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I-beams, D-tubes, Round tubes, part 103.

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b7gwap

Well-Known Member
Joined
Sep 1, 2014
Messages
585
Location
UT
Hi everyone.
I'm trying to tackle the heavy pilot issue on a Sandlin-style airchair. I've gone back and forth between just using bigger diameter spars or redesigning the wings altogether to have I-beam spars, perhaps made from sheet metal for the web and L-channel for the caps. Obviously the I-beam is more efficient than a round tube for bending, but is perhaps not so ideal for the compressive loads that an externally-braced wing transfers to the spars. Is this the reason (aside from convenience of shape) that most part 103-legal designs seem to gravitate toward round tube spars? I don't necessarily want to make the Goat a cantilever design (seems too heavy?), but if it can be done with reasonable portability and stay under 155 lbs, I wouldn't be opposed to it. I suppose in that case a D-tube structure would be in order. Not sure how well foam, wood or glass bonds to alodized aluminum, but maybe sitka spruce would be the ideal material in that case anyway.. Any thoughts on the matter? Not looking for engineering analysis, just general ideas and opinions, other projects or similar designs. Essentially trying to make a goat4 (or BUG4) for myself (240 lbs) that flies at the 1.7 lbs/sqft wing loading suggested by Mr. Sandlin. I've even considered doing it as a tandem wing like a part 103-compliant Peyret Tandem, or as a tail-less airchair, plank or delta.

Thanks

Austin
 
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