Voyage to LOP

[jlunseth]

A year ago my old engine was switched out for a factory new engine. Both were/are TSIO360-LBs. The intention was to get the engine up and running LOP particularly at cruise. That could not be done immediately because TCM required that the factory injectors had to be used for engine break-in. The plan was to install GAMI's at the first annual after break-in and the first stage of that process has now been completed, that is, we have good working GAMIs in the engine and I will be conducting some tests to see if we need some fine tuning or if they are going to work as they now are. The process was not without hiccups.

I thought it would be helpful, since over the years there have been many questions about how to run the 231 LOP, if I document what has been done and the fine tuning work I will be doing. The purpose of this post is to just lay some groundwork, and then I will write posts about the progress.

I bought the plane in 2009, shortly after getting my PPL. It was in Scottsdale, and I flew home with my then-instructor (not a Mooney instructor). The engine was not in great shape. The turbo was rebuilt that summer at about 700 engine hours. A couple of years later I experienced a loss of oil pressure due to the quick drain eating a piece of plastic (I have written about it here ). That resulted in an emergency descent from 19k to a landing in Canada and shortly after the engine was IRANd because of piston slap at around 1200 hours. I then went to the GAMI live course in Ada, OK to learn how to run the engine and figured out a good way to run it LOP. From that point on the engine made it to nearly 2400 hours before it was replaced, and probably could have gone on living for quite awhile longer, but it was at that point more than 20 years old so I elected to replace it.

Engine break-in is 50 hours, during which TCM wants the engine run ROP with their injectors. At cruise they want the engine to alternate every hour between 65 and 75% HP. That is what I did over a good part of last year, until the engine was well broken in. When I run ROP, my fuel flow is normally 13.3 gph or higher, RPMs 2450, MP at about 30". If the CHT's and EGTs start to go higher I ran the engine at as high as 14.5 gph to keep them cool. The engine was looked over by my A&P and borescoped once last year. He found that the break-in was going great and the cylinders were in very good condition. I have a Merlin wastegate controller and a Turboplus intercooler.On one or two occasions I tried to run the engine LOP to see if the TCM injectors were up to the task. I read that TCM has been putting "positionally tuned injectors" in engines and had some hope that the factory injectors would work but they did not, the engine would immediately go rough once on the lean side of peak and it was difficult to keep the temps down, so I waited for the chance to put in GAMIs, which came over this past winter.

A few things about LOP operations in a 231. I have excellent instrumentation in my plane, a JPI 930 which has updated at least once by JPI. A GTN 750 TXi is my major GPS, and it is connected to dual revisionary 275's which drive my KFC200 AP through an Icarus SAM GPSS. It all works really well, and of course I see separate EGTs and CHT's for each of the six cylinders as well as TIT. My 930 also provides both Compressor Discharge Temp (the temperature of the induction air coming out of the turbo) and Induction Air Temp (the induction air temp after it has passed through the intercooler). IAT is the temp of the induction air when it is introduced into the engine. When the new engine was installed I also had new baffling put in and that has helped tamp down some of the CHT differences I saw in the old engine. The difference between the hottest (#2) and coldest (#6) in the old engine was generally around 85 dF and higher. It is now about 40 dF. The #6 cylinder sits in the big cowl hole that is unobstructed and tends to run cooler than the others, the others are within roughly 20 dF of each other in the new engine.

Running an engine LOP in the 231 requires a clear understanding of what LOP is and how engine monitors generally operate in "lean function" mode. LOP is an air/fuel ratio, it is not by itself a power setting although it can certainly be used to make a power setting that is easy on the engine. As has been written about before in this forum and is taught by the GAMI people, there is a formula that can be used to determine %HP when operating LOP. The formula is fuel flow in gph times a constant that is dependent on the engine compression ratio, divided by rated horsepower. In the 231 the formula is GPH * 13.7/210. However, it needs to be emphasized that this formula only applies if the engine is operating on the lean side of peak. It does not apply at all if the engine is operating on the rich side of peak. %HP on the rich side must be determined from the POH tables. On the lean side, %HP is driven entirely by the fuel flow - increasing and decreasing the MP will not change the power output it will simply change the air/fuel ratio. More on that later. On the rich side, changing the MP definitly changes the power output.

