M20K Power Settings..?

[CoffeeCan]

Need some advice here from you more experienced Mooniacs, particularly the turbo drivers.  I’m 6 weeks and 47 hours into my new-to-me M20K, and the learning curve isn’t quite so steep now as it was. I’m currently studying engine settings and I’m a tad unsure about where my climb and cruise settings should be.  

My airplane is a 1985 M20K, recently purchased from Jimmy and David at All American in Spring Branch, TX.  The engine had total overhaul 135 hours ago, and is equipped with an intercooler and Merlyn wastegate with GAMIjectors. It has a JPI installed, but lacks fuel flow and oil temperature transducers... my local avionics shop is a JPI dealer and will be installing those in September. 

My question stems from an article on the MAPA website, I’m unsure of the author... I’m sure y’all are familiar with it. Former Mooney test pilot in the 80’s, when the 231 and252 came out. (Ed ?)

Ive been using the POH data card for my cruise and climb power settings to date, but I’ve been bothered by the high oil temps I’m seeing on my panel (analog, noncalibrated) oil temp gauge.  POH says cruise at 75% power is 30.7” and 2500RPM for 173 KTAS at 12,000 MSL. I’m getting closer to 178 KTAS with those numbers, which brings me to think I’m running the engine too hot. I  have to run ROP-TIT by 125 degrees or more (which means I’m burning 12+ gph) to keep oil temps in the green, and cowl flaps half open unless OATis under 10 C. The MAPA article says that with an intercooler I should be running at 28” and 2500 and mixture at 50 degrees ROP, or I’ll overstress the engine.  Makes sense, I guess. But it also says with a wastegate I can run at factory settings, 31” and 2500, and 50 degrees ROP TIT. I’m equipped with both intercooler and Merlyn wastegate, so which recommendation  should I be following for best cruise power without burning up my cylinders?

Which the brings up the next question... can I and should I be running this engine LOP? I ran my 172 XP’s Continental IO-360 at 25 degrees LOP, and it was a beautiful thing.  I am reading contradictory recommendations on LOP for the 231 on the innanet, so want to pick y’all’s brains.  

Thanks in advance for the opinions. 

[Bryan]

I started with a 231 and now a 252 Encore from AAA.  Can you run LOP - YES, you can, if you can:)  I am trying to get there now but my GAMI spread is preventing me at the moment.  My 231 before would easily get there.  I would say wait until you get your FF installed before you start because you really need to know your FF spread.  What type of JPI do you have installed today?

My 231 had an Insight G2 with FF and the 252 I have now had a EDM 700 with a Shadin FF.  I upgraded it because it was easy and cheap to an EDM 830 (adding JPI FF, MAP, RPM) which gives me all the parameters I need without major surgery for the EDM 900 - I want.

Here is a card that my 231 had and I still use it today sometimes when planning.  To be honest, I use the JPI 830 (with %HP, FF) along with the other temps for flying today.  I set a particular profile I want to run: 75% ROP, 65% LOP.  I download the data an upload to savvyanalysis.com.  I have already realized using this data my ignition system was not as healthy as it should be.  I just went to tempest fine-wires and will be installing GAMI's next. Data is powerful.

 

 

[milotron]

Nice chart.  Does your 252 have the SB or MB engine? 

Are those fuel flows based on LOP or ROP or book 50 degree ROP values?

 

iain

[CoffeeCan]

Bryan, that chart is awesome. Was that made with an intercooled engine?  Thanks. 

Edited August 18, 2018 by CoffeeCan

[Bryan]

This chart was from my 231 with a Merlin WG and Intercooler. ROP if I remember right, but you could lower the FF for the 65% and below to get to LOP on my 231.

My Encore has a SB engine. A standard 252 that gets converted to an Encore will get that designation. The SB engine changes several things including max MP (39”), max rpm (2600), and higher max FF (26gph)

[gsxrpilot]

I fly a 252 with the MB engine so my numbers might not help you that much. But I'd say for any engine, get a good engine monitor then learn how to read it and use it. These engines are too expensive not to.

On the climb out, I'd leave throttle, prop, and mixture where they are for take off, all the way to your cruise altitude. Then after you level off and it builds some speed, back the power/prop/mixture down to at least 75% power or lower. If going LOP, I back down to 65% power. My 252 runs very well LOP at 9.6 gph and 65% power.

[CoffeeCan]

Bryan, my JPI monitor is an EDM 830.

