deformation in Baggage Bulkhead

Hi folks,

Could you look this over and tell me if you can figure out what I did wrong?

Today, I attached (cleco only) the tail cone and noted that there appears to be deformation of F-1207A Baggage Bulkhead that prevents alignment with that part and the tail cone itself. I didn?t notice it earlier in the build as it?s not evident until I try to mate up those parts.

The first photo shows the divergence of the tabs from the tailcone and 1207A as it reaches the midline of the structure. It appears that the F-1232A Roll Bar Brace is pushing it too far aft. The distance between the leading edges of the inner most tabs is about 7/16?.



The only anomaly that I have been able to identify so far that could cause this is the alignment of the roll bar with respect to the longitudinal axis of the plane.

Photo 2 is from the right side of the plane. It looks like there is a 1/16? gap at the forward edge of the roll bar. Using the width of the roll bar as 1.5" and the height of the roll bar as 23?, a little bit of trigonometry shows that there would be 0.95? of aft motion at the top of the roll bar due to that 1/16?. Solving the other direction and using the measured displacement of 7/16? at the top of the fuselage works out to only needing the roll bar to be 1/32? off of the surface. In other words, the math seems to confirm that this may be the culprit.



Since the front faces of the F-1231D Roll Bar Braces were pre-drilled, that 1/16-1/32? gap is not something I can control at installation. I?ve verified that the bases are tight against the airframe.

I?ve thought about removing and replacing the 1231D Roll Bar Braces, but realized that since the front faces are pre-drilled, I wouldn?t be able to change anything on re-assembly. The only other idea that I?ve come up with so far is to loosen the Roll Bar Braces and place one or two 1/64? shims on the rear edges. That doesn?t sound like a good idea so I'm doing nothing for now until some smarter ideas emerge.

Thanks in advance,
-dbh

I just looked at my roll bar. The gap that you measured at 1/16" on your plane is 1/32" on my plane, both on the forward and rear side. The gap is the same on each side. My roll bar does not looked like it is tilted towards the rear like yours does in picture 2. It sounds like you have already figured out the problem. Good going with the trigonometry. Now the problem is, how to fix it.

Dave,

Maybe it's just the photo, but it looks like you could rotate the tail one and get the holes to line up.

Rich

Be very circumspect with regard to "adding shims" on the RV-12. If shimming appears to be needed, it usually means something is not right elsewhere. Triple check your work leading up to that point.

Need more photos

This is very hard to tell from the photos are the laps on the bottom all the way the drawing shows.

My guess if you start from the bottom and install clecos working from the center and up both sides and shifting the support places at the tail cone and or the fuselage and a little shaking the tail cone will move into place.

Loosen the bolts at the bottom of the roll bar to see if this helps, if this is the problem leave the bottom front rivets in place and remove the other 10 rivets in each of the roll bar braces, this will allow the roll bar to rotate backward.

Page 24.03 Step 3 may have to be redone with new roll bar bases or larger or longer rivets ( call Van's )

A longer rivet ( LP4-5 ) will fill the slightly over size hole when it crushes. The worst hole will be at the opposite corner and may need a larger rivet. ( call Van's )



Also check the 4° inboard bend at 76-3/8" at the back of the Longeron ( page 23.02 Figure 1 )

If you can send photos from the outside.
Good luck

Joe Dallas

Also, be sure the pitot line is not pinched between the tail cone and the fuselage.

Jeff

curiosity

David

How is your tail cone working out
You got my curiosity killing me
I hope you found the problem

All I can say is that the assembled the parts fit perfectly, the quality of the fit still amazes me.

Joe Dallas

stay tuned

Joe,

I haven't worked on it yet since the posting, as I have discovered that sometimes my own best advice is "Don't just do something?stand there!" In other words, I often figure things out when I'm not thinking about it.

In this case, nothing new has percolated into my brain, but I did receive my new roll bar bases. I won't be able to go to work on it until next weekend. I'll be sure to post my findings.

-dbh

The Rest of the Story

joedallas said:

David

How is your tail cone working out
You got my curiosity killing me
I hope you found the problem


Joe Dallas

Click to expand...

Well, it looks like I got things taken care of. I ordered new roll bar bases in anticipation that I would need to remove/replace them to change the angle of the roll bar, but I will be able to return them to Van's. I removed the F-1254 support frames and drilled out the rivets securing the roll bar to the roll bar bases. Viola! The roll bar promptly cooperated with rotating forward and straightening out the F-1207 baggage bulkhead. I could not see any appreciable movement at the roll bar bases and could see daylight when I looked through the sides (left to right of the entire plane, not just each roll bar base.)

I fully clecoed the turtle deck skins to ensure that everything aligned properly. I placed two rivets on each base, and was unable to move the roll bar with some vigorous manipulation. Holes were still well aligned, so everything got riveted back together and I'm back on track.

Conclusion: My error when I situated the roll bar. It was a year ago, but I think I had to use a great deal of verbal lubricant (4 letter words) to get the bar to fully seat. That should have clued me that this was a critical junction and I should have been more careful about finishing the rest of the aft structures to ensure good fit elsewhere. As it was, I didn't notice that the baggage bulkhead was bowed toward the rear when I built that section last year.

-dbh

dbhill916 said:

I removed the F-1254 support frames and drilled out the rivets securing the roll bar to the roll bar bases. Viola! The roll bar promptly cooperated with rotating forward and straightening out the F-1207 baggage bulkhead.-dbh

Click to expand...

dbh... Glad to hear you got things to fit. One solution for new builders that worked for me is to build the roll bar with the roll bar bases "pre-installed" inside the roll bar before riveting up the roll bar.

Jeff