IO-360 low rpm LOP cruise power?

[jetdriven]

It is interesting that you cited Norman's old thread, Ward. It was after reading in this very thread that CAFE speed can typically be found at 65% power for most GA airplanes, and then recognizing that under APS theory the redbox disappears at this same percentage of power that the light bulb came on. Why not just fly at 60 to 65% LOP, while reaping most of the efficiency benefits that are available and being "kind" to the engine, minimizing work load, and still moving along at a decent clip? That is what I have been doing ever since.

Jim

Yes me too. Full throttle, set prop to 2400-2550, set 15-30 LOP and it's always around 8-9 gph. Unless I'm late, which seems to be a lot lately. It was surprising to run 50 LOP at 2700 RPM and see 3-4 knots more speed for the same FF.

[PTK]

Me three! WOT, 2450 RPM, 30-40 LOP ~8 gph.

Very interesting though to see an increase in speed with higher rpm lop.

[pinerunner]

Two points

 

1. If you're on the LOP side Manifold pressure and RPM do not give you the power you're generating so those tables are out the window. 14.9 HP per GPH  which is quoted above (kwmfM20S) is what you want to use. MP and RPM work on the ROP side because air (actually the oxygen in it) is what us chemist call the limiting reagent. On the LOP side fuel is the limiting reagent. It seems obvious to me once you think of it this way.

 

2. I wouldn't try any of this without a good engine monitor, which I assume you have. Given that, checking the CHT's and making sure they don't go too high should keep you out of trouble. 

 

I think at very low power settings peak EGT may be better than LOP or ROP.  In one of Busch's vids he mentions fouled plugs in fish-spotting planes that operate a lot in the "loitering" mode.  The lead-scavenging additives need a certain minimum to do their job well. Busch (or was it Deakins?) was responding to a question "Is there such a thing as too low a CHT?"  

 

I haven't slowed my E model down to absolute maximum range yet, but I've been pondering doing it and lead-fouling is what gives me pause. I suspect that if you're set up to deposit lead on the plugs you're also likely to deposit lead on the valve stems. That's something I want to minimize.

 

As for VERY low rpms consider; if you're generating 50% power (and feeling pretty safe about it) and running 50% RPM (I guess that would be 1300 RPM) you're generating the same power per stroke and probably the same temperatures and pressures inside the cylinder but with twice as much time for heat to transfer to the piston and cylinder walls instead of doing work for you. Sounds like a bad recipe to me, not that I imagine you're talking about running that low.

[ArtVandelay]

Speaking of slowing down...the Va speeds (especially when weight is light), are so low (103), I don't think I could fly that slow :-)

[DaV8or]

I think at very low power settings peak EGT may be better than LOP or ROP.  In one of Busch's vids he mentions fouled plugs in fish-spotting planes that operate a lot in the "loitering" mode.  The lead-scavenging additives need a certain minimum to do their job well. Busch (or was it Deakins?) was responding to a question "Is there such a thing as too low a CHT?"  

 

I haven't slowed my E model down to absolute maximum range yet, but I've been pondering doing it and lead-fouling is what gives me pause. I suspect that if you're set up to deposit lead on the plugs you're also likely to deposit lead on the valve stems. That's something I want to minimize.

 

I'm starting to think very low CHTs are a concern also. My cylinders run cold no matter what and so at 65% power LOP, they are well under 300 degrees. I have now experienced lead fouled plugs, a sticky valve and observed lead deposits on the tops of my pistons. I lean all the time, on ground and in air. Full rich on take off (given my sea level status), but use target EGT method in the climb. On approach, I go full rich for the few minutes in the pattern until on the ground, then lean again. I'm starting to think there might be something to this scavenging thing and I'm on the fence about starting to use TCP in the fuel.

 

Given my cold cylinders, I now run very close to peak most of the time now. My engine runs crappy deep into LOP anyhow, so if I want to go slower, or save gas, I lean to peak and then throttle back. I pretty much stick to 65% power, either by fuel flow, or the ROP, the POH. I guess if you have a plane where the cylinders run hot and you have to watch going over 380, then running well into LOP makes sense, but for me, peak, or slightly lean of peak, like 5-10 degrees, seems like the better and more efficient choice.

