Duplicating a canopy - surely the finest minds can solve this problem!

[trillian]

OK, I'm looking for a viable solution and I'm hoping with all the collective brainpower and experiences on here, there's got to be a way to do this.

I have a canopy that is a one-off, it's a custom made thing and there is no way to go buy another and it's very rare so it will never ever turn up on Ebay, etc. etc.

The shape is very similar to the TDR but it's a bit bigger and the lines are slightly different but the main point is that there are no tricky curves or recesses etc. it's a very smooth and simple shape.

I'd like to make another one or two (or three) using this one as the plug / mold. But obviously I do not want to damage it in any way.

So, the traditional GRP method would require a mold to be made and then you can make as many from that mold as you want. However, I have asked for some advice on this from someone that is making fuselages and apparently the materials cost is a fairly hefty investment, like about £400.00.

Other thoughts are: Vac forming - it's a suitable shape, the first question would be about being able to vacuum form onto the canopy without damaging it and it would just require building some kind of skirt to go around each half which would both support it on the vac table and prevent the plastic going underneath it. And the skirting form would have to be made for both halves as you'd form one half at a time. One advantage here is that you could run a bunch of copies very easily once.

Thinking outside the box a bit - in my mind I'm picturing some other way to make a mold or to form some kind of resin around it - think about what if you cover it with cling film then it's possible to spray on some kind of coat that hardens and do a few successive coats and soon you have a plastic shell - I'm just trying to think of other ways to do this that don't require a big investment of either time or money.

So how would you duplicate this canopy?

[bigpops]

My first thought on making a plug would be builders expanding foam.

You'd have to line and mask the outside and line the existing canopy to prevent the foam sticking to it. Spray in the foam with the canopy held like a bucket, let it expand and set, pull out the foam and then fill any holes with something structural. Car body filler, wood filler, something similar that can be sanded smooth. That could possibly be strong enough to vacuum form, and would easily cut in half.

If not, you could make a silicone mold (or a mold for each half) that you could in turn use to make an epoxy plug that would certainly be strong enough for vacuum forming or making glass fibre canopies. Maybe the foam would be strong enough for glass fibre, I wouldn't know.

No matter what you do, I don't think there's an easy way. The spray method sounds plausible, if there were a suitable product to spray in. There might be, but I've no idea what it is or would be called.

[trillian]

The expanding foam is an interesting idea. To make a plug out of the foam would require adding filler and sanding because the inside of the canopy is not smooth. But the foam could definitely help keep the canopy rigid in the case of using the canopy itself to vac form it in plastic.

Then of course, a mold could be made from a pair of vac formed halves, but I'd think the plastic itself could produce a perfectly good canopy if it's the right thickness and it would be easy to knock out 10 copies while you're at it.

Alternatively, it may be possible to make a mold using expanding foam. Cover the canopy with something like clingfilm, make a box around it where half is 'submerged' so-to-speak, and the foam expands around it.

[mole hunter]

Hi trillian,


If you really, really want to do this I would say - use the existing canopy as your plug to make a two part mould.

Make a parting flange (out of plasticard or MDF etc) to fit snugly along its centre line and attach boarders to the feather edges of the canopy. Prep with mould release agent and lay-up the first half of the mould. Once cured, remove the parting flange and with the original canopy still insitu repeat the process on the other half.

You might like to have a look at some of the videos here. I used a lot of their gear when making my plug and moulds for the Wessex and that is 6 foot long.

https://www.easycomposites.co.uk/#!/composites-tutorials/how-to-make-complex-split-multi-part-mould-for-composites



Cheers, Marty

[Gixxer]

Bees wax on the outer of the canopy. Make a fairly thick fibreglass mould around it. Allow to set and release the mould. Cover the inside of the newly formed mould with bees wax, then use fibreglass matting and resin (a very small amount of both, or it'll weigh a ton.) to make a new canopy. Use an initial coloured gel coat if you want colour.

[trillian]

I have spoken with someone that does vac forming for rc plane parts but he cannot do something quite big enough for this. I have emailed Sarik Hobbies as it looks like they might be able to do larger vac forming. So we shall see what they say.

One suggestion is to try 'drape forming' where you use the same kind of plastic sheet material but without the vacuum and apparently this can work quite well for some things and it's by far the easiest thing to try. Just not totally sure what kind of material to try. Clear petg might be the easiest, but what would be ideal would be a black opaque sheet, approx 1mm thick.

[mole hunter]

I've used PETG for vac forming cockpit glazing but they are relatively small parts formed over a solid plug. You would need to fill your canopy with something pretty solid to prevent it being crushed. Also, 1mm PETG would need a good heat soak to 130* to form well.

I would experiment with something not as precious as your one-off canopy. Let us know how it goes.

Cheers, Marty

[trillian]

Yeah I would try it first on something I have lying around and see how the material reacts, how hot it needs to get etc. how much pressure / weight it takes. The canopy being formed-over will need to be filled with foam or something to keep it relatively stationary but the bottom line is the heated sheet needs to be pliable enough to where it doesn't need too much weight pulling it down.

I've used PETG for vac forming cockpit glazing but they are relatively small parts formed over a solid plug. You would need to fill your canopy with something pretty solid to prevent it being crushed. Also, 1mm PETG would need a good heat soak to 130* to form well.

I would experiment with something not as precious as your one-off canopy. Let us know how it goes.

Cheers, Marty