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Wrapping my head around U/L design practices

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Grimace

Well-Known Member
Joined
Jan 2, 2009
Messages
319
Location
Chicago, IL
Coming from a background in certified aircraft, there's a lot about ultralights that scare me. I see some things that you wouldn't be caught dead doing on a normal-speed experimental. Sometimes I think, "well, they'll never see anything above 80mph in a dive, so it should be fine.." Other times I think, "That'll never hold up over time...."

I see pop rivets used extensively and that makes sense for the most part. But I see people (pop) riveting metal to composite structures and that gives me the willies. I see some metal tubing ribs use nothing more than a dimple in the tube to secure it to a plastic attach point on the aft spar. And then there's foam ribs. Yikes!

I don't mean to disparage what any builders are doing. You all know better than I do and you can't really argue with success. I guess what I'm trying to do is just come up with a method of construction that I would feel comfortable with.

One thing I thought about is a box spar made of foam wrapped in uni of various orientations. The spar thickness would provide torsional stiffness and you could mount plywood ribs to it very easily.

Cutting all the ribs at once and then gluing them on with some angle stock would be easy as pie... but then how do you sew on the fabric? Or is sewing the fabric really unnecessary, as some U/L manufacturers have suggested?

Any thoughts?
 
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