Good message, incomplete data.
It's a start. Unfortunately, the history of science is littered with examples where something that worked perfectly in the laboratory and in small scale trials had unforeseen problems in the field.
AMEN to that!
What you really need is an experiment where you run many engines to TBO, some with LOP procedures, some with the old ROP procedures. The conditions need to be as close as possible to identical for each sample i.e. no significant difference in pilot population etc. You then compare the number of engine problems in each sample.
It's a difficult experiment to run. It needs massive resources. Probably the only practical way to do it would be to put the same engine in different aircraft types, and write ROP procedures in the POH for one, and LOP procedures in another.
Yeah, but as you say, that's difficult to impossible, and we really don't need it.
Wait a moment - did someone say that some aircraft had LOP procedures in the POH while the identical engine in other aircraft specified ROP procedures? Maybe someone has been collecting data and evaluating LOP vs. ROP results in the field....
The 1985 Turbo Centurion "Information Manual" for the T210R has the following comment on page 4-26:
"The recommended cruise mixture is at peak TIT or 1750℉, whichever occurs first. Leaner mixtures may be used but are not recommended considering that only a very small gain in economy is possible, accompanied by a loss in speed and possibly cabin comfort. However, richer mixtures may be used as desired for smoothness or power at the expense of increased fuel consumption."
Now, the ignorant might say, "SEE, SEE, I told you so, it's right there in black and white, DON'T RUN LOP! And they slam the door of their mind shut. They say you've got to follow that advise to the end of time, OR go through an expensive re-certification process to get it changed.
We (George, Walter and John) look at that language from 1985, and think it's sorta like reading respected (in their day) technical journals that insist the Earth is flat (written a few years earlier).
Now look. The turbo (with the Inconel rotor) will take 1750℉ all day long, but you're asking for trouble with the EXHAUST PIPES, which probably won't. Run it richer or leaner but stay away from 1750. The ENGINE MANUFACTURER doesn't know what kind of pipes the AIRCRAFT manufacturer is going to hang on it.
It does say that LEANER MIXTURES MAY BE USED! It flat out permits it, but offers some caveats. With fuel a $1.00 per gallon, it may be cheaper to throw some more fuel on the fire by running it richer.
"Possibly cabin comfort."
We really scratched our heads over this. What could they possibly mean? I'll tell you, they meant "VIBRATION from a ROUGH RUNNING ENGINE! The factories to this day do not understand the problem, or the simple solution to it! It took the genius of George Braly to produce GAMIjectors, of which there are now over 22,000 engine-sets out there. If all those engines had six cylinders, that's 132,000 individual injectors!
Look at the February 1990 "Maintenance and Operator's Manual" for the TSIO-520-BE engine, for the original Malibu. At high power, the ONLY mixture setting is LOP! IT IS NOT AUTHORIZED TO RUN ROP! IT IS FORBIDDEN TO RUN ROP AT HIGH POWER, BY LIMITATION!
I'll give you a hint. There is one minor adjustment to the engine that turns it into a LOP-ONLY engine. Does any know what it is?
In fact there is a document on the Advanced Pilot web site that quotes Lycoming: "the technique of operating lean of peak and power recovery was discontinued due to the resulting increase in service issues."
What were these "service issues?" Engine roughness when LOP! We say fix that, and you can run LOP again. Lycoming did not know how, because they did not, and do not understand why the engine runs rough.
It isn't clear to me whether APS employ anyone with a science degree, or a statistician.
George happens to hold an Aeronautical Engineering Degree from Brown University. When he graduated, AEs were plentiful, and jobs were very scarce. So he went back to college, and got a law degree as well. He put himself through both by Flight Instructing. His first aero job was with Ted Smith aircraft, builder of the Aerostar. His initials are on the original drawings used to build that airplane.
In summary, I believe that engines can be operated LOP as shown by APS. I believe that they can be very reliable when operated by a fastidious owner.
Thanks. I'll quibble a little bit, because IF AN ENGINE CAN BE OPERATED LOP, it's easier to do so, and a good deal safer, with OR WITHOUT an EMS.
John Deakin