DVA

M20M LOP Discussion

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Note the limits from the fuel and Compression ration in Don's sheet above, but also read it in conjunction with the Lycoming PoH "Lean Limit" curve 13490:
1862990964_TIO540-AF1FFvsBHP.thumb.JPG.264d09f93a7180483e03bf05b5df9f39.JPG

Note that when you get over 220BHP or so (75%) the BSFC is getting substantially worse - this is around the 16.5GPH. Unfortunately the Lycoming curve has nothing about the surrounding parameters, of which the likely most significant is RPM, so as they say, YMMV!

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10 hours ago, Awful_Charlie said:

Note the limits from the fuel and Compression ration in Don's sheet above, but also read it in conjunction with the Lycoming PoH "Lean Limit" curve 13490:
1862990964_TIO540-AF1FFvsBHP.thumb.JPG.264d09f93a7180483e03bf05b5df9f39.JPG

Note that when you get over 220BHP or so (75%) the BSFC is getting substantially worse - this is around the 16.5GPH. Unfortunately the Lycoming curve has nothing about the surrounding parameters, of which the likely most significant is RPM, so as they say, YMMV!

Could you break that down in layman’s terms?  

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Could you break that down in layman’s terms?  


Just curious, have you read the very first post in this thread? If so, what could I have done better to help others understand the idiosyncratic nature of the Bravo at LOP?

Thanks
DVA


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Could you break that down in layman’s terms?  


Also, you might find this useful as far as power and MAP settings are concerned.

TLS Bravo Percentage of Power... Redux. (UPDATED 11/2016)
https://r.tapatalk.com/shareLink?share_fid=55491&share_tid=18699&url=https://www.mooneyspace.com/index.php?/topic/18699-TLS-Bravo-Percentage-of-Power%2E%2E%2E-Redux%2E-%28UPDATED-11-2016%29&share_type=t



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1 hour ago, DVA said:

 


Also, you might find this useful as far as power and MAP settings are concerned.

TLS Bravo Percentage of Power... Redux. (UPDATED 11/2016)
https://r.tapatalk.com/shareLink?share_fid=55491&share_tid=18699&url=https://www.mooneyspace.com/index.php?/topic/18699-TLS-Bravo-Percentage-of-Power%2E%2E%2E-Redux%2E-%28UPDATED-11-2016%29&share_type=t



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DVA, interesting read for sure, thank you.  The author mentioned running 100df rich of peak on the way up.  I have read where others don’t lean untill established on cruise altitude.  Wondering what others do?  In my J I always leaned as I climbed out but was thinking now I would leave it rich in my Bravo.  Any advise greatly appreciated.

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Leaning is based on MP...

J MP fades with altitude... so leaning is common during climb above 3k’...

Climbing in a NA plane ROP, is often done in a range from 2-300°F ROP...

100°F ROP in a climb at high power doesn't Sound accurate...

What does your POH say for climb power settings? Is it confusing?

Transition Training can potentially save you a lot of money.... :)

Flying in the flight levels can be really tough on the machinery and human body with just a simple mid-judgement...

PP thoughts only, not a TC’d engine operator...

Best regards,

-a-

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Cruise climb at 34/2400 doing 140 kias - I set the TIT at 1550 and forget about until level in cruise when MAP is set (usually 27-29" at 2400 rpm) and mixture leaned to 100 ROP.  Easy peasy.

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On 11/10/2018 at 6:52 PM, Knuckledragger00 said:

Could you break that down in layman’s terms?  

In addition to Dave's pieces, I'll try to add a bit:

Let's have a quick look at torque and power before we get too far:

Torque you are probably familiar with via the use of a torque wrench. Is is a measure of how hard you can turn something, and the typical example is one of a bucket in a well, where the drum on which the rope is would has a diameter, and the handle with which to wind also has a length. It doesn't matter about the diameter or the length of the handle for the amount of torque required to hold the bucket in one position, and to hold it stationary required no power, you have to apply so much force over a lever of a length which is why the unit is lb/ft or kg/m - like a see-saw used in the CofG calculations, you can apply half the force at double the distance for the same effect.

