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F-711 bulkhead prep

Draker

Well Known Member
VAF searches show several builders encountering skin fit issues with this F-711 bulkhead. During prep I see mine are quite warped along the vertical axis:

IMG_0916-M.jpg


Could this be related to later skin fit issues? Is there a way to straighten these so they lay flat? I know fluting tends to straighten about the horizontal axis (perpendicular to the flute) so I doubt that would help. I noticed other bulkhead ribs don't lay flat either.

Also, look at the flanges on F-711B as they come from Van's. Are these supposed to be squared like that? The instructions don't suggest it. I have an irresistible urge to round off those corners.
 
I don?t think any adjustments are possible, they get riveted together back to back with some beefy flat aluminum bars (the ones used to bolt on the VS).

http://www.mykitlog.com/users/displ...roject=2288&category=11189&log=252573&row=354

I don?t think outside corners are as critical as inside corners (if at all ?). I took if the sharp edges because I didn?t want them to scratch the skin when I fitted the skin.

Also remember, as both F-711 and F-712 are both two parts back to back, the flanges are bent in opposite directions, confirming to the cone shape of the tail.
 
Bulkheads

The single thickness bulkheads are not an issue. Don't mess with them much except to adjust the flanges so the fit against the skin properly. If you don't, lots of shims and frustrating riveting is ahead. Don't mess with any top skin flanges. You can adjust them when the time comes.
The double bulkheads require lots of flange adjusting. Forward side is different from aft side. Adjust all of them so they fit and the longeron is correctly positioned. Don't drill the skin to flange holes till everything fits. If you don't want the external rudder stops, look at Flyboy for a hidden Delrin stop.
Not an expert opinion. Just my $.02.
 
What i did

I tweaked them ever so slightly to make them flat. Also the flange needs to be at the proper angle with a tight bend. If the flanges tend to fan apart before the sharp flange bend, this could cause fit issues. I would suggest clecoing the double bulkheads together and then checking fit to side skin and bottom piece. Much easier to do this now before riveting the two bulkheads together. Also make sure front bulkhead is dead center on rear bulkhead before match drilling the rivets that hold the double bulkheads together. The more perfect the fit now, the easier assembly later.
 
Thanks, folks. I will do a test fit with the skins before riveting the bulkheads. I've also decided to round off those square flange corners. I can't believe that would hurt anything.

I remember when initially prepping all the ribs I squared the flanges on these pieces with a hand seamer. Looks like I may have to bend them back if the angle to the skin is not 90 degrees. Bad assumption based on all the wing work. For every step on the Fuselage, there are lots of other "unwritten" things you can do--the trick is to figure out which unwritten things you need to do and which unwritten things not to.
 
Hi Ryan,

Like the others said, just rivet them together. Mine looked very similar, but once you rivet them to the bars, you'll be fine.
 
Yep the warpage you see won't be much issue. The problem is when the bottom skin goes on because it doesn't conform very well. This in turn will not let the holes on the side skins line up. Definitely round the corners a bit to help with this. All I can say is, no matter what you do you will fight this area to some degree. This was one of the most frustrating parts of the build for me. In the end I had to replace a few rivets with slightly larger rivets. You can use oops rivets to some degree but I like NAS1241 rivets better as they are only enlarged 1/64 of an inch.
 
Great. After some "motivation" with a hand seamer, test fit against the bottom aft skin is... not too bad:

IMG_0918-M.jpg


IMG_0919-M.jpg


I'll make sure the flanges are the right angle before drilling through the skins, but I'm no longer concerned about riveting these bulkheads together now.
 
Bottom skin

Yep the warpage you see won't be much issue. The problem is when the bottom skin goes on because it doesn't conform very well. This in turn will not let the holes on the side skins line up. Definitely round the corners a bit to help with this. All I can say is, no matter what you do you will fight this area to some degree. This was one of the most frustrating parts of the build for me. In the end I had to replace a few rivets with slightly larger rivets. You can use oops rivets to some degree but I like NAS1241 rivets better as they are only enlarged 1/64 of an inch.

Thanks for reminding me. Yes, that bottom aft cone skin is really thick. Took a lot of massaging to get the shape right.
 
To make riveting the bulkhead slightly easier, you can ?sandwich? the empennage support bars in between the two bulkhead parts. But this only works on non-punched kits. With the bars sandwiched it?s much easier to buck the rivets that otherwise are tricky to get to, especially along the bottom.

Chris
 
Cool, looks like there was indeed nothing to worry about. No problem with the fit of any of the bulkheads to the skins. This was suspiciously painless. Thank-you again everyone.

IMG_0946-L.jpg
 
Looks nice

The fit looks really good. I struggled with this fit during fuse assembly, then pulled the bulkhead out and reshaped until I got a better fit. By making this fit well now, you are ahead of the game. Good job.
 
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