Brian Meuser, based at Sonoma Valley Airport, Sonoma CA, heat-formed windscreens for his Curtiss-Wright 12W Sport Trainer project, and sent us a recipe with photos. Brian says:
I had a good day bending Acrylic today. Thanks to Chris Prevost at Sonoma Valley Airport and his great oven. I am self taught so there may be better ways, this is just how I did it.
An aluminum template was used as a pattern for the windscreen. The windscreen acrylic material was rough cut on the band saw and then trimmed to size with a wooden template (made from the aluminum template) and a router. A radius was scraped onto the top edge using a shape scraper I bought at Tap Plastics. The top edge was then flame finished using great caution and a propane torch (practice on scrap first).
Template design - There are two radii to consider in a windscreen. The first is the radius to be used for the form. The width of the fuselage will determine this radius. Mine was 12.5 inches (25 inch diameter). The second radius will determine how vertical the windscreen will sit. It is the radius of the base of the windscreen. The larger radius the more upright it will sit. I couldn’t decide between two possible radii (23 inch and 24 inch) so I made two windscreens as I had enough acrylic. Also, as the width of the windscreen increases so will the height and cockpit depth. Too much width and you can't get into the cockpit. I used .040 3003 aluminum for the template. I used my slip roller to shape it into a 25 inch half circle. I made it a larger width began a process of trimming the top edge till I thought it was correct. A template is important.
The form is an aluminum wrapped plywood box with a center support. Basically you want a half circle the radius determined by the width of your fuselage.
The oven is the tricky part. It is important to find a proper oven large enough to get your windscreen in. I was luckily to have available a large commercial oven. I heated my acrylic (3/16 inch) at 380 degrees for 7 minutes. It was heated on the smooth floor of the oven sitting on a wool felt sheet. I attached wood sticks to the edges of the felt so I could grab the sheet with the windscreen and transfer it to the form (the oven wasn’t large enough for the form to go in the oven so the windscreen had to be heated and moved to the form. You have about 20 seconds before things start getting hard). Use some scrap pieces until you get the time correct. Temperature is determined by the type of acrylic you use.
Once heated properly the acrylic becomes very flexible. That’s when you swiftly move it out of the oven to the form. If it is hot enough, it will drape over the form nicely. If not, back in the oven.
Let it cool off and you're ready for final fit and install.