M20K Fuel Flow, CHT and Power Settings

[KLRDMD]

I've had my 231 about six weeks and just took it for the first trip of any significance.

My first question, what cylinder is the factory CHT probe on ? 1985, serial # 25-878, the normal LB engine. My #3 CHT temperature is limiting everything I do with the airplane and I'm wondering if the factory CHT probe is there and the JPI probe for #3 is on the spark plug. In another airplane it was and the spark plug probe read 50º higher than after I placed it into the same area as the other CHT probes with a relocation kit. The other five cylinders are 45-70º cooler than #3. My TIT was running around 1450 and EGTs were in the 1300-1400 range so I seem to be plenty cool in other parameters.

I have to climb at significantly reduced power and climb rate to keep #3 under 400º in climb. I was at gross, but it was cool and starting at sea level. Also, to keep the #3 below 380º in cruise I have to fly at more reduced power than I want. I haven't looked that closely at it yet but the Continental TSIO-360-LB engine is a 7.5:1 compression ratio. 65% power LOP should be exactly 10.0 GPH. I have to run 9.0 GPH to keep the temperatures under control (30", 2500 RPM, 9.0 GPH, 380 CHT). That's 59% power according to the calculations. At 9,500 ft I was getting 158 KTAS (based on the TAS dial on the factory A/S indicator which seems reasonable).

Thoughts ?

[milotron]

On my 1981 20K the factory sensor is on #5 and was doubled up in the same well with the JPi sensor. It tends to read about 30 deg lower than the rest.  Does your #3 have the spark plug sensor on it?

 

How much cowl do you have open? I have the 252 mod, but even then I need about 25% cowl opening to maintain the highest CHT ( #2 on mine ) below 380, even at 65% power when above 6000 feet or so. Better when LOP, at 65% HP fuel flow, but gets worse the higher I get.  Your TIT is much lower than mine at that power setting; I tend to be in the 1550-1600 range when LOP.

 

I am always way cool in the climb when full rich. Cruse climb at 700fpm or more and it will get quite hot unless I richen it up or put the nose down a bit.

 

I have only had mine for 6 months, so still definitely on the learning curve.

[KLRDMD]

Just now, milotron said:

On my 1981 20K the factory sensor is on #5 and was doubled up in the same well with the JPi sensor. It tends to read about 30 deg lower than the rest.  Does your #3 have the spark plug sensor on it? How much cowl do you have open? I have the 252 mod, but even then I need about 25% cowl opening to maintain the highest CHT ( #2 on mine ) below 380, even at 65% power when above 6000 feet or so. Better when LOP, at 65% HP fuel flow, but gets worse the higher I get.  Your TIT is much lower than mine at that power setting; I tend to be in the 1550-1600 range when LOP. I am always way cool in the climb when full rich. Cruse climb at 700fpm or more and it will get quite hot unless I richen it up or put the nose down a bit. I have only had mine for 6 months, so still definitely on the learning curve.

I don't know which cylinder has the factory probe on it and therefore if my high CHT #3 can be explained away by being a spark plug sensor on the JPI. I hope it is.

I think I'll change the oil on Tuesday so will know more once I get a good look at everything under the cowl, including the baffling. I have cowl flaps full open in the climb. In cruise I can have them fully closed at 9,500 ft, 59% power LOP and keep the CHT below 380º. I haven't gone above 9,500 ft yet; I have a leak in my oxygen system that I need to get fixed.

I thought I wanted to run 65% power LOP since that's what I've done in most of my airplanes but I'm not sure if I want to add 1 GPH (a 10%+ increase in fuel flow) to get 6% more power (from 59% to 65%) as it will probably give me less than 5 KTAS increase (theoretically).

[N231BN]

How tight are your cowl flaps when they are closed? One of the main problems with the 231 is cooling exit area. Your mechanic should be able to adjust them so they are open about an inch. 10 GPH LOP should be no problem with normal temps.

I don't remember if they moved the CHT to #3 on the -LB's or not until the 252.

[KLRDMD]

34 minutes ago, N231BN said:

How tight are your cowl flaps when they are closed? One of the main problems with the 231 is cooling exit area. Your mechanic should be able to adjust them so they are open about an inch. 10 GPH LOP should be no problem with normal temps. I don't remember if they moved the CHT to #3 on the -LB's or not until the 252.

