Monday, June 15, 2015

deformation of Baggage Bulkhead

my letter to Van’s Support:

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 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.  

IMG 4377

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.  


IMG 4373

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 is the culprit.
Since the front faces of the F-1231D Roll Bar Braces are 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 replace 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’ll wait to hear from you instead.
Thanks for looking this over,

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