Leaning on taxi question?

RyanB

RyanB

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Ryan
So yesterday i was taxiing out from the tarmac and backtaxied the runway, before i taxied i leaned the mixture, gave it a little throttle and got onto the runway, i needed a little more power to get the airplane moving so i gave it more throttle, well i must have had it leaned to much because the engine coughed so i enrichened the mixture and the rpms went up and i pulled the throttle back and taxiied normally. Question was i obviously had the mixture too lean, so from now on i will lean it less than what i had it at, did i do damage to the engine by having it leaned out to where the engine coughed when i gave it enough throttle? It was leaned like this for maybe 30-45 seconds or so before i had to enrichen to keep the engine from not dying on the throttle input. I have read that lean of peak can be bad, and i just wonder if that pertains to this. Thank you!
 
This is what I thought of when I saw the title of this thread:

IMG_1291.jpg


:D

To the OP: It's just about impossible to hurt the engine with the mixture at taxi power settings. In fact, you might actually have been helping your engine avoid fouled plugs. Many people recommend leaning so drastically on taxi that the engine stumbles when more power is applied, just as you described -- that way, it would be impossible to take off without being reminded to go to full rich.
 
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That is a good idea, question answered, thank you, just wanted to be sure that "stumble" was not hurting the engine by not getting enough fuel to it when i added throttle.
 
Should be fine,if you over lean,the engine will shut down.
 
Ryan,

On the ground, you want to lean the engine so much that it will die when you advance the throttle. This keeps you from taking off leaned out. So, no, don't lean less next time. Lean just like you did. You'll never hurt your engine taxiing around no matter how lean it is.

Edit: oops, I see Pilawt beat me to it.
 
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And no, the engine stumble on taxi has nothing to do with "lean of peak" operation. Here's an introduction to what LOP operation is all about. Be aware that LOP techniques don't work well with most smaller carbureted engines (because carburetors don't distribute fuel evenly among cylinders as do fuel injectors), but it's good to understand the concept.
 
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Allow me to thread jack a bit. I recently took a trip in the Bonanza. IO-540. I leaned for taxi as I normally do. When I got to the end of the runway, I retarded the throttle to idle and the engine died. It happened twice on the trip, so it wasn't just a fluke.

Is there something about that engine that requires the mixture be richer for idle than for a low taxi power? Or should I be concerned that something isn't right with that engine?


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In Oklahoma I would always lean for taxi int the Cherokee six until the rpms drop then I would advance a little. If I wouldn't it would foul the plugs every time.

Now in Colorado I lean immediately after starting the engine and don't advance the mixture again until I'm taking off in the turbo toga

The fouled plugs can be a true pain and once I figured that out as a new pilot I've always leaned as soon as the engine is started. Simply no reason to be using full rich while taxiing.
 
Read up on what Lycoming recommends here and here. In particular, lean hard on the ground. After start, set 1200 RPM and lean until it starts to go rough, then enrich enough to get smooth. Leave it there until run-up, and after run-up, lean it again until you're ready to take off. Since you can't get above about 1500 RPM with the mixture set there, you can't take off with it that lean, so it's not a safety issue, and it won't hurt the engine if you advance throttle too far -- worst case is the engine stops and you have to restart. Upon clearing the runway after landing, lean it again as after start, and keep it lean until you cut it for shutdown.
 
I thought lycoming recommended leaning at all times except takeoffs at lower altitudes and during startup. You should be doing your runup leaned, you'll have to enrichen some or it will stumble, but you don't go full rich. A runup with a leaned engine is a better test of your engine, full mix can hide problems, you do want to find engine problems on the ground don't you?
 
Ryanb said:
So yesterday i was taxiing out from the tarmac and backtaxied the runway, before i taxied i leaned the mixture, gave it a little throttle and got onto the runway, i needed a little more power to get the airplane moving so i gave it more throttle, well i must have had it leaned to much because the engine coughed so i enrichened the mixture and the rpms went up and i pulled the throttle back and taxiied normally. Question was i obviously had the mixture too lean, so from now on i will lean it less than what i had it at, did i do damage to the engine by having it leaned out to where the engine coughed when i gave it enough throttle? It was leaned like this for maybe 30-45 seconds or so before i had to enrichen to keep the engine from not dying on the throttle input. I have read that lean of peak can be bad, and i just wonder if that pertains to this. Thank you!
Click to expand...

Actually, that is how lean I recommend for taxi. If I feed it throttle anything but delicately and deliberately, I want it to stumble. It hurts nothing in the engine, and it helps prevent you from forgetting the mixture on takeoff. You can't be too lean on the ground if you're still running.
 
Ryanb said:
That is a good idea, question answered, thank you, just wanted to be sure that "stumble" was not hurting the engine by not getting enough fuel to it when i added throttle.
Click to expand...

How is this different than what you do at every engine shut down by moving mixture to idle cutoff?
 
Richard said:
How is this different than what you do at every engine shut down by moving mixture to idle cutoff?
Click to expand...

ICO is a smooth shutdown, stumbling is a lot of 'make and break' pulses, but they are ok.
 
bluesky74656 said:
Allow me to thread jack a bit. I recently took a trip in the Bonanza. IO-540. I leaned for taxi as I normally do. When I got to the end of the runway, I retarded the throttle to idle and the engine died. It happened twice on the trip, so it wasn't just a fluke.

Is there something about that engine that requires the mixture be richer for idle than for a low taxi power? Or should I be concerned that something isn't right with that engine?


