M20M LOP Discussion

[jlunseth]

Thanks Dave, but my question is different.  What I am asking is not whether the density controller holds MP as ambient pressure changes.  What I am asking is whether, at a constant altitude and ambient pressure, MP falls by itself when you lean the fuel flow back.  Does it?

[DVA]

Thanks Dave, but my question is different.  What I am asking is not whether the density controller holds MP as ambient pressure changes.  What I am asking is whether, at a constant altitude and ambient pressure, MP falls by itself when you lean the fuel flow back.  Does it?

It sure was different! I'm taking a reading course next week, I'll get better at this ... lol

Yes, when I lean I get a small change in MP, on the order of .5 +/- I ignore it.

[jlunseth]

Thanks Dave.  I would probably ignore .5 .  An inch, it would depend on how far I had leaned, In my engine, if I had leaned from 13 to 11 it would matter.  If I had leaned from full rich (24) to 11, probably would not matter so much.  It would also depend on how many degrees lean the JPI is reporting.  If it is reporting 20 degrees, that is a small margin, and because of the MP fall you wouldc not actually be at 20 degrees, maybe closer to 10.  That would be the concern.  On the lean side, small changes make a big difference.

[Rick Junkin]

Thanks to DVA and Awful_Charlie in particular for all of the data and insight. And to all in this thread for the many questions and inputs. I've gained from them all.

I've officially joined the LOP club.

I installed Tempest fine wires (URHB32S) last fall, had the ignition system thoroughly checked and tweaked during the annual in August, and completed the GAMI tuning process today after the third iteration of injector swaps. Today's check flight yielded a GAMI spread of <0.2 gph (!!!!!!!!!!) with the power set at 26"/2400RPM, and 30"/2200RPM yielded 143KIAS at 4,500', ~50F LOP with FF 14.2gph. CHTs were all in the 340's. I was able to lean to 10.5gph at 30/2200 with no engine roughness, but stopped there as power had dropped off steeply. The engine ran as smoothly at 2200 as it did at 2400. I should add that my engine has about 800 hours SMOH, and 200 hours since a top with cylinders flow balanced by Lycon.

My wife and I are taking a flying vacation next week and I'll be taking the opportunity on the 3 hour legs to gather some more data, but I'm pretty happy with what I saw today. We should be able to make 180KTAS at 15,000' on 14.2gph, which will make me even happier.

Next investment - dynamic prop balance.

Cheers,
Rick

[Danb]

Sweet Rick, I've got a .5 spread without getting the gamis contacting them they recommended I keep my injectors with the spread I have. I've recently tried 2200 and 2300 it's unbelievable how smooth and quiet it is at 2200 rpm. On trips I still fly rop for speed. Otherwise I've been Lop but the best I do is 14.5 gph. Nice going.

[Rick Junkin]

Here’s what I saw on our vacation sortie:

Altitude: 15,000 (PA 14,860, DA 16,495 with 0C OAT and altimeter 30.06)

Airspeed: 138KIAS/176KTAS

MP/RPM: 30/2200

FF: 13.5GPH

TIT: 1620 (-60F LOP)

CHT: 348-362F

Increasing only the MP to 32 and holding everything else constant gave me 180KTAS, raised the TIT to 1640 and raised the CHTs by 10. I tried increasing only the fuel flow to 14.5 and holding everything else at the original values above but I didn’t like where the TIT was going so I pulled it back to 13.5. I can’t get my head around the idea that “TIT doesn’t matter”, espoused by some experts. And I’m extremely happy with what I’m getting at 32/2200. And it’s QUIET!

Hope this helps the next guy looking for targets and what’s possible LOP.

Cheers,

Rick

[LANCECASPER]

6 hours ago, Junkman said:

Here’s what I saw on our vacation sortie:

Altitude: 15,000 (PA 14,860, DA 16,495 with 0C OAT and altimeter 30.06)

Airspeed: 138KIAS/176KTAS

MP/RPM: 30/2200

FF: 13.5GPH

TIT: 1620 (-60F LOP)

CHT: 348-362F

Increasing only the MP to 32 and holding everything else constant gave me 180KTAS, raised the TIT to 1640 and raised the CHTs by 10. I tried increasing only the fuel flow to 14.5 and holding everything else at the original values above but I didn’t like where the TIT was going so I pulled it back to 13.5. I can’t get my head around the idea that “TIT doesn’t matter”, espoused by some experts. And I’m extremely happy with what I’m getting at 32/2200. And it’s QUIET!

Hope this helps the next guy looking for targets and what’s possible LOP.

Cheers,

Rick

TIT absolutely matters on the M20M. Run high TITs and you'll be changing out TIT probes often and replacing exhaust components. I keep TIT at 1600 or below.

If you or the previous owner ran high TIT your TIT probe may be burned up and giving low readings while it's actually much hotter.

[Rick Junkin]

15 hours ago, LANCECASPER said:

TIT absolutely matters on the M20M. Run high TITs and you'll be changing out TIT probes often and replacing exhaust components. I keep TIT at 1600 or below.

If you or the previous owner ran high TIT your TIT probe may be burned up and giving low readings while it's actually much hotter.

Thanks for the head's up! Individual EGTs are running 1515-1550 with the TIT at 1620, which seems reasonable. I'll keep an eye on it for any signs of degradation. 30/2200 at 13.5gph looks to be a good combination for reasonable cruise speed and range for me that will also be kind to my engine.

Cheers,
Rick

[DVA]

re: TIT

IMHO there are three factors to consider here; 1) we should all agree TIT matters, and we should all agree that EGT absolute temps don’t “really” matter. 2) We should agree that there is much more incorrect (folklore) vs factual information out there as to why TIT matters and why EGT doesn’t “really”, and 3) we should agree that a Mooney airplane / engine combination is generally no different from that of any other like-type airplane / engine combination.

No one will successfully argue against the fact that the hotter you make steel and aluminum the more they will fatigue and eventually fail. So given that, my comments below are driven by a cooler is better premise, however, I am not afraid of recommended heat ratings or running my engine at those temperatures. 

I recently had a long discussion at KOSH with a design engineer at Hartzell and we talked extensively about turbochargers from the manufacturers' perspective. I’ll abbreviate the convo here but I would love to discuss any of this in more detail.

I asked specifically about the M20M’s dual max POH TIT (1750 max lower altitudes to 1650 max at higher altitude) I just couldn’t wrap my head around why the diff in max temps? The turbo has no idea it’s higher up in the air and temp is temp as fast as the materials are concerned - so why the diff and why don’t we see that on most “other” turbocharged piston airplanes? His answer surprised me and immediately made complete sense.

Paraphrasing: Hartzell rates that particular turbocharger for a max *continuous* TIT of 1750dF, and that turbo will run all day long and with expected longevity at that TIT. He went on to say that Mooney (not Hartzell) lowered the max TIT to 1650dF at altitude to increase detonation margin due to the higher and unmonitored compressor discharge temps at altitude.

Ah ha! I get that! So I said that I monitor CDT and Inlet Air Temp and at higher altitudes I can see little difference than in the mid teens so I suspect my detonation margin is not changing based on CDT, right? To which he replied: because you monitor those parameters you will know if your intercooler is working properly or not, you (me) should be able to safely ignore that lower TIT limitation as long as the CDT remain low and reasonable. 

Interesting - so what about metal fatigue? His answer was simple - we design the turbo to withstand and tolerate that max TIT of 1750 and there is a adequate safety margin there for metal fatigue and blade stretch. We don’t want these units coming back for repair, so we set the max operating parameters with care.

So the take away is, if you trust the manufacturer, then our collective arguments of running TIT lower than allowable to “protect the turbo” is largely flawed.

So what about the rest of the exhaust system? Some argue that this is the weakest part of the mooney’s engine and by running TiT less than max you will preserve the exhaust components. Maybe - likely - but no one can really say for how long or in what consistency owner-to-owner. But more importantly, TiT is not directly representative of the “rest of the exhaust system”. 

