Leaning question on my Lycoming I0-360

[Don Patterson]

After reaching my cruse altitude I set my power and turn on the peak detect system on my AFS 3400 Engine monitor. As I start leaning, the EGT temps rise until they peak. As I continue to lean the EGT temps fall, and at some point (well below peak) the display shows ROP. Along with a number that represents a temperature on the rich side of peak. While continuing to lean the display changes from ROP to LOP temperatures until the engine is not happy and I need to enriched a bit.
Hear comes the big question.

Why do I get ROP temps after the cylinders have peaked and not before?

I would think the ROP temps would show before the EGT temps reach their peak point. The only time ROP ever shows is after my EGT temps have peaked.

[erich weaver]

Originally Posted by Don Patterson

After reaching my cruse altitude I set my power and turn on the peak detect system on my AFS 3400 Engine monitor. As I start leaning, the EGT temps rise until they peak. As I continue to lean the EGT temps fall, and at some point (well below peak) the display shows ROP. Along with a number that represents a temperature on the rich side of peak. While continuing to lean the display changes from ROP to LOP temperatures until the engine is not happy and I need to enriched a bit.
Hear comes the big question.

Why do I get ROP temps after the cylinders have peaked and not before?

I would think the ROP temps would show before the EGT temps reach their peak point. The only time ROP ever shows is after my EGT temps have peaked.

Something is screwy with the display setup if it says ROP after you have passed through peak EGT while progressively leaning. Bt definition, you are LOP. Not sure what you mean by "ROP temperatures". You can get the same temperature both LOP and ROP (for the range of temps in which LOP operation is possible).

[Mel]

Is it possible that you leaned too rapidly and the system didn't recognize passing "peak"?

[RV10inOz]

Folks…..here is a statement that is going to ruffle a few feathers, but after the dust settles you will find what we at APS say about this topic is correct, so please bare with me.

The Lean Find function is one of the worst understood and almost useless functions, along with the JPI CLD and DIFF functions.

The hysteresis in probes and the maths algorithms are just not up to the task, and there is a physics experiment going on while you use them.

The Lean find does help when determining the GAMI spread, but after that forget about using them. The reason being is if you use them as most people do, you will end up at a far greater (less efficient) LOP setting than you actually think you are at. If you don't believe me go try it.

Also most EMS are not well configured in the % power calculations. The Dynon is, the AuRacle is, and I am not confident about the rest. So onto the ROP and LOP indicators, if you are using a fixed pitch prop, the ROP/LOP function is useless, RPM and thus EGT fluctuations confuse the heck out of the EMS so it gets easily confused.

The best calculator is between your ears Ignore the ROP/LOP indicators.

So Don here is an extract from a recent post I made.

1. Line up, boost pump on, mixture rich and roll.
2. Climb at a sensible airspeed, not Vx or Vy, in the -10 that is 120KIAS through to TOC using a Target EGT method as described by APS.
3. Level out…..DO NOTHING….as John Deakin would say, an airline pilots favourite thing!
4. Once the plane has accelerated and the CHT's start falling close cowl flaps if fitted (yes I know RV's don't normally have them). then do nothing some more.
5. After a few minutes of doing nothing you will get fidgety, having dealt with ATC, checked your flight plan etc, now set the cruise up by setting say 2400/2436/2372/2490 RPM Yes whatever is a smooth setting for your plane, then do a Big Mixture Pull, and leave it there.
6. Once the CHT's have rolled off a fair bit sneak up to peak FROM THE LEAN SIDE, and find the first one to peak, then roll back leaner and set that to the appropriate amount LOP. Be that 10/25/40/60 or 80 LOP.
7. Another 10 minutes down range turn off the boost pump.
8. Continue the flight until just before TOD do a AMG check for 10-15 seconds on each mag (leave mixture alone) and only touch RPM (reduce to say 2000) on descent, and then throttle only to stay out of the yellow arc, until at the hanger door, shut down with mixture to ICO. Flight over.

