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Rigging/adjusting the cowl flap


NicoN

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Recently, we had a damage to the control cable for the cowling flap (M20K/1980).

Now, we have a new one and the cowl flap moves easy.

But, we have now another problem: The cowl flap does not stay in the closed position while in the air. It automatically returns to the intermediate/trainling position. The open position is fine.

The rpair manual simply says something about an overcenter position. In closed position (control rod all in), the arm where the connecting rods are stays in a "11 o' clock" position. I can manually push it then a little further using my hand (on ground).

 

From my point of view there are  3 possible point of adjustment:

1. the connecting rod from the scissors to the cowl flaps.AFAIK they only can control how far the cowl flaps close in the closed position. Longer rod means, that the cowl flap stays more open. The overcenter position should not be affected (only with too short rods).

2. on the cowling  end of the cable there is a threaded rod screwed on the cable. On the old cbale it was all in. Turning it anti-clockwise should bring the arm a little more to the 12 o'clock position or more.

3. The housing of the cable has also an adjustable thread on the cowling side.Does the positioon has any influence on the arms psoition? I am not sure if it does. In case it should have the same result as #2

(4. The pedestal side of the cable has a thread, tooo. But it should not have any influence on the scissors near the cowling)

 

Any hints fro the rii´gging? Especially welcome is an idea how to avoid removing the lower cowling

Nico

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If your cowl flaps are set to close tight, the pressure inside the cowl will not let the mechanism over-center. The 231 cowl was designed without enough exit area with the flaps closed tight creating too much pressure in the cowling.

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I would suspect that your newly installed cable is not adjusted correctly and is not allowing the scissors to lock “over centre”. Adjusting the outer sleeve, the cable end or both may be required.

Clarence

 

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Seems to be right.

I corrected the thread at the #5 angle. Now it is better, but the arm still does only come close to the 12 position but not further;

I think I have to screw out #6 a few turns

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  • 3 weeks later...

Okay, it is done and working flawlessly.

But the process of changing the control cable and adjusting is a little tricky and some planning may save you lots of time.

So, let me share my experiences with the community.

Changing the control cable:

- the new part came from Mooney, but is made by McFarlane. SO, you may save some money getting the part from there

- plan 3hours + with 2 persons working

- take a lot of photos from the cowl flap mechanism in both end positions and between from both sides!  The scissor mechanism is rocket science. It may save you time and avoid mistakes

- I pushed a piece of tightrope into the outer bowden cable before removing the old cable as a guide wire for the new one.

- Make sure the cable stays clear from the flight controls!

 

Rigging the cowl flap:

The scissor mechanism locks the cowl flap in closed and open position. The trailing position is something in between.

It is a rotating bar with lever arms on both sides left and right.

What you need:

- new cotter pins

- some shims may be needed to reduce play

I made the mistake to simply "copy" the rigging from photos according  to  the old cable. That did not work.

It turned out, that in closed position of the cowl flap handle the lever arm on left side stopped in a close to  11-12 o'clock position (viewed from the left side). together with play it failed to keep the cowl flap closed.

The lever arm MUST reach a clear over-center position ( 1 o'clock position). I recommend that the lever/bar reaches the mechanical stop with a little travel on the control cable left.

The problem is, that the major part of the rigging has to be done withe the lower cowling removed. In case of failure you have to remove the lower cowling again.

I recommend to do it the following way:

1. the firewall-side threaded end of the outer bowden-cable should be adjusted to have most of the threads ABOVE the #5 angle. WIth your own extra long arms, short fingers, short wrench and a lot of talent you may do corrections later on without removing the lower cowling.

2. The next thing to adjust is the threaded bar with the 2 holes for the scissor arms in it. Don't gforget a hex nut  before you screw the bar onto the control cable thread! Check your photos for correct positioning.

3. Turn the control bar to the closed position mechanical stop and the control cable also to the closed position.

4. check the scissor arm which goes to the far-end hole of the bar before inserting the bolt

5. It is now hanging more or less near the hole in the bar.

6. Adjust the length of the bar by turning to bring the distal hole LOWER than the hole in the hanging scissor arm.

7. insert the bolts and secure them with cotter pins. Additional shims may help to reduce play.

I needed 3 iterations of the procedure. After the first attempt, the cowl flap did not stay closed. After the second, the cowl flap stayed closed, but only if I managed to close it below 125kts. Now it is easy to handle and can be closed at any speed without much force.

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  • 4 years later...

Hi,

I just lost the cowl flap control cable in my 231 as well.  Looks like it broke at about the same place.  I am ordering a replacement from Lasar as I can’t seem to find a salvaged one.  I guess this will have to be ordered from Mooney, approved, the then manufactured per Lasar.  This process could take “months or even a year”…that’s crazy. 
 

Matt

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22 minutes ago, blackdogair said:

I just lost the cowl flap control cable in my 231 as well.  Looks like it broke at about the same place.  I am ordering a replacement from Lasar as I can’t seem to find a salvaged one.  I guess this will have to be ordered from Mooney, approved, the then manufactured per Lasar.  This process could take “months or even a year”…that’s crazy

I don't know if they have (or can make) these, but McFarlane has a lot of stuff.  866-920-2741

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McFarlane has a custom fabrication shop that will make it, I think, provided I send exact drawings or sent the entire assembly in for them to replicate.  Not FAA/PMA approved so one would need a 337, etc.  I am looking into this option.  If McFarlane did manufacture NicoN’s unit, then maybe they already have all the specs?  

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1 hour ago, blackdogair said:

McFarlane has a custom fabrication shop that will make it, I think, provided I send exact drawings or sent the entire assembly in for them to replicate.  Not FAA/PMA approved so one would need a 337, etc.  I am looking into this option.  If McFarlane did manufacture NicoN’s unit, then maybe they already have all the specs?  

You won't need a 337 as it is not a major alteration or major repair.    You can do it as an Owner Produced Part, or if your IA is good with it just replace it with a logbook entry.   McFarlane makes a lot of the cables for the factory, anyway, so there may be no difference between what you get from them and what you'd get if you ordered it from the factory.

I've replaced all of my engine control cables through McFarlane, two as OPP and one using a Mooney part number.   The OPP parts made using their form fit better than the one from the factory drawing.

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2 hours ago, N201MKTurbo said:

That cowl flap cable is a bit of an oddball. It has a very long throw. Longer than most standard cables.

It’s also one piece.  The actuator rod handle is fused, crimped I guess, to the cable itself.  So cannot just replace the cable.  

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57 minutes ago, EricJ said:

You won't need a 337 as it is not a major alteration or major repair.    You can do it as an Owner Produced Part, or if your IA is good with it just replace it with a logbook entry.   McFarlane makes a lot of the cables for the factory, anyway, so there may be no difference between what you get from them and what you'd get if you ordered it from the factory.

I've replaced all of my engine control cables through McFarlane, two as OPP and one using a Mooney part number.   The OPP parts made using their form fit better than the one from the factory drawing.

The 337 req. is what McFarlane told me would be necessary.  So I’m not really sure.  

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1 hour ago, blackdogair said:

The 337 req. is what McFarlane told me would be necessary.  So I’m not really sure.  

Your IA has the opinion that matters, since his name goes in your logbook.

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10 hours ago, blackdogair said:

The 337 req. is what McFarlane told me would be necessary.  So I’m not really sure.  

I think that McFarlane is just saying that you have to come up with some way to get it approved because they don't manufacture an approved part. I'd discuss this with the mechanic that will be signing the logbook, but if you send the original part to McFarlane and they duplicate it for you, that should qualify as an OPP.

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