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Pulleys on kites

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dylan*
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Re: Pulleys on kites

Postby dylan* » Mon Jan 01, 2018 10:06 pm

wind chaser wrote:
Mon Jan 01, 2018 8:58 pm
I have a 10m 2014 RPM with pulleys and bought a 10m 2016 RPM with no pulleys. Use the same bar and can’t tell much of a difference. Does it matter that much?
not really apples to apples since they are using bungees instead of pulleys

personally i dont think pulleys make a big difference one way or the other. i love the simplicity of kites without them, but now that brands have figured out how to make shorter bridles, they can feel pretty similar in terms of responsiveness even with one or two pulleys on each side. not sure about the bar pressure argument. my 2016 12m envy has pretty light bar pressure with zero pulleys.

i think the old days of the 9 pulley cabrinha kites are behind us, brands have figured out how to make kites more responsive and still keep big depower ranges etc, whether they have pulleys or not.

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Re: Pulleys on kites

Postby Faxie » Mon Jan 01, 2018 11:08 pm

windrider1 wrote:
Mon Jan 01, 2018 10:04 pm
In engineering a pulley is a tool used to apply what is called mechanical advantage to a task . In other words its used to reduce the amount of force required to move a heavy load, In kiting in general were dealing with heavy loads and a constant changing in force required to moved this load . Right at this point in time there is no better simple mechanism to use to manage and control these forces better than a pulley on a kite . Going pulley less is just a fad that has no basis in science . Some of the negatives of pulley less kites are heavy bar pressure, off and on power delivery and instability of the kite at certain times . now these can be controlled in various ways but u always loose something in the return.


iriejohn wrote:
Mon Jan 01, 2018 8:19 pm
windrider1 wrote:
Mon Jan 01, 2018 6:57 pm
i don't know wht people have against pulleys this nonsense pulley hate started a few years back but is not based on any science a good kite needs a pulley to perform smoothly and efficiently . That's 100 % fact.
What is the incontrovertible science that proves that kites can only "perform smoothly and efficiently" if they have pulleys?
windrider1 wrote:Some kites may have a boomerang springy feel to it with pulleys but its designer choice and not automatic because the kite has pulleys. A kite without a pulley has more negatives than positive in my opiion .
What are the negatives that kites without pulleys always suffer from?
Pulleys on a LEI kite transfer a linear load. Total force on the bridle is the same as with pulleyless. The only 'advantage' is that a designer doesn't have to account for the relation of the LE arc in different angles of attack to the bridle shape so much. Thus quick fix.

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Re: Pulleys on kites

Postby iriejohn » Mon Jan 01, 2018 11:11 pm

windrider1 wrote:
Mon Jan 01, 2018 10:04 pm
In engineering a pulley is a tool used to apply what is called mechanical advantage to a task . In other words its used to reduce the amount of force required to move a heavy load, In kiting in general were dealing with heavy loads and a constant changing in force required to moved this load . Right at this point in time there is no better simple mechanism to use to manage and control these forces better than a pulley on a kite . Going pulley less is just a fad that has no basis in science.
No scientific proof there. And see below*.
Some of the negatives of pulley less kites are heavy bar pressure, off and on power delivery and instability of the kite at certain times . now these can be controlled in various ways but u always loose something in the return.
No, not always heavy bar pressure. No, not necessarily on or off power delivery - kites/wings don't work like that*, and neither are they rigid wings*. Re: stability see the previous point*. And losing something in return is yet another unsubstantiated statement.
windrider1 wrote:
Mon Jan 01, 2018 10:06 pm
2 pulleys on a kite are quite unecesasry and thst why u don't see them anymore. A good kite needs a pulley. some people just don't know what a good kite is.
;-)
Last edited by iriejohn on Mon Jan 01, 2018 11:22 pm, edited 1 time in total.

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Re: Pulleys on kites

Postby kitexpert » Mon Jan 01, 2018 11:19 pm

dylan* wrote:
Mon Jan 01, 2018 10:06 pm
but now that brands have figured out how to make shorter bridles,
It's not that difficult, shorter bridles are made by using shorter pieces of line :wink:

I just finished a kite with very short bridles, probably shorter than what is ever seen in traction kites. However there is some twist in it and still I was a bit worried if I pushed it too far. In first tests it seemed to work well and I didn't find out any issues. I don't know if it could be even shorter.

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Re: Pulleys on kites

Postby grigorib » Mon Jan 01, 2018 11:36 pm

Liquid Force managed to screw up using wrong type of Ronstan pulleys up to 2013. They’d fill with sand, stuck, the bridle would cut through plastic wheel and then the metal will cut the bridle.

How about this “science”?

Pulley-less is simple and more reliable
Pulleys give better bridle/LE load distribution
Pulleys have very little to do with bar pressure

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Re: Pulleys on kites

Postby kitexpert » Mon Jan 01, 2018 11:52 pm

kitexpert wrote:
Mon Jan 01, 2018 11:19 pm
I just finished a kite with very short bridles
Compared to a bit smaller same category FS kite distances from kite to mixer are: FS 4,3m vs 1,65m in my kite. Quite a big difference even though comparison is not 1:1 due to differences between the kites.

I don't know LEI bridle design so well I can say much about pulleys. I've considered all LEI bridles quite trivial, most complex or challenging to design are probably pulleyless ones with some extra feature like spider bridle. Most LEI's I use have pulleys, but I know there is good pulleyless kites. If kite don't have to have pulleys it is fine for me. I also remember a bit stiffer feel with pulleyless kites I've used, but it is not decisive thing to me.

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Re: Pulleys on kites

Postby kitexpert » Tue Jan 02, 2018 12:03 am

grigorib wrote:
Mon Jan 01, 2018 11:36 pm
How about this “science”?

Pulley-less is simple and more reliable
Pulleys give better bridle/LE load distribution
Pulleys have very little to do with bar pressure
I agree with your "science". I don't know if load distribution is better with pulleys, but for sure it is more even.

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Re: Pulleys on kites

Postby marlboroughman » Tue Jan 02, 2018 1:16 am

To understand how pulleyless system give you less bar pressure do this exercise.
Look at the five line kite from the side. Front lines are behind fifth line, right, so they hold certain amount of load even before you touch the back lines.
Look at the side of the pulleyless bridle. Do you see how the bridle does basically the same.
Put the pulley on it and what do you think that holds? It is all on back lines, now.

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Re: Pulleys on kites

Postby bragnouff » Tue Jan 02, 2018 1:37 am

Pulleys allow to spread the tension on the leading edge bridle attachment points at various angles of attack, so all parts of the bridle are pretty much equally tensioned on a range of AOA, and across the windrange. So in theory, the intended profile and bar pressