Proppastie, have you seen....

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plncraze

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Chris Heintz's book Flying in your Own Wings? He pays a lot of attention to the inboard part of the spar and explains why as well. He is the "H" in the HR prefix of Robin aircraft because he designed their metal wings.
Also the Stressing Structure series in Kitplanes had a discussion on crippling, buckling and MMOI.If you get a $20 online subscription you get a lot of back issues.
These articles make a good addition to Bruhn and billski by explaining things a little differently you can compare answers from their different methods.
Also, as always, thank you for sharing your journey! You're testing complete assemblies!!! Very cool!
 

proppastie

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The good thing, it bolted together like it had eyes....so I can still design (once in a while) I think the Autocad ability to calculate "I" is fantastic, I think my first posting in 2012 was about that feature even though I did not understand the significance. I also have checked the crippling of those angles from Bruhn C7. I have a better understanding of the drag spar now and I think I see why it did not stiffen the center as if it had a wide attachment to a fuselage bulkhead would have.......the single tube structure has some quirks.

The 150 lb load is worse case tip load from Glider Criteria, the angles as shown are 1/4x3x1.5 6061-t6......There may be more "angle clips" I am taking the day off as I thought I would lose the wing yesterday it was so bad. Wanted to get it back in the basement today....very awkward takes two and have to rotate slightly through the bottom of the Bilco.
 

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proppastie

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I learned on my first spar test that a riveted stack up of thin cap strips is not anything like a single thick solid bar or angle extrusion in compression stability.
added a spread sheet....I am thinking the problem is not enough moment of inertia I. in the airplane X direction. (fore and aft)
 

proppastie

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The D-cell skin provides buckle resistance fore and aft. Might want to use thicker skin at the root.
you found another problem I noticed.....looking at pictures .....the skin that would bridge from LH to RH wing is not in place for testing only the LH wing. So yes how about "need skin at the root of the wing. "....Probably the capability will be addressed with added angles but still probably will not be installed for the limit test....that could change as I have lots of scrap aluminum for a half piece.
 
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