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Old Jan 29, 2013, 06:35 AM
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United States, TX, San Antonio
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where's the spruce ?

Tried a couple of local hobby shops yesterday, and could find no spruce. Worse yet, the kid behind the counter in one place had no idea what I was talking about. I asked "do you carry spruce sticks ?" and he actually said " I don't know what that is". What is the world coming to ?! Do LHSs not carry it anymore ? I see a place or two online that carry it, but I am kinda not wanting to pay $15 for shipping $10 worth of sticks. Is anyone out there using something different, other than spruce for wing spars ? I have obtained some carbon fiber for reinforcing what I thought would be spruce spars, but if we are using other than spruce nowadays, someone please enlighten me. I have been out of the hobby for a good many years now, and it seems that a lot has changed. I have a Lanzo Bomber on the board right now (OK, for the past year and a half), and that is strictly balsa and a ply firewall, but might like to start on the Sagittas that I finally got plans for. Those call for a bit of spruce. Or whatever folks are using nowadays. I would really prefer to use spruce, but if there is a viable alternative, I guess I'll just roll with it. Any ideas?
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Old Jan 29, 2013, 06:49 AM
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Joined Jan 2007
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i ve had to use bass wood instead of spruce but you pay a weight penalty, hobby shops are falling apart in this economy, most of my airplanes are foam now because of cost and such, just seems like every thing is working against us flyers now days
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Old Jan 29, 2013, 07:10 AM
Flying = Falling (Slowly)
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Tulsa, OK
Joined May 2004
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Check out Aircraft Spruce. They sell spruce for full size planes and, surprisingly, have some sizes that are useful for our spars.

Happy Landings,

Don
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Old Jan 29, 2013, 07:33 AM
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Charleston, SC
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I'll second Aircraft Spruce. Get enough to last a while. If you are using enough carbon, hard balsa is OK for spars. The carbon takes all the bending load. The "spar" just needs to be strong enough to tie in the shear webbing.
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Old Jan 29, 2013, 07:52 AM
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With kit building on the decline, scratch building is probably on further decline.

You might try Michaels or one of the other general crafts stores. They often have balsa and other sticks for construction of doll houses and other crafts products.
http://hosted.where2getit.com/michaels/

The train hobby shops also carry wood stock

I am not a builder of any accomplishment, but have to agree with AMBeck.

I know there are purists who want all wood spars and that is fine. However if I was building I would use whatever was available, like hard balsa. then I would cap it with carbon and wrapped with carbon or kevlar thread or unwaxed dental floss to prevent delamination. With good woods hard to find and becoming expensive, carbon makes more and more sense. And the cost of carbon is fairly low for this kind of application.

Carbon strips
http://www.cstsales.com/carbon_laminates_48.html


Once you add a substantial amount of carbon, the carbon takes all the stress and the wood is just a carrier and, as AMBeck said, a glue surface to tie in the shear webs.

The spar of the the Drela Bubble Dancer would be my reference model. The Bubble Dancer can stand up to full pedal winch launches so, natuarlly you don't have to builid it as strong, use as much carbon, as Drela did, but that would be my reference point.

BD Spar Layup
http://www.charlesriverrc.org/articl...Fs/spar_V2.pdf
BD Plans
http://www.charlesriverrc.org/articl...edancer-3m.htm


I can't give you authoritative numbers but if you go hard balsa rather than spruce, .020 on top tapering as you go out, and .014 on bottom tapering out, should be able to stand up to hi-start loads and a tapped winch launch on a 2 to 2.5 meter wing. .030 on top for a 3M wing.

Someone else please comment on the carbon thickness. I am just offering suggestions that seem consistent with what I have read. Clearly if you want competition launches you go thicker.
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Old Jan 29, 2013, 09:12 AM
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National Balsa in Ware, MA carries Sitka spruce in sheets, 24",36" and 48" legnths and 6 pages of assorted sizes. Good people to deal with.

http://www.nationalbalsa.com/default.asp
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Old Jan 29, 2013, 09:16 AM
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I order it in from Sig if I need 36" inchers, and I order it from one of my plastic model distributors if I can use shorter lengths, from Midwest.
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Old Jan 29, 2013, 10:02 AM
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Chico, California USA
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I ordered a bunch from SIG in 2010 including 48" lengths....great quality. I just checked their web site and could not locate any spruce, the item numbers I ordered are invalid. Did I miss something?

Wayne
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Old Jan 29, 2013, 10:17 AM
Flying = Falling (Slowly)
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Tulsa, OK
Joined May 2004
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Just a note on carbon spar construction.

I have built 2 1/2 Bubble Dancers and an Allegro using Drela's carbon cap construction method and it is great.

And as an engineer I took Drela's engineering information and devised a computer program for designing similar spars for other planes. Clearly, his designs were the result of wanting to be able to withstand 200 to 250 pound winch line loads. And they do.

But we have sort of fallen in a rut when it comes to designing spars for electric planes which use more or less the same construction. We have unnecessarily added to the cost and complexity of builds FOR ELECTRIC SAILPLANES.

There is nothing in the spectrum of loads that we can reasonably expect for our electric planes which requires anything more than the "old school" spruce cap and balsa shear webs that worked so well for our Aquilas and Olys. AND ITS NOT EVEN A CLOSE CALL. The loads on electric planes do not even approach the loads that our "old school" planes withstood.

I have looked at several wing designs for electric sailplanes and have concluded that it is easily possible to use conventional materials and construction techniques to withstand electric sailplane loads AND weigh less than Drela's Bubble Dancer standard.

Happy Landings,

Don
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Old Jan 29, 2013, 10:38 AM
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Don,

I don't know that we are talking about an electric sailplane in this discussion but I agree that most, but not all, electric sailplanes don't need the spars of our winched planes. Hotliners may be an exception to that. I am not sure.

If you can build 3 meter electric sailplanes that are lighter than the bubble dancer (31 ounces) you have my deepest respect and admiration.
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Old Jan 29, 2013, 11:01 AM
Flying = Falling (Slowly)
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Tulsa, OK
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Quote:
Originally Posted by aeajr View Post
Don,


If you can build 3 meter electric sailplanes that are lighter than the bubble dancer (31 ounces) you have my deepest respect and admiration.
I can build electric BD WINGS that are lighter than Drela's. I suspect the total plane would come out around 38 ounces.

Besides replacing the spar material with spruce (not for weight savings, but for simplicity), the center panel sheeting on the BD is 3/32 and could be replaced with 1/16, his shear webs are the full width of the spar caps and could revert to the 1/16 webs like on the Aquila and wing joiners could be reduced in size. Further, he has triangle reinforcements on each rib bay that tie the bottom sheeting to the wrapped spar -- this would be unnecessary with "old school" construction. Of course, both use mostly contest balsa in their construction. Finally, the wrapped "beam" that he uses to connect the wing to the fuselage could be substantially lightened.

I am looking forward to the day when vendors start designing and selling "purpose built" electric planes rather than the current crop of TD planes with the noses chopped off. Properly designed fuselages with space for the components and proper moments for the motors and batteries will result in planes which consistently weight less than similarly sized TD planes. Come on, ballast!

Happy Landings,

Don
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Old Jan 29, 2013, 02:50 PM
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USA, IL, Wheeling
Joined Jan 2003
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Balsa USA, Bud Nosen, Lonestar Balsa all have spruce in various sizes, lengths.

My LHS stocks a little, but the amount of building going on does not support stocking wood, since it ages for the worse over time. We have a few guys who get together and make up a special order for what they want and order through the LHS.

The days of pawing your way through a bin of wood searching for that perfect piece of AAAA quality, light and straight balsa sheet are, sadly, long gone.
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Old Jan 29, 2013, 04:43 PM
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Bud Nosen has it , Aircraft Spruces' wood is so beautiful you'll almost hate to cut it . My suggestion is to stock up with the standard sizes you'll need and get the shipping done all at one time . Aircraft Spruce is well worth the wait .
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Old Jan 29, 2013, 06:15 PM
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United States, CA, Ontario
Joined Mar 2002
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Aircraft spruce is second to none , i ordered 8 pieces from them thinking at least 4 will be good , all 8 were perfect , You have to remember their main business is for full scale aircraft.....
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Old Jan 29, 2013, 07:58 PM
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United States, OH, St Paris
Joined Apr 2000
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Also try www.wicksaircraft.com very good quality
Dan
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