GMC 4107 Roof Airs

[Vanderbus]

The PO cut a couple of holes in my roof to install vents. The holes are cut through 2 of the center roof "stiffeners" and framed around with 2x2 (see picture). I read in another thread on this board that at least one member thinks that wasn't such a great idea by him, so I have a couple questions.

Is my 4107's structural integrity severely threatened by these cuts?
Is there any way I can put roof airs in place of the vents? Would replacing the 2x2 with steel be necessary/sufficient?
Does anyone else have experience with roof airs in the center of a GMC? Photos?

Thanks,
Joe


Here's a link to the full resolution image (click the magnifying glass on that page for best quality): http://picasaweb.google.com/lh/photo/0RLutnof6przLDs9f2bQ4g?feat=directlink

[Airbag]

The cut-outs for roof airs are 14.1/4" x 14.1/4". I would think they would be ok to put them there but you do need to beef that area up a little to bring back the strength lost from the cut center member. Now if your interior won't let you weld a frame in place an external doubler on top will bring back the lost strength. You could install one with blind rivets shot wet with sealant for water leakage prevention. They make blind rivets that are sealed on the bulbed end and won't leak thru the stem. Just my two cents. I can post some doubler repair data if you like from the aircraft bible that will do the trick.

[FloridaCliff]

Is my 4107's structural integrity severely threatened by these cuts?
Is there any way I can put roof airs in place of the vents? Would replacing the 2x2 with steel be necessary/sufficient?
Does anyone else have experience with roof airs in the center of a GMC? Photos?

Joe,

You need to replace the structural support that was removed by the PO cutting out the center rib.

But basically you need to put a support/rib on each side of the opening that runs fore and aft to next cross section.

I welded mine in and put a support cross wise on each side of the opening.

The opening edges new supports were riveted and bonded with Sikaflex.

I believe I have some pictures of my install on our 4905 at home, I will post them later.

Cliff