Yet another LOP question... WOT, Low altitude..

dans2992

dans2992

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Dans2992
OK, so I have a Comanche 260B (Normally aspirated Lycoming IO-540). Most of the time, I cruise around 8-10k+, so I run it at peak EGT, or slightly ROP, because I need the power up there. CHTs stay below 400.

The other day I went on a roundtrip flight of about 0.5 hours each way. I was at around 4000 ft., and decided I was going to go LOP. I do not have GAMIs, but I do know that my GAMI-spread is about 0.9 gph. Reading some of the Deakin (and other) material, I know that when LOP there is a rule of thumb saying that "HP produced = 14.9 x FuelFlow".

.65 x 260 hp = 169 hp for 65%.
169 hp / 14.9 = 11.3 gph

Since when LOP, the limiting factor for power is fuel, I figured that if I was at 11.3 gph, I would be at 65% (hence OK to be LOP), so wide open throttle, and 2300-2400 rpm, and 11.3gph LOP should be ok at 4000 ft. (all cylinders were LOP) CHTs were 360 max (and often much lower.)

Was this a mistake? Is it bad to run the engine like this?

My concern was elevated today when a look at the oil filter yielded more ferrous (and some non-ferrous) metal than normal, along with more carbon than would be typical. The only other "out of the ordinary" thing occurring between the last oil changes was six weeks of sitting due to interior work.

Would these findings be at all related to about 1 hr. of these sorts of LOP ops? Any thoughts? The mechanic says check the filter in another 25 hours, and see where we're at.
 
Once you're down at 65% power, you're not likely to damage the engine no matter where the red knob is set. Continental pretty much flat out tells you that once you're at or below max cruise, you can set it where you want. Lycoming won't go that far, but I suspect it is true for them.

Just slightly ROP is exactly where you DO NOT want to be at higher power settings. You're eating up all the detonation margin. That Lycoming WILL tell you.

I don't think one hour of flying no matter what you do to the engine is going to make a significant change in your oil analysis.
 
I only go to slightly ROP when at higher altitude (ie 10k or so). MP is already low enough then.

So, is it possible to set 65% power using the calculation I described? Setting power by MP/RPM values does not take into account the mixture setting... Using the MP/RPM % power chart in the manual, I'd be over 65%, but the manual does not consider limiting power via mixture...
 
Probably not, but just wanted to bounce it off you guys.
 
With CHT's in the 360 degree range, I wouldn't worry. Detonation would rear its ugly head via the CHT gauge if it was an issue.
 
Here's my 2 cents for what it's worth...
I have a Carbed. O-470 in a 68' Skylane.
I usually run lean, & what I have been thinking was 25 ROP...
At annual, the #2 (pilots side back cyl) had a sticking exhaust valve. also had lots of burn area around the exhaust flange .. Shop replaced valve, guide & seals & honed & new rings. 1 other Cyl. had exhaust heat issues, but only needed to re face the exhaust flange. & both had exhaust stems replaced. Engine / Cylinder shop said that I have been too Aggressive in leaning. "All the pilots running LOP are trying to save an ounce of gas, at the cost of faster wear & tear on the cylinders." The shop went on to say just running a few 25-50 ROP will not show a great change in fuel burn, but will save LOTS on the lives of the 6 cylinders.
 
capg2000 said:
Here's my 2 cents for what it's worth...
I have a Carbed. O-470 in a 68' Skylane.
I usually run lean, & what I have been thinking was 25 ROP...
At annual, the #2 (pilots side back cyl) had a sticking exhaust valve. also had lots of burn area around the exhaust flange .. Shop replaced valve, guide & seals & honed & new rings. 1 other Cyl. had exhaust heat issues, but only needed to re face the exhaust flange. & both had exhaust stems replaced. Engine / Cylinder shop said that I have been too Aggressive in leaning. "All the pilots running LOP are trying to save an ounce of gas, at the cost of faster wear & tear on the cylinders." The shop went on to say just running a few 25-50 ROP will not show a great change in fuel burn, but will save LOTS on the lives of the 6 cylinders.
Click to expand...

LOP Operations are primarily for IO engines
 
A few years ago a mechanic told me during the annual I was running too lean. So I read up on ROP vs LOP engine management, and started running the engine even leaner than I had been.