 

Life will be so much better when they do finally get rid of lead in the fuel IMO.

[DaV8or]

Speaking of slowing down...the Va speeds (especially when weight is light), are so low (103), I don't think I could fly that slow :-)

 

No kidding! Who else comes cruising along down to the pattern altitude riding the yellow arc and then hits a bunch of bumps and thinks "How the hell am I supposed to get this thing down to VA??!" It seems crazy slow, but I guess there must be a reason.

[jetdriven]

You can slow from 200 MPH IAS to 140 MPH in 3 miles if you hold altitude.

[aaronk25]

I'm starting to think very low CHTs are a concern also. My cylinders run cold no matter what and so at 65% power LOP, they are well under 300 degrees. I have now experienced lead fouled plugs, a sticky valve and observed lead deposits on the tops of my pistons. I lean all the time, on ground and in air. Full rich on take off (given my sea level status), but use target EGT method in the climb. On approach, I go full rich for the few minutes in the pattern until on the ground, then lean again. I'm starting to think there might be something to this scavenging thing and I'm on the fence about starting to use TCP in the fuel.

Given my cold cylinders, I now run very close to peak most of the time now. My engine runs crappy deep into LOP anyhow, so if I want to go slower, or save gas, I lean to peak and then throttle back. I pretty much stick to 65% power, either by fuel flow, or the ROP, the POH. I guess if you have a plane where the cylinders run hot and you have to watch going over 380, then running well into LOP makes sense, but for me, peak, or slightly lean of peak, like 5-10 degrees, seems like the better and more efficient choice.

Life will be so much better when they do finally get rid of lead in the fuel IMO.

If you have a 201 have you tried adjusting the cowl flap linkage so they are closer to flush in cruise?

[jetdriven]

I think it's an F. A friend of mine bought a 1975 M20F and I noticed it runs 320 at 75% power on a warm day.

[Marauder]

I think it's an F. A friend of mine bought a 1975 M20F and I noticed it runs 320 at 75% power on a warm day.

My 75 F also runs in the low 300s on warm days. At Vy+10 I will see 340 to 360 on the climb (warm weather).

[PTK]

I'm starting to think very low CHTs are a concern also... I have now experienced lead fouled plugs, a sticky valve and observed lead deposits on the tops of my pistons. I lean all the time, on ground and in air. Full rich on take off (given my sea level status), but use target EGT method in the climb. On approach, I go full rich for the few minutes in the pattern until on the ground, then lean again...

Dave, POH aside, have you considered not going to full rich on the approach? By going full rich when cylinders are cooling down they get assaulted with all that fuel. This alone I think will go a long way in reducing your lead deposits.

[fantom]

You can slow from 200 MPH IAS to 140 MPH in 3 miles if you hold altitude.

 

2.5 miles if you use speed brakes

[fantom]

Dave, POH aside, have you considered not going to full rich on the approach?

 

That IS what Dave does.

 

 

On approach, I go full rich for the few minutes in the pattern until on the ground, then lean again....

[PTK]

That IS what Dave does.

No. He states he goes full rich on approach in pattern.

I said "have you considered NOT going full rich on the approach."

[jetdriven]

2.5 miles if you use speed brakes

I guess you've been trying my descent profile?

[DaV8or]

Dave, POH aside, have you considered not going to full rich on the approach? By going full rich when cylinders are cooling down they get assaulted with all that fuel. This alone I think will go a long way in reducing your lead deposits.

 

I've considered it, but I know me, I would never remember to go full rich on go around, so I stick to procedure. I put the prop full forward in the pattern for the same reason. I of course have to make adjustments for high altitude airports, but I rarely go there.

 

In a normal pattern, I do my first GUMPS check as I enter downwind and that's when I go full rich. So, midfield downwind to roll out I'm full rich, that's like what, maybe two minutes? I figure back in the day people used to run these planes rich all over the place and if two minutes of rich operation causes maintenance issues, well, back in those days planes would have been grounded all the time.