TiT is higher than individual EGT’s because it represents the additive effects of the pulses of heat collecting at one point AND under increased pressure at the entrance to the turbine hot side. Before that inlet, the individual EGTs are cooler (some can be 100dF cooler ) and after the turbo, the aggregate exhaust is at least 100dF cooler. On my Bravo I have a second TIT probe (TOT actually) at the exit of the turbo just past the V-clamp. I added that to monitor for a (unlikely) sudden failure of that section and it's always 125dF lower than real TIT.

What this says to me is that if you are running the max TIT of 1750,  you will be likely be 1650 or less in the main exhaust system. If you run 1650 max TIT then the math works out to be 1550 or less EGT and that is where we find most non-turbo systems running at decent power levels. Happily I might add.

Some may argue that you’ll burn probes out faster at higher temps. Probably, but again how much faster? I think Mooney recommendation is to replace the TIT probe at 200 hours regardless, but I think that’s overdone as well. Thermocouple probes have gotten way batter in just the last decade, so they are lasting longer and staying accurate for a longer period of time.

All that said - we agree that cooler is better, so run your engine where you want. But I would suggest that we should not be afraid to run the power up and go fast while not exceeding the limits, and also not being shy of approaching them.

OK, let me have it! :-)

 

 

 

[Rick Junkin]

10 hours ago, DVA said:

OK, let me have it! :-)

Thanks for the turbo details and the recage, Dave. Looking back over my notes and articles, it was indeed EGT that was referenced as a "not so important" parameter, not TIT. I crossed the streams between my turbo and non-turbo references and incorrectly concluded that they were asserting that "TIT doesn't matter". Fortunately that didn't seem right to me in actual operation, and I kept the TIT where I was comfortable. Details are important.

However, I'm glad my error precipitated your post. Lots of good information there on design considerations and limits, particularly the background on the 1650/1750 duality.

We came home from JKA yesterday at 8K so that I could gather some lower altitude empirical data for those times we don't want to be on O2, and 32/2200 at 13.8gph got us 158 true with TIT at 1620, EGTs in the low 1500's and CHTs 345-360. That looks pretty good to me for my mission, with a little room to push it up a bit. Although I'll always push Glennie to consider the higher altitudes for more KTAS...

Cheers,
Rick

[carusoam]

Nice technical review, Dave!

1) Single EGTs are always lower than a collective EGT, like TIT... we see this in the three into one exhaust systems of the O... this is a time average of EGT.  What we really want to know, is what the metal temperature really is...

2) Bravo exhaust systems may see some strong thinning over a long time, in the first sections of exhaust pipe heading to the turbine... somebody posted pictures of their Bravo pipe that they poked a hole in during maintenance...

3) Single EGT sensors are sensitive to placement down stream.  This is because the exhaust is dropping pressure quickly as it goes downstream.  A quick pressure drop equates to a quick temperature drop according to thermodynamics...

4) What we are seeing in the DVA highly instrumented plane is the TIT and TOT difference of 100°F is being caused by the thermodynamic drop in pressure, Thanks to the turbine throwing in some resistance to exhaust's flow...

5) It looks like the metal temperature is hard to measure.  The relationship of stress, strain, and temperature of the metal is pretty well documented.

6) the relationship of these variables seems to be best known by the aircraft and engine suppliers.  They just might not be very open to sharing it very well...

7) the peak EGT still happens right outside the exhaust valve (maybe before it gets even measured.)

8) the extended peak EGT happens when three exhaust flows come together into one. Time is included in this measurement.

9) The TIT is further downstream, but is critical to the engine operation...

10) The difference between TIT and TOT is sort of measuring the turbine doing something... if the turbine stops, the TIT and TOT are probably so close together it would be an alarmable point of information...

11) In some cases high TITs have lead to blade stretch and contact with the turbine case.

12) It sounds like having really good instrumentation is the best way to follow what the POH is trying to tell us.?.?

13) the thermodynamics is hard to follow.  But, the combination of high pressure and high temperature don't let up until after the turbine...

14) Is there a good maintenance method of measuring the exhaust pipe thickness in the pipe prior to the turbo?

