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There have been some really good comments made in this thread, but there are a few statements that I'd like to address:
1) The main reason to operate LOP is not fuel savings, although that is a really nice thing as 100LL prices go up. The real reason to run LOP is that it is where the BSFC(min) is located, the CHTs are cooler and the ICPs are lower and the enigne is likely to last longer. Any internal combustion engine is happier if these issues are addressed.
2) Quite to the contrary of popular statements, it is MUCH MORE important to have an engine monitor if you operate ROP. This can be easily proven as there is no LOP setting which is harder on the engine than 25-50dF ROP. There is a really neat little presentation we give which demonstrates the reality of this where a clogged injector is concerned. engine monitors are a very valuable tool and I won't fly serious IFR without one any more. I've seen too many engine saves and a couple of lives saved through their use. They tend to pay for themselves all at once! The least value they have is for leaning.
3) I find that LOP operation requires far less engine management concentrationand attention than ROP operation. At the top of the climb I set the mixture LOP in less than 3 seconds and I do not again touch the red knob until I'm back on the ground ready to shut down. How much easier can it be? (Well, I do understand this stuff fairly well, too.) Actually, it's a lot harder to manage an engine ROP. All of the bad things are experienced when ROP. Detonation, high CHTs, high pressures, hottest exhaust valves, highest fouling and dirty combustion chambers... all found ROP.
4) If TCM were to void the warranty on engines run LOP, how would you suugest they handle the TSIO-520BE which is LIMITED to ONLY be run LOP in cruise. NO ROP operation is allowed in cruise on that TCM engine. TCM has never refused warranty claims for LOP operation. Anyone who told someone that is either woefully mis-informed or just plain misleading them on purpose. Recently one of the VPs of TCM gave a presentation at an OEM factory and the thrust of his presentation was that what we teach at Advanced Pilot Seminars is correct and in harmony with the science. He even used some of the terms WE invented. That's cool.
5) I have yet to see anyone make negative statements about LOP operation who knows anything about it. Those statements eminate from the poorly educated or ill-informed. ONce upon a time, I said any of those silly things. I educated myself and I don't say them anymore.
6) I run LOP at 85-90% power. How is that less power than 75% power ROP, the max power settign recommended? Granted, if you are NA, there are some issues which must be understood to make things optimal. In a NA Skymaster I would give up about 3 knots to gain about 5 gph in fuel efficiency while running the engines about 20dF cooler. I call that a good trade. 3 knots will be difficult to measure over the normal flight. what's that worth? 30 seconds? A minute?
6) One day, in the not-to-distant future, Lycoming is going to become very embarrassed by their "Experts are Everywhere" document(which was written about my partner, George Braly). It's not even in harmony with their own data. If you read it carefully, what it really says is that LOP is fine and works, but that pilots are too stupid to do it right. No kidding, that's what it says.
We recommend ROP and LOP operation. Just do either correctly. Most pilots (like me) were trained poorly and operate under terrible misinformation. We are trying to correct that pilot education deficiency.
Just for fun, about seven years ago, we offered a $1000 reward to anyone who could provide any data which suggests that running ROP is better for an engine than the SAME HP LOP. So far, we've still got our money.
That oughta be enough stuff to heat up a thread for a while! <gg>
Walter Atkinson
Advanced Pilot Seminars
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