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Line Tension

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blacklotusninja
blacklotusninja
WA
26 posts
blacklotusninja blacklotusninja
WA, 26 posts
22 Oct 2005 9:24am
Now i know kite lines have a huge amount of tension in them while the kite is flying. Does anyone know how much there actually is? Anyone been hit or injured by a kite line, i haven't really heard any storys. Just wondering what sort of damage they are capable of inflicting. Been pondering this for a couple of days now, can't seem to get it off my mind.
Cheers
Tim
Soonee
Soonee
VIC
147 posts
Soonee Soonee
VIC, 147 posts
22 Oct 2005 11:38am
Well have a look at one of the old videos, (I think it is either Awake or Small Craft Warning and there is a guy (I think it was Mark Shinn) with a huge welt around his neck. He almost killed himself in the surf when he got his head in his lines in the surf and his kite relaunched. I will try and find it on my movies to confirm.
Spacemonkey!
Spacemonkey!
SA
2288 posts
Spacemonkey! Spacemonkey!
SA, 2288 posts
22 Oct 2005 11:10am
ahah physics in schol does have a point

Tension is a type of force

F=m.a (Newtowns Second Law
m=mass (of you)
a=acceleration

and...
a= Change of Velocity divided by time
by looking at a particular sequence of photos (multiimage phootos) you could calculate the average acceleration and hence find the force
but it would vary a lot and would be hard to measure accuratley this way.

anton
anton
202 posts
anton anton
202 posts
22 Oct 2005 9:44am
stick a (fishing) spring scale any where inline
blacklotusninja
blacklotusninja
WA
26 posts
blacklotusninja blacklotusninja
WA, 26 posts
22 Oct 2005 10:27am
I posted the question on the physics discussion board at uni. will be interested to see what they come up with.
sprouse
sprouse
WA
78 posts
sprouse sprouse
WA, 78 posts
22 Oct 2005 11:24am
I reckon you could just use the spring constant, just have a massive spring with a trigger on your chicken loop and you can record the change in the spring when you load up. (NEWTONS SECOND LAW)
carbine
carbine
WA
1450 posts
carbine carbine
WA, 1450 posts
22 Oct 2005 11:50am
First of all they don't have tension in them, they are placed under tension.

Secondly it depends on the wind strength, the size of the kite, the type of kite, the relative position of the kite in the window, the trim of the kite and how fast the kite is flying. You can't just randomly pick a figure out of thin air and say thats the stress.


A kite line will take your fingers and toes off quite easily. Get if wrapped around your neck while powered and your likely to die.
carbine
carbine
WA
1450 posts
carbine carbine
WA, 1450 posts
22 Oct 2005 11:52am
quote:
Originally posted by Spacemonkey!


a= Average Velocity divided by time





would be change in velocity divided by time for average acceleration.


quote:
i mite be going with another mate from here aswell, its on a week after my yr 12 exams finish wha sweet timing.


I hope your not doing physics, coz your going to get ****ing owned.
kitecrazzzy
kitecrazzzy
WA
2184 posts
kitecrazzzy kitecrazzzy
WA, 2184 posts
22 Oct 2005 1:02pm
each line is going to be sharing a different amount of pull, maybe we should find out the max pull of the kite first as the conditions change so much we could have a list of controlled variables a mile long.
i think i fluked my exam of these things, will find out on Monday 8:38 am
HungLong
HungLong
WA
859 posts
HungLong HungLong
WA, 859 posts
22 Oct 2005 1:11pm
who give's a sh!t ?

I've been buzzed twice by a tight line, it phuking hurt !

regards browneee
carbine
carbine
WA
1450 posts
carbine carbine
WA, 1450 posts
22 Oct 2005 2:33pm
quote:
Originally posted by Spacemonkey!

practically the same thing carbine i cant believe u bothered correcting me on such a trivial thing.

i was trying to put it in simple terms for all the people who havent done pysics

who gives a **** how much pull a kite has anyway


Well its not the same thing, not even close.