I had seen an industrial measuring technique using a ball bearing inside the pipe and the sensor measuring how far away the ball bearing was.... it was measuring thickness in the range of mils... .001”

My M20C exhaust pipes showed some surface characteristics that were nothing like the day they left the factory...they had seen some red hot temps over a lot of time...

PP thoughts only, not a thermodynamicist

Best regards,

-a-

 

 

[Danb]

18 hours ago, DVA said:

re: TIT

IMHO there are three factors to consider here; 1) we should all agree TIT matters, and we should all agree that EGT absolute temps don’t “really” matter. 2) We should agree that there is much more incorrect (folklore) vs factual information out there as to why TIT matters and why EGT doesn’t “really”, and 3) we should agree that a Mooney airplane / engine combination is generally no different from that of any other like-type airplane / engine combination.

No one will successfully argue against the fact that the hotter you make steel and aluminum the more they will fatigue and eventually fail. So given that, my comments below are driven by a cooler is better premise, however, I am not afraid of recommended heat ratings or running my engine at those temperatures. 

I recently had a long discussion at KOSH with a design engineer at Hartzell and we talked extensively about turbochargers from the manufacturers' perspective. I’ll abbreviate the convo here but I would love to discuss any of this in more detail.

I asked specifically about the M20M’s dual max POH TIT (1750 max lower altitudes to 1650 max at higher altitude) I just couldn’t wrap my head around why the diff in max temps? The turbo has no idea it’s higher up in the air and temp is temp as fast as the materials are concerned - so why the diff and why don’t we see that on most “other” turbocharged piston airplanes? His answer surprised me and immediately made complete sense.

Paraphrasing: Hartzell rates that particular turbocharger for a max *continuous* TIT of 1750dF, and that turbo will run all day long and with expected longevity at that TIT. He went on to say that Mooney (not Hartzell) lowered the max TIT to 1650dF at altitude to increase detonation margin due to the higher and unmonitored compressor discharge temps at altitude.

Ah ha! I get that! So I said that I monitor CDT and Inlet Air Temp and at higher altitudes I can see little difference than in the mid teens so I suspect my detonation margin is not changing based on CDT, right? To which he replied: because you monitor those parameters you will know if your intercooler is working properly or not, you (me) should be able to safely ignore that lower TIT limitation as long as the CDT remain low and reasonable. 

Interesting - so what about metal fatigue? His answer was simple - we design the turbo to withstand and tolerate that max TIT of 1750 and there is a adequate safety margin there for metal fatigue and blade stretch. We don’t want these units coming back for repair, so we set the max operating parameters with care.

So the take away is, if you trust the manufacturer, then our collective arguments of running TIT lower than allowable to “protect the turbo” is largely flawed.

So what about the rest of the exhaust system? Some argue that this is the weakest part of the mooney’s engine and by running TiT less than max you will preserve the exhaust components. Maybe - likely - but no one can really say for how long or in what consistency owner-to-owner. But more importantly, TiT is not directly representative of the “rest of the exhaust system”. 

TiT is higher than individual EGT’s because it represents the additive effects of the pulses of heat collecting at one point AND under increased pressure at the entrance to the turbine hot side. Before that inlet, the individual EGTs are cooler (some can be 100dF cooler ) and after the turbo, the aggregate exhaust is at least 100dF cooler. On my Bravo I have a second TIT probe (TOT actually) at the exit of the turbo just past the V-clamp. I added that to monitor for a (unlikely) sudden failure of that section and it's always 125dF lower than real TIT.

What this says to me is that if you are running the max TIT of 1750,  you will be likely be 1650 or less in the main exhaust system. If you run 1650 max TIT then the math works out to be 1550 or less EGT and that is where we find most non-turbo systems running at decent power levels. Happily I might add.

Some may argue that you’ll burn probes out faster at higher temps. Probably, but again how much faster? I think Mooney recommendation is to replace the TIT probe at 200 hours regardless, but I think that’s overdone as well. Thermocouple probes have gotten way batter in just the last decade, so they are lasting longer and staying accurate for a longer period of time.

