Mixture full rich for landing?

RyanB

RyanB

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For this exercise let’s assume an O360. As I understand it, general procedure advises mixture full rich as part of the landing checklist, but is it really necessary? I was under the impression that the POH and checklists state full rich for landing in the event of a go-around, however if it’s left an inch or so out once we join the pattern in preparation for landing, what’s the harm? Seems as though it would help keep the plugs cleaned up while under low power, rather than being full rich. What sayeth thou?
 
Full rich provides a slightly cooler combustion temp, and reduces the chance of taking a cylinder over lean during a sudden power application. Over lean and it’s easier to have detonation, or hot spots. Both are detrimental to an engine. Take a look at some of the drag guys that show lots of their data when there is a failure.

Full rich will vary with density altitude.....
 
Craig said:
Full rich provides a slightly cooler combustion temp, and reduces the chance of taking a cylinder over lean during a sudden power application. Over lean and it’s easier to have detonation, or hot spots. Both are detrimental to an engine. Take a look at some of the drag guys that show lots of their data when there is a failure.
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Full rich will vary with density altitude.....
 
Palmpilot stated it a bit clearer than I did.

RG: Did some flight ops out of Colorado Springs in a stock C-152 a number of years back. Also some work in a Cherokee 140 out of Killeen in 100+ temps, would that give me enough of an idea? :)
 
Full rich (and prop full forward) are in case of a go around. You can learn to go Mixture - Prop - Throttle or Prop - Mixture - Throttle. And don't forget carb heat Off.

For training, it is like full rich for most flights, until you start flying XC, just to keep things more simple for the student. One less thing to forget, but it builds in bad habits.
 
Palmpilot said:
So for high-elevation airports, maybe the rule needs to be "mixture to takeoff setting." :dunno:
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That or something similar makes sense regardless of airport elevation. My personal checklists use the medical shorthand, Mixture...PRN.
 
I feel I fell into a bad habit. While taking my instrument checkride the DPE mentioned in her opinion for a 172 that you could set the mixture 1" out and forget it.
So I kind of got in that habit.
Not sure about this but about 3-4 times since then while lean I pushed the throttle in for a go around on practice approach and one time climbing in IMC and the engine stumbled. Like the accelerator pump did not have enough pump shot to enrichen the mixture?
So that got my attention and my CFII. So since then I have been going full rich before landing or climbing and have not experienced that since. YMMV
 
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A motor will make max power at 12:1 air/fuel ratio. Generally that requires full rich.

I have not gotten to super high altitudes, but if i leave the mixture full rich other than using more gas the motor has never died due to being 'to rich'.

Fuel will not magically flow into the engine without air, so i don't know how the engine can suck to much fuel and cut out.
 
I never touch mixture until I add power, so typical landings are leaned. Especially in warmer temps. A carb that flows enough fuel to operate in cold weather (Alaska) will be too rich for ops in warm weather without leaning. The only time I use full rich is for full throttle. In flight I’m leaned a couple of inches to achieve the fuel flow I want. I lean by flow, not temperature or engine stumble.
 
Craig said:
Palmpilot stated it a bit clearer than I did.

RG: Did some flight ops out of Colorado Springs in a stock C-152 a number of years back. Also some work in a Cherokee 140 out of Killeen in 100+ temps, would that give me enough of an idea? :)
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Sure enough! My comment was directed to Ryan. I wanna see his butt out here doing some Western flying.
 
Density altitude varies by temperature no matter where you live. An east coaster will see 100° operating temperature ranges. The amount of fuel required within that range varies significantly. That’s why we have mixture controls.
 
pfarber said:
A motor will make max power at 12:1 air/fuel ratio. Generally that requires full rich.

I have not gotten to super high altitudes, but if i leave the mixture full rich other than using more gas the motor has never died due to being 'to rich'.

Fuel will not magically flow into the engine without air, so i don't know how the engine can suck to much fuel and cut out.
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I don’t know what super high altitudes are, but if you don’t lean on a climb to 8,000 feet, climb performance suffers and if you don’t lean en route you are using a lot more fuel and your fuel planning will have a large error.
 
