Horizontal Stabilizer Rear Spar Misalignment

Hi Folks,

My horizontal stabilizer rear spar is misaligned. I have looked at E’s blog, and hiplanesdrifter’s posts and my symptoms vary somewhat from theirs.

All rivet counts are from outboard edge.

1) The LEFT BOTTOM skin holes align perfectly.

2) The LEFT TOP skin holes misalignment begins at the 19th hole and gets progressively worse toward the outboard edge. Progressively worse meaning the angle at which the rivet sits in the hole increases.


3) The BOTTOM RIGHT skin holes are misaligned from hole 10 and move outboard.



4) The Top RIGHT skin holes are misaligned from hole 29 and move outboard.



5) Additionally, if I cleco the skins to the spar without cleco’ing the spar to rib holes, the 2nd and 3rd (from inboard) LEFT inspar ribs holes are misaligned.




I have contacted Van’s and they are willing to send me a new rear spar with no holes prepunched in the flanges. I’m appreciative of the good customer service and see no better solution, however, I do have some apprehension with match drilling all of those holes. My concerns are these.
1) The skins are already dimpled, will that affect the accuracy of match drilling?

2) Dimpling likely enlarged the skin holes slightly, will drilling through them, as a guide hole, enlarge them further or misshape them?

3) Is there a particular order I should follow when drilling. I’m thinking inboard to outboard, top and bottom of one side, then the other?

Any thoughts would be appreciated.

Problem solved

As usual Van's offered me great customer service to help resolve this issue.

I ended up remeasuring the HS for twist by comparing plumb lines along the end ribs' tooling holes and determined there was a twist of approx. 15/32 of an inch. I have no idea how or why this occurred as all holes during construction lined up. I went on the assumption that I had somehow introduced the twist while riveting the end ribs, as I had taken the structure out of the cradles and laid it flat to rivet those holes. On that assumption, I drilled out the rivets in the end ribs, then cleco'd the rear spar into place with a cleco in every hole. I then re-riveted the end ribs. After doing that the twist was measured at approx. 7/32. I then riveted the rear spar (my original spar) to the ribs, starting inboard and working outboard, alternating between the left side and right side after each rib. After that the twist was down to about 1/8" and the rivets for the skin to spar lined up perfectly. After riveting the skin to the spar the twist is down to about 1/16 - 3/32, which, I assume, is irrelevant.

Now, on to the elevators.