All that said - we agree that cooler is better, so run your engine where you want. But I would suggest that we should not be afraid to run the power up and go fast while not exceeding the limits, and also not being shy of approaching them.

OK, let me have it! :-)

 

 

 

Wow..Dave you totally lose me during your analysis, I'm not educated or have enough experience in the true operational aspects of our Bravos,I merely have a relative handle on my 12 yrs of Bravo ownership and don't dispute the outline. I really do wish I knew they best way to fly our guys to our advantage. Keep the posts coming I copy and read them often in an effort to safely and efficiently fly them.

[donkaye]

I've had my Bravo 25 years, making me one of the longest owners.  Been through one engine and ¾ through the second.  Have taken the APS course and installed Gami Injectors.  Gami spread is .5.  Having said that, I'm running ROP except on descent.  No matter what the Hartzell rep said he's not flying the airplane and his life is not at risk.  I don't like anything above 1625° TIT.  Even with this conservatism, a couple of years ago I needed to have 2 cylinders overhauled due to leaky intake valves.  Also cracked exhaust pipes coming out of cylinders 1 and 3 one time and 2 and 4 another.  At midtime on both engines the turbo and waste gate needed to be overhauled.  I always mouse milk the waste gate at each oil change.  I fly at 75% power most of the time and usually at altitudes of between 15 and 17K.  I maintain O2 sats no less than 96%.  I won't be testing higher temperatures anytime soon.

[Rick Junkin]

20 hours ago, donkaye said:

I fly at 75% power most of the time and usually at altitudes of between 15 and 17K.

Don, my apologies as I'm sure you've posted this elsewhere, but what are your nominal cruise parameters? 29/2400 at what fuel flow, TIT, and average CHT? KTAS? Thanks!

Cheers,
Rick

[donkaye]

2 hours ago, Junkman said:

Don, my apologies as I'm sure you've posted this elsewhere, but what are your nominal cruise parameters? 29/2400 at what fuel flow, TIT, and average CHT? KTAS? Thanks!

Cheers,
Rick

75% Power = 29"/2400rpm, 18.4 gallons first hour, then 18 for the remainder at the same power setting.  CHTs are low, around 350°.  They were higher with the JPI probes on the 700.  I checked with EI and they said their probes are accurate (MVP-50).  TAS, of course, varies with altitude.  At 17K it's about 200 knots.

[Rick Junkin]

Thanks for the info Don. My bad on the airspeed request, I meant to ask KIAS to keep apples to apples, but I can do the math. Interesting detail on the JPI vs EI probes though. I recently installed new JPI CHT probes to feed my 700 (replaced washer TCs and Tanis heating elements with JPI bayonets) and am seeing 350's-360's at about 72%. That seems to check against your EI temps as compared to your former JPI temps. My LOP temps are tracking your ROP temps, perhaps slightly lower, for the same power settings. Thanks again for your data.

Cheers,
Rick

[bcwiseguy]

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

 

 

Dave, awesome write up! Thanks for sharing this. I am looking at purchasing a turbo Mooney soon and the Bravo is definitely on my list (along with the 231 and 252/Encore). It's nice to know that the TIO-540 can be run LOP with the right tuning. My biggest concern with the Bravo has been the TIO-540 and this helps ease my mind a bit about its operation and the resulting maintenance.

[DVA]

 
Dave, awesome write up! Thanks for sharing this. I am looking at purchasing a turbo Mooney soon and the Bravo is definitely on my list (along with the 231 and 252/Encore). It's nice to know that the TIO-540 can be run LOP with the right tuning. My biggest concern with the Bravo has been the TIO-540 and this helps ease my mind a bit about its operation and the resulting maintenance.

Thanks for the kind words. That was written a few years ago and nothing has changed in my Bravo. I’m mostly airplane agnostic, I think there are a number of great aircraft out there for us GA pilots. But with all the planes I’ve had and flown over the last 30+ years the bravo is my favorite SE.