An engine is operating properly lean of peak when the EGT of the cylinder that is closest to peak starts to go down when the fuel flow is further reduced. If a reduction in fuel flow causes the temp to go up, then you are still on the rich side of peak and the power formula does not apply. There is a footnote to this which we saw when conducted the GAMI lean test on my new engine, which is that if the engine is already well on the lean side of peak and the pilot continues to lean it well out, there will be a point where the EGT may rise. However, this second rise is not the lean of peak point. An engine is operating rich of peak when the EGT of the cylinder closest to peak falls when more fuel is introduced. "Peak" of course, is the point where the EGT of a cylinder is hottest. It is preferable to use the temperature of the cylinder closest to peak, whether on the lean or rich side, because that means that all the other cylinders are running comfortably further away from peak EGT.

Engine monitors have a "lean function." As has been said many times in this forum, the lean function operates using an internal algorithm that makes certain assumptions. The primary assumption is that the pilot starts the lean function while the engine is operating on the rich side of peak. When a pilot engages the lean function and begins to lean the engine, the engine monitor makes the assumption that all other parameters, mainly manifold pressure, remain where they were at the start of the lean function and only the fuel flow is changed. If the MP is materially changed then the entire lean function test is invalid. As I will write later, we ran into this issue in spades when ordering the GAMI injectors for the new engine. Also, when the engine monitor is put in ROP mode, the monitor assumes that the pilot is starting the lean function on the rich side of peak and leaning back towards peak, and because it is desirable to find the cylinder that is operating closest to peak, it finds the first cylinder to peak and uses that to display a "degrees rich of peak" number. Similarly, the monitor assumes that when conducting leaning in the "LOP mode" the pilot starts on the rich side of peak, leans across peak, and the monitor then finds the last cylinder to peak, which is the cylinder operating closest to peak on the lean side. It is important to understand that the monitor has no way of knowing whether the engine is actually running ROP or LOP, it is making assumptions. So ---- putting the monitor in ROP mode simply tells the monitor to find the first cylinder to peak, and putting it in LOP mode simply finds the last cylinder to peak, and that is all. If you have allowed the MP to change during this process, the process is invalid and the monitor has no idea whether the engine is running LOP or ROP.

This is important in the 231 because the Merlin wastegate controller is not a truly automatic controller. It is a differential controller; it maintains a set difference between the induction air going into the engine and the air coming out of the compressor. The purpose of that is to tamp down bootstrapping (increasing the MP increases the exhaust flow into the turbo which then increases the MP even further). The Merlin does not maintain a set MP, it is up to the pilot to monitor and set the MP. Changes in the fuel flow in the 231 will change the MP for two reasons. One, there is an interlink in the 231 fuel system that is specifically designed to link fuel flow to MP, so that if the pilot makes a power setting and then decides he wants to slow to let's say, approach speed, he/she can simply pull back the MP and the interlink does its best to maintain the original air/fuel ratio by also pulling back the fuel flow. This does not work quite as well in the opposite direction, that is, when pulling the fuel flow back the relationship to MP is not maintained quite as well, but it does operate. The other factor is the turbo itself. If you pull back the fuel flow you reduce the exhaust flow to the turbo which further reduces its output, meaning the MP is reduced. The point is, if the 231 pilot starts the leaning process with a rich of peak MP and fuel flow and then leans the fuel flow back and does nothing to adjust the MP, the MP will start coming back as well, invalidating the "lean function" process. 

These are challenges in running a "GAMI lean function" in the 231 and in making power settings, but although it sounds complicated, it can be very much simplified in operating the aircraft. However, the 231 pilot needs to understand what is going on in this detail to operate a healthy engine.

Next post: engine break-in of the new engine and ordering new GAMI's, and the mistakes we made and fixed.

[Ragsf15e]

@jlunseth

What was your gami spread with the TCM injectors that couldn’t run LOP?  Also are you using fine wires (with new plugs it’s probably not a big difference).

What MP/rpm were you using when you tried LOP?  I’ve read your earlier posts about using “very” high mp and low rpm (something like 31/2350 and ~10gph).  I know these aren’t your exact numbers, but if I recall your earlier posts, they are in the ballpark?
 

