When to lean?

azpilot

azpilot

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azpilot
When do you all lean the mixture?

During my primary flight training (KCHD - FE 1243 - DA would regularly be 4k+), I was taught to always lean the engine for takeoff. The normal procedure was to lean for max EGT, then enrichen the mixture to get 50F below the peak. This was the procedure I used on my check-ride as well.

However, since I earned my private, my flight school went out of business and I've flown with several other instructors and multiple FBO's. All my other instructors have just said to just go full rich for takeoff.

I'm curious what others here do for take off. At what Density Altitude do you decide it's appropriate to lean for takeoff?

I'll be flying into KFLG on Sunday. Density Altitude will likely be 8k plus. I will absolutely be leaning for takeoff on the trip home.
 
I was taught to lean above 3k. I've pretty much only flown on the Gulf Coast and Florida though so I've never had to for takeoff, do in cruise above that.
 
If I weren’t on vacation I would step into the kitchen and make popcorn.

Lean as much as you can and it still runs any time you are on the ground except when on the runway. Never lean during engine break in under full power. Don’t lean at 75% power or more. You will probably fall below 75% power several thousand feet up. Without an engine monitor to show you your power level you will need to do some studying in order to know your power level under the varying settings.


Those guidelines said, we are now ready for comments from the LOP proponents.
 
Full rich for start up, lean for taxi, run up - lean until it drops rpm and enrichen until it’s smooth and leave it there for take off. This is at 2,600’ on the ground. Then I lean it again when I reach 5000’. Then again at 7 and 9000’.
 
bflynn said:
What does your POH say?
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Good point, that's always a good place to start isn't it? Per the 1978 172N POH (digital copy) that I have, it says to lean for takeoff to max RPM above 3k feet. That does seem like a good threshold to use. My home airport has a FE of 1243, but DA is just about always North of 3k.

I looked at the POH's for two other planes I have time in. The 182S POH says to lean for takeoff above 5k feet "pressure altitude". The Archer POH just says "Mixture - Set" without elaborating. Not sure what to make of that.

At the time I type this, KPAN in AZ has a Pressure Altitude of 4928' and a Density Altitude of 6856'. Taking off from KPAN right now with the mixture at full rich seems like a pretty bad idea to me. But that's what the POH would say to do in a 182S.
 
I start full rich, do a monster lean for taxi where practically dies if it's over 1500 RPM..

Then during the run up I lean until it gets rough and enrich until it is smooth

If you have a good EGT and CHT gauge then you can ride the sweet spot of smooth/<400/~1,450

Remember that it's just basic chemistry in the cylinder, and these are all ancient hand-built engines. Lean it out to the plane is operating optimally. Things like 3K/5K we're just blanket rules of thumb, it is worth actually understanding what is happening with your engine when you play with the mixture
 
You told use where and the DA, but not what aircraft. It matters.
 
The POH may or may not be useful for proper leaning procedures, depending on the vintage. But you can check your engine manufacturer's recommendations, too.

I lean aggressively during taxi, and anytime in cruise at or below 75% power. Full rich on takeoff unless above 5000 DA and the engine runs rough or at less than full power full rich (Lycoming's recommendation). By inference you can lean in climb above 5000 DA if full rich operation is rough or less than optimal power. Without an engine monitor, you can lean to slight roughness due to lean misfire then enrich to smooth operation, and that will be best economy in a carbureted engine, where the leanest cylinders are just lean of peak. (Lycoming procedure.) Or you can lean to peak rpm (best power) at more fuel flow (ideal for high DA takeoff). I think most POH fuel charts likely assume best economy leaning at cruise.

Follow the engine recommendations and you get good fuel economy and clean plugs.
 
Scott@KTYR said:
In a steep turn I lean into it every time!
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I had a student that would do the same thing. I finally told him that the doors in this old 152 are not very secure and might come open in flight if he leans on it... and that solved that problem.!!

But then he started slamming the doors....
 
Don’t forget to lean in cruise also.
 
