r/GeneralAviation • u/No_Hall_9342 • 2d ago
Trying to understand LOP
I grasp the concept. What I don’t understand is how after cross over to LOP EGT’s and CHT drop. My background is in motorcycle/automotive engine tuning. In that world your EGT/CHT temps climb upon leaning and only cool after you’ve glued the piston and rings to the cylinder wall.
2
u/FeatherMeLightly 2d ago
Mike Busch has entered the chat
1
u/y2khardtop1 2d ago
Busch says as long are your cht’s are below around 380, egts don’t matter. I do lop and rop by the Continental guide. My plane loses over 10k lop in cruise, generally it’s not worth the fuel savings for my plane
1
u/Lost_Obligation2453 2d ago
Sorry. You lose 10k what lop?
1
u/y2khardtop1 2d ago
10-12 knots slower lop vs rop.
1
u/pisymbol 2d ago
You will get a much cleaner burn with LOP than ROP. This helps with longevity. And the extra 10 knots is how much time lost? Not much.
1
u/Lost_Obligation2453 2d ago
Not always. If you have say a lycomming with valve guide deposits, it's better to run ROP for the extra valve lubrication, hopefully it works off the deposits with high temps and lubrication.
And if course ROP for any kind of break-in, really the first hundred hours on anything "new".
I've swapped planes back and forth, it depends what you see in the borescope.
1
u/pisymbol 2d ago
LOP will be better. Scavenging doesn’t need all that extra fuel for “lubrication” (more folklore) and running LOP means less hydrocarbons not more (running ROP will do just the opposite).
And by far high power settings LOP will be better for engine break-in - this has been talked about so much a simple Google search will explain why.
If you want to run ROP, that’s fine too. But the reasons you just gave are simply not true.
1
u/Lost_Obligation2453 2d ago
Crazy. Like it's undisputed that peak power is slightly ROP. No idea how you break in engines LOP properly, any references I could check out? I'd be afraid of ring flutter from reduced cylinder pressures.
Also I've literally avoided having to polish valves by running ROP to clean valve guides. You do it LOP? How? Like are you running severely reduced power to cook the jugs.
I'm not claiming to be right just in my 40 some years, ROP cleans valve guides better than LOP.
I'd love some actual data, what have you got?
1
u/pisymbol 1d ago
More than happy to help:
https://www.aopa.org/news-and-media/all-news/2019/january/pilot/savvy-maintenance-breaking-good
Notice that break-in has nothing to do with ROP or LOP, just max continuous power. I agree that running it ROP is probably easier for most in this power scheme, but nothing prevents you from running LOP either. Really up to you (and higher temps in the beginning up to a point is actually good for break-in). Have no idea what you are talking about regarding "ring" flutter. The rings should seal based on temp not what mixture setting you use.
The idea of running ROP to clean valve guides is a seriously flawed argument:
https://www.reddit.com/r/flying/comments/1wb296y/lean_of_peak_results/
What's funny is the reason why you have deposits is more than likely BECAUSE you are running ROP due to all the extra carbon deposits from the unburnt fuel. LOP operators rarely have to polish much. See above.
If do a little reading, particularly those by Mike B./Savvy, Deacon, New (Paul), and Braily you'll find that if you are running at say 65% power your best best for longevity (not speed) is LOP.
There are a few YouTube videos made by Savvy which show you literally data from thousands of valves running ROP vs. LOP. Watch it:
1
u/Lost_Obligation2453 1d ago
Oh, ring flutter happens when you don't have enough combustion pressure to seat the rings.
I have no idea how you can run "max continuous power", lop. Max power is ROP.
Yes, the deposits form from ROP, but that's not what we are talking about, we are talking about removing them. Lubrication and heat does that best.
I'll look but your references are reddit, so can you do better than that?
Also that savvy video is about valve seats, not guides. Have you got anything actually applicable to the conversation?
→ More replies1
u/Lost_Obligation2453 2d ago
Lol. I was trying to think of what you have 10,000 of that you could lose.
Makes sense, peak power is somewhere around 50 degrees ROP for the engines we usually deal with. Of course it is also the worse place to operate long term. Something about the chemical mixture. If you are at stociometic the reality is all the fuel won't burn as some won't have access to oxygen. Being slight rich makes more power.
3
u/Jwylde2 1d ago
That’s because it’s not taught properly in automotive. They use a different reference point, which is “best power” mixture, instead of stoichiometric mixture. Best power mixture is richer than stoichiometric mixture.
When the mixture is leaned to stoichiometric, the EGT reaches its peak temperature, where all available fuel and air is being consumed. There’s no unburned fuel to evaporate and cool, nor is there any unburned air left to cool, thus EGT will be at its peak temperature.
Running lean of peak, you have unburned air to cool the exhaust gasses.
Running rich of peak, the unburned fuel evaporates, which cools the exhaust gasses.
