Wood questions - Public Lumber Company, determining species at the lumberyard

http://www.publiclumber.com/2x4sitkaspruce.html Anyone had any
dealings with them? They sell "aircraft/spar-grade" 2x4 spruce for
$4.50 / lin.ft. Their prices on marine ply are about what I can get
locally, but the price on spruce beats most I've seen. Of course,
it's only a good deal if the wood is actually high-quality. Or is the
wisest course of action to just suck it up and pay AS&S's prices for
your spars and longerons?

Some plans call for specific species in specific places. At the
lumberyard, how do you tell the difference between pine, spruce, and
fir in dimensional lumber? Are they marked somehow? Guidebooks
aren't very useful - by the time the trees get to where I can buy
them, the bark and needles are long gone. :-)

Corrie

Generally, the wood itself will be stamped or marked on one or both ends
with SOME ID, which may be a little cryptic. "Western Woods" is one common
ID here in Californis, which can be about a half dozen different species.
Luckily, they all have pretty similar mechanical properties.

For a key to wood ID, try "Wood Structure and Identification", Core, Cote,
and Day. Or "What Wood Is That - A Manual of Wood Identification.

Bring a 10X loupe, and a razor knife.

BUT IT JUST DOESN'T MATTER. Read what Veeduber has to say about wood
selection in this group and in the FLY5K yahoo group. Wood selection for
QUALITY is more important than SPECIES. If the grain is OK, the wood will
probably be OK.

Sitka Spruce has lower mechanical properties than just about any commonly
available softwood used for structures - worse than Western Hemlock, Douglas
Fire, etc. But it's lighter than they are, and it's strength/weight ratio
is very high, which is why it's often called for in aircraft work.

You can build a plane just as strong with other woods, it will just weigh a
wee bit more.
--
Ryan R Young
Oakland, CA
http://users.lmi.net/~ryoung

"Flightdeck" wrote
Their "marine" ply price is good and we used some in a non-structural
application.

Does marine plywood have any specs regarding voids within intermediate plys?

Eric

On 08 Sep 2003 10:12 AM, Eric Miller posted the following:
"Flightdeck" wrote
Their "marine" ply price is good and we used some in a non-structural
application.

Does marine plywood have any specs regarding voids within intermediate
plys?

Marine plywood is supposed to not have any voids. There is an excellent
article on the making of marine plywood in the current issue of
Woodenboat magazine.

----------------------------------------------------
Del Rawlins-
Remove _kills_spammers_ to reply via email.
Unofficial Bearhawk FAQ website:
http://www.rawlinsbrothers.org/bhfaq/

Thanks for the detailed response. Can you explain more about
compression damage and how to spot it?

"Flightdeck" wrote in message link.net...
Corrie,

Their "marine" ply price is good and we used some in a non-structural
application. However, the specification for "aircraft ply" includes a lot
more than just the "boil" spec. We didn't do the 1/4" strip sectioning to
look for voids. I have not ordered "Spruce" from them. Before I would buy
any "spar stock" from a source that does not routinely supply the aircraft
industry, I would get a sample from them and check it against the specs.
Here is a link to a Word document file of AC 43.13-1B
http://av-info.faa.gov/dst/43-13/Ch_01-01.doc This AC gives you some basic
information.

Each species of wood has some tell-tail characteristics that can be used to
help identify it after it has been milled. Some of the characteristics are
so apparent that a visual examination will get you the general species, some
require specific mechanical tests or examinations. It is fairly easy to
identify the gross differences between some species, but harder to identify
the different sub-species. A explanation of some of the more subtle
characteristics sound like one is describing wine or food... "A soft gold
sheen with a subtle silken ribbon effect when the face grain is held to the
light...." Some sub-species identification is made more difficult because of
the amount of "plantation grown" material on the market. A lot of this
stuff is cut young and is grown for harvest volume under "fast growth"
conditions. As a result, some of the more subtle differences in sub-species
are blurred. Regardless of the species, or sub-species, the faster growth
and younger stuff makes it difficult to obtain stock that meets the "growth
rings per inch" specification for spar stock. And, because of the fact that
it is machine cut and felled for speed and without regard for much "TLC",
even a lot of the remaining "old-growth" stock ends up with compression
damage. The trouble with compression damage is that it often takes a
well-trained eye to spot it.

