badangle

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I'm having trouble getting the size balsa I need and want to know your opinion on gluing smaller strips together..
I need 3/4 x 5/8 balsa for wing spar but can't find exact size. Also want to strengthen wing so I was thinking
1. Get 3/4 x 3/4 and cut ribs deeper.? I can get this size.
2. Get 5/8 square and glue on 1/8 x 5/8 strip of harder wood ?
3. Get 1/2 square. And glue on 1/8 on 3 sides, also maybe top strip of harder wood.?
Also wondering if I can straighten bent wood in the process of laminating. ....I did a small test and it did seem to straighten out ???
Any experience you may have is helpful. ...

carlgrover

Holy cats. What are you building that requires a 3/4" x 5/8" spar?

My choice would be to buy 3/4" x 3/4" and cut it down to 3/4" x 5/8" on a bandsaw.

carl

badangle

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Plane is world engines robin hood 99.
big trainer type.
I must say that as I get balsa in 48" lengths its not very straight....
IF I get 4 pieces of straight 3/4 square I would rather sand ribs deeper to avoid cutting them....this plane has warnings on print
"robinhood 99 is not stressed for acrobatic maneuvers.workable wing struts are necessary for such maneuvers.it will be necessary
To reinforce wing saddle for such maneuvers."
So I was thinking stronger / thicker wing spar ?
But I have noticed I can get warped balsa straight if I laminate 2 pieces together.

Pylonracr

With that information, I would do it a little differently. I would take 3 layers of 1/4" Divinycell and 4 layers of carbon uni and laminate a composite spar. You will of course need to modify the ribs for the 3/4" spar thickness. It will come out lighter and far stronger that a balsa spar, and you can make it straight. There are few things more frustrating than trying to make a straight wing with a warped spar.

Scott

badangle

My Feedback: (1)

Wow pylonracr...that would be one expensive spar.

Pylonracr

How expensive will it be if the wing folds? The instructions say the wing will not survive aerobatic flight without wing struts, that tells me the wing design is not strong enough.
Scott

Pylonracr

A less costly alternative would be to laminate 2 pieces of 3/8 x 3/4 balsa with 3 layers of carbon. It would add a little weight but a tremendous amount of strength. 1" carbon uni tape is less than $3 a yard at US Composites.

CARBON FIBER - GRAPHITE - KEVLAR

Last group at the bottom of the page.
Any quality epoxy laminating resin will work.

Scott

BMatthews

I can't find the plans for the 99 inch but the little .10 powered version uses fairly normal looking top and bottom caps with webbing in between.

Can you take a picture of the wing section and post it? I'm in the same boat and thinking that somehow you've misread the plans. I simply can't imagine using that big a balsa spar. And even if it does show that we can do SO much better and make your life easier by using something more easily found and more suitable than a balsa log for a wing spar.