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LOP Newbie

A

andrewbutler

Member
Hello,

I have a zero timed IO360 with a Lycoming core and Superior Millennium cylinders. Engine is equipped with Silverhawk EX FI, One Slick Mag on the bottom sparks and one PMAG on the top sparks, both timed to 25 degrees BTDC (I haven't connected the MP to the PMAG yet).

I checked out LOP operation yesterday on a cross country at 8,000 feet using the LOP mode on my AFS3500. Everything happened as expected (from reading JDs Pelican's Perch articles), and the engine ran smooth as I leaned all the way to a noticeable power drop. I stopped when the power drop of the engine became excessive. See picture for the numbers I was getting at 25.5 litres ph (6.6gph). A couple of times though when I was tweaking with the mixture, and power dropped even further, the EGTs shot up. This was rectified by increasing the mixture. Is this normal behaviour? If so, what is happening in the cylinders/exhaust to cause it? If not, what may be the cause?

AFSFlightData


I checked it again today on the return leg, albeit as a lower altitude of 2,000ft. To compensate, I kept the power below 55%. The same thing happened when I went way lean, with EGTs dropping back down again immediately when I reduced the lean slightly. I didn't leave it like that long enough to observe any changes in the CHTs, which hovered around 320 or below throughout.

Running LOP is must have in a country where AVGAS costs ?9 per US Gallon, thats about $13 at today's exchange rate!

Any help would be much appreciated. I want to make sure I am not inadvertently cooking my new engine!

Thanks for your help,
Andrew Butler
RV7 EI-EEO
17 hours flying
Galway Ireland.
 
I have seen the exact same thing

There have been some threads trying to explain the EGT rise after peak. Do a search and read carefully.

This occurs in my engine (IO-360, RSA/AFP injection) at about 50 or so beyond LOP, depending on per cent power.

I am not sure the threads reached a consensus as to what causes this, but there does seem to be a consensus that it is not harmeful. No gurantee, evaluate for yourself.

When not in a hurry, or trying to stretch legs, I end up running 25 - 50 LOP. If I lean too much into the EGT rising area, I richen slightly and fly on. Fuel flow around 7.5 gph at 8,000' or so.
 
I think you will find that when the mixture is so lean it is so hard to get going the pressure pulse and major portion of the combustion event is so retarded that you are getting some of the combustion process happening out the manifold, hence the rise in EGT.

There is no value in running that lean in my opinion. At around 65% power, 10-30F LOP is the go, and if you are up high enough us peak or slightly ROP.

Keep reading all the JD articles, and read them over and over until you know them better than he does. And then make sure you understand the science behind it. :)
 
Thanks

Thanks for the replies. I got a bit of a fright when I saw the EGTs shoot up. I had read the relevant JD articles over and over and this behavior isn't mentioned. Cross referencing several articles he says if the cylinders are properly balanced, on continued leaning after best economy, the power will drop off suddenly and the engine will quit. No mention of rising EGTs.

Also, what would be normal operational EGTs when running LOP? The reason I was leaning so much is because one of the EGTs stubbornly refused to drop below 1,400 - then it suddenly shoots up to 1,500 on additional leaning! JD talks a lot about target CHTs, but he doesn't really say what is an ideal EGT. Is their risk a higher risk that the exhaust valves will get cooked over time? If so, what EGT ranges mitigate that risk.

Thanks,

Andrew.
 
EGT's are relative, not absolute...

andrewbutler said:
Thanks for the replies. I got a bit of a fright when I saw the EGTs shoot up. I had read the relevant JD articles over and over and this behavior isn't mentioned. Cross referencing several articles he says if the cylinders are properly balanced, on continued leaning after best economy, the power will drop off suddenly and the engine will quit. No mention of rising EGTs.

Also, what would be normal operational EGTs when running LOP? The reason I was leaning so much is because one of the EGTs stubbornly refused to drop below 1,400 - then it suddenly shoots up to 1,500 on additional leaning! JD talks a lot about target CHTs, but he doesn't really say what is an ideal EGT. Is their risk a higher risk that the exhaust valves will get cooked over time? If so, what EGT ranges mitigate that risk.

Thanks,

Andrew.
Click to expand...

There are variables that affect the EGT like distance from the exhaust flange. I follow the theory that the upshoot of temps is post combustion, and I do not believe it to be harmful in a short term event, however sustained it might burn a valve.
I don't feel you need to get all hung up on the numbers. Lean to engine roughness or significant loss of power, enrich 1/4 turn or until engine smoothness, basically just beyond the "knee" of the curve, and you will be conservatively LOP.
Try this with your Engine Monitor in LOP mode and study your data log later and you will find that this method works perfectly as long as you are balanced enough to run LOP in the first place. This procedure has been around well before the modern Engine Monitors or talk of balanced injectors and it still works.
Lean to Roughness, enrichen 1/4 turn. What's old is new again.
 