 

I don't disagree, lean in the pattern would be good, but like I said, I would never remember the full rich in the go around and then I might have even bigger maintenance issues!

[N201MKTurbo]

I leave my plane LOP all the way to the hanger. I know two things: 1. I can go to full throttle without hurting anything. 2. It is more then enough power to arrest my decent while I retract the gear and flaps. After it is all cleaned up and I'm not in a hurry I can move the prop and mixture to climb power.

 

I'm cheating of course because i have a turbo, so it behaves the same at any elevation.

[EDNR-Cruiser]

Shame on you! This thread is about normal Mooneys, not about turbo-normalized people... 

[Immelman]

Well I had the rare pleasure of using my plane to commute to work yesterday for a trip, will come back in a few days, so I decided to do a quick experiment. Really I would like to do several and come up with a better data set. So far, the result? Well, not exactly conclusive, a brief synopsis:

 

Conditions:

- 3,500' MSL, warm atmosphere, approx +20C OAT

- Mixture leaned to LOP on all cylinders (the richest cylinder just past peak)

- Fuel flow 8gph = 60% power, ram air ON

- Established cruise at 2400 RPM and let the airplane stabilize for a few minutes. Noted IAS, TAS, CHTs, and EGT spread (the data is in my airplane, so no specific numbers here, just highlights)

- Backed off RPM to 2000 and adjusted throttle to nearly wide-open to get back to 8gph once again, mixture set the same, and then again let the airplane stabilize for a few minutes

 

Results:

- Speed: At 2000 rpm I got 1-2mias more speed, MAYBE than 2400rpm. I say maybe because even thought the air was mostly smooth, there were a few nibbles of convectiion starting at that altitude and hour of the morning which of course causes the airspeed to bob around a bit.

- CHTs were all within a few degrees of each other and stable just above 300dF, at both 2000 and 2400. No real difference in one being hotter than the other

 

Either way I enjoyed very nice mileage and the engine ran smooth at both settings.... the question then comes back to - with all other things being equal, what's better for long term engine health - 2400 or 2000rpm at 60%? It sure wasn't a significant speed difference.

[kmyfm20s]

It will take you longer to reach TBO at 2000 RPM.

[TTaylor]

If you are using a recording tach that is based on a ratio of rpm then as kmyfm20s said you will get lower hours on engine by nearly 20% at cruise.  In addition, overall you are just not turning as many revolutions on all the parts in the engine.  There will slight difference in torque so that may all balance out, but that should really only be on the crankshaft and not all the rest of the parts. 

 

I am looking forward to trying it on my next flight.  I hope Byron will try some more tests as well to explore the earlier results as well. All tests should be at or lean of peak, anything rich of peak would not be a valid comparison as the stoichiometry then allows for fuel to be expelled without burning. 

 

I fly in the 9 to 12K range most of the time so it will be interesting to see at those altitudes.

[pinerunner]

I've considered it, but I know me, I would never remember to go full rich on go around, so I stick to procedure. I put the prop full forward in the pattern for the same reason. I of course have to make adjustments for high altitude airports, but I rarely go there.

 

In a normal pattern, I do my first GUMPS check as I enter downwind and that's when I go full rich. So, midfield downwind to roll out I'm full rich, that's like what, maybe two minutes? I figure back in the day people used to run these planes rich all over the place and if two minutes of rich operation causes maintenance issues, well, back in those days planes would have been grounded all the time.

 

I don't disagree, lean in the pattern would be good, but like I said, I would never remember the full rich in the go around and then I might have even bigger maintenance issues!