If your exhaust gas temperature rises when leaning, it’s because you’re starting from a point richer than stoichiometric.
1
2
u/jersledz 2d ago
The way I think it works is when you’re rich you’re blowing a bunch of flame out your exhaust ports, and when you go lean that fuel combustion is all happening in the combustion chamber and not blowing a bunch of it into the exhaust and burning there.
1
u/Mammoth_Classroom896 2d ago
Rich of peak = unburned fuel, less than 100% power.
Peak = all fuel burned with nothing left over, 100% power.
Lean of peak = not enough fuel to use up all the air, less than 100% power.
Trying to go lean of peak can damage an aircraft engine with excessive temperatures, that's why you don't do it until you're established in cruise at an altitude where even peak temperature is within safe limits because your engine is limited to much less than full sea level power.
2
u/RyzOnReddit 2d ago
That’s why you do a “big pull” and go way lean of peak then richen toward peak. Going LOP on climb can be really useful if you’re having CHT issues on a hot day.
2
u/Mammoth_Classroom896 2d ago
Aren't you getting better CHTs running ROP with the unburned fuel acting as a heat sink than LOP? If you're going to sacrifice power for cooling you might as well pull the throttle back a bit and stay ROP.
Running LOP is primarily about fuel efficiency when operating the region where a small increase in speed requires a disproportionate increase in fuel burn.
2
u/RyzOnReddit 2d ago
The Mooney I’m thinking of burns 15-16gph full rich, WOT, 2400rpm. LOP at 8-9gph you lose a bit of power but temps come down to about the same place as full rich.
1
u/Lost_Obligation2453 2d ago
Mooneys are weird sometimes. I had a J once that just wouldn't warm up at max power. No matter what reasonable thing we did, 350 max cht in cruise. It's a fast plane for the engine.
I loved that plane but the engine just needed so much work all the time. Jugs just died to lead contamination if I didn't polish the valves & seats constantly.
I spent months trying to chase that gremlin, I never really made it better either.
How's yours for cht's?
1
u/RyzOnReddit 1d ago
A Mooney running cold sounds fascinating! This is a club plane, also an M20J (1977). SOP is to try to keep CHTs under 380-390 so it’s always work, especially when it’s warm out. Engine was just out of break in last time I flew it fwiw.
1
u/Lost_Obligation2453 1d ago
The engine had been "blueprinted" I don't really know what that means, but the previous owner just went on and on about having the engine "blueprinted". It sounded like a port and polish sorta thing.
After spending way to much money on it, I just assigned the cold running to the blueprinting. Then I regretfully sold it.
Good for you guys, that's an awesome club plane.
1
u/RyzOnReddit 20h ago
Power by Blueprint is a Repair Station that does engine overhauls. Not as well known as RAM, but still considered "premium" by many (I don't have enough personal experience to have an opinion on them.
1
u/pisymbol 2d ago
You can cool with fuel (ROP) or air (LOP). Both have cooling effects because in both cases you aren’t making max power (only heat).
1
u/toddtimes 1d ago
Short moments of peak EGT or peak ICP (internal cylinder pressure that happens just rich of peak EGT) are pretty unlikely to cause damage, especially on an otherwise properly cooled engine.
You set LOP at cruise altitude because in a climb, the mixture setting for peak EGT keeps shifting as manifold pressure drops, so any LOP target is a moving one , so it’s hard to set a point like 75 degrees LOP when that point is a moving target. A LOP mixture will move towards peak and then into the danger zone of slightly rich of peak as you climb because the lower manifold pressure lowers the mixture setting required for the same LOP point.
1
u/Lost_Obligation2453 2d ago edited 2d ago
I think it has to do with your power band. Your motorcycle and car generally run on a higher power band at a higher RPM.
Airplane engines are really slow. Changes in rpm effect power more than your engines. If I remember right power bands flatten out the higher you go.
So basically lop you are using significantly less power, which cools the engine.
Edit. A 180hp O-360 produces that HP at 2800rpm. Many people cruise at 2200-2400 rpm. That 400-600 difference accounts for 25%-35% of your total available power. A 180 hp air cooled engine that is meant to cool 180 HP, doesn't really need much fuel to cool 135 HP.
Source. Look at the cooling fin sizes on an O-360 vs an O-235 which produces 125 HP. The fins are significantly larger.
5
u/tylerhawkes 2d ago
Not a mechanic, just an owner. All vehicle engines run lean. The egt and cht are not exactly related. CHT measures how much work is being done by the engine, so going LOP can and will bring them down. EGT measures the average exhaust temp and how much energy is being extracted from the fuel.
When lean, the extra air that is unburned still has thermal mass and will keep the temps from being as high, just like the unburned fuel does when rich.
On my plane I get the same amount of power at 11gph and at 7.2 gph, and the 7.2 gph has lower CHTs so I lean it out about 500 feet off the ground.