Best practices for leaning

[-]

jacenborne@reddit

Oh boy, this is a contentious topic.

I fly a Mooney with an IO-360 engine and will give you the basics on the red fin theory. Ignore what's in the POH when it comes to leaning and lets just focus on the mechanics for a minute.

The red fin theory, based on engine manufacturer data, states that there is a correlatory relationship between EGT, CHT and Internal Cylinder Pressure (ICP). High ICP and High CHT are bad for cylinder life and therefore engine longevity. Therefore, you want to avoid both. The good news is, they are roughly on the same curves, as EGT changes, CHT changes and ICP changes. So we can understand based on leaning where we are approximately at with ICP and thus avoid the high ICP zones where we are reducing our engines life. Mixture also controls power output in its own way, less fuel (LOP) means the engine is producing less power as the throttle (Air coming in) is constant, so you're changing power with fuel.

The red fin is this anti-abuse zone. It changes based on the power setting, so lets just use 75% and 65% power as proxies.

At 75% power, your ICP is at its highest at peak to about 125deg ROP. Therefore, you want to enrich OVER 125deg ROP (usually 150) or lean UNDER peak (usually 20-50 deg LOP) to reduce the ICP (and thereby CHT due to that similar relationship) and maximize your cylinder life. Most POH's love to do 50deg ROP or right at peak which is right smack-dab where ICP is at its highest.

At 65% power, the red fin shrinks considerably, almost to the point it doesn't exist, which is again backed up by the engine manufacturer data (you can see CHT / EGT / FF charts against % hp in the Lycoming IO-360 operators manual if you want to check it out). So at <65%, you can essentially run the mixture wherever you want, though I like to conserve fuel in my Mooney so run at 20deg LOP for cylinder cooling and best trade-off of range, fuel, airspeed, and still reduced ICP/CHT.

[-]

Fabulous-Golf7949@reddit

Not to be that guy, but peak ICP and CHT is about 40-50° ROP. They occur basically at the same point and right around this temperature. Best Power is about 75-100° ROP and we enriched beyond this — ideally — at any power setting above 75% power for detonation margin.

If you enriched that much, you’ll foul the plugs assuredly in cruise and you’re reducing fuel efficiency and power unnecessarily. You’re enriching beyond even the best power mixture significantly.

[-]

jacenborne@reddit

You're right on where it occurs, not right on where the danger-zone for ICP is (the red fin) would recommend reading through this article to see how this is applied in theory while flying: https://www.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2012-12_red-box-red-fin.pdf.

Check the fin diagram out on page 3 for a good visual. You will not foul spark plugs at 125deg ROP at 75% power in cruise unless the plugs or some other component of the ignition system was weak already.

[-]

Fabulous-Golf7949@reddit

Interesting! My apologies. I was definitely incorrect. Looks like Mike Busch also has a video on these same topics on Youtube so I’m going to watch that now.

I don’t own an airplane but think it’s good stuff to learn in any case.

[-]

jacenborne@reddit

No worries 😄 , part of being a pilot is we're always learning something (myself included)! John Deakin is the one who really created the theory and has some good articles to dive into as well.

[-]

RiccWasTaken@reddit

Just to confirm, these degrees are F right?

[-]

jacenborne@reddit

In this example, yes.

[-]

BeeDubba@reddit

With any fancy animal, I did rich during a show climb, or at cruise climb or cruise, lean to stumble, then add a bit until it runs well.

That way you're either rich enough at slow speeds to not cause damage, or lean enough with enough airflow to keep things cool and prevent fouling.

This doesn't necessarily work during extended pattern work.

[-]

BozoThePilot@reddit

At 65% power just lean until EGTs get to 1450 and monitor your CHTs. If it's below 400 you're good (that's the margin, Mike Busch from Savvy mentions 420 CHTs).

Do not fly lean above 75% power, you will contribute to the degradation of that engine's life.

Don't lean if you're climbing at Vy, pick a good cruise climb speed (e.g. 90 kts is what I use in a 172) and you can lean as you climb but do not lean aggressively (leaning to high EGTs while climbing is likely going to result in high CHTs because you're not allowing good airflow through the cowling - it's still better than what you'd be doing at Vy).

This is all assuming you care about this airplane and you should in a club. Good practices means less maintenance and less fuel burn which equals lower rates or more money for upgrades.

A lot of what I'm saying can be confirmed by watching Savvy Aviation's YouTube videos. He has many videos about EGTs and leaning, specifically mentioning that EGTs shouldnt be used for leaning alone. Now I do use it because it usually gets me around to where I want to be and then adjust from there based on CHTs. Remember EGTs just measure how much extra fuel burn is going out the exhaust (lower temps = more fuel burned).

[-]

AlexJamesFitz@reddit

Does your club have a best practice they'd like you to follow?

[-]

andrew17798@reddit (OP)

I’ve asked around, but they all say different things such as “Do what your CFI taught you”. Do yours?

[-]

usmcmech@reddit

FWIW, CFIs generally are ill informed about how to properly manage big bore aircraft engines. Most just follow their school SOP and never dig into the theory.

