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Permalink Reply by John Austin on July 20, 2012 at 5:55pm

I used a 4" thin abrasive cutting disc. Cover the intended area with painter's tape and mark your cut line on that and cut right through it.  Go slow and keep it cool so you don't get a lot of melting and gum-up. The real key to cutting or drilling is to back-up the acrylic and firmly weight it down so you don't get a bunch of flexing going. (I laid a heavy piece of padded 2" angle iron alongside the cut line.) Drill pilot holes with bits intended for acrylic - step drills work fine for enlarging holes - again, back it up where possible. You sort of want to "warm up" the hole with the friction of the bit - a little melting of the edges smooths the hole and helps prevent cracks.

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Permalink Reply by Dr. Edward L. Olds III on July 20, 2012 at 6:01pm

John,

Were you responding to the issue of working on the windshield??  I think so, If correct, great insight.  I was looking for shotbags and angle iron, padded would work just as well, I hope!

Ed

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Permalink Reply by John Austin on July 20, 2012 at 6:06pm

Yes - the windshield - it's made of acrylic, not Lexan. John

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Permalink Reply by Dr. Edward L. Olds III on July 21, 2012 at 8:27am

OK, here go my nerves!

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Permalink Reply by Mark Maltais on July 9, 2013 at 7:44am

Resurrecting an old thread! 

I'm getting ready to install my top window and can't find any Butyl tape anywhere!  Acklands has it but it's either round or comes in "square" tape which is 3/8" thick!  Anybody know where I can find this stuff in tape form??  Seems like a pretty rare animal. 

Also, for those who have left the window overhang the side sills, how much are you letting it overhang by? I'm really liking the idea of letting hang out a bit which would mean I don't have to kill myself getting a super smooth edge!

Thanks guys.

Mark

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Permalink Reply by John Austin on July 9, 2013 at 8:12am

Mark,

There's plenty of it on Ebay including 1/8" thick - just search "butyl tape." Also, the RV (rec vehicle, not the airplane!) industry uses it for windows, vents, etc. If you happen to have a RV repair shop nearby, they probably have it, too. I used the 1/8" along the tops of the tubes above the sills on the sides (and also across the back edge of the window where it meets the rear fuselage) and then stepped-down to ? 1/16 or 3/32 over the rivet line on the back corner gussets (I suppose a bead of RTV would work just as well over the gusset.) The thinner 1/16" tape is much harder to find, but some Googling will eventually turn some up - but RTV probably would work just as well.

1/8" tape seems the ideal thickness on the tubes, however. When you rivet the Lexan down, it squeezes out just right to fill the void between the round tube and the Lexan.

If you're doing the flat window with the diagonal support (Ed. 2), I highly recommend my modificaton of the top window trim that holds down the acrylic windshield to the top window and spar carry-through. I used RTV between the acrylic and Lexan and butyl tape to seal between the trim and acrylic when I found the original installation leaked like a sieve when washing the plane!

John

N750A

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Permalink Reply by Mark Maltais on July 9, 2013 at 8:33am

Thanks for the info.  I was also going to change the trim piece above the window and add some sealant in there.  Zen has too many "flimsy" pieces that should be updated to thicker pieces IMHO.

I like how you did yours.  How wide was the tape you used on the tubes?  I'm thinking about getting 1" or 3/4" and trimming whatever goos out past the tubes.  That way I know the seal is solid.

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Permalink Reply by John Austin on July 9, 2013 at 8:41am

I agree - I couldn't stand those waves between the screws in the original trim piece! Be sure and run a flanging roller along the edge facing forwards to slightly turn it down - it'll further stiffen the piece and make a straight edge where it touches the windshield. I put a piece of butyl tape (1/16) under the trim to cushion and seal it against the acrylic.

I "think" it was 3/4" width (by 1/8") on the tubes, but either would be fine.\

John

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Permalink Reply by Dr. Edward L. Olds III on July 15, 2013 at 12:46pm

Mark,

Have been traveling and not on the web.  John gave you great advice on the tape.  I had no trouble getting it, but I ended up getting it from AC Spruce in wide size and then trimming it to my width.  

As for overhang, I don't think it would be a problem to let it stick over a good bit.

Ed

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