Hi Group:

Cla

Looking at the calculations for the spar, spar.pdf I do not see your
interpretation. The 67000 psi value is Bearing Ultimate, not tensile.

A MATWEB lookup is in order:

6061-T6

Tensile ultimate: 45000
Tensile yield : 39000

Bearing ultimate: 88000
Bearing Yield : 56000

The values presented in the spar calculation are correct, and the
bearing ultimate of 67000 is below spec.

So where is the spar calc using bad values except, as you say, in the
initial assumptions of 244 pounds versus 288?

Curtis Scholl


Just a little more input from another more knowledgeable than
myself. The material that the plans and the airplane use is 6061t6
correct? The calculations show the material or the identifier as being
6061. The problem in the shown calcs is that the numbers he is using
at 68000psi tensile is higher than the ultimate strength of 2024-t4
which is given at 64000. 6061t6 is only 45,000psi ultimate and 39,900
yield.

It's no wonder the wing was failing at 2g.

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