[jlunseth]

FIrst, on whether you should use fuel flow settings published for the Merlyn, or those published for the intercooler, here’s how that works.  The Merlyn does not change your fuel flow settings from factory.  You can distill the Merlyn’s effect down to two things.  One, it prevents bootstrapping, so once you make a power setting it will stay stable.  Two, it allows the wastegate to fully close, which the factory wastegate could not do, and that, in turn, gives you a higher critical altitude (the altitude at which the engine can no longer make full power).  The Merlyn probably allows the turbo to work a little less hard, but it does not change fuel and MP settings.  

The intercooler changes power settings.  The intercooler cools the discharge air from the turbo, which makes the air denser.  Denser air has more molecules of O2.  Therefore, MP for a given %HP (on the rich side) is lower that the factory equipped engine, for a given %HP power setting. The charts that are published with the intercooler are based on using the difference between Compressor Discharge Temp and Induction Air Temp, or differential temp.  You make your power setting based on how much cooler the IAT is from the CDT.  

So you should use the intercooler power settings.  Now, I have the Merlyn and the intercooler, and most people with experience with that set up will tell you that the power setting charts for the intercooler are a little conservative.  If it says, for example, to use 28” to be equivalent to a non-intercooled 31 or 32”, probably 29 or 30 is the right setting.  The article you read is probably the one that says find a 252 chart and use that.  That will work ok, but I think you will find the MP settings are about an inch too low if you do it that way.

I operate LOP quite a bit.  However, if you are planning on putting in a JPI, then wait until you have a good engine monitor to do it, because you can toast a cylinder or two pretty easily and without knowing what is happening, if you are relying on a single cylinder’s EGT only, or just on TIT.  To operate LOP, you have to treat each of the six cylinders as a single engine, and you have to make sure that the cylinder closest to peak EGT, is far enough away from peak EGT that it is not being damaged.  If you only have a single cylinder EGT readout, or just the TIT readout, then you can have, say, four cylinders far enough lean of peak to be safe, and one or two running right at peak or even a little rich of peak, which is not good for them.  Once you have your engine monitor you can do a lean test (see GAMI’s website for how to do that) and figure out if your engine can do LOP or needs some tweaking.

I have a JPI 930.  What I have found with my engine is that any cruise power setting that has a 12 in it, is the wrong place to be.  It is called the “red box” by people who know LOP operations.  I know the POH has lots of 12 something power settings.  It also has a CHT redline of 460 dF.  You should never be anywhere near 460.  The magic Rich of Peak fuel flow in my aircraft is 13.3 GPH.  Use that and 29 or 30” of MP until you get your engine monitor.  I usually run at 2450, but that is my own superstition, I just like the number for my aircraft, if you want to run at 2500 feel free.

Edited August 18, 2018 by jlunseth

[CaptRJM]

I also have a 231 with Turbo Plus Intercooler and Merlyn.  I agree, it is best to run with a good engine monitor ... IMHO at least a JPI 830 with fuel flow.  This will make your life a whole lot easier and possibly prevent you from accidentally damaging the engine.  Not knowing when all the cylinders are LOP will cause you problems as you could easily be running 1 or 2 cylinders at peak. Turbo motors last the longest when handled smoothly and with low CHTs.  I personally avoid 390+ degrees at all time.  Until you get the JPI, I would err on the side of caution and run a little overly rich.

When I purchased my plane it did not have the intercooler.  From experience I can tell you that it drops about 2" of Manifold Pressure at cruise altitude. I typically run LOP; 28"; 2500 RPM at 9.9 GPH which gives me 65% power. In the mid/upper teens I cruise at 170-175 Kn at that power setting.  CHTs are in the 340-350 range except for #6 which is around 300.  Continental does not recommend LOP operations above 65%.

If your engine runs rough LOP (mine did initially), contact the boys at GAMI and send them the downloads from the JPI.  They will tell you what injector(s) need to be removed and  recalibrated.  I had 2 injectors that ran much too rich.  The previous owner installed them and were not in warranty.  GAMI fixed both for $100 and gave me another 2 year warranty on all injectors for free.  Now all 6 cylinders come in LOP within 1/4 turn of the mixture with a GAMI spread of 0.1 GPH.  Couldn't be happier !!!

I have a 252 Power chart that you can use as a guideline.  If you want it, PM me.  I would also contact the manufacturer of the intercooler for all the proper documentation if you don't have it.  

