question about closed tube vs open ended tube strength ????

[richg99]

This is, I know, a silly little application for you guys..but..it is
important to me. It might also be important to a lot of other airplane
modelers.

I am building light-weight foam model r/c airplanes from scratch. Some of
the kits that I formerly purchased used a small ----1/8th by
.014 --BENT--aluminum tube to support the dihedral in the wings. The tube
is glued onto the underside of the wing.

I am in the process of replacing a wing. The aluminum tube kinked when the
wing folded at the bottom of a dive. ( don't ask!! ha ha ).

I was wondering if, by placing a small amount of amazingly strong hot melt
glue onto each end of the new tube (rendering it a "closed" tube"), ..would
I add any stiffness?

Thanks for your help and advice. richg99

[ecarecar]

I don't think so. Why do you think it would?

Post by richg99
This is, I know, a silly little application for you guys..but..it is
important to me. It might also be important to a lot of other airplane
modelers.
I am building light-weight foam model r/c airplanes from scratch.
Some of the kits that I formerly purchased used a small ----1/8th by
.014 --BENT--aluminum tube to support the dihedral in the wings. The
tube is glued onto the underside of the wing.
I am in the process of replacing a wing. The aluminum tube kinked
when the wing folded at the bottom of a dive. ( don't ask!! ha ha ).
I was wondering if, by placing a small amount of amazingly strong hot
melt glue onto each end of the new tube (rendering it a "closed"
tube"), ..would I add any stiffness?
Thanks for your help and advice. richg99

[richg99]

Mostly because I don't understand engineering. I thought that the air
inside of the tube would, if captured...be put under pressure when the tube
was put under bending stress......therefore...a closed tube with air trapped
inside of it, would be "stronger" than an open tube. what say you? thanks
& regards, Rich

[ecarecar]

Not that it makes any difference, but the first entry said "stiffness"
and this entry says "stronger."
They are different but the answer is the same. Also the question would
have been more clear if
you had specified axial torsion (twisting) or bending the tube
longitudinally. In either case, the effect
of the gas is so overwhelmed by the strength of the aluminum tube as to
make it irrelevant, in my
humble or non-humble opinion.

If the question were about a tube shaped balloon, it should be obvious
that the answer would be
different.

Also, if the gas (air) in the tube were under significant pressure and
it were under repeated loading and unloading
such that a fatigue analysis would be appropriate, that would be an
entirely different question.

Post by richg99
Mostly because I don't understand engineering. I thought that the air
inside of the tube would, if captured...be put under pressure when the
tube was put under bending stress......therefore...a closed tube with
air trapped inside of it, would be "stronger" than an open tube. what
say you? thanks & regards, Rich

[richg99]

Thank you for a very well explained answer to a newbie. So, if the tube was
a "balloon" then, obviously..the pressurized air would stiffen it..

But, being an aluminum tube, the relationship of the volume of air and the
minimum pressure on the air.... is insignificant to have a similar effect..
Now I've got it..?? right? thanks for your help...regards, rich