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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 |
#2
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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 |
#3
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"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 |
#4
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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/ |
#5
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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 |
#6
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"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 |
#7
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#8
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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 |
#10
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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 |
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