If you want to move the bucket up, you need to exert not only torque, but maintain this over a period of time. So you could have a "low geared" well lift, where you wind the handle lots of times to move the bucket up one foot, or a "high geared" one when maybe only a fraction of a turn is required, but in the latter case you would need to apply a lot more torque.

Power comes from multiplying the torque (which is already a product of the force and the lever length) and the rate of rotation, so consequently something at 0 RPM is making zero power, but back to the well, a tiny motor with very little torque but running through a reduction gearbox maybe able to lift the bucket - however a big motor at low RPM may have the torque to lift it without the gearbox. At the end of the day, if they lift the same weight bucket over the3 same distance in the same time, then they are making the same power. You can put a torque wrench in the vice and hang a few bags of sugar on it, and you can get a torque reading, but there's no power being produced!

One way you can get power by burning fuel. You can burn fuel in a variety of ways, many of which are terribly inefficient, but if you want to extract more power (at a given efficiency) in a normal IC engine, there are two ways to do it:

a) turn the engine faster (so it draws in more fuel and air) - as long as the torque doesn't diminish to much, as power=torque x more RPM ie more power
(lift the bucket up faster)
b) Ram more air and fuel in - this will (should!) give us more torque, so again power=more torque x RPM ie more power again
(lift a heavier bucket up in the same time)

Problem with a) is we need to keep the prop tips sub-supersonic (or the prop goes very inefficient) There's loads of reading out there on this too, but in summary, we need to keep the tips below about 0.85 mach or so. As the speed of sound is dependant on temperature (not air pressure!), then at high altitudes (in the cold), the speed of sound is lower, and a 75" dia prop (as we have on the Bravo), with a high TAS (which adds to the tip speed) we can get quite close even at 2400RPM. If you get up in the (very!) cold you can try this by setting max power at 2400, and then trying 2575 - if the tips get over the critical mach then you will actually slow down. (Obviously I hope, race/consumer engines for cars/bikes etc have different constraints)

Problem with b) is you can only ram in so much with the compression  before detonation comes a problem. The effective overall compression ratio is not that terrible, just some of the compression has taken place outside of the cylinder. A NA engine at FL180 only gets half the ambient sea level pressure, but a turbo'd one can get sea level or more, so that 10:1 ratio N/A is effectively 5:1 at FL180. In a turbo'd engine you can get the whole sea level pressure, but you're constrained by all sorts of other stuff such as the incoming charge temperature that it is principally the engine designers job to manage.

With all that out of the way, we could over simplify things to say that if you burn fuel in the most efficient way possible (ie about 25-50 LOP) in an IC engine, for rotating shaft output, then the amount of power is dependant on how much fuel you lob in, hence the figures in Don's spreadsheet. Problem we have is primarily cooling and the speed of combustion, and to manage these the designer has specified an overly rich mixture at high power settings. This means we don't burn the fuel efficiently - we are putting extra in to cool the combustion and get a burn speed that allows us to get more power, albeit at an efficiency cost.

Conversely, at low power, we are still making all the ancillaries and internals do their work, and these have an overhead (eg, take all the spark plugs out of your engine and spin it over by hand - hard work isn't it! Now spin it at 2400RPM and see how much power that needs!) That power is gone no matter how much fuel you put in. This is one of the factors the engine designer copes with for the idle speed - the engine might be making 10 or 20% of maximum rate power from the fuel ingested, but so much is used to internally before there is any to spare - if he makes the idle any slower, then there is not enough power to run the internal before we get anything useful for the prop, and hence the engine stops.

The graph can be converted into BSFC (Brake Specific Fuel consumption), which is a measure of efficiency - how much power do you get from each pound of fuel. (Lots of reading out there on this too is you are interested) Really efficient engines (diesels) get down to maybe 0.35, gasoline engines rarely do better than 0.38, and even then only at a very controlled output. By converting the units in the graph we get a peak efficiency in the AF1A/B of about 0.45 or so which is pretty rubbish, but it is an abysmal 0.6 at max power, and over 0.5 below 50% power. The "sweet spot" for efficiency in that graph is thus in the 175-215BHP area, and outside of that it is starting to drop off Some of the good gas aero engines are getting to about 0.41 - 0.42 or so, only 0.04-0.03 difference, but this does represent 10%

Hope that helps!

