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FAR 103 wing construction

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pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,815
Location
North Carolina
This has been bugging me for a while, how to build wings that are light, strong and won't leave me with a limb shortage after paying for them.

FAR 103, it's based on a Flying Flea. I know there is a FAR103 plans out there, but there's no way it'll meet the stall in reality or on paper wit it's wing area. My design is sorta HM360, with a bit more wingspan and a lot less weight, which means a major redesign.

The wings are being tricky. I am currently messing around with an airfoil that looks good. It's flat bottomed, currently 18% thick and is heavily reflexed, which means a sizeable concave area. L/D at cruise is about 30, which I'm pretty happy with, but it's sensitive to shape changes. That seems to suggest that frame and fabric isn't going to work very well. I'd like to do a fibreglass skin, but from reading other threads, the suggestion is to use ~20oz/yd2 which is going to add up with 150ft2 of wings. How fragile is 10oz? will insects damage 6oz? I'm hoping I can get away with 1 layer of +/- 45 over the whole wing and either 0/90 or uni on the front half. I'm not rich enough for carbon skins

I have a foam honeycomb core idea, well several. I'v estimated the volume of my wings to be 120 cu ft. No prizes for guessing that I can't use solid foam... First idea is to drill 2-3" holes in a hex grid through an xps block before hotwiring, that'd reduce weight by up to 80%, which is still a bit much. 90% lighter is where the holes touch. Hexagonal holes aren't something I've worked out yet. A second idea is to cut corrugated ribs, then weld them together with a hotwire, I've never had any luck heatforming EPS, I doubt I'd get on better with XPS. That'd be even fiddlier than the drilling, but weight could go way down. A 3rd option is heat form pvc foam into corrugations and then weld/glue them into a honeycomb, that one will be annoying to get an even shape, it's be easy to punch out further lightening holes though for bugger all core weight. All three honeycomb cores to be sheathed in ~1/8 pvc foam then glassed. Thinking of a shear web at about 30% chord.

I'm not sure if a 2-3" cell size is enough to keep skin buckling at bay, I need a better book...

A final option is sandwich skins and foam ribs.



Suggestions, comments, ridicule?
 
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