[CoffeeCan]

2 hours ago, jlunseth said:

....So you should use the intercooler power settings.  Now, I have the Merlyn and the intercooler, and most people with experience with that set up will tell you that the power setting charts for the intercooler are a little conservative.  If it says, for example, to use 28” to be equivalent to a non-intercooled 31 or 32”, probably 29 or 30 is the right setting.  The article you read is probably the one that says find a 252 chart and use that.  That will work ok, but I think you will find the MP settings are about an inch too low if you do it that way.

I operate LOP quite a bit.  However, if you are planning on putting in a JPI, then wait until you have a good engine monitor to do it, because you can toast a cylinder or two pretty easily and without knowing what is happening, if you are relying on a single cylinder’s EGT only, or just on TIT.  To operate LOP, you have to treat each of the six cylinders as a single engine, and you have to make sure that the cylinder closest to peak EGT, is far enough away from peak EGT that it is not being damaged.  If you only have a single cylinder EGT readout, or just the TIT readout, then you can have, say, four cylinders far enough lean of peak to be safe, and one or two running right at peak or even a little rich of peak, which is not good for them.  Once you have your engine monitor you can do a lean test (see GAMI’s website for how to do that) and figure out if your engine can do LOP or needs some tweaking.

I have a JPI 930.  What I have found with my engine is that any cruise power setting that has a 12 in it, is the wrong place to be.  It is called the “red box” by people who know LOP operations.  I know the POH has lots of 12 something power settings.  It also has a CHT redline of 460 dF.  You should never be anywhere near 460.  The magic Rich of Peak fuel flow in my aircraft is 13.3 GPH.  Use that and 29 or 30” of MP until you get your engine monitor.  I usually run at 2450, but that is my own superstition, I just like the number for my aircraft, if you want to run at 2500 feel free.

jlunseth... Thanks for your detailed reply. And yes, that is the article I was referencing. Your recommendation of about 29-30" MP and 2450-2500 RPM is where my initial CFI advised me to run, if I recall correctly, in my initial training in this aircraft. 

I do have a JPI already (EDM 830), it just doesn't  have the fuel flow and oil temperature transducers installed yet. On the extended trip I took in my 231 last week (2200 NM over 4 days) I was watching EGT's and CHT's on all 6 cylinders, and they seemed to be running very uniformly. CHT's were in the mid-300's IIRC, but I haven't figured out the download process yet. Sounds like learning that and getting the Savvy app running are steps I need to take in the near future. 

Interestingly, I found 13.3 GPH seemed to be the "sweet spot" for maintaining 75% power and oil temps in the green range on the analog oil temp gauge, with a TIT of just above 1400. 

[Bryan]

If you have an EDM 830, between the two buttons is a cover for a USB stick. Plug a USB in there when it is powered on and a menu item will pop up and ask you to download. From there, a file will be placed on your USB. Take that to a computer and go to the Savvy website, setup a free account and upload that file to the Savvy dashboard and use their tools to look at your data.

[topsun1]

Rutherford Mooney 1152G Merlyn Intercooler Power Settings.pdf

 

I also have the Merlyn waste gate and Airflow Systems intercooler.  This PDF is their recommended power settings.

 

Enjoy your bird!  We have for 12 years now. 

[jlunseth]

PS when you get your JPI installed and start experimenting with LOP, its worth knowing that even fuel flows are not the only key to LOP operations. LOP requires good ignition.  Over time, I went to fine wires, changed the spark plug harness, and I keep my mags in good shape.  If the engine starts getting a little rough at LOP, the plugs and mags are the first place to look.

[gsxrpilot]

5 minutes ago, jlunseth said:

PS when you get your JPI installed and start experimenting with LOP, its worth knowing that even fuel flows are not the only key to LOP operations. LOP requires good ignition.  Over time, I went to fine wires, changed the spark plug harness, and I keep my mags in good shape.  If the engine starts getting a little rough at LOP, the plugs and mags are the first place to look.

Well said... and easy to diagnose with a good lean, in flight, mag check. Normalize the display on the JPI for best indications.

[jlunseth]

“ I was watching EGT's and CHT's on all 6 cylinders, and they seemed to be running very uniformly.”

