ROP

[A64Pilot]

  On 5/23/2022 at 2:02 PM, Fly Boomer said:

The GAMI guys hold (or used to hold) 3-day Advanced Pilot Seminars in Ada OK.  Learned more about engine management than I thought possible.

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They are against the big pull? I can’t imagine why, it’s the safest way to LOP

Edited May 23, 2022 by A64Pilot

[Fly Boomer]

  On 5/23/2022 at 2:11 PM, A64Pilot said:

They are against the big pull?

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I think they coined the phrase.  They are the reason I don't like to linger anywhere close to peak (TSIO-520).

[PT20J]

  On 5/23/2022 at 2:13 PM, Fly Boomer said:

I think they coined the phrase.  They are the reason I don't like to linger anywhere close to peak (TSIO-520).

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They may have coined the phrase, but the technique was described in a Piper Warrior POH from the mid-1970s. It turned out that the PA28-161 with a carbureted O-320 had even enough mixture distribution to run LOP and Piper described how to set power with the mixture control.

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[A64Pilot]

  On 5/23/2022 at 2:42 PM, PT20J said:

They may have coined the phrase, but the technique was described in a Piper Warrior POH from the mid-1970s. It turned out that the PA28-161 with a carbureted O-320 had even enough mixture distribution to run LOP and Piper described how to set power with the mixture control.

Skip

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Yes, I believe they just popularized and or marketed something that’s been done forever, as I’ve said numerous time my Father used to “Lean out” his C-210 with its IO-520 he bought new in 1968 or maybe 69.

They knew they were LOP of course, just didn’t give it a name

Edited May 23, 2022 by A64Pilot

[Fly Boomer]

  On 5/23/2022 at 2:58 PM, A64Pilot said:

They knew they were LOP of course, just didn’t give it a name

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Given the instrumentation, how did they know?

[PT20J]

  On 5/23/2022 at 3:18 PM, Fly Boomer said:

Given the instrumentation, how did they know?

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They didn’t need to know. The Lycoming technique of leaning until rough and richening until just smooth (starting from a MAP/rpm combination yielding 75% power or less which will avoid the red box) will be LOP in most Lycoming fuel injected engines. No instrumentation required. 

[Fly Boomer]

  On 5/23/2022 at 3:34 PM, PT20J said:

Lycoming technique of leaning until rough and richening until just smooth (starting from a MAP/rpm combination yielding 75% power or less which will avoid the red box) will be LOP in most Lycoming fuel injected engines

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So, onset of roughness was well lean of peak on all cylinders regardless of the induction system, ignition system, etc.?

[Cruiser]

  On 5/23/2022 at 3:37 PM, Fly Boomer said:

So, onset of roughness was well lean of peak on all cylinders regardless of the induction system, ignition system, etc.?

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This is the main reason LOP got such a bad rap in the beginning of this modern age of instrumentation. The written procedures for leaning assumed the engine was in good operating condition and the procedures rarely suggested these systems be checked. So when problems developed it was LOP fault. 

 

[PT20J]

  On 5/23/2022 at 3:37 PM, Fly Boomer said:

So, onset of roughness was well lean of peak on all cylinders regardless of the induction system, ignition system, etc.?

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Well, as George Braly often starts out, “On a conforming engine, using conforming fuel …”

And, I’m not sure what “well” LOP is. 

The roughness is caused by cycle to cycle variations which, while always present, are greater when very LOP due to the slower flame propagation. It’s smoother if you don’t lean past the point of best economy which is between 25F and 50F LOP.

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[Fly Boomer]

  On 5/23/2022 at 4:27 PM, PT20J said:

And, I’m not sure what “well” LOP is. 

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My only point is to say that I doubt most pilots in the 1960s had any knowledge (or interest) regarding where our EGT peak was, and whether all cylinders were far enough on the lean side to be sure all cylinders were safe.  That said, I don't remember engines blowing up left, right, and center back then.

[Pinecone]

LOP was standard operating for the big radials in the heyday of piston airliners.  Except they set it by torque, not EGT.  They leaned to peak torque (peak power) then leaned it X torque amount.  Torque on the big radials was actually oil pressure in the reduction gearing, so it was in psi.

