Cable Sag 3

[chopin73]

Hi
I'm looking to calculate the sag of a flight control cable under it's own weight (zero tension). The cable is in steel, 5/32" diameter. Does anybody knows the formula to calculate the sag?
Thanks,
Chopin

 

[monkeydog]

Do a search on "catenary" or "catenary curves".

 

[chopin73]

The equation of a catenary is:
y = a cosh(x/a).

Now how do I determine "a"?

Thanks,
Chopin

 

[rb1957]

i think the post was not about the shape of the curve, but the engineering analysis (force balance) for it ... wiki for a start has something

 

[rb1957]

ty this (searched "catenary tension" ...

http://mysite.du.edu/~jcalvert/math/catenary.htm

or this ...

http://spaceagecontrol.com/calccabl.htm

 

[monkeydog]

I looked in two of my mechancial reference books, they have a lot of words, equations and pictures. I can't seem to be able to relay that info into this mode of comunication.

Try looking for an old guy where you work, and ask to see his mechanical reference books.

 

[MiketheEngineer]

The equation is:

H = wl^2 / 8d
l = span
H = tension at mid-span
w = load in plf or klf - keep track of units
d= sag

As you can see - the more sag - the less the load and vice versa.

You will NEVER get all the sag out - so make some guess - like 1'' or 2'' or whatever

 

[rb1957]

maybe more like 0.01" or 0.02" ...

w = 0.005 lbs/in
L = 100"
H = 200 lbs

d = 0.005*100^2/(8*200) = 0.03"

 

[MiketheEngineer]

rb1957

Check your units - I think you might have a problem

 

[rb1957]

which one ?
w is weight (lbf) per in run
L is in of run
H is tension in lbf

(lbf/in)*in^2/lbf = in to me ??

 

[MiketheEngineer]

I mis-read. Thought it is was 100 feet. Sorry

These old eyes and Walgreen glasses sometimes just don't work as good as they used to!!