Windshield mounting questions.....

[RadialFox7]

I didn't catch the discussion about the butt rib swap before I installed mine as per the manual. I'm wondering now if the limited edge distance will cause cracks in the windshield when enlarging the mount holes to .25 inches. It looks like there will only be about 1/8th of an inch edge distance. Thought I'd trim after enlarging the holes and possibly leaving an additional 1/8th inch material beyond the butt rib as that should easily overlap the wing #1 rib. Any thoughts and/or recommendations would be appreciated.

[mr bill]

To prevent cracking in metal I have used 1 1/2 hole diameters minimum from the center of the hole to the edge. In plastic I would use 2 diameters minimum. If it is not possible to do this, then slot out the hole to the edge.

[jiott]

I installed my butt ribs per the book and have the reduced edge distance. I did leave about 3/16" to overhang the #1 wing rib. I made sure my holes were drilled with an acrylic bit and were nicely chamfered and smooth. So far (2 years) no cracks.

[HighWing]

Not sure on the current build manual, but in the "Old Days" we always cut the windshield "glass" to overlap the wing surface. Not sure of the clearance issues today as we used the Polycarbonate and it could move a bit if the clearance was slightly tight. My current airplane - Model IV completed 2012 - overlaps about 5/8". It keeps the rain out. Just guessing, but I think if I had the issue, I might shim the top of the butt rib a bit to make sure there was adequate spacing for the wing clearance. Everything in my airplane framewise is black so I think I would put a strip of black adhesive felt - Michaels - at a minimum to give a little lift to the skylight - did it on my IV. Another thing I have used is the felt side of velcro. A bit pricey, but it is tough, a bit thicker than felt and the adhesive is designed to stick. I also used nutplates rather than rivets and it allows tightening to a desired tension rather than whatever the rivet squeezer gives you. The one down side as I think about it is when the wing is folded the forward spar will sag a bit, so when repositioning it might require a bit of a lift to get the spar over the carry through attachment. Lift a bit too much and I suppose it might add pressure enough to crack an Acrylic windshield.