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Click to expand...

That is a rare bonanza. I've only ever seen one. Care to share details of it?
 
When I first started training, in a Warrior, the guideline was "lean one inch" on the mixture lever. Not really knowing all the hows and whys, that's what I did. It finally kicked into my brain a little while later and now I lean pretty aggressively, too.

I even had a ramper get concerned enough to come out of the hangar, and then ask me about it after I got back (he was training in the same plane I was flying, and wanted to make sure nothing was wrong with it.) The plane was parked at the fuel pump, and there is a small incline you need to maneuver around. I had leaned after start, and was trying to taxi around that incline, but needed to add power to cut the corner and one of the mains went up the slope a little. The engine stumbled when I did that and caught his attention. But if you don't lean that particular plane heavily on the ground, it will nearly always have a fouled plug at runup.
 
If you lean aggressively enough on the ground, you WILL be running lean of peak, in which case, if you advance the throttle, all you do is make the mixture more lean and you will have to increase the mixture in order to develop more power. Same as in the flight regime as well.

You control power by varying whatever constituent is present in deficient quantities. If you're running rich, the air flow determines the power, and if you're running lean, the fuel flow will determine the power.

CFI asked me once during a BFR, "If you had a throttle cable failure, what would you do?" Depends on the failure mode, but many fail wide open, in which case I'd simply use the mixture as the "throttle" to control the power in the pattern, and accept the roughness that might be incurred.
 
bluesky74656 said:
Allow me to thread jack a bit. I recently took a trip in the Bonanza. IO-540. I leaned for taxi as I normally do. When I got to the end of the runway, I retarded the throttle to idle and the engine died. It happened twice on the trip, so it wasn't just a fluke.

Is there something about that engine that requires the mixture be richer for idle than for a low taxi power? Or should I be concerned that something isn't right with that engine?


Sent from my iPhone using Tapatalk
Click to expand...

Your engine should idle just fine. Pulling to idle should enrich the mixture. The only time this should ever be an issue is if you enrich too much at high density altitude and flood the engine. In that case, restart will be difficult.

Talk to your mechanic. I think you want that looked at. Suppose you pulled the engine to idle over the numbers and started to sink a little fast, and "added" power. Not fun.

Some injected engines seem to have trouble with fuel metering at low throttle.
 
JHW said:
That is a rare bonanza. I've only ever seen one. Care to share details of it?
Click to expand...

I believe Machen did an IO-540 STC for the Bonanza. Not very popular as you had to add blisters to the cowl and it had heat problems if you tried to use the 300hp.
 
My experience is that I don't lean enough on the ground which can result in excessive RPM drops during magneto check right before departure when full rich. Reason I feel the excessive drop is from lack of leaning is because leaning hard and doing a long run up at high RPMs (over 2000) seems return the magnetos to normal parameters during the check. I remember once seeing -400 on both magnetos at a high altitude airport!!!! So I taxied back the the ramp and tried running the engine hard while leaned heavily. In a couple minutes the mags were absolutely happy again. I suspect people are more likely to run too rich on the ground. At least that's my experience in 172s and especially a Continental 182.
 
My school uses Cherokee 160 and the CFI's never lean for taxi. And we've never had any spark plug issues that I'm aware of since I've been training there. We are at 81' elevation, so basically at sea level.

The only time we lean is in cruise.
 
orange said:
My school uses Cherokee 160 and the CFI's never lean for taxi. And we've never had any spark plug issues that I'm aware of since I've been training there. We are at 81' elevation, so basically at sea level.

The only time we lean is in cruise.
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Actually, I should say this really became an issue for me in a 182N. Carburetor 172s seem much more tolerant of being taxied and flown over-rich.
 
WhiskeyPapa said:
My experience is that I don't lean enough on the ground which can result in excessive RPM drops during magneto check right before departure when full rich. Reason I feel the excessive drop is from lack of leaning is because leaning hard and doing a long run up at high RPMs (over 2000) seems return the magnetos to normal parameters during the check. I remember once seeing -400 on both magnetos at a high altitude airport!!!! So I taxied back the the ramp and tried running the engine hard while leaned heavily. In a couple minutes the mags were absolutely happy again. I suspect people are more likely to run too rich on the ground. At least that's my experience in 172s and especially a Continental 182.
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And that's why you NEVER EVER run full rich at high density altitude.

Sometimes, not even for engine start.

Lean for taxi, during run-up lean for best power, then take off leaned. When landing, don't enrich more than you need to keep the engine smooth.

Some aircraft seem much more subject to plug fouling than others, even among the same model. I suspect that has to do with blow-by or valve bell mouthing, especially if accompanied by enhanced oil use.
 
orange said:
My school uses Cherokee 160 and the CFI's never lean for taxi. And we've never had any spark plug issues that I'm aware of since I've been training there. We are at 81' elevation, so basically at sea level.

The only time we lean is in cruise.
Click to expand...

Another example of instructors falling down on the job. Lycoming says that you can lean at any time and at any altitude when operating at less than 75 percent power (Source: Key Reprints from the Lycoming Flyer). Do you normally taxi at 75%? I spent all of my primary instruction time at Piper school at sea level and I know that it is easy to fall into the full-rich trap. Don't do it. Follow the advice of others in this thread and lean almost to the point of killing the engine. You can't possibly do any harm.

Remember: Just because an instructor says something, it is not necessarily correct...it may be what his/her instructor learned way back when.

Bob Gardner
 
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