Cowl Flap Setting

[T. Peterson]

Good evening all,

 I recently purchased a 1979 K model. I have noticed that in the fully closed position the cowl flaps are not flush with the fuselage but still droop about one inch. I called the previous owner to ask if he had the flaps rigged that way to provide better cooling, but he said he had not done so and didn’t realize they were so rigged.

 I am tempted to have my mechanic rig them flush, but am not sure that is wise. Is it possible that this one inch droop is factory set and should not be disturbed? I welcome your informed insight.

Torrey

[jrwilson]

Mine are flush when closed and it is a fairly easy adjustment.  How are your temps when they're closed?  Do you think you need them open a little?  Is it helpful?  With your model, you only have three cowl flap settings, "Closed", "Trail" which is about half open and full open.  If my cowl flaps are fully closed, depending on OAT, my CHT's and oil temp will gradually creep up so I have to open them to Trail.  So maybe a little droop is a good thing, depending on your temps.  

[jrwilson]

13 hours ago, T. Peterson said:

Good evening all,

 I recently purchased a 1979 K model. I have noticed that in the fully closed position the cowl flaps are not flush with the fuselage but still droop about one inch. I called the previous owner to ask if he had the flaps rigged that way to provide better cooling, but he said he had not done so and didn’t realize they were so rigged.

 I am tempted to have my mechanic rig them flush, but am not sure that is wise. Is it possible that this one inch droop is factory set and should not be disturbed? I welcome your informed insight.

Torrey

BTW, that's a fun, aggressive N#   

[201er]

13 hours ago, T. Peterson said:

Good evening all,

 I recently purchased a 1979 K model. I have noticed that in the fully closed position the cowl flaps are not flush with the fuselage but still droop about one inch. I called the previous owner to ask if he had the flaps rigged that way to provide better cooling, but he said he had not done so and didn’t realize they were so rigged.

 I am tempted to have my mechanic rig them flush, but am not sure that is wise. Is it possible that this one inch droop is factory set and should not be disturbed? I welcome your informed insight.

Torrey

Because it not only provides better cooling but also faster that way. But more like 1/2".

 

[kortopates]

13 hours ago, T. Peterson said:

Good evening all,

 I recently purchased a 1979 K model. I have noticed that in the fully closed position the cowl flaps are not flush with the fuselage but still droop about one inch. I called the previous owner to ask if he had the flaps rigged that way to provide better cooling, but he said he had not done so and didn’t realize they were so rigged.

 I am tempted to have my mechanic rig them flush, but am not sure that is wise. Is it possible that this one inch droop is factory set and should not be disturbed? I welcome your informed insight.

Torrey

You most certainly don't want them closed flush. Not only will it cause a heating issue, it will also significantly slow it down. I know the Continental engineer that worked with Mooney on the initial TSIO-360-GB installation. They learned when the cowl flaps weren't open sufficiently that it caused back pressure at the cowl inlets behind the prop that adversely effected the prop thrust much more than the area just in front on the cowling inlets which significantly decreased speed. I may not recall precisely how far open the closed cowl flaps should be but I recall about 1.5" - which is more than the J's, but will refer you to the maintenance manual for the proper rigging.

As in all things in aviation, resist temptation to deviate from the manufacturers guidance/documentation without having really good reason not too such as better data to the contrary.

Good to hear 231FU has a new home. I heard recently this resurrected Mooney was sold. Enjoy your new to you Mooney!

[N231BN]

I agree with Paul regarding cowl flap rigging. The 231's cowl was poorly designed. It has too much inlet area and not enough outlet.

I do adjust mine seasonally to keep oil temps up but a better solution would be a blocking plate for the oil cooler. The 252 has a factory option for that.

[T. Peterson]

Gentlemen,

Thank you very much for your knowledge and advice. I had no idea that was the factory setting. I certainly won’t deviate but I will ask my mechanic to ensure they are measuring IAW with the specifications.

Once again you fellows impress me.

 Thank you!

