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Engine management / leaning / peak / lean of peak (merged)

@jacko
Considering a conforming engine set, valve overlap can be disregarded.
In a race engine set up, all tricks are available, but a certified aero engine should be used with a very limited spark timing variation, and only one cam set up.
Unburned fuel and Carbon Monoxide in the exhaust should be limited for as much as possible.
Fly lean and green.
In the context of this thread EGT’s in a piston engine are therefore totally meaningless as an absolute value.
CHT’s are very meaningful as an absolute value.

Last Edited by complex-pilot at 15 Jan 11:57

@aviathor
You are correct regarding Lycoming’s leaning “instructions”. BTW -They are not instructions, of course. Only a recommendation by Lycoming.
As an engine manufacturer they can’t give instructions how to fly an aircraft whatsoever.
Anyway, I have checked and the old document has been recently edited (once again).
They have removed the bit regarding “LOP is not recommended”.
I know the boss of Lycoming has stated LOP works, it is just the user who does usually not understand proper procedure and goes too rich when LOP.

Last Edited by complex-pilot at 15 Jan 12:15

(found this unanswered post when doing some admin)

What has been your experience with these power settings in terms of engine longevity, over the years?

Peak EGT seems to have no bad effect whatsoever on the IO540 engine. Mine was stripped down a total of 3 times during its 2000hrs life (1x for shock load, 1x for the crankshaft swap, 1x finally) and was always clean.

BTW I merged some general engine management threads into this one.

Administrator
Shoreham EGKA, United Kingdom

Not sure if this old topic is the right one, but: How does one lean without any engine temperature instruments? Yesterday I flew an Archer II up to 5000ft high, which I thought would be the kind of altitude where one should lean (I usually don’t touch the red lever if flying below 3000ft). Since I learned to fly on a Rotax-powered aircraft, I have never been taught about leaning in any depth.

The aircraft I fly don’t have modern engine monitoring like an EDM900 or similar. In fact, the PA28 doesn’t have a single temperature indication for the engine. Under such circumstances, how would you lean? Lean until engine runs rough, then enrichen the mixture a bit again?

Also, when do I reverse leaning during descent?

Low-hours pilot
EDVM Hildesheim, Germany

There is a procedure which works well enough, in cruise at 75% or less power:

Pull the mixture back, slowly, until you feel a sudden drop in power. It is very noticeable; with a fixed pitch prop especially your speed suddenly drops. Then enrich just enough to restore the bulk of the sudden drop. Now you should be at peak EGT or so.

Most engines don’t run quite as smooth at peak EGT (or LOP) as they run when ROP. So, if there is too much vibration for your liking when you have done the above, just enrich a bit more.

The climb can be done full rich, so long as you are not going much above 5000ft. To do it better, you do need an EGT monitor.

The descent is less critical because, ahem, you are going down anyway If you are starting at only say 5000ft, you don’t need to enrich during the descent, but if you do gradually enrich a bit, it does no harm. On short final go full rich (as per POH) in case of a go-around.

Administrator
Shoreham EGKA, United Kingdom

MedEwok wrote:

In fact, the PA28 doesn’t have a single temperature indication for the engine

That can’t be true. All Archers come with an engine gauge cluster including oil pressure, oil temp, and cyl head temp. Of those, only the cyl head temp is of any use for leaning. Its limitation is that it is only giving you info on the cyl containing the probe and relying on that one data point is risky as you don’t know if it’s the coolest, hottest, on in between.

MedEwok wrote:

Under such circumstances, how would you lean? Lean until engine runs rough, then enrichen the mixture a bit again?

Yes, that’s normally the recommended technique if the aircraft doesn’t have an engine monitor providing info on all cylinders. But check the cyl head temp anyway afterwards just to confirm that at least it is not over 400°F.

LSZK, Switzerland

chflyer wrote:

That can’t be true. All Archers come with an engine gauge cluster including oil pressure, oil temp, and cyl head temp. Of those, only the cyl head temp is of any use for leaning. Its limitation is that it is only giving you info on the cyl containing the probe and relying on that one data point is risky as you don’t know if it’s the coolest, hottest, on in between.

Did you mean to write exhaust gas temp.? I’ve yet to see an Archer with an CHT gauge, but the one in my club (a PA-28-181 Archer II) has an EGT gauge. The EGT gauge is also described in the POH, while there is no mention of a CHT gauge so it is not a modification of that particular aircraft.

Anyway, a CHT gauge is not useful for leaning as the CHT doesn’t react quickly enough.

ESKC (Uppsala/Sundbro), Sweden

A CHT gauge is useless except for checking the max is not exceeded; usually this is possible only in slow high power flight.

The PA28s I have flown never had an EGT gauge but had CHT gauges. When I was doing the FAA IR is Arizona, 2006, the instructor showed me how to lean, by leaning for max CHT. I kept my mouth shut

Peak CHT is reached at the wrong point.

I wrote some notes on this here and it mentions non-instrumented engines.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Pull the mixture back, slowly, until you feel a sudden drop in power. It is very noticeable; with a fixed pitch prop especially your speed suddenly drops. Then enrich just enough to restore the bulk of the sudden drop. Now you should be at peak EGT or so.

Most engines don’t run quite as smooth at peak EGT (or LOP) as they run when ROP. So, if there is too much vibration for your liking when you have done the above, just enrich a bit more.

Good description. I think the bottom line on a carburated engine in particular is that your fuel economy is set by what level of slight roughness (or margin from roughness) you’d like to tolerate, and therefore how much you enrichen from clearly rough. In that situation instrumentation is not really the key item. As with many things most of the benefit comes from doing something (attempting to lean by this method) versus doing nothing. For a carb engine that’s only burning say 8 US GPH anyway, being obsessive won’t save you a great deal of money per hour and in cruise CHT is usually not an issue for a smaller engine.

Once you’ve set the mixture in cruise attention to fuel flow over a couple of minutes will help check if your technique was about right, if you have a fuel flow gauge.

Last Edited by Silvaire at 24 Jun 19:23

Am I understood correctly, that by leaning until roughness and then giving back 2-3 twists to enrich you should be in the ballpark of -50* F LOP EGT?

Last Edited by igor at 15 Oct 08:45
Czech Republic
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