Lean of Peak: Ignorance Returns (Or Maybe It Never Left)

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Wisdom and ignorance reside at the opposite ends of the metaphysical spectrum, but of the two, ignorance is by far the more persistent. If you wanted a permanent, one-time-forever paint for your house, you’d make it out of ignorance. Or maybe ignorance is like the tide, for as soon as it recedes, it’ll be back later.

What inspires this rumination on the peculiar robustness of being as dumb as box of hammers? A phone call I got this week from a friend who had been seeking advice about how to lean the IO-470 in his Cessna 182. And now, you know where this is going. Not quite 20 years ago, I made a sub-career of writing, critically, about operating engines lean of peak EGTS. Ten years ago, I threatened to douse myself with 100LL and strike a match if anyone made me write one more word about it. But here we are.

My friend had been seeking advice from various people in the industry about leaning and, surprisingly—to me, anyway—had been hearing negative reports on lean of peak ops, mostly having to do with burning up the engine. Seriously? It’s 2015 and we are still having this discussion? Where’s that jug of avgas I had in the shop? Got a match?

This issue erupted in the mid-1990s when General Aviation Modifications Inc. made a nice little business out of selling calibrated fuel injection nozzles. These matched the fuel flow to a cylinder to the available air and evened out the inconsistencies caused by compromised induction design. Engines usually ran smoother but, more important, they could be leaned to the lean side of peak EGT, so they ran cooler and burned less fuel. GAMI had its own sophisticated test cell to generate mountains of data confirming all this. It unearthed more mountains of technical data going back 50 years on LOP that been buried in recidivist ignorance during the intervening years.

In other words, it wasn’t a new idea. It was the resurrection of an old one. Nonetheless, despite scientific data that was, you know, incontrovertible with tables and graphs and stuff, the idea generated plenty of pushback from engine shops, from owners and mechanics. Even Lycoming and Continental weren’t exactly warm to the idea. The arguments against LOP were largely emotional and anecdotal, with a heady dose of not invented here. Both engine companies eventually came around, Continental more than Lycoming. Continental, as you may know, supports lean of peak in turbocharged Cirrus engines, having been led there by GAMI.

But, as my friend discovered, there are still isolated posts of ignorance out there. Or, could it be LOP ignorance is making a comeback? Who can say? But just as the Middle East is doing its level best to revert to the 12th century, I wouldn’t be at all surprised. I’m not going to devolve into an essay on the merits of LOP for the simple reason that this website is already the world’s leading repository of such information. For as good an essay as you’re ever going to read on the subject, I’d suggest John Deakin’s Pelican’s Perch series, beginning with this one. Mike Busch treated the subject in this column some seven years ago and the information is as good now as it was then.

I was a little depressed to hear my friend describe that he had heard the same old arguments against LOP: You’ll burn up your engine, you really have to be careful in doing this and, the all-time classic, avgas is cheaper than valves. The people who make these arguments never seem to have an explanation for how it is that cooler EGTs and CHTs on the lean side will burn up an engine, while hotter ones on the rich side won’t. The only way that works is if you simply deny the science and if you do that, there’s little hope of applying reason. And for understanding the concept, give me three minutes and a whiteboard and I can get you up to speed. In another three minutes, you can be a PhD on the subject.

The last refuge of someone really backed into the corner in opposition to LOP is the old valve lubrication argument and yes, my friend told me he had heard that, too. This holds that lead builds up on the valve seats and lubricates and protects them, preventing something called valve seat recession. The engineering on this is mixed, but there’s nothing in the historical technical data that suggests lead was added to aviation gasoline for anything other than to increase octane.

The FAA’s technical center tackled the valve seat recession issue in a test (PDF) more than 25 years ago when unleaded fuels were being considered. In a test cell, it ran like engines on both 100LL and unleaded fuel. The conclusion: “… the results indicate that no significant difference in effects were observed in the valve seat recession of intake or exhaust valves between the unleaded fuel and 100LL aviation gasoline.” A second study (PDF) found limited recession in test cell runs, but no evidence of it actually occurring at all on automotive engines.

The aforementioned technical arguments against LOP can be, well, religious and based on faith independent of scientific fact. But having said all this, there can still be rational arguments against not running LOP. One is a little silly. Maybe you don’t really care that much about saving a couple of gallons an hour. Some owners really don’t. Or perhaps you don’t have a fuel-injected engine; LOP really isn’t practical for carbureted engines, in my view.

And you do need a multi-probe engine monitor to do this correctly and while many owners have these, not all owners do. Also, some engines don’t run smoothly lean of peak. The TSIO-360 in our Mooney was temperamental this way. Sometimes it was happy and cool 40 degrees lean, sometimes a little stumbly. But I remember one non-stop trip from Kansas to Florida with a moderate tailwind clocking along at 170 knots on 8.5 GPH. What’s not to like about that? Well, one thing: an engine makes less power when operating lean of peak and you’ll go slower. It’s a tradeoff some don’t wish to make. Nothing wrong with that. Just let’s not pretend it’s damaging the engine. In fact, leaner, cooler and cleaner implies just the opposite.

So as the tide of ignorance floods back in—if indeed that actually is happening—I’m hoping that the 2015 apostates will use one of the above arguments, just to show they understand how all this works, grasp the physics and can read graphs. Good people can disagree and are entitled to their own opinions. But as Daniel Patrick Moynihan famously observed, they’re not entitled to their own facts.

A Word About Blogs

From time to time, I feel the need to redefine what the pixels in this section of AVweb are supposed to do. This is a blog. Here’s how dictionary.com defines a blog: “a website containing a writer’s or group of writers’ own experiences, observations, opinions, etc., and often having images and links to other websites.”

What moves me to this periodic declaration is that we occasionally get notes from readers that comments in this section don’t represent the high standards of journalism normally expected from AVweb. The reason for that is that blogs are not journalism, or at least traditional journalism of the kind I learned in newspapers and magazines. In a way, they’re a distorted mutant of the digital age, a response to the fact that digital publishing is a bottomless pit of content absorption without the limits of a 64-page magazine or a broadsheet newspaper. Even radio has more limits than a website.

I tend to write blogs like op-eds, occasionally salted with quotes or technical reference, but in the main, still opinion. You know the crudity about opinions being like certain nether regions of the anatomy, but the other thing about an opinion is that it represents a viewpoint, a sentiment or an assessment not wedded to a claimed fact. In other words, although an opinion may be based on flawed thinking—enough of mine have been—it can’t exactly be wrong. The same applies to comments below that a blog opinion might generate. (They can be offensive, however.)

I think it’s important to keep this in mind. The journalism on this site is to the left, the blog to the right. Whether it’s for good or bad, I can’t say. But the two are different.

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