Not leaning enough?

[Fearless Tower]

What happens when you aggressively lean and a cylinder melts down?

Costlier than fouled plugs (or does it not happen in a lycoming?)

Leaning doesn’t ‘melt down’ cylinders. As Pinecone pointed out, leaning in cruise typically results in cooler CHTs not hotter.

The danger with leaning too much comes into play with high HP, fuel injected engines at lower altitudes and it is more about pressure than heat. Your highest internal cylinder pressures occur around peak EGT. That is what Deakin and others refer to as the ‘red box’.

 

[RussR]

Leaning really aggressively LOWERS temperatures. The only place you do no want to lean at all is for take off and climb, until you reduce power.

I learned to fly at an airport at 6500 MSL. I never once (except maybe for a demo) put the mixture control at full rich at any time during my Private Pilot training. You lean for every operation, including takeoff and climb.

More generally, you should set the mixture appropriately for every phase of flight. If that’s full rich, then that’s fine, but don’t do it by rote, do it knowing why you’re doing it.

 

[LesGawlik]

I watched the Mike Busch video again. The key point is that following the POH may be the correct legal procedure, but it is not necessarily the best procedure.

One of the key points was that Embry Riddle bought a lot of 172s and operated them according to the POH. They experienced a significant number of engine problems, to the point where they got a group from Cessna and Lycoming to look at the problem. That team's efforts led to the SB which has been discussed here above. Turns out that the POH provided less than optimal advice regarding engine operation.

 

[mandm]

Hi, as a renter pilot, I try to use many of the tactics necessary for proper operation to help keep costs low. I don’t believe in this “FULL RENTAL POWER” stuff, that’s horrible, horrible advice.

Anyway, I Cherokee Archer with the 180bhp Lycoming at the club. Our house instructor hounds us about leaning it to the hilt on the ground and leaning til the tachometer peaks while in cruise flight. My protocol general is, START (full rich) and right after start-up, I run it to 1000RPM and then pull the mixture back as far as I can possibly go without the engine quitting. Obviously full rich for climb and once I get in cruise flight, I do the lean til peak RPM method taught by our house CFI. Basically once the engine sounds like it’s losing power and the tachometer indicates such, I bring the mixture control forward just enough to smooth it back out and then leave it! Some may call this lean until it stumbles and richen up until it smooths out. Anyway, I put it away, the next guy goes to fly it and it has a bad magneto check. They come back on me and blame me for running it too rich to the point of fouling a plug. I hop in my sedan and dash back over to the flying club to assist in troubleshooting. Pull the top cowl, remove the spark plugs and sure enough, there’s a plug full of lead. Now I’m on the hook to replace it because they claim I don’t lean enough. Question is, does this method that I’m describing not prevent plug fouling? If so, how may I educate our CFI that his teachings are incorrect?

Tell us you didn’t pay for those spark plugs and started searching for another flight school…

 

[PaulS]

Tell us you didn’t pay for those spark plugs and started searching for another flight school…

Sounds like he may have. What probably happened is the next pilot forgot to lean after starting, took his time getting to the run up fouling the plug in the process. I would tell them the engine was running great while I had it, I followed all your instructions until shut down, it was fine while I had it, must be the guy who did the runup who fouled it. You have to be quick in these situations.

 

[L J Donelson]

Leaning on taxi ...

View attachment 110495

Not actually relevant as these are not Lycoming's. But thanks for enforcing the point with an excellent visual.