Some "lumber yards" still have folks who actually know the source
sub-species of the wood they stock. However, most of them today buy stock
based upon a fairly wide window of mechanical properties rather than an
exact sub-species identification. You may see "pine", "spruce", "fir",
hemlock, etc. listed. However, there can be a big difference in the native
mechanical properties across the sub-species. In fact, the actual
properties can be widely different based upon where the tree was grown.
Some of the best sources for learning to identify milled woods come from the
older books on cabinet and furniture making.

"There is a bunch of "spruce" on the consumer market, but most of it is not
suitable for aircraft structural construction. The same thing applies to
the other species. In a pinch, you might be able to find some longeron
stock by hand sorting through the entire inventory of a lumber yard and then
doing some basic moisture content and strength tests. Commercial logs are
milled in a manner that produces the greatest number of board-feet from the
bore, but there may be a small portion of the slices that can be classified
as "straight grain" or "quarter-sawn". You just need to find those slices
and then count the growth rings, and check for pitch pockets, grain run-out,
compression wood, moisture content, etc. But, that is a lot of trouble.
That is why many folks "trust" the aircraft suppliers to have specifications
in place and just spend the bucks to buy from them. However, there is
nothing "magical" about Sitka Spruce. In fact, it became a "de-facto"
standard due more to the original availability (before 90% of the good stuff
was shipped to the Pacific Rim countries) than anything else.

Aircraft designers specify the species of the wood to be used (given that
the stock meets the "aircraft use" specifications) because of mechanical
properties, dimensional, and weight issues. Under ideal A:B comparisons
between species, each species will have properties that are used to
calculate for the specific application. In some instances the selection
will be based upon a specific property versus the dimension needed to meet
the structural specification. For example, one species may have certain
mechanical properties in simple bending that is very close to another
species. However, a specific species is specified because there is a weight
advantage at a given dimensional size. Some times a species is specified
because it is better able to handle "shock loads". Some times it comes down
to the "tool-ability" of the species. For example, Douglas Fir is stronger
(stiffer) than Spruce in certain load applications. But it is heavier for a
given volume and can be more difficult to "tool" across the ends of the
grain.

There have even been a couple of "home-built" (one "ultra-lite" in
particular) designs that used "Southern White Pine" throughout the
construction because the kit manufacturer had a "qualified source" and hand
sorted each piece delivered to the customer. This is a case where the
original design was plenty strong for its intended use. However, folks
quickly got in trouble when they stuck too much power on the nose and went
past the design's intended gross weight and performance envelope.

It is getting more difficult to purchase "aircraft spruce spar specification
stock" in the dimensions needed for both "certified" and home-built aircraft
when the spar is a "one piece" design. For a while, it was possible to get
Western Hemlock "old growth" spar stock in the larger dimensions. In most
"home built" applications one could do a direct substitution of Hemlock for
Spruce and actually end up with a better spar because of the native
properties of the Hemlock and the availability of stock with better "rings
per inch" than the available Spruce.

At one time there was a fellow up in B.C., Canada with a company called
"Western Aircraft Spruce" who had access to large, old-growth Hemlock and
some good Spruce. I bought some Hemlock spar stock from him and it was
"el-primo" stuff. The main spar stock counted out at about 32 rings per
inch with so little grain "run-out" that it was not worth mentioning. That
is old slow-growth stuff! His prices were very reasonable, considering the
quality, and he had connections to ship via "space available" cargo on some
of the passenger flights out of B.C. The last telephone number I had for
him is 250-355-0003.

I guess the one caution I would offer about substitution of one wood species
for another in aircraft structural application is that there is more to the
engineering specifications than just the "inspectable" characteristics and
weight.