When the airplane manual is a bit lacking, you can always look at the engine manual. Here's a section from a slightly different Lycoming manual:

On engines with manual mixture control, maintain mixture control in “Full Rich” position for rated takeoff, climb and maximum cruise powers (above approximately 75%). However, during take-off from high elevation airport or during climb, roughness or loss of power may result from over-richness. In such a case adjust mixture control only enough to obtain smooth operation – not for economy. Observe instruments for temperature rise. Rough operation due to over-rich fuel/air mixture is most likely to be encountered at altitudes above 5,000 feet. Always return the mixture to full rich before increasing power settings

That's consistent with the POH's in the O-320 and 360 engined PA-28s I've flown. You can lean in flight over 5k, or at 75% power. I lean for taxiing, to avoid fouling, and at 75% or less power in cruise or about 5k. I've never leaned for takeoff, because I've never read in any POH or engine manual that I should, here in the northeast. That's all Lycoming. The Continentals I've flown didn't have mixture controls at all.
 
I lean for taxi, cruise, and high altitude airports. Also if I'm idling for a long time.

I've had spark plugs foul and take down a cylinder before, so I'm paranoid about fouling.
 
The "target EGT method" is popular with many pilots, myself included. If you know what EGT you are getting on take-off from a sea-level (or near sea-level) airport with a correctly set up fuel system, that is the EGT you should aim for - your target EGT. At this EGT, you know the engine is making close to maximum available power while staying away from excessive temperatures and internal cylinder pressures. At high-DA take-off, push the throttle forward and lean to that target EGT.

In the climb (whether from a sea-level airport or a high-DA airport), you can gradually reduce the mixture to maintain that target EGT. If you have a digital engine monitor with an EGT readout, pick any one cylinder as a reference (just make sure it's always the same one).

Using CHT as reference for leaning is bad enough in cruise (despite what Mike Busch says), but it's a horrible idea for mixture setting on take-off. CHTs lag behind so much when you make changes; there is no way you can see any meaningful stabilized changes in CHT before the runway is well behind you.

- Martin
 
Martin Pauly said:
Using CHT as reference for leaning is bad enough in cruise (despite what Mike Busch says), but it's a horrible idea for mixture setting on take-off. CHTs lag behind so much when you make changes; there is no way you can see any meaningful stabilized changes in CHT before the runway is well behind you.
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I agree that EGT is the most immediate indication of what's happening in the cylinder. But the CHT is good to monitor as well, it's important to ideally stay in the 360-370 range. People have different baffle arrangements, cowl settings, general cooling design, climb habits, speeds, etc. An EGT may give you an optimal chemical power setting but if you're cruising around at 450 CHT for hundreds of hours that's not going to do your engine or wallet any favors

My method in the Cirrus was to set based on POH FF target, then fine tune with EGT, and then use the CHT as a periodic means of further fine tuning that throughout the flight, IE.. if 18.3 is giving me 385 let's try 17.5, which may yield 375.. for instance.. and stick to that. For a plane being flown ROP the inverse would be true. I have found in a 182 with the cowl closed it can be hard to keep that optimum EGT while not exceeding 400 CHT in cruise. You can either drag the cowl, or give the mixture a few turns to rich. I believe flying around with a cowl dragging in the wind sloppy so I prefer the "few turns to rich" method

As a side note, the Aztec I fly either has bad gauges or very peculiar issues with the right engine. It seems regardless of FF the oil temp and CHT are always high (just above 200 and right around 400) while the EGT is unusually low.. they're in the green, but totally off (and not logical) when comparing against the left engine (which runs text book). So unfortunately in the Aztec I drag the right cowl and fly 1-2 gph richer on the right than the left (which I use as my litmus)
 
Really?.....you tried it much? It works great. You just need to know the fuel flow first. I do it all the time in my factory turbo V-tail. ;)
Martin Pauly said:
Using CHT as reference for leaning is bad enough in cruise (despite what Mike Busch says), but it's a horrible idea for mixture setting on take-off. CHTs lag behind so much when you make changes; there is no way you can see any meaningful stabilized changes in CHT before the runway is well behind you.

- Martin
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