Devfus foam

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stanislavz

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Kids mini willy needed an hood. Given a shot for foil over foam mold.

Cheap eps foam, some cnc cutting, foil glued using spray glue. After some fiddling with heat gun - it was ok. Not perfect.

4 layers of 280gsm and two of 200gsm. Will see result tomorrow.
 

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stanislavz

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Hood trimmed and removed from mold except one bulge formed due to not using any kind of vacuum and to thin epoxy (for infusion) hood is totally adequate for the task.

An hour in total time. Including g code prapration for cnc cut.
 

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stanislavz

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Sanded smoth. Totally happy with results. And added some reinforcements. Easy and fast for 2d shapes. Next time - would lay all fibers with epoxy on flat foil, add double tape or infuzion tape on side, add peel ply / soaker and another layer of foil. Sligth vacuum And then put it on foam sprayed with glue.
 

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Vigilant1

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Somebody is going to be very happy with that. And no rust!

Maybe consider covering the edges (front edge only?) with some plastic comb/edge trim or small diameter vinyl tubing with a slit, then glued on. We all know how kids are--somebody's head (or "somebody's" sister's head) is going to make contact with that edge.

Looks great.
 

stanislavz

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Somebody is going to be very happy with that. And no rust!

Maybe consider covering the edges (front edge only?) with some plastic comb/edge trim or small diameter vinyl tubing with a slit, then glued on. We all know how kids are--somebody's head (or "somebody's" sister's head) is going to make contact with that edge.

Looks great.
Kids have to learn responsibility. But i am really happy how nice and easy it is done..
 

stanislavz

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Painted. About an 3 hours in total time. Would be 2, if used some sork of fixture to hold flat fiberglass while still wet. Or used proper epoxy for hand laminating.
 

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stanislavz

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what 'foil' did you use? Looks like a roll of plastic film.
Ordinary PE foil, 200 mil thick from local warehouse. Happy with results. Any imperfections was sanded down using few moves of 200 grid paper.

On aircraft will use same foil, plus thin layer of gealcoat. If all goes well - no filler will be required. Just light sanding.
 

stanislavz

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New foam cutter is taking shape.


Why did i do not have this idea before... It is rigid enought for foam cutter, and you are not limited by static rail length - you can bolt them to base each 20 cm or similar. Movable rail at 1200 mm for foam look ok to.
 

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stanislavz

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While cnc foam cutter was on delay, did some interesting run on FEA:

PVC foam rib with ud carbon caps caps VS corrugated cf rib. Both are 0.2" / 5 mm thick, plate is Rib is rectangular 400x185 mm, loaded at upper portion with 0.21 N/mm2 - same if we have 1.02 psi load on surface with ribs spaced each 6" / 150mm.

PVC was 80 kg/m3, ud - 300 gsm, corrugation were 0.2", spaced each 2". __--__-- , from 180 gsm cf.

Results are as follow, for same RF, on pvc rib, i had to add 3 times more ud in caps. And pvc core is 30% heavier already..

1608211943947.png
 

Vigilant1

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PVC foam rib with ud carbon caps caps VS corrugated cf rib. . . .

, corrugation were 0.2", spaced each 2". __--__-- , from 180 gsm cf.
Very nice. What have you got in mind as a way to fabricate those ribs?
1) Make a big flat sheet of corrugated cf and then cut them via CNC flatbed router (messy, tough on cutters)
2) Make individual molds for each rib, layup cf in the molds (lots of labor, still need to trim)
3) A smarter way than 1 or 2
 

stanislavz

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Wrong thread. Will ask to move to trace based analysis..

2) Make individual molds for each rib, layup cf in the molds (lots of labor, still need to trim)
It is. Molds done from eps - using piece left from main mold making if kerf is ok. Or done from new piece. Essential part - ribs molded and glued in one piece. Or you are gaining too much extra glue..

Will make a drawing of this idea. Just got some flue. Or Covid :)
 

Vigilant1

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2) Make individual molds for each rib, layup cf in the molds (lots of labor, still need to trim)
It is. Molds done from eps - using piece left from main mold making if kerf is ok. Or done from new piece. Essential part - ribs molded and glued in one piece. Or you are gaining too much extra glue...

Will make a drawing of this idea. Just got some flue. Or Covid :)
So, maybe (before I see your idea and get disgusted with mine):
1) Get a big sheet of 2" thick EPS. Cut the undulations with a hotwire splitting the thickness of the whole thing. Keep both halves together.
2) Cut out your rib outlines in this panel. If it is practical to make joining flanges on these corrugated ribs (the have sufficient straight sections), cut the forms undersize so the ribs will be the right height including the folded over flanges.
3) Somehow wet out the CF cloth on a plastic film, slurp up extra resin, place it in each undulating rib mold, with the mating EPS piece on top, fold the CF over one side of the EPS mold to form flanges on the the straight sections. While still wet, place the ribs and mold into the waiting wing skin portion (with peel ply recently removed at rib join locations. Straps, female skin mold, or bag pressure to press skin to ribs until everything is cured.

Details are left as an exercise for the reader. It may be a good idea to retain the services of a small, smart monkey to remove the EPS molds from inside the wing after the ribs cure. Or, use a stick to reach in and coat the EPS with peanut butter, leave it in the back yard and let the squirrels remove the EPS. Or, maybe just devise a way to coax it out using a Weed wacker ("string trimmer') and a shop vac. Details....

Thinking about this a little, Option 1 is starting to look better. Can a router with appropriate cutters cut a CF sheet like this if held in an EPS mold? Would the CF edge be a frayed, debonded mess, or okay?
 
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Hephaestus

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So, maybe (before I see your idea and get disgusted with mine):
1) Get a big sheet of 2" thick EPS. Cut the undulations with a hotwire splitting the thickness of the whole thing. Keep both halves together.
2) Cut out your rib outlines in this panel. If it is practical to make joining flanges on these corrugated ribs (the have sufficient straight sections), cut the forms undersize so the ribs will be the right height including the folded over flanges.
3) Somehow wet out the CF cloth on a plastic film, slurp up extra resin, place it in each undulating rib mold, with the mating EPS piece on top, fold the CF over one side of the EPS mold to form flanges on the the straight sections. While still wet, place the ribs and mold into the waiting wing skin portion (with peel ply recently removed at rib join locations. Straps, female skin mold, or bag pressure to press skin to ribs until everything is cured.

Details are left as an exercise for the reader. It may be a good idea to retain the services of a small, smart monkey to remove the EPS molds from inside the wing after the ribs cure. Or, use a stick to reach in and coat the EPS with peanut butter, leave it in the back yard and let the squirrels remove the EPS. Or, maybe just devise a way to coax it out using a Weed wacker ("string trimmer') and a shop vac. Details....

Thinking about this a little, Option 1 is starting to look better. Can a router with appropriate cutters cut a CF sheet like this if held in an EPS mold? Would the CF edge be a frayed, debonded mess, or okay?
It would be a shame if some acetone hit that EPS left behind and you ensured a path for the resultant liquid mess were made to ensure it dripped out...

😉
 

berridos

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May i ask why your ribs have ud caps? Shouldnt ribs be ribs composed of 45º biaxial?
 
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