I agonized over just this issue and then decided to do it. My procedure is to drop power in the pattern just to the point where the prop comes out of governance and set it at 2500 rpm with the throttle. Then lean to maximum power (RPM drop and re-enrich to bring back to max RPM). Then I leave the mixture alone throughout the rest of the landing, making things simple for myself, like a 172.  I tested this setting at altitude to make sure that applying full power wouldn't make it cough and sputter like if you lean for idle and try to take off and that was fine and CHT's didn't take off. I'm active enough on this leaning stuff that I'm pretty sure alarms would go off if I hit the throttle first and left it lean. SOP for go-around is mixture first then throttle of course. It should be less critical than if you did it on takeoff since you have flying speed and good cooling (not like the start of the takeoff roll).

 

I always go rich for high power settings. Retraining yourself is a tricky business and its hard to honestly promise yourself what you might do in a tight situation. 

 

Dave

[PaulB]

Is going full rich for the 3-4 minutes you're in the pattern really causing that much of a problem?  Maybe you could argue that going rich increases lead deposition and maintenance costs but in a go-around seconds count and the second it takes to go full rich may be the difference between life and death.  I know this isn't the case 99% of the time but it goes back to the same issue with gear ups.  Distractions and unusual circumstances complicate things when time matters most.

 

I second the notion that lead free avgas is gonna be great.

[Bob - S50]

If you are using a recording tach that is based on a ratio of rpm then as kmyfm20s said you will get lower hours on engine by nearly 20% at cruise.  In addition, overall you are just not turning as many revolutions on all the parts in the engine.  There will slight difference in torque so that may all balance out, but that should really only be on the crankshaft and not all the rest of the parts. 

 

I am looking forward to trying it on my next flight.  I hope Byron will try some more tests as well to explore the earlier results as well. All tests should be at or lean of peak, anything rich of peak would not be a valid comparison as the stoichiometry then allows for fuel to be expelled without burning. 

 

I fly in the 9 to 12K range most of the time so it will be interesting to see at those altitudes.

I'm in the Mike Busch camp. I don't care about TBO and tach hours. If the engine is running well, isn't using too much oil, compressions and borescopes look good; I'll keep flying it. 2000 RPM will put more load on the main bearings but 2400 will put more reps on the cam lobes. Who knows which is better?

Bob

[pinerunner]

Is going full rich for the 3-4 minutes you're in the pattern really causing that much of a problem?  Maybe you could argue that going rich increases lead deposition and maintenance costs but in a go-around seconds count and the second it takes to go full rich may be the difference between life and death.  I know this isn't the case 99% of the time but it goes back to the same issue with gear ups.  Distractions and unusual circumstances complicate things when time matters most.

 

I second the notion that lead free avgas is gonna be great.

Hmmm. Well first it only takes a second or so to do both mixture/throttle and second I can just give it throttle and follow up with the mixture a few seconds later if I'm in some split second decision kind of scenario. Assuring myself of that was why I took the trouble to try at altitude and make sure I was comfortable with the way the CHT's behaved.

 

 If you work at staying ahead of the airplane and the situation in general those cases are very rare; you have plenty of seconds to take care of business. I think you're also saying that setting up the mixture the way I do is complicated and might distract me from the gear but I find it easy and hardly any more complicated than going full rich on entering the pattern. I read/listened to both Deakins and Busch discuss this, agonized over it for a while, and then took it up and tried out what they said came back down and did the data dump from my UBG-16 and was satisfied. Maybe I'll do it again in a few months and show the data (need $$ for annual, insurance, etc.,  doing carpet while I save $$).

 

Retraining is a bit hard so I agree that most should stick with what they're comfortable with and not make changes frequently, changing their mind a lot.

 

My bottom line was that I decided there wasn't a good enough reason to run full rich in this low power region of flight when I was learning to use the best possible mixture settings for all others. I chose a compromise setting that would be reasonably lean and offer maximum simplicity throughout a normal landing and be OK, though not ideal, for a brief excursion to full power. So I'm not afraid of forgetting or not having time to go for the mixture first, but I still train to do mixture then throttle (RPM already at max when landing). 

 

As for the avgas I sure think they should fast track GAMI 100LL and/or the Swift fuel. I think the GAMI guys said the typical refinery could blend it up for you right now if only it were approved. I'd love to be part of the testing program.