Proper leaning

airslo

So I know this is a "hot topic" like politics. I am looking for some good insights.

How do you guys like to run your engines? I am an airline pilot, so by that, I really don't like doing things against the manufacturers way of doing things. With that in mind, my 1978 Arrow 3 POH states to run at peak for best economy and peak plus 100 for best power. This of course goes against what Mike B. likes to preach.

My question is, do you trust some new technology and new ideas, or do you continue to run the way the book says too even though the book was written 50 years ago?

Thanks.

slo

jacobsja

I go with Mike B's philosophy as he appears to come from an engineering perspective based on review of data. Naturally though, the final mixture depends on equipment installed. To the core question, Yes, I am trusting the new technology installed in the current plane and adjusting to data supported practices as opined by Mike B. Am also submitting data collected by the tech and am getting good feedback from independent reviews.

When in a more rustic cockpit with limited instrumentation, I leaned to peak RPMs. That engine lived a good long life. Put another way, stayed within the POH as that plane had original equipment and no modern tech.

I know of one organization which went off-script from the POHs and preached to lean to a hard-number EGT no matter what altitude, temperature, density, or power setting. That engine management was a sore topic as the engine repeatedly fell well short of TBO. Yet, the head honcho of the group wanted to stick with the set temperature and ignored the aircraft / engine manufacturer POHs. Head honcho did not want to pay for the early overhauls either, and the expense was forced on others. Put another way, that plane had original equipment, POHs were ignored, and things did not go well.

Circling back on the ask. Yes, I appreciate the intent is to determine how people are managing the mixture and understand that I am not providing a hard answer. In reality, the answer is: 'it depends' as chances are that no two planes are identical here. Have high confidence that upcoming responses will come back with inputs based on personal comfort zones and supporting equipment. Some are good with LOP, some stick with ROP / Peak. It all depends on the flight envelope and equipment. More robust equipment (ie: multi probe engine analyzer coupled with GAMI injectors) will open up the possibilities of what the engine will support. With OE equipment (read: same as the day the plane was built), folks will likely stick with the POH which means ROP or Peak.

Unit74

What engine monitor are you running?

tshugart3

I still just follow the POH for my '80 Archer II (Carb'd, of course), and run at peak EGT (old-school single-input gauge) or at the leanest smooth setting if I can't get that far.

The POH may be 42 years old, but the guidance seems consistent with what Lycoming is putting on their website today. I'm about to pass 2000 hrs, just replaced 2 original cylinders due to cracks, and hope to get another several hundred hours out of her before major.

airslo

Nice tshugart3!

I have a cgr30p, and like i said earlier, I am running an Arrow 3

empannin

Generally speaking at 65% power settings or fuel flows you can run anyway you want from full rich to full lean and the power setting is low enough that there is no risk of detonation.

With fuel so expensive these days I think 65% power at peak is a good compromise. For a Seneca III, 65% power is 24 gal hr at 12,000 and 31 MP/2500 rpm. 75% is 32.5M/2500 and 29 gal/hr. That is 178kts true at 65% or 182kts true at 75%. On a 2.5 hr x country 65% is 65.5 gal and 75% is 3 minutes faster and burns 74.9 gallons. That is almost an extra 10 gallons - for me that is ~70 bucks.

These are all book performance values but the trend will hold true.

FYI, at 55% you can pull the prop back to 2200 and 28.3 MP burning 18.7 at 164 kts. That is 57.4 gallons and an 15 extra minutes for an 8 gallon savings. At this power setting/rpm the cabin would be quiet. If you have a good tailwind would be even more savings at 55. The route I was looking at was KHIO to KSTS. The driving distance is 616 miles. at 55% that is about 11 mpg which is not bad for a 6 seat 80's twin. The biggest plus is it is a 10 hr drive vs 2.5 hr flight....

airslo

Thanks all.

I just wish lycoming would come out with something new and updated. There SB still matches my poh, Peak or Peak plus 100.

I like what Mike B and others have to say, but how much of it is opinion and how much is fact. For example who made the "red Fin" that they talk about with cylinder pressure? I cant find lycoming or Cont. ever talking about it, so made that up and how accurate is it?

