DIY Electric Ultralight on YouTube

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proppastie

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It's tough stuff.
Will you use it like fabric? if not need a compression/tension yield strength, ultimate strength, E, Shear, Bearing, u, to stress analyze it as I am sure you know. (others might not) Fabric is a know quantity, with known fabrication techniques. You should have lots of fun learning how to test for all these numbers, as I doubt they are listed. If I am wrong please provide a link because it does look like interesting stuff.
 

pictsidhe

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No, not like fabric, it'll be a rigid skin, so more like metal. Will need very few ribs behind the spar. While looking for something to build a FAR103 from, I found that the problem is the tradeoff between weight and abuse resistance. Strong enough for 103 flight surfaces are fragile, Hangar rash resistant surfaces get heavy, fast. Coroplast will take a heavy blow and bounce back. Fabric is the only really light way to build, but it needs lots of ribs and sags between them. i was hoping for a laminar wing, but coroplast over a carbon spar is going to be so much easier to build, it seems a good idea for an experimental first design.

I'm also a contrary sod who likes to be different. Lets face it, if I do start building a coroplast aircraft, you lot are going to be glued (NOT riveted!) to the build thread! I'm kinda busy right now and lack a workspace, but maybe next week, some of my coroplast stash and some simple moulds will find their way into the oven. Once I fix the thermostat...

From Coroplast website:
Density, g/cc ASTM-D782A-2 0.90
Notched Izod Impact (FT-lbs/in.) ASTM-D256-A @ 70 degrees F 3.0
Tensile Strength at Yield (psi units) ASTM-D638 2in/min. 4000
Elongation at yield (%) 10
Deflection Temp. degrees F 66psi 194
Water Absorption - 24 hrs, % ASTM-D570 0.02
Falling Weight Impact Strength @ -29degree F (ft.lbs.) 23
Coefficient of Linear Thermal Expansion (MM/MM/C x [10 to the -5th])
-30 degrees C to 0 degrees C 12
0 degrees C to 30 degrees C 14
30 degrees C to 60 degrees C 21
Normal temperature performance range -17 degrees F to 160 degrees F
Melting point 162 degrees C, 324 degrees F

Polypropylene wikipedia properties as first guess for E:

Modulus, GPa 1.3-1.8

I'll test for the actual modulus at some point. that'll be easier if I'm using a known brand and dimensions rather than my roadside harvest...
 
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pictsidhe

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A further feature of coroplast is that rods or tubes can be slid inside some flutes to stiffen it. I've done it with steel rods on a ground application. On a flat wrap tapered wing, most would have to be curved, which could make it awkward.
 

proppastie

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A further feature of coroplast is that rods or tubes can be slid inside some flutes to stiffen it. On a flat wrap tapered wing, most would have to be curved, which could make it awkward.
off the top of my head....

The CF rods/or Tow, with epoxy matrix on a mold or curved to shape to fix the curve when curing the epoxy. If the rods extend attach at Trailing edges. Expose bottom of the CF at the spar where the sheet hits the spar and attach there. Say every inch (or 2 or 4 inch ???)(need some analysis) have a filled corrugation. A little heavier but very positive stiffening and attachment.
 

pictsidhe

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Sliding in ready made rods is a piece of cake. Making your own rods is much harder. The vastly different CTEs mean you don't want it stuck too well, filling a corrugation seems a bad idea to me. In cold temps, the coro will shrink onto the rod and stop contracting, unlike unrodded bits. A recipe for distortion. Round rods aren't a great fit in square holes...
It may be that bends required are gentle enough that pultrusions can still be used.

I've compared 4mm coro to solid Al, CFRP and ply. Stiffness the same. I was lazy and didn't factor for shear in the coro core. This is probably a fair approximation in the flute-wise direction, but not so good across the flutes. In metric because this IS the 19th century.

spacesCorospaceAluspaceCFBiaxspaCFunispacePly

Espace1.25spac70spacespa70spaces130space12

Thicksp4.0space0.7space0.7space0.57space1.27

Weight 0.7space1.9space1.1space.9space0.86

So, there we have it, 4mm Coroplast is lighter than solid sheets of equivalent stiffness in Aluminium, CFRP and ply. It costs peanuts. Pity the special hot glue needed doesn't. I think that it's time I ordered some and burned my fingers. I've been wondering how to build a sandwich skin UL and this looks like the way. Yes, it's weak, but an UL skin doesn't need a lot of strength. It's flimsy feel should also give some protection from abusers.
 

aeroallan

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Thank you for posting all the URLs for Peter Sripol's UL airplane build videos. I had somewhere gotten sidetracked keeping up with his 1-time UL airplane project some years ago. Watching them again has gotten me wondering if somebody has invented a clean mechanism for detaching a wing into thirds for transport. By "a clean mechanism" I mean a lightweight but super-strong fastening system that allows for quick detachment/reattachment of the wingspar or D-cell part of the wing and the same for the outboard flaperon/aileron control linkages that impressed you. I guess if it were truly clean it would also have a wrap-around plastic film or some other means to seal the gaps between the thirds.
 
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