Round vs. Square section

[JCaste]

Hi all,

I have a design in mind (Bensen-type gyrocraft) and the question inmediately came up, when should I use square and when a round section pipe?

At first sight, is a lot easier to work with a square tube, but a round one will also be lighter and work better at spreading the loads. It's quite likelly I'm worng, those are just some quick thoughts. :rolleyes:

Perhaps some of you guys have some info about this. Knowing the general pros and cons would be nice, but I'd prefer - when possible- to have the equations.

Thanks in advance!

[The Other Dave]

Hi all,

I have a design in mind (Bensen-type gyrocraft) and the question inmediately came up, when should I use square and when a round section pipe?

At first sight, is a lot easier to work with a square tube, but a round one will also be lighter and work better at spreading the loads. It's quite likelly I'm worng, those are just some quick thoughts. :rolleyes:

Perhaps some of you guys have some info about this. Knowing the general pros and cons would be nice, but I'd prefer - when possible- to have the equations.

Thanks in advance!

IMHO square tube for a given weight/length is allways stronger/stiffer than
round tube.

Round tube is used because it is easy to bend during construction.
Square tube twists when it is bent.

[bd5wingnut]

Sorry "the Other Dave"

Square tube will buckle before round tube will. Yes round tube will also bend smoother, but not because it is weaker. It bends better because the load is distributed throughout the tube MORE evenly, square tube will generate stress risers at each corner, and violla, a kink. Without proper fitting mandrels round stuff will eventually fail (kink) too. You can cheat a little with heat but watch out it will just kink faster if pushed too fast.
If you are confusing spar caps for the square stuff? Spars are loaded on two opposing surfaces, one in tesion and one in compression and the spar webs between are JUST strong enough to keep those two surfaces parallel. Round tube can also work as a spar, since the load is evenly distributed. However, there is a little bit of a trade off since the walls are the same thickness all the way around. Jim Bede designed the famous BD5 using a round tube spar because it would be easier for the "Homebuilder" to fabricate a wing without having to assemble all the pieces of a conventional spar.

Peace, Wolf