Other can chime in and agree or not but here are my Bravo takeaways for your consideration:

1. You can get behind this aircraft quickly. It goes fast, does not want to slow down quickly and is as complex a “complex” aircraft as you can find.
2. People land Mooney’s too fast. Don’t do that, especially the Long bodies. Other than that it’s a regular flying airplane. Get transition training, it’s worth it for myriad reasons.
3. It only holds two people, those extra seats in the back are for decoration only.
4. It costs more to operate than you think. The annual, when done right, is a 40 hour job don’t be fooled by cheap shops.
5. You can’t have more fun with a totally unnecessary investment toy like this unless you do something illegal. :-)

I’ll considering a twin, pm me if you want to chat.


Sent from my iPhone using Tapatalk

[LANCECASPER]

On 10/6/2017 at 11:36 PM, DVA said:

I recently had a long discussion at KOSH with a design engineer at Hartzell and we talked extensively about turbochargers from the manufacturers' perspective. I’ll abbreviate the convo here but I would love to discuss any of this in more detail.

I asked specifically about the M20M’s dual max POH TIT (1750 max lower altitudes to 1650 max at higher altitude) I just couldn’t wrap my head around why the diff in max temps? The turbo has no idea it’s higher up in the air and temp is temp as fast as the materials are concerned - so why the diff and why don’t we see that on most “other” turbocharged piston airplanes? His answer surprised me and immediately made complete sense.

The 1750 was mentioned early on, but in recent years Lycoming has said that 1650 is maximum period. (see the March 2006 TIO 540 operating handbook).

 

 

[DVA]

The 1750 was mentioned early on, but in recent years Lycoming has said that 1650 is maximum period (green highlighting is Lycomings). (see the March 2006 TIO 540 operating handbook below).

 
Lycoming TIO 540 series operating handbook.pdf

Not arguing anything here with respect to how an owner decides to operate his to her own aircraft. Could not agree more that cooler is better - but fact is the POH is the definitive source for the operation of the aircraft and the engine installed. Many parameters are changed, limits increased or decreased etc based on the manufacturer's design criteria. That includes the operation of the engine installed.

The POH states 1750dF within limits. When there is a discrepancy between the EOM and the POH, the POH wins.

If you ask Lycoming what the max TIT is for the TIO540-af1b installed in the Mooney M20M they will tell you to reference the POH.

Best regards,
Dave



Sent from my iPhone using Tapatalk

[LANCECASPER]

On 1/28/2018 at 8:20 PM, DVA said:

 

Not arguing anything here with respect to how an owner decides to operate his to her own aircraft. Could not agree more that cooler is better - but fact is the POH is the definitive source for the operation of the aircraft and the engine installed. Many parameters are changed, limits increased or decreased etc based on the manufacturer's design criteria. That includes the operation of the engine installed.

The POH states 1750dF within limits. When there is a discrepancy between the EOM and the POH, the POH wins.

If you ask Lycoming what the max TIT is for the TIO540-af1b installed in the Mooney M20M they will tell you to reference the POH.

Best regards,
Dave



Sent from my iPhone using Tapatalk

 

Lycoming or Mooney or the FAA may very well say that, but thankfully this is an owner forum where we fly the airplanes and pay for the repair bills and have come to realize that in 1989 when the airplane was certified and the POH was written there wasn't any long-term, real-world data on a newly certified engine.

Twenty nine years later there's a lot of cylinders, TIT probes and exhaust systems that were pre-maturely put out of service so that we now know better. Any owner who runs the "POH approved" 1750 TIT or 500 CHT or 245 Oil Temps gets  the privilege of paying for the new engine, not Lycoming or Mooney. Any of those temperatures cause the original valve guide material to go away in 100-200 hours. Before finally going to the wet-head they even developed another valve guide for some of the early TIO-540-AF1A owners that had a much higher chromium content. It still didn't last 200 hours at the POH numbers.

During 1991-1993 after problems started with the valve guides, Lycoming publicly, at seminars, recommended 1650 TIT, but didn't put it in print. This took the range of the TLS below numbers that marketing wanted and caused Mooney President Jacques Esculier to scrap Lycoming engines from future airplanes on the drawing board. (He left Mooney pre-1995.)

