Roof Vent Woes. (Cracking)

[Mooneymite]

When I researched the archives about "roof vents", most of the threads discussed linkage problems.  I've attached a couple of photos of the problem I'm having with metal fatigue.  Apparently, when the vent's open, there's too much stress on the bracket that holds the control cable sheath.

 

Anyone else see this sort of cracking/metal fatigue issue?  Is this common in the short body Mooneys?

 

What did you do about it?

 

I'm guessing the best repair would be to remove the entire vent assemly and find a new one (someplace?) and rivet it in and paint it.  However, that's a huge job and I'm not sure it's worth it.  An exterior patch might work, but the vent wouldn't shut completely.

 

The last picture shows my "interim fix".  The PK screws allow me to use the vent, but they don't stop the cracking, or give proper support to the cable.

 

Ideas?

 

 

[flyingvee201]

Is it possible to weld the crack?  or place a support piece ("doubler") underneath and rivet it on?

[N601RX]

Do you have the 201 windshield? I've read that it will put a lot more air through the vent as the original window directs a lot of the air up over the vent. It may also put more stress on the vent when fully open.

[Mooneymite]

Do you have the 201 windshield? I've read that it will put a lot more air through the vent as the original window directs a lot of the air up over the vent. It may also put more stress on the vent when fully open.

I haven't heard about the 201 windshield mod evvect on the vent, but mine is stock. I have no clue why mine is cracking.

I'd like to say it is because mine is so much faster than stock, but it isn't.

[Mooneymite]

Is it possible to weld the crack?  or place a support piece ("doubler") underneath and rivet it on?

.

I don't think the thin gauge aluminum would weld well. However, I am considering applying some JB Weld over the PK screws.

The problem would be cleaning up the mess if it doesn't hold.

I'm hoping someone out there has successfully dealt with this and can share the remedy.

.

.

[Shadrach]

Why did your A&P not stop drill this when it started? I have to believe it's happened in increments. I would not use JB weld. If you can get the pieces flush again, you maybe able to patch with a very thin piece of aluminum cut to cover the crack utilizing an adhesive like 3M 2216. There is a reason to pay 3 times the cost for the proper adhesive (check the spec, I think it's ideal for what you're trying to do). I would patch first and then mask off the the roof and paint the patch with the best match I could find. If done correctly, no screws should be needed. Some airplanes are assembled with structural adhesive. I don't know how your IA will feel about this type of repair. Best of luck! Oh and have that thing stop drilled ASAP....

http://www.ellsworth.com/3m-scotch-weld-ec-2216-epoxy-adhesive-gray-43ml-duo-pak/?gclid=CNe7l_Hw8LoCFU8V7AodNwsADg

[Mooneymite]

One of the reasons it was never stop drilled is I never brought pointed it out at annual time.  As you know, the roof vent is not an airworthiness item.  It has always "operated" just fine.  This is a perfect example of how a "little crack" in an out-of-the-way location becomes progressively worse.

 

The idea of "glued patch" has merit.  The IA who signs off my Mooney would probably not care since airworthiness is not in question.

 

Thanks for the suggestion.

 

And if you haven't looked down into your roof vent lately, you might want to!  

[PMcClure]

Just a thought - you may want to look at the cable attachment clip . Could you slide the cable housing down a little? It looks like the cable housing is moving and putting stresses on the aluminum. My question would be what caused the crack and how to prevent it again- in addition to fixing the current damage.  

[Mooneymite]

Just a thought - you may want to look at the cable attachment clip . Could you slide the cable housing down a little? It looks like the cable housing is moving and putting stresses on the aluminum. My question would be what caused the crack and how to prevent it again- in addition to fixing the current damage.  

 

Yes, you are correct.  The cable housing is moving....now that the material holding the bracket is cracked.  Looking at the "big picture", it appears that the material that Mooney used is just too thin to handle the stress imposed by air loads on the vent door.  The cracks look to me like "fatigue" induced cracking.