Ben

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18 hours ago, Awful_Charlie said:

In addition to Dave's pieces, I'll try to add a bit:

Let's have a quick look at torque and power before we get too far:

Torque you are probably familiar with via the use of a torque wrench. Is is a measure of how hard you can turn something, and the typical example is one of a bucket in a well, where the drum on which the rope is would has a diameter, and the handle with which to wind also has a length. It doesn't matter about the diameter or the length of the handle for the amount of torque required to hold the bucket in one position, and to hold it stationary required no power, you have to apply so much force over a lever of a length which is why the unit is lb/ft or kg/m - like a see-saw used in the CofG calculations, you can apply half the force at double the distance for the same effect.

If you want to move the bucket up, you need to exert not only torque, but maintain this over a period of time. So you could have a "low geared" well lift, where you wind the handle lots of times to move the bucket up one foot, or a "high geared" one when maybe only a fraction of a turn is required, but in the latter case you would need to apply a lot more torque.

Power comes from multiplying the torque (which is already a product of the force and the lever length) and the rate of rotation, so consequently something at 0 RPM is making zero power, but back to the well, a tiny motor with very little torque but running through a reduction gearbox maybe able to lift the bucket - however a big motor at low RPM may have the torque to lift it without the gearbox. At the end of the day, if they lift the same weight bucket over the3 same distance in the same time, then they are making the same power. You can put a torque wrench in the vice and hang a few bags of sugar on it, and you can get a torque reading, but there's no power being produced!

One way you can get power by burning fuel. You can burn fuel in a variety of ways, many of which are terribly inefficient, but if you want to extract more power (at a given efficiency) in a normal IC engine, there are two ways to do it:

a) turn the engine faster (so it draws in more fuel and air) - as long as the torque doesn't diminish to much, as power=torque x more RPM ie more power
(lift the bucket up faster)
b) Ram more air and fuel in - this will (should!) give us more torque, so again power=more torque x RPM ie more power again
(lift a heavier bucket up in the same time)

Problem with a) is we need to keep the prop tips sub-supersonic (or the prop goes very inefficient) There's loads of reading out there on this too, but in summary, we need to keep the tips below about 0.85 mach or so. As the speed of sound is dependant on temperature (not air pressure!), then at high altitudes (in the cold), the speed of sound is lower, and a 75" dia prop (as we have on the Bravo), with a high TAS (which adds to the tip speed) we can get quite close even at 2400RPM. If you get up in the (very!) cold you can try this by setting max power at 2400, and then trying 2575 - if the tips get over the critical mach then you will actually slow down. (Obviously I hope, race/consumer engines for cars/bikes etc have different constraints)

Problem with b) is you can only ram in so much with the compression  before detonation comes a problem. The effective overall compression ratio is not that terrible, just some of the compression has taken place outside of the cylinder. A NA engine at FL180 only gets half the ambient sea level pressure, but a turbo'd one can get sea level or more, so that 10:1 ratio N/A is effectively 5:1 at FL180. In a turbo'd engine you can get the whole sea level pressure, but you're constrained by all sorts of other stuff such as the incoming charge temperature that it is principally the engine designers job to manage.

With all that out of the way, we could over simplify things to say that if you burn fuel in the most efficient way possible (ie about 25-50 LOP) in an IC engine, for rotating shaft output, then the amount of power is dependant on how much fuel you lob in, hence the figures in Don's spreadsheet. Problem we have is primarily cooling and the speed of combustion, and to manage these the designer has specified an overly rich mixture at high power settings. This means we don't burn the fuel efficiently - we are putting extra in to cool the combustion and get a burn speed that allows us to get more power, albeit at an efficiency cost.