Mechanic now says the valves look great. He has no idea I'm running LOP.
 
capg2000 said:
Here's my 2 cents for what it's worth...
I have a Carbed. O-470 in a 68' Skylane.
I usually run lean, & what I have been thinking was 25 ROP...
At annual, the #2 (pilots side back cyl) had a sticking exhaust valve. also had lots of burn area around the exhaust flange .. Shop replaced valve, guide & seals & honed & new rings. 1 other Cyl. had exhaust heat issues, but only needed to re face the exhaust flange. & both had exhaust stems replaced. Engine / Cylinder shop said that I have been too Aggressive in leaning. "All the pilots running LOP are trying to save an ounce of gas, at the cost of faster wear & tear on the cylinders." The shop went on to say just running a few 25-50 ROP will not show a great change in fuel burn, but will save LOTS on the lives of the 6 cylinders.
Click to expand...

That is very backwards.

http://www.sportaviationonline.org/sportaviation/201212#pg28
 
Backwards or not... If an engine is run too lean, the valves will suffer the heat. Only thing that will suffer is the pocket,,, if you run a little rich.
This is with my 35+ yrs flying IO Bo's & 172's n now a 182 & using the same A/P .
 
Non Compos Mentis said:
A few years ago a mechanic told me during the annual I was running too lean. So I read up on ROP vs LOP engine management, and started running the engine even leaner than I had been.

Mechanic now says the valves look great. He has no idea I'm running LOP.
Click to expand...

Squeeze the **** out of the fuel... See what will happen. Detonation..... Save the 2oz. per gal. You will need the $$$ for valve / cylinder work. Remember to check the exhaust flanges for torque, as they will burn the gaskets up with the heat.
 
also remember who pays the A/P... us. He's happy to see you save the fuel, to put the $ into his side.
 
capg2000 said:
Backwards or not... If an engine is run too lean, the valves will suffer the heat. Only thing that will suffer is the pocket,,, if you run a little rich.
This is with my 35+ yrs flying IO Bo's & 172's n now a 182 & using the same A/P .
Click to expand...

Well.... You are entitled to your opinion. The debate and science are pretty well settled on this one. Over 65% power run very rich or very LOP. Under 65% you can't do much harm. In any case or power setting, your advice of 25-50 ROP is the hardest on your cylinders.

I run mine very rich until in cruise where I run very LOP.
 
capg2000 said:
Backwards or not... If an engine is run too lean, the valves will suffer the heat. Only thing that will suffer is the pocket,,, if you run a little rich.
This is with my 35+ yrs flying IO Bo's & 172's n now a 182 & using the same A/P .
Click to expand...

Free tip: Clue is in the word, Lean of Peak. After Peak, you have less thermal load than at peak, and the same thermal load 50 lean as you do 50 rich of peak. This assuming the engine would be an "ideal engine", which it most definitely isn't. Still it works out pretty much the same, as long as your mixture distribution is good enough to allow enough combustion pressure without knock.

(detonation never ever happens on a piston engine. sorry, had to say this again ;))

If airplane piston engines would be designed by people who actually knew anything about piston engines, we would be so much better off.
 
My understanding is that high CHT is what does the damage and CHT has nothing to do with "peak". The damage has nothing to do with ROP vs LOP and it has everything to do with CHT. You can reduce CHT by going more rich or more lean. So I'm not sure why anyone is saying that running "too lean" will damage things if it only gets cooler the further lean you go.

If I'm wrong, I'm all ears. If I'm right, half this thread is pointless.
 
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capg2000 said:
Backwards or not... If an engine is run too lean, the valves will suffer the heat. Only thing that will suffer is the pocket,,, if you run a little rich.
Click to expand...

Curious...

...which do you think runs "hotter" - 75º ROP or 75º LOP?

Anyway, here's a convert to the "Church of LOP", spreading the Gospel:

15811940540_48217193a9_z.jpg
 
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FastEddieB said:
Curious...

...which runs hotter - 75º ROP or 75º LOP?
Click to expand...

LOL! Case in point. Thank you.
:mad2:

Since CHT doesn't equal EGT/Peak, the notion that running ROP or LOP is good or bad doesn't make sense. What makes sense is understanding where your CHT runs at given mixtures. And keep it somewhere less than 400. That somewhere can be ROP or LOP. Or even right on peak.
 
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I just stumbled upon this:

0032_ccikcb_bg.jpg


That "red fin" is to be avoided. You can see how this profile would do that, except momentarily for the "Big Mixture Pull" to get you to the lean slide.

Its not running LOP, per se´, that can cause problems. Its not leaning enough, so as to put you into that Red Fin area of high cylinder pressures, which can lead to high CHT or even detonation.
 
That's exactly what I learned when I decided to research this in detail. The conjecture and old wives tail were driving me nuts. High CHT causes the damage. High CHT does not follow peak. Highest CHT is generally just rich of peak.

