ROP versus LOP and the Lycoming IO-360

[Jsavage3]

For those of us with the Lycoming IO-360 and for education purposes only, who is running ROP vs Peak vs LOP?  If ROP, how much ROP and why.  If LOP, how much LOP and why?  Please include performance numbers to include KTAS, GPH, CHTs, etc that you typically see as well as power settings and altitude.

 

Currently, I run 25 ROP off of #2 (first to peak) using a UBG-16 and I like to run 65% power at WOT (using the "47" number) around 9,000 feet...usually 22" & 2500 RPM or 21" & 2600 RPM.  My CHTs are usually 340-360, 9.3 to 9.6 GPH and 161 KTAS.  My GAMI spread is 0.2.

 

We all know why the big 6-cylinder engines are running LOP, but I would like to better analyze how & why we're operating our 4-cylinder Lycomings.

[201er]

After 8 pages of flaps... let's talk LOP

[pinerunner]

What about M20E's and M20F's ? If you're really after all fuel injected Mooneys I'll vote too.

[Bob_Belville]

I have a gami spread of only 0.1 so I can and do run LOP now and then but I would usually rather burn 10.5-11 gph and gain 10 or more knots running 125 ROP. Who buys a Mooney to go slow?  

[aaronk25]

Peak egt in winter 10-20 degrees lop in summer. Last night I ran at -6c 4000 ft WOT 2700rpm 11.3gph at peak for 4 hours at 162true. 330chts.

Wouldn't get away with that in the summer, in summer is have to pull fuel back to 10.6gph to get to 10-20lop to keep cht in 360-380 range at that high of power setting.

[HopePilot]

If there were an afterburner I'd use it.  Think of it this way.  It's more efficient and cost effective to fly a 201 ROP than buy the next model up and fly LOP at the same speeds.  Think of flying ROP as saving money, and the hassle, of having to trade-up.

[aaronk25]

If there were an afterburner I'd use it. Think of it this way. It's more efficient and cost effective to fly a 201 ROP than buy the next model up and fly LOP at the same speeds. Think of flying ROP as saving money, and the hassle, of having to trade-up.

Ok but the difference between peak and say 100ROP is about 3kts on my bird. But takes 35% more fuel. I run peak at 4k and 2700rpm if in a hurry!

[Bob_Belville]

You 201ers have an advantage with engine cooling which seems to be as much as 40F. Running at peak or close to it @ 75% power will put my #3 CHT over 400F.

[KSMooniac]

Peak egt in winter 10-20 degrees lop in summer. Last night I ran at -6c 4000 ft WOT 2700rpm 11.3gph at peak for 4 hours at 162true. 330chts.

Wouldn't get away with that in the summer, in summer is have to pull fuel back to 10.6gph to get to 10-20lop to keep cht in 360-380 range at that high of power setting.

I hate to alarm you, but CHTs are only one half of the issue with power settings.  The other concern is the peak internal cylinder pressure (ICP) that is "working" on your pistons, cylinders, valves, etc.  At that power setting (85%!) you are absolutely murdering those components with very, very high loads.  You might not see any ill effects in the near term, but that power setting is a recipe for long term issues with cylinder cracking and valve wear.  We have no way to directly measure Peak ICP and must use EGT/mixture settings as a surrogate for controlling that value.

 

Long cylinder and engine life has to be thought of in terms managing the fatigue loads and temperatures.  Lower temps and lower peak loads are the key to long life.

 

FWIW, 85% power LOP is my long term dream power setting with a turbo-normalizer setup.  At 30" MP and 11-11.3 GPH that should be in the neighborhood of 70-80 deg LOP and that is a wonderful place to be.  At 26" and 11.3 GPH...absolutely not.

[KSMooniac]

I have a gami spread of only 0.1 so I can and do run LOP now and then but I would usually rather burn 10.5-11 gph and gain 10 or more knots running 125 ROP. Who buys a Mooney to go slow?  

 

To put an economic spin on that sentiment... you realistically give up ~5 knots or so for 1.5-2.0 GPH of savings if you're flying an appropriate LOP setting at typical Mooney cruise altitudes (ie not 50 LOP).  At $6/gallon and say 1500 hours of cruise flight, you're looking at $18,000 of savings for a 3% increase in trip time.

 

That pays for a field overhaul, or an autopilot, or an Aspen and a new GPS...or a nice used car.  All for 3% more time in the plane.  