Conversely, at low power, we are still making all the ancillaries and internals do their work, and these have an overhead (eg, take all the spark plugs out of your engine and spin it over by hand - hard work isn't it! Now spin it at 2400RPM and see how much power that needs!) That power is gone no matter how much fuel you put in. This is one of the factors the engine designer copes with for the idle speed - the engine might be making 10 or 20% of maximum rate power from the fuel ingested, but so much is used to internally before there is any to spare - if he makes the idle any slower, then there is not enough power to run the internal before we get anything useful for the prop, and hence the engine stops.

The graph can be converted into BSFC (Brake Specific Fuel consumption), which is a measure of efficiency - how much power do you get from each pound of fuel. (Lots of reading out there on this too is you are interested) Really efficient engines (diesels) get down to maybe 0.35, gasoline engines rarely do better than 0.38, and even then only at a very controlled output. By converting the units in the graph we get a peak efficiency in the AF1A/B of about 0.45 or so which is pretty rubbish, but it is an abysmal 0.6 at max power, and over 0.5 below 50% power. The "sweet spot" for efficiency in that graph is thus in the 175-215BHP area, and outside of that it is starting to drop off Some of the good gas aero engines are getting to about 0.41 - 0.42 or so, only 0.04-0.03 difference, but this does represent 10%

Hope that helps!

Ben

Needed to read that a few times to comprehend but great info Ben!

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On 6/19/2016 at 3:00 PM, DVA said:

Hi!

I hope this will help other Bravo owners who struggle to run the TIO-540-AF1B at Peak or LOP TIT.  But first, in full disclosure I am not an A&P and this is not advice. I am simply illustrating my experience with this engine, and it or may not apply to you. Always follow the POH when you are not sure that your deviation from that document is in your best interest.

I am a lean of peak fan, always have been. It comes back from my days of working on non-aircraft internal combustion engines and proving that an engine run LOP operates cooler, cleaner and lasts longer than a similar engine run ROP.  I have taken the Advanced Pilots Seminar course on advanced engine management http://www.advancedpilot.com and had numerous discussions with Lycoming engineers, the folks at GAMI and engine builders, and I have used this knowledge to come to a few conclusions about this engine that I would like to share. I am not poking the sleeping “ROP vs LOP” dog. :-) and I realize that Lycoming - in some instances but not all - does not recommend operating LOP.  I also believe that if they could, they would revise that language to say:

If you have a good engine monitor, tuned injectors, and a knowledge of how your engine operates, you should run LOP whenever your heart desires - except on take off.

My opinion is that Mooney, when they introduced the TLS, continued their fine mission to make the fastest commercial SE piston airplane. To do this, they needed a lot of power -and- in a weight package that would not cause the flight envelope of the long body to get too forward on the CG, the TIO-540 was the answer. Bravo owners know that the airplane is already pushed forward CG and many have Charlie weight for aft ballast installed (which lowers the already skinny useful load). The TIO-540 is a complex high performance engine and should not be grouped with most other ground boosted engines for performance discussions,  The reasons for this, IMHO, are due in part to two things: 1) a complicated (but effective) turbocharging controller system, and 2) the requirement that the engine runs at very high percentage of power levels to make book speeds. I did a post a few weeks ago on the Bravo’s power percentage here.

Because this engine is normally operated at greater than 80% power during cruise by most people, this engine is very working hard and making a lot of heat for a lot of the time. It is also doing so with rather loose factory tolerances on the precision of fuel flow to the cylinders which makes it extremely difficult to run this engine in an wide and efficient range of power settings.

The POH states only two settings: 1) ROP TIT by at least 125dF for “best power"; and 2) Peak TIT as long it’s below 1750dF (1650dF at high altitudes) for “best economy" - the latter is sometimes impossible to achieve with this engine at higher power levels (30” MAP and above) because of poor fuel distribution which causes engine roughness. When near peak TIT (or EGT) the roughness is normally due to some cylinders running leaner than others. The leaner cylinders produce less power than do the richer cylinders which give you the impression that there is something wrong because you feel that power imbalance as roughness. (Note: that slight roughness is not a bad thing, your engine won’t fly apart, it really doesn’t care, only you do.) Spark plugs play a key role in this too - more on that in a bit.

