Tips for installing Windscreen

[kiwicubber]

We are close to installing the windscreen in our PA-18A-150 We have heard that it can be tricky to do without breaking the new screen. Are there things we should/ shouldn’t do?


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[Steve Pierce]

Warm hangar so as not to break. Do you have the old windshield and are the wings on? I check the fit of the old and then put it over the new as a start. I also make sure the top of the windshield is even with the top of the wings. Drives me crazy to see the humps where the windshield sticks up above the wings because someone doesn't trim enough. I use a black magic marker and a cut off wheel initially and the use a 3" sanding disc to fine tune. It goes on and off a lot. I mark the holes with the marker through the glass and drill with a Unibit oversize or use a drill bit that has been sharpened to a sharp point and heat it with a torch to melt the holes. The holes need to be bigger than the hardware because the windshield does flex and will crack.

 

[skywagon8a]

or use a drill bit that has been sharpened to a sharp point and heat it with a torch to melt the holes.

Turning the drill backwards does the same thing. Clear off the melted plastic before it cools. A larger hand turned drill works for this.

 

[wireweinie]

In addition to the above advice, sand/polish the edges before final install to prevent cracking in the future. Also, I've had good results drilling holes in windshields, using paste wax. I drill a small pilot hole, fill it with plain old Johnson's paste wax, then drill with a uni bit at slow speeds. This produces a clean almost polished hole.

Web

 

[wireweinie]

Oh, and don't pull the protective paper off the new windshield until it is completely installed. lol

Web

 

[skywagon8a]

Turning the drill backwards does the same thing. Clear off the melted plastic before it cools. A larger hand turned drill works for this.

This used to be my preferred method. The drill turning backwards does melt it's way through the plexi without catching and breaking the plexiglass. Now I have discovered the uni-bit drill. That does a fantastic job with a nice clean no catch hole. And is now my preferred method.
This is a collection of unibits: https://www.irwin.com/tools/browse/drill-bits/unibit-step-drills

They are available from many sources.

 

[RaisedByWolves]

I have some unibits only used for plexi. they stay sharp

 

[skywagon8a]

In addition to the above advice, sand/polish the edges before final install to prevent cracking in the future. Also, I've had good results drilling holes in windshields, using paste wax. I drill a small pilot hole, fill it with plain old Johnson's paste wax, then drill with a uni bit at slow speeds. This produces a clean almost polished hole.

Web

In addition to Web's advise maintain smooth edges after each cut while you are trimming the windshield for the fit. Cutting the plexi leaves numerous small nicks which can be a source of a crack starting while you are handling the windshield. This is especially true if the temperature is low. You can think you are not applying damaging forces until suddenly there is a crack. Keeping the edges very smooth is the key. It is usually very tough and can take a lot of abuse. But put a nick on the edge along with a bending force /\/\/\/\/\/ ! There are methods of repairing cracks, though I suspect you would not be happy with a repair on your plane.

Tip: Drill the holes along the door post last after all the fitting is done.

 

[Steve Pierce]

Yep, I deburr with a big countersink in a dogleg like this using light pressure.

 

[55-PA18A]

If the windshield has the blue protective plastic film, don't let the fuselage sit out in the sun while you're working on something else. That stuff dries on, and is a real chore to get off.

I've melted holes in plexiglass using a heated rifle cartridge of the appropriate caliber, but that many holes you would probably be better off carefully drilling. Heed everyone's advice about carefully smoothing all cut and drilled edges.

 

[kiwicubber]

Thanks for all the responses, very useful. So far I have installed and sealed the lower edge of the windscreen and will do the top and sides tomorrow. Are the top and sides normally sealed, or left nude?

 

[Steve Pierce]

I go back after everything is installed with a bead of urethane sealant.