S

Stewie

Well Known Member
Patron
Hi all-
I have an "old school" -4 fuse that has the original non-split 410 bulkhead. I didn't realize 410 was split until comparing my old full size plans with my newer preview plans. Just curious if I am setting myself up for a major PITA by leaving 410 as is (fuse is still inverted and just about to rivet on bottom skins)? I know the stab needs to fit in there. It looks like it will be tight but there is enough wiggle in the bulkhead that I can't get a precise measurement. Any comments or suggestions welcome...
Thanks,
Eric
 
410 bulkhead

I cant remember the exact scenareo you are describing..and I dont have my plans handy. Refresh my memory of which bulkhead this is? If I am thinking correctly, its the one at the aft end of the upper deck skin.I believe I split mine, and the upper half is slightly forward of the bottom.
 
Correct

Yes, it is the aft bulkhead before the last two double-thickness bulkheads. My only concern about splitting it (other than the time it will take) is that it will no longer conform to the turtle deck curvature, although I suppose I could just order a new upper half from Vans. Just thinking there are some old timers out there with single-piece 410s who could tell me whether that is worth the trouble or not.
 
Split bulkhead

After splitting, it will be attached by a 90 degree angle riveted to the bottom,and it will not be moved far enough forward to create a contour problem with the skin. If you need, you can cut a strip of .032 and lay on top of the flange to make up the difference. The empenage fairing will cover well forward on the skin, and will likely need some modification to fit correctly anyway, so minor dimensional changes in this area are irrelevant. Meant to get some pictures together for what I did there, as I took many, but they are "old school" film...before my digital leap in photography.
 
I made this change as a retrofit to my completed RV-4. I had an issue with not enough nose-down trim available with passenger/bags, especially during long high-speed cruise descents from altitude. After making a change in the empty C/G by switching from a wood prop to metal, I still had a need for more nose-down trim. I wanted to raise the leading edge to reduce the tail down-force and increase the nose-down trim capability. The access to the attach points is very difficult because the horiz stab spar attach bolts go forward through the bulkhead and the bolt heads are only accessible by crawling into the aft fuse. Also, in order to raise the spar I would have had to slot those holes in the bulkhead.

I drilled out and trimmed out out the top of that bulkhead and installed the new one from Vans. I installed it in the reverse orientation (flanges pointing aft) so I could easily set the rivets. I did not install it in precisely the same location as the drawing; rather I determined where it had the tightest fit to the inside mold line of the skin and marked that position before cutting back the skin. I then had more room to install new mounting angles to attach the spar to the longerons, and could easily use shims to adjust the incidence.

I definitely recommend making this change now during the build if you can. Inspecting the tail attach points is much easier, and if you ever need to remove the tail for maint or repair it is a one man job. Also, if you need to adjust the incidence like I did, you can.

I will try to post pictures of this job later when I have time.

Regards,
Marc
 
Thanks Bill and Marc, your comments are greatly appreciated! If you have a chance to post pics, that would be great too.
Eric
 
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