aft fuselage alignment problems - need help

[IowaRV9Dreamer]

I'm having trouble getting the F-779 tailcone skin and it's 2 bulkheads (F-711 and F-712) to align with the side fuselage skins.

With the stringers in place (but not drilled) I can get a good alignment of everything, but the F-779 holes don't align with the side skins holes. I can't put clecos in and pull it together because the stringers are in the way.

For fun, I pulled out the stringers (whoopee). Now I can get the tailcone clecoed to the side skins, but the bulkheads are now "too high" for the holes on the side skins.

I've spent a ton of time improving the shape of the tailcone skin - I think that's OK.

I've been working hard on the F-711 and F-712 bulkhead flanges - I may need to make some modifications there to "lower" the bulkheads down into the curve of the tailcone.

I know others have had problems there... is there a magic bullet? I think I really want everything to align perfectly without the stringers, so I can slip them in without changing anything. The problem is that the stringer holes also attach the tailcone skin...

Thanks in advance...

 

[pmccoy]

Clamp the F779

Dave-

I had trouble with this area as well. I found the only way to get everything in alignment, was to clamp the fuselage skin and F779 skin. With the clamp moving a rivet hole or two in front, I was able to start at the forward side of the F779 and work my way back. This was the only way I could get the F711 & F712 anywhere close on the bottom line of rivets.

 

[Randy]

Absolutley verify that the two bulkheads that get put together are in the correct order. It is possible to get them together backwards and it is not readily apparent, but will cause serious hole misalignment.

 

[alpinelakespilot2000]

Dave-
I too had trouble here. Clamps can help as mentioned above.

Also, this is one area where I would strongly recommend not match drilling the tailcone to the side skins. Instead just drill up the holes to final size beforehand. Because of the difficulty in getting those layers to match up nicely, it's really easy to elongate holes as you're match drilling. I did this and ended up going with AN4's to get the holes round again. Since I'm building a taildragger, I'm actually happy to have AN4's back there, but that wasn't my original intention!

My though would be to not even attempt to put the stringers in until everything else is clecoed together.

Good luck. This was easily the most challenging part of the fuselage for me and I have a couple relatively ugly shop heads to prove it!

 

[Wes Hays]

I feel your pain!!! That is exactly what I am doing today. I got the stringers in and the tailcone on, and it just wasn't going to happen. I went back and re-read the instructions, and unless I am wrong, (and I would appreciate a head's up) they say to drill the stringers to the side skins BEFORE putting in the tailcone. This will allow you to cleco the tailcone on to the skin and stringers at the same time since the stringers will have the matching holes for the tailcone and skin.

After thinking about this it makes pretty good since to me. By having the stringers drilled to the skin, you can pull the tailcone in with cleckos and rivets. I must admit, mine is not perfect, but when I put the tailcone on, all the holes matched up with the skins so I think it will be OK.

Let me know if I am off base here.

 

[cnpeters]

Just did mine a couple weeks back. First, I screwed up the first -779 skin when I attempted match drilling and had elongated holes (too long for OOPS or AN4 rivets). Also fought the bulkheads a bit (clamps helped) getting them to seat.
So, I ordered a new skin and drilled and dimpled the skin, bulkheads and side skins SEPARATELY. I made sure the flanges of the F-711 and 712 bulkheads were angled a bit to follow the F-779 skin shape first. Everything went together MUCH better with all holes aligning well. Bulkheads were fitted and riveted first. I believe I added the F-710 bulkhead next, then the F-779/bulkhead assembly was slid forward on the stringers then aligned with the side skins (the side skins were splayed out at first so the F-779 fore edge could get past). Everything clecoed - went much better this way.

 

[Wes Hays]

Dave,
FWIW, I finished drilling in the stringers and tailcone yesterday. I drilled the stringers with the tailcone removed. Once finished, I slipped the tailcone in like Carl described and the dude is now clecoed in and ready for match drilling.

One tip that was invaluable was from a good friend (Rick Liles in Lubbock) who told me to install the bottom portion of the baggage bulkhead and to put on as many top skins as possible. This held the fuselage straight and rigid while doing all the drilling. Came out extremely true, and it was amazing how rigid it was after the stringers were drilled in.

I know the instructions tell you to check that the tooling holes in the bulkheads are plumb before drilling, but the top skin(s) really held the entire tailcone straight and true.

YMMV!

 

[IowaRV9Dreamer]

I can see the light at the end of the tailcone tunnel

Hi Guys - thanks for the good input. I like the idea of drilling the stringers first, even though it's the opposite of what my instructions say. Seems like a better way.

