How to measure balsa consistency?

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fdf4
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How to measure balsa consistency?

Post by fdf4 » March 5th, 2017, 1:26 pm

My towers will do well in practice, but sometimes during competition, they break early and I'm pretty sure it's because I don't have wood of uniform density for the legs. How do I find if the balsa is uniform throughout the stick?

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Re: How to measure balsa consistency?

Post by Balsa Man » March 5th, 2017, 2:58 pm

Are you using same density (i.e., same stick weight) in test and competition; doing buckling strength testing and using sticks of same buckling strength? If not, your problem/difference in performance is simply difference in leg strength. Sure, there are defects in some sticks, but usually visually detectable, and by pulling the stick through two fingers so that you put a slight bend in, if there is a....soft/weak zone, you'll feel/see it.
The other thing that could cause performance difference like you're seeing, even if you are using same strength/density, is if you're building without a decent jig, and towers aren't symmetrical, same shape, is that the loads on some pieces will be significantly different, and overloaded piece breaks first.
Len Joeris
Fort Collins, CO

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Re: How to measure balsa consistency?

Post by fdf4 » March 5th, 2017, 3:02 pm

I do not use your buckling strength test, but yes, I use sticks of balsa that are closest in density. I think I'll just have to be more careful then. Thanks!

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Re: How to measure balsa consistency?

Post by Balsa Man » March 5th, 2017, 3:38 pm

Cool, you're welcome.
The limitation of just density matching is that buckling strength can vary by 20% or more, and without buckling strength testing, you don't/can't know what variation you're dealing with.
Len Joeris
Fort Collins, CO

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