M7-260

[Rosswycoff]

Anyone else fly the IO540 260hp?

Just wanted to check and see if others were seeing the same engine ops as me. Normal cruise is 24" / 2400 and I see about 16 gph, 125 knots indicated.

Also, I used to fly a conti 550 lean of peak for many hours with great results. Anytime, I even think about LOP in the lycoming it starts to bog down and reaallllyy lose power once I hit peak and I haven't had the cajones to go any leaner so I have just been staying rich.

Normally seeing 380 - 400 cht and close to 1500 egt. Seems high but I just can't get it to drop without really reducing power.

Thought I would ask in case I am doing something totally stupid.

[Brenton C]

Injected or carbonated? (Grrrr -- auto incorrect . . . you can see what I'm trying to type)

I've read if injected, run wide open throttle, adjust prop, then lean to roughness, and enrichen just enough that it's no longer rough.

If Carbed, run just under wide open throttle (apparently some of these engines go extra rich at wide open to facilitate climb out) . . . set prop, and lean tip roughness, and add carb heat to see if that smooths it out. If not, richen till it smooths out.

In either case, according to Mike Busch's webinars, ignore EGT and focus on CHT with 380 being your general max temp, and 400 being treated as a redline. (contrary to engine manufacturer's published limits, which are way too hot.)

Admittedly, this all comes from my reading. I've had no experience playing with these things.

Do you have an engine monitor with probes on all cylinders?

[Rosswycoff]

Injected

I got a very interesting response on backcountrypilot.org that really has me concerned about LOP in the 540 Maule regarding the exhaust temps. I am currently running as Mike Busch describes except backing off the throttle because of the noise volume in the cabin.

I do have a JPI 700 and monitor for the temps.

[Brenton C]

I'm pretty new to general aviation, so I don' t know well enough for myself.

I notice that Mike Busch, probably the best example, as well as others who publish on LOP operations seem very confident and make it sound like the issue is well settled. It would seem to be easy so long as you have instrumentation on all cylinders.

But then when you read around on this, and other boards, or at least when I do, I get the impression that it's not so clear cut.

Oh, one other thing I remember reading -- if you're flying at an altitude where your (near) full throttle setting has your engine running under 65%, then you can run pretty much anywhere -- even at peak EGT, without doing damage.

I might not be recalling the numbers correctly, but if you watch Mike Busch's second, advanced webinar on the EAA site on the topic of LOP operations, he elaborates on the "red box" concept, which becomes the "red fin" when different power settings are added to the mix. (added to the "mix", yuk yuk yuk).

If you trust that info, then you don't have to worry about how much or whether you are even LOP.

But if I were you, having tried and had difficulty getting the engine to run LOP, I'd see if I could buy an hour of Mike's time for a personal consultation.

[Mountain Doctor]

+10 on Mike Busch.

I have studied his essays. I respect the amount of thought, time, and true science that go into his articles.

I run a carbureted O-360 but with my JPI engine analyzer I employ some of his techniques with great success. I can usually run safely and stay cool at peak, and under some conditions a little LOP.

Do you have GAMI injectors?

Do you run a wide (>40 degree) EGT spread?

I agree with Brenton. Absolute EGT is irrelevant. Peak pressures, which correlate with CHT not EGT are what matters. I usually run EGT's in the mid 1,500 range.

How are your cooling baffles? On some planes they need to be perfect for proper cooling.

[Rosswycoff]

All good points. I attended the Advanced Pilot Seminar in Ada a few years back when I was operating a turbo-normalized IO-550. Got some great information and the IO-550 would run soooooo smooth after the big pull and I always ran LOP.

The main concern I had was every-time I get close to peak the engine stumbles so bad that I never even make it LOP. And I am not doing this slowly. Maybe making the transition in a matter of seconds. I am not running GAMInjectors yet but I have a decent spread ~50 degrees.

The EGT concern I have is in regards to the Maule exhaust and pipe cracking issues I have heard about.

[Mountain Doctor]

The exhaust cracking is due to vibration and not heat. I also think it's more common on the 360's than the Sixes.

I'll wager your issue is uneven fuel distribution.

Others here know tons more than I do, but I suspect that's the situation.

[Brenton C]

Do I recall correctly that, in the absence of GAMI's, you can narrow the "spread" by swapping around injectors of the richest and leanest cylinder? Or was it hottest and coldest?

