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Sideskin to outboard seat rib

C

ccrawford

Well Known Member
Hiya Folks,

I'm working on the final steps before riveting the center/forward fuselage together, and I need to drill the outboard seat ribs to the side skin (the outboard seat rib is not prepunched).

But, when I go to do that, there is a significant bow in the side skin that keeps it from running along the outboard seat rib. Check the photo:

sideskin.jpg


If I uncleco it from the 705 seat-back bulkhead, it'll sit flat against the outboard rib but then the prepunched holes on the 705 and the skin are off by about half a hole diameter.

Anyone else run into this?

I could redrill the 705 holes, but they wouldn't be cleanly away from the original holes (in many cases, the new hole would start at the edge of the original hole).

Any advice or ideas what might be going on?

Thanks!
 
Corey: It's been a few years since I've done this and I'll have to go home and check, but I believe there is a wrong way to mate the front of that rib. As I recall there's a joggle there that comes into play somehow. But I can't quite remember it now and maybe someone else will jump in. I'll check it out when I get home and take a look. Of course, I reserve the right to be completely wrong.


In the meantime two things:

-1- When the holes on the kit don't match up, it's usually not the fault of the manufacturer. So if they're lining up, don't drill new holes. It means something is wrong somewhere else that'll come back to bite you later if you don't identify and fix it.

-2- Can you take an interior shot of how that's mating?
 
Seat rib must be fluted

Corey, the bow you are seeing in the side skin looks about right. The true shape of the curve is defined by the outer row of rivets in the floor skin that attaches the outer seat rib to the floor. The seat rib flanges need to be fluted to make the seat rib match this curve. When done right, the seat rib should lay against the outer skin.
 
Flutes? Seat pan?

If I recall correctly those ribs are supposed to have a slight outward curve.

It's been a while for me too but I think I had to flute the rib so it had the proper curve. Is this the seat rib that has no holes in the top flanges for the seat pan? I think it had to be drilled with a 3/32 offset to the outside to allow the removal of the seat pan. I'dtry clecoing in the seat pans to see that help. Of course if you already have them in then I guess I'm no help :rolleyes:
 
Hmm

You can see here that the skin is almost 1/2" away from the seat pan and the outboard seat rib:





I haven't drilled the rib to the seat pan yet, so it's not showing the correct outside lip yet - even if it was, the skin is bending too far away from where it'd be. I think the lip is only 1/16" or so, it wouldn't extend very far from the seat pan. The bottom of the rib is already riveted to the bottom skin (along the centerline of the brace), so that should be right.

Here's the 'big picture' for that side:





Unless the seat rib is way off - which seems hard to believe if I rivet along the centerline (but maybe I should be looking harder at that, since it's the only thing *not* pre-punched), I don't know what else it might be.

Thanks for the advice so far!
 
Last edited:
Not sure this solves the gap problem you're having, but in one of your pictures it appears the forward flange of the outer seat rib is outside of the F-704 bulkhead vertical angle. On the -9 the seat rib flange sits inside of the angle. Not sure on the -7 but would assume it's similar.
 
Try this

Corey,

Do you have the same situation on the left side?

If yes, hum...

If not, try to fit the left skin on the right side, just cleco the holes between F-704 and F-705, and see what happens...

Just a suggestion.

Guy D.
 
good eye

I think Mike is right. The forward offset of f-715 seat rib should be on the inside of the center section. This could be forcing the skin out enough in the front to cause the bow.
 
You might have something there

MTBehnke said:
Not sure this solves the gap problem you're having, but in one of your pictures it appears the forward flange of the outer seat rib is outside of the F-704 bulkhead vertical angle. On the -9 the seat rib flange sits inside of the angle. Not sure on the -7 but would assume it's similar.
Click to expand...

Looks like you might be on to something. I looked for a few pictures on some other builder's websites and saw what they were doing (vs what I was doing). I may have to order new outside seat ribs, but at least those are pretty simple parts!

When I get home I'll look over the plans too, maybe I missed something. I will probably drill them out and try fitting them again on the inside and see if that helps them bow properly.

Thanks a lot! (I hate waiting for Van's to open on Monday!!)
 
Yes, that's the problem I was trying to remember...the rib flange fitting on the sinside, not the outside. BTW, I went up to Mike's house today to look at his project... he's done a beautiful job. Listen to what he says. (g)
 
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