Seneca38173

I would be stunned if a major engine manufacturer gave engine management information more detailed than what appears in their current technical bulletins. The manufacturers are full party to every NTSB investigation, and employ a whole team of consultants (an old classmate is one) who attend all the hearings, tear down the engines, and review all the data under discussion, including that recovered from engine monitors. Every fatal results in a lawsuit, and the doomsday scenario is one where excessive leaning is found to be a contributing factor, and the judge believes the manufacturer was complicit in this practice. Since the manufacturers are believed to have much deeper pockets than the third parties, they will bear the entire financial burden of the judgement, which these days, could exceed $100M. The only thing about Lycoming 1094D that surprises me is that the statement “EGT probes on individual cylinders should not be used for leaning,” isn’t in all capitals!

All that said, the arguments of the third parties – the engine monitor builders, etc – are absolutely based upon sound physics. That’s why my wife’s car produces double the horsepower, at same gas mileage(1), as the car I drove 25 years ago. But that magic is accomplished, without degrading engine reliability, using wideband – hundreds of kHz – sensing and actuation applied on a cylinder-by-cylinder basis. No degreed engine designer I know believes adding equalized fuel nozzles and 5 Hz temperature sensing, without a rigorous life testing program and flame-front testing that’s way beyond the means of third parties, is a prudent means to achieve lean-of-peak operations in a continuous-flow, magneto-ignited engine.

So what do we do? Following Eric’s recommendation seems pretty good to me. At 65% or less you buy yourself considerable margin in the leaning practices your engine will tolerate. At higher power settings you want to run rich-of-peak. Of course, this is exactly what 1094D recommends, too.

My $0.02,

Bob

griff390

Much of what I was going to write has already been covered, so I'll just share my experience.

Running LOP is more difficult on a carbureted engine because there is no easy way to ensure equalized air/fuel distribution between cylinders. If done wrong, engine damage could result.

My last engine (160 hp carbureted, fixed pitch) was nearing 2,200 hrs., so it was on borrowed time. I already had a new engine in a crate from Lycoming, so I figured I had nothing to lose by trying LOP operations on the old engine. Didn't have an engine monitor, so my method was to watch the single probe EGT and lean until the engine began to run a little rough. It turned out to be pretty close to 50 deg LOP. Then I added carb heat which was supposed to help. It did, and the engine smoothed out. I flew a number of cross countries that way.

The results: fuel burn dropped by about 0.5 to 0.6 gal/hr., but it came with a slight RPM drop, so I also lost a handful of kts. I didn't test it, but it's possible that if I had simply pulled the throttle back to the LOP RPM, I may have seen a similar drop in fuel consumption. I calculated the fuel savings, and running LOP would have saved about 1,000 gallons over the life of the engine (2,000 hr TBO). The fuel savings are great, but there's also a caveat. Leaning an engine improperly may do serious damage, and will instantly wipe out any fuel savings.

I never pushed testing beyond the x-countries because with nothing more than a carb and a single EGT probe, the exercise would never amount to anything beyond an experiment.

I've had 2 carbureted engines go well beyond TBO by following the manual and running ROP. I'll stick with that formula because of the successful history.

kzadora

Great discussion.

Does anyone fly 75% or 65% at lower RPM settings, and why? Taking TSIO-360 as an example, I mean something like 34” and 2300 RPM.

Up high one might not be able to get the required manifold pressure at lower RPM, but lower it should be possible, and quieter, so I like that.

jacobsja

AVweb appears to support oversquare in cruise.

https://www.avweb.com/features_old/why-over-square-is-good/

Looks like the only caveat is to remain within POH boundaries.

Scott Sherer

I fly my turbo arrow at 75% almost all of the time (excluding descents, approaches and rough air down low). I fly at 33.5"/2,400RPM/13.5gph. I can do this all the way to FL190.

Seneca38173

Scott,

those numbers make me think you have a Merlyn, and are operating between 100-150 rich of peak EGT. Is that right?

Bob

empannin

https://piperowner.org/talk/discussion/comment/1438818#Comment_1438818

I like flying at the lowest feasible rpm. At the very least it is quieter. Friction is also related to rpm and lower rpm is ~ lower friction although for the same power output the friction is not going to be dramatically different as there is also friction related to the power pulses/total power delivered.

The other advantage with a fixed wastegate is higher MP means the throttle plate is more open and therefore some of the pumping losses are less without the TP restriction.

Scott Sherer

Hi Bob,

Right you are, and I always fly rich of peak. I watch my JPI EDM-830 CHT's, EGT's and TIT. I lean to the correct fuel flow for 75% power and then confirm on the engine monitor. If I'm in doubt, I always go rich.