 

Closed are completely closed now, I can ask to open them up an inch.

[N231BN]

That will make a huge difference. This thread has lots of good info on operating the 231:
http://www.mooneyspace.com/index.php?/topic/9165-M20K---Leaning-and-Engine-Temp-Practices

[DonMuncy]

Ideally, I think you need a summer setting and a winter setting on your cowl flap adjustment. But I suspect Tucson is like Dallas, in that it is hard to know when the season is over.

[Zwaustin]

Factory probe is on number 5 cylinder. Typically this will lead to it reading higher not lower temps but depends on where it is mounted. Should read hotter on bottom and lower on top. This is especially true if you have a JPI set up and this is on their website. 

As for take off temps is your fuel flow set up properly? You should be able to see about 24 GPH on full power take off and 18 gph in cruise climb. My intercooler install manual requires 27GPH on full power for ground run and asks that it be leaned to 24.9 for take off, this almost always keeps it cool in climb. I climb at about 105 knots indicated depending on the temperature outside and most CHT's are usually in the low to mid 300's with number 2 and number 5 being my hottest (up to 360 degrees) and number 6 being my coolest (in the 200's). Climb TIT is roughly 1400. In cruise CHT's vary with altitude but I can usually keep them all at or below 360 degrees but have seen higher up to 380's on number 2 and number 5 when hot, humid, high and heavy. My TIT in cruise is usually about 1550 at 70 percent power 30 degrees LOP (plane doesn't like to run leaner than that even with GAMI's) and my EGT if I recall correctly usually run high 1400's. 

If you are concerned about the difference in your CHT's I wouldn't stress much about it but check your baffling. This engine compartment is not known to be the coolest running set up nor was the LB engine. It runs fine with proper care, a good waste gate and an intercooler and will get the job done.

The higher you go the hotter it will run especially above 18k feet. Down hesitate to pull the cowl flaps and try to keep temps under 380 at all times and preferably 360 if able...

Enjoy your new bird. 

[KLRDMD]

4 hours ago, Zwaustin said:

Factory probe is on number 5 cylinder. Typically this will lead to it reading higher not lower temps but depends on where it is mounted. Should read hotter on bottom and lower on top. This is especially true if you have a JPI set up and this is on their website. As for take off temps is your fuel flow set up properly? You should be able to see about 24 GPH on full power take off and 18 gph in cruise climb. My intercooler install manual requires 27GPH on full power for ground run and asks that it be leaned to 24.9 for take off, this almost always keeps it cool in climb. I climb at about 105 knots indicated depending on the temperature outside and most CHT's are usually in the low to mid 300's with number 2 and number 5 being my hottest (up to 360 degrees) and number 6 being my coolest (in the 200's). Climb TIT is roughly 1400. In cruise CHT's vary with altitude but I can usually keep them all at or below 360 degrees but have seen higher up to 380's on number 2 and number 5 when hot, humid, high and heavy. My TIT in cruise is usually about 1550 at 70 percent power 30 degrees LOP (plane doesn't like to run leaner than that even with GAMI's) and my EGT if I recall correctly usually run high 1400's. If you are concerned about the difference in your CHT's I wouldn't stress much about it but check your baffling. This engine compartment is not known to be the coolest running set up nor was the LB engine. It runs fine with proper care, a good waste gate and an intercooler and will get the job done. The higher you go the hotter it will run especially above 18k feet. Down hesitate to pull the cowl flaps and try to keep temps under 380 at all times and preferably 360 if able...

I'm heading out to the airport now to do an oil change. While the cowl is off I can verify the factory CHT placement and look closely at the baffling. I'll also get the shop to adjust the fuel flow to 25 GPH on takeoff. I'll clean and gap the plugs too and verify magneto timing if we have time. Wednesday I have a flight so I can see what the results are of the changes we make.

[Marcopolo]

Am I missing something here?

 

  My POH (1981 M20K, no intercooler) shows 30" x 2500rpm x 9500' to be just about 71% power.  Is it the 9.0gph that changes the percentage by so much or just the intercooler on the OP's model?

