When it comes to the windshields, Fly Baby builders have two sets of two choices.
While many prefer the look of the wrap-around model, I really recommend going with the stock three-pane version. There's no plastic forming on the stock model...you just cut out three flat pieces of clear plastic, bend some metal for edges and frames, and bolt it all together. With the wrap-around model, you have to either find a pre-molded windshield that fits, or build a mold and oven to soften the plastic and form it into shape. Certainly possible, but it may take a few tries to get an acceptable version that will fit on your plane.
The second reason for going with the stock windshield comes when one has to *replace* a windshield. With a one-piece, not only do you have to set up the forms and oven to bend the plastic, you have to bend the plastic to match the bends of the OLD windshield. Otherwise, it may not fit the bolt holes that are already in your cowling.
I'm sweating my own windshield right now...it's the wrap-around type on the right above, and over twenty-five years, it's gotten a bit crazed and scratched. I just don't think I can make a three-dimensional mold to match, which would mean I'd probably have to drill new mounting holes in the fuselage sheet aluminum. I'd *love* to replace my windshield, but don't want to have to patch all the mounting holes for the old one.
Contrast that with the days when I was operating N500F, with the flat-angled configuration. When a windshield panel developed a crack, I removed it (it was mounted with 1/8" bolts), laid it atop a fresh sheet of flat Lexan, traced out the shape, and marked the bolt holes. Then it just had to be cut out, the holes drilled, and re-installed. Took just an evening...and I kept the old windshield pane for a pattern so I could make new panes in the future without having to disassemble the windshield.
You basically have two choices: Plexiglas and Lexan. Back in August 2005, Don Glewe posted a good explanation of the two types:
Both are trade names --like Kleenex or Puffs-- for two different types of plastic: polycarbonate and acrylic. Both are available in many brands.All right: which type should you use?
Plexiglas is ACRYLIC. it is harder and therefore more brittle, making it tougher to cut/machine --you can still do it, as long as you're careful and use fine-toothed blades and be careful not to feed it too fast. Holes can be drilled safely by merely relieving the "corners" on the ends of the bits so they don't grab. it is easy to heat form: a handheld air heater can be passed over the desired bend location, and a pretty decent bend can be formed by draping the sheet over a half-mold or just clamping the sheet to the edge of a workbench and letting it fall onto a board held to the desired angle. Downsides: it scratches easily --but can just as easily be sanded/polished. The biggest con is that it will shatter/break into nasty sharp pieces if broken --dunno if I'd want that in front of me.
Lexan is POLYCARBONATE. it is "softer" --that makes it easier to cut/machine, lbecause it won't chip as much. It also makes it good from an impact protection standpoint, because it won't shatter as easily as acrylic --I forget exactly, but I think 1/8" of the stuff will stop a 22-round. The downside comes from the same softness: polishing out/removing scratches in polycarbonate is a nightmare! It is also harder to heat form --so if you go with a one-piece you'll probably end up having it done by a company with a big enough oven to heat it consistently.
Telling the two apart --if they don't say what they are on the label-- can be done by looking at the sheet edge: poly will look dark, acrylic light or "clear". You can also whip out a pocketknife and try to carve a little sliver off the edge: poly will peal up like a soft wood/metal, while acrylic will be very resistant and may only chip/flake.
Both have advantages and disadvantages. But I vote Lexan.
Why? Well, Lexan has two disadvantages. It scratches a bit easier than Plexiglas, and it doesn't tolerate fuel spills as well. That's one reason I need a new windshield; I spilled a bit of gas on the old one years ago and it got a bit wavy. Only near the bottom in one spot, but as time went on, the windshield looks like it's becoming crazed around that location.
The advantages of Lexan? One great big one: Unlike plexiglass, Lexan doesn't break.
This isn't much of an operational advantage (if you're encountering .22 caliber rounds in flight, you've got BIGGER problems than a windshield), but it's a big baby blue plus when you cut and drill it. Forget the special drill bits, forget the special sawing techniques. Just run the Lexan pane through the bandsaw (or even saber saw), and drill the holes with a conventional drill.
You'll find a lot of helpful advice for cutting Plexiglas; comments about how to modify drill bits to cut it, and how to minimize the potential for breaking when you cut it. Plexiglas will develop networks of cracks if not worked with the proper tools.
But Lexan? Cut it on a bandsaw, smooth the edge on the benchtop belt sander, pop the holes with a hand drill. Beat it, abuse it, whang on it. It just doesn't care.
Another plus...Lexan is common. You can buy it at Home Depot. In fact, the 2'x 4' sheet they sell is enough for two or even three windshields.
Yes, Lexan will scratch easier and need replacement more often. But Lexan is cheap, and if you go with the three-piece windshield, you can easily replace the panes every couple of years if you want. Just remove the old pane, trace out the outline on a new piece of Lexan, cut it with a bandsaw or saber saw, match-hole-drill the bolt holes, and mount the new pane. $100 from Aircraft Spruce or Wicks will buy you a lifetime supply of Lexan for windshields.
Plastic has a different coefficient of thermal expansion than metal. When the plane sits in the sunlight, the plastic will want to grow larger (Tony Bingelis says a 24" square sheet will lengthen by about 1/8"). If the holes are exact size, or the bolts are tight, it can't expand and stresses are induced. See Bigelis' "The Sportplane Builder."
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