And for some reason, this is rarely taught leaving most people horribly misinformed.
 
mtuomi said:
Free tip: Clue is in the word, Lean of Peak. After Peak, you have less thermal load than at peak, and the same thermal load 50 lean as you do 50 rich of peak. This assuming the engine would be an "ideal engine", which it most definitely isn't. Still it works out pretty much the same, as long as your mixture distribution is good enough to allow enough combustion pressure without knock.

(detonation never ever happens on a piston engine. sorry, had to say this again ;))

If airplane piston engines would be designed by people who actually knew anything about piston engines, we would be so much better off.
Click to expand...


At high power setting and 50 ROP my CHT's would be very high, more than 430. At the same power settings and 50 LOP they would be under 350. I think you are missing quite a bit of what happens due to speed of the burn and ICP's when ROP vs LOP.

Somebody page Dr. DuPuis.
 
Pedals2Paddles said:
That's exactly what I learned when I decided to research this in detail. The conjecture and old wives tail were driving me nuts. High CHT causes the damage. High CHT does not follow peak. Highest CHT is generally just rich of peak.

And for some reason, this is rarely taught leaving most people horribly misinformed.
Click to expand...

Not entirely. Due to uneven cooling and environmental factors such as OAT, you can have cylinders under 400 that are getting abused like crazy. The relationship to peak EGT really does matter.
 
James_Dean said:
Not entirely. Due to uneven cooling and environmental factors such as OAT, you can have cylinders under 400 that are getting abused like crazy. The relationship to peak EGT really does matter.
Click to expand...
True. Cylinder pressure remains high even if the CHT is bring brought down by a cold OAT. But again, this remains covered by knowing where your dangerously high CHT/ICP is across the range of RPM/MP and where that ends up being in relation to peak.
 
Pedals2Paddles said:
True. Cylinder pressure remains high even if the CHT is bring brought down by a cold OAT. But again, this remains covered by knowing where your dangerously high CHT/ICP is across the range of RPM/MP and where that ends up being in relation to peak.
Click to expand...

Is your power the same at the same MP/rpm combinations in all atmospheric conditions?
 
Don't look at me. Way over my head, I don't know jack about managing power on a CS prop.
 
cht kill cylinders and valve assemblies, if it's naturally aspirated the only thing that matters is CHTs. Egt is just wasted heat out the exhaust. The extra fuel doesn't "cool", the leaded gas doesn't lubricate and genius that said your saving 2oz of fuel is a idiot. It's not 2oz it's more like 2-4gallons per hour on a big six cylinder.

Ambient temp (winter vs summer) and IAS have a lot to do with how close or in the red box you can run with out high CHTs.

Sure internal cylinder pressures are at the highest 10rop to 50rop, but I believe the main factor is CHTs. A cylinder head at 400 degrees had only 1/2 it's tensile strength. Combine that with high internal pressures (just slightly rich of peak) and your asking for early cylinder failure. This can come as burned valves, cracked cylinder heads or yes the possibility of cylinder head separation although even if manufacture was completed properly this still should happen.

If CHTs are cooler you can get away with more. Im in the club you can't hurt anything as long as your CHTs are 380-400 or below.


Have fun flying your plane and enjoy running it lean. Running rich soots up the exhaust valve stem and drags that crap up into the exhaust valve guide.

Oil gets black sooner too.
 
capg2000 said:
The shop went on to say just running a few 25-50 ROP will not show a great change in fuel burn, but will save LOTS on the lives of the 6 cylinders.
Click to expand...

25-50 ROP is exactly where you DONT want to be. Unless you are significantly below 65% power, then knock yourself out.

At 65% power you need to be well lean of peak or well rich of peak.

In your carb'd 470 you may have a tough time running it lean of peak due to roughness. Assuming you have an EGT gauge, set you RPM and MP to a setting the book defines as 75% power (best power mixture) then begin leaning and watch your egt gauge. See if you can get it to run 25-30F LOP smoothly. If it is a bit rough you can try and smooth it out with a little carb heat.

If it won't run smoothly I would just run it rich of peak all the time. 100F ROP at least between 65-75% power. Above 8000' I would lean to 50F ROP.
 
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Aaronk25 said:
If CHTs are cooler you can get away with more. Im in the club you can't hurt anything as long as your CHTs are 380-400 or below.
Click to expand...

Most of the time if your cylinders are below those numbers, you're fine. However on a really cold day with 10F air rushing over those cylinders you could be detonating at 350F
 
capg2000 said:
Backwards or not... If an engine is run too lean, the valves will suffer the heat. Only thing that will suffer is the pocket,,, if you run a little rich.
This is with my 35+ yrs flying IO Bo's & 172's n now a 182 & using the same A/P .
Click to expand...