Say the Velocity was constant at 10m/s for 10 seconds. Therefor average velocity is 10m/s, using your formula the acceleration is 10/10 = 1m/s^2. When clearly their is no acceleration
HungLong
HungLong
WA
859 posts
HungLong HungLong
WA, 859 posts
22 Oct 2005 7:40pm
Dont worry Spacey I got what you ment and I think others did too... Carbone chill out buddy, cut your hair, get rid of the perm and go kiting...

regards browneee
greenleader
greenleader
QLD
5283 posts
greenleader greenleader
QLD, 5283 posts
22 Oct 2005 9:49pm
a seagull once bounced off my front line. i was going fast he was going fast. boiing!
i secretly wanted it to slice in half.[}:)]
only cause it would have made a really good story.
carbine
carbine
WA
1450 posts
carbine carbine
WA, 1450 posts
22 Oct 2005 10:10pm
quote:
Originally posted by HungLong

Dont worry Spacey I got what you ment and I think others did too... Carbone chill out buddy, cut your hair, get rid of the perm and go kiting...

regards browneee

Yeah I wish I could.

seabreeze.com.au/graphs/wa.asp

nothing nothing nuclear nothing nothing nothing nothing.
HungLong
HungLong
WA
859 posts
HungLong HungLong
WA, 859 posts
22 Oct 2005 10:22pm
I'm hearing ya !

regards browneee
nebbian
nebbian
WA
6277 posts
nebbian nebbian
WA, 6277 posts
22 Oct 2005 10:34pm
Ahh here's where some physics comes in handy.

Forget all those formulas, forget trying to figure it out using F=ma, just think of this:

When boosting, the kite lifts you up (slowly). Therefore the force on the lines is roughly the same as your weight. Therefore the force on any line is roughly:
(your weight / number of main lines).

So for a kiter of let's say 80 kg's with two main lines, you've got 40 kg's or roughly 400 Newtons on each line. People have had fingers cut off with less pull using fishing line, so it's plenty to leave some nasty chafe marks

Obviously the force is less when you're not being lifted into the air, but this method is good enough for a ballpark figure.
jan
jan
WA
1119 posts
jan jan
WA, 1119 posts
23 Oct 2005 2:24am
quote:
Originally posted by nebbian
Obviously the force is less when you're not being lifted into the air, but this method is good enough for a ballpark figure.


Good description :)

Force would be roughly the same when not being lifted into the air, the kite is pulling you along still, just not vertically.
Spacemonkey!
Spacemonkey!
SA
2288 posts
Spacemonkey! Spacemonkey!
SA, 2288 posts
23 Oct 2005 8:20pm
ok i feel so bad about this,

today just kiteboarding along enoying myself, then i feel the lines twang a little.

Keep riding thinking nothing more of it. I take a quick glance back 5 seconds later when it occured to me.

Seagull on the ground, big gash in it's neck, turned it's feathers red. Couldnt move.

And thats the end of my story.

Im pretty sure it died it was jus lying there on the sand and i stayed and farewelled it

thats how much force lines have, still don't knowhow i managed to get it so bad.
Kitepower Australia
Kitepower Australia
NSW
4382 posts
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Kitepower Australia Kitepower Australia
NSW, 4382 posts
24 Oct 2005 8:08am
quote:
Originally posted by carbine

First of all they don't have tension in them, they are placed under tension.

Secondly it depends on the wind strength, the size of the kite, the type of kite, the relative position of the kite in the window, the trim of the kite and how fast the kite is flying. You can't just randomly pick a figure out of thin air and say thats the stress.


A kite line will take your fingers and toes off quite easily. Get if wrapped around your neck while powered and your likely to die.


It has nothing to do with just the kite alone, the tension occurs because of two forces in opposition, the ballast/rider is a very important part of your calculations.

Another way to look at it is to assume there is somewhere between zero tension while it is all still in the bag, and the tension required to break the lines.

I once had a seagull get caught in my lines when I was buggying at approx 70kph, it was totally stuck in the line, when I stopped and landed to remove to flapping gull, the line had cut into its wing. It flew off OK though after biting me a couple of times!

Cya and

Goodwinds

Steve McCormack
AJ175
AJ175
ACT
17 posts
AJ175 AJ175
ACT, 17 posts
26 Oct 2005 4:23pm
OK guys... you all seem to be a bit right and a bit wrong (some more than others I think, if my high school science memory is good)

Brownee is on the right track...

The easiest method, and one that will yield the most accurate result, in a do-able manner, is to stand on a newton register (bathroom scales will probably do nicely) that is between you and the board. The most accurate result will be shown when your legs are angled halfway between the kite line angle and the angle of gravity (i.e gravity of weight = lift of kite). This will leave you with approximately the pull (and hence force of tension) in the entire scenario.

The tesion in the lines cannot be greater than that in your legs unless your legs break.

Or, keep it simpe, ruin your set up, and insert in-line scales between your bars and your lines, as suggested before.

nebbian
nebbian
WA
6277 posts
nebbian nebbian
WA, 6277 posts
26 Oct 2005 2:45pm
Nitpicking physics hat on

quote:
The easiest method, and one that will yield the most accurate result, in a do-able manner, is to stand on a newton register (bathroom scales will probably do nicely) that is between you and the board. The most accurate result will be shown when your legs are angled halfway between the kite line angle and the angle of gravity (i.e gravity of weight = lift of kite). This will leave you with approximately the pull (and hence force of tension) in the entire scenario.