I have an SB engine, so a little different, but mine wasn’t particularly happy at similar settings.  It was much smoother at a little lower mp which puts it ~20 degrees lean of peak at 10.4gph (65% on my engine).  I’ve left rpm at 2350.  11.3gph and ~31” for 70% works as well and keeps it about 20f lop.  I guess my point is that at 65 or 70% power, you don’t need to be very far lop to be “safe” and efficient.  At all of the above power settings, I am below 1575 TIT and CHTs are low 300s (or even cooler, sometimes I’d actually prefer a bit warmer). 
 

*for the record, our engines are different as I have an SB with a TCM intercooler and waste gate control and 10 more hp.  I have gamis and fine wires.  Both were put on when the engine was oh by previous owner, so I don’t know how it ran on stock injectors.

 

[jlunseth]

Engine break-in and ordering new GAMI's:

Engine break-in of the new engine went smoothly. I used Philips XC 20W-50. There were a few long trips involved, which are ideal because the break-in instructions want you to change %HP from 75% to 65% and back roughly every hour. Takeoff and climb was always full power full rich. The principal idea behind break-in is to run the engine with strong compression, which forces the rings against the cylinder wall. The cylinder wall has micro-ridges from honing, and the idea is to smooth the top of the ridges and mate the rings and walls to each other. I made one trip last spring from Minnesota to SoCal for a Mooney PPP, with stops in Albuquerque and some backtracking over AZ to wait out weather. As mentioned, the cylinders were borescoped by my A&P last summer and I was told the break-in was going really well. The engine broke in in less than 50 hours, but I had about a hundred hours when the plane went into this year's annual and we moved to install GAMI injectors. Also as mentioned, during the late stages of break-in I tried to run the engine LOP with the factory injectors in it, but once on the LOP side it was too rough. My old engine had had GAMIs and they worked really well for LOP, so I elected to go back to GAMI's in the new engine at this year's annual.

The A&P ran the GAMI lean test and ordered injectors from GAMI, which were installed, and I got the aircraft back in February. I went to test fly it but elected not to leave the ground. The engine was running rough even at idle and while rich. There were major differences between the EGT's in a couple of the cylinders, again, even at idle. I reported these back to my A&P and also had a text message discussion with them about how the GAMI lean test had been conducted. They found an induction leak and fixed that. The lean test had originally been done in the classic way, setting a ROP power settings, then leaning the engine back across peak by only reducing the fuel flow and letting the MP do what it wanted, then downloading the data and sending it to GAMI. The A&P said they assumed the GAMI guys had seen enough engine data to be able to interpret the result. I explained all the stuff I put in my first post about how leaning is different in a 231 from all the other Mooney turbos that I put in my first post. We decided that the A&P would reinstall the TCM factory injectors and we would fly the lean test together, recording the result manually on paper. My A&P flew and I manipulated the fuel and MP controls and did the recording. Unfortunately, it was all on a handwritten sheet which I left with my A&P so they could immediately fax it to GAMI so I did not keep a copy, but I can tell you the significant results.

The GAMI instructions are to start the lean test at approximately 65% power and with fuel and MP on the rich of peak side. We started at 25 inches of MP and 10.5 GPH, which I know from past experience is about that. The instructions say to lean in increments of 0.3 gph, so that is what we did, leaning all the way down to 7.5 GPH. The first thing we noticed were the changes in MP that occurred as I reduced the fuel flow. Roughly, a reduction in fuel flow of 0.3 gph did not have a material affect, the MP might go down .1 or stay the same. However, making the second reduction (two increments, that is 0.6 gph) caused the MP to go down by about a half inch. The controls in my aircraft are a vernier for the fuel flow and a straight stick for the MP. I would generally roll the fuel flow down the prescribed 0.3 gph, give the fuel flow and MP a chance to settle, adjust the fuel flow just slightly if needed to get back to the 0.3 increment, and then address the MP. As those who fly a 231 can appreciate, hitting an MP number to the tenth of an inch with the straight stick and variable response from the wastegate controller and turbo are a bit of an art. With persistence, I was able to keep the MP within 0.2" of the original 25". Cylinder #6 peaked nearly right away, at 10 GPH, and cylinder #5 peaked one increment later. The other four cylinders peaked well down from that, a full gallon per minute plus. As mentioned, we did the test all the way down to 7.5 gph, where the engine was getting a little unhappy and there were a few cylinder misses. We did notice that, particularly 5 & 6 saw a second slight rise in EGT when the fuel flow got down around 8 gph. As I understand it, this happens right before the flame goes out.

