Lean of Peak

[PeteCO]

This is contrary to the the principals on which every internal combustion engine operates. Leaning the fuel increases combustion chamber/cylinder head/exhaust gas temperature, a rich mixture cools the same. So how do you enrichen the mixture "so the temps don't get to cold". At any altitude I lean the mixture until I see a slight increase in RPM's or slight roughness, then I richen the mixture about 1/4 turn. If I have an EGT guage, it will be at peak everytime with this procedure. Now if I did not turn the mixture 1/4 back in, it would be lean of peak. It would be very likely that I would have detonation but would not hear it because I'm wearing a headset.

No. Peak means just that - peak temp. On either side of this peak, the temps decrease. Rich or lean, doesn't matter. The old radials were run lean of peak all the time. Arguably, slightly rich of peak is the worst place to run your engine, even though Lycoming and Continental recommend it. The biggest barrier to successfully running LOP is fuel distribution - that why GAMI-jectors are pretty much needed to run LOP.

This is especially safe when making less than 75% power. Since I operate from a field at 5000 feet, I lean ruthlessly. At low power levels you simply cannot do damage to the engine with this technique. I lean so ruthlessly on the ground that the engine can't exceed say 1200rpm without stuttering.

Read Deakin's excellent articles on Avweb and you too will become a convert just as I have.

 

[JimG]

This month's edition of Flying has an interesting article on the Lancair that I just read.

Even Lancair's test pilot claimed it "stumbles and splutters" at 50 lean of peak.

That's a comforting thought.

I used to fly my normally aspirated Bonanza just barely rich of peak, but with new Ram VI's in my 340....I'll pay for the extra gas and go 100 rich. Big difference in overhauls/maintenence.

 

[Bryan D]

No. Peak means just that - peak temp. On either side of this peak, the temps decrease. Read Deakin's excellent articles on Avweb and you too will become a convert just as I have.

When I lean an engine after peak all the temperatures increase. This makes no sense to me. I have an open mind though, I'll try this on my lawnmower tommorrow.

 

[TDTURBO]

Brian, you thought you leaned them all (6) or (4) cylinders LOP. If you did, I assure you, the temps drop.


The trick is to have a "compliant" engine, ie; no induction leaks, good baffaling, ect.....

What kind of engine monitor were you using? If you only had a single probe, there is no way you can fly LOP with confidence. Meaning, you could have 5 cyliders LOP and one 20 degrees rich, that is the worst place to be if you are a cylinder running higher than 65% power, hence the OWT's regarding bad dogma regarding LOP.

You can't hurt the engine with the red knob if you are flying BELOW 65% power, so it doesn't hurt to try with a normally aspirated engine or turbo, just keep it at low power setttings until you are confident that ALL cylinders are running LOP.

Read Deaken

 

[Moonfly201]

This is especially safe when making less than 75% power. Since I operate from a field at 5000 feet, I lean ruthlessly. At low power levels you simply cannot do damage to the engine with this technique. I lean so ruthlessly on the ground that the engine can't exceed say 1200rpm without stuttering.

Keep in mind, it is not hard to keep power levels under 75% ... even full throttle at sea level, when operating LOP. You are literally choking off the fuel supply to the engine, and power settings are easy to reduce below 75%. In my case, I confirm this with indicated airspeed readings. If I was fortunate enough to have a fuel flow gauge, it would even be quicker and more accurate.

 

[Moonfly201]

But the economy is impressive. I once flew a Cirrus SR-22 at 55% power lean of peak MMU-DAB nonstop. Fuel burn 10gph and TAS 150kts. Landed with 20 gallons remaining.

I give up about 7 to 8 knots indicated airspeed to operate LOP, when compared to the ROP power settings I formally used.

LOP, my IO-360 is burning 7 to 8 gal/hr, and the Mooney's TAS is 140 to 148 kts., depending upon altitude and load. I can cross the entire country (in both directions) with 2 only fuel stops and IFR reserves, with 64 useable gallons.

I'm sold. No more old wives tales for me.

 

[A Squared]

I used to fly my normally aspirated Bonanza just barely rich of peak, but with new Ram VI's in my 340....I'll pay for the extra gas and go 100 rich. Big difference in overhauls/maintenence.

Uhh, yeah, just rich of peak is the absolute worst place to run it, highest danger of detonation and highest chts.

When I lean an engine after peak all the temperatures increase. This makes no sense to me.

It really does make it cooler, I was just noticing this the other day in my 180, if I lean aggressively (below 65% power) the CHTs drop noticably.

For those who are having trouble with the concept think of it this way. when you're operating very rich your cooling with extra fuel, when you're operating lean, you're cooling with extra air. this is not eactly precise, but it may be a useful way of understanding it.

A more correct way of looking at it is this: you'll get the hottest flame when the mixture of oxygen and fuel is perfect, too much fuel and it doesn't burn as hot, too much oxygen and it doesn't burn as hot.

 

[421Driver]

For those who are having trouble with the concept think of it this way. when you're operating very rich your cooling with extra fuel, when you're operating lean, you're cooling with extra air. this is not eactly precise, but it may be a useful way of understanding it.

Well said. As everyone else said, you need a good engine monitor, but don't forget GAMI-jectors, all of the cylinders need to peak close together. A piston engine is really like 4 or 6 separate engines, depending on the model. No two cylinders will perform exactly the same.

Check out the Avweb columns, they really are enlighteneing!

 

[GravityHater]

When I lean an engine after peak all the temperatures increase. This makes no sense to me. I have an open mind though, I'll try this on my lawnmower tommorrow.

The one thing that takes learning on this is you can't hamfist the mixture to do it properly. You need a vernier mixture control as well. The difference between peak and stumbling is often less than one-half turn of the mixture. I have used a JPI fuel flow guage as a measure of how much I am leaning or enrichening. A half turn might mean one GPH which is HUGE. You have to take your time and just nudge it a tiny bit during your adjustments.

 

[VNugget]

When I lean an engine after peak all the temperatures increase.

Think about what you just said....