Too bad I didn't know that last night! I ended up pulling the stringers forward, clecoing the F-779 to the side skins, and then spending a bunch of time working on the bulkhead bottm flanges. I found that with just the right flange angles, I could get the bulkhead holes to line up with the side skin holes, while leaving the F-779 attached to the side skin.

I started with the F-712, and when it was finally installed I put in the F-711. I had to bend the rib flanges way more than I thought. I got a cleco in every other bulkhead hole.

When that was finally done, I gently removed the clecos holding the F-779 to the sideskins. Nothing moved (much) and I gently slid the stringers into place. I reattached the F-706 bulkhead (removed to move stringers forward) and I'm now ready for match drilling. I put the plumb bobs on and everything looks straight. I'm not sure I could twist it much if I wanted to... certainly not without moving the tailcone skin out of alighnment.

Looking at it, the worse case misalignment is <1/2 of a hole between the F-779 and side skin. This happens at the very aft end. The front end is dead on. I think that if I start drilling the stringers from front to back I will be able to pull everything into alignment.

Crossing my fingers - I'm ready to move on the the next step. This has been a bigger pain than I expected.

 

[boom3]

I too had a lot of problems with this area. I used the duct tape method and rolled the F-779 with a 2" piece of pipe. That helped alot. Once I got the flanges of the bulkheads perfectly lined up with the skin I was able to cleco every hole. Some of the clecos were slightly angled, but when I drilled the holes to #40 it took care of it. It's now riveted and looks great.

It's funny how great things go for awhile and then something frustrating like this always seems to come along.

Cleco anyone?

 

[alpinelakespilot2000]

It's funny how great things go for awhile and then something frustrating like this always seems to come along.

Jeff-
You'll be really frustrated again if you actually rivet that rudder stop on! Search the archives for rudder stop and you'll see that people usually have to make multiple versions of it. Don't rivet those on until you actually have the rudder on the tail to check for travel. Ideally, don't drill them to the fuselage until that time as well because your first ones probably are not going to be your last ones! Good luck otherwise.

 

[IowaRV9Dreamer]

Jeff-
You'll be really frustrated again if you actually rivet that rudder stop on! ....(snip)....your first ones probably are not going to be your last ones! G

Excellent - a cool tip! I wonder if there is a better design out there? I saw the delrin stop but it isn't for me. Would it be better to cut the rudder side "big" (leave" material) and fit it later to avoid making multiple stops? I hate my bandsaw and the less time I spend with it the better...

 

[boom3]

Jeff-
You'll be really frustrated again if you actually rivet that rudder stop on! Search the archives for rudder stop and you'll see that people usually have to make multiple versions of it. Don't rivet those on until you actually have the rudder on the tail to check for travel. Ideally, don't drill them to the fuselage until that time as well because your first ones probably are not going to be your last ones! Good luck otherwise.

Thanks for the heads up. I looked long and hard at it when I was at this stage and did decide to wait and haven't drilled it yet. (I did drill one hole)

 

[mike109g6]

Rudder Stop

Excellent - a cool tip! I wonder if there is a better design out there? I saw the delrin stop but it isn't for me. Would it be better to cut the rudder side "big" (leave" material) and fit it later to avoid making multiple stops? I hate my bandsaw and the less time I spend with it the better...

Design is fine, just don't things so literally on the fuse. You'll find that the fuse plans are 'generalizations' and not absolutes. The stops cannot be finalized until you mount the vertical stab/rudder and adjust the bearings for vertical alignment. Once done, then you will determine the stop shape, in relationship to the elevators. The stops are there to prevent the rudder from being pierced by the elevator TE.
FYI-if you think that this has been fun wait until you try and align the midfuse/cabin with the aft section. And then of course the front cabin - exciting times await.
Mike H 9A/8A

 

[RV7Factory]

I'll echo the statements of several others... this was the worst fitting area of the kit I have experienced so far, and I am glad it is behind me.

I ended up boogering up my F-779, and since I am building a T/W I didn't want to take any chances so I ordered a new one. The new skin fit MUCH better than the old.

In the picture below the new skin is on top and the old on the bottom. You can see that the bends on the new skin were much better from the factory the second time around, and this is after I tweaked the bends in the bottom skin. The new skin fit with no problems whatsoever, where I had previously spent a lot of time wrestling the original skin into place (with a lot of swearing involved). Even though I had it clamped in several places, the holes didn't want to line up (using the old skin). When I installed the new skin, all the parts went together so easily I had tears of joy rolling down my face (almost).

I don't know if I got a bad one, or maybe Van's has improved this part, but if your skin is bent like my original, my suggestion would be to do whatever it takes to improve the bends on the skin before trying to fit it to the fuse. Just my $.02.