 

Curious,

Ron

[Pritch]

On my 84k the factory probe is on #3 with the JPI piggybacked there.  Have just installed the JPI and still getting use to it, so the included pictures are not well defined yet.  The #3 always runs cooler

Pritch

[KLRDMD]

4 hours ago, Marcopolo said:

Am I missing something here? My POH (1981 M20K, no intercooler) shows 30" x 2500rpm x 9500' to be just about 71% power.  Is it the 9.0gph that changes the percentage by so much or just the intercooler on the OP's model?

Your 71% power figure is not at 9.0 GPH, correct ?  I think you're missing the difference between LOP and ROP.  LOP, power is determined exclusively by fuel flow.  For a 210 HP engine with a compression ratio of 7.5:1, 9.0 GPH is 59% power. 10.0 GPH is 65% and 11.5 GPH is 75% power. Personally, I cruise at 65% power or below and I prefer to "turbo normalize" my airplane versus turbocharge it in cruise so I like 30"MP in cruise. 30", 2500 RPM and 9.0 GPH is 59% power LOP. Excel file attached.

LOPFFvsHP calculator.xls

[KLRDMD]

I changed the oil and filter today. Cylinders #1, 2, 3, 4 & 5 have the CHT probes on the spark plugs and #6 has the probe on the cylinder. The factory CHT probe is on #5. Cylinders #1, 2, 3 & 4 have a Tannis heater installed in on the cylinder. The baffles look good with one area that may need a slight touch up but it isn't near my high temperature cylinder #3. At 37", 2700 RPM I was getting 21 GPH. I had my mechanic tweak it and it came up to 23.6 GPH. He tweaked it again and it went to 26.2 GPH. I told him to leave it there and I'll fly it a while. My intercooler chart suggests a maximum fuel flow of 24.9 GPH so I'm OK a bit rich.

I'll fly tomorrow and also try Paul's recommendation from a different thread of climbing at 37" and 2700 RPM versus the POH recommendation of 33" and 2600 RPM.

[Zwaustin]

4 minutes ago, KLRDMD said:

I changed the oil and filter today. Cylinders #1, 2, 3, 4 & 5 have the CHT probes on the spark plugs and #6 has the probe on the cylinder. The factory CHT probe is on #5. Cylinders #1, 2, 3 & 4 have a Tannis heater installed in on the cylinder. The baffles look good with one area that may need a slight touch up but it isn't near my high temperature cylinder #3. At 37", 2700 RPM I was getting 21 GPH. I had my mechanic tweak it and it came up to 23.6 GPH. He tweaked it again and it went to 26.2 GPH. I told him to leave it there and I'll fly it a while. My intercooler chart suggests a maximum fuel flow of 24.9 GPH so I'm OK a bit rich.

I'll fly tomorrow and also try Paul's recommendation from a different thread of climbing at 37" and 2700 RPM versus the POH recommendation of 33" and 2600 RPM.

That fuel flow will make a difference. Do you have an airflow systems intercooler? If so max power is at 37/2700 whereas cruise climb is 31/2600 and the POH must be supplemented with the IC power chart. Many people will argue to climb all day long at full power to keep things cooler on the LB engine. After all the engine is rated for continuous redline power. I have posted the airflow systems power schedule along with fuel flows on here prior so you can grab it if needed. If you can't find it let me know and i can send to you.

[KLRDMD]

1 hour ago, Zwaustin said:

That fuel flow will make a difference. Do you have an airflow systems intercooler? If so max power is at 37/2700 whereas cruise climb is 31/2600 and the POH must be supplemented with the IC power chart. Many people will argue to climb all day long at full power to keep things cooler on the LB engine. After all the engine is rated for continuous redline power. I have posted the airflow systems power schedule along with fuel flows on here prior so you can grab it if needed. If you can't find it let me know and i can send to you.

Yes I have the Airrflow Intercooler. I'll try Paul's recommendation of climbing at 37/2700 tomorrow and se what I think. I'm also flying Wednesday.

