ROP versus LOP and the Lycoming IO-360

[jetdriven]

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.

You can still exceed a safe continuous ICP value on a cool day with acceptable CHTs. You still need to take a look at EGT to see where you are at on the curve, and take that into account. 11.0 GPH 83% LOP power is 83%, but its alright at 50 LOP and not OK at peak EGT.

[aaronk25]

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.

I see your #1 and #4 cht are hotter than others. On the #1 you can cut down the front air blocking baffle by 1" and bend the #4 baffle up about 3/4" to steel a little air from the oil cooler. Those 2 jugs will drop 40 degrees in temp!!!! Just a idea.. Others have done it to.

[aaronk25]

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. You can still exceed a safe continuous ICP value on a cool day with acceptable CHTs. You still need to take a look at EGT to see where you are at on the curve, and take that into account. 11.0 GPH 83% LOP power is 83%, but its alright at 50 LOP and not OK at peak EGT.

Hey Byron, I understand what your saying but at peak configuration lets say we're making 180hp. 180hp isn't that much compared to other 360 cubic inch motors . If it will stay cool why not? Other motors have to have high icp? Aaron

[mike_elliott]

I see your #1 and #4 cht are hotter than others. On the #1 you can cut down the front air blocking baffle by 1" and bend the #4 baffle up about 3/4" to steel a little air from the oil cooler. Those 2 jugs will drop 40 degrees in temp!!!! Just a idea.. Others have done it to.

 

Good catch, similar thoughts have ran thru my mind, but will defer to let the owner make the call. #1 is the one cyl that sets off the alarm when climbing too slow, and when he gets here in January, I plan to teach him how to change his oil and go over the baffles and cylinder cooling at his direction.

[Jsavage3]

Ok, so here is the question that always makes me ponder the why-go-LOP question:

1. Is it just about savings?  How much fuel does one feel they save per flight hour and at what cost ... slower cruise speed = putting more time on their engine and you get to sit there longer?  
2. Does one really believe that they have a better chance of reaching TBO by going LOP?  
3. Is the engine being better cared for enroute?   CHT/EGT within limits is CHT/EGT within limits.                   
4. Is not the Mooney the best in the market at providing speed AND efficiency at the same time -- we all know it is.  So, what am I missing...why LOP?

Please help me "see the light" because my current way of thinking is such that 9.5 gph at 157ktas is hard to improve upon -- what would LOP do for me?  Save me less than 1 gph and slow me down by 10-15 knots?  I bought my Mooney so I could go fast -- why slow down to p-b-c speeds for a measly 1/2 gal or so savings per hour?

 

If I was feeding a big fuel-guzzling 6-cylinder, then LOP would make more sense to me, but, for us Lyc IO-360 operators, that is not the choice we made.

 

Without fail, every trip we take, the shorter the ETE, the bigger my wife's smile...

 

Why does 2/3 of our group (estimated) fly LOP?

[Shadrach]

 

Ok, so here is the question that always makes me ponder the why-go-LOP question:

1. Is it just about savings?  How much fuel does one feel they save per flight hour and at what cost ... slower cruise speed = putting more time on their engine and you get to sit there longer?  
2. Does one really believe that they have a better chance of reaching TBO by going LOP?                         
3. Is not the Mooney the best in the market at providing speed AND efficiency at the same time -- we all know it is.  So, what am I missing...why LOP?

 

1) depends on the flight and the power setting. If you like to fly max power ROP, you'l never get an apples to apples comparison unless you're TSIOd and can add back MP to get the same power LOP.  If say you were cruising at 65% power at 4500ft, the FF for ROP in an IO360 would be ~9.6gph. 65% LOP would be ~8.6 and would be cooler and cleaner across the board and speed would be the same, manifold pressure would be higher LOP. 

2) probably not, but the oil stays cleaner, longer and CHTs are certainly lower.

3) If I had to guess, I'd say you've still not really gained a basic understanding exactly what happens inside the combustion chamber. If you did, you'd likely not be asking what you're missing, but asking more about the details of how to optimize your power settings.

I'm not advocating one or the other, I use both, but I think that what's optimal for a given situation becomes somewhat more clear when you have a basic understanding of combustion science. Some are happy to use the POH listings and leave it at that. I'd not try to argue that they should do otherwise, but if they're interested, I will talk about the different possibilities so they can decide for themselves.   

