I've been wondering how to calculate the shear loading and bending moments of a canteliever wing for a while, so I decided to look it up. I found a good paper and a helpful wikipedia article. I decided to make a spreadsheet to do the calculations for me. It determines the Limit Shear and Bending moments using the Schrenk elliptical approximation, then on the next spreadsheet you can design an I-beam spar using the data. I also included several common building material strengths and had the spreadsheet determine if these materials were strong enough in bending moment for the spar at the given section points.

Its has some limitations mostly that you cannot tell what will happen when you use different materials for the spar caps and shear web. Also it doesn't determine if the spar is strong enough in shear, but it is my assumption that if it is strong enough in bending it should be strong enough in shear.

Use:

Place your aircraft information into the purple boxes. Go to the next spreadsheet and design your spar by changing the data in the purple boxes making sure the material you wish to build with can handle the stress.

Paper:

http://www.lightaircraftassociation....roximation.pdf
Wikipedia:

http://en.wikipedia.org/wiki/Second_...l_axis_theorem
Scott