Lean of Peak: One More Time
Heres my definition of hell: Being marched at gunpoint into a small, windowless room with a laptop and being forced to write about lean-of-peak flying for eternity. Such is my fatigue with the subject, that where you have dreams about flying above sun-warmed cloud tops and landing on seaside runways, I have nightmares about peak pressure traces and runaway CHTs. The reason this is so is because 15 years ago, I got caught up in the thick of the leaning debate, wrote reams about it and figured it was time for the world to move on.
But it hasnt moved on. Comes this note from a reader: “My crusty, dinosaur belt-and-suspenders-old-school mechanic disabused me of lean of peak when I suggested it for my O-550. Instead, per his instructions, I cruise at 20 inches with 2300 RPM, 50 to 75 degrees ROP and burn an astounding 15.6 GPH…the engine went for 1500 hours before needing a top and in 20 years with two O-470s, Ive had to overhaul only one jug. Using this anecdotal evidence, I suspect that its the overhaul companies that are advertising the fuel savings by pushing LOP procedures…Ol Crusty wins this one.”
As I was researching what I futilely hope will be the last article I ever write on the subject of leaning, Walter Atkinson of the Advanced Pilot Seminars covered on page 11 of this issue explained that APS had reduced the number of courses it offers to a couple of times a year partly because they too figured the war against ignorance had been won. But Im beginning to think that all APS has done is to push the barbarians over the most distant ridge. They may be marshalling for another run at the gate.
Lost in the debate over lean versus rich engine operation is the fundamental truth that this isn’t a binary condition. Its not either-or or all black and all white. One is not all good, the other all bad. There are shades of gray. Whats important here is not philosophy, but the intellectual path-the critical thinking-that got you to believe whatever it is you believe.
So if we sat old Ol Crusty down in the test cell and showed him how the EGT/CHT traces behave, what the temperatures and pressures in a cylinder l ook like, he would then have at least the vaguest clue of how combustion really works. He could then opine from this base of knowledge on why he thinks lower pressures and lower temperatures in a lean cylinder cause more valve wear. He could explain how cooler metal must be more stressed than hotter metal. But Ol Crusty doesnt know any of this and, more important, he doesnt know what he doesnt know.
Im not sure the engine companies do, either. I was frankly alarmed to see that Lycoming is still passing out the notorious “experts are everywhere” reprint that clings to the argument that we don’t have the proper instrumentation to run an engine lean of peak. I wonder if anyone at Lycoming has seen an Avidyne E-max, much less flown behind one. The television-size display graphically charts more critical engine parameters than you could ever want and if you want to record them for posterity, it does that, too. So does a JPI EDM-700, for that matter, albeit more modestly. More alarming yet, a Lycoming tech rep told Walter Atkinson that an engines highest detonation risk occurs at peak EGT when APS attendees know by the first day that it actually occurs 40 or 50 degrees rich of peak. They know this because APS sits them in an engine test cell and shows them the spikey tracks of incipient detonation.
My worry is that as the industry continues to retract, the large body of well-founded technical knowledge that APS has passed on to hundreds of owners and pilots will be lost because the technical staffs at Lycoming and Continental continue to push back against it with claims and information that are just wrong, in my view. To inform the debate, I wish a few of these guys at the highest level would attend an APS school. If it would save me another session in my darkened little room and you hearing about me whine about it, how great would that be?
-Paul Bertorelli