DENSITY altitude is what matters. You hot weather guys are used to leaning. Try that when DA is -7000’ and you’ll burn up your cylinders.

I set my airplanes up to have 200° of low altitude cruise power leaning authority. Any less and there’s not enough fuel for cold temps. In summer I’m leaned for all ops except takeoff, and even at 65% cruise lean there’s no problem for go-arounds. Full power only lasts for 10 seconds at most. Carb heat is more important than mixture in that moment. My own carb heat goes off on final. Mixture stays as set.
 
Stewartb said:
DENSITY altitude is what matters. You hot weather guys are used to leaning. Try that when DA is -7000’ and you’ll burn up your cylinders.
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When density altitude is such a high negative number like that, can you ever actually get the engine rich enough? It seems as though “full rich” isn’t actually going to be rich enough in a situation like that. No?
 
Lots of planes fly here all winter. No problem as long as there’s adequate fuel flow. My target flows weren’t a random choice. It’s what works.

Some guys think with cold dense air we shouldn’t use full throttle or full flat prop settings. I use both. Throttle for fuel flow and prop to reduce the time necessary to operate at full power. And FWIW, I always dial my prop down as soon as airborne and flaps cleaned up, or clear of obstacles, but I don’t reduce throttle until I reduce the climb rate. Usually at 1000-1500 agl. That applies all year round.
 
Pinecone said:
Full rich (and prop full forward) are in case of a go around. You can learn to go Mixture - Prop - Throttle or Prop - Mixture - Throttle. And don't forget carb heat Off.

For training, it is like full rich for most flights, until you start flying XC, just to keep things more simple for the student. One less thing to forget, but it builds in bad habits.
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Full rich will vary with density altitude....and with PHYSICAL altitude. Students should learn correctly from the beginning.
 
pfarber said:
Fuel will not magically flow into the engine without air, so i don't know how the engine can suck to much fuel and cut out.
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There's a lot you don't know.

Gasoline will burn at mixtures of 8:1 to 18:1. Get it richer than 8:1 and it will quit. Get it even close to that and it will stumble. Some airplanes need some intelligence to manage that mixture properly. The R182 has an O-540J3C5D with an HA-6 carb that has an extremely rich setting at full rich; I complained to the carb makers, Precision Airmotive, and they told me that it was the way Lycoming wanted it for that engine. The engine would start missing and running rough at full rich, carb heat on, on a DA of 4000 or more. Much higher than that and it was blowing black smoke as well.

From the R182 POH that nobody ever reads before complaining about it:

upload_2022-7-28_10-2-19.png

upload_2022-7-28_10-4-58.png

Yeah. With carb heat on you'll have to lean it.

From the expanded procedures:

upload_2022-7-28_10-8-8.png

Look at that. May be leaned above 3000 feet. That would be a DA of 3000, and that's easily experienced on a warm day at a much lower altitude.

In that engine, on a high-DA day, if you use full rich in the runup you will get large mag drops. If you leave it running on one mag the RPM will sometimes continue to decrease. I never let it quit, but it was sure headed that way. Leaning it got normal mag drops.


Edit: There's an AD on that HA-6 carb. It had the possibility of the mixture control valve mechanism coming loose inside the carb and flooding the engine. At least one accident happened due to that. So yes, it is possible to overfuel an engine and kill it.

Another edit: That HA-6 AD addresses the loose mixture sleeve cutting off the fuel flow, not increasing it. Memory getting faint. I had to recall an airplane in flight, headed for the mountains, the morning I received the emergency SB that eventually resulted in the AD. That airplane had the defective version of the carb. Must be 12 or 13 years ago.
 
