Leaning for Acro?

Ed Haywood

Ed Haywood

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Big Ed
Aircraft is Super Decathlon. I used to set to 25 squared. Lately have been setting to 2550 RPM and full throttle. Usual practice altitude is 3K-4K MSL.

I have always flown acro full rich. Also always based at sea level.

Wondering if I might lean for the sequence to get a little extra oomph on verticals?
 
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I am by no means an expert but I have two thoughts on this.

Lean for the altitude you are at. You would get best power output that way. (I think.)

Stay with full rich. You need all the cooling you can get.

How is that for an ambiguous answer? LOL
 
I have always wondered about mixture and engine settings for acrobatics, but I think you just answered one of my bigger questions: you must burn a crap ton of fuel when flying acro!
 
I don't do much acro, but my opinion is lean about 100 rich of peak for about your max altitude. As I recall Decathlons seem to run richer than I like anyway. Better is if you have a CHT guage, if you are keeping the CHT under about 380 you are probably fine were ever you lean it to.

Brian
 
I wouldn't bother unless you're doing acro in Colorado. Cooling the cylinders as much as possible is a good thing.
 
Doesn’t the POH say to go full rich? When I did acro in a Super D, we were full rich the whole time.
 
If your running hard why not wet. Not sure you’d see that much of a performance boost with leaning at 3-4K anyway right?
 
From Lycoming's Aerobatic Engines Operating Manual: "Maintain mixture control in "Full Rich" position for rated take-off, climb and maximum cruise powers (above approximately 75%). However, during take-from high elevation airport or during climb, roughness or loss of power may result from over-richness. In such a case adjust mixture control only enough to obtain smooth operation not for economy."

You're above 75% power so it is very clear.
 
High power settings at low air speeds (climbs, up lines) are tough on cylinders. Full rich makes life a little easier on them.

m
 
I’m just thinking there’s a range between ‘50 degrees LOP’ & full rich. When I was doing maneuvering, generally same power setting, varying altitude somewhat, I would lean some, but still keeping it rich.
Maybe it doesn’t mean anything, but not full rich, but also not what I would normally do in cruise flight at that altitude.

Like the old adage(I think it’s one) about ‘leaning above 5000’. One can lean at 2500 MSL if they want, all the more so if back on the power.
 
It has been a few years since I did acro in a Super D, but as I recall, we did not lean. We are based in the Mississippi River delta, so there isn't much worry about density altitude, but we were flying about 5,000' MSL. Full rich would burn more fuel and may build up more "gunk" in the engine. Still, I think it would be easier on it.

Let us know what you decide.
 
I decided not to lean. I am at sea level, home airfield elevation is 200 feet, and I usually practice at 2000-3000 AGL.
 
Two things to thing about, full rich for cooling but also for available fuel. Keep it rich,
 
Acro can never be learned only practiced!
 
I typically use 14-15 gal/hr in a Super D at around 4000 feet and 25 squared. I just then keep an eye on the temperatures and it works out pretty well. I do notice an improvement in engine power at that setting.
 
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