 

However, if no other C model Mooney owners are having this problem, it is peculiar to my vent and may well be a mis-rigged cable housing or other issue....(like the exceptional airspeeds achieved by my Mooney!)

 

Unfortunately, getting to the bracket holding the housing cannot be done from the outside.  I'd have to remove the interior overhead and..... well, it would be a huge job.  That's why I'm looking for an exterior repair.

 

The next choice would be to just keep the vent closed and move to a cooler climate!

[PMcClure]

Yes, you are correct.  The cable housing is moving....now that the material holding the bracket is cracked.  Looking at the "big picture", it appears that the material that Mooney used is just too thin to handle the stress imposed by air loads on the vent door.  The cracks look to me like "fatigue" induced cracking.

 

However, if no other C model Mooney owners are having this problem, it is peculiar to my vent and may well be a mis-rigged cable housing or other issue....(like the exceptional airspeeds achieved by my Mooney!)

 

Unfortunately, getting to the bracket holding the housing cannot be done from the outside.  I'd have to remove the interior overhead and..... well, it would be a huge job.  That's why I'm looking for an exterior repair.

 

The next choice would be to just keep the vent closed and move to a cooler climate!

I know that cable is a B@#%# to get to. We replaced ours on our F. But…. if you patch it, and it continues to cold work or stress the area, it could just become a bigger problem. Not a mechanic, not an expert, just saying what I would be worried about. 

[Shadrach]

One of the reasons it was never stop drilled is I never brought pointed it out at annual time.  As you know, the roof vent is not an airworthiness item.  It has always "operated" just fine.  This is a perfect example of how a "little crack" in an out-of-the-way location becomes progressively worse.

 

The idea of "glued patch" has merit.  The IA who signs off my Mooney would probably not care since airworthiness is not in question.

 

Thanks for the suggestion.

 

And if you haven't looked down into your roof vent lately, you might want to!  

PMcClure's advice has merit, however, I think that the cable is attached a mount that is riveted to the skin, so I would also look at the door, if it is not actuating with ease, that may be the cause of your issue. also if the cable is binding at the mount, it could cause the cable to flex.  There is a good chance that time and fatigue are the problem.  While the vent operation is not an airworthiness item, I think the case could easily be made that a crack in the fuselage skin is an airworthiness item. There are a couple of practical issues at play, most important to me would be that it allows moisture to enter into an area where you have steel joined to aluminum.  Probably a good idea to remove the ceiling panel and get a look at everything.  Is the plane hangared?  How long has it been this way? 

[KSMooniac]

I think you ought to drop the headliner and look at the backside of the mess, and fix it correctly.  Yes, it is a PITA, but better to do it right once than covering it up with an external patch only to find that the problem hasn't gone away and you end up cracking a larger portion of the skin.

 

I hate those vents and once of my upgrades on the wish list is to eliminate it entirely and retrofit a later model ventilation system with the intake near the vertical stabilizer...but that is a lot of work.  

[Shadrach]

The overhead vent assembly is not that big of a job. The biggest hassle is the vent covers, and you'd not need to remove those to access the cable and mount.  If you want a really permanent fix. I'd make an "adhesive sandwich" using the 3M Scotch Weld I mentioned (2216) with .20" 2024-T3 sandwiching the cracked skin in between.  Maybe someone more credentialed might ring in... Kelly? 

[PMcClure]

I see now how the housing retainer is riveted to the aluminum. Moving the housing down would not help, in that case. Ross's suggestion to check for free movement sounds like a good action. I was thinking only of damage from wind and prop wash. But just excessive force to open and close could cause the crack. Good luck!

[KSMooniac]

That Scotch Weld that Ross mentioned is good stuff.  I know it is used for various non-structural repairs in the aircraft industry during the production process at places I've worked.  It sticks like excrement on a wool blanket.

[Mooneymite]

Ross's suggestion to check for free movement sounds like a good action. I was thinking only of damage from wind and prop wash. But just excessive force to open and close could cause the crack. Good luck!