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eman1200 said:
there are student pilot ways of doing things, then there are ways of doing things once you learn how to actually fly a plane (and manage your engine, etc..).
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The problem there is Primacy. Once someone learns it by rote, it's hard to start thinking differently.
 
pfarber said:
I have not gotten to super high altitudes, but if i leave the mixture full rich other than using more gas the motor has never died due to being 'to rich'.
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Clip4 said:
I don’t know what super high altitudes are, but if you don’t lean on a climb to 8,000 feet, climb performance suffers and if you don’t lean en route you are using a lot more fuel and your fuel planning will have a large error.
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Good news is that you can get away with improper leaning right up until the time you can’t, so you probably won’t die from it more than once.
 
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RyanB said:
For this exercise let’s assume an O360. As I understand it, general procedure advises mixture full rich as part of the landing checklist, but is it really necessary? I was under the impression that the POH and checklists state full rich for landing in the event of a go-around, however if it’s left an inch or so out once we join the pattern in preparation for landing, what’s the harm? Seems as though it would help keep the plugs cleaned up while under low power, rather than being full rich. What sayeth thou?
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Here is what is boils down too.
Are you preparing for best case; normal landing. Or worst case, emergency go around on short final to avoid the other plane which pulled onto the runway?
If you are preparing for a normal landing, the argument will be to leave the mixture alone. Save fuel, it is easy to push in as needed on go around.
If you are preparing for a balked landing, the debate will then descend into how rich; full, one inch out....

Personally, I am a flat lander, on a balked landing if I have to worry about correcting mixture away from anything which is not full-rich as I try and make full power. I am likely screwed. Best bet for me is to adjust mixture before the sh** hits the fan.
Therefore, I always put the mixture for what I expect is my go-around flow; below 3K that is usually full rich. Above 3K, I pull back about 1GPH from full rich for each thousand feet above 3K. This worked well in my N/A Cirrus; up to about 7K which is the highest airport I recall using in a Cirrus.

The result for me, I prepare of for the worst, but hope for the best.

Tim
 
Leaving it full rich also fouls the plugs much more quickly, and fouled plugs, once you get enough of them, will kill that engine.

That's on top of the risk of running out of fuel because you trusted the POH cruise charts, without paying attention to the fine print:

upload_2022-7-28_12-4-7.png

And their "recommended lean mixture" is pretty aggressive leaning.
 
Dan Thomas said:
And their "recommended lean mixture" is pretty aggressive leaning.
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Thing is, they don’t specify, so it’s left pretty open ended. Is their recommended lean mixture best power or best economy? If we lean til rough and then richen just enough til smooth, are we close to the book numbers?
 
Threads such as this make me rue the FAA and the difficulty in getting changes approved. Any aftermarket EFI for a car is far superior to any carb or mechanical FI system in our air-cooled boxers. I didn't go "full rich" on very hot days, I went to where max power would be made. Our O-300 wasn't detonation prone, of course.
 
RyanB said:
Thing is, they don’t specify, so it’s left pretty open ended. Is their recommended lean mixture best power or best economy? If we lean til rough and then richen just enough til smooth, are we close to the book numbers?
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From that same 172M POH:
upload_2022-7-28_12-14-19.png
 
The pilot needs to decide between best power or best economy.

Point of interest. Electronic ignition doesn't produce a lean stumble. It'll run smooth right through peak and well into LOP as temps rise and fall. FWIW I use the book for fuel flow in my EI/FI airplane. Translation? I lean aggressively. Cruise will have the mixture knob pulled out 2" plus. Once I know the fuel flow-CHT relationship, I rarely watch EGTs. I lean to my target fuel flow for the power setting. If I apply that to my magneto-carburetor airplane? The flow gauge validates that the lean to stumble and push back in to smooth works darn well.
 
Dan Thomas said:
The problem there is Primacy. Once someone learns it by rote, it's hard to start thinking differently.
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I agree, but there also is a limit to how much someone can handle while learning. By checkride though, the student pilot should eventually be taught and be able to do more advanced things. He better be able to explain mixture control to the examiner!
 
texasclouds said:
I agree, but there also is a limit to how much someone can handle while learning. By checkride though, the student pilot should eventually be taught and be able to do more advanced things. He better be able to explain mixture control to the examiner!
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Yup. But too many seem to be taught to "pull the knob out an inch" or something like that, and not much more. I've even heard of students being told that "we never touch that knob except to shut down."
 
