Here's a short article with good, basicinformation on the differences between the two as far as us biplane builders are concerned.
Summary:
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"
uploads/20070918_060821_DougFirVsSpruce.pdf
Summary:
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"
uploads/20070918_060821_DougFirVsSpruce.pdf
