Leaning (again)

[ahramin]

From the Lycoming O-320 Operator's Manual

Maximum Power Cruise (approximately 75% power) Never lean beyond 150°F on rich side peak EGT unless aircraft operator’s manual shows otherwise.

What does this mean exactly? My tentative interpretation is that from full rich, note EGT and start leaning, don't go beyond 150° hotter than what you noted, even if it hasn't peaked yet. Anyone read this differently?

[DanWEC]

The way I read it is as you lean from full rich your EGT will max peak eventually. At that peak you note EGT, then enrichen back until the EGT drops by 150 degrees, minimum.
As you get close to peak the cylinder pressures are at the highest about 75 degrees rich of peak if I recall.

[ahramin]

I knew I wasn't reading it right. That makes way more sense, thanks.

[crazyaviator]

What i believe is meant is this : Lean the engine to PEAK EGT, then richen until the egt is 150 degrees cooler, dont lean it out so that its hotter than 150 degrees cooler than peak egt. On engines with good fuel/air distribution, im ok with as high as 50 rich of peak at 75% or below power settings. 100 degrees rich of peak in an average C-206 engine seems to work well

[ahramin]

Strange thing is, if you don't have an EGT gauge and lean according to Lycoming's procedure without EGT,

3. LEANING WITH MANUAL MIXTURE CONTROL (Economy Cruise, 75% power or less, without flowmeter or EGT gage).
a. Slowly move mixture control from "Full Rich" position toward lean position.
b. Continue leaning until engine roughness is noted.
c. Enrich until engine runs smoothly andpower is regained.

you'll be much closer to peak than 150°F.

[SuperchargedRS]

I lean for target CHTs, just as long as I'm not knocking a EGT off the chart or anything.

[photofly]

Strange thing is, if you don't have an EGT gauge and lean according to Lycoming's procedure without EGT,

3. LEANING WITH MANUAL MIXTURE CONTROL (Economy Cruise, 75% power or less, without flowmeter or EGT gage).
a. Slowly move mixture control from "Full Rich" position toward lean position.
b. Continue leaning until engine roughness is noted.
c. Enrich until engine runs smoothly andpower is regained.

you'll be much closer to peak than 150°F.

They're probably working on the theory that with a sufficently low power setting, you can run the mixture anywhere you like without generating excess cylinder head temperatures. In which case, as lean as you can without dropping power on the leanest cylinder (which is the onset of rough running) is close to as economical as you can get, and screw the temperatures.

Personally I set my favourite RPM, lean to my favourite fuel flow, then adjust the MP according to OAT to get the best IAS for that gph.

[Rookie50]

Mike Busch:

http://www.avweb.com/news/savvyaviator/ ... 162-1.html

[DanWEC]

The reference that you posted was also for economy cruise under 75% power, where, as stated, the 150 degrees ROP restriction doesn't apply.
It's all magic anyways, like dolphins, and Jose Bautista.

[crazyaviator]

The onset of roughness is the first cylinder that leans out too much. 3 issues with that, roughness is NOT good for the whole A/C, Increased wear for that cylinde,r and power loss.
If you had gamis and flow improved intakes, etc,, all cylinders would lean out at the same time and your fuel consumption would go down while retaining power at a higher EGT

[photofly]

We're taking about a slight loss of power on one cylinder, and roughness that you can hear rather than feel. We're not shutting one cylinder down completely. Why would that be bad for the aircraft, and why would that cylinder wear any faster?

[DanWEC]

Well, for one, when that one cylinder starts losing power it's gone past peak and is now LOP, even though maybe your overall power hasn't yet peaked because the rest haven't. So then when you enriched again you end up putting that one cylinder possibly right at peak or slightly rich- the zone of highest internal pressure.

Not that the airplane will explode into a black hole of antimatter when that happens, but might possibly take some time off your TBO.

[photofly]

Perhaps, but hopefully we all agree that having the engine run rough for a second or two while you find the leanest mixture that runs smooth (per the POH) isn't going to wear your cylinder to oblivion or shake the aircraft off it's perch.

Busch points out that rough running due to unequal mixtures is more wearing on the passengers and pilot than the aircraft.

[human garbage]

I lean for target CHTs, just as long as I'm not knocking a EGT off the chart or anything.

Same here. I try and keep it below 400*F. Nice having a JPI to monitor each cylinder.

[Rookie50]

I lean for target CHTs, just as long as I'm not knocking a EGT off the chart or anything.

Same here. I try and keep it below 400*F. Nice having a JPI to monitor each cylinder.

Same. I like below 380. Interesting enough, as I lean per Mike Busch, as it gets a little more lean, CHT's are actually lower even as EGT's are higher than a richer mixture. The carb heat trick does help, too, I think.