Speed Line Force?

[Jamin_Mayer]

Can anyone help with the force factors when we have a load on a horizontal or slanted speed line?

Say the span is 125ft and we had a 400lb. log directly in the middle.

What is going on physically with the load there?

 

[jmcscrap]

Treespyder may have something on his website?

 

[Mark Chisholm]

Oh no you didn't Jamin!

You have to know the angle of the rope when the load is static to start to figure that out.

 

[Jamin_Mayer]

[ QUOTE ]
Oh no you didn't Jamin!

You have to know the angle of the rope when the load is static to start to figure that out.

[/ QUOTE ]

I know... I start some crazy stuff around here.

So, I'm wondering what the force on the line would be at horizontal.

Then, what the force on the line would be at 10º.

 

[KBacks1]

Real good question; two thumbs up..

 

[oldoakman]

Somebody just HAD to bring up math and physics didn't you jamin. Actually very good question especially for those who use speedlines on a regular basis. Even though we don't calculate the force out to the ounce, we all do mental calculations of the forces we generate in our work. I was wondering when I would ever use that calculus that I forgot about 20 minutes after the final exam.

 

[lumberjackson]

This answers your original question:

http://www.slacklineexpress.com/force.php with 5 feet of sag, just over 2500 lbs

ALSO, I like to play with this other one too for stuff like stretching cable and zip lines where you are using heavier line, just to see what it takes to get the slack out:

http://www.wolframalpha.com/input/?i=sag+of+an+inclined+span

I wish I had any idea how either of these calculations work, but I don't. that's why I love the internet

 

[Jamin_Mayer]

That was an awesome link!

Now, I wonder if the force on an angled line changes while moving along the line?

In other words, would there be more force on the line in the middle versus a fourth of the way down the line?

 

[JeffL]

I believe the peak force is with the load at the middle of the span and decreases towards the ends, right?

 

[Mark Chisholm]

The force at each anchor point will change as the load moves. "Feet of sag" is hard for me to envision with any accuracy. The math I learned really calculated loads based on the angle created by the load and how much the load weighed.

 

[mark_sauls]

http://www.google.com/imgres?q=sling+ang...&ved=1t:429,r:8,s:0

I was looking for a chart the shows the load going to infinity to demonstrate the what can happen with a super tight speed line.


Similar concept from a different "angle"

Speed lines are great for bombproof spars.

The one variable that we all have control over is the size of the piece-weight-load. Smaller is often better.

 

[treeness]

With angles in mind, will a steeper angle generate less force on the tree or vice-versa?

 

[Norm_Hall]

[ QUOTE ]
With angles in mind, will a steeper angle generate less force on the tree or vice-versa?

[/ QUOTE ]

A steeper angle will put more 'downward' force on the tree.
The shallower the angle, the more 'side' force is generated.
When speedlining, there is a lot to consider:
rope construction
rope fiber
rope diameter
how much rope is in the system

It's really hard to calculte the forces being applied. They will vary with each piece.

Mahk Adams had a nice article on speedlining a couple of years ago. Very informative.

 

[JeffL]

I've wondered before, if you were to anchor the high end of the speedline to an adjacent tree, maintaining a shallow angle, regardless of the angle of the working side, could you not convert that sidewards pull to be almost a completely vertical load, where it would be compressing the stem as opposed to side loading it? You'd essentially just be using the tree you're in as a redirect as opposed to an anchor.

Sound plausible?

 

[Norm_Hall]

Absolutely!

Mahk's articles:
http://treebuzz.com/pdf/speedline_variations_1.pdf

http://treebuzz.com/pdf/speedline_variations2.pdf

 

[Jamin_Mayer]

Eric Frei, of Oz, has a good thread on the subject. There is a thread where a guy wants to set up a zipline for his kids and asks sort of my same question.

Scroll down about 15% and Eric answers it well (I think). However, if I use the scenerio on his thread. Eric isn't correct, when I punch in the numbers on the Slack Line Express site. The site calculates the force is 3,751lbs. If this is correct, Eric is grossly wrong. Eric's premise is that the force at the terminals is 5x the weight. Can anyone allude on this more?

 

[joe]

There are 2 sets of equations available for predicting tension in speedlines when the loads are static. One set is published in TCIA magazine and written by Graeme McMahon. The article is titled "Opposing Pendulums". The equations calculate the load from each rigging point.

The 2nd set of equations are on the Treespyder's site. They were written by "ME" before Graeme's article appeared in TCIA magazine . These equations figure the tension in the line from the load. These equations were also applied in a computer program by Dave Spencer from Canada, which are now on Ken's site . Both equations represent the load in a static situation. But, they are both accurate for the static situation they represent. The load should lead the sling and carabiner or pulley on the line. So, the angle of the sling in relation to the line when the load is static should be different as opposed by a dynamic situation. Therefore, the upper rigging point will experience a different tension than when it is static. A 20 degrees lead difference from 180 degrees or absolute downward hang can give a start when figuring tension in a speedline.

Joe

 

[Jamin_Mayer]

Joe. Can you provide a link to Ken's site? I can't remember what it is called. Thanks.

 

[joe]

The calculator doesn't seem to be there. An archived thread where those equations are written are there.

http://www.mytreelessons.com

Joe

 

[Jamin_Mayer]

Nice. Here is a good thread at Ken's site.

http://www.mytreelessons.com/Forces%20on%20a%20SpeedLine.htm