[Bob_Belville]

To put an economic spin on that sentiment... you realistically give up ~5 knots or so for 1.5-2.0 GPH of savings if you're flying an appropriate LOP setting at typical Mooney cruise altitudes (ie not 50 LOP).  At $6/gallon and say 1500 hours of cruise flight, you're looking at $18,000 of savings for a 3% increase in trip time.

 

That pays for a field overhaul, or an autopilot, or an Aspen and a new GPS...or a nice used car.  All for 3% more time in the plane.  

Well, you know the old saw about what can be done with figures. Let me do the calculations another way:

 

Even if I use extreme figures for the difference, say 8 gph LOP vs 11 gph ROP and that the speed difference is more like 15 knots or about 10% which is what I see for those FFs, and if I fly 75 hours per year and we assume about 50 of those hours are at cruise where I could elect to be ROP or LOP, that's 45 hours ROP, vs. 50 LOP. For those hours I'm either using 8 x 50 or 11 x 45 gallons.The difference is 95 gallons or ~ $570 per year. Minus the cost of putting 5 more hours on the engine, oil, etc.(Jimmy Garrison deducts $13 per hour for engine hours and $1.80 per hour for airframe time for my vintage E.) That's $75 hidden cost or the extra 5 hours - docked for the time I was up in the sky.

 

So I could save about $500 a year if every hour possible was flown at LOP. That would not even pay my Garmin subscriptions, let alone buy one of their boxes. To get to $18000 will take me 36 years. I'll be 107 so I'll be celebrating, I guess.

[mulro767]

I also agree that it's not just about CHT's, it's also about internal pressure. I use both LOP and ROP depending on the length of flight, altitude, OAT, bank account and ego. But I always stay out of the Red Box!

[Shadrach]

I hate to alarm you, but CHTs are only one half of the issue with power settings.  The other concern is the peak internal cylinder pressure (ICP) that is "working" on your pistons, cylinders, valves, etc.  At that power setting (85%!) you are absolutely murdering those components with very, very high loads.  You might not see any ill effects in the near term, but that power setting is a recipe for long term issues with cylinder cracking and valve wear.  We have no way to directly measure Peak ICP and must use EGT/mixture settings as a surrogate for controlling that value.

 

Long cylinder and engine life has to be thought of in terms managing the fatigue loads and temperatures.  Lower temps and lower peak loads are the key to long life.

 

FWIW, 85% power LOP is my long term dream power setting with a turbo-normalizer setup.  At 30" MP and 11-11.3 GPH that should be in the neighborhood of 70-80 deg LOP and that is a wonderful place to be.  At 26" and 11.3 GPH...absolutely not.

You know Scott the infamous red box is funny, fuzzy thing. You don't know (and neither do I) that he's murdering anything. We can certainly say that it's a pretty aggressive power setting, but I'd not go so far as to say it's murderous! I'd be tempted to say that about Kromer's recommendation to climb at 100 ROP from PRGU, but I digress. In my experience CHTs tend to fall fast after peak regardless of OAT. This graph taken from one of Deakin's columns shows exactly what I mean. Furthermore he's correctly running at 2700 RPM (higher piston speeds bring peak pressure away from TDC). I think that APS has been conservative in there recommendations, and rightly so given they're a for profit enterprise with liability risk to think about...

[201er]

Even if I use extreme figures for the difference, say 8 gph LOP vs 11 gph ROP and that the speed difference is more like 15 knots or about 10% which is what I see for those FFs, and if I fly 75 hours per year and we assume about 50 of those hours are at cruise where I could elect to be ROP or LOP, that's 45 hours ROP, vs. 50 LOP.

Or look at it this way. If you saved 95 gallons, that's 10 more hours of free flying you could do that year. At 75 hours, I'm sure you and your bird could use it

 

Mooney is not about flying fast. There are other planes that can fly fast. Mooney is about flying fast efficiently!

[mike_elliott]

8.2 GPH, 159 KTAS, 1984 J 7000'

 

8.4 GPH 146 KTS 1970 F 8000'

 

Aspen photos to prove both.

 

I pick up about 4 kts running 11 GPH in the J, about 3 in the F.

 

LOP is my vote with 2 different IO360's, but its your money and your plane, fly them the way that makes economic substance to you.

[Jamie]

Enough rich of peak to show < 400F CHT (it's hard to see 380F) on the engine monitor, at 55%. I have no idea how many degrees this is, only looked a few times, and then promptly forgot.