Here’s the rub... Because most of the TIO-540-AF1Bs have unequal cylinder fuel distribution, when Bravo owners try to run the engine per the Sun Visor chart at Best Economy (Peak TIT) they may find an disconserting “roughness” and feel a slight loss of power.  That combo causes some consternation, and when that happens, some operators I’ve spoken with will simply dial the Bravo’s red knob in just a little richer and go slightly rich of peak TIT just enough to cure the roughness. Thinking that they are now 'just fine’ they fly the engine at that setting - when in fact they are not “just fine." They are now operating the engine “slightly ROP TIT” at a mixture setting that causes the most cylinder head heat, the highest internal combustion pressures and at a place where the engine can easily begin to exhibit detonation. (See graph below, which was taken from the Lycoming Flyer publication) The Mooney POH does not say it is OK to run the engine “slightly” ROP TIT because both the factory and Lycoming know that is a very bad mixture setting.  All of the experts I’ve spoken to agree that no internal combustion engine should be operated “slightly” (10-60dF) rich of peak. If you can’t make Peak TIT for whatever reason, better to just go greater than 80-100dF and accept the extra fuel costs and keep things in the engine cooler and happier.

I have not found anyone who disagrees that sustained high heat weakens, fatigues and shortens the life of the metals used in engines, and that’s why we see all kinds of advice about keeping cylinder head temps below 400dF. The Bravo’s POH advises that you use a combination of gauges when setting power - TIT and CHT as the most prominent. The POH also says that the CHT redline for this engine is 500dF - which everyone (experts or not) agrees is simply ridicules.

If you have an older Bravo, and especially one where a field AF1A to AF1B conversation was done, you may want to check to see on which cylinder the panel’s CHT temp probe is located. The AF1A probe was located on cylinder #5, and Mooney Service Instruction M20-101C states that it should be on cylinder #3 for the AF1B. Check yours, especially if you rely on the single panel CHT gauge, I’ve spoken to three Bravo owners where the CHT probe was still on #5 (mine was too). There is a big difference in the cooling between #3 and #5 - #3 being as much as 50dF hotter.

That all said, in summary the TIO-540-AF1B is a hot running, high power, high performance engine, different from many others. In the M20M it is asked to operate at the top of its performance range in order to make POH (book) performance numbers, and us Mooney drivers like to go fast! Adjusting the mixture on this engine can be  tricky due to engine’s generally unequal cylinder fuel distribution and, in many cases, the wrong type of spark plug being used.

I wanted my Bravo to act like most other well-tuned and instrumented airplanes I’ve flown. While always keeping the cylinder head temps below 400dF, I want to be able to safely set the engine for maximum power when I want to go fast, and I want the ability to safely save fuel when fast doesn’t matter as much. I don’t want complicated instructions to do this, and I want to feel as if the engine is happy and smooth no matter what.  Before I started this trek, I could not run my Bravo at Peak TIT at MAP higher then 29” without noticeable roughness and/or what I felt was unacceptable power loss. And there was no way this engine would run LOP.  I would flow about 22 GPH of fuel in cruise at 100dF ROP TIT (on hot days I needed to to be richer to keep the CHTs below 400dF).

Here’s what I did.