 

Actually, the vent moves very freely.  I released the door from the control cable and both the door and the control cable have complete freedom of movement, so I don't think it is a binding issue.  I think airstream buffetting is the issue.  Based on that, returning the vent housing to "original" is only going to restart the clock.  The same issue(s) will exist.

 

I'm leaning toward a "doubler sandwich" using the previously mentioned adhesive with strips of aluminum and new bracket rivets, but this will entail removing the headliner.

 

However, I'll keep my options open (not do anything    ) as long as I'm getting input from this forum.

 

Hopefully, there's someone out there who's found a perfect (and easy!) cure.

 

Thanks for all the input.

[jetdriven]

I think you ought to drop the headliner and look at the backside of the mess, and fix it correctly.  Yes, it is a PITA, but better to do it right once than covering it up with an external patch only to find that the problem hasn't gone away and you end up cracking a larger portion of the skin.

 

I hate those vents and once of my upgrades on the wish list is to eliminate it entirely and retrofit a later model ventilation system with the intake near the vertical stabilizer...but that is a lot of work.  

 

It looks like the bracket is loose, bent, or broken, and the cable itself is putting pressure on the inside of the skin, which pulled through and cracked all around the base of the bracket. Aluminum will crack when pressure is put on it like that.  You can repair it with a doubler from the inside or the outside. Inside will look much cleaner, especially if its flush riveted. If you put a doubler on the outside, you are going to have to relieve or drill holes in the doubler to clear those rivets to the right which hold the bracket under the skin for the cable. Plus you are going to have to trim the doubler very carefully so it comes close to, but not under, the roof scoop when it closes. Else it wont close fully.

 

Looking further, Id remake the cable bracket where it extends further to the left to go under the skin which isnt cracked, to spread the load.

[jamesm]

My roof vent open while in-flight, kind of scare, my brother was flying and had  just close the cowl flaps and then all of sudden  BAM sound.

 When we landed  and found that the cable had fatigued   that connects to the roof vent. The roof vent had been what I call ground adjustable for a number of years. Since  I really didn't want to jump into interior  so I have been putting off the "project" until winter time. 

I guess I am lucky since I don't see any cracks in the roof.

But It seems to me the that earlier  design was better design at least on paper (pg 272 of IPC). The vent  had a link  that connected  to a  bell crank the other end of the  bell crank connected  to the cable knob overhead. It  looks like the same  cable mechanism used in later C models but with no bell crank and linkage assemblies.

It seems  like a goofy design  to me to  have the cable support the air load of the vent.  Then  to have the cable sheath do couple of s-turns  causing friction to the cable.

 I was hoping someone had come up re-design rather then replacing the cable mechanism.

I don't look forward in tearing into overhead  interior.

 

 I wonder what  the  in drag / speed penalty by having the vent on the roof versus  having vent in dorsal fin area?

Is there difference in amount air flow  to cabin by vent on roof versus the dorsal fin area?

 

James

'67 M20C

[jetdriven]

I hear the dorsal NACA vent is quieter, less drag, and more air.  But at a cost of around 3 grand to convert it, we suffer on with the scoop.

[carusoam]

The tail version seems to work well. The roof version was stuck in one position.

My experience, and apples to orange comparison,

-a-

[06q]

I had the cable break on a early morning flight in my 67 F, Baam I thought I had been shot. Got lucky no damage to the vent.

[carusoam]

Welcome aboard 06Q

Best regards,

-a-

[Mooneymite]

Got lucky no damage to the vent.

 

Any damage to your nerves?  

[Ratherbflying]

Sorry about the poor lighting on this photo. The plane was stuck in the hangar today due to ice.

 

My 65 C seems to have a completely different control linkage, it doesn't put any stress on the metal.

[carusoam]

My 65C had a corroded cable issue. It just didn't work as designed...

Best regards,

-a-