Torrey

[T. Peterson]

4 hours ago, jrwilson said:

Mine are flush when closed and it is a fairly easy adjustment.  How are your temps when they're closed?  Do you think you need them open a little?  Is it helpful?  With your model, you only have three cowl flap settings, "Closed", "Trail" which is about half open and full open.  If my cowl flaps are fully closed, depending on OAT, my CHT's and oil temp will gradually creep up so I have to open them to Trail.  So maybe a little droop is a good thing, depending on your temps.  

I have not had a problem with over-temp, but that may very well be due to the droop. Also hot summer has not yet arrived. Furthermore, since I am brand new to GA and piston airplanes, I am trying to be very conservative. I can’t get any better than about 12.4 gph at any altitude from 6000 to 13000 feet. My TIT is about 1550 and cylinder temp 340 to 380.  The belly of the airplane is filthy, but that is going to be remedied on the 28th. I thought that maybe the dirt and cowl flaps were costing me, but I guess not. TAS runs between 157 and 162.
The former owner said he got 11 gph at 11000, and I suppose if I pulled MP back I could do better. I cruise at 2500 rpm and 28 inches. 

[Tom 4536]

2 hours ago, T. Peterson said:

I have not had a problem with over-temp, but that may very well be due to the droop. Also hot summer has not yet arrived. Furthermore, since I am brand new to GA and piston airplanes, I am trying to be very conservative. I can’t get any better than about 12.4 gph at any altitude from 6000 to 13000 feet. My TIT is about 1550 and cylinder temp 340 to 380.  The belly of the airplane is filthy, but that is going to be remedied on the 28th. I thought that maybe the dirt and cowl flaps were costing me, but I guess not. TAS runs between 157 and 162.
The former owner said he got 11 gph at 11000, and I suppose if I pulled MP back I could do better. I cruise at 2500 rpm and 28 inches. 

T. Peterson: I have a 1979 M20K-231 with GAMIs, Intercooler, Merlyn and JPI-900. For the 12 months I have been running LOP in cruise mode. At 11,500, my cruise setting have been 30"MP, 2400RPM, 10.9-11.1gph. This results in TAS of 185-190mph, CHT 320-360, TIT 1580, oil temp 180 (winter) 190-200(summer). I live in Tucson.

My plane is at an MSC for annual. I asked the MSC to report back to me as to the engine health after 12 months (200hrs) of running LOP as described above. The MSC reported that the cylinders and valves look excellent and all the compressions are 77-79/80.

Hope this helps with your concerns regarding your engine settings.

[A64Pilot]

Since someone quoted me at the beginning I’ll state what I’ve done, I go for 1/4 inch in Winter and a 1/2” in Summer, that keeps me in the middle or just under in cruise when closed. I run them wide open or fully closed, doesn’t seem to be any need for in between for me. I think I could go with factory setting year round and leave them in trail in Summer, but I want them open as much as I can get in climb in Summer, and adjustment effects both ends so that why I do it.

I’m a NA J model so don’t know how that differs from a K

Cowl flap adjustment is real easy, no safety wire etc involved, just a locknut. But I can’t advise on where the line is as to what a pilot is or isn’t allowed to do.

Edited April 21, 2022 by A64Pilot

[T. Peterson]

1 hour ago, Tom 4536 said:

T. Peterson: I have a 1979 M20K-231 with GAMIs, Intercooler, Merlyn and JPI-900. For the 12 months I have been running LOP in cruise mode. At 11,500, my cruise setting have been 30"MP, 2400RPM, 10.9-11.1gph. This results in TAS of 185-190mph, CHT 320-360, TIT 1580, oil temp 180 (winter) 190-200(summer). I live in Tucson.

My plane is at an MSC for annual. I asked the MSC to report back to me as to the engine health after 12 months (200hrs) of running LOP as described above. The MSC reported that the cylinders and valves look excellent and all the compressions are 77-79/80.

Hope this helps with your concerns regarding your engine settings.

Wow! That’s wonderful performance! I don’t have Gami injectors or an intercooler, though I do have the Merlyn wastegate. Therefore I cannot do the LOP, or so I have been told.

 Thank you for your input! Someday I hope to install those extras and achieve a little better performance. In the meantime my wife and I very much enjoy our new flexibility in being able to visit family! I have never before owned an airplane and it is a blessing notwithstanding a few glitches to overcome!

