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Cowl flaps not closing


Vlakvark

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Hope everyone is geared for the holidays. Plane went in for the annual last week and got her back. Went up for a flight to take her home. Notice that the cowl flaps dont want to stay close in-flight. On the ground I can open and close it but in the air the airflow pushes it open again. Any suggestions?

JT

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7 minutes ago, carusoam said:

JT,

Which control knobs do you have for the flaps on your K?

Electric motors?

Twist setting, button locking type knob?  (Similar to a 65C's rpm knob)

Other?

Best regards,

-a-

 

Push/pull type. I will look at the spring that is on there. 

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The mechanism is clever. It has two stable states, open and closed. Either the cable or the rods going to the flaps is adjusted too tight so the mechanism can't go to the closed state. You can test them on the ground by pulling them open. You shouldn't be able to.

Edited by N201MKTurbo
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1 hour ago, Vlakvark said:

Any pictures of the mechanism or the coil spring. 

 

Here is a picture.

 

I, too, have a M20K and broke the handle last week for my cowl flaps. After an expensive order from LASAR, I got the cable shipped overnight. I replaced it with my A&P the next day and learned a lot about the mechanism. After the new install, I found that the cowl flaps would not stay closed in flight. I had to remove the cowl and adjust the cable adapter to be longer. As you see in the picture, the mechanical push from the cable cams-over the X brackets to lock them open (or closed). I have a spring on the left (pilot side) cowl flaps that assists the opening and closing of the flaps but the “throw” of the mechanism dictates locked open or closed. 

I have an illustrated parts catalogue picture I can dig out if you need further explanation.

43F2BF21-C886-4A34-A039-48B21E26FFB0.jpeg

B4590601-C00F-42FC-A7A5-F5E7473D7360.jpeg

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I've had a lot of problems with my cowl flaps over the years and almost every time it came back to the scissors linkages were not working as designed.  My anchor point for the cable out on the motor mount would twist, allowing the scissors linkage to "go past center" and throw off the whole working process.  After the last diagnosis, I found a way to get the anchor clamp to not move anymore and I also operate the control with a tender touch.  I think the problem derived from operating the control with too much force.

Make sure you view the scissors mechanism as you operate the flaps to ensure they have not gone over center.  The flaps will still work if you have, but they will not operate full range and also will not stay in position.

Tom

 

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I don't know if this is an issue in the K, but in the J the cabin heater SCAT tube is routed above the cowl flap bellcrank with almost zero clearance.  If the SCAT tube got replaced or moved at annual, it could be interfering with the movement of the cowl flaps (and the mechanism will eat a hole in he side of the SCAT tube.

In the end, my mechanic ended up squashing the SCAT tube a little bit to keep adequate clearance between the SCAT tube and the cowl flap mechanism.

Edited by jaylw314
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Just now, markejackson02 said:

I am curious what you find.  My J model (77) has never been able to have the cowl flaps in anything other than fully opened or fully closed.

 

 

Maybe mine is weird, but it will do closed, half, or full open.   I leave it at half a lot depending on temps or for stuff like pattern work.

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Mine would not stay shut during flight. The log books showed the spring being replaced. I fixed it by rotating item number 11 in M20Cdocs exploded view. I rotated it about 180 degrees to preload the spring a little more and then snugged that detail down tight. Hasn't given me any problem since. Cheap fix to a non complicated problem.

 

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