Second scariest thing I ever did when I started flying. I went mixture full rich while landing here in Arizona where density altitude was pretty high, and then tried to go around. No power from the engine and the guys waiting for me to land told me there was a lot of black smoke coming out of the exhaust. I landed, taxied back, did a normal run up and leaned for take off. Tucked my tail between my legs and flew home. Now I lean on the way up, at cruise, and enrich on the way back down. The only time my mixture is full rich is when it is started - and then quickly leaned.
 
Timbeck2 said:
Second scariest thing I ever did when I started flying. I went mixture full rich while landing here in Arizona where density altitude was pretty high, and then tried to go around. No power from the engine and the guys waiting for me to land told me there was a lot of black smoke coming out of the exhaust. I landed, taxied back, did a normal run up and leaned for take off. Tucked my tail between my legs and flew home. Now I lean on the way up, at cruise, and enrich on the way back down. The only time my mixture is full rich is when it is started - and then quickly leaned.
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That there. One needs to know this stuff and be thinking and evaluating. We're too used to cars that have computers that dumb down driving skills. Push a button. Press go or stop and point the thing. And yet some can't even manage that...
 
texasclouds said:
I agree, but there also is a limit to how much someone can handle while learning. By checkride though, the student pilot should eventually be taught and be able to do more advanced things. He better be able to explain mixture control to the examiner!
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Unfortunately when trying to minimize time and expense for training, a lot of things slip through the cracks, or are things that fall under the thought process of “we did before, but for the sake of time we’re going to skip,” without explicitly stating that.
 
MauleSkinner said:
Good news is that you can get away with improper leaning right up until the time you can’t, so you probably won’t die from it more than once.
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Better news, without dying, is the POH recommendation to lead above a certain (density) altitude. If the POH says "3,000" that gives you an idea how large the ballpark and how accurate you have to be.

The 20 years I lived in Colorado, I leaned for takeoff based on runup RPM. For landing it was a guesstimate. (Of course, it enddd up being a very experienced guesstimate.)
 
upload_2022-7-28_15-12-18.jpeg

90°F degree day at 1000 feet ASL, and the DA is already at 3400 feet.
 

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Dan Thomas said:
Yup. But too many seem to be taught to "pull the knob out an inch" or something like that, and not much more. I've even heard of students being told that "we never touch that knob except to shut down."
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Taught that by an Examiner no less!
 
Timbeck2 said:
Second scariest thing I ever did when I started flying. I went mixture full rich while landing here in Arizona where density altitude was pretty high, and then tried to go around. No power from the engine and the guys waiting for me to land told me there was a lot of black smoke coming out of the exhaust. I landed, taxied back, did a normal run up and leaned for take off. Tucked my tail between my legs and flew home. Now I lean on the way up, at cruise, and enrich on the way back down. The only time my mixture is full rich is when it is started - and then quickly leaned.
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I was in line for departure at KAPA. A Cherokee was cleared for takeoff. Started moving onto the runway and the engine quit. Didn't lean. Less scary than yours but a good lesson.
 
Flatlander here airport is 1000msl.

Anytime DA reaches 2500 I lean for takeoff and landings. Carb heat also makes the 182 run very rich so being partially leaned offsets that as well.

I practiced on one of our longest runways in the region when we would have DA > 3500. Definitely makes a difference and glad that I took time to learn it.

Definitely no substitute for crazy high mountain and desert DA's but at least I am less naive. Definitely a bit anxious about the higher ground speeds on landing and longer take rolls whenever that day happens!

We can easily get DA below -2000 and I think I recall -3000. When that happens its a whole other story, almost impossible to lean during startup and one mechanic said to use carb heat as well to richen it up if needed. Haven't had to start with carb heat at -10F though. Also hard to lean very much during cruise.
 
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