The whole thing that lead to APS and GAMI was some long discussions on AVSIG on Compuserve.  And, at the time, we had several people with a lot of hours flying R3350s and R-4360s, as well as R-2800, -2600, -2000 engines.

If you read Deakin's articles in AVWEB (another outgrowth of AVSIG), he mentions that LOP was also in the engine manuals from Lycoming and Continental back in the day.  But seemed to have been removed.

BTW, AVSIG still exists.  A lot smaller, but a great bunch of people.

[Shadrach]

The BMP is a convenient procedure that minimizes (hopefully) fiddling with the mixture knob.  It does not "save the engine".  Even if you use the vernier to twist all the way to your LOP setting, your not going to hurt a normally aspirated or even TN'd engine.  Maybe (and it's a big maybe) there are some Turbo engines that might approach detonation under high boost conditions but detonation margins required for certification mean that most any aero engine must be abused for quite sometime before detonation comes into play.  Relax, operate you controls smoothly, don't sketch out your passengers with power loss or roughness they can feel.   There is no need for the drama.  APS has done great things. They are an Aviation business.  Aviation businesses especially have to be mindful of messaging, language and liability.  They managed it pretty well.  People have interpreted the red box in a "you'll blow up your engine" kind of way. APS has apparently contributed to this by not clarifying that it's an area where continuous ops should be avoided but transient ops are nothing to worry about.  Yanking the mixture back to roughness or notable deceleration is not needed. Shoot for a fuel flow or shoot for a target EGT on the correct cylinder gently pull and then fine tune from there. should take all of a few seconds and then an additional check and fine tune a few  seconds later.  Stop playing with your knobs and fly the plane.

Also, folks should stop treating peak EGT like it's some danger zone. It's just about ideal from a performance and cooling standpoint. Lycoming's BSFC graph is a very close representation of the operational reality. Peak EGT ops will generate roughly the same CHT as 100° ROP.  Certainly best to use richest cylinder. However,  my POH says the mixture can be set anywhere below 75% power. While not the most conservative advice, it is likely true.  It's one thing to understand how the mixture knob affects the engine and performance. It's quite another to dramatize it into the likes of disarming a bomb.  There are only a small handful of "NoNos", don't do those for any significant period of time and things should go fine.

 

[Shadrach]

  On 5/23/2022 at 5:04 PM, Pinecone said:

LOP was standard operating for the big radials in the heyday of piston airliners.  Except they set it by torque, not EGT.  They leaned to peak torque (peak power) then leaned it X torque amount.  Torque on the big radials was actually oil pressure in the reduction gearing, so it was in psi.

The whole thing that lead to APS and GAMI was some long discussions on AVSIG on Compuserve.  And, at the time, we had several people with a lot of hours flying R3350s and R-4360s, as well as R-2800, -2600, -2000 engines.

If you read Deakin's articles in AVWEB (another outgrowth of AVSIG), he mentions that LOP was also in the engine manuals from Lycoming and Continental back in the day.  But seemed to have been removed.

BTW, AVSIG still exists.  A lot smaller, but a great bunch of people.

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I think you’re confusing Lycoming in continental with Pratt & Whitney and Wright.

[PT20J]

  On 5/23/2022 at 5:04 PM, Pinecone said:

Torque on the big radials was actually oil pressure in the reduction gearing, so it was in psi.

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The radial torque meters were driven by oil pressure, but calibrated to read BMEP in psi (probably because they were designed engineers )

One fact that often gets overlooked is that the airlines generally used very low cruise powers for the big radials. For instance, most DC-6s used P&W R-2800s rated at 2400 bhp. But cruise powers were set at 1000 - 1200 bhp. According to several of my DC-3 manuals, the smaller R-1830 were pushed a little harder to around 55%.

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[Pinecone]

  On 5/23/2022 at 8:31 PM, Shadrach said:

I think you’re confusing Lycoming in continental with Pratt & Whitney and Wright.

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And engine is an engine.

[Shadrach]

  On 5/23/2022 at 5:04 PM, Pinecone said:

LOP was also in the engine manuals from Lycoming and Continental back in the day.  But seemed to have been removed.

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  On 5/24/2022 at 8:50 AM, Pinecone said:

And engine is an engine.

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Yes but I was referring to manuals not engines.  

