Windshield pattern layout

Rowdyflyer1903!

Active Member
Joined
Jun 7, 2019
Messages
211
Location
Bryan, Texas
Aircraft
Cessna 140, Stinson 108-1, Culver V, Parsons Trainer
Total Flight Time
1000 hours
I have been struggling with 7 th grade geometry in attempting to create a flat pattern when bowed to a windshield shape which will intersect and mate to my fuselage mock-up properly. Do you use an ellipse or a parabolic curve to do this? Hell if I know! I tried the two-point-string and marker thing to create the parabolic tracing but failed. Primarily it is very difficult with my lack of understanding of the complicated geometric world of conical intersections. How do you trace the intersection of 1/2 of a cylinder as it intersects a flat plane at 35°? Well I did it! And without math involved!

Here is how and most of you have the tools to do so. You need an inclinometer which shows degrees and a laser which can be leveled and projects a horizontal line. You need something which can be bowed to represent as a substitute for your proposed windshield. I used luan door skins but that plastic card board look-a-like political sign material, coroplast will work, I think. What ever you use must be able to maintain a consistent curve while it is bowed.

In my case I needed a 42x20” wide board bent to a 32” curve. I used a long pipe type clamp to temporarily hold the bow while I secured it with duct tape. Once again the bow has to be fairly consistent. Now grab your inclinometer and tape or otherwise secure it to the centerline of your bowed apparatus. If your bowed 1/2 “cylinder is square and the surface is flat, the inclinometer should read 90° when it is sitting up right.

Next is a complication of minor proportions if we understand what we are after here. And that is a curve which will intersect a flat plane at what ever angle you need and when your are done it opens up to a flat piece which can be duplicated as a pattern. I used a 42x20” bowed to 32” and will project a laser to represent the intersecting surface.

Does it really matter where you project the laser?Not really because you will cut out the curve and transfer that curve to the windscreen material be it polycarbonate or other. The laser should be leveled and projected at the center of your bowed material. The perhaps is the most accurate section of the 1/2 “ cylinder.

Next then tilt the bow to the degrees you have determined the windshield will rest. A good friend, in my case my sweet and most patient wife, holds the bow with the inclinometer attached at the angle desired. Now trace the laser line as projected to the inside of the bow.


Now undo the duct tape and allow the material to flatten. Clean up your shaky hand tracing of the laser and cut this out with whatever tool is require.

Now bend it to where the now cutout traced line lays flat on the floor. The bow should lay at the same angle it was traced. I am going to get fresh material and redo this with photographs to illustrate the method. It really is simple and the description is far more complicated than doing it. I do serious simple or not done at all.

More to come.
 
I always build the frame first and then fit a template to it.... (easier said than done)
This might take a couple iterations of templates, it's just the process.
List of template materials:

1. Formica, awesome stuff, but has become expensive.
2. Very thin aluminum sheet, .015" to .020" I usually have scraps, don't know if I would buy it intentionally....
3. Thin acrylic. (Also not cheap anymore)
4. Poster board/ thick kraft paper. (There are rolls of heavy craft paper for protecting floors during construction also for protecting table tops)
5. Corroplast. (Only works for mild bends)
6. Thin ABS. (lots of thicknesses, easy to tool, not too expensive. Need a good plastics supplier, they may have ridiculous retail for small quantities, so shop around)
7. Cardboard. (Great for first iteration, usually free. dial it in with the better materials...)

The alternative is if you know someone good with "Solid Works" you can have it modeled and print the shape to overlay on your final material.
 
I just make a mockup with poster board.

This allows me to adjust things for aesthetic appeal without spending a lot of time sawing up plastic.
 
Well it worked but with some effort. I used the diffusion plastic for light fixtures. One side is smooth and the other textured. It comes in 24x48” for $13.00 at Lowes. The down side it too flimsy. I ended up making foam end pieces on the top and bottom to stiffen It enough to even tilt to the degrees I wanted.

As the member ‘Aerofoam’ suggested, Formica would be an excellent choice. Yes, a Solid works God could have given me the layout. I dink with Trimble SketchUp but unfolding a shape requires other plugins and well I’m cheap and it is not the best program for compound shapes. In fact it will drive you insane to even try.

The leveling of the laser then projecting to the inside of the tilted 1/2 cylinder worked well. I traced it and then cut it out with a Drimmel tool. This was somewhat of a pain because the cutting wheel melted the plastic and it took a couple of passes.

when folded back from 42 to 32, it did achieve very close to the angle what I wanted. Of course the test fitting will tell the tale. I will have to round the top edge in some form.

The upside to all of this is I have a method to the madness which can achieve many sizes to many angles. Onward though the fog! ( with synthetic vision of course )
 
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