Full Rich for landing?

RyanB

RyanB

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Why is this the general practice? My gut feeling is it’s only so the pilot doesn’t forget in the event of a go-around. Otherwise I don’t see a purpose for it from the perspective of an engine that burns leaded fuel. Powering back at top of descent and slowly enriching on the way down seems to work well and then leaving it 1/2 inch leaned or so until the wheels touch; to which point you lean aggressively on the ground. It seems a slightly leaned mixture during the final descent would help keep the cylinders a little hotter and reduce the chance for lead buildup at lower power settings.

What says the crowd? Full rich for landing, or leave it slightly leaned?
 
RyanB said:
What says the crowd? Full rich for landing, or leave it slightly leaned?
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I've used both but have the habit now of carb heat off & full rich on short final. On roll out I retract flaps & lean the mixture ...
 
Under most circumstances, the engine will continue to run just fine if you descend and land without touching the mixture to change it from the leaned setting you used in cruise. Whether that is a wise choice is something you'll have to work out for yourself. I'm sure there will be no shortage of opinions on the matter however.
 
RyanB said:
Why is this the general practice? My gut feeling is it’s only so the pilot doesn’t forget in the event of a go-around. Otherwise I don’t see a purpose for it from the perspective of an engine that burns leaded fuel. Powering back at top of descent and slowly enriching on the way down seems to work well and then leaving it 1/2 inch leaned or so until the wheels touch; to which point you lean aggressively on the ground. It seems a slightly leaned mixture during the final descent would help keep the cylinders a little hotter and reduce the chance for lead buildup at lower power settings.

What says the crowd? Full rich for landing, or leave it slightly leaned?
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Depends. I’ve flown some planes that are prone to fouling. Those I keep the red knob out a ways on final. Go arounds are the usual, everything gets pushed in/forward. Substitute lever for knob as necessary.
 
I set full rich and full prop on short final. When I'm short final approaching the numbers I normally have my hand on the throttle, just to make it quicker/easier to correct a landing or go around.

Part of that is probably that I learned in an aircraft without mixture or an accelerator pump, so I'm used to a smooth/rapid throttle advance, and I want to use the same throttle advance on a go around that I do on takeoff, because I know it works. I suppose a little stumble wouldn't be that big of a deal, but just seems like good practice to keep it the same. I have no idea if mixture matters if the accelerator pump doesn't work, in terms of affecting ease of stumble on acceleration.

I do lean immediately after start, because I've failed mag check on run up because of fouling. Also lean as soon as I'm clear of the runway after landing.

I'm only flying east coast, and think the highest field I fly out of is 1500 or so, so no concern that short periods of full rich are going to make the engine stumble at all.
 
My thoughts are…

Full rich is more for us flatland pilots, it’s mixture (as required - best power) for landing and the purpose is to keep the engine running and have full power available for a go around.

One thing I’m learning is that you want to be more conservative with the prop setting (blue knob). You can do props full forward on final and verify 3 green again, I’m finding this a great way to make sure your gear is down for landing.

Mixture, you want best power, this you can do your GUMPFS check on downwind (hold the prop forward until final). The engine sounds much happier instead of throwing mixture prop full forward while reducing power to traffic pattern speeds.

If you are at higher DA airports, I’m guessing 5000’+ and probably more then you might lean for takeoff and landing respectively. I haven’t had issues yet with spark plugs but I lean aggressively on the ground and on the roll out after landing - while bringing up the flaps and turning off fuel pump. After losing a fuel pump and having to replace one, you learn to respect your fuel pump a little more, I run it as little as possible now.
 
I was taught "full power" mixture setting for landing. not necessarily full rich. When taking off or landing at a high DA location, I wouldn't be full rich.
But back at the 1-2k DA in Chicago I'll go full rich on takeoff/landing and then lean out as soon as I'm cleaning up the plane off the rwy :).
 
All this assuming NA engine. Tubos are different. Full rich on short final at any altitude.
 
I only did that during PPL training. Once I got my own plane, I didn't touch the mixture until shutdown.
 
I live at sea level, and full rich is my takeoff setting. I go to full rich on landing in case I need to go around (one less thing to configure in that case). I would modify that if I were in a high DA environment.
 
182H carbed 470. If I start a descent that I am pulling power carb heat on. Mixture full rich when starting descent as well.
On warm humid days will hear a miss or stumble here or there when power back. I think too rich. I’ll sometimes lean slightly and is better.
 
On descent/final I set the mixture for take off for the field I'm landing at. And it's NEVER full rich.
 
In which situation are you more likely to make a mistake and in which situation is the consequence of a mistake greater. A go around or after landing and stopped on a taxi way?
Place the additional task in the situation where you have more time, and the consequence of the mistake involves only ego, not bent metal or body parts.

Tim
 
I don’t worry about mixture for going around. The engine makes plenty of power. Having carb heat on may kill you. Mixture won’t. I never touch down with carb heat on.
 
