Are fishmouthed round tube WELDS much stronger than square tube ones? 1

[DasKleineWunder]

I've read somewhere that the semicircular (fishmouthed) welds in round tubes are much stronger than those straight line ones found in square tubes.

Is that true?
If so, Why? Aren't square tubes supposed to have more weld length? Does the curved weld shape helps?
Is there a big difference in weld strength?

Please only focus on weld strength, not wishing to restart the round vs square tube debate.

Thanks guys

 

[MikeHalloran]

For a tee joint between square tubes, the welds perpendicular to the plane of the tee are not super effective because the branch face of the run tube is stressed in bending. ... or something like that. Solder up some old tin can stock, bend it and see where it buckles.

Also, ISTR an assertion in Peary that full circumference welds are not real good from a fatigue perspective because of the severe section changes. Peary suggests fishplates in slots instead. I think a Super Cub fuselage is made that way under the fabric.



Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

Get hold of a copy of AC-43-13 and turn to the section on welded tubular repairs. You will see illustrations and comments.
B.E.

You are judged not by what you know, but by what you can do.