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Fluting fuselage frames (tailcone)

kritsher

Well Known Member
When fluting these frames, is the idea to get the whole part flat, which would require a lot of fluting on the short inside flange, or do you just need to align the rivet holes on the outside flange? I'm guessing the latter, because it looks like the frames create sort of a truncated pyramid (for stiffness, I'm guessing) and that to flatten them would be 1) very difficult and 2) a bad idea.
 
Generally flat is fine.

They are fairly floppy anyway. If you get them decent, you'll find it is good enough I'd say. Just get the flanges generally to look like they all match up fairly well also. That helps in not causing wrinkles in the skin.

John Bender
 
it will also help the appearance of your skins on top of the fuse if you "break" the edges with a breaking tool so they don't "stick out" on the curves. The best one you can buy is from Cleveland Tools.
 
Need some additional advice from you seasoned experts. I am somewhat confused on the fluting of the tailbone frames. I understand the premise of aligning the holes on the outside flanges. Looking at the F1208 pieces the only place where there is a slight bow that fluting would correct is in the bottom flange where there are 10 holes in a continues flange. I was able to flute them and get the bow out there. The rest of the smaller flange segments appear to be fairly well aligned. If there is a bow it is concave vs convex and flutes would make bow worse. Hope that makes sense. Also as noted above if the inner flange lays on the table the entire outer flange is elevated about 3/8 inch all around. Is there any issue with that? I have not been able to tell looking at others build pictures how much fluting actually has been done. I did similar fluting at bottom of F1209 frames and the smallest ones nothing so far. Any additional guidance would be appreciated!
 
Need some additional advice from you seasoned experts. I am somewhat confused on the fluting of the tailbone frames. I understand the premise of aligning the holes on the outside flanges. Looking at the F1208 pieces the only place where there is a slight bow that fluting would correct is in the bottom flange where there are 10 holes in a continues flange. I was able to flute them and get the bow out there. The rest of the smaller flange segments appear to be fairly well aligned. If there is a bow it is concave vs convex and flutes would make bow worse. Hope that makes sense. Also as noted above if the inner flange lays on the table the entire outer flange is elevated about 3/8 inch all around. Is there any issue with that? I have not been able to tell looking at others build pictures how much fluting actually has been done. I did similar fluting at bottom of F1209 frames and the smallest ones nothing so far. Any additional guidance would be appreciated!

I did minimal fluting only as required by the instructions, shown in the videos, and had no problems with the holes lining up fwiw. The frames are pretty flexible.
 
RV-12 Tailcone Frames

I just started the tail cone section on my -12 and hit a road block.

Step 4: Flute the F-1208-L & -R, F-1209-L & -R, and F-1210A-L & -R Fuselage Frames to align the flange holes. Flute the 'hump' of any humped flanges toward the web of
each fuselage frame.


Where do you flute to make the frame lay flat. Tried the outside flange and that made it worse. Tried one spot on the inside flange but I think its too short (may have even cracked, reaching out to Vans on that one). Would like to hear some input from others who have gone before.

Thanks
Frank
 
An inside flange should technically never have to be fluted because the forming process is actually stretching the material to form the flange and fluting is essentially shrinking it.
As described in the plans, try checking the hole alignment on each flange segment with a straight edge and flute between the P. P. holes until the holes are aligned with each other. If you over do it slightly, lessen a flute by squeezing it back with some flat faced pliers padded with some tape.
 
I too was confused for a bit here. Because of the way the parts are sprung/warped/twisted it is not obvious where fluting will help until you try to force the part flat on a bench. In the example shown below you can see that when the bottom portion of the frames are forced flat there are two humps, one on the left half of the frame, one on the right. Fluting as shown will fix this. Repeat this process around the other sides of the frame. Doesn't have to be perfect as others have said since the frames are quite flexible.

RV-12-Tailcone-Fuselage-Frame-Fluting-Example.jpg
 
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