  • I first ensured that magneto timing was correct. This is very important with high performance engines; you can often get away with inexact timing on lower power engines, but never on engines like the TIO-540. Mine were pretty close, but not exact - they are now. I had new Champion massive plugs installed about a hundred hours earlier, on inspection they looked okay and they passed the tester test. We gapped them at .016.
  • I installed a new set of GAMI TurboInjectors. When I spoke with the factory rep John-Paul he cautioned me that this engine was a hard tune and that I should expect to have to work at, and that there might not be the success that others have with GAMIs on other engines. I love honesty - these guys at GAMI are true pros. 
  • The first set of injectors made a marked and clear difference. I was able to run at Peak TIT smoothly for the first time, but I was unable to run LOP without roughness. I did a GAMI lean spread test and found that my spread was about 1.4GPH, while better, it was not ideal. I contacted the factory and John-Paul immediately sent out two replacement injectors for a better match. After that a test flight or two it showed that I actually picked up about two knots at peak TIT and fuel flow was down a little. I could now get a little bit LOP with a GAMI spread of .9GPH.  Also noticed CHT were generally cooler by about 20dF. This was due to the fact that the better fuel distribution was allowing all cylinders to run more equally, so at Peak TIT all cylinders were closer to their peak EGT. Fuel was saved for the same reason - unnecessary rich cylinders were now leaner for any given mixture setting.
  • Because this engine seems finicky at different MAP/RPM settings, I decide to tune to a specific sweet-spot for the GAMI spread - I picked 29”/2400 for this as it is, according to the Lycoming power graphs, about 75% power on a standard day, at mid altitudes. This might have been the most important step I took in achieving success with this tune, on this engine to allow for good LOP performance.
  • I sent the new GAMI lean test to John-Paul - not satisfied he sent me a single replacement for the one cylinder that was off a bit. (no charge for all of this and no questions asked). We installed that one injector and then did a test flight. The biggest change was that I could get more LOP without roughness, at 2400/29” I could get to about 20dF LOP. I would lose about 9 knots, but I was able to save almost 6 GPH of fuel. While I still couldn't get much past Peak TIT at higher power setting I was happy with the trade off; now I could achieve both fast and efficient settings. My GAMI lean spread was now a very comfortable .3GPH as you can see from the graph below. I thought that was all I needed to do but it wasn’t ...
  • I have a Savvy Aviator account, I upload my JPI engine analyses data there, and I happily buy their yearly analysis service. I uploaded a flight and was looking at the graph and saw something on one of my lean spread tests that I could not understand. During a lean test, you should see all EGTs rise as you get leaner and leaner, then they should all peak (at slightly different times, that’s the fuel flow “spread”) and then they should drop off. On my test, there was a second peak? I submitted the flight for review at Savvy and Paul Kortopates wrote back and explained it, and as soon as I read his explanation I understood: He said "That second "peak" is actually what happens when the mixture goes lean enough to fire only one plug. You are seeing the same rise we would see if you switched off one of the magneto's so that there was only one plug firing- which is what we're seeing here. On one plug alone, combustion is slowed and therefore when the exhaust valve opens we are seeing more of the combustion event and the associated higher EGT because of it”  That’s when we discussed the last step I needed to take to get this whole project right - new plugs - but specifically fine wire plugs. It seems as if the fine wire plugs work better than the massives in two instances 1) older wet and oily engines (not the case here) and; 2) in lean mixtures. They’re expensive, about $80 a shot, but they also are suppose to last hundreds of hours longer.
  • After researching both Champion and Tempest, I opted for the Tempest Fine Wires and installed 12 of them. Paul was right on! From the moment I turned the key I could tell that something was different. The engine started better and ran smoother on the ground and in the air, and I am now able to run LOP at 32” MAP and below if I chose. My CHTs are generally 30dF cooler than when I started this project, and I am saving fuel at every power setting. Where I use to run 22GPH at 2400/32 ROP, I now run 20GPH with the same airspeed, and if I want to throttle back to 2400/29, I loose about 10 knots and run about 15GPH at about 20dF LOP. 

In all, I have about $2500 invested here, but in fuel savings alone that will pay back in short order and then keep paying back. The big benefit is that I have more power options now with the aircraft and my engine will be much cleaner with less carbon deposits on the heads, the values, the plugs and the exhaust system. 

My flight profiles are not religious LOP, and yours don’t have to be either to get a benefit from the cleaning and cooling aspects of running your engine with a proper mixture, which, for me includes LOP at times. Typically I will run lower power and LOP in tail winds of any speed, because why not? If I loose 10 knots true in LOP but I make up some or all with a tail wind, I’m saving 5-6GPH of fuel AND cleaning the engine as I go.

Thanks for reading! I attached some pics - happy to try to answer any questions.

Dave

 

Second Peak.jpg

GAMI Spread.jpg

Power Curve.jpg

JPI.JPG

Hi DVA,

Thank you so much for the detailed explanation of your process.  I am following your lead and I'll report back when done.  This forum is so helpful....so many smart minds!

 

Alex

 

 

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