Bulkhead F-608 / F-708 repair

[FireMedic_2009]

I bought the plane back in April. The plane was involved in a ground loop 4 yrs ago and the left wing tip was damaged and repaired by the seller. A prop strike was also involved in the ground loop.

The bulkhead (F-608L and R) looks less deformed in the photos. There are a couple of loose rivets on the bottom right corner of the bulkhead. On the RV-7’s the bulkhead number is the same but F-708L and R. See dwg 17 (RV-7) or dwg 22 (RV-6) to see location of the bulkhead in the fuselage.

I know worse case I can remove the bulkhead and replace it but will be a bit of a pain and involve touch up paint of the rivets. I was looking for ideas on how to repair it. What’s a interesting is there is no skin waviness or buckling on the sides or the bottom of the fuselage. I have not yet tried to straighten the buckle in the lower part of the bulkhead. I assume even if I can straighten it I’m sure it will not be as strong as it originally was, therefore prone to buckling again. Would adding a flat doubler to the opposite side of the raised strengthener be acceptable? The doubler would simply be a flat piece (no 90 edge to rivet to the bottom skin) at the bottom of the bulkhead and up around the bottom up to the 2nd longeron on both sides. I could rivet it together with a row at the top and bottom with 2” spacing. Another option could be to use triangular brackets, 4ea evenly spaced out along the bottom of the bulkhead, perpendicular to the bulkhead. Even though it would require riveting to the bottom of the skin, it wouldn’t be visible, unless you were underneath the aircraft. Of course, after looking at the pictures, I might have to add another triangular bracket on each side at the first longeron from the bottom

Thanks
Daren

 

[Ralph Inkster]

One of my rebuilds had bulkhead damage similar to yours. It looked so tempting to try to straighten it with a bodymans hammer backed up with a large bucking bar but I realized the real problem was the crimped or stretched outter flanges. If the web portion was straightened, the flanges would most likely round out & affect the skin & dimples. I ended up drilling & cutting out the warped bulkhead portions & grafting in new portions from new bulkhead parts and dealing with the replaced skin rivets later.

 

[PaulvS]

What plane is this, I assume it is RV-6?
I've seen worse damage on a RV-6 that ran over a runway cone marker, creasing the bottom skin and deforming some bulkheads and the aircraft engineer's advice was to leave it as-is.
I can't visualize your proposed repairs with triangular gussets etc but would consider a repair consistent with the design of F-611 so as to distribute the load evenly between the bulkhead and the skin (stressed skin monocoque construction).
Van's support should be able to advise if any repair, or even just a minimal repair (replace loose rivets) is necessary.

 

[kentlik]

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I bought the plane back in April. The plane was involved in a ground loop 4 yrs ago and the left wing tip was damaged and repaired by the seller. A prop strike was also involved in the ground loop.

The bulkhead (F-608L and R) looks less deformed in the photos. There are a couple of loose rivets on the bottom right corner of the bulkhead. On the RV-7’s the bulkhead number is the same but F-708L and R. See dwg 17 (RV-7) or dwg 22 (RV-6) to see location of the bulkhead in the fuselage.

I know worse case I can remove the bulkhead and replace it but will be a bit of a pain and involve touch up paint of the rivets. I was looking for ideas on how to repair it. What’s a interesting is there is no skin waviness or buckling on the sides or the bottom of the fuselage. I have not yet tried to straighten the buckle in the lower part of the bulkhead. I assume even if I can straighten it I’m sure it will not be as strong as it originally was, therefore prone to buckling again. Would adding a flat doubler to the opposite side of the raised strengthener be acceptable? The doubler would simply be a flat piece (no 90 edge to rivet to the bottom skin) at the bottom of the bulkhead and up around the bottom up to the 2nd longeron on both sides. I could rivet it together with a row at the top and bottom with 2” spacing. Another option could be to use triangular brackets, 4ea evenly spaced out along the bottom of the bulkhead, perpendicular to the bulkhead. Even though it would require riveting to the bottom of the skin, it wouldn’t be visible, unless you were underneath the aircraft. Of course, after looking at the pictures, I might have to add another triangular bracket on each side at the first longeron from the bottom

Thanks
Daren

I have for several years been repairing a very bent plane. Initially, I was removing the entirety of the bulkhead and replacing it and or them.
I had one more to do and heard from another builder I could just replace the top portion. I checked with Vans and sure enough that was authorized.
I wish I had known that earlier!
Anyway, I would as proceed as Inkster and I did and remove the damaged section, making sure it has significant portions on each leg. A doubler with 6-8 rivets between the cut section.
One more thing. Make sure the skin isn't buckled substantially, that may indicate additional work needs to be performed. And getting the new section in difficult.
You can check my build log on this site in the builder's section.

Added point: I replaced an entire side skin and top skin because of buckled bulkhead, FYI
Cheers!

 

[planenutz]

Wow. Lots of wow's in fact.

If this deformation occurred in the wingtip incident you refer to then the fuselage has had a good whipping. I'm surprised you've not got creased skins on the fuselage.

Or have you?