 

Lean mixtures (beyond Stoichiometric or LOP) are where many of the recent improvements in auto MPG have come from (with a few others like VVT and solenoid actuated intake valves that eliminate the pumping loses by eliminating the throttle butterfly).  It's why the auto industry has focused on direct fuel injection. We are lucky in that our AC engines are the perfect platform to run Lean of Stoic (LOP) because they run in a steady state for the majority of the time they are in use. A fuel injected automobile will also run lean of stoic when it can (steady state highway cruising), but spends a lot of time at variable throttle settings and engine loads that require variable mixtures (at least with the technology currently available). However, there is a fair amount of research being done into "lean burn" engines to get greater efficiency from running at extremely lean efficiency ratios (Air/fuel ratios upwards of 3 times leaner than what's possible in our engines).

[KSMooniac]

What Ross said. Except that 65% power LOP on a IO-360 is more like 8.7 GPH, is it not?

Jim

 

Yes.

[Jsavage3]

1) depends on the flight and the power setting. If you like to fly max power ROP, you'l never get an apples to apples comparison unless you're TSIOd and can add back MP to get the same power LOP.  If say you were cruising at 65% power at 4500ft, the FF for ROP in an IO360 would be ~10.6gph. 65% LOP would be ~9.6 and would be cooler and cleaner across the board and speed would be the same, manifold pressure would be higher LOP. 

2) probably not, but the oil stays cleaner, longer and CHTs are certainly lower.

3) If I had to guess, I'd say you've still not really gained a basic understanding exactly what happens inside the combustion chamber. If you did, you'd likely not be asking what you're missing, but asking more about the details of how to optimize your power settings.

I'm not advocating one or the other, I use both, but I think that what's optimal for a given situation becomes somewhat more clear when you have a basic understanding of combustion science. Some are happy to use the POH listings and leave it at that. I'd not try to argue that they should do otherwise, but if they're interested, I will talk about the different possibilities so they can decide for themselves.   

 

Lean mixtures (beyond Stoichiometric or LOP) are where many of the recent improvements in auto MPG have come from (with a few others like VVT and solenoid actuated intake valves that eliminate the pumping loses from having a throttle butterfly).  It's why the auto industry has focused on direct fuel injection. We are lucky in that our AC engines are the perfect platform to run Lean of Stoic (LOP) because they run in a steady state for the majority of the time they are in use. A fuel injected automobile will also run lean of stoic when it can (steady state highway cruising), but spends a lot of time at variable throttle settings that require variable mixtures (at least with the technology currently available). However, there is a fair amount of research being done into "lean burn" engines to get greater efficiency from running at extremely lean efficiency ratios (Air/fuel ratios upwards of 3 times leaner than what's possible in our engines).

 

Shadrach, regarding your response to my #3, it's a bit of a cheap shot...

 

We're talking about normally-aspirated Lycoming IO-360 engines, not TSIO engines and 4500-foot cruise is not where I'm trying to focus, but fyi, I wouldn't see 10.6 there...it'd be closer to 9.5.  I don't cruise at 4500 feet except for very short hops.

 

So, in an effort to make this process easier, let's look at J-model ROP to J-model LOP, cruising at 10,000 feet.

 

In my normally-aspirated J at 10K, I will see 20-21" MP at WOT, ram air open, 2500 RPM, peak EGT (first to peak), CHTs 340-360 (depending on OAT), 9.3-to-9.5 GPH and 157 KTAS.

 

Can a J-driver who does LOP provide some comparable numbers for these conditions?

[Shadrach]

What Ross said. Except that 65% power LOP on a IO-360 is more like 8.7 GPH, is it not?

Jim

 

 

Yup.  My plan in the last post was to do a 75% comparison, but given that 75%  LOP is likely not feasable at 4500ft I went with 65%, but I spaced on changing the numbers... My bad! ;-)  Edited!

[Shadrach]

Shadrach, regarding your response to my #3, it's a bit of a cheap shot...

 

We're talking about normally-aspirated Lycoming IO-360 engines, not TSIO engines and 4500-foot cruise is not where I'm trying to focus, but fyi, I wouldn't see 10.6 there...it'd be closer to 9.5.  I don't cruise at 4500 feet except for very short hops.

 

So, in an effort to make this process easier, let's look at J-model ROP to J-model LOP, cruising at 10,000 feet.

 

In my NA J at 10K, I will see 20-21" MP at WOT, ram air open, 2500 RPM, peak EGT, CHTs 340-360 (depending on OAT), 9.3-to-9.5 GPH and 157 KTAS.

