engineering question for riggers

[phildthedildo 0]

ok i have a question that has me wondering......

if you have a canopy that has a continuous a/b line ,how much load (theoretical) would those 2 lines hold before breaking? in other words, if you have an A suspension line made of say 600lb material(vectran spectra whatever) that attaches to the A line attach point on the canopy,then runs down thru the connector link then back up to the B l.a.p.,would it be able to take 1200 lbs? or would it break at 600?

[airtwardo 7]

a continuous a/b line ,how much load (theoretical) would those 2 lines...

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600 lbs...(+ -)

It's still just one line right?

~ If you choke a Smurf, what color does it turn? ~

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[DougH 270]

I would guess it is going to be somewhat stronger than a single continues line that only goes from riser to one line group.

The actual number I haven't a clue, I would guess the radius and size of the link, along with the distance between the line groups would be a variable when calculating the real number.

Am I wrong? Engineer is the last job title I would put on my resume.

"The restraining order says you're only allowed to touch me in freefall"
=P

[phildthedildo 0]

thats what i thought. but remember safety flyer reserves? they had continuos a/b lines.

[hackish 8]

If I understand your question correctly then I believe the answer is 2x the breaking strength of the line. When I was told this I didn't believe it but I watched the crane operator take his 6000lb cable, loop it through the hook and the crane end twice and lift a 20,000 fixture...

-Michael

[skydiverton2 0]

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ok i have a question that has me wondering......

if you have a canopy that has a continuous a/b line ,how much load (theoretical) would those 2 lines hold before breaking? in other words, if you have an A suspension line made of say 600lb material(vectran spectra whatever) that attaches to the A line attach point on the canopy,then runs down thru the connector link then back up to the B l.a.p.,would it be able to take 1200 lbs? or would it break at 600?

1200lbs if you make the connection at the bottom strong enough

Using your droque to gain stability is a bad habid.
.
.
Also in case you jump a sport rig!!!

[dgw 8]

The answer is 1200, if you are looking at a 'pulley' arrangement - see link below.

However, I believe that the way the line is looped at the base may affect the local strength of the line in this region. Personally, I would use two lines. The loop would be subject to friction and wear, if I follow you correctly


http://www.google.com/imgres?imgurl=http://www.phys.unsw.edu.au/~jw/graphics/blocks1.GIF&imgrefurl=http://www.phys.unsw.edu.au/~jw/blocks.html&h=360&w=333&sz=4&tbnid=Nmnk-oPh1eMJ::&tbnh=121&tbnw=112&prev=/images%3Fq%3Dpulley%2Bload%2Bdiagram&sa=X&oi=image_result&resnum=1&ct=image&cd=1

[airtwardo 7]

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The answer is 1200, if you are looking at a 'pulley' arrangement - see link below.

However, I believe that the way the line is looped at the base may affect the local strength of the line in this region. Personally, I would use two lines. The loop would be subject to friction and wear, if I follow you correctly


http://www.google.com/imgres?imgurl=http://www.phys.unsw.edu.au/~jw/graphics/blocks1.GIF&imgrefurl=http://www.phys.unsw.edu.au/~jw/blocks.html&h=360&w=333&sz=4&tbnid=Nmnk-oPh1eMJ::&tbnh=121&tbnw=112&prev=/images%3Fq%3Dpulley%2Bload%2Bdiagram&sa=X&oi=image_result&resnum=1&ct=image&cd=1

Diagram (i) shows a pulley being used just to change the direction of a force. You can pull on the end of rope marked a with force F and the end b moves an equal distance with load force L


Am I missing something?

How does (i) in your example double the strength of the 'rope' used to apply the force?

Guess there's a REASON i was a business major!

~ If you choke a Smurf, what color does it turn? ~

[airtwardo 7]

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thats what i thought. but remember safety flyer reserves? they had continuos a/b lines.

'continuous' as in looped from a to b...or as in non-cascaded?


I don't remember seeing one...

~ If you choke a Smurf, what color does it turn? ~

[ryoder 1,590]

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thats what i thought. but remember safety flyer reserves? they had continuos a/b lines.

'continuous' as in looped from a to b...or as in non-cascaded?

I don't remember seeing one...

Heck I owned one and don't remember much other than there were no cascades, and a funky brake system
Of course even if they had 600lb lines on it, that doesn't mean they needed that much tensile strength. I have lots of jumps on canopies with 400lb lines. Imagine what light lines we could use if we didn't need to make allowance for slider wear.

"There are only three things of value: younger women, faster airplanes, and bigger crocodiles" - Arthur Jones.

[DougH 270]

Self lubricating plastic slider grommets maybe? Less friction = less heat = less wear?

"The restraining order says you're only allowed to touch me in freefall"
=P

[airtwardo 7]

Here's my thinking on the double line thing...


Is my logic flawed here, or am I missing something?

