Strut tension strength

[flyguy]

Just fiddling with my calculator and using my front strut as an example; it is about 3.1 inches wide and has a .049 wall, in tension would take 13,000+ lbs before it would fail. That is figured for mild steel at 45,000 psi. I did it for two flat sheets 3.1 X .049, it should be a little more due to the extra volume of the curved surface. If it was rusted down to .025 all the way round it would be 1/2 or about 6,500 lbs remaining.
I though about the truss loading calculation for say 4 g's and put away my calculator. LOL (I'm an electronics guy.)
Darryl

[TimHicks]

Re: Strut tension strength

It's not too hard to make the next steps:
If the airplane weighs 1200 #, and the air is smooth, each wing lifts 600# in level, unaccelerated flight.
If the angle of the strut is 30°, and the main strut takes all of the lift load, (none of this is exact, but it approximates a conservative view and the math is easy), the tension in one strut is 1/sin(30°) or twice the lift load, 1200#.

So if the struts have 6500# ultimate strength they should fail at 6500/1200 = 5.4 G
If the angle of the struts is 20°, the tension in the strut goes up so it would fail at 3.7 G.

[flyguy]

Re: Strut tension strength

Thanks Tim I was starting to see a trend in that direction fooling around with vectors, ie as the angle becomes flatter the load on the strut would go up rather fast.
I'll copy that down, interesting.
Thanks again.

[Len Petterson]

Re: Strut tension strength

Mild Steel 1010 is 30000 psi yield stength according to the Machinery hand book. Standard Category aircraft is 3.8 G positive and 1.8 negative if I am right. Would you calculate all 1200 # on one wing or 600# per wing?
I dont know. I tryed to work it out as well. Just to still my curiasety.
Len

[Guest]

Re: Strut tension strength

Mild Steel 1010 is 30000 psi yield stength according to the Machinery hand book. Standard Category aircraft is 3.8 G positive and 1.8 negative if I am right. Would you calculate all 1200 # on one wing or 600# per wing?
I dont know. I tryed to work it out as well. Just to still my curiasety.
Len

Len,

Check out Military Handbook 5 for stresses that's what FAA uses.

I think they usually use ultimate stresses too and the Mil Hdbk has a little higher values too. maybe 55 ksi

Oh, and they adjust the values depending on the specific application and welded joints factor in too.