I've been trying to decide on which aluminum tubing to go with for my quadcopter motor arms. Looking here and elsewhere there appears to be a mixture of square and round tubing being used by builders and companies. The question is, which would be a better choice?
From previous experience I guessed the round tubing would be stronger. One thing I did find from researching online is: although round tubing is stronger than square when compared by weight, the square tubing will generally be stronger when compared by size. For example, a 20mm square tube would be stronger than a 20mm round tube.
Another interesting factor is described here. Apparently square tubing loses rigidity advantages when the force is applied from a non-square direction.
This leads to the question of: how often will the motor arms be subjected to non square forces?
Here are some discussions and data about square and round tubing within other uses: