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Cable Sag
3

Cable Sag

Cable Sag

(OP)
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

RE: Cable Sag

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

RE: Cable Sag

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

Now how do I determine "a"?

Thanks,
Chopin
 

RE: Cable Sag

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

RE: Cable Sag

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.

RE: Cable Sag

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

RE: Cable Sag

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"

RE: Cable Sag

rb1957

Check your units - I think you might have a problem

RE: Cable Sag

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 ??

RE: Cable Sag

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!!

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