[Marcopolo]

12 hours ago, KLRDMD said:

Your 71% power figure is not at 9.0 GPH, correct ?  I think you're missing the difference between LOP and ROP.  LOP, power is determined exclusively by fuel flow.  For a 210 HP engine with a compression ratio of 7.5:1, 9.0 GPH is 59% power. 10.0 GPH is 65% and 11.5 GPH is 75% power. Personally, I cruise at 65% power or below and I prefer to "turbo normalize" my airplane versus turbocharge it in cruise so I like 30"MP in cruise. 30", 2500 RPM and 9.0 GPH is 59% power LOP. Excel file attached.

Gotcha KL, thank you for the spreadsheet, nice tool.

[carusoam]

%ROP power numbers are tough to get correct...  the percentage of fuel that gets used for cooling vs. power is not easily detected.  Different instrument suppliers may use a different calculation...

 

%LOP power numbers are easier to use... but the calculation detail also requires the compression ratio of the engine.

 

If you are using Ken's chart, make sure you verify the CR is the same for your engine.  TC'd engines usually use a lower CR than TN'd and NA engines...

PP knowledge only, not a mechanic...

Best regards,

-a-

[KLRDMD]

Just now, carusoam said:

If you are using Ken's chart, make sure you verify the CR is the same for your engine.  TC'd engines usually use a lower CR than TN'd and NA engines...

It isn't my chart, someone else created it, I just passed it along. You can Google the compression ratio of your engine and change that parameter on the spreadsheet and it will repopulate the entire spreadsheet for you.

[carusoam]

Siri told me that the CR for the IO550 is 8.5:1

The Lyc O540 uses 8.7,. A turbo version of the 540 is 7.3:1

Continental  TSIO360 uses 7.5:1

 

These are All wiki details, not actual fact.  But it does illustrate the importance of using the proper CR for the engine to determine %hp while LOP.

Best regards,

-a-

[KLRDMD]

On 10/17/2016 at 4:33 PM, KLRDMD said:

The baffles look good with one area that may need a slight touch up but it isn't near my high temperature cylinder #3. At 37", 2700 RPM I was getting 21 GPH. I had my mechanic tweak it and it came up to 23.6 GPH. He tweaked it again and it went to 26.2 GPH. I told him to leave it there and I'll fly it a while. My intercooler chart suggests a maximum fuel flow of 24.9 GPH so I'm OK a bit rich. I'll fly tomorrow and also try Paul's recommendation from a different thread of climbing at 37" and 2700 RPM versus the POH recommendation of 33" and 2600 RPM.

On takeoff today full rich, full power was 28+ GPH. It wasn't climbing well until I leaned it back to 25 GPH. I've asked my mechanic to turn that down closer to 25 GPH tomorrow. Yesterday I also looked very closely at the baffles. Generally the baffles were in very good shape except for the rear (looks like a firewall). I sealed probably four square inches of leaks, one leak itself was about two square inches.

I climbed at full power to altitude today, 2700 RPM, 37", 120 KIAS, 800 FPM and 25 GPH. The hottest CHT is still #3 but today #3 never got above 350º and generally was running around 330º in climb. Sunday I was lowering the nose to 200 FPM and pulled power back to 2500 RPM and 30" in an attempt to keep #3 CHT below 400º. What a difference !

Cruise was the same, 30", 2500 RPM and 9.0 GPH for 59% power LOP. That seems to be what this airplane likes. I'm getting +/- 160 KTAS in the 10,000 ft range. I'm happy with that.

[KLRDMD]

Today I had my mechanic adjust the fuel flow to 25 GPH when at full power. Now I have just two more squawks and I'm good. When I bought the airplane the Shadin fuel flow wasn't hooked up to the 530W so when I swapped the 530 for the Avidyne 540 it didn't get hooked up either. Also when I bought the airplane the oxygen tank was timed out. The seller agreed to buy me a new one. I had it installed but there's a leak somewhere. Hopefully both of those will be addressed next week when I'm out of town.

[carusoam]

While connecting the JPI...

- Fuel level

- Fuel flow

- GPS 

 

This connects fuel to distance and will help keep you from running out of fuel before you get there.  Having the snazzy new digital fuel level floats would be a nice touch of modern accuracy...

Best regards,

-a-