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John,

        Some data for your inquiry:



Material                Modulus         Comp.   Linear strain

                                        Stress  to failure



Spruce perp.            1.57 msi (flex) 5.6 ksi 0.4%

to grain



E-glass/epoxy           2.4 msi (comp)  44 ksi  1.8%

equal 0/45/90/-45



E-glass/epoxy           2.72 msi (comp) 64 ksi  2.4%

equal 0/90



Low mod carbon/epoxy    5.37 msi (comp) 34 ksi  0.6%

equal 0/45/90/-45



Low mod carbon/epoxy    7.15 msi (comp) 52 ksi  0.7%

equal 0/90



Low mod carbon/epoxy    9.97 msi (comp) 64 ksi  0.6%

70% uni



        Thus, in a pure tug the spruce will fail first,

the carbon second, and the glass last. However, when

you build a sandwich panel with a symmetric laminate,

and then add higher stiffness material to one face,

you CAN shift the neutral exis faster than you

increase the section inertia, thereby reducing the

section modulus and therefore the beam bending

strength.

        More importantly to the fastidious, the

coefficients of thermal expansion between carbon and

glass are quite different (0.02e-6 v 8.6e-6 mm/(mm-C))

meaning that temporary, and possibly permenant,

deformations will show at each modification, making

your beautiful Lancair look, ahem, shall we say, lumpy?

(Permenant deformations occur because of shrinkage,

temporary because of temperature and humidity changes.)



Food for thought,



Guy Buchanan

Buchanan & Newcomer