Stewartb said:
I don’t worry about mixture for going around. The engine makes plenty of power. Having carb heat on may kill you. Mixture won’t. I never touch down with carb heat on.
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Why? I have almost zero experience with carb. So I am curious.

Tim
 
Go full throttle with carb heat and the engine blubbers and doesn’t spin up with authority. Mine doesn’t miss a beat with it leaned at go-around. I dragged my gear through trees once when the plane wouldn’t climb as expected when going around. Carb heat was on. Since then I push carb heat in on final and may or may not adjust mixture. It depends on the day.
 
tspear said:
Why? I have almost zero experience with carb. So I am curious.

Tim
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Carb heat adds hot air to the system. Hot air, less dense, reduced power output. Some aircraft with carb heat use it as a preventive - on when power is reduced to a certain level. So generally off for the landing sequence, but you need it for the go.

The typical checklist has carb head on until touchdown, but says to turn it off in the go. Most pilots probably do it that way. But others opt for turning carb heat off on final.

There are a number of items for a go-around not needed for landing. Checklists tend to divide them into things we do before landing and things we wait to do until we are on the go. Pilots will move them around. Apparently, @Stewartb decided turning off carb heat before landing was a better operating practice for him in his airplane.
 
@midlifeflyer

Your post jogs a few brain cells, but they are kinda hazy. I thought when you pulled power back, the reduced air flow in the venturi could freeze the water in the fuel or when temps are below some number, such as 10C. Hence that was why you had carb heat on for anything but full power. Did I not recall that correctly?

Tim
 
tspear said:
@midlifeflyer

Your post jogs a few brain cells, but they are kinda hazy. I thought when you pulled power back, the reduced air flow in the venturi could freeze the water in the fuel or when temps are below some number, such as 10C. Hence that was why you had carb heat on for anything but full power. Did I not recall that correctly?

Tim
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It's not a reduced airflow, but a pressure drop that leads to the temperature drop within the carb. The ice ends up collecting in the carb blocking airflow to the engine. The outside temperature can be 20°C or more. My big carb ice emergency was when the OAT was about 24°C.
 
Carb heat makes the mixture very rich. Not a good thing when powering from idle to full throttle. When carb heat goes off, that’s a good time for mixture to go full rich, as long as DA warrants it.

On a short, narrow strip when the wind bucks the plane all the way down and gives it a big kick close to the ground requiring a go-around, your hands are full. Missing closing the carb heat is easy to do. It’s a task best done on short final. On short strips every landing is an aborted go-around.
 
midlifeflyer said:
It's not a reduced airflow, but a pressure drop that leads to the temperature drop within the carb. The ice ends up collecting in the carb blocking airflow to the engine. The outside temperature can be 20°C or more. My big carb ice emergency was when the OAT was about 24°C.
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Closing the throttle restricts the airflow, alright, and it does that by making a much smaller area for the air to pass the throttle plate into the induction system. The air, in squeezing past that plate, accelerates a whole bunch, and if we listen to Bernoulli, as the speed of a fluid increases, its static pressure decreases, and then the Gas Laws show us that as pressure decreases, so does temperature.

So the biggest temperature drop in a carburetor is not in the venturi. It's in the throttle plate/carb bore wall area, and that's why we get the carb icing charts looking like this:

upload_2023-6-9_9-38-30.jpeg

Now, see and understand: the biggest risk of carb ice occurs at glide power, or throttle closed or nearly so. You can get ice at ambient temperatures up to 100°F that way, and serious ice up to 90°F, and in a very wide range of dewpoints. The cruise power ice risk is far smaller.

So closing the carb heat on final, especially when the temp and dewpoint aren't far apart, introduces a risk that you need to understand.

Now, that chart is pretty general. Different engines and airframe installations have different risk factors, with carbed Continentals being, generally, more ice-prone than Lycomings. But Lycs will still ice up, contrary to popular belief. I've had it several times in Lycs, and seen it on the ramp many other times. Students and instructors very often did not recognize it.

Another popular belief is that carb ice is a wintertime thing. False, absolutely false. That carburetor is an efficient little refrigerator, and makes ice the same way a freezer does: using a pressure drop.

upload_2023-6-9_9-45-28.jpeg
 
If I ever fly a plane with carb, I can foresee I will need some remedial training.

Tim
 
In the R182 (Lyc O-540), the rich mixture setting was very rich. That's the way Lycoming wanted it, as I was told by the folks at Precision Airmotive, the carb manufacturers. So rich that we often had to lean the engine on runup in order to get satisfactory mag drops. If one went full rich with the carb heat on, that engine threatened to quit, so I told the instructors and students to lean it until it ran smooth. I never went full rich on final; I'd set it where I knew it would run smoothly but still be rich enough for an abort.

From the R182 POH:

upload_2023-6-9_9-55-43.png

Our airport was at nearly 3000' ASL. On a warm day, the DA was easily 5000'. Going full rich was asking for trouble. It would run rough, indicating far too much fuel.