[Pinecone]

  On 5/24/2022 at 9:05 AM, Shadrach said:

Yes but I was referring to manuals not engines.  

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No, based on Deakin and others over the years, the earlier Lycoming and Continental manuals had LOP info, but it did not make it into the POHs.  And as time went on, it was taken out.

[A64Pilot]

  On 5/23/2022 at 3:18 PM, Fly Boomer said:

Given the instrumentation, how did they know?

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We had EGT gauges back in the day, but they didn’t become common until at least the 60’s probably late 60’s. Single probe, but a big clue is the reduction in power you get LOP. I don’t think they were concerned about EGT so much, they knew at altitude it didn’t matter. Leave the throttle wide open of course, RPM where it’s smooth and screw back the mixture until it starts to get rough or excess power loss, screw it back into a FF/ Airspeed you can live with, if your in a hurry adjust to highest speed.

People will argue this but just about everything that is known about piston aircraft engines was known 75 years ago.

People flew LOP since the 20’s at least, supercharged radials run more smoothly LOP than any flat motor, and people have always been about saving fuel. 9 identical cylinders with identical intake pipes, plus a supercharger to ensure prefect fuel atomization etc makes for perfect distribution.

Many, maybe most at least fighters in WWII had auto lean and auto rich settings, I’m not sure how they worked but they didn’t adjust mixture like we do. A friend did the restoration of the XP-82 and part of what interested me was the different automatic settings.

This is a cut n paste of how to operate the Lockheed P-38, they ran LOP, just didn’t call it that. 

“The engine ls fitted with a Bendix-Stromberg carburettor Instead of the usual two-position mixture control, as fitted to British engines. the mixture control has the following 4 main positions:

FULL RICH: In this position there is no automatic compensation for altitude and temperature

AUTOMATIC RICH: This is the position for the richest mixture which is automatically maintained by the compensating device.

AUTOMATIC LEAN: This is the normal position for weak mixture. The automatic device maintains the mixture at this setting also.

IDLE CUT OFF: For stopping the engine and while priming during engine starting operations.

Furthermore, the mixture strength can be progressively weakened by moving the lever from the AUTOMATIC HIGH position towards the IDLE CUT-OFF position, the weakening being effective also in the region beyond the AUTOMATIC LEAN position up to the point where the IDLE CUT-OFF operates (at the extreme end of the travel). At any point in this range the automatic compensating device is in operation.

Although placing the mixture control in the AUTOMATIC LEAN position gives a considerable reduction in fuel consumption, it is possible to obtain a consumption of about 5% lower by adjusting the mixture control as follows:

1. Obtain the desired engine cruising conditions

2. Change the airscrew control from AUTOMATIC to MANUAL. In this position the airscrew becomes effectively a fixed pitch airscrew

3. Set the mixture control to the position determined by weakening the mixture until a drop of 40 to 50 R.P.M. is indicated. The position may possibly be between AUTOMATIC LEAN and IDLE CUT OFF

4. Return the airscrew control to AUTOMATIC

If changes in altitude or cruising conditions are made, this setting should be checked by repeating the above operations.”

On edit, they had rules of operation of course like above xx boost, use only auto rich, takeoffs are performed full rich. Auto lean only to be used below xx boost, but I don’t have a copy of those rules.

Just like back in the day there were “rules” about when to “lean it out” like don’t unless MP is less than 22 I think is what I remember. Or another way is don’t “lean it out” below 7,500 and don’t lean at all below 5,000.

If you follow those simple rules you can do and you please with mixture and it won’t matter.

‘Some assumptions are made, like you don’t cruise at takeoff RPM or run car gas etc.

Edited May 24, 2022 by A64Pilot

[Shadrach]

  On 5/23/2022 at 4:32 PM, Fly Boomer said:

My only point is to say that I doubt most pilots in the 1960s had any knowledge (or interest) regarding where our EGT peak was, and whether all cylinders were far enough on the lean side to be sure all cylinders were safe.  That said, I don't remember engines blowing up left, right, and center back then.

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It’s true that engines didn’t blow up but it was not uncommon to need mid time cylinder work without really knowing why. The saving grace being that most stock Lycomings have “good enough” fuel air distribution to make a single cylinder a decent proxy for the others.  Continentals, not so much.