We sent the lean test in to GAMI and got a new set of injectors back in a couple of weeks. Those went into the engine. I have been able to fly the plane three times for a total of about 5 hours since then. The engine is now really smooth and the injectors are working very well. My standard LOP setting in the old engine was 34"/2450/11.1 GPH and I am immediately able to go to that setting with the new GAMI's. Although I used EGT's in the first testing I did to arrive at this setting, I use TIT in practice once the power setting is made. I want to keep TIT at or under 1600. My past experience was that if TIT drifts up over about 1610 it tends to run away and pretty soon you are looking at TITs that are knocking up against the "continuous operation" redline of 1650. So if a LOP cruise the TIT starts moving over 1600 plus a few degrees, I adjust the fuel flow down a tentho or two. Around here, standard maneuvering altitude is about 3000 MSL/1000 AGL and I have not tried higher altitudes yet.

On the simple operation side, the fuel flow/MP interlink in the 231 makes operations really eas in the 231 once you understand how to get to a good LOP cruise setting. I will make my 34"/2450/11.1 setting, which gives me very good speed at 3,000, about 141-142 KIAS and a little more TAS. I cruise from one western MN airport to the next at that speed and practice VFR instrument approaches. To slow for an approach all I need to do is to pull the MP back to 24.5-25" and the plane will slow to about 120 TAS. I do not adjust the fuel flow at all, the interlink adjusts it down to about 8.5-8.8 GPH  automatically. I find that the exact MP to use for this varies with OAT and the time of year, and rather than use a fixed power setting (i.e. 25") I pull the power back to about that and then adjust MP as needed to get to 120. 

Next up, in the next few flights I intend to run a GAMI lean test with the new injectors to see if we need any fine tuning, but the engine is running very well and I don't think so. I will also test to see how many degrees lean of peak my power setting is in the new engine and report back. Testing for degrees LOP is a little challenging in the 231. As stated, you can't just make a ROP power setting, put the engine monitor in lean mode, lean down until it give you a signal, and use the degrees lean of peak that the engine monitor reports. The MP is changing by an inch or more when you do that and the result you get is from changing the power settings, not changing the air/fuel ratio. The trick is to pull the engine over to the lean side and then put the monitor in ROP mode, you read that right, ROP mode. Since you are already on the lean side and are going to enrich back to peak, you want to know the first cylinder to peak and that is what ROP mode gives you. The advantage of this is that while there is some movement because of the interlink it it not nearly as much and you can get a decent number for degrees lean of peak.

I can already say that EGT's go up when LOP, as they are expected to, and CHTs go down. Where normally my CHT's would be in the vicinity of 380 dF when ROP, they are down about 40 degrees when at LOP cruise. 

[jlunseth]

14 minutes ago, Ragsf15e said:

@jlunseth

What was your gami spread with the TCM injectors that couldn’t run LOP?  Also are you using fine wires (with new plugs it’s probably not a big difference).

What MP/rpm were you using when you tried LOP?  I’ve read your earlier posts about using “very” high mp and low rpm (something like 31/2350 and ~10gph).  I know these aren’t your exact numbers, but if I recall your earlier posts, they are in the ballpark?
 

I have an SB engine, so a little different, but mine wasn’t particularly happy at similar settings.  It was much smoother at a little lower mp which puts it ~20 degrees lean of peak at 10.4gph (65% on my engine).  I’ve left rpm at 2350.  11.3gph and ~31” for 70% works as well and keeps it about 20f lop.  I guess my point is that at 65 or 70% power, you don’t need to be very far lop to be “safe” and efficient.  At all of the above power settings, I am below 1575 TIT and CHTs are low 300s (or even cooler, sometimes I’d actually prefer a bit warmer). 
 

*for the record, our engines are different as I have an SB with a TCM intercooler and waste gate control and 10 more hp.  I have gamis and fine wires.  Both were put on when the engine was oh by previous owner, so I don’t know how it ran on stock injectors.

 

I was writing post two when you replied, I hope it answers most of your questions. Now that you mention it, I don't know if I am running fine wires, I think so, but I will check back with my A&P because now I am curious also. I ran fine wires in the old engine and it made a big difference for LOP ops.

