Cowl Flap Rigging

[pilot_jb]

Anyone have a photo of the position of the cowl flaps arm when it’s rigged properly?  

Mine wont stay closed in flight Due to the air pressure inside the cowl and I believe it’s because the arm ends up in the wrong position when closed. 

This is mine in the closed position from the right side. 

[Prior owner]

Someone will chime in here, but also check where the assembly clamps to the engine mount- mine wasn’t clamped tightly enough and it was sliding up and down under pressure. Will definitely affect your opening

 

[carusoam]

Fantastic pic, JB!

My M20C dripped oil onto the clamps, thus lubricating the motion...

See if Doc @M20Doc is around for thoughts on cowl flap control configuration...

Best regards,

-a-

[pilot_jb]

Just bumping this to the top.  

[Shadrach]

On 4/18/2019 at 9:47 PM, PilotCoyote said:

Someone will chime in here, but also check where the assembly clamps to the engine mount- mine wasn’t clamped tightly enough and it was sliding up and down under pressure. Will definitely affect your opening

 

This is a common issue after re-installation. Once the issue is solved, it usually remains trouble free.

[Shadrach]

52 minutes ago, pilot_jb said:

Just bumping this to the top.  

I'll take a pic sometime this week.

[pilot_jb]

I really appreciate it. 

[Shadrach]

On 4/23/2019 at 6:22 PM, pilot_jb said:

I really appreciate it. 

Hope this helps. I have additional angles if needed...  Our birds are 150 serial numbers apart. Mine was airworthy 07/03/1967 yours was airworthy 01/16/1967.  I cannot see the entire actuator in your photo, but my guess is that your cable sheath is not secure and is moving around under pressure.  If you look in the last two images, you can see the engine side firewall clamp (red arrows). There is also a corresponding cabin side firewall clamp that locks the sheath in place.  Neither of these are a lot of fun to get to but both are absolutely necessary. I'd not be surprised that some frustrated mechanic in the past said "good enough" without fully securing one of the clamps or worse yet neglected to reinstall one of them.

You can also see what happens when the actuator isn't properly secured to the engine mount. It slides down the tubes and then interferes with the firewall leaving those unsightly scares.  Ours passed several MSC annuals this way.  When I started flying the plane I was irritated at how stiff the cowl flaps were. Partner said that they were always stiff.  He even priced converting to electric. It did not take a lot of investigation to find out why they were stiff. This was about 3 months after a $7000 annual.  That was the last annual conducted outside of my hangar.  Manual cowl flaps should be an easy one handed operation at all speeds. If not, something is wrong.

Let me know if I can be of further assistance.

 

 

 

Edited April 29, 2019 by Shadrach

[Ross Taylor]

Fantastic and helpful photos, sir!  Thank you.  I'll need to check ours, because actuating them is a two-handed affair right now.  These photos will help me know what to look for... much appreciated!

[Shiny moose]

I will also add to check the clamp bolt that attaches the cowl flap Assy  to the motor mount, these can become loose and the whole assy will slide down, causing the rod end to contact the firewall and if loose, your cowl flaps will not stay in adjustment. I have not been able to find a measurement for the correct placement, but mine were loose,  I was able to move mine up 1/2 inch, leveled both sides, getting space between the rod ends and the firewall then adjust cowl flaps.

As stated before if your rod ends are hitting the firewall you will struggle with pushing and pulling the cowl flap knob. 

After reading again I see this was already address by shad

[Shadrach]

57 minutes ago, Ross Taylor said:

Fantastic and helpful photos, sir!  Thank you.  I'll need to check ours, because actuating them is a two-handed affair right now.  These photos will help me know what to look for... much appreciated!

That is reminiscent of how mine were when I first started flying it.  If it is still stiff and the rod ends are not rubbing, the next thing to do is ensure the cable is well lubed in its entirety.

[Shadrach]

16 minutes ago, Shiny moose said:

I will also add to check the clamp bolt that attaches the cowl flap Assy  to the motor mount, these can become loose and the whole assy will slide down, causing the rod end to contact the firewall and if loose, your cowl flaps will not stay in adjustment. I have not been able to find a measurement for the correct placement, but mine were loose,  I was able to move mine up 1/2 inch, leveled both sides, getting space between the rod ends and the firewall then adjust cowl flaps.

As stated before if your rod ends are hitting the firewall you will struggle with pushing and pulling the cowl flap knob. 

After reading again I see this was already address by shad

Echo...Echo..Echo.   It bares mentioning twice!