That’s a good sign.  Just be aware that having all EGT temps be approximately the same does not necessarily mean that the fuel flows are even. EGT is a relative temp, we don’t care what the absolute number is very much.  There will virtually always be EGT differences because of placement of the temp probes.  They are not all the same distance from their respective exhaust port because of obstructions or the shape of the particular pipe.  What is important is the fuel flow at which EGT for each cylinder hits peak.  You want them peaking within .5 GPH of each other.  That’s the GAMI lean test.  If you have differences bigger than that, then you want to start by getting the injectors clean, test again, and if they are still out of line, GAMI is usually pretty good about swapping injectors. One thing that sometimes happens with 231’s that have been around awhile, is that not all mechanics pay attention to the fact that each injector belongs to a particular cylinder.  The injectors are supposed to have metal tags for their cylinder.  They are not interchangeable.  If someone, somewhere along the way, did not pay attention to that and moved the injectors around, well, they are GAMI injectors alright, they are just not doing what GAMI designed them to do.  

[Oldguy]

If you go to Savvy, I recommend getting the Pro pack for the first year and have them do the analysis on the data you upload. Specifically, they have a diagnostic flight test profile to check out the items mentioned in the posts above that once you execute and load the data into their site, they can do a fairly thorough analysis of many aspects of your engine. I find is especially helpful about two weeks prior to my annual to point my mechanic in the direction of anything that shows up in their report. @kortopates can enlighten you a bit more on this, if he is around.

[Bryan]

Agree on the Pro version, I am doing the same now.

Here is what they recommend for testing for LOP operations: https://www.savvyanalysis.com/articles/in-flight-diagnostics

[Parker_Woodruff]

Steps to LOP in the M20K

- Make sure the induction system has no cracks or leaks

- Get Tempest Fine Wire spark plugs

- Do a GAMI lean test

- Get GAMI Injectors

- You may need to set up the fuel flows again after all this is done.

 

@don.muncy and I were cruising along at ~65% power in his 1982 M20K over the weekend and still had economical performance despite having to stay low for summer cloud buildups.

6500' MSL

30", 2600 RPM, 10 gph (LOP) - 150 KTAS.  Cowl flaps fully closed and all cylinders nice and cool in the Texas summer.

[kortopates]

On 8/18/2018 at 3:36 PM, CoffeeCan said:

jlunseth... Thanks for your detailed reply. And yes, that is the article I was referencing. Your recommendation of about 29-30" MP and 2450-2500 RPM is where my initial CFI advised me to run, if I recall correctly, in my initial training in this aircraft. 

I do have a JPI already (EDM 830), it just doesn't  have the fuel flow and oil temperature transducers installed yet. On the extended trip I took in my 231 last week (2200 NM over 4 days) I was watching EGT's and CHT's on all 6 cylinders, and they seemed to be running very uniformly. CHT's were in the mid-300's IIRC, but I haven't figured out the download process yet. Sounds like learning that and getting the Savvy app running are steps I need to take in the near future. 

Interestingly, I found 13.3 GPH seemed to be the "sweet spot" for maintaining 75% power and oil temps in the green range on the analog oil temp gauge, with a TIT of just above 1400. 

You're getting great advice from John @jlunseth and others here. You mention you have a EDM 830 without FF, but then below you say the sweet spot for you was 13.3 GPH - so I'll assume you a have an independent FF such as the popular Shadin. If so, you don't need a separate FF transducer for the JPI, you just need to get the existing FF transducer wired up to the EDM 830 in parallel with your other FF display unit. Most likely its compatible (the shadin is) and just needs to be wired up so that you'll have downloadable FF data with the rest of your EDM 830 data. FF data is critical to engine diagnosis as well as running LOP. In fact I wouldn't recommend experimenting with LOP ops till you have the FF on your EDM and measure your gami spread to be within satisfactory results (within 0.5 GPH). Also, once you're ready to start downloading data from your EDM be sure to first re-set the data sampling rate from 6 sec default to its fastest 2 sec rate for the 830. The default 6 sec rate won't provide enough data resolution.

Regarding power settings, they don't need to be that complicated. Starting with the intercooler STC guidance, just pick the altitude range you want to optimize and calculate the 75%, 65% and 55% sum or MAP inches and rpm/100 to get whole numbers. For example, for my 252/Encore I use 53, 50, and 47 for 75%, 65% and 55%  ROP power settings respectively. With these number we can use any reasonable combination of MAP and RPM/100 that totals the number. For your intercooled LB the numbers are going to be a bit higher such as 55, 52, and 48 or in that ballpark. Its really not necessary to follow the POH tables that precisely, but its your choice as PIC.

