Air Tractor 401B canopy

[LRFitch]

I have an old AT-401B arf in 1/4 scale (153" ws) that I would like to get up and running and in the air tugging. However I need to build a canopy for it, and not sure how to make it happen. The top and rear section is fiberglass on the full size, so thinking of how I might be able to use fiberglass and resin. I have very little experience making molds for fiberglass, and wondering how the more experienced folks would start this effort. I think I could make a carved foam replica of the canopy, but then what?? Thoughts/recommendations?
For those unfamiliar with the 401B, it was (no longer in production) similar to a Pawnee, but on steroids with over a 50' wing span, and a big P&W radial up front.

Larry Fitch

[lenb]

Hi Larry.

There are many ways to get the same result. Some are glamorous and some are down and dirty. The latter is my favorite.
I will make the plug as smooth as possible with foam or even balsa, fill and sand it smooth and be sure to be certain there are no negative angles that will trap the plug inside the part and not allow release.

Then you have options.

1) Epoxy over the plug with micro balloons mixed in ( dry mix will sand much easier. ) If using foam, epoxy is a must or polyurethane will melt most foams.
Sand and repeat until satisfied.
To ensure a good release, you need to wax the part 5 or 6 times and use mold release wax or PVA release just before making the part.

1a )
Instead of mold release, I typically will use good old duct tape applied very carefully and smoothly over the mold. This is difficult with a round shape though. Nothing will stick to the duct tape so thats the only release you need before making the part.

Either way, it always comes down to how good the plug is. If the plug is perfect, chances are the part will be excellent as long as you take care in the layup.


Len

[ARUP]

That airplane has flat windows. The rear section that covers the rollover pylon is curved. Can you just take a canopy 'footprint' from the plan view then use front and side views to build the canopy framing? Build it from balsa, glass and finish the exterior then cut holes for the glazing. There are many was to skin the cat!

[LRFitch]

Thanks guys for the advice. ARUP, the side windows are flat as you state. The front windscreen varies depending on version. Some had a one piece curved screen, some had a three piece, with a flat center section, and rounded side panels, and some had three flat panels. The top windows (or turning windows) are all curved pieces, but not all airplanes were equiped with them.