Perspex Windscreen Fabrication

[Tildensboy]

Reference Thread 712-89331
My son and I have built a Mosquito Helicopter here in Costa Rica and we would appreciate some help on the steps to build a compound curved windscreen over the pilot

http://www.innovator.mosquito.net.nz/mbbs2/boxx/knowledgebase.asp?Type=4&Cat=5

We have built a single foam plug that defines the shape of the windscreen and the streamlined nose cone that will contain the tail rotor pedals and on the inside an instrument panel. The windscreen part will be attached to the mast over the pilot's head and then join the nose cone at the pilot's knees. I have experience building fibreglass molds and my thought was to build the female mold from the plug then do the fibreglass nose cone and the windscreen separately from the mold? Or should I melt the perspex over the finished Male Plug(finished in Bondo)?I have never worked with Perspex so I appreciate any advice to get this project started in the right direction

 

[btrueblood]

Google thermoforming and/or vacuum forming. Basically, make a female mold for the windscreen, heat the sheet material in an oven, place hot material over mold opening, pull a vacuum in the mold cavity until the material "sucks in" to the cavity. Allow to cool, and remove from mold.

Then, trim to fit the canopy structure, and attach with fasteners/trim ring.

 

[Demon3]

Also you might seriously consider making it from polycarbonate instead of Perspex (PMMA). Polycarbonate has excellent impact resistance and PMMA doesn't. That's why they make safety glasses and motorbike helmets from polycarbonate.


There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[Tildensboy]

Thank you both for your input. I have been to the web and read up on thermoforming. First thing I had better do is separate the project into two--fibreglass nose section and windscreen. That way I can close both ends of the windscreen mold and get the vaccum to suck in the hot plastic. I know of no oven large enough to heat 18" wide (probably 24 " in radius) by 6 feet long. So would several tiger torches do the job or do you have another suggestion? Is the tooling gelcoat going to survive the heat of all this? is there anything special used as a release agent? How is polycarbonate sold and do you have a suggestion for a supplier if I can't find it in Costa Rica.

 

[patprimmer]

Polycarbonate is a lot harder to thermo form as it must be dried first.

You will need a large oven to dry the polycarbonate and to do a good job for forming compound curved surfaces. Simple straight bends can be done with a strip heater.

There will be a plastic sheet fabricator in your region. Possibly he will be a large outdoor illuminated sigh manufacturer. He will have a large oven and expertise. He may be prepared for you to contribute effort in the mould making under his advice and direction, while he makes the moulding from that mould.

Plastic sheet suppliers will be able to ofer technical bulletins with fabricating techniques and details. They should also be able to advise someone in your region who has a suitable oven.

Regards

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[Tildensboy]

Ok Thanks so much for all the guidance.I will proceed with this plan. I will let you know how it turns out