~ If you choke a Smurf, what color does it turn? ~

[JerryBaumchen 1,439]

Hi All,

A simple course in STATICS will answer all of your questions.

Jerry Baumchen
Registered Professional Engineer

[DanG 1]

Each side of your line only has to support 1/2 of the weight. The strength of the line doesn't go up, but the load that each side has to hold goes down.

Sum the forces (taking into account direction) so they equal zero.

- Dan G

[mjosparky 4]

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ok i have a question that has me wondering......

if you have a canopy that has a continuous a/b line ,how much load (theoretical) would those 2 lines hold before breaking? in other words, if you have an A suspension line made of say 600lb material(vectran spectra whatever) that attaches to the A line attach point on the canopy,then runs down thru the connector link then back up to the B l.a.p.,would it be able to take 1200 lbs? or would it break at 600?

Continuous lines are not actually continuous. The “a” line goes from the attachment point down to the connector link, goes around the link and returns to the “b” line attachment point. But it is not free floating. Just above the link the “continuous” line is zigzagged to itself thus creating 2 individual lines starting at the canopy and ending at the link. If the line is 600 pounds then each leg of the line will support 600 pounds.

I hope this helps.

Sparky

My idea of a fair fight is clubbing baby seals

[airtwardo 7]

The strength of the line doesn't go up...

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That's my point.....(i think )

~ If you choke a Smurf, what color does it turn? ~

[980 0]

in my experience with trying to convince people of this very same situation applied to break cord arrangements used to static line in basejumping:

it's no use to show people the theory, pictures, logic, etc. if they refuse to let go of the notion of the single line at the pulley point

easiest is to get them to do a little experiment themselves and that quickly settles it

so rig yourself up your little 10lb thread setup or similar and let us know what the results are ...

[dgw 8]

Respectfully, yes..

The line strength is not doubled, but the load it can support is doubled. So, if the load is constant, the line only has half the tension (which is a uniform load).

Plus, as another poster pointed out, a 'simple course in statics' would easily show this. The top connectors for the line each share half the load at the base (loop at riser).

If you extend the analogy, and consider a canopy rigged from a single looped line, you can see intuitively that the canopy is not supported by the strength of a single line, rather the number of 'looped sections' of line.

[airtwardo 7]

If you extend the analogy, and consider a canopy rigged from a single looped line, you can see intuitively that the canopy is not supported by the strength of a single line, rather the number of 'looped sections' of line.

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Like I said...business major!

~ If you choke a Smurf, what color does it turn? ~

[RiggerLee 61]

I'm not sure I understand your question but I'll take a shot at it. I think I understand what you mean by a continous a/b. The normal failure point tends to be at the end of the finger trap where the line ends inside the outer line. I don't know what percentage loss that is and I would be interested if some one has the number handy. That failure point is still there at the top of the line. Are you going to finger trap it through itself and back out right above the conector link? If so you now have the exit point of the fingure trap exposed to the full force. Normaly it's in the section where the end is run double above the bartack and protected from half the force. I'm not sure if there is more loss there from that or the ending inside the line. Even at a cascade the lower line is subjected to twice as much and it of course failes there before it really gets the chance to load exit point. Kind of an interesting question. You might be better off with two seperat lines and not load it that way.

Lee

Lee
lee@velocitysportswear.com
www.velocitysportswear.com

[billvon 3,071]

A few issues here:

1) Tensile strength is different than working load. A line might have a working load of 600 lbs and have a tensile strength of 1800lbs. That is to say, a brand new line tested over a wide capstan might break near 1800 pounds - but a 6 month old line with finger traps on each end, and a 1/4" radius turn at the end, might break at 700lbs.

2) As soon as you have any friction at all (say, at your pulley point due to motion of the line) you get massive amounts of heat/wear and the line fails rapidly.

[riggerrob 643]

Properly done fingertraps (angle cut ends, etc.) usually hold the full rated strength of the suspension line.
Fingertraps are stronger than any other type of knot I have tested.

[sundevil777 102]

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Here's my thinking on the double line thing...


Is my logic flawed here, or am I missing something?

The two pics you made actually result in the same tension in the line. In both cases the suspended weight is pulling down with 9 pounds, and the other end of the line has an equal force pulling with 9 pounds. In one case the force is provided by the wall, in the other case the force is provided by the weight on the other side of the pulley.

A line subjected to 9 pounds of tension has a force of nine pounds pulling on both ends of the line, but that does not make it 18 pounds of tension.

If the line didn't have the equal and opposite force pulling on the other end, then it wouldn't be stationary, it would be accelerating in the direction of the larger force.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[airtwardo 7]

So what you're saying is...


As far as my understanding of engineering goes, I'm a heck of a fry cook!

~ If you choke a Smurf, what color does it turn? ~

[riggerrob 643]

One difficulty with a continuous AB line is that it will slip out of trim before it has finished opening for the first time.

Tee!
Hee!