LOP in Cold Dense Air

[David-aviator]

Noticed something a bit weird today down low and slow. When leaning to peak and down the back side of the curve, the engine suddenly ran very rough. It did not like the situation at all. The mixture was pushed forward and as the numbers came down the front side of peak, it ran smooth as can be.

Seems like in cold, dense air, 50 ROP is better. At least the engine likes it better and so do I.

[Geico266]

Down low I see the same issues.

[frankh]

Down low?..Hmm can't say I've noticed this..then again I'm rarely below 4000ft LOP anyway

Frank

[pierre smith]

...running LOP.

I spoke with Bart at Aerosport (they built the engine) about LOP. Y'know, I'm an old-school guy and needed some encouragement but I came away with a ROP sentiment. The reason is that unless you have a set of closely matched injectors, when the leanest cylinder is 50 LOP, some of the others will be at max EGT, as a couple of mine were....a situation that you really do not want.

I also noticed a power loss at LOP and several MPH. I came to the conclusion that ROP suits my engine better and the extra 2 GPH is the cost of admission

Best,

[petehowell]

Maybe not an option for the injected guys, but carb heat solves this issue for knuckle dragging carb guys. I ran from Minne to Fargo last Saturday in the flippin' cold, 2 feet of snow, uphill, LOP, both ways.

I do seem to need more Carb Heat when is it bitter out - gotta believe it is b/c the cold liquid fuel is harder to vaporize. Hard to quantify b/c my Carb Heat cable is not calibrated and neither am I.

Global warming will soon solve this issue for all of us...........

[David-aviator]

Originally Posted by petehowell

Maybe not an option for the injected guys, but carb heat solves this issue for knuckle dragging carb guys. I ran from Minne to Fargo last Saturday in the flippin' cold, 2 feet of snow, uphill, LOP, both ways.

I do seem to need more Carb Heat when is it bitter out - gotta believe it is b/c the cold liquid fuel is harder to vaporize. Hard to quantify b/c my Carb Heat cable is not calibrated and neither am I.

Global warming will soon solve this issue for all of us...........

You may have hit the nail on the head with thoughts on vaporization of cold fuel. I have a sump they call "cold air intake" and that may be part of the problem also. Cold air and cold fuel can't be all that conducive to making LOP work. My concern is plug fowling with so much fuel (and lead) going through the system with this cold air, so I try to lean it out, 50 ROP is about as good as it gets for smoothness and power. This was all with less than 23" of MP so I don't think it could have hurt the engine.

Seems like it been global cooling around here this fall and winter - come on global warming!

[the_other_dougreeves]

Originally Posted by pierre smith

...running LOP.

I spoke with Bart at Aerosport (they built the engine) about LOP. Y'know, I'm an old-school guy and needed some encouragement but I came away with a ROP sentiment. The reason is that unless you have a set of closely matched injectors, when the leanest cylinder is 50 LOP, some of the others will be at max EGT, as a couple of mine were....a situation that you really do not want.

Not to reignite (haha) the LOP debate, but FWIW, Lycoming seems to recommend operation at peak EGT and not LOP. From their "Lycoming Flyer Operations" document:

"Operation at peak EGT, particularly on long flights, can be an advantage not only for purposes of increased range, but there is less likelihood of spark plug fouling as well.
...
As far as the pilot is concerned, operating on the lean side of peak EGT can only be accomplished with fuel-injected engines of at least 250 HP or higher because the fuel flows in the lower horsepower engines are so small. It isn?t possible with float-type carburetors because of the fuel/air distribution problem. In any case, leaning past the peak is not recommended."

TODR

[pierre smith]

Thanks for the 1/2 GPH advice, Doug. Lesseee......100 hours a year = 50 gallons....= $200....where do I send your half?

Best,

[Steve Sampson]

Pierre, you know far more about this than I but I thought below around 60-70% power Lyco really were not too fussed where you ran your engine in terms of richness. In fact my Operator Handbook describes one way to be, basically, lean it 'til it misses, and then richen slightly (p3-7, half way down). That actually puts me lean of peak usually. O-320 by the way. I trundle around between 55 and 60% and with the P-mags the fuel flow is down at 22 - 24 lits or even less. Why are you not happy with the Lyco advice?

I agree the getting the fuel fully vaporised can be hard. I have used carb heat and have ended up with the cyls far more balanced, and I assume altitude/low pressure helps vaporisation also. (Thinking about it, it sounds like an argument for MOGAS in the cold. Not sure!)

I would like the oil to be hotter, that would help, but its nigh on impossible.

[JonJay]

Originally Posted by David-aviator

Noticed something a bit weird today down low and slow. When leaning to peak and down the back side of the curve, the engine suddenly ran very rough. It did not like the situation at all. The mixture was pushed forward and as the numbers came down the front side of peak, it ran smooth as can be.

Seems like in cold, dense air, 50 ROP is better. At least the engine likes it better and so do I.

I noticed the same thing the other day. It was 4deg f. and I pushed the power up and the nose into a climb in an effort to get my oil temps up. I leaned to ROP, but evidently my mixture verneer stuck a bit due to the cold then released at some point leaning my mixture. I did not think it was too lean but after a minute or two the roughness occured. Mixture full rich, reduced power, trim to best glide, find a field, then things smoothed back out. I tried to repeat the event but I could not. I think you are onto something here and I feel better about my event now.