I think it was richest and lewnest. Then see how you go... Then, based on the results continue this shell game til diminishing returns.

[rbowen]

To fly LOP with any accuracy you need to have a fully-instrumented engine gauge (six probe EGT and CHT; fuel flow).

Unless the fuel flow spread from the first cylinder to peak and the last to peak is about .5 gallons or less, it'll be hard to get it to fly LOP smoothly.

And yes, you can swap the injectors on the first cylinder to peak (the leanest) with the last to peak (the richest) to narrow the spread. Ditto for the second to peak and the fifth to peak. This is sort of a poor man's GAMI set-up.

Personally, I don't want any cylinders over 380dF.

Busch makes a mistake (I believe) in ignoring EGT. EGT's respond very quickly; CHT quite slowly. Mike has flown his C-310 so many hours he knows what fuel flow will produce what CHT. That may not be true for the rest of us. The APS approach is best. Also, in cold temperatures you may have CHT under 380dF but with very high internal cylinder pressures. So in winter time, 380 degrees is way too hot for long cylinder life, IMO.

[Mountain Doctor]

Interesting point about winter temps there.

I have considered this, and Mike does address it in one of his articles, IIRC.

My understanding is that he agrees with you. The superior cooling on a winter day will keep CHT's down but not the intra-cylinder pressures.

On the other hand the metallurgy/fatigue limits on the cylinder are based more on temperature than pressure so there is a safety net here, as it were.

On the third hand (I missed that day in anatomy I still don't think, and agree with Mike, that the EGT's absolute temperature is relevant. True it responds much faster, but it intrinsically harmless, as opposed to CHT which is a marker for metallurgy compromise.

[rbowen]

You're right in all respects. Re: the "third hand," I agree that absolute EGTs don't mean much (except perhaps as to their effect on exhaust components, and I haven't seen any tests of that). The APS model does use EGTs to park mixtures well lean, then richens mixtures to achieve the power vs. CHTs that you want. Mike just pulls back mixtures to a predetermined fuel flow that should give the desired CHT. Busch's approach works when, like him, you know from long experience what fuel flow produces what CHT. APS doesn't like his approach because, among other things, it's not intuitive and is more difficult to get right by someone new to LOP operations.

Mike Busch used to deny the effect of OAT on internal cylinder pressures. I got into a long "discussion" with Mike about this once. Maybe he's since seen the light and modified his views.

APS makes the point that, while high internal cylinder pressures produce heat that may be dissipated by cold winter temperatures, the pressure remains, along with the higher wear that it produces on nearly all the power train components. Thus almost a linear reduction in targeted max. CHTs for OATs that are below standard.

[Mountain Doctor]

In my opinion this should be all automated and computerized and mathematically based and monitored by a CPU.

Just like any car since about the past 20 years...

Shame on the Powers That Be for stifiling cost effective innovation.

[Mountain Doctor]

Do you have a chart or graph of the recommended CHT maximums based on sub-standard OAT's?

[rbowen]

I saw one on cirruspilots.org that someone prepared, but didn't make a copy of it because my "take-away" was that the effect is surprisingly linear. Not exactly, but pretty darned close. I concluded that I could reduce targeted max. CHT by the amount that actual OAT is less than standard, and be quite close.

You're right; the FAA and its regulatory drag has prevented much automotive technology from appearing on the GA scene that would improve safety and reduce emissions. Not bad for an organization that's supposed to be all about safety, is it?

As to CHTs, the APS folks recommend 380dF as a maximum because that gives a bit of a margin between that number and 400dF, which is where the cylinder starts losing a lot of its strength. They believe it's a reasonable margin, because if a preignition event occurs, CHTs rise so rapidly that they can shoot past 400dF very quickly. Using 380d gives a bit more time to do something about it.

[Mountain Doctor]

Thanks for the info on the linear nature of the OAT adjustment. I will incorparate that into my technique.

I keep going back to my 'Hyundai Argument'.

A multi-hundred thousand dollar aircraft should have at least the technical sophistication of a bottom of the line small car. One that goes 100,000 miles on $2 spark plugs, adjusts its mixture, fuel injection and spark timing based on multiple sensors and parameters, has low emmissions, burns swill with low octane and/or alcohol contamination, and goes 200,000 miles between 'rebuilds'. (In reality the car is disposable, but you get my message...).