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Old Aug 11, 2015, 06:15 PM
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Lithobraking Expert
United States, CO, Boulder
Joined Feb 2015
18 Posts
EPP Design Questions

Hello Everyone,

I am currently redesigning a foam board flying wing that I build in the spring to be made from (CNC) hotwire-cut EPP. I have never used EPP before, so I am taking a lot of influence from a friends Popwing since he has had so few problems with it, but I am left with a couple questions that are more specific to my airplane than the Popwing.

The first question I have is what kind of a carbon spar should I use (tube, rod, or strip spar)? My design is 32" span with 16" root chord and 8" tip chord. The airfoil is 12% thick. I hear the Popwing uses an approximately 1/8" x 1/2" vertical strip spar. Is there any advantage to going with a strip spar or a tube/rod spar? If the tube/rod spar is better, what size should I be looking for? I am limited to cutting a spar channel in the bottom of the wing, so the spar will be mounted closer to the bottom wing surface than the center of the airfoil if that changes anything. There will also be a spar in the elevons, but I think I can figure out size/shape based on the main spar.

My other question is how thick should the control surface hinges be? I am hoping to cut hinges a la Popwing or Crack Yak, although if that is difficult/impossible I have plenty of CA hinges in stock. My elevons have 4" chord at the root, 2" at the tip, and should never move more than 30 degrees in either direction, if that.

EDIT: One more question... For a flying wing of this scale, which is more appropriate: 1.3lb or 1.9lb EPP?

Thanks in advance for all the help!
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Last edited by avigator; Aug 11, 2015 at 07:54 PM.
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