Big gap between LOP and ROP

[varlajo]

2 hours ago, bigmo said:

I can never get my #1 & #4 to 300F in cruise during the winter. Oil temps are totally fine. Correct me if I'm wrong, but I thought Lycoming specs 150F-400F as the range for continued operations??? I've not been at all concerned with CHTs around 250F (especially when it's -10C out - or colder).

Same. I routinely see 240..260 dF CHTs operating deep LOP in winter, and I am not particularly concerned about lead scavenging as I see zero evidence of deposits on spark plugs. 

[A64Pilot]

Just for kicks yesterday I climbed to 6500 on the way back from Lunch, Running full throttle and roughly 100 ROP I had from memory about 23.5 “ MP with ram air closed, fuel flow maybe 11- 12 GL and hour, but Cyl head temps with full open cowl flaps was in the high green so if I had stayed there it would have cost I guess about 2 more GPH to get them back in the middle of the green. Altimeter setting was 30.07

Reducing to my normal 23 squared and 8 GPH which is real deep LOP cost me at least 10 kts but cyl head temp was in the middle of the green with cowl flaps fully closed.

Cyl head temp was my issue running full throttle and 2500 RPM at 6500, high green is within limits but it’s my belief that it reduces engine life, so I slowed down, saving the engine and cut fuel burn by 1/3, once you factored in the lower speed maybe only 1/4 but still significant. To keep the speed I think I would have had to add another 2 GPH to get the temps down. 14 GPH when I could be burning 8 is to me foolish, I’m just not in that big of a hurry

[A64Pilot]

20 hours ago, varlajo said:

Same. I routinely see 240..260 dF CHTs operating deep LOP in winter, and I am not particularly concerned about lead scavenging as I see zero evidence of deposits on spark plugs. 

I think unless mistaken they may allow as high as 475 continuous, my gauge anyway I don’t think has a yellow range just red and green with 475 annotated at the red.

400 I believe has become the accepted number for continuous if you factor in engine life. Is there hard data to back that number up? I doubt it but don’t dispute that the closer to the middle of the green the better. I think it’s a sliding scale and not some one number, by that I mean that it’s my belief that the hotter, the shorter the life, but that there is also too cool, hence my belief that middle of the green is optimal.

Some want the most speed they can get, period and they can afford it too I guess, and there is nothing wrong with that. Just as I have gotten older I guess the need for speed has lost its appeal. The RV guys in my neighborhood fly wide open all of the time, only reducing power to land. Another with a 182 does also, but he denies it comically. The Bonanza crowd mostly seem to but some of them have backed off it seems, I think form listening to me, some haven’t.

I get a little lead, not much and it’s not hard to get out.

Edited yesterday at 04:25 PM by A64Pilot

[AndreiC]

Interesting. What I take from this is that my MP gauge may be mis-calibrated, despite having been to the shop not so long ago. Is there a way to check it out somehow? It is the classical steam gauge with fuel pressure on one half and MP on the other.

My CHTs were not a problem at all at the power setting I was at. It's true here in WI temps are much lower than in FL, but I was below 300 dF CHT on all cylinders, I could barely keep them in the green. But my impression from reading the Mike Busch articles (and others), when it is cold outside low CHTs are not the whole story -- you want to control internal cylinder pressures, and when it is very cold outside CHT does not measure this accurately.

[Hank]

24 minutes ago, AndreiC said:

Interesting. What I take from this is that my MP gauge may be mis-calibrated, despite having been to the shop not so long ago. Is there a way to check it out somehow?

Before engine start, your MP should equal the reporter barometer setting.

At altitude, WOT should not be higher than shown on your Performance Tables. 

Other than that, I can't help much.

[Pinecone]

6 hours ago, A64Pilot said:

I think unless mistaken they may allow as high as 475 continuous, my gauge anyway I don’t think has a yellow range just red and green with 475 annotated at the red.

400 I believe has become the accepted number for continuous if you factor in engine life. Is there hard data to back that number up?

380 max for Continentals.

Talk to GAMI or Savvy about what is a good max CHT for you plane.  Assuming you want max life.

[A64Pilot]

17 hours ago, AndreiC said:

Interesting. What I take from this is that my MP gauge may be mis-calibrated, despite having been to the shop not so long ago. Is there a way to check it out somehow? It is the classical steam gauge with fuel pressure on one half and MP on the other.

My CHTs were not a problem at all at the power setting I was at. It's true here in WI temps are much lower than in FL, but I was below 300 dF CHT on all cylinders, I could barely keep them in the green. But my impression from reading the Mike Busch articles (and others), when it is cold outside low CHTs are not the whole story -- you want to control internal cylinder pressures, and when it is very cold outside CHT does not measure this accurately.

Even in Fl in Winter at 23 squared I have trouble keeping my Cyl head temps out of the bottom of the green with cowl flaps fully closed. When that happens usually just a gl an hour richer brings the temps up to where I’m comfortable. With middle of the green cyl head temps and power well below 75% I don’t think you can harm a Lycoming with mixture myself.

Its been long ago since I learned to fly, but back then what was taught in the trainer aircraft was don’t lean below 5,000 ft, and above in cruise slowly lean until it got rough, then very slowly enrichen until it just got smooth, many aircraft didn’t even have an EGT, but that leaning procedure put them usually just barely ROP, right at what many swear is the absolute worst mixture, yet those engines almost always ran well past TBO. They were carbureted aircraft and just simply wouldn’t run LOP.

In 2003 as part of the Army test activity we did Winter testing in the UP of Wisconsin, air density there in Winter is something us Southern guys have to experience to believe, it may be that your MP gauge isn’t that far off?

Edited 6 hours ago by A64Pilot