 

Can a J-driver who does LOP provide some comparable numbers for these conditions?

Not meant to be a cheap shot. My apologies! Do you understand what brake mean effective pressure (BMEP) is? If so, do you understand that the the same mean number can be achieved a number of ways. When it comes to the piston, ROP ops are sort of a hammer blow versus a slow even and direct push. If you were trying to turn a ratchet, and could only apply force from one vector, would you choose to hit the ratchet with a hammer 8 degrees off said force vector or apply slow direct force starting at 18 degrees off your force vector and continue to push as the ratchet moves. If you do not understand this difference regarding LOP/ROP, then you don't understand what's happening in the combustion chamber... It's not an exact analogy, but what I'm getting at is that a same brake mean effective pressure (power) can be done with a high peak pressure or sustained moderate pressure. Which has to do with flame front speeds. Which are directly affected by mixture setting. Which is especially important given it's the only parameter that is controllable in flight for our fixed timing engines...

 

 

I also apologize for screwing up my numbers, but that's what happens when I change parameters in the middle of a post while rushing at work (edited).  I typically run ~ peak or 5 LOP at 10K. In my world, I often find myself at 4500ft when West bound to stay out of the wind. East bound I often find myself at 11,500ft. I flew from Lima OH (KOAH) to Hagerstown (KHGR) a few years ago at 11,500 and made ~225kts across the ground in level flight. 296NM in 1:38... I knew it was going to be a record trip for me when I saw we were making 178Kts GS climbing at 1000FPM through 5000ft. IIRC we burned a little under 13gph for the whole trip. I could have burned 15 gals and landed 5 minutes sooner...but why?

[Shadrach]

Peak is almost as efficient as LOP, and at 10,000 feet is probably an ideal way to run. Just make sure that it is your richest cylinder that you use to find peak and not your leanest.

The real experts are Ross, Scott, Byron and several others. Not me, however.

Jim

I'm no expert, just studied a lot... And I agree whole heartedly with your advice above...

[Lood]

I generally fly at FL085/095, WOT, 2500rpm, 75 - 80 deg ROP burning 10gal/hr, 142KTAS, CHT's range between 290 deg - 340 deg on average and EGT's around 1360 deg.

 

I've flown LOP a couple of times, loose about 8kts and fuel burn comes down to around 8.5 gal/hr,but for some or other reason, I'm just not comfortable with it.

[jetdriven]

You should only lose around 3-4 knots when running LOP. 

[Seth]

I responded no only because when I flew my F model for just under 500 hours, I flew ROP.  I did not have an engine monitor nor Gamis, though you may not need Gamis as the factory setup may have the correct spread.

 

If I had an engine monitor and the engine could run LOP, I may have tried it.  3-4 knots for 2-3 gallons is nice.  Especially in with the fuel prices today.

 

-Seth

[DS1980]

You can still exceed a safe continuous ICP value on a cool day with acceptable CHTs. You still need to take a look at EGT to see where you are at on the curve, and take that into account. 11.0 GPH 83% LOP power is 83%, but its alright at 50 LOP and not OK at peak EGT.

This is true, but a statistical anomaly. I was going to edit my original post to include this, but I'll do it now.  The only way to have unacceptable ICPs with acceptable CHTs is with artificial cooling/heating, in this example, a cool day. It is also possible to have unacceptable CHTs with acceptable ICPs, such as having incorrectly rigged cowl flaps causing the engine to become heat soaked. Under normal engine operation, acceptable CHTs is an indication of acceptable ICPs.

 

I don't quite understand where the % HP statement comes from, as it's a blanket statement for the avocation of LOP rather than about ICPs. Yes, it's correct, at 83% HP I would not run at Peak as it would cause high CHTs. And 50 LOP is lean enough to be running pretty much at any % HP. I missed the correlation, but it doesn't mean it's not there.

 

Oh, and I take off with flaps. That discussion is to page 9 now!!

[DS1980]

 

I've flown LOP a couple of times, loose about 8kts and fuel burn comes down to around 8.5 gal/hr,but for some or other reason, I'm just not comfortable with it.

 

 

Can you explain why you're not comfortable with it? Seems you may be running too lean. Not too lean to burn, but leaner than best economy, which defeats half the purpose of LOP.

