# Stress analysis on spars for an airfoil

1. Dec 27, 2014

### wahaj

1. The problem statement, all variables and given/known data
If I have two spars running through an airfoil, which can be assumed to be two dimensional, which method would I use to find the stresses at the points where the spars are fixed? The loads would be lift and drag and what I need are the bending and shear stresses. Because I have more than one spar, I am looking at a statically indeterminate problem.
Another question, my professor said that to simplify the problem, I can apply the lift and drag forces at the quarter chord point. Would these forces act on the mean camber line or at the upper or lower surfaces?
2. Relevant equations

3. The attempt at a solution
I don't think I've been taught how to do this yet. I am willing to read ahead but I don't know what I should be reading. I have access to the Beer and Johnston Mechanics of Materials textbook

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2. Jan 2, 2015

### Greg Bernhardt

Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?

3. Jan 3, 2015

### CWatters

I would assume that the drag force acts on the centre line of the spars so that it doesn't cause any twisting of the wing (and to make the problem easier :) )

Aside: Real wings have a "pitching moment" that tends to twist the wing nose downwards. It's why the tail on most aircraft is set at a negative angle of attack.

That should allow you to work out how the lift force is shared between the two spars.

I'm not a mech. eng. so not sure how you work out the rest.