[Guest]

From the IPC clamps are not installed on the outer sheath of the cowl flap cable.  

Clarence

[Shadrach]

3 hours ago, M20Doc said:

From the IPC clamps are not installed on the outer sheath of the cowl flap cable.  

Clarence

 

That's a different IPC then the one I have but the lower part of the illustration is the same.  While your's shows 2 clamps (#37), attached to a bracket in the upper part, that set up does look like mine. Interestingly, my IPC does show a clamp for the C & D models on the engine side  of the fire wall clamp (#4).  So if you're indeed correct about the clamp that means mine was modified by someone at some point long before I started caring for the plane.   The question is, what is the correct means of holding the sheath in place?  Neither my MM or IPC offer much in the way of information on the cable.  I am guessing that the control is one piece ( cabin control, cable and firewall mount) mine must have failed at the fire wall and an A&P must have utilized  the clamps as a fix.  The thing is, they look factory...they are very similar if not identical to the clamps on the ram air cable.   Can you speak to what is supposed to keep the cable sheath in position?  The OP's symptoms are seem to suggest his is moving.

[Guest]

I had to go look at item 37, it says 2 of MS21919DG4 clamp used on 1969 E and F.

The clamps on your cable appear to be AN742-XX. Likely added because the outer sheath is slipping in the firewall connector.

Clarence

 

[pilot_jb]

Thanks a bunch, Shadrach.

Sure enough, the clamp is not there.  In fact, the sheath has been trimmed back too far for a clamp.  My guess is that the adjustment wire is bending under the load of the pressure inside the cowl.  I'll be at the airport tonight.  Who am I kidding?  I there almost every night.  I'll take a look under the panel to see if there's enough slack in the cable length to expose more in the engine compartment.

My plane was stripped down and refurbished by the previous owners years ago.  Overall, they did a really good job, but there are some small issues, as there always are.  The cowl flap control cable was changed to this version.

https://www.aircraftspruce.com/pages/ap/controls_thandle/a1870.php

Cheap enough to replace leaving the sheath longer if necessary.  

I'll let the thread know how this goes.  

Thanks!

[Shadrach]

2 hours ago, pilot_jb said:

Thanks a bunch, Shadrach.

Sure enough, the clamp is not there.  In fact, the sheath has been trimmed back too far for a clamp.  My guess is that the adjustment wire is bending under the load of the pressure inside the cowl.  I'll be at the airport tonight.  Who am I kidding?  I there almost every night.  I'll take a look under the panel to see if there's enough slack in the cable length to expose more in the engine compartment.

My plane was stripped down and refurbished by the previous owners years ago.  Overall, they did a really good job, but there are some small issues, as there always are.  The cowl flap control cable was changed to this version.

https://www.aircraftspruce.com/pages/ap/controls_thandle/a1870.php

Cheap enough to replace leaving the sheath longer if necessary.  

I'll let the thread know how this goes.  

Thanks!

So, in looking at you detailed pic, I have some thoughts. The sheath may not be a problem.  If it secured to the firewall, no need to clamp it.  As @M20Doc  graciously pointed out, the clamps are not shown in the IPC for model year 1967 so they must have been added to my aircraft at some point years ago.  Give your cable a gentle pull to verify the cable sheath is not moving.  If the cable sheath is secure, I suspect your issue actually has to do with rigging.  Notice that when my cowl flaps are fully open the arm that the cable is attached to almost butts up against the sheath/clamp (no inner cable exposed).  In this position the cable is housed almost entirely within the sheath. Conversely, when my cowl flaps are in the closed position, the amount of cable exposed is only enough to allow full travel of the push/pull control. Your plane appears to have a lot more cable exposed.  The arm looks to be attached to the inner cable in such a way that leaves a lot of it exposed when the cowl flaps are in either position.  The way to check this is to put the cowl flaps to max open position (which pulls the cable toward the firewall) and see how far the arm is from the sheath.  Ask your A&P to take the slack out of the cable when the control is in the open position. This will ensure that there is enough exposed cable for the control to actuate and no more.  The internal cable is rigid but it will flex. Kind of like trying to push a garden hose...you can push a few feet but not 20 feet.   Your's appears to have well over 2" of exposed cable in the closed position (See image)... that is likely flexing under load.  Please understand that the whole system will need to be re-rigged if the cable is adjusted. After adjusting the cable, both cowl flaps will likely need to be adjusted up (closed) to meet specs.  Do let us know how it works out.