Note that when you know which is your last to peak (from the rich side) richest cylinder, lets say it is number 3, you can just pull to a known fuel flow or better still do a BMP, then after everything has cooled off sneak up and watching the RAW DATA only for that cylinder, find peak. Then lean back to XdF Lop and be done with it.

You will be the correct amount LOP and not far more so, you will be at the best BSFC and not excessively leaner than you need to be and life will be good.

Don, let me address one other point,

After reaching my cruse altitude I set my power

What do you mean by this? I assume all you are doing is pulling RPM back to a smooth RPM level, anywhere from say 2300-2600 would be fine. You may find in the 2450-2550 range works well, you may find its a bit less. But please leave the throttle wide open.

You want most of the time to be operating LOP, so WOTLOPSOP is the idea.

If you really want to understand the whole combustion event, how engine monitors work and how best to understand what they are telling you (how to save money) and a lot of flight safety topics, get along to the APS class that John, Walter And George will be running in March.

Hope that helps.

[Don Patterson]

Originally Posted by Mel

Is it possible that you leaned too rapidly and the system didn't recognize passing "peak"?

Mel,

That was my first thought, but don't think that was the problem. It repeats the same results every time. Even if I vary my method of speed that I start leaning.

Thanks

[skybolt31]

Your instrument does not know you are at peak until you are, well, at peak. When you lean and a temp starts decreasing, the instrument now knows you have peaked. Of course at this point, you are past peak, or what you may refer to as lean of peak. If you want to run ROP, you need to first richen to get back to peak an then however far rich of peak that you want to go.

[Don Patterson]

David,

I do run WOT and let things settle before doing my leaning. By pulling to a known fuel flow or a BMP, would that not be a moving target due to varying atmospheric conditions from one flight to another?

[Gash]

David,
Nice post above. Thanks for that.

Question: why do you suggest leaving the boost pump on for this long? I'm trying to learn new techniques--not disagreeing. I usually turn off my boost pump when I perceive that the takeoff phase is complete and that I could lose the engine driven fuel pump and have time (altitude) to maintain aircraft control, analyze the situation and take appropriate action.

[RV10inOz]

Originally Posted by Don Patterson

David,

I do run WOT and let things settle before doing my leaning. By pulling to a known fuel flow or a BMP, would that not be a moving target due to varying atmospheric conditions from one flight to another?

Don, if you do a BMP and with your eyes closed, you will be safely LOP every time. So there moving target is still in your gunsights

Then follow the rest as per above. Once you "know your engine" the variance of the day makes very little difference, although it is there. You will get good at it eventually. but follow the above techniques for a while until you see what I mean.

[RV10inOz]

Originally Posted by Gash

David,
Nice post above. Thanks for that.

Question: why do you suggest leaving the boost pump on for this long? I'm trying to learn new techniques--not disagreeing. I usually turn off my boost pump when I perceive that the takeoff phase is complete and that I could lose the engine driven fuel pump and have time (altitude) to maintain aircraft control, analyze the situation and take appropriate action.

Quite simply the climb at high fuel flow may not need the boost pump, but going through the 6-7000' feet it quite likely will. Usually on a hot day with hot fuel. Grab a TN SR22 or TN Bonanza POH supplement and read what it says about climb. Just remember they have a different fuel delivery so they do not use the pump quite the same way we do.

Secondly, after levelling out, there is a heap of heat soak in the engine bay, and what do you do? Slow down the fuel flow by say half. Thus the fuel gets twice as long in the "pre-heater" and you have a lower outside tank pressure. Even with Avgas RVP this easily gets you vapour lock. Hence the Vans cooling shroud.

Leave the pump on for a while, cool things down by a BMP and LOP ops and after 10 min the fuel pump etc is cooler.

PS: This critical thinking is not all my doing, most is learned from Deakin Atkinson and Braly. I am just lucky enough to work with these guys.