People have done some terrible things to cover up incidents like this in the past and photos are present on this forum where subsequent owners have used auto-filler to hide problems. Is this a possibility on your machine? I'd hope not, but it has to be asked.

I would strongly recommend that you inspect the Rear Spar bolts, rivets and the structure that makes up the Rear Spar Carry-through. Often an impact at the tip can shear rivets in the center of the aircraft or buckle that area. People often overlook this area when inspecting wingtip damage but when you consider the leverage involved it is easy to understand where the loads end up.

Replacement or repair of that Bulkhead shouldn't be too difficult. You could even pull the entire half out and replace it with a new half without too much hassle.

One other point to ponder if there is nothing else of concern other than this bulkhead - could this have been deformed by an overweight bucking-bar-holder when the top skin was installed? Or somebody who doesn't understand the fragility of 0.025" aluminium bulkheads? Just a thought.

 

[FireMedic_2009]

In the first posting I mentioned, “What’s interesting is there is no skin waviness or buckling on the sides or the bottom of the fuselage. ”. No wrinkling of the fuselage skin. I’ll check the rivets in the rear spar. The bulkhead halves are Left n Rt, not upper and lower

 

[FireMedic_2009]

Update. I was able to view the front part of the rear spar by removing the seat pans and looking with a mirror down the tunnel. Im unable to view back side of the rear spar unless I cut out inspection holes

 

[PaulvS]

My opinion: I suspect the damage to the F-608 bulkhead was caused by something else, probably during construction, and not by the ground loop. Otherwise, there would be more damage to other components including the skin and stringers in that area from a ground loop.

If the rear spar or carry through was damaged then there would be skin wrinkling or distortion in that area.

The fit of the F-608 parts was never very good and was a known problem that required the builder to improvise. In this case maybe the builder just forced it. See another example of how builder Sam Buchanan resolved that type of problem by splitting and re-joining the bulkhead (halfway down the page):
http://home.hiwaay.net/~sbuc/journal/fuse3.html

 

[rvbuilder2002]

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Darin

My opinion is that this damage didn't happen during the ground loop incident/accident.

I think it occurred from picking up or supporting the airplane under this bulkhead. Possibly during recovery after the ground loop.

I think this could have happened from some skin deflection that didn't cause any permanent crease or buckling in the skin.

It sounds like you have a good understanding regarding once a buckle failure has occurred, even if you can straighten it, it will likely be susceptible to future buckle failure at a lower load value.

Adding a doubler of sufficient stiffness like you suggest could restore the damaged portion of the bulkhead to the point it was before being damaged but I have concerns that there may be additional damage at some of the rivets.
In the top photo it looks like there is a tear in the bulkhead at a point common with one of the flange notches and the flange tabs on both side look like they are pulled away from the skin slightly at some of the rivets, but that may just be the level of fit that the original builder achieved.

Based on those things, if I were doing the repair, I would section out the lower portion of the bulkhead by making a cut on each side to coincide with the notch for each j-channel that is right above the rudder cables, and then install a new lower bulkhead section using a doubler on each side to join the new bottom section to the upper portion that was left in place.

As long as the paint thickness isn't excessive, if good technique is used during disassembly, You could do the job with only paint touch-up on rivet heads being needed, and most of the ones effected wouldn't be very visible anyway.

 

[Roadjunkie1]

Bulkhead damage....and more.....

My opinion is that this damage didn't happen during the ground loop incident/accident. I think it occurred from picking up or supporting the airplane under this bulkhead. Possibly during recovery after the ground loop.

Agreed. It doesn't appear there is enough surrounding damage (skin, stringers) to be caused by the ground loop. This looks like a problem with construction. Looking at the rivet shop heads in the last photo on the bulkhead splice makes me think you should replace those while you are in there. It also makes me want to inspect a lot of other rivets to see what the shop heads look like. Those are some of the easiest rivets to drive as the bulkhead is not in the airplane when those are driven (as I recall.....) You have likely inspected the other bulkheads in the fuselage......

In the top photo it looks like there is a tear in the bulkhead at a point common with one of the flange notches and the flange tabs on both side look like they are pulled away from the skin slightly at some of the rivets, but that may just be the level of fit that the original builder achieved.

Agreed. It might be worth getting your angle drill in there and stop-drilling that/those cracks, if you can get to them.

I would also take a close look at the fuel tank support bracket, both on the tank side and the fuselage side. That is (should be) notched to allow it to let the tank slip out if the wing hits something, rather than ripping the support bracket out of the tank eek:FUEL SPILL!) Look to see if there has been any obvious movement of the tank bracket on the fuselage bracket. I would be tempted to replace those bolts, regardless. Overkill? Perhaps... Look for damage on the tank side of the bracket to see if there is any bulging of the skin out of the tank end from that bracket being pulled inboard as the wing was rotated aft. Again, there would likely be more evidence of damage if this area is a problem but......

As an aside: looking at these pictures make me SO HAPPY I decided to blow a thin layer of zinc chromate on the inside structures! Not that the corrosion in these pictures is going to amount to much but.....