Windshield problem

[airguy]

With all the airplanes currently flying like this, I'm sure others have found and fixed this problem before. Sorry for the big pics, I wanted to show good detail.

I installed the windshield on my 9A per Vans plans with small aluminum clips riveted to the forward skin, then covered that joint with flox and a couple layers of glass cloth over the top, then skimmed that over with microbeads prior to paint. For 140-ish hours this was fine and showed no problems whatsoever - but now just 28 hours out of paint that area is cracking, showing definite flex outward. I have kept the pictures here full size to show the detail. I'm only showing pics of the right side in this case but the problem is duplicated on the left, both show bowing outboard at the same spot along that joint.

What I'm thinking is that, Vans plans or not, the aft corner is simply not supported adequately and needs to be immobilized with another clip in the area of the triangular steel gusset that is the base of the forward canopy bow. I'm thinking I need to use a grinder to remove the overlaying layers of glass to expose the joint, drill a hole just below the plexi through the aluminum and steel triangle, and install another clip with a screw going inward from the outside. I'll use a nylock on the inside and trim the excess screw length, then re-bury the head and clip with flox and microbeads before repaint.

What sayest the brain trust here?

[jwilbur]

The front windscreen of an RV10 is similar. My airplane is not painted yet but I had an issue where while working FWF I was leaning on the aluminum just in front of the windscreen and caused the glass-work to crack. It was easy for me to fix since it's not painted yet. But before I paint, I'm planning to flex that whole area and see if it cracks anyplace else and deal with it now.

I say this because I wonder if it the same thing in your case - not so much the plexi pulling away as it is the aluminum pressing inward.

[Dbro172]

The bottom of the plexi is a good distance North of that crack, almost looks like the plexi would have had to push inward, not outward for that crack to open up like that. I know that I have a bead of epoxy/flox behind the plexi at that area, between the plexi and forward top skin, looks almost like a need of sealant and keeps the plexi from moving inward. Don?t recall if the plans said to do that or not, cant imagine I would have thought of that on my own, unless there was a very unsightly joint there. Maybe its all that fuel!

[Mark H]

The crack appears to be at the bottom of the fiberglass layup and it looks like the fiberglass is not adhering to the aluminum and pulling loose. The fiberglass layup is meant to be the structural support of the wind screen, so it should hold even without the clips. That said, fiberglass just doesn?t hold very well to aluminum unless it is prepped really, really well. I believe that?s why the plans call out optional blind rivets embedded in the layup to the top skin. I think I would sand down the cracked area to the aluminum, prep the surface, layup up several layers of cloth, and then use some blind rivets or other mechanical fasteners to reinforce the fiberglass adhesion to the skin and hopefully make sure it doesn?t get pulled away again. You can micro over that to the final shape.

[rv7charlie]

Sikaflex sticks really well to aluminum, and to plexi. And it, well, flexes.

FWIW.... :-)

[airguy]

After thinking on it for a while and looking at it again, I agree with Mark H that it appears the fiberglass layer is lifting up off the aluminum rather than the windshield flexing the glass. It's definitely an outward movement of the plexi that created the crack - I'm wondering if the canopy pushes on that area when closing and I didn't notice it before, but I haven't had a chance to look at that yet.

If I have a mechanical interference with the slider section that's pushing it out (unverified), that has to be fixed first - then I'll need to anchor that section down to the skin beneath it and re-bury the anchor, then touchup paint.

[Raymo]

I used Sika with no clips on the my -7A windshield. The day after it cured, one side popped loose at the bottom of the fuselage just fwd of the roll bar so I installed two clips on each side with a fresh layer of Sika to keep it in place. Did the fiberglass and micro afterward. All is still well with 110 or so hours on the Hobbs.

[Steve Melton]

bolted, no clips, epoxy. I made sure there was some down pressure (interference) on the fwd part of the glass to the canopy frame when assembled.