 I am going to try your power settings and see how that works out, 2400/30.0

Thanks again, 
Torrey

[Tom 4536]

40 minutes ago, T. Peterson said:

Wow! That’s wonderful performance! I don’t have Gami injectors or an intercooler, though I do have the Merlyn wastegate. Therefore I cannot do the LOP, or so I have been told.

 Thank you for your input! Someday I hope to install those extras and achieve a little better performance. In the meantime my wife and I very much enjoy our new flexibility in being able to visit family! I have never before owned an airplane and it is a blessing notwithstanding a few glitches to overcome!

 I am going to try your power settings and see how that works out, 2400/30.0

Thanks again, 
Torrey

T. Peterson: FYI, my LOP cruise engine settings were based entirely on information provided by the very knowledgeable contributors to Moneyspace. The support here has been invaluable.

GAMIs are not expensive. They cost about 1amu and my MSC charged about 3 hours labor. My engine runs smoother and I can run LOP.

[T. Peterson]

4 minutes ago, Tom 4536 said:

T. Peterson: FYI, my LOP cruise engine settings were based entirely on information provided by the very knowledgeable contributors to Moneyspace. The support here has been invaluable.

GAMIs are not expensive. They cost about 1amu and my MSC charged about 3 hours labor. My engine runs smoother and I can run LOP.

Thank you Tom,

My airplane goes to Maxwell in August for an annual. I may just do it then!

[T. Peterson]

2 hours ago, A64Pilot said:

Since someone quoted me at the beginning I’ll state what I’ve done, I go for 1/4 inch in Winter and a 1/2” in Summer, that keeps me in the middle or just under in cruise when closed. I run them wide open or fully closed, doesn’t seem to be any need for in between for me. I think I could go with factory setting year round and leave them in trail in Summer, but I want them open as much as I can get in climb in Summer, and adjustment effects both ends so that why I do it.

I’m a NA J model so don’t know how that differs from a K

Cowl flap adjustment is real easy, no safety wire etc involved, just a locknut. But I can’t advise on where the line is as to what a pilot is or isn’t allowed to do.

Thank you! I appreciate the input. I will measure mine when I get home from this trip. I think my droop is more like an inch and a half. 

[carusoam]

T P,

If not familiar… read up on measuring your Gami spread…

Most Mooney engines are capable of running LOP… M20C and M20M are the most challenging….

The smaller the Gami spread the more likely you will run LOP… without Gami injectors…

But, if you are building the perfect M20K foreverplane… +1 for Gamis and an intercooler!   
 

PP thoughts only, not a mechanic…

Best regards,

-a-

 

[Will.iam]

4 hours ago, T. Peterson said:

Thank you! I appreciate the input. I will measure mine when I get home from this trip. I think my droop is more like an inch and a half. 

Hey Torrey, glad you found mooneyspace, sorry I didn’t get to talk to you when you were shopping for a Mooney, fly up to 5TX0 and come say hi.  Jaden, and Erin also live in the air park so you could see them as well. Does that 231 have an engine monitor? That is the first thing I’d get if not to monitor your LOP flying. My plane is down for a throttle body, fuel pump overhaul that had a 6 week lead time or I’d come see you.  Which airport in Ennis are you at? Or did you sell that bull and put a runway in the field?  What is your max fuel flow on takeoff? With summer coming up you will need to make sure that is adjusted on the high side of the range to keep your engine cool when climbing out on takeoff. I was struggling with temps up to 400F last summer and once I got my fuel flow increased, I can keep it under 380F.

See you soon,

will

 

[T. Peterson]

Good morning Will!

Great to hear from you! I do have an engine monitor and my ff is 24 plus on takeoff. I have no overtemp issues, just higher gph than I think is normal. Take care! About to push.

