Best suited windshield transparent material

[stearmoth]

Hi Hatzers,

During tankage we got a bad experience when a little bit mogas fuel swept over the center section and hit the pilot's windshield. We made those from UV resistant Polycarbonate cold bent held by a single bottom aluminum frame attached by screws to the fuse top decking. The shield immediately cracked and had to be replaced. We are very disapointed about this mate-rial, however we don't think this could be an issue during flight, as then the fuel would not hit the shield due to the airstream, but we would be happier with a better suited transparent mate-rial.
Any hints to a better suited material, that is better resistant to fuel and scratches?

Hans & Sam, H.C.#78, Switzerland

[alvinsager]

Hello Hans & Sam,
Polycarbonate is best at impact strength. It's chemical resistance is poor. Acrylic (Plexiglass) is resistant to most chemicals but has a low resistance to cracking. If you use acrylic, make sure the edges are polished so there is no place for a crack to start. Drilling also has to be done with a drill that has the cutting edges modified so it does not grab. Plexiglass is also far more resistant to scratching.
There is also a grade of polycarbonate that is coated to impart scratch resistance. I do not know if the coating makes it more gasoline resistant.
Good luck,
Al

[mtaylor]

I'm in the process of replacing my rear windscreen also. And, thanks to your post, I now know what caused the major cracking. It wasn't stress and vibration, after all. I remember that I accidentally over flowed the fuel tank at a fuel stop as I was returning from OSH. When I got to my home airstrip, I was surprised to see a complete disintegration of the left rear attach points of my rear windscreen. Mine is made up just like yours, Hans and Sam, cold bent polycarbonate attached at the base and no frame. I have been using .093 because the hardware stores carry it. This time I special ordered .125 thinking the heavier gauge would stand up to vibration better. Now it dawns on me that it was the fuel spillage. It also dawns on me why the front windscreen has had no cracking at all.
From now on I will place a towel behind the filler neck to catch any fuel over flow when refueling.
Thanks for the post.

Mark Taylor

[alvinsager]

All,
Polycarbonate has been used for some time for eyeglass lenses, both for the refractive index as well as impact strength. The lenses are coated with a type of varnish to improve the scratch and chemical resistance.

[stearmoth]

Hi all,

Thanks for the input! It seems, that polycarbonate is quiet suitable for the task. However the opinions are different: I ask a Swiss airplane restorer about the choice of material for this purpose and he just laughed about using Polycarbonate! He told me only experimental builders are using this! He advised to use Plexiglass (Acrylic), but to carefully smoothen the edges in order to prevent the craking as his material is more critical in cracking and also cracking:
We will make a test with this material as well, but we feel Polycarbonte is not to bad!

Kind regards
Hans & Sam, H.C.#78, Switzerland

[mtaylor]

I agree that plexi is the better material, unless you need to bend it. Then it has to be Polycarbonate as far as I know. I'm going to place a plastic cover over my windscreen from now on when I am refueling.

[painless]

Hans, if you go with plexiglass, one thing you can do to accomplish the curve you need is to make a form and then heat the plexiglass in an oven to allow you to bend it. Screw some wood "handles" on opposite edges of the plexiglass sheet to allow you to pull it over your form.

[Ebby]

As I work through my condition inspection my rear windscreen has taken a beating due to fuel spillage. My windscreens have a frame and three separate panes. I will be replacing them with plexi.

Towel behind the filler neck a must. I dislike fueling.