Broken windshield salvageable?

[Pbruce]

Yeah. It’s a bad day at Bearhawk Works; I clipped the corner of the windscreen putting it away and took a chunk out where it meets the wing root. Obviously exploring options to avoid buying a new one. Thinking maybe the fibreglass fairing at the interface between wing root and windscreen might cover. Opinions from anyone who has finished this or thought/planned it out?
Thanks

[alaskabearhawk]

Can you do something like what spinningwrench did on his Patrol and extended it a bit? Drop down to post #10 for the pic.

https://bearhawkforums.com/forum/tools-technics-and-best-practices/81716-wing-to-fuselage-fairing

[Pbruce]

Yes, I think that is the only answer. I have the two chunks which got knocked out. I made some poster board templates while viewing Spinning Wrench’s work. It looks do-able. I intend to glue the pieces back in and reinforce the crack with fibreglass front and back. Then try to construct an elegant fairing like Bruce’s. Hopefully it will cover fairly naturally (like his) since it’s exactly at the leading edge of the wing-root cutout. Thanks for the point-out. Man what a sick feeling!

[jaredyates]

Just thinking out loud here... The missing material seems to be in an area subject to stress, which is probably why it broke there. Do you worry about its ability to transfer the airflow loads to the fuselage?

[Battson]

That is so frustrating for you. Sorry to see this PB.

I wish it would be an easy fix - it seems a shame to waste so much good windscreen. But on the other hand, it might be quicker and easier to replace it complete, the repair sounds like a lot of work. Obviously a personal decision.

I would suggest carefully smoothing out all the cracked edges to ensure no new cracks form there in future. There will be stress-risers in that area (little sharp edges) which could initiate new cracks, especially at the innermost part of the void. I believe it is acrylic, which is prone to crack anyway. Could have that wrong.

[Hewko]

I've stitched a small windshield crack by step drilling and safety wiring, which lasted for years, but this is definitely a more elaborate repair

[Pbruce]

Thanks for the discussion points. At this point I’m intending to glue the pieces back in with a vulcanizing glue made specifically for acrylic. Then I think I’m going to sand the surface and laminate some layers of fibleglass with CA glue over the area which encompasses the damage inside and out. Hopefully this provides adequate reinforcement to work the windshield into shape. The entire area will be covered by the fibreglass fairing, as near to what Spinning Wrench did as possible. I’m considering laminating the fibreglass faring, layer by layer, directly to the windscreen in order to insure that it’s very strong. That’s my plan for now. Not sure if it’s a good one, but I will proceed until/unless I get a sense that it’s not going to work.

[rodsmith]

Be sure to test your epoxy on a scrap piece of plexiglass before laminating directly to it. Acrylic doesn't get along with a lot of chemicals.

[Pbruce]

Good idea. I’ll probably adhere the first layer (s) of glass with CA, (recommended by acrylic manufactures), then subsequent layers with epoxy. I won’t take anything for granted though. I’ll test and practice the whole layup on scrap panels first. That will allow destructive testing too.

[Pbruce]

Repair is going pretty well. I made up test pieces and tested them to destruction. I experimented with epoxy vs CA and epoxy had the edge. Using a layer of 6” cloth on each side of a break glued with ca, the epoxyglass-strapped joint was stronger than the CA one and the parent material. Im going without the carbon since it’s a bit too stiff to work in this small repair area. I’ll paint and cover with the fairing. I think I’m ok