[TopCat]

Maybe their lawyers advised them that a 65% recommendation was more likely to avoid claims than the earlier statement.

For normally aspirated engines, the 65% recommendation in the article in your link has nothing to do with leaning, over- or otherwise:

For maximum service life, maintain the following recommended limits for continuous cruise operation:
Engine power setting – 65% of rated or less.
Cylinder head temperatures – 400˚ F. or below.
Oil temperature – 165˚ F. – 220˚ F.

I can't see any references to 65% in the context of leaning technique other than the bit about supercharged engines I mentioned.

[Flyin'Dutch']

The 65% is referred to in the linked to article for normally aspirated, turbo- and supercharged engines.

But whilst it in that new article is referred to 'for maximum service life set 65% power or less' in an older publication they were much bolder.

[Paul_Sengupta]

Lycoming state you can't damage an NA engine under 75%. It's Continental which say 65%.

Maybe search for 75% instead of 65%!

[TopCat]

Lycoming state you can't damage an NA engine under 75%. It's Continental which say 65%.

Maybe search for 75% instead of 65%!

Citations for these please?

There is no reference to a safe power setting below which damage is impossible when leaning, in FD's linked article.

For things like this where anecdote and hearsay could catch the unwary, it would be good to get it from official Lycoming and Continental sources.

[Irv Lee]

What always concerns me is the thought that if I spend a relatively short time with someone on mixture and leaning, the 45 to 60 hours of the ppl course involving ignoring the control altogether may override in times of overload, ending in an engine failure. I suppose it is no different from training for retractables though.

[Paul_Sengupta]

Citations for these please?

Ok, I CBA looking for the Continental one now, but for Lycoming, you have to look at the manual for the engine in question. Let's take an example of the typical 320/360 normally aspirated engines:

https://www.lycoming.com/sites/default/files/%28L%29IO-360-M1A%20Oper%20%26%20Install%20Manual%2060297-36.pdf

(a) Leaning to Exhaust Gas Temperature. (Normally aspirated engines with fuel injectors or carburetors)
:
(2) Best Economy Cruise (approximately 75% power and below) - Operate at peak EGT.

Operating at peak EGT is the hottest you're going to get that engine for any particular power setting, pretty much burning the fuel/air at the stoichiometric ratio. Any richer or leaner and it'll be cooler.

For turbocharged or supercharged engines the advice is different, and there it's 65%.

e.g.

http://peter-ftp.co.uk/aviation/misc-euroga/Lycoming%20Flyer%20Key%20Reprints_OPERATION.pdf

D. LEANING THE SUPERCHARGED TEXTRON LYCOMING POWERPLANTS.
:
3. Recommended standard cruise power for the supercharged engine is 65%. At 65% power or less, this type of engine may be leaned as desired as long as the engine operates smoothly, and temperatures and pressures are within manufacturer's prescribed limit.

[Paul_Sengupta]

This is quite correct. 3000 feet is in fact a magic altitude, above which engines work differently.

And as everyone knows, it is impossible to recover from a stall in less than 3000 feet.

Since this is the student forum, can I just clarify that this is sarcarm.

The 3000ft must have a different origin as you correctly state that 65% can easily be exceeded with WOT at that altitude, also by other jalopies than the mighty Cheetah.

Perceived wisdom is that 75% power can be achieved up to around 8000ft density altitude, though it depends on the aeroplane. 75% air density is at about 9200-9500ft but an engine will produce 75% power on full throttle somewhere between 8000 and 8500ft generally.

In some POHs I believe Cessna state that you have to lean above 3000ft, so it's probably got something to do with the engine running too rich if you try and run it full rich above that. Some people have taken this to mean "never lean below 3000ft" which is incorrect logic.

I just saw something on a US forum where someone states, "Lycoming say never lean above 75% power." This is also wrong, it's just that above 75% power you have to be careful to do it properly, running sufficiently rich (or lean!) to cool the engine. 100 degrees F rich of peak EGT is where the perceived wisdom lies. This is also where LOP (Lean Of Peak EGT) wisdom also lies but that's another discussion.

[TopCat]

This is quite correct. 3000 feet is in fact a magic altitude, above which engines work differently.

And as everyone knows, it is impossible to recover from a stall in less than 3000 feet.

Since this is the student forum, can I just clarify that this is sarcarm.

I know we've been bemoaning the quality of flight instruction recently, but surely it's not so bad that a student pilot would actually need this clarification...

It would have to be both unbelievably bad instruction, combined with a student IQ of about 40.

In which case....

[cockney steve]

IIRC, my mete's Chief was built in '47....No electrics except 2 mags (Armstrong starting)
No mixture control. For the hell of it, he went to Blackpool one day and managed to get it up to 10,000 feet. his comment was on the lines of " bloody cold, no con-trail, just a big black line of smoke. Engine was choking to death on over-rich mixture and the last thousand or so took forever." As skiving car mechanics who dabbled in boats and bikes
(OK, anything with an engine) we had a good appreciation of mixture.

There used to be a really good thread on the Dark Side's Aussie Forum, about running LOP -v- ROP. the debate, even among proper mechanics ( who should know better) raged on.

[David Wood]

Leaning is an area where theory and practice don't always align perfectly, it seems to me. I've used the 'lean it until it splutters, then make it richer' technique in the past. It works, but it's a bit crude and if you don't have proper CHT/EGT metering you are taking a bit of a risk.

On the other hand, in my Arrow I have a smart EDM700 that meters each cylinder and in theory allows me to lean it 'automatically' to either ROP or LOP using its internal magic. But, y'know what? I find what works best in my Arrow is just to lean it to about 34-36 lph at the top of the climb, depending on altitude and to keep an eye on the CHTs. It runs smoothly, sounds good, burns clean, I still get around 117 kts IAS and it just feels better. Works for me.

[Paul_Sengupta]

I've used the 'lean it until it splutters, then make it richer' technique in the past. It works, but it's a bit crude and if you don't have proper CHT/EGT metering you are taking a bit of a risk.

But according to Lycoming, it's only a bit of a risk if you're over 75% power. Below that, fill yer boots!

Personally I cruise at around 45-65%, so I'm not that worried...

[riverrock]

Generally I'd say "do what the POH says" unless you do your own serious research or make changes to the aircraft.

Mine has instructions for rich on first take off, Best Power for climbing and aeros (Rich), Best Economy for cruising. Lean by pull till its rough, then enrichen a bit. Mine does also has some altitude compensation within the induction system, so I don't have to constantly lean in a climb (although it isn't perfect).