My Wooden Airplane
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6/24/2014 - 9/10/2014

Windshield

I finally finished the windshield! This obviously took way longer than I originally expected, and there was a steep learning curve along the way. There are several nuances to this installation, which I will attempt to cover completely.

First of all, I knew I would be using a technique called "cold-forming". This is where you bend the material into the shape you want, and hold it in place with mechanical fasteners. I didn't want to use any heat, because I didn't have an oven big enough to fit the entire windshield, and using a heat gun would just cause distortion. On most high-wing planes (i.e. Cessnas), the top of the windshield spans almost the entire width of the fuselage. This causes a rather sharp bend in the upper corners where it wraps around the wing roots. I figured it would be almost impossible to accomplish this with "cold-forming", so I cheated, and extended the wing roots inboard about six inches or so. This means the top of the windshield does NOT span the entire width of the fuselage, and allows those upper corners to use much more shallow bends.

Then I made a template out of poster board. That wasn't too bad, and actually boosted my confidence a little bit!

For the next step, I tried to use acrylic (i.e. Plexiglas), and failed miserably. Aircraft manufacturers typically use acrylic (as opposed to polycarbonate, i.e. Lexan) because it is harder, less likely to scratch, and if it does get scratched, can be polished smooth again. Also, it doesn't turn yellow if left out in the sun too long. The problem with acrylic is that while it is reasonably flexible, it is fairly brittle, so any amount of mis-handling will cause it to crack. (It also doesn't respond too well to bird strikes!) It also apparently can't be "cold-formed". The complex curves in a typical front windshield require a large mold (and even larger oven) to "melt" the material into the shape it needs to be. I went through four pieces of acrylic before I figured this out! When I called the distributor and explained what I was trying to do, right away he said "Oh, you can't do that with acrylic. You can do it with polycarbonate, though." So, I ordered a 4' x 8' sheet of polycarbonate, and when it arrived, it was rolled into a tube about 1 foot in diameter! Talk about being flexible!

I used the posterboard template to cut a piece out of polycarbonate. It took a bit of trimming and some trial-and-error, but eventually I got it to fit. One of the keys is using two people, and anchoring the windshield at the top first, and then bending it around the sides. The top and sides are held in place by using strips of aluminum to hold the windshield into "tracks" or "grooves", very similar to the side windows. There are no holes in any of the windows for screws (or anything else, for that matter).

The bottom is held in place by several aluminum "tabs" about 1 inch long by 1/2-inch wide.

The upper corners are wrapped with fiberglass fairings.
These are only decorative, and are not structural.

The bottom of the windshield is covered with another fiberglass fairing. Again, it is only meant to be decorative, and not structural. All of the fairings will be sealed with caulk (or something similar) to keep the wind and rain out.

Since the polycarbonate material is softer and more prone to scratches, I was thinking about using some automotive window tinting film on the outside of the windows as sort of a sacrificial surface. It may even help guard against the eventual yellowing of the material. If that doesn't work, it would probably only take me half a day or so to replace the entire windshield if that ever becomes necessary.

Total Time: 74.5 hrs.