Single-seat ultralight puddlejumper: the "Carbonmax"

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Hephaestus

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Mylar is DuPont's name for a polyester film. Of course there are dozens of versions with different properties based on other additives used in the process.

Polyethylene is something different.
 

autoreply

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Shall we ask guys from here Projects - Airframe & conceptual design - Nieuwenhuize Engineering

How much they want for their excel slreadsheet and some trainng ? And make a group buy.

But - i will test some pieces of mine cf for buckling resistance. Truss is are truss still.
The more the better!

Joking aside; the engineering effort that goes into it is significant. I'd happily share tips&tricks, but if it requires dozens or hundreds of hours of engineering, I'll charge a commercial rate. The fundamental issue all too often is that you can't cut corners on these kind of things, you either to a full load analysis and structural design, or you cut corners that'll get you in the end.

A further discussion about "wave shear webs" probably warrants it's own thread so we don't spoil Bob's ;-)

I am still a bit confused.

Is PE polyester or another form of polyethylene?
Both.

Polyester is a wide collection of materials, including PET and raw polyester resin.

Mylar is polyethylene terephthalate that is stretched into film. Chemically almost identical to isotropic PET (plastic bottles) and fibers (Terylene, Dacron), but structurally very different because of the orientation of the molecular chains.
 

Jay Kempf

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Same as drawing mylar only without the matte finish one side and thick. The stuff we used was 12 mil. 10 mil would be fine as well. The reason you want stiff is because it doesn't take the shape of the substrate which was raw hotwired foam. So basically you lay up the laminates onto the plastic. Then put that in the bag then put the bag in between the mold halves you hot wired. Then you weigh that so that the plastic (on the outside of the layup) gets bent into it's shape while it cures under vacuum. This takes having the tool have to hold up under vacuum out of the picture.

CNC will work as well as long as it isn't too crazy a 3D shape. I just did an experiment with some plastic sheet and packing tape believe it or not seaming the plastic sheets. Laid up over the whole thing and pull out a part that only required a little trimming and sanding in some spots. I just ordered some stretchy self adhesive film from Uline to try to do a vacuum bag over a foam tool to see if I can seal it and have it stay stuck so I can remove the vacuum to use it for infusion. Trying to lower the overall workflow hours of prep of a one to six off tool.
 
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Jay Kempf

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The big surprise was making some mods to one of my molds. Just hand carved. Sanded to 400 grit, vacuumed, put packing tape on overlapping the epoxy surface. Those are the best looking surface finish on the whole part. Go figure. They released better too.

For those who suggested leave out the wax when using PVA as a mold release. Tried it. Stuck like crazy, almost lost a mold and part. Pulled a lot of the paint off of the mold surface. PVA and wax works. Wax by itself works if the surface is perfect and fully shiny but is less reliable.

I'll be trying self adhesive stretchy film on the next mold. Doing tool paths for a 4 part mold set for a large UAV fuselage right now. Working my way up to full size.
 

Steve C

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Seems like every time I get lured into trying something other than partall + pva, it sticks. You'll hear johnson floor wax is great or hair spray. It isn't.
 

davidjgall

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This might be worth a look. The pictures aren't very telling but the text in the section called "A focus on Manufacturability" is interesting if you read between the lines:

 

davidjgall

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I'll be trying self adhesive stretchy film on the next mold. Doing tool paths for a 4 part mold set for a large UAV fuselage right now. Working my way up to full size.

I think you might be on a path to reinvent this:
 

autoreply

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This might be worth a look. The pictures aren't very telling but the text in the section called "A focus on Manufacturability" is interesting if you read between the lines:

I've been doing this for a few years with great success. Especially for big, light parts (aircraft), this saves tens of thousands of dollars on moulds that'd otherwise be necessary. Pretty easy to get a perfect outside surface with infusion, compared to one-shot infusion with sandwich cores and all.
 
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