 

This is the way I have come to look at LOP: you are asking your engine to do less. You're asking it to burn less fuel, to put out less power, and to plain do less work. In a sense, you are asking it to jog. Now while I don't understand people that jog for fun, as I have tried it, I do understand this.

[Shadrach]

You can still exceed a safe continuous ICP value on a cool day with acceptable CHTs. You still need to take a look at EGT to see where you are at on the curve, and take that into account. 11.0 GPH 83% LOP power is 83%, but its alright at 50 LOP and not OK at peak EGT.

 

 

I'm not sure the above statement is entirely true... Look at the attached graph it appears that (at least at full power ops) that peak is kinder than full rich (250 ROP)...

[Hondo]

Ok, so here is the question that always makes me ponder the why-go-LOP question:

1. Is it just about savings?  How much fuel does one feel they save per flight hour and at what cost ... slower cruise speed = putting more time on their engine and you get to sit there longer?  
2. Does one really believe that they have a better chance of reaching TBO by going LOP?  
3. Is the engine being better cared for enroute?   CHT/EGT within limits is CHT/EGT within limits.                   
4. Is not the Mooney the best in the market at providing speed AND efficiency at the same time -- we all know it is.  So, what am I missing...why LOP?

Please help me "see the light" because my current way of thinking is such that 9.5 gph at 157ktas is hard to improve upon -- what would LOP do for me?  Save me less than 1 gph and slow me down by 10-15 knots?  I bought my Mooney so I could go fast -- why slow down to p-b-c speeds for a measly 1/2 gal or so savings per hour?

 

If I was feeding a big fuel-guzzling 6-cylinder, then LOP would make more sense to me, but, for us Lyc IO-360 operators, that is not the choice we made.

 

Without fail, every trip we take, the shorter the ETE, the bigger my wife's smile...

 

Why does 2/3 of our group (estimated) fly LOP?

 

Don't know that I can add much to what Shadrach and others have said, but here are my reasons for LOP operation, primarily for cruise.

The motivation was an article in AOPA magazine titled"So wrong for so long" which praised the merits of LOP operation.

Monty Barrett ihas an engine shop called Barrett Performance Aircraft.  He said engines run LOP were very clean with no carbon buildup.

Since he does the engines for the US Aerobatic Team and overhauled my engine, I decided to check it out.  Mike Busch also got my attention.

 

For your questions, at an aircraft weight of 2500 lbs , these are my observations at 8000 with OAT 57F. Altimeter was 30.38,  Highs have sinking air which can slow you a little.

1.  For WOT at 8000 running  25 ROP, 8.6 GPH, book is ~154, I got 152.  At 30 LOP, 8.0 GPH airspeed dropped to 147.

2.  I think so.  I no longer see carbon pieces in my oil filter.  My compressions have improved to 77-78 since switching to LOP.  Time will tell.

3.  CHT is usually about 15-25 degrees cooler than best power CHT and EGTs are not a problem.

4.  The speed penalty here is 5 knots, but with less fuel and a cleaner and cooler running engine.

 

This data  shows the effect of varying RPM.

Alt 8000,  OAT 57F, 13.9C

Engine  RPM 2400, MP 21.8   MP adjustment for nonstandard temperature =  -(OAT - STD DAY)*.04 = -(13.9 + 1)*.04 ~ -.60,   Adjusted MP = 21.2 ~ 60% power

Aircraft 2500 pounds, Cowl flaps closed, JPI EDM 700 with OAT and JPI FS 450 fuel flow

 

For N W S E run at 30 LOP average GPS GS using Garmin 496 was 147.  

RPM    MP    FF   GS    EGT1  CHT1   EGT2  CHT2   EGT3  CHT3   EGT$  CHT4

2500  21.8   8.2  148    1410    354     1380     328     1390   306      1410   348

2400  21.8   8.0  147    1430    357     1390     337     1400   314      1420   350

2300  21.8   7.8  146    1420    352     1400     334     1410   311      1420   347

2200  22.0   7.6  143    1400    356     1400     337     1420   312      1430   347

 

To lean in climb, I use step to select my hottest cylinder, #1, and adjust the mixture to maintain takeoff EGT.

At 1000 AGL, reduce RPM to 2600 and transition to cruise climb.  When MP drops to 26, lean till smooth.

Do what is required to keep CHT below 380. Go to 30 LOP for cruise at 6000 to 12000..

[mike_elliott]

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?  