I generally agree with you that you don't have to be very far LOP. 10 or 12 degrees is ok, 20 is better. At the ADA live seminar the GAMI guys recommended running any turbo at 60 degrees LOP in the seminar, but at least at the time, most of their experience was big bore engines and ours are "little bore." I had several email discussions with Walter Atkinson back then and he kept saying just that, that they did not have much experience with our TSIO360's. I can tell you that my old engine made it a long way at the LOP cruise setting I was using, my CHTs were cooler and my airspeeds were actually significantly better than ROP. Bear in mind that a ROP power setting in the 231 is a little complicated. You have to take the numbers in the POH and then find the Differential Temperature that you are operating at (difference between CDT and IAT), then look up in a chart how much to adjust the POH MP for the factory nonintercooled engine downward in light of the DT. My experience was that the settings I derived that way were too low because my airspeeds were persistently lower at ROP than what they should have been. Then I started operating LOP using the formula and presto, they were right where they should be for a given power setting, or slightly better. 

 

[Ragsf15e]

I would agree that as you get to higher Lop power, you’ll want to be more lop to be “safe”.  I’ve only gone as high as 70% and I feel comfortable with ~20ish lop.  You’re running above that (~73%, so not much), so being deeper lop makes sense.

Our chts seem to indicate the engine is fine there.

[Ragsf15e]

And wow, the tcm injectors weren’t close!

[kortopates]

Unless you get a platinum edition TCM engine the stock injectors are terrible yielding 1.5 or worse Gami spread.

The TCM Position Tuned injectors will get you just above 0.5 at 0.6 - 0.7 on average.

I have yet to see a TSIO-360 that will run any where near 60F LOP. About 35F is the limit with good mixture and fine wires; partly due to the Slick mags. A Surefly can help some and a few have switched to Bendix mags.


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[jlunseth]

@kortopates -The total spread was 1.3 if I recall. I can tell you that the engine would run rough the minute the mixture went past peak. The GAMIs are way better.

I am going to do some testing to see how far LOP I can get and report back, but that creates limits on choices. To get more lean you either have to subtract fuel, which reduces power, or you have to add air and I am already using 34". When I originally derived my favorite setting I was worried I would be overworking the turbo. That did not turn out to be the case. I started to have it borescoped at every annual once it got up around 1500 hours, but Willmar reported no adverse wear or conditions. The turbo got to around 1700 hours without a hiccup and I ran LOP every opportunity I could. My TIT is right at, say, 1598 and I don't want it to go higher. Don't want to task the turbo more. So 34" may be arbitrary, but I don't think I want to add any more air than that.

@Ragsf15e - A little over 72% HP. I get really nice speeds for a 231 at my LOP setting so I was hopeful I could get the new engine to work with it which appears to be the case. Better speeds at 72% LOP than I used to get at 75% ROP  calculated using the tables and POH.

[kortopates]

John, you can very accurately measure your spread at much lower power setting, such as 20-22” MAP or more closer to 22-24 with a lower prop rpm; capture your sweeps with your engine monitor.
Plus at that lower power setting you can do full 30 sec LOP May checks to check the health of your ignition. With the lower power setting your TIT won’t spike so high.

You mentioned your holding with couple tenth of the target MAP doing the spreads - that’s excellent but up to 1/2” is usually good enough. But that is more challenging with very poor mixture compared to very good mixture.

BTW, if you still have your old GAMI injectors i’d just send to John-Paul and they’ll clean and bench test to insure they’re still to spec and return for a modest fee.


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[jlunseth]

I am pretty sure that is what we did with the GAMI's, returned the old and got new in exchange, but I left that up to the A&P.

I will try the lower power setting to get the spread. I have often wondered about how well that works with the very untuned induction system in the 231. Just a "log" that ends abruptly at a flat plate with droppers to the cylinders at intervals along the log. One might expect a pressure wave (back pressure) to build off the end plate of the dropper and extend back a varying length depending on the power being output, toward the droppers, affecting the pressure at the dropper, among other variables dependent on power. Also, the first dropper obviously is alot closer to the air source than the last. So it has always intrigued me whether the fuel spreads in the 231 would be the same at, say, 22" of MP as they would be at 34". No way to measure though except try them and see. I was impressed that we took our measurements at 25 inches and seem to have very even spreads at 34" so I am not going to worry about it.

Thanks as usual Paul. When I get the engine all settled down I will send in some data under my Savvy subscription and start watching what it is doing in more detail.