J

"Corrie" wrote in message
om...
http://www.publiclumber.com/2x4sitkaspruce.html Anyone had any
dealings with them? They sell "aircraft/spar-grade" 2x4 spruce for
$4.50 / lin.ft. Their prices on marine ply are about what I can get
locally, but the price on spruce beats most I've seen. Of course,
it's only a good deal if the wood is actually high-quality. Or is the
wisest course of action to just suck it up and pay AS&S's prices for
your spars and longerons?

Some plans call for specific species in specific places. At the
lumberyard, how do you tell the difference between pine, spruce, and
fir in dimensional lumber? Are they marked somehow? Guidebooks
aren't very useful - by the time the trees get to where I can buy
them, the bark and needles are long gone. :-)

Corrie

"Corrie" wrote in message
om...
Thanks for the detailed response. Can you explain more about
compression damage and how to spot it?

I've seen more extensive articles on this that I can't find/recall right
now, but I know Ron Alexander covered it in Sport Aviation Feb '99.

Eric

(Corrie) wrote in message . com...
Thanks, Ryan. Veeduber is indeed generous with his wisdom. Fly5k has
been rather terribly OT of late, but I suspect there are gems in the
archives.

What you say makes a good deal of sense as well. I'd hesitate to
substitute fir for spruce in spars or longerons, as fir is reputed to
be stiffer. The expected amount of 'give' of the beam is likely to
have been designed into the structure. But for other parts, I suppose
it doesn't matter all that much. It struck me as odd, though, that
the Evans VP front spar bulkhead (carries the instrument panel, and
your legs stick through a big opening in the middle) calls for Douglas
Fir for the spar and strut carry-through, spruce for the vertical
members, and pine for a transverse member. I've asked on the vp group
on yahoo, but haven't gotten a definitive answer.

Spent a little while at the local Huge Orange Store tonight looking at
lumber. Lotsa knots and center cuts from little trees. :-(



Ryan Young wrote in message ...
Generally, the wood itself will be stamped or marked on one or both ends
with SOME ID, which may be a little cryptic. "Western Woods" is one common
ID here in Californis, which can be about a half dozen different species.
Luckily, they all have pretty similar mechanical properties.

For a key to wood ID, try "Wood Structure and Identification", Core, Cote,
and Day. Or "What Wood Is That - A Manual of Wood Identification.

Bring a 10X loupe, and a razor knife.

BUT IT JUST DOESN'T MATTER. Read what Veeduber has to say about wood
selection in this group and in the FLY5K yahoo group. Wood selection for
QUALITY is more important than SPECIES. If the grain is OK, the wood will
probably be OK.

Sitka Spruce has lower mechanical properties than just about any commonly
available softwood used for structures - worse than Western Hemlock, Douglas
Fire, etc. But it's lighter than they are, and it's strength/weight ratio
is very high, which is why it's often called for in aircraft work.

You can build a plane just as strong with other woods, it will just weigh a
wee bit more.

The EAA has a book available on aircraft woodwork, but I don't know if
it has some of the same stuff on selecting and grading wood that is in
an old publication of theirs that I bought 20 years ago. The selection
process and the moisture content of the lumber is pretty critical. I
chose to use Spruce in my Jungster II because I could obtain stock
that was graded for aircraft and the quantity of wood in an aircraft
is so little that the price difference was not as important as the
peace of mind. Also Spruce is much easier to work with than Douglas
Fir for instance. There are other wood as good or better than spruce,
but they are scarce, such as Port Orford Cedar. Most of the wood
expense on my project was in the plywood and the metal wing struts
cost almost as much as all the other material.

Ed Sullivan

Thanks, Eric. A bit of googling turned up some information - it's
hard-to-spot damage that can come from a tree growing at an angle,
being felled onto a slope, a whole range of things. I was actually
looking for something on the compression *strength* of hoop pine vs
birch to respond to a post elsewhere, but "compression damage" kept
coming up in the list.

