after my carb temp install,  just like it did when I thought I had ice.  Turns out I was just running a bit rich.  Carb temp was nowhere close to icing.  

Its nice to know what you did not know in the past....it solves one piece of the puzzle....

its a good excuse to install a JPI 900 and get rid of all the inaccurate technology.

 

[Jim Peace]

2 hours ago, carusoam said:

 

• One MSer recently had a carb heat system get replumbed incorrectly... quirky story, but being knowledgeable about carb heat saved the situation from getting worse... search for carb heat and MSC in the same sentence...

I would have never known how bad a MSC messed up my carb heat if not for my CRB temp on my JPI 900.

[gsxrpilot]

I flew an M20C for two years and 400 hours. And a good bit of that was IFR/IMC. The only time I ever used carb heat was every run-up prior to take off. 

I did install a GEM G2 shortly after purchasing the airplane. It includes Carb temp. I never saw carb temps anywhere close to icing.

[Boilermonkey]

I have heard that ever since I owned a Mooney and so I only used carb heat at run up. Big mistake....engine almost quit on me three times this year and each time carb heat resolved the issue. It's a roll of the dice.

I flew an M20C for two years and 400 hours. And a good bit of that was IFR/IMC. The only time I ever used carb heat was every run-up prior to take off. 
I did install a GEM G2 shortly after purchasing the airplane. It includes Carb temp. I never saw carb temps anywhere close to icing.

Sent from my SM-G960U using Tapatalk

[gsxrpilot]

2 minutes ago, Boilermonkey said:

I have heard that ever since I owned a Mooney and so I only used carb heat at run up. Big mistake....engine almost quit on me three times this year and each time carb heat resolved the issue. It's a roll of the dice.

 

That's pretty unusual for an M20C...

Of course if the engine ever did stumble... it would be carb heat then switch tanks... all in the space of about 5 seconds. But mine never did.

[Boilermonkey]

I agree. Going to have the carb overhauled just in case there isn't something else going on.

That's pretty unusual for an M20C...
Of course if the engine ever did stumble... it would be carb heat then switch tanks... all in the space of about 5 seconds. But mine never did.

Sent from my SM-G960U using Tapatalk

[Skates97]

I was bummed when I had my EDM830 put in and learned that my carb did not have a plug where the sensor would go that could easily be removed to install the sensor. They would have had to drill and tap it to put them temp sensor in...

17 minutes ago, gsxrpilot said:

I flew an M20C for two years and 400 hours. And a good bit of that was IFR/IMC. The only time I ever used carb heat was every run-up prior to take off. 

I did install a GEM G2 shortly after purchasing the airplane. It includes Carb temp. I never saw carb temps anywhere close to icing.

 I only have couple hundred hours in my plane (no IMC but some rain showers) and have not had any indications of Carb Ice. 

[Jim Peace]

8 minutes ago, Boilermonkey said:

I agree. Going to have the carb overhauled just in case there isn't something else going on.
 

 

great idea....let us know who does it...I am thinking of doing the same.  Not because I have issues with the carb its more like just because its Tuesday type thing....maybe I do have issues...

[gsxrpilot]

41 minutes ago, Skates97 said:

I was bummed when I had my EDM830 put in and learned that my carb did not have a plug where the sensor would go that could easily be removed to install the sensor. They would have had to drill and tap it to put them temp sensor in...

That also seems very unusual for an M20C.

[Skates97]

7 minutes ago, gsxrpilot said:

That also seems very unusual for an M20C.

Maybe because it started its life as a M20D?  I'm not sure. The carb is a Marvel Schebler MA-4-5, part # 10-3878.  I have the sensor, when I get to the point I am going to overhaul the carb or replace it with an overhauled one I will have it installed.

[carusoam]

See if somebody posted the Marvel Schebler technical document around here...

I saw it go by one day... it had complete drawings and details.  That may include various service entries...threaded holes with plugs...

Best regards,

-a-

[carusoam]

See if somebody posted the Marvel Schebler technical document around here...

I saw it go by one day... it had complete drawings and details.  That may include various service entries...threaded holes with plugs...

Best regards,

-a-

Dev posted the link a while ago...

http://www.expaircraft.com/PDF/marvel-schebler-OH.pdf

yes, it’s not exactly the one you have...

we’ll still need to get more specific...

 

[Skates97]

10 minutes ago, carusoam said:

See if somebody posted the Marvel Schebler technical document around here...

I saw it go by one day... it had complete drawings and details.  That may include various service entries...threaded holes with plugs...

Best regards,

-a-

Dev posted the link a while ago...

 

Thanks, I'll take a look and see what I can see, but I'm not hopeful. They have installed a number of 830's so if they say the carb is missing the plug where the sensor would go I'm inclined to believe them.