Enjoy your new 231.

 

[gsxrpilot]

5 hours ago, Parker_Woodruff said:

@don.muncy and I were cruising along at ~65% power in his 1982 M20K over the weekend and still had economical performance despite having to stay low for summer cloud buildups.

6500' MSL

30", 2600 RPM, 10 gph (LOP) - 150 KTAS.  Cowl flaps fully closed and all cylinders nice and cool in the Texas summer.

JD (SWTA) and I made a breakfast run to T82 on Sunday morning. It was really a return from annual test flight. This gave us the opportunity to get in a LOP mag check... this verifies the ignition system is in great shape (mags are only about 100 hours old and firing tempest fine wires). 

We were getting almost exactly the same numbers at 6500' MSL. 30", 2500 RPM, 9.6 gph (LOP) - 150 KTAS, Cowl flaps closed. All cylinders nice and cool.

[Parker_Woodruff]

17 hours ago, gsxrpilot said:

JD (SWTA) and I made a breakfast run to T82 on Sunday morning. It was really a return from annual test flight. This gave us the opportunity to get in a LOP mag check... this verifies the ignition system is in great shape (mags are only about 100 hours old and firing tempest fine wires). 

We were getting almost exactly the same numbers at 6500' MSL. 30", 2500 RPM, 9.6 gph (LOP) - 150 KTAS, Cowl flaps closed. All cylinders nice and cool.

Are you still running a 2-blade prop?

[gsxrpilot]

1 minute ago, Parker_Woodruff said:

Are you still running a 2-blade prop?

Yes. The original paddle prop.

[DaveAnderson]

Been running my 231 at > 25LOP at 32" / 2400-2500 @ <= 9gph getting  ~155 true.  I can lean it down to 7.9 or so and it runs just as well.  Gamis, no intercooler (never needed in once in 4 years...ever, at any altitude up to 18-19k), and the JPI EDM 830.  

[jlunseth]

I got my copy of Aviation Consumer today.  There is an article about intercoolers.  It has an excellent explanation of what the effect of an intercooler is, particuarly something we have not talked about here at least for awhile, which is that the structure of the radiator causes a drop in pressure across the intercooler, so that the turbo must work a little harder to generate a given MP.  One thesis of the article was that intercoolers generally do not increase the power produced at a given MP, although they do reduce the IAT significantly.  I don’t know that I completely agree with that entirely, but it does support what most of us find who have the intercooler, and that is that the charts for adjusting MP with the intercooler installed seem to be conservative.

[Warren]

21 hours ago, jlunseth said:

I got my copy of Aviation Consumer today.  There is an article about intercoolers.  It has an excellent explanation of what the effect of an intercooler is, particuarly something we have not talked about here at least for awhile, which is that the structure of the radiator causes a drop in pressure across the intercooler, so that the turbo must work a little harder to generate a given MP.  One thesis of the article was that intercoolers generally do not increase the power produced at a given MP, although they do reduce the IAT significantly.  I don’t know that I completely agree with that entirely, but it does support what most of us find who have the intercooler, and that is that the charts for adjusting MP with the intercooler installed seem to be conservative.

I don't have access to Aviation Consumer but my engine development experience and engineering background disagree completely.  When running stoichiometric or ROP, an engine's power output is based on air consumption.  Air consumption in aviation is primarily determined by MP and RPM.  However volume is only one part of the picture as the combustion process cares about the molecules of O2 available for combustion.  At lower manifold temperatures and similar MP, the same volume of air has a higher density, thus has more oxygen available and can produce more power.  It is true that an intercooler reduces pressure and temperature causing the turbocharger to work a little harder to create the same manifold pressure at a lower temperature.  This is because there is more air being compressed due to the change in density.  More air equals more power.  If you take engine operating parameters from an non-intercooled engine running 150 ROP and add an intercooler while keeping MP constant you have added more air with the same fuel.  You now are closer to peak temperature and risk getting into the "Red Box".  At high power settings this is a risk as you are increasing the engine output and running nearer to peak temperatures.

The intercooler manufacturer guidance or a 252 manual will provide good reference to adjust for the intercooler.  It is critical to make adjustments and not rely on the original 231 settings.

Stoichiometric or ROP, engine power is based on air consumption (density is important) as all the oxygen is consumed which limits the power.

LOP power is based in fuel consumption as all the fuel is consumed and here the fuel limits power.