The owner forums that were held once a year at the MAPA convention back in the 90's that Mooney and Lycoming engineers attended provided much of the feedback needed that led to the Bravo "wet-head" conversion. I did not own a TLS in the early 90's but a 231, but I still sat in on the M20M forum, since I wanted to move up to a TLS eventually. At all of the M20M seminars I attended from '93 on, owners were told by the Lycoming rep not to run over 1650 TIT and some owners were still saying that the POH said 1750 and they were going to fly them that way.

Finally in 1996 when flight testing and engine tear downs showed that the </=1650 temps and the oil cooled valve guides were working - Service Instruction 1479 came out introducing the Bravo "wet-head" conversion. This allowed owners to stand a chance of making it to TBO. The first airplane to get the wet-head conversion was serial number 209 (N9153Z). The president of Mooney, Bing Lantis, was flying this one back and forth to his home in CA. (After not much more than 100 hours operating it at "marketing TIT", it was using a quart every 5 hours.)  I bought it as a "factory demonstrator" in September 1996, after the wet-head conversion. 

Lessons learned have caused Lycoming to amend their recommendations on other TIO-540 engines as well. As late as 2006 Lycoming was saying in seminars such as MMOPA (Malibu/Mirage Owners and Pilots Associtaion) to run no higher than 1650, but in print they were still saying that 1750 was recommended TIT on the TIO-540-AE2A which is used in the Piper Mirage. However in 2009 they finally printed this recommendation for that engine:

, 

So, do what you want - yes, you are legally able to operate your aircraft according to the POH (if there's no revision). But personally I think it's wise to consider the (1) shorter engine life (2) shorter TIT probe life, which is particularly bad since then your TIT reads artificially low (3) shorter exhaust life and (4) possible shorter life expectancy (a strong argument could be made that the M20M accidents where v-clamps gave out and the exhaust burned through the firewall and killed the occupants happened because the clamps and the exhaust gaskets they were holding were heated beyond what they were designed for).

 

 

[Knuckledragger00]

Once you have set LOP and your altitude, MP or RPM have not changed is it necessary to recalibrate LOP after say an hour or so or can you just leave it alone?  Just wondering what changes in OAT would do to settings and if that requires readjustment?

[carusoam]

If things drift... it is an artifact of the turbo bootstrapping.

Are you familiar with turbo ops in general? Related to how to avoid MP overshoots.

The Bravo engine is pretty well refined in terms of upper deck pressure control...

The only thing the Bravo didn’t get was nicely balanced air intake tubes... LOP is possible with the Bravo.  Often, people describe smooth operation of the Bravo engine, LOP, occurs at a power setting too low to make desirable...

Bravo lovers often prefer fast flight over efficient flight...

Do as much reading on the subject as you can. there isn’t much written on the topic compared to other Mooneys...

For comparison see pictures of Continental twin turbos and curvy intakes to go along with the pair of inter coolers...

watching TIT and CHTs are important skills.  Air cooling in the thin air can be challenging under high power settings...

Getting good Transition Training from a Bravo owner probably saves a few AMUs... want a recommendation?

Best regards,

-a-

[Knuckledragger00]

Car,

This is my first turbo so no I am not very experienced with them.  Have read a lot about it and actually ran LOP for the first time ever from Las Vegas to Central Oregon a few days ago.  Was down as low as I could be due to strong headwinds.  Flew back at 10,500 and 20 degrees LOP.  Running at 29 & 23 I saw FF at 12.8 which seems amazingly low.  TIT was just over 1600 and CHT hightest was 385.  

 

[donkaye]

45 minutes ago, Knuckledragger00 said:

Car,

This is my first turbo so no I am not very experienced with them.  Have read a lot about it and actually ran LOP for the first time ever from Las Vegas to Central Oregon a few days ago.  Was down as low as I could be due to strong headwinds.  Flew back at 10,500 and 20 degrees LOP.  Running at 29 & 23 I saw FF at 12.8 which seems amazingly low.  TIT was just over 1600 and CHT hightest was 385.  

 

Good luck running LOP on the Bravo, however, if you should do it, here is the spreadsheet showing power at various fuel flows.

 

LOPFFvsHP.xls