I also just received the 1994 EAA publication on wood building
techniques - appears to be a collection of reprinted articles. On
page 11 is a reprint of an article by Volksplane designer W.S. Evans
that goes into some detail on the subject, with the conclusion that
it's not worth the risk for spars and longerons to use
non-certificated (and possibly compression-damaged) wood. Even so, he
advocates cutting off 2" of each end of the stock and inspecting it
for obvious fiber damage. THAT could get expensive!

Corrie

"Eric Miller" wrote in message .net...
"Corrie" wrote in message
om...
Thanks for the detailed response. Can you explain more about
compression damage and how to spot it?

I've seen more extensive articles on this that I can't find/recall right
now, but I know Ron Alexander covered it in Sport Aviation Feb '99.

Eric

AHA! It's all in the wrist, or in getting the correct search terms in
google. Depends what you want to do. Anyway, here are a couple of
links to info:

http://www.lsuagcenter.com/Communica...e/3nws0806.htm
http://www.safnet.org/archive/0703_howtointerpret.cfm

From that second site, here's some interesting info:

"...species groups ... are denoted by these abbreviations:
Spruce-Pine-Fir S-P-F
...."

I saw a *lot* of lumber at the yard stamped S-P-F. Spruce-pine-fir,
doesn't matter for wall studs. Oh joy, or rupture.

THIS is interesting, though:
http://www.wclib.org/results2.asp?mn...&Submit=Search

No idea if they'd sell in less than truckload quantities. Worth a
call, maybe.


(Corrie) wrote in message . com...
Thanks, Ryan. Veeduber is indeed generous with his wisdom. Fly5k has
been rather terribly OT of late, but I suspect there are gems in the
archives.

What you say makes a good deal of sense as well. I'd hesitate to
substitute fir for spruce in spars or longerons, as fir is reputed to
be stiffer. The expected amount of 'give' of the beam is likely to
have been designed into the structure. But for other parts, I suppose
it doesn't matter all that much. It struck me as odd, though, that
the Evans VP front spar bulkhead (carries the instrument panel, and
your legs stick through a big opening in the middle) calls for Douglas
Fir for the spar and strut carry-through, spruce for the vertical
members, and pine for a transverse member. I've asked on the vp group
on yahoo, but haven't gotten a definitive answer.

Spent a little while at the local Huge Orange Store tonight looking at
lumber. Lotsa knots and center cuts from little trees. :-(



Ryan Young wrote in message ...
Generally, the wood itself will be stamped or marked on one or both ends
with SOME ID, which may be a little cryptic. "Western Woods" is one common
ID here in Californis, which can be about a half dozen different species.
Luckily, they all have pretty similar mechanical properties.

For a key to wood ID, try "Wood Structure and Identification", Core, Cote,
and Day. Or "What Wood Is That - A Manual of Wood Identification.

Bring a 10X loupe, and a razor knife.

BUT IT JUST DOESN'T MATTER. Read what Veeduber has to say about wood
selection in this group and in the FLY5K yahoo group. Wood selection for
QUALITY is more important than SPECIES. If the grain is OK, the wood will
probably be OK.

Sitka Spruce has lower mechanical properties than just about any commonly
available softwood used for structures - worse than Western Hemlock, Douglas
Fire, etc. But it's lighter than they are, and it's strength/weight ratio
is very high, which is why it's often called for in aircraft work.

You can build a plane just as strong with other woods, it will just weigh a
wee bit more.

Corrie wrote ...
... an article by Volksplane designer W.S. Evans
... with the conclusion that
it's not worth the risk for spars and longerons to use
non-certificated (and possibly compression-damaged) wood.


Certificated by whom? Anybody with a chainsaw & a porta-mill can
declare whatever grade they wish on any lumber they produce. Heck,
take the basic quality designations for #2 construction lumber & see
what percentage of the ordinary wall studs at Big Orange even meet the
specs stamped on them. I think a plane builder is far better off
performing his/her own pass/fail inspections than trusting Larry the
Lumberjack to have done so correctly at the mill.

Daniel