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HS-405 (Main Rib) to HS-603PP (Rear Spar) Drilling

J

John R. Graham

Active Member
The plans tell you to draw a centerline on the HS-405 rear flange and then align the centerline to the pre-punched holes in the HS-603PP rear spar. When I do this, the top flange of the HS-405 aligns perfectly with the inboard edge of the HS skin but the bottom flange sticks out beyond the skin by 5/64". I can think of three ways to address this perceived issue:
  • Align top and bottom flanges with the inboard edges of the HS-601PP skin, check that I don't have a minimum edge distance issue, and, if not, drill it that way.
  • Align the flange per the instructions and then trim the lower flange to fit the skin edge.
  • As above but don't trim the flange because the protrusion is minimal and trivial.
I have already very carefully checked that the HS-405 is properly fluted and very straight. Am I missing something?

- John
 
Align the centerline on the rib flange with the holes in the skin, drill and don't care about the small amount of flange sticking out of the skin edge. Just be sure the centerline is correctly centered on the flange.
Just my opinion.
 
Mark the centerline along the flange. Use strips of scrap aluminum clamped to the top and bottom flanges of the rib (simulating skin) to center the rib on the spar. The side profile there conforms to the airfoil shape so the spar flanges won't be 90 degrees and the rib widens from the spar so it's impossible otherwise to really align them.
 
Thanks. Actually, the contemporary instructions call for the rib to be fitted and drilled with the skin attached, so it's not necessary to use the scrap aluminum method for vertical alignment to the spar: with the skin on, the rib sits in there with a very modest amount of interference resistance. Makes it easy to put it in the right place before clamping.

- John
 
Having just completed mine, I followed Vans instructions. I found that in a few places on either rib the flange stuck out a little from under the skin. I figured that as long as I have edge distance and the rib is true to the skin then no problem! After getting it to that position and cleco'd then I drilled per plans. It will be covered by the fairing anyways.

Cheers and Good Luck!
 
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