Torrey

[jrwilson]

20 hours ago, T. Peterson said:

I have not had a problem with over-temp, but that may very well be due to the droop. Also hot summer has not yet arrived. Furthermore, since I am brand new to GA and piston airplanes, I am trying to be very conservative. I can’t get any better than about 12.4 gph at any altitude from 6000 to 13000 feet. My TIT is about 1550 and cylinder temp 340 to 380.  The belly of the airplane is filthy, but that is going to be remedied on the 28th. I thought that maybe the dirt and cowl flaps were costing me, but I guess not. TAS runs between 157 and 162.
The former owner said he got 11 gph at 11000, and I suppose if I pulled MP back I could do better. I cruise at 2500 rpm and 28 inches. 

Power settings sound good. I do slightly higher for fuel burn, at 12.7 and don't go over 350 in cruise for CHT with about the same TIT.

[T. Peterson]

14 hours ago, carusoam said:

T P,

If not familiar… read up on measuring your Gami spread…

Most Mooney engines are capable of running LOP… M20C and M20M are the most challenging….

The smaller the Gami spread the more likely you will run LOP… without Gami injectors…

But, if you are building the perfect M20K foreverplane… +1 for Gamis and an intercooler!   
 

PP thoughts only, not a mechanic…

Best regards,

-a-

 

Thank you -a-,

 I believe I am building my forever airplane, so a bunch of stuff is on the horizon!

[T. Peterson]

14 hours ago, carusoam said:

T P,

If not familiar… read up on measuring your Gami spread…

Most Mooney engines are capable of running LOP… M20C and M20M are the most challenging….

The smaller the Gami spread the more likely you will run LOP… without Gami injectors…

But, if you are building the perfect M20K foreverplane… +1 for Gamis and an intercooler!   
 

PP thoughts only, not a mechanic…

Best regards,

-a-

 

Thank you -a-,

 I believe I am building my forever airplane, so a bunch of stuff is on the horizon!

[jrwilson]

On 4/20/2022 at 7:30 PM, T. Peterson said:

Good evening all,

 I recently purchased a 1979 K model. I have noticed that in the fully closed position the cowl flaps are not flush with the fuselage but still droop about one inch. I called the previous owner to ask if he had the flaps rigged that way to provide better cooling, but he said he had not done so and didn’t realize they were so rigged.

 I am tempted to have my mechanic rig them flush, but am not sure that is wise. Is it possible that this one inch droop is factory set and should not be disturbed? I welcome your informed insight.

Torrey

So looks like flush is the factory setting for closed position according to the service manual.  With an allowable .25” gap for warm weather

[T. Peterson]

17 hours ago, jrwilson said:

So looks like flush is the factory setting for closed position according to the service manual.  With an allowable .25” gap for warm weather

Thank you!!

Torrey

[Q The Engineer]

Adjust the cowl flaps cable to leave a .5" gap at the back of the flaps at full close.  

[hubcap]

The Mooney engineer guest speaker at MooneyMax earlier this year was very specific in that the cowl flaps on the "K" should be 1" open when closed all the way. As was mentioned earlier by @kortopates it provides for better cooling and higher speed because of better airflow. Mine are closed all the way now, as that is the way they were rigged when I bought the plane. She is going in for an oil change this week and I am going to set them at 1" open. I cannot run with them closed in the summertime or my CHT's get up around 380-400. I am anxious to see how much the CHT's cool off with the cowl flaps open 1".

[Tx_Aggie]

On 4/21/2022 at 6:31 PM, A64Pilot said:

Since someone quoted me at the beginning I’ll state what I’ve done, I go for 1/4 inch in Winter and a 1/2” in Summer, that keeps me in the middle or just under in cruise when closed. I run them wide open or fully closed, doesn’t seem to be any need for in between for me. I think I could go with factory setting year round and leave them in trail in Summer, but I want them open as much as I can get in climb in Summer, and adjustment effects both ends so that why I do it.

I’m a NA J model so don’t know how that differs from a K

Cowl flap adjustment is real easy, no safety wire etc involved, just a locknut. But I can’t advise on where the line is as to what a pilot is or isn’t allowed to do.

Does the quick connect rotate along with the locknut? Don Maxwell had mine adjusted so that I’d have 1” open when “closed” but somehow they’ve been adjusted back to fully closed after this annual. CHTs are too hot during the summer and I’d like to adjust them back to 1” open. Seems easy enough to adjust I just haven’t tinkered with it yet personally.