[-]

AlexJamesFitz@reddit

Yeah, but we also have a chief maintenance officer who sets the SOPs. Is there anybody in the club with that kind of weight or background who you could trust?

I'm in my club for the long haul, so I lean for best engine health/longevity.

[-]

redditburner_5000@reddit

The science is settled that LOP is fine if you're doing it right. And you're doing it right if you get it and aren't just following a cookbook power setting chart. If you don't know why the red box is dangerous, then either dedicate the time to learn or stick to ROP.

End of the day, you should ask your school how they want you to run the planes. They're paying the bills after all, and they've priced WOT ROP into the pricing scheme they're using.

Start here:

https://www.avweb.com/features/avweb-classics/pelicans-perch/pelicans-perch-63where-should-i-run-my-engine-part-1

https://www.avweb.com/features/avweb-classics/pelicans-perch/pelicans-perch-64where-should-i-run-my-enginepart-2-the-climb

https://www.avweb.com/features/avweb-classics/pelicans-perch/pelicans-perch-65where-should-i-run-my-enginepart-3-cruise

https://www.avweb.com/features/avweb-classics/pelicans-perch/pelicans-perch-66where-should-i-run-my-enginepart-4-descent

Download these and save them as PDFs. Someday they'll be hard to find.

[-]

MeanwhileInSovietRus@reddit

Since your club doesn’t have a set policy, I’ll share what we do in my club for reference.

If you have an engine monitor(which I presume you do if there are digital EGT and CHT readouts), the policy we try to follow involves leaning to max EGT then enriching 50-75 degrees. If you’ve got a fancy engine monitor with lean assist this gets even easier to do. This will keep CHT’s pretty low, I seldom see anything over 380 in our IO-360 powered aircraft.

I’d caution against running lean of peak unless you have good engine monitoring and a strong understanding of LOP operations, it can carry more risks to the engine than ROP if you don’t understand the nuance and process behind what you’re doing.

[-]

Former_Farm_3618@reddit

Yikes. Rich of peak?! I’d suggest reading up from AOPAs ask the A&Ps.

Lean of peak should be taught more as the norm and better practice.

My understanding is rich of peak leads to fouling the plugs, more deposits elsewhere and wasting fuel. Why is this a good thing?

[-]

Snoo-48784@reddit

Vne and never look back

[-]

Frosty_Piece7098@reddit

If you are paying wet, just run it at best power. I own my plane and when I’m running for economy I’m at about 55-60% power and there I lean till rough then a couple spins in. I’ve done this for years and have never had any issues with it.

[-]

scottyh214@reddit

Blindly keeping CHTs low is not a great practice. Yes, given a choice between too rich and too lean, I would generally prefer you run a little too rich but the fact of the matter is, both are bad. My club actually has more issues with cylinders not getting hot enough and building up lead. We teach the typical “stumble lean” approach for airplanes not equipped with a digital engine monitor and we teach 50-75° ROP for those that are.

These methods have allowed us to get nice long lives out of our engines. We just took a 3400 hour O-320 out of service and our O-360 is running like a top with 2400 hours. We also have a Conti O-470 with just a tick under 2,000 hours that is also running beautifully and made it 1600 hours before needing a top overhaul (usually Contis need tops every 700-1,000 hours). Our AEIO-320 is doing great too but it only has like 400 hours or something g on it.

[-]

thatTheSenateGuy@reddit

If the club has no guidance; what does the POH say; if the POH is poor, Lycoming has operator manuals for each engine and they have leaning techniques. Don’t exceed EGT or CHt temps listed.

There will be 10 ways to do it; some people like the Mike Busch approach.

[-]

Swimming_Way_7372@reddit

10 different people will give 10 different answers on this topic. Ask your club how they do things. That way you can rest assured that you're doing it their way.

[-]

rFlyingTower@reddit

This is a copy of the original post body for posterity:

I’m currently in an undisclosed Flight Club with access to a couple non-complex aircraft (let’s say a 172s) powered by the Lycoming IO-360. They do have digital gauges for measuring EGT and CHT

I have heard there are many, many not agreed on things when it comes to leaning, but the main gist of it is to keep CHTs low. In 75% of missions, which are just 300nm hops round trip, should I not care about how much fuel I burn (because the wet lease cost are flat) and lean for best power? I plan on running at 7/8k at WOT. Should I set power according to the POH and lean until the fuel flows match the book number?

Then there are the questions of leaning for the 25% of use cases: longer XC so I have more options. I’ll probably be more like at 65% power here. I’ve heard, but haven’t verified that “Best Economy” really is just peak EGT and not something like 100 degrees lean of peak. In this case should I not follow book and run a set determined LOP setting?

Of course I would like to keep engine longevity and keep rental prices down in this economy haha

What even is the red box? Should I just follow the rule of thumb is enriching it until it doesn’t run rough anymore for all cases?

Please downvote this comment until it collapses.

Questions about this comment? Please see this wiki post before contacting the mods.

I am a bot, and this action was performed automatically. If you have any questions, please contact the mods of this subreddit.