[A64Pilot]

  On 5/24/2022 at 2:07 PM, Shadrach said:

It’s true that engines didn’t blow up but it was not uncommon to need mid time cylinder work without really knowing why. The saving grace being that most stock Lycomings have “good enough” fuel air distribution to make a single cylinder a decent proxy for the others.  Continentals, not so much.

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You can’t really make that statement, even if we restrict ourselves to Lycomings there are significant differences in them, for example my IO-540W1A5D with gami injectors and a tight “gami spread” just would not run LOP well, and then of course there I are bet more carbureted Lycomings than injected. For whatever reason the FI 200HP 360’s seem to run exceptionally well LOP, but they are the exception I think.

However back in the 60’s I believe there were more Cessna’s than pretty much anything, and going on memory all Cessna’s ran Continentals and from memory I think there are more cylinder failures now than then, just like I think more Lycoming cam failures occur now, which isn’t logical, I can’t explain why, nor can I prove it, I just don’t remember all these problems, perhaps it’s an internet thing, back in the day you only had knowledge of far fewer aircraft.

Not everyone ran rich in the 60’s, at cruise many ran “leaned out” and most ran peak or close to it, almost everyone was taught don’t touch mixture control below 5,000 ft and once at cruise altitude slowly pull the mix cable until it starts to roughen, then slowly push back in until it’s smooth, for most carb engines that’s pretty close to peak EGT.

 

Edited May 24, 2022 by A64Pilot

[Shadrach]

  On 5/24/2022 at 2:23 PM, A64Pilot said:

You can’t really make that statement, even if we restrict ourselves to Lycomings there are significant differences in them, for example my IO-540W1A5D with gami injectors and a tight “gami spread” just would not run LOP well, and then of course there I are bet more carbureted Lycomings than injected. For whatever reason the FI 200HP 360’s seem to run exceptionally well LOP, but they are the exception I think.

However back in the 60’s I believe there were more Cessna’s than pretty much anything, and going on memory all Cessna’s ran Continentals and from memory I think there are more cylinder failures now than then, just like I think more Lycoming cam failures occur now, which isn’t logical, I can’t explain why, nor can I prove it, I just don’t remember all these problems, perhaps it’s an internet thing, back in the day you only had knowledge of far fewer aircraft.

Not everyone ran rich in the 60’s, at cruise many ran “leaned out” and most ran peak or close to it, almost everyone was taught don’t touch mixture control below 5,000 ft and once at cruise altitude slowly pull the mix cable until it starts to roughen, then slowly push back in until it’s smooth, for most carb engines that’s pretty close to peak EGT.

 

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I should have specified common Lycoming injected engines.  The intake design utilized on most Lycomings make them inherently better with regards to Fuel and Air distribution from cylinder to cylinder.  The "log runner" intake design on many Continentals almost guarantees that GAMIs will be needed because fuel migrates from the first cylinder aft meaning the last cylinder in the bank is being fed fuel from its injector plus a little from every cylinder in front of it. GAMI came into existence by offering a solution to this Continental specific problem. I'd bet the bulk of their business is precisely reducing the flow of the rear (wrt intake position) fuel injectors of Continental engines.   QC issues with injector to injector flow rates, are often the culprit with injected Lycomings. Every injected 4 cylinder Lycoming I've ever operated ran acceptable smooth across the usable mixture spectrum, I've never flown one with GAMIs that I recall.  There are some less common Lycoming engines that can be routinely problematic but the problem is different. With Lycomings lousy tolerances from injector to injector cause imbalance F/A ratios where as Continentals require different but precisely corrected flows from injector to injector to balance F/A mixture from cylinder to cylinder.

[A64Pilot]

My 540 FI engine wouldn’t run LOP well, it got rough at -25 LOP max, to be smooth it was barely if any LOP.

I didn’t try with factory injectors, I should have as I don’t think the Gami’s did anything, fine wire plugs is the reason I could even get to -25 LOP.

I don’t know about other Lycomings, I don’t know why my 540 wouldn’t run LOP, but have heard the complaint from other 540 owners.

On the other hand my Gann performance 360 with stock injectors is almost like a Diesel, that’s to say you could almost control it with just the mixture knob, it stays smooth so LOP that it’s not making enough power to maintain level flight, but it’s still smooth.