Even at at a 1500' ASL airport, the density altitude will be 3000' on a 30°C day, assuming standard barometric pressure.
 
I was taught that carb heat in the pattern is to address ice that may have formed on the reduced power descent to the pattern. If you pull heat on the downwind and push it off on final there’s near zero potential for ice formation. I had carb ice in a 150 when I was a student. Having the engine stumble and pop was alarming. When you pull heat, expect a response. Doing it a little higher than a 900’ pattern altitude isn’t a bad idea.
 
Stewartb said:
If you pull heat on the downwind and push it off on final there’s near zero potential for ice formation.
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My little Continental would ice up within a minute after startup when the conditions were right. In the glide, the prop is being driven by the relative wind, and that causes a much bigger pressure drop at the throttle plate than one gets at idle. The engine is sucking harder. That can lead to ice forming real quick. Maybe not enough to notice on the abort, but there would be some, especially if the carb body cooled off enough after the heat was turned off.
 
Dan Thomas said:
In the glide, the prop is being driven by the relative wind, and that causes a much bigger pressure drop at the throttle plate than one gets at idle. The engine is sucking harder. That can lead to ice forming real quick. Maybe not enough to notice on the abort, but there would be some, especially if the carb body cooled off enough after the heat was turned off.
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In that particular low power configuration, is there enough heat in the exhaust manifold that pulling the carb heat knob will make a difference?
 
asicer said:
In that particular low power configuration, is there enough heat in the exhaust manifold that pulling the carb heat knob will make a difference?
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The exhaust will cool off, which is why the instructional syllabus has, or should have, the recommendation to "clear the engine" occasioanlly. That makes sure it's still firing, it clears out any accumulated fuel from the induction system that might cause hesitation from flooding or even a failure, and it warms the exhaust.

Descending from downwind to the runway doesn't take that long and the exhaust will still have some heat even if the throttle was fully closed when turning base. There is still idle power. In a practice forced landing, though, the risk of it turning into the real thing due to carb ice is very real. From the Canadian Flight Instructor Guide, on practice forced landings:

upload_2023-6-9_10-44-8.png
 
Dan Thomas said:
So the biggest temperature drop in a carburetor is not in the venturi. It's in the throttle plate/carb bore wall area, and that's why we get the carb icing charts looking like this:
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You don't have to convince me. The ice was so severe in my case the throttle was locked in place.
 
asicer said:
In that particular low power configuration, is there enough heat in the exhaust manifold that pulling the carb heat knob will make a difference?
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I always wondered why the very first item on a carbureted airplane manufacturer's emergency engine out checklist wasn't "Carb heat --- HOT."
 
Understanding the phenomenon and how the various systems work is really

IMPORTANT for safe operation under varying conditions.

In addition to Dan’s comments you might want to consider:

Carb Heat also effectively RICHENS the mixture.

This can be in addition to the Economizer and Accelerating Pump doing similar.

IDLE MIXTURE is another circuit and is generally set slightly on the Rich side.

Proper adjustment is important.


On a go-around much of the preceding can come into play.

Mismanagement might even be worse than hitting the deer on the runway.
 
RyanB said:
Why is this the general practice? My gut feeling is it’s only so the pilot doesn’t forget in the event of a go-around. Otherwise I don’t see a purpose for it from the perspective of an engine that burns leaded fuel.
...
What says the crowd? Full rich for landing, or leave it slightly leaned?
Click to expand...
You are correct. There is no reason to be at full rich unless you are at 70% or higher power. Any time you are below 70% power, even at sea level, the engine wants to be leaned. It will run cleaner and better.

So the ONLY reason to go full rich for landing is in case you have to go around and you forget to push the mixture in. However, this comes at a cost. On approach to landing you are at low power, often near idle and being full rich risks fouling plugs. So if you have to go around you might get engine hesitation or worse. And if you are at high density altitude you don't want full rich even at full power, so it could train your muscle memory in counterproductive ways. Furthermore, rich mixtures increase the liklihood of the carb icing you are trying to avoid. So the advice for full rich on approach to land is a trade-off between different risks: you reduce one risk while increasing another.

My personal take on this risk management is to lean the engine whenever I'm below 70% power. That includes on approach to land, where it is leaned more than just "slightly". If I have to go around I push all the knobs forward: throttle, carb heat, and mixture (prop will already be full forward).
 
asicer said:
Well that certainly won't work at a high DA airport. And if you're used to doing that, why not a little bit for planes that run a little too rich on final or prone to fouling?
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True ... I lean to stumble and then enrichen slightly entering the pattern ... it works at my airport in west Texas (4100 AGL) as well as when I've been to Telluride Colorado. Doing that with that extra twist or two after stumble will be enough for a potential go-around. Leaning during taxi at high elevation is required unless you want to foul plugs ...
 
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