[carusoam]

When the questions get that technical I’m inclined to ask the guy who has the answers... or knows where the answers are stored...

 

I’m not sure what the question is... a few have come up...

1) The OP was asking what the latest carb heat procedure is for his M20C...

2) The next question is how to add a carb temp sensor to the Marvel Schebler MA-4-5.

3) The last question is how to put a sensor hole in a MS MA-4-5 that doesn’t have a threaded hole for a sensor in it yet.

4) We have an MSer that sells JPI equipment.

5) We have an MSer that specializes in used JPI equipment and installation.

6) We have an MSer that specializes in all things Mooney, and 8 cylinder Lycoming...

 

See if @M20Doc has any technical answers about adding a temp sensor to Mooney carbs...

 

Best regards,

-a-

[carusoam]

1 hour ago, Skates97 said:

Thanks, I'll take a look and see what I can see, but I'm not hopeful. They have installed a number of 830's so if they say the carb is missing the plug where the sensor would go I'm inclined to believe them.

It would be easier to find... if somebody with a sensor could point to where their sensor is located...

( @Hank is a great resource for mechanical things and M20Cs...)

Essentially it would need to be in or after the Venturi where the air temp and pressure has dropped completely (or a significant amount near completely...)

It is possible there’s is a boss (flat spot) for drilling and tapping the hole... reading through the various drawings and parts lists in the manuals above, I didn’t see anything that said temp sensor location.

I did see one spot that looked like a boss for a sensor, but it had no note to say what the spot was...

it looks like it would be a $5 hole that would take about 1amu to get put in place...

Best to be done during annual when the cowling is off... even better if the carb comes off for OH...

It would still be better to have the temp sensor, than not...

And... don’t fall for the ice detector alternative... a pilot needs to know he has the conditions right to not produce ice in the carb.  The ice detector is too simple and only automates the decision to turn the carb heat on fully... the carb temp sensor allows the pilot to modulate the carb heat to eliminate the probability of ice and maximize the HP that can be produced.... at the same time, and done very quickly...

Floats, accelerator pumps, jets and a few other items get some discussions around here... 

Does MS have a person that specializes in carbs?

Best regards,

-a-

 

[Hank]

I need to backtrack through thus whole thread . . . Yes, the Optional Carb Temp Gage is a wonderful thing. In six years' flying along the Ohio River, I pulled carb heat in flight to get the needle out of the orange stripe twice, both on winter instrument training flights with my CFII (once in the clouds, once below some darkish-gray clouds). Flights in IMC over southern WV, through light snow that didn't stick anywhere I could see, carb temp was fine even if my nerves were not. The 4 years since I moved back South, none at all. This covers almost 700 hours' tach time, more than that in my logbooks.

Checking carb heat function is in the Post-Engine Start checklist, but my Owners Manual doesn't say near as much about its use as the 172 manuals when I was getting my PPL. Let's see what I can find . . .

Right, not much. Because I am so equipped, I live by the first sentence affer the word "Warning":  Do not use partial carburetor heat unless the aircraft is equipped with a carburetor air temperature gage. Although it doesn't explicitly say so, I use enough carb heat to get the needle out of the marked orange stripe, which is in °C while my OAT is in °F . . . . .

More later, it's bedtime.

[Skates97]

Yes, a $5 hole that would take about 1AMU to create. That's about what the shop said as well. From the pics I can find online here is where they are installed and looking at the new ones for sale there's a screw/plug there that you would remove to put the sensor in. I'll take a look when I'm at the hangar next but it don't recall anything there. 

[ragedracer1977]

Well this is interesting.  I have a carb temp sensor in my carb, but no gauge on the panel.  Wonder where those wires go...

[carusoam]

Great pics, Rich! @Skates97

there are two rough casting flat spots... or bosses... one above the label. The other below...

in the top pic there is a sensor.

in the bottom pic there is a brass plug...

 

See if you can get a pic of your actual carb.  With the M-S label on it, it should be pretty easy to focus on where the hole should be...  or should have been...

It is possible that the D got some pretty annoying cost cutting things done to it... but, the program at the time included the ability to upgrade to a full C... gear, prop and everything else...

Later with the Eagle... There was no intention to bridge from Eagle to Ovation...

Some engineer’s desire to make things right for the next owners down the line.... is all it takes...

 

Bryce @ragedracer1977you gotta trace those wires back to the panel... somebody connected them to something... once...

If you have a JPI it may require telling it to look for the carb temp... or a way to have the JPI scan for it... somebody has covered that topic around here before...

It would be really cool if they were attached already, just not activated....?

Best regards,

-a-