Diesels of course are the ultimate LOP machines, there is no throttle, you only add or reduce fuel, my Duramax from memory idled at about 250F EGT it was so lean.

Edited May 24, 2022 by A64Pilot

[GOJAC]

I believe the concern about damaging an engine by operating LOP dates back to the days of the airliners with large radial engines and flight engineers.  In order to obtain maximum advantage from operating LOP on these engines it is necessary to advance the ignition timing to about 40degrees BTDC.  This produces a significant reduction in specific fuel consumption and extended the range of the old airliners.  The timing was controlled by an extra lever in the care of the flight engineer.  The procedure was to set up the desired RPM and MAP, weaken the mixture to LOP and then advance the ignition to restore power without additional fuel consumption.

The risk to the engine arose from the consequence of inadvertently enriching the mixture without first retarding the ignition to about 20 - 25 degrees BTDC.  Detonation would almost certainly occur and the engine would be seriously damaged.  Current GA aircraft do not usually carry flight engineers and are therefore not permitted to have a means of advancing ignition timing to 40 degrees BTDC and we are prevented from damaging our engines by its misuse. 

What we need is an electronic ignition system that will monitor RPM, MAP, air flow and fuel flow and calculate the optimum ignition advance and implement the advance with no pilot intervention.  This would give us a real fuel saving with a small loss of speed, if the authorities would approve it.

Roger  

[A64Pilot]

  On 5/24/2022 at 5:44 PM, GOJAC said:

 

What we need is an electronic ignition system that will monitor RPM, MAP, air flow and fuel flow and calculate the optimum ignition advance and implement the advance with no pilot intervention.  This would give us a real fuel saving with a small loss of speed, if the authorities would approve it.

Roger  

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I deleted the rest of that as I read the Gami article about it 20 years ago, but was unaware the Engineer could advance timing.

‘But you need to read the article where the Pax river test pilot ran a series of tests running LOP etc on a fuel injected 200 HP lycoming in his RV-8  and had electronic ignition that allowed him to change timing. It’s in one of these threads.

His take was that it didn’t make as much difference in fuel consumption, that climbing just a few thousand feet would do better.

So I guess we should take this Naval Test Pilot and group him with the engine manufacturers, that is they don’t know what they are all talking about.

There are gains, but they aren’t nearly what people want to believe

[jaylw314]

  On 5/24/2022 at 5:44 PM, GOJAC said:

I believe the concern about damaging an engine by operating LOP dates back to the days of the airliners with large radial engines and flight engineers.  In order to obtain maximum advantage from operating LOP on these engines it is necessary to advance the ignition timing to about 40degrees BTDC.  This produces a significant reduction in specific fuel consumption and extended the range of the old airliners.  The timing was controlled by an extra lever in the care of the flight engineer.  The procedure was to set up the desired RPM and MAP, weaken the mixture to LOP and then advance the ignition to restore power without additional fuel consumption.

The risk to the engine arose from the consequence of inadvertently enriching the mixture without first retarding the ignition to about 20 - 25 degrees BTDC.  Detonation would almost certainly occur and the engine would be seriously damaged.  Current GA aircraft do not usually carry flight engineers and are therefore not permitted to have a means of advancing ignition timing to 40 degrees BTDC and we are prevented from damaging our engines by its misuse. 

What we need is an electronic ignition system that will monitor RPM, MAP, air flow and fuel flow and calculate the optimum ignition advance and implement the advance with no pilot intervention.  This would give us a real fuel saving with a small loss of speed, if the authorities would approve it.

Roger  

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It's hard to imagine that there's realistically much more efficiency to be had.  The IO-360 at 130hp at Mooney's POH "best economy" of 25 ROP uses about 9.3 gph.  By my calculations, that's a BSFC of 0.43.  I'm guessing here, but LOP might bring it down to about 0.42 or so.

In contrast, the 200hp Ford EcoBoost has a BSFC of 0.40.  Granted, that's comparing apples to oranges, but it's hard to see a gasoline engine gaining significant efficiency moving forwards.  LOP is a low-risk, low-effort, and low-cost method for improving efficiency.  OTOH, investing money in high-cost, high-risk and high-effort methods like electronic ignition are unlikely to be worthwhile for most people or manufacturers

Edited May 24, 2022 by jaylw314