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Doug Fir VS Spruce

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Radial Skybolt Builder: 220.45% completed
Aug 21, 2006
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South Jersey
Here's a short article with good, basicinformation on the differences between the two as far as us biplane builders are concerned.

1 - Bending Strength: Fir is 23% stronger than Spruce
2 - Elasticity: Fir is stiffer than Spruce (no % mentioned)
3 - Compression Strength:
a. Parallel to grain Fir is 39% stronger
b. Perpendicular to grain Fir is 55% stronger
c. Not only is a Fir spar stronger, but the bearing strengths of bolts in Fir
are higher by the same percentage
4 - Fir is 23% stronger than Spruce but weighs about 26% more

When choosing Fir look for VERTICAL grain that is from 8 to 14 grains/inch in 15"


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