The cylinders run much cooler lean of peak. For example on my plane 30F LOP at 25 squared results in 320-330 CHT's on the IO continental. 100F ROP at 25 squared is average 360-370F. 50F ROP would be even hotter.

If you've been running between peak and 50F ROP that is probably the cause for your cylinder damage. If you can run it well lean of peak with no roughness, you can save the fuel and your mechanic will comment on how clean everything looks at the next annual.

If not, run it at least 100 ROP. Get an EGT gauge if you don't have one. Most Cessnas have a single sensor and that works fine. On a single sensor I would go to 125F ROP just to ensure none of the other cyldiners are leaner than 100 ROP
 
dell30rb said:
Most of the time if your cylinders are below those numbers, you're fine. However on a really cold day with 10F air rushing over those cylinders you could be detonating at 350F
Click to expand...




I think you would find it next to impossible to get ANY naturally aspirated aircraft engine to detonate at 350 degrees CHT regardless of power setting.

Detonation is caused by a combination of fuel not having enough resistance to burn (octane) prior to the spark, compression and temperature.

100ll is really really good stuff. It's not even on the same scale as car gas octane. It's on the motor scale not the research scale. If you compared premium 91 octane auto gas on the aircraft octane scale it would be in the mid 80s range.

I bring that up because as the experimental guys know if you take the most high strung NA aircraft engine the 4 cylinder Lycoming 360ci 200hp a3b6d which has 8.7 to 1 compression and 25degrees of timing it is impossible to get this engine into detonation running on 91 octane, no ethonal auto fuel in less the CHTs are higher than 360. Now fuel it with 100ll and temps can approach 450 with out detonation (reportedly as I haven't done this as that temp will cause premature failure of the cylinder heads, resulting in cracking).

You would know detonation if you hit it as your engine monitor would show a rise in CHT with a decrease in egt. This is because the burn is starting sooner so more energy is spent I the cylinder and less heat goes out the exhaust resulting in decreased egt.

For the sake of time I'll keep using the term detonation and not pre-ignition or other terms, but I believe we are discussing more things than just detonation here.

One thing you risk doing as I think you were pointing out is at 10f you very well could be running at a power setting that is in excess of what the engines continuous rating is due to the cooler, denser air. This means you may be operating at a higher level of internal cylinder pressure, primarily because your producing more power. Not sure this is detrimental, but your outside of the engine manufactures normal operating range.

Hope that helps.
 
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From a Lycoming newsletter..

http://www.legend.aero/pdf/Lycoming-Flyer.pdf

Unless detonation is heavy, there is no cockpit evidence of its
presence. Light to medium detonation may not cause noticeable
roughness, observable cylinder head or oil temperature increase,
or loss of power. However, when an engine has experienced
detonation, we see evidence of it at teardown as indicated by
dished piston heads, collapsed valve heads, broken ring lands
or eroded portions of valves, pistons and cylinder heads. Severe
detonation can cause a rough-running engine and high cylinder
head temperature.
Click to expand...
 
capg2000 said:
Squeeze the **** out of the fuel... See what will happen. Detonation..... Save the 2oz. per gal. You will need the $$$ for valve / cylinder work. Remember to check the exhaust flanges for torque, as they will burn the gaskets up with the heat.
Click to expand...

Once you're down at 65% power as posited in this case you're not going to detonate no matter where you set the red knob. It just can't happen.

Starting at Sea Level (or close there to), I start with the mixture full rich and bring it down to 18GPH with the first power reduction. That's still way ROP. After setting cruise power I lean to LOP (25 degrees or so). That tends to be around 13-14 GPH.

Continental says this is fine. Even Lycoming doesn't gripe about this.

dell30rb said:
From a Lycoming newsletter..

http://www.legend.aero/pdf/Lycoming-Flyer.pdf
Click to expand...


You then conveniently skipped the next paragraph that says:

Detonation may occur in an aircraft engine as a result of maintaining a manifold pressure that is too high for the specific
engine speed and mixture setting being used.​

In fact most of that section of the article covers overboosting turbocharged engine, not running cruise LOP in a N/A engine.
 
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flyingron said:

Detonation may occur in an aircraft engine as a result of maintaining a manifold pressure that is too high for the specific
engine speed and mixture setting being used.​

In fact most of that section of the article covers overboosting turbocharged engine, not running cruise LOP in a N/A engine.
Click to expand...

I was using that excerpt only to show that light detonation does not necessarily present itself with extra high cylinder temps. The poster above me stated that if the cylinder temps are 380 or below, you are not detonating.

If I run the swift, which has excellent cooling, at 26" MP and 2600 RPM and then lean to 50F ROP it will be running smooth, the cylinder/oil temps will be reasonable, but the engine is likely detonating at those power/mixture settings.
 
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