 

I cant think of anyone, but having it down to replace cylinders before TBO because of consistent running with high ICP's is a real slow way to fly. Not saying properly run ROP will cause this, but improperly run sure will.

Ill run mine LOP high with a tail wind every time. With a stout headwind, Ill go lower and run ROP 125. I set with fuel flow now vs actual temps.

Its not about the fuel savings or the speed, its about the CHT's and exhaust valve life for me. YMMV

[Bob_Belville]

I cant think of anyone, but having it down to replace cylinders before TBO because of consistent running with high ICP's is a real slow way to fly. Not saying properly run ROP will cause this, but improperly run sure will.

Ill run mine LOP high with a tail wind every time. With a stout headwind, Ill go lower and run ROP 125. I set with fuel flow now vs actual temps.

Its not about the fuel savings or the speed, its about the CHT's and exhaust valve life for me. YMMV

Hi Mike, well my prop strike got me into my engine @ 700 SFR. We found cam/lifter corrosion, no doubt caused by periods of inactivity. The cylinder/valves are fine.

 

I've only put a little more than 100 hours on the engine, the prior owner, retired air force, a little over 200 in 6 years and the folks before him who did the engine change, a Delta captain, a little more than 400 hours in 5 years. The AF guy told me he believed in keeping cruise power @ 65% or below. Not sure about how the 1st owner flew. 

 

But a cylinder replacement doesn't compare to an engine tear down as to down time! I swallowed a valve in 9249M years ago. the plane was back in service in a week. My little prop strike will have me out of commission for about 3 months.

[Jsavage3]

You should only lose around 3-4 knots when running LOP. 

 

Wouldn't this "3-4 knots" depend on how much LOP a person chose to run though?  10 LOP vs 50 LOP can make quite a difference...right?

[Jsavage3]

A dumb question here, but would someone care to expound on the details of the Red Box ....specifically, for 65%, is 100ºF-ROP-to-Peak the area to avoid or is this the recommended area to operate?

 

Red Box = No Fly Zone 

 At and below about 60% power, there is no red box. Put the mixture wherever you want it. 

 At about 65% power or so, 100ºF ROP to Peak. 

 At about 70%, 125ºF ROP to 25ºF LOP. 

 At about 75%, 180ºF ROP to 40ºF LOP. 

At about 80%, 200ºF ROP to 60ºF LOP. 

[carusoam]

Essentially the red box ends at 65%. High enough altitude or pulling back the throttle will keep things out of the red....

Other ways to avoid the red box include running well ROP.

Mooney uses a Blue box on the EGT gauge (for M20Rs) to help maintain ROP levels while climbing.

For an ordinary person performing a full power assault on altitude, using the ROP side makes sense.

That's my understanding today, ymmv...

Best regards,

-a-

[Super Dave]

A dumb question here, but would someone care to expound on the details of the Red Box ....specifically, for 65%, is 100ºF-ROP-to-Peak the area to avoid or is this the recommended area to operate?

Red Box = No Fly Zone

 At and below about 60% power, there is no red box. Put the mixture wherever you want it.

 At about 65% power or so, 100ºF ROP to Peak.

 At about 70%, 125ºF ROP to 25ºF LOP.

 At about 75%, 180ºF ROP to 40ºF LOP.

At about 80%, 200ºF ROP to 60ºF LOP.

That's the area to be avoided, although some might say overly conservative for the Lycoming 360s.

[mike_elliott]

Hi Mike, well my prop strike got me into my engine @ 700 SFR. We found cam/lifter corrosion, no doubt caused by periods of inactivity. The cylinder/valves are fine.

 

I've only put a little more than 100 hours on the engine, the prior owner, retired air force, a little over 200 in 6 years and the folks before him who did the engine change, a Delta captain, a little more than 400 hours in 5 years. The AF guy told me he believed in keeping cruise power @ 65% or below. Not sure about how the 1st owner flew. 

 

But a cylinder replacement doesn't compare to an engine tear down as to down time! I swallowed a valve in 9249M years ago. the plane was back in service in a week. My little prop strike will have me out of commission for about 3 months.

 

How true, Bob. Corrosion is what kills these lycs. more than anything. Swallowing valves usually happens as an effect of running to high of CHT and coking the little fellers, which can be an effect of running the thing about 50 ROP and/or not getting enough oil down those pushrod tubes to the valves.

Have you decided on Ney nozzels or Centrilube or stock with the weird new lifters yet?