Ummm... so you're standing on some scales, and let's say the kite is just about overhead and it's pulling like a train, you're just about to take off, wouldn't the tension in the lines just about equal your mass, therefore the bathroom scales will read almost nothing?
Try top-to-tail'ing your vectors. As the angle of the lines increases to almost vertical, the resultant force (combining kite pull with human mass) approaches zero.

quote:

The tesion in the lines cannot be greater than that in your legs unless your legs break.


In the scenario above, tension in the lines will be a lot greater than the compression in your legs. Think about when you take off... compression in your legs is pretty much zero, while tension in the lines is high.


I think you're missing the fact that the human body has mass.
Spacemonkey!
Spacemonkey!
SA
2288 posts
Spacemonkey! Spacemonkey!
SA, 2288 posts
26 Oct 2005 7:44pm
DOn't they weigh sharks by hanging them by a spring. Clearly scales will not be able to measure the force accurately not to mention the reading on the scales is

F=m.g (mass)(gravity)
it just converts it just to read your mass.

So if u use bathroom scales you will be measuring the mass, not the force, so you will need to convert it.

A shark sping thingy would be the only thing that could measure the ammount of force we are talking about not ur standard bathroom scales. By attaching this spring to your chicken loop no need to wory about vectors.
dachopper
dachopper
WA
1806 posts
dachopper dachopper
WA, 1806 posts
26 Oct 2005 6:46pm
the origional question was that you wanted to know how much damage a kite line is capable of. The main factors will be the type of line( waxed) or unwaxed spectra, or cotton, and the diameter of line VS max load rating. , and the other main factor is where it hits you or gets wrapped around.... i think a line could skin a finger, with friction due lines moving in the one spot, but if the line is wrapped around your harness, same tension, i doubt it would do anything..also depends on the speed, if kiter a gets hit by kiter b's lines in the neck, both doing 30 kts in opposite directions..ie 110km/hr crossing rate .. he'll be headless pretty easily i think. so to answer the question... the worst it can do is kill you... but then again, pretty much anything can kill you these days.
blacklotusninja
blacklotusninja
WA
26 posts
blacklotusninja blacklotusninja
WA, 26 posts
26 Oct 2005 7:19pm
Cheers for all the input guys.
I didn't get to much from the physics discussion board. they all tended to agree that the easiest way to find the tension would be to attach a newton spring scale to each line and take a measuring. Times this number by our good friend gravity (9.8) and thats the approximate tension in the lines. Eventually the discussion devolved to attaching children of different weights to the kite to see how many are needed to hold the kite down. Then somehow it managed to get onto the topic of chocolate and polony, still not sure how it got there but it did. Physicians can be pretty trippy sometimes hey. Is there anyone around who has actually sustained an injury from their kite lines? Any cool stories?
Cheers
Tim
Spacemonkey!
Spacemonkey!
SA
2288 posts
Spacemonkey! Spacemonkey!
SA, 2288 posts
26 Oct 2005 8:52pm
i have had line burn but that is about it, it just stings like hell.
windnkite
windnkite
QLD
90 posts
windnkite windnkite
QLD, 90 posts
26 Oct 2005 9:41pm
well i heard that a while ago someone was launching in strong winds on the beach and the kite rushed along the ground before taking off and happened to hit some chick lying down and took all the skin off the top of her arm, meaning it cut right to the bone. understandably, she was upset.
kitecrazzzy
kitecrazzzy
WA
2184 posts
kitecrazzzy kitecrazzzy
WA, 2184 posts
26 Oct 2005 8:03pm
i suffered a nervous breakdown when my lines got affectionit with each other, ending a much needed session
HungLong
HungLong
WA
859 posts
HungLong HungLong
WA, 859 posts
26 Oct 2005 8:30pm
I've been buzzed by my own lines (stupid moment of lost concentration)... I've been pitch 20m down wind and smashed into the beach when my brother inlaw and I were piss farting around near the shore (again stupid moments) and my fav of all time, this is classic... Two stupid ****ing euro's were learning at my local, right in the main zone. After being asked (politly) to move down wind, they refused. Awhile later I was cruzing around when they lost control of the kite, without yelling out to anyone their kite landed at full speed on my head. The lines buzzed and burnt into my neck and through my wetsuit !... After a rather heated discussion they moved down wind...

regards browneee
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