I too have a question

.. even after reading all the articles over and over I am still wondering about this one thing.

Hope I am not hi-jacking but merely shamelessly tagging along
I was wondering what everyones technique is regarding the loss of power while leaning to LOP.
for instance:
I start out with lets say 70% power on the ems by reducing the throttle (low alt, so there is still some MAP 'left')
Then I lean the mixture to LOP while adhering to the Deakin articles and staying out of the red box. While doing that the power output decreases (obviously) and now the EMS is displaying only 55% power (or something around that).

What do you guys do with the throttle? leave it alone? Push it up to recover the loss? Or do you start out with 75%+ power and account for the power drop while leaning?
Also as far as the red box values are concerned what power setting do you base everything on? The 70% you start out with or the lower power output you end up with?

Maybe I am over thinking this, but this has been bugging me for a while and I am really curious what everyone else is doing.

sorry if I am out of line with the thread, my sincere apologies.

Marco
RV-7 IO-360, Flying (with high oil temp :confused:)
North Texas
 
Lean to Roughness, enrichen 1/4 turn. What's old is new again.
Click to expand...

Well that comment is true to a point, however when you do not have well matched cylinders, like my Lycoming factory new IO540 was if I did this I would have several cylinders in mild detonation, one at peak and one just lean of peak and boy was she rough.

I have seen others straight out of the box with a spread of under 0.3GPH.

What was old once was the principle being used on well matched radial engines.

Leaker 311

My thoughts are start with a higher MP, such as WOT. Why would you reduce MP unless you wanted to stooge around doing a scenic? In which case 55% power is what you wanted anyway.

But lets assume you want a low level say 3500' quick and economical trip somewhere. Climb out, level off, reduce RPM only to say 2300-2500 where it runs smooth, and assuming your injectors are well balanced go LOP and use the table below.

You will most likely be around 40F LOP as a guess. Its not hard to do. Once you get used to where your fuel flow is, you will not even look at EGT too much rather ust pull back to a known fuel flow, which is what I do. On your IO360 I would assume the fuel flow will be around the following. 180HP engine = 28.4LPH (7.5GPH) or for a 200HP = 31.5LPH (8.3GPH)


________________________________________
Red Box = No Fly Zone
? At and below about 60% power, there is no red box. Put the mixture wherever you want it.
? At about 65% power or so, 100?F ROP to Peak.
? At about 70%, 125?F ROP to 25?F LOP.
? At about 75%, 180?F ROP to 40?F LOP.
? At about 80%, 200?F ROP to 60?F LOP.
________________________________________


________________________________________
Outside the Box
? At 65% power, use richer than 100 ROP, or leaner than peak EGT.
? At 70%, use richer than 125?F ROP, or leaner than 25?F LOP.
? At 75%, use richer than 180?F ROP, or leaner than 40?F LOP.
? At 80%, use richer than 200?F ROP, or leaner than 60?F LOP.
________________________________________

You guys in the USA are so lucky you can attend an APS course. Best bit of education you can spend money on.

In my opinion, EVERYONE should do one, and I consider myself well informed in this area, and I would attend one if I could get to one next time I am over there. Its almost worth paying for a trip to the states just to attend.

The fact is its not just learning how to run LOP, its understanding what your engine and engine monitor is doing, and trying to tell you. How to diagnose faults and know what is going on up front.

I'll say it again, best bucks you will ever spend on your life long aviation budget.

DB:cool:
 
Andrew, your rise upon further leaning seems to be typical. I suspect you'll notice a change when you get the timing advance at low MAP's activated. Lean, low pressure mixtures burn slower.
 
Well, yes, but...

RV10inOz said:
Well that comment is true to a point, however when you do not have well matched cylinders, like my Lycoming factory new IO540 was if I did this I would have several cylinders in mild detonation, one at peak and one just lean of peak and boy was she rough.
I have seen others straight out of the box with a spread of under 0.3GPH.
DB:cool:
Click to expand...

that's why I said 1/4 turn or until engine smoothness, and added that you need to have balanced injectors to start with if you expect to go LOP successfully.

Personally, I do not believe pre-detonation is possible in the average Lycoming 4 cylinder or there would be students in Cessna's falling out of the sky all the time, but that might open up another discussion.....
 
Personally, I do not believe pre-detonation is possible in the average Lycoming 4 cylinder or there would be students in Cessna's falling out of the sky all the time, but that might open up another discussion.....
Click to expand...

I would have to agree with you there, the old IO540 is pretty hard to kill off as well, but the detonation margin is greatly reduced and all you need is for some things to not be running right.........

DB:)
 
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