 

Mike Busch makes the CHT point firmly enough that that's my guide. And as far as ICP, I'm running at 55%. Apparently I can't really hurt the engine there. I lose 10kts, use 9.5 gph and seem to get what the LOPers get without worrying about special injectors.

 

(Seem. Seem. I'm not against LOP. I just don't have a modern engine monitor and injectors to be able to play with it. Until then, this seems to be the kindest way to run my engine.)

[Shadrach]

Most 4cyl lycs don't need injector mods...

[Shadrach]

8.2 GPH, 159 KTAS, 1984 J 7000'

8.4 GPH 146 KTS 1970 F 8000'

Aspen photos to prove both.

I pick up about 4 kts running 11 GPH in the J, about 3 in the F.

LOP is my vote with 2 different IO360's, but its your money and your plane, fly them the way that makes economic substance to you.

Your F numbers seem about right for what I see out of mine LOP. Your J numbers seem at the upper tear for ROP ops; if they're accurate, you have the fastest and most efficient J I've ever heard of...183mph@22.3mpg. Most people wouldn't believe it... ;-)

[DS1980]

I hate to alarm you, but CHTs are only one half of the issue with power settings.  The other concern is the peak internal cylinder pressure (ICP) that is "working" on your pistons, cylinders, valves, etc.

 

 

Because we don't have ICP gauges in the cockpit, we need to use another measure to determine these values. CHT is directly proportional to ICP. If the CHTs are under control, that means that the cylinders are producing acceptable ICPs as well. When it comes to ICP, CHT is the only issue.

[Jsavage3]

Earlier this summer on one particularly hot day, my CHTs were pushing up to 380...65% @ peak and 9500' MSL, if I remember right.  As a result, I ever so slightly cracked open my cowl flaps -- the result was almost instantaneous and there was no visible drop in KIAS -- the temps dropped to 350-360 and stayed there as long as I kept the cowl flaps cracked open.  When I closed the cowl flaps, the temps again started a slow climb to 380...

[aaronk25]

Earlier this summer on one particularly hot day, my CHTs were pushing up to 380...65% @ peak and 9500' MSL, if remember right. As a result, I ever so slightly cracked open my cowl flaps -- the result was almost instantaneous and there was no visible drop in KIAS -- the temps dropped to 350-360 and stayed there as long as I kept the cowl flaps cracked open. When I closed the cowl flaps, the temps again started a slow climb to 380...

I adjust the linkage at the flap so they stay open about 1/2 inch in summer

[mike_elliott]

Your F numbers seem about right for what I see out of mine LOP. Your J numbers seem at the upper tear for ROP ops; if they're accurate, you have the fastest and most efficient J I've ever heard of...183mph@22.3mpg. Most people wouldn't believe it... ;-)

 

I wish it were my J Im just the caretaker until mid jan for it. Yes, it is the fastest J I have flown, and that's been quite a few

of them. I have a pic (actually 2 enclosed) one showing the Aspen displaying 158kts, the other showing the JPI730 showing 8.5 GPH. They were shot at the same time, but honestly, I have seen it true out at 159 and 8.2 GPH when I was lighter in fuel. It is a fast J for sure. Ill take it to WInterhaven tomorrow for the Florida Mooney fly in.

My F isn't the fastest F I have ever flown, but it has to be one of the nicest to fly.

[201er]

I just want to point out that LOP isn't a camp. There's no bonfire or singalongs. It's just an understanding of all ways to operate your engine.

 

I could not vote on this poll because I do not belong to a "camp" on the subject as I run my engine LOP, ROP, and at peak depending on the purpose and circumstances. When in a climb, I predominantly fly ROP and lean by target EGT compensated for reducing power (i.e. lean more aggressively as altitude increases and power declines). In cruise, I usually fly LOP but at some altitudes or power settings peak works out better. Sometimes in a rush or high altitude, ROP ends up being the way to go. So I'd rather say that I like to think I understand all 3 modes and use them appropriately given the mission.

 

That said, when in doubt LOP is probably a safer place to be than 50ROP.

[John Pleisse]

Like a shoe sale at DSW.

[scottfromiowa]

On the Left side of the Misty Mountain top there is a circle of white robbed prophets that sing in hushed tones of efficiency and cleanliness and speed. They sing their song quietly so not to disturb the dragon under the misty mountain top. To the right of the Misty mountain top are the red robbed worshippers of speed...and speed and blah, ha ha SPEED! They feed the dragon offerings of 100 Low Lead and sing of getting there fast and, and and SPEED!.

The dragon under the misty top is appeased and letss both camps live in peace and harmony....