Mixture, Carb Heat, and Pitot Heat

CC268

CC268

Final Approach
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CC268
Hey guys,

I have a couple questions regarding mixture, carb heat, and pitot heat:

1. How do you know how much to lean the mixture as you ascend to higher altitudes? How much to enrichen when descending?
2. I live in Arizona where the environment is very dry...how do I know when I should use carb heat? Should I always use it when descending? Always when landing?
3. Pitot heat - When do you guys generally use this? I know some plans (like the Cirrus) automatically turn it on at a certain threshold, but the 172 I train in doesn't do this.

I asked my instructor these questions (except the first one), but I would like to hear what you guys have to say as well.
 
1. Depends on the engine you have. First place to look is in the POH.
2. Depends on the engine you have. First place to look is in the POH.
3. General suggestion is anytime you're in visible moisure (a cloud, rain, etc...). First place to look is in the POH.
 
Those are very good questions. If you do not have a good understanding when and how to use each system, study it to understand and be able to apply your knowledge in use.
Not knowing why you're doing what you're doing, especially with advice from them Ynterwebs, is a good way to get into trouble. :)
You will get a LOT of information here, sometimes conflicting, get ready for it. Leaning and carb heat questions tend to start a lot of religious wars.

1. If you don't have a FF meter or EGT gauge, you have to lean in climb by experience and in cruise by ear.
2. Usually no carb heat required in dry climates. Unless you're descending through a cloud deck.
3. Pitot heat needed only in freezing conditions (especially when your ASI "freezes"). Hope you won't be flying into freezing clouds/rain during your PPL training!

Btw, your CFI should be able to point you to the right book/chapter to read up on these.
 
Though carb heat is probably unnecessary in Arizona, you won't fly there your whole life. Make habits that work outside of your narrow situation. It does rain there occasionally, so it's not always completely dry. It's also VERY hard to estimate water content in the air without a hygrometer, unless it's saturated or nearly so. It's not always dry at altitude in the desert, particularly if rain shadowing is significant.

I just did a ferry flight 75 miles from Sacramento to Palo Alto, in a carbureted 182 equipped with a carb temp gauge. Weather was 4000 overcast over most of the flight, clear on departure, temperatures mid 60s at the surface, occasional drizzle, sufficient VFR weather. It needed half carb heat the entire flight, including the climbout, in order to keep the carb temp acceptable. Full carb heat on descent.

If you don't have a carb temp gauge (a few 172s do, most don't), use the green arc on your tach, like the POH says. Only use full carb heat without a temp gauge. If you lose RPM without the throttle moving, apply full carb heat (but do check the friction lock -- it happens).

Mixture leaning is usually done with an EGT gauge -- POH says 50 rich of peak. But you can do it with a fuel flow meter much more quickly (use the POH cruise performance table). Lacking either instrument, lean until you lose a little RPM, then enrich four half turns. See the POH.

Pitot heat is for clouds, mostly. Or at least rain (you can have VFR in the rain -- it's actually not that rare -- as long as you have the requisite cloud clearance and visibility).

This is a conversation you should be having with your instructor.
 
While he alludes to a 172, we don't know which 172 he has. The older ones with Continentals are different than the Lycoming ones which are different from the later injected ones (though since he does mention carb heat, he doesn't likely have one of them).

The BOOK calls for carb heat on a 172 anytime you're in flight at reduced power (mostly because that's good for the O-300 but they never changed it for the later lycoming-powered ones).
 
With a carbureted engine, you lean to "slight rpm drop" and then enrichen 3 half turns at takeoff above 5000' DA.

In cruise, if below 60% power, lean to slight rpm drop and then enrichen to peak rpm.

This works with both fixed and constant speed props on every plane Ive flown.
 
flyingron said:
While he alludes to a 172, we don't know which 172 he has. The older ones with Continentals are different than the Lycoming ones which are different from the later injected ones (though since he does mention carb heat, he doesn't likely have one of them).

The BOOK calls for carb heat on a 172 anytime you're in flight at reduced power (mostly because that's good for the O-300 but they never changed it for the later lycoming-powered ones).
Click to expand...

1979 172N
 
coloradobluesky said:
With a carbureted engine, you lean to "slight rpm drop" and then enrichen 3 half turns at takeoff above 5000' DA.

In cruise, if below 60% power, lean to slight rpm drop and then enrichen to peak rpm.

This works with both fixed and constant speed props on every plane Ive flown.
Click to expand...

Thanks - I guess I would be worried about leaning it and having the motor quit? I guess that is why you go to just a slight RPM drop and then enrichen...
 
The motor won't quit if you lean it slowly. Try it on the ground first and see to reasure yourself.
 
CC268 said:
Thanks - I guess I would be worried about leaning it and having the motor quit? I guess that is why you go to just a slight RPM drop and then enrichen...
Click to expand...

If you hear it stumble, turn it in.

Your passengers won't like it, but the engine takes several seconds at least to quit, and will restart right away if you do kill it. Unless you're flying a Cub.
 
Don't just take our word for it. Don't forget your CFI should be able to demonstrate on how to properly lean, per POH, as alluded to earlier.
 
It won't die. You can leave it at the sligthly lean, it just runs with less RPM. If you are operating at reduced power (such as your cruise setting or even WOT at 5000') you'll not hurt the engine no matter what you do with the red knob.
 
My CFI was such a wise@ss, when I asked him him to demonstrate proper leaning. He stood up, and did this:
13001256(300x300).jpg
 
At least he didn't lean forward.
 
Lol thanks for the help guys
 
CC268 said:
1979 172N
Click to expand...
Yes, you can get carb ice in a 172N. I routinely pull the carb heat on in mine below 2200 rpm. I'll pull it on momentarily at higher rpms to check it if I suspect icing might be in progress.

And yes, you can get carb ice in Arizona. It ain't always a "dry heat" (can you say "monsoon" ... ?)
 
Pilawt said:
Yes, you can get carb ice in a 172N. I routinely pull the carb heat on in mine below 2200 rpm. I'll pull it on momentarily at higher rpms to check it if I suspect icing might be in progress.

And yes, you can get carb ice in Arizona. It ain't always a "dry heat" (can you say "monsoon" ... ?)
Click to expand...

Ahh okay so you use it quite frequently then
 
AggieMike88 said:
My CFI was such a wise@ss, when I asked him him to demonstrate proper leaning. He stood up, and did this:
13001256(300x300).jpg
Click to expand...

I may not like the answer, but why was he dressed like that when you asked? And, where were you two, what were y'all doing? :eek::(
 
Does your FO ever address you as "Captain Literal" ??
 
Retired, I don't have an FO.

But then you didn't answer the question either. ;):D
 
dang, I did a search here for "fire your" and not one hit. Things are looking up!
 
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