Rings per inch for spruce?

[Esstern]

I've been offered some spruce for spars that's pretty much perfect in every
way except there's 21 rings per inch instead of the recommended 12-15. Good
stuff or no? I don't really see the problem with finer grain spruce and in
fact, can't even remember where iread it's advisable to use 12=15 rings
per inch.

[Morgans]

"Esstern" > wrote in message ...
> I've been offered some spruce for spars that's pretty much perfect in
every
> way except there's 21 rings per inch instead of the recommended 12-15.
Good
> stuff or no? I don't really see the problem with finer grain spruce and in
> fact, can't even remember where iread it's advisable to use 12=15 rings
> per inch.

If you have never read this publication, and you are going to build an
airplane with a wood spar, and possibly other wood parts, take the time to
read it. You will learn things that you didn't know that you didn't know.
Every answer is in there. (really)

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm

As I recall, more grains = more strength = more weight. As long as it has
the desired maximum grain divergence of 1 inch to 15 inches run, and no
pitch pockets and knots, you should be golden.
--
Jim in NC

[Highflyer]

"Esstern" > wrote in message ...
> I've been offered some spruce for spars that's pretty much perfect in
> every
> way except there's 21 rings per inch instead of the recommended 12-15.
> Good
> stuff or no? I don't really see the problem with finer grain spruce and in
> fact, can't even remember where iread it's advisable to use 12=15 rings
> per inch.

The more rings per inch the slower the growth. The slower the growth the
better. 12 to 15 rings per inch is the minimum recommended in ANC14.

Highflyer