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Dual Spar calculation for cantilever wings. (new-bee question)

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SpainCub

Well-Known Member
Joined
Nov 27, 2012
Messages
376
Location
Madrid, Spain
Hello all,

I am contemplating deviating from the design for a set of plans that I own for the spar. The plans call for solid Spruce for F.Spar and R.Spar, and I am considering an I-Beam spar design to save about 10lbs from each wing, while also incorporating new material for my build that should make the wing stronger.


As a result from this, I was trying to calculate Moment of Inertia from my design (I) and although I can easily calculate this with the formula:
I=Mc/s where:

c=distance of neutral exist to the outer edge of the Spar station
s= Modulus of Rupture (Sitka Spruce = 9400psi or Scots Pine = 12000psi)

I can come up with the value per spar,
But then I then I look at the formula fro deflection (d):
d= WL^3/8.0EI

I don´t know how this works for dual spar wing?
The noted example that I have is from a single spar design that came from one of the contributors on the site (sorry took the notes down but no the name, I will look you up) and I don´t know it I divide the value of M in half for I or if there is something else I am missing.

I have read the post about several books referenced to find this, which I will check out at the library if they have them to evaluate which is the best read for the subject, but since I like to learn by doing and until I get that material, could someone pint me in the right direction?

All the best,

JM
 
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