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Single-seat ultralight puddlejumper: the "Carbonmax"

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BoKu

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I decided to start with a two-foot section of leading edge D-tube as a test article. My plan is to fit it out with chordwise stiffeners of the same sort as the fuselage 8" OC, and load a section of it to see how well it supports sectional shear loads incurred from wing lift.

I started by cutting a piece of aluminum sheet to the required dimensions, and lightly creasing it at the leading edge location. Then I laminated the carbon skin onto the aluminum while on the bench. After that I carried the sheet over to where the cradle is, then applied vacuum.

20200525_213907.jpg

I dropped the aluminum sheet down into the cradle.

20200525_214030.jpg

And then inserted the matching internal form for each of the end cradles.

20200525_214255.jpg

Here's the leading edge skin curing under vacuum as I left it.

20200525_214632.jpg

The next step is to add the chordwise stiffeners using 3/4" backer rod cores as I did for the fuselage skins. I'll try to get to that this week.
 

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Victor Bravo

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Wowza ! That looks really good. Is that number on the scale in grams or ounces??? :)

Would triangular cross section backer rods (sawn out of very light EPP foam billet) give you a more rigid or lighter stiffener shape for the false ribs?

Dang, Bob, 4 foot sections of that leading edge material, butted together with the butt joint overlapping a T-flange structural rib every 4 feet, and the rear edges overlapped onto flanged spar caps with lots of safe glue area... wow, what a fast way to build a smooth wing leading edge. And making a "mold" for a different airfoil becomes a very easy/cheap/small-space endeavor.

You'se be onto something there, my good man!
 

Vigilant1

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seems to me I had to have external contour boards on my leading edge at each rib station.
If it turns out that the LE looks a little wavy with BoKu's method, it wouldn't be hard to make a hotwired female cradle for 8' lengths of the wing. They'd just replace the intermittent MDF forms he uses as a cradle for the AL sheet now, and the intermittent male MDF (or foam) formers would still go inside. By keeping the (reusable) AL sheet in the process, he'd retain the easy "wet it out flat" approach, the smooth outer surface, and a "forgiving" way to get the part out of the mold.
 

BoKu

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Wowza ! That looks really good. Is that number on the scale in grams or ounces??? :)
The 20-inch section weighs 1.07 lbs, so for the tapering 25-foot wing leading edge, it'd be around 16 lbs, 8 lbs on a side. My mass budget for the wing pair is 70 lbs, so I think it's on track.

Originally I wanted to mold each wing leading edge with a 10-foot section, with a molded wingtip outboard of that, but I'm gravitating towards two 6-foot sections spliced together at the middle.
 

Victor Bravo

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Shipping cost, your shop fabrication space, structural rib spacing, raw materials layout, and walking around to access the mold during fabrication may well favor 4 foot instead of 6 or 10. Actually, the width of the roll of carbon, being rolled out onto the aluminum at the right angle, may be as much of a mfg./materials economy factor as anything else???

Additionally, would thick Mylar or Teflon sheet be easier to lay the flat sheets out on than aluminum, or eliminate the release film or wax?

i.e. lay up the carbon on the Mylar, and lay the Mylar into the mold that has the aluminum permanently screwed into the airfoil shaped wood formers? Saves wear and tear on the mold, keeps the mold from changing shape as much, etc.
 

Jay Kempf

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Shipping cost, your shop fabrication space, structural rib spacing, raw materials layout, and walking around to access the mold during fabrication may well favor 4 foot instead of 6 or 10. Actually, the width of the roll of carbon, being rolled out onto the aluminum at the right angle, may be as much of a mfg./materials economy factor as anything else???

Additionally, would thick Mylar or Teflon sheet be easier to lay the flat sheets out on than aluminum, or eliminate the release film or wax?

i.e. lay up the carbon on the Mylar, and lay the Mylar into the mold that has the aluminum permanently screwed into the airfoil shaped wood formers? Saves wear and tear on the mold, keeps the mold from changing shape as much, etc.
Done this for wing skins in the past. Has to be pretty thick mylar but gives a mirror finish. If you have foam cut male and female molds you can just put the bag around the mylar and plies, then weight the core halves together nested with the laminate in between. Works well and no prepping the forms.
 

proppastie

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gravitating towards two 6-foot sections spliced together at the middle.
Airparts in Kansas City sells aluminum cut off the roll.....You could do the whole wing at once as I guess the fabric comes in a roll. Lot bigger fixtures though. Lot harder to ship too.
 

Hephaestus

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Curious - have you done any testing to see how as-built it compares to design/calculated layups?
 

Jay Kempf

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Yes, you can reuse mylar. Mylar just provides shiny surface like metal. I think it was all 12 mil. Mylar is just PE sheet if you have a source.
 

proppastie

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Yes, you can reuse mylar. Mylar just provides shiny surface like metal. I think it was all 12 mil. Mylar is just PE sheet if you have a source.
Mylar is polyester, PE is Polyethylene.....(I think that is right) I used to draw on Mylar, never made a drawing on construction plastic sheet. Mylar is stiff, Polyethylene is flaccid (soft). I see layups are often on construction plastic and then transferred while still green.....Was your plastic soft or stiff.
 
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Hephaestus

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Mylar is stiff, Polyethylene is flaccid (soft).
Depends on thickness - space blankets are mylar with reflective coating...

Once you get past 10mils it starts getting stiffer - but you'd probably be using thing for this task.
 

Vigilant1

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It is a bit confusing because Mylar (tm) is also known as PET (same stuff as soda bottles, recycling #1 plastic). It is polyethylene terephthalate.
 
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Jay Kempf

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You're correct. I got my PolyE's mixed up. 12 mil is what we used. Drawing mylar was like 4 mils and matte finish. The stuff we used for layups was Very stiff. Could pull off a leading edge on a model airplane wing at 12" chord but you could on full scale at 3'.
 

jedi

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It is a bit confusing because Mylar (tm) is also known as PET (same stuff as soda bottles, recycling #1 plastic). It is polyethylene terephthalate.
I am still a bit confused.

Is PE polyester or another form of polyethylene?

For review:

Space blankets are mylar with reflective coating...

Drawing mylar is about 4 mils

Once you get past 10mils it starts getting stiffer.

12 mills is about as stiff as thin cardboard as in a cereal box.

Please comment if any of the above is not correct.
 
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