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F-706B, DWG 21

wirejock

Well Known Member
Anyone
I'm prepping F-706B. There is a Detail A and Note 2 (5/8" hole) showing holes for manual trim or wiring. Notice my photo. The hole will clearly bust edge distance for all four rivet holes around it including the rivet holes for F-727-L & R Baggage ribs. Am I missing something?
16m0u9s.jpg

25h0fb9.jpg
 
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Rib clearance

You are correct to question the plans dimensions. Apparently acceptable to Van's engineers, it's not just the edge distance for the rib flange rivets that is potentionally compromised. Be sure to adjust that 7/8" horizontal dimension to clear the transitional bends of the rib flanges to the webs. When I drilled mine per the plans, the hole centered perfectly between the rivet holes, but I later saw that the full size hole cut a little into the bend for F-729A. A sixteenth of an inch inboard and I would have hit the web. Check the dimension for your parts and adjust horizontally as needed.

Also if you haven't gotten to the F-705 assembly yet, you will have the same concern with clearance for the associated holes there. Check the dimensions with your ribs clecoed in position to verify clearance before drilling the large holes.
 
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Holes

You are correct to question the plans dimensions. Apparently acceptable to Van's engineers, it's not just the edge distance for the rib flange rivets that is potentionally compromised. Be sure to adjust that 7/8" horizontal dimension to clear the transitional bends of the rib flanges to the webs. When I drilled mine per the plans, the hole centered perfectly between the rivet holes, but I later saw that the full size hole cut a little into the bend for F-729A. A sixteenth of an inch inboard and I would have hit the web. Check the dimension for your parts and adjust horizontally as needed.

Also if you haven't gotten to the F-705 assembly yet, you will have the same concern with clearance for the associated holes there. Check the dimensions with your ribs clecoed in position to verify clearance before drilling the large holes.

Thank you!:D
 
Getting to that part of the fuselage. I don't like it.

I measured the distance between two diagonal prepunched holes (they don't seem to be quite on a rectangle, but close enough), and it is ~1.015, center to center. Subtract 0.630" (5/8" with unibit), halve it, and I get ~0.192" "theoretical" edge distance. And I haven't looked at a potential rib flange issue yet.

I guess, it is still more than 1.5D (0.188") at least, but these are thousands I am talking about here. They are not so easy to hit on a sheet aluminum. To me, anyway.

Debating if I want to do it per plans (I am sure thousands of planes are built that way) or just drill a hole in a different place. Drilling in a different area might cause some downstream effect, though.

P.S. What really adds insult to an injury, is a Note 3 on DWG 22: "now that you probably think you blew up edge distances a bit, go and upsize the hole to 3/4" ". That's for F-705, though, where situation is not as grim as in case of F-706. Also, only if installing battery aft.
 
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