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wing spars - 3/11/2012 8:56 PM   
biam


 

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From: desloge, MO, USA
Status: offline 		I have inherited a fifteen year old basket case, it is a gret planes .40 size cub. There are no instructions, but thats o.k. the plans are there. the question is, the plans are indicating basswood spars, I think this maybe over kill, would balsa spars in the same size suffice? Seems like all the other kits I have built have had balsa spars, or am I remembering wrong? A lot of the pieces are missing but I have a box of repair wood I can draw from. If I was home I could look at other plans and maybe answer my own question, but I am at the home away from home four states away.

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RE: wing spars - 3/11/2012 10:41 PM   
Gray Beard


 

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Status: offline 		The GP Cub wing tends to cavatate and flex if the plane is flown too fast, then the wing explodes. Happened to one of mine when the throttle broke on my OS .70FS. It takes bass wood for a reason. Some planes designs will allow balsa or bass but this Cub likes Bass wood.
I cut my own stringers {scratch bulder} and when I can't get Bass Wood I will buy some clear Poplar and cut my stringers from that. I found out it depends on what state you are in what type of wood is common. I have a hard time finding bass wood and my son in law in Mi can get it all day long.

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RE: wing spars - 3/12/2012 12:10 AM   
biam


 

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Status: offline 		Thank you for the quick response! learn something new every day! Looks like a trip to the hobby shop is in the future. Definetly going to make a list, I thought this kit was pretty complete, lot of parts missing, but I am stubborn enough to stay with it and see it in the air some day.

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RE: wing spars - 3/12/2012 3:27 PM   
Rodney



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Status: offline 		Clear close grained pine will also work well, I would prefer that over bass wood given a choice. If you can upsize the spar cross section you could also use balsa, probably have to increase the cross sectional area at least by 1/3. Also, putting webbing between the upper and lower spar will greatly increase the stiffness of the wing. The webbing can be quite thin, usually 1/16 inch is adequate.

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RE: wing spars - 3/12/2012 6:41 PM   
Gray Beard


 

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Status: offline 		Rod, the GP Cub has shear webbing in the plans and it is 1/16 balsa. You just need to make sure the grain is going in the right direction.
I cut my own spars and I have used pine but found it just a bit brittle. That and finding a clear board without knots is often hard. My local high end wood store doesn't stock Bass wood so I have tried several different woods for spars. I even have some cut from OAK, strong but heavy!! I found a stick in the scrap bin and was in need of a couple of 3/8 X 36 so what the heck!! I have found the poplar a pretty good spar. It's a light weight hard wood but it is strong. I can find it in pieces of clear boards with almost no knots. It cuts really well!! Last plane I built called for 1/8 X 1/4 TE stock. I ws able to cut a bunch of it in 10 foot lengths. It even dazzled the guys in my wood working club that I was able to get it that thin and long without breaking. Well, several didn't break. I'm not 100% one with perfection but I have several sticks of it in my shop in 10 foot lengths. We do have two of the best table saws I have ever used and I use new blades!!
Gene

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RE: wing spars - 3/13/2012 12:31 AM   
exsailor62


 

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I built a M.E.N. Trainer 20 back in the 1980’s and it had some spruce members in the wing that were very light and very stiff. Look for a dark, close grained spruce. Let me know if you find a good source. 


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