Complex running lean of peak

P

Piper18O

Pre-takeoff checklist
Joined
Mar 18, 2016
Messages
294
Location
Wichita KS
Display Name
Display name:
Piper18O
So my question is, is it possible to safely set up and run lean of peak in a normally aspirated engine, say a Lycoming 0-540 with constant speed prop if you only have a single egt and cylinder gage? (one of each) The guy I talked with at the fly-in said it could be done by quickly pulling mixture control to roughness and then increase just until it smoothes out. Is this accurate? Or maybe is it accurate at certain power settings? Can you indeed avoid running in the red box with this method at any power settings or some power settings or no power settings without having an “all cylinders” egt and cht gauge and a normally aspirated powerplant?
 
Sounds like he was just doing "lean until rough/enrich until smooth" and was probably ending up near peak egt/best economy without being LOP anyway. Without that fancy temperature gauge, he'd have no way of knowing that some cylinders are ROP or LOP or anywhere in between, which is likely with a carbed engine.
 
GeorgeC said:
Sounds like he was just doing "lean until rough/enrich until smooth" and was probably ending up near peak egt/best economy without being LOP anyway. Without that fancy temperature gauge, he'd have no way of knowing that some cylinders are ROP or LOP or anywhere in between, which is likely with a carbed engine.
Click to expand...

Yes, but is what he was doing safe, or is he damaging his engine at any or all power settings?
 
He won't hurt anything at low power settings.
 
I think 65 is the rule of thumb.
 
Piper18O said:
So my question is, is it possible to safely set up and run lean of peak in a normally aspirated engine, say a Lycoming 0-540 with constant speed prop if you only have a single egt and cylinder gage? (one of each) The guy I talked with at the fly-in said it could be done by quickly pulling mixture control to roughness and then increase just until it smoothes out. Is this accurate? Or maybe is it accurate at certain power settings? Can you indeed avoid running in the red box with this method at any power settings or some power settings or no power settings without having an “all cylinders” egt and cht gauge and a normally aspirated powerplant?
Click to expand...

This isn't a technique used to find LOP, it's basically the standard technique for leaning at all in an engine with minimal gauges. It's how I was taught in that first 172 I flew with no EGT gauge at all. Lean until it's rough, then push it in a little. Easy. But it doesn't get you lean of peak.

I'm not sure why he mentioned you need to lean it "quickly". It's true that using this method, since you don't have to watch the EGTs and let them stablilize/etc., you can do it in just a few seconds by using your ear. But I wouldn't say there's a necessity to "do it quickly".
 
RussR said:
I'm not sure why he mentioned you need to lean it "quickly".
Click to expand...

His claim was that to do it quickly avoids time in the "red box". He also claimed that it was necessary to only enrichen just barely to smoothness. He claimed that would be lean of peak. I guess if it is possible to run normally aspirated engines lean of peak, that would make sense.
 
Normally aspirated isn't the issue, it's injected vs. carbed.
 
It's possible that his induction happens to be so well balanced that he can run smoothly with all cylinders LOP. It's also possible that this is "I am doing the big mixture pull therefore I am running LOP" cargo culting, some cylinders are running hot, and he doesn't know it.
 
Piper18O said:
Is this accurate?
Click to expand...
No.

-The quick leaning part is partially true.. but that applies more when you are actually LOP. In the Cirrus you move the mixture back fast to limit the amount of time the engine spends in the hot zone, see below


--
Not sure why engine mixture settings are such a dark art to people. And just goes to show how poor instruction is in this area (and as a corollary why we desperately need better training here or FADEC engines).. anyway, it's very simple:

Combustion needs fuel and air. If you add more of both you get more combustion, less you get less. There's an optimum mixture ratio for gasoline piston engines.. about 14.7 .. IE, 1 part gas to 14.7 parts air

rich: you have too much gas and not enough air
lean: you have too much air and not enough gas
optimum: you have 14.7 parts air for each part gas
too rich or too lean: the engine dies. Yes, a running engine CAN be flooded.

The engine will run hottest at the optimum (obviously, that's the optimum combustion point).. so people fly either rich, or lean, of that optimum point so they don't bake their engine. In carb'd engines it's hard to perfectly control the amount of fuel and air going into each cylinder so rule of thumb is to go rich. In some injected engines you can go lean. I prefer lean when possible as it's more efficient

The reason the engine gets "rough" when leaning is because some cylinders will start getting *too lean* and combustion starts to suffer. That's the roughness you feel. With good EGT probes you can find that sweet spot at the optimum, when it is hottest, and lean based on that. People usually go about 50-100 degrees rich to help with temps, and ensure that there are no cylinders still at the hottest zone

By default, all diesel engines and jet engines run lean. There is no throttle, you simply regulate the amount of fuel going in

Oh, running "rich" also has the added benefit of keeping an engine cool, not just because you're out of the optimum combustion zone, but also because the fuel itself has a cooling effect when introduced to the cylinder. That's why even in planes that are meant to fly lean, like the Cirrus, you climb rich (sometimes very rich) to help keep temps down
 
GeorgeC said:
It's possible that his induction happens to be so well balanced that he can run smoothly with all cylinders LOP
Click to expand...
I often hear this from people claiming that their X is able to run LOP even though it's carb'd. I've always been skeptical of this claim.. but who knows, maybe there are some near perfect carb'd Lyco and Conti out there that can do it
 
I have a 520 in my Wagon. When I bought it, it had a 6 point egt/cht, but it was one that you had to switch from cht to egt, and switch to each cylinder. Now I have a fancy JPI, that is a wonderful thing.
There are days where I can run LOP very nicely, temps from cylinder to cylinder are VERY consistent, I can get fuel burn down under 9gph while still cruising at 110 indicated at altitude. Some other days, however, I can't get the temps close enough while it runs smooth and I have to go rich of peak. One thing to keep in mind however, is that where I fly most of the time, my power setting is very low. I start at 6000' elevation and to get anywhere need to go to at least 8500. A scenic morning flight usually goes to 11,000 or more. I'm by default at such a low power setting leaning won't hurt anything.
LOP can happen with a carb, try messing with carb heat to get improve consistency in the temps.
 
Wagondriver said:
I have a 520 in my Wagon. When I bought it, it had a 6 point egt/cht, but it was one that you had to switch from cht to egt, and switch to each cylinder. Now I have a fancy JPI, that is a wonderful thing.
Click to expand...

I can't imagine NOT having a full engine monitor. Such peace of mind when you're lean enough to see the CHTs start to come down in cruise.
 
You must log in or register to reply here.
Back
Top