Aircraft canopy construction

Discussion in 'Workshop Tips and Secrets / Tools' started by oriol, Jan 2, 2012.

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  1. Jan 2, 2012 #1

    oriol

    oriol

    oriol

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    Hi all!


    I m trying to find some info about how to properly conform aircaft canopys.

    I more or less undestand the info about how to heat the plastic and let it drop onto the male mould. vacuum forming.jpeg
    What I don t understand is how to put holes onto the mould to suck the plastic without damaging the plastic.

    If the holes are too big you won t be abble to get the final desired shape, the holes would deform the shape, they would suck some plastic onto them, plus you re deforming you re mould with a lot of holes.
    On the other hand if the holes are too small they won t suck enough.

    Would it be possible to get the desired shape without using a vacuum pump but only with heating the plastic and letting it drop?

    If someone has succesfully built a canopy with a bubble shape could you please post some photos of the holed male mould?


    Thanks in advance for your help!



    Oriol
     
  2. Jan 2, 2012 #2

    oriol

    oriol

    oriol

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    One more question:
    Is it safe to use the kitchen oven for heating the plastic. Is it unhealthy to use it for cooking and for occasionally heating plastics?


    Many thanks!

    Oriol
     
  3. Jan 2, 2012 #3

    orion

    orion

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    There are several ways of forming canopies and windows, each with advantages and disadvantages and of course a variety of costs. The simplest is blow molding. This is a process that's utilized by Todd's Canopies - this is where the peripheral edge is secured and heat is applied to the center, allowing the Plexi to droop under its own weight. Templets are then used to check the droop to arrive at an approximate shape. This process is generally thought of as the least precise however someone who really knows what they're doing can get a pretty nice part out. It is however generally the least expensive since it does not require any tooling outside of the peripheral edge and a few templets.

    The second simplest is where a heated sheet of Plexi is draped over a male tool. This requires a bit more manpower and a pretty good heat box or oven. It works best for flat wrap geometries however with a bit of work and a good clamping fixture you can get some pretty nice compound shapes as well. The draping process can be done with strictly a male tool or a male tool combined with a peripheral clamping shell. The forming can also be done with the aid of vacuum however that requires more extensive tooling since you'll have to form a good edge seal.

    Pulling the Plexi into a female tool is the most amount of work since the tool will have to be dead-on accurate since any blemishes or non-perfect geometry will be imprinted onto the glass. The cavity can also stretch the material so the tooling and design will have to account for the variation caused by the forming. Advanced methods of forming will use an oil filled cavity but this is beyond what most homebuilders can do.
     
  4. Jan 2, 2012 #4

    Dan Thomas

    Dan Thomas

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    Be careful of the gasses released when heating plastics. Polycarbonate in particular releases deadly stuff if it's just a bit too hot. And polycarbonate absorb small amounts of water over time that cause fogging when it's heated, so it need to be heated very slowly.

    There should be plenty of info on the internet.

    Dan
     
  5. Jan 2, 2012 #5

    oriol

    oriol

    oriol

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    Thank you very much Orion for your quick answer!


    I just contacted an Epoxy, composite supplier in my hometown who happens to sell the products for blow molding, it doesn t seem much expensive at all.
    Blow molding seems to be the easiest process. It allows you to build complicated bubble shapes without the need for big oven or a vacuum pump.


    It would be simply great to develop my skills for this homebuilt construction technique!


    Oriol
     
  6. Jan 2, 2012 #6

    oriol

    oriol

    oriol

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    I suspected something like that, thanks for your warning!


    I tried to get some info through the internet but I just get some overview comments about the multiple ways of acrylic shaping, not many details.

    Neither a youtube tutorial for homebuilders.


    A few years ago some folks from here around tried to start a mass production LSA (the esqual). Apparently they had some troubles with the canopies they finished to pay a lot of monney to french people to build it for them.

    Anyway I will try it by myself.


    Oriol
     
  7. Jan 2, 2012 #7

    topspeed100

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  8. Jan 2, 2012 #8

    Mac790

    Mac790

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    Custom Bubble Canopies


    Not the best example (not canopy), and not vacuum but might be useful for somone.


    There wasn't much besides those pictures, unfortunately for whatever reasons I can't publish link for original thread.

    Seb
     

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  9. Jan 2, 2012 #9

    oriol

    oriol

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    Supernice links, many thanks!


    Oriol
     
  10. Feb 19, 2014 #10

    oriol

    oriol

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  11. Feb 19, 2014 #11

    DangerZone

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    Maybe this video with pictures of the process might help too:
    [video=youtube;h9ODMVdoWXM]http://www.youtube.com/watch?v=h9ODMVdoWXM[/video]

    We used wood instead of metal for forming the plexy contour, it is cheaper and easier to get the exact bubble canopy shape. Even better would be to go to a company that sells/processes/works plexy and poly sheets so they do the blowing according to your instructions, it is cheaper and they will surely do a better job than ourselves. All you have to do is design your canopy, cut the wooden frame(s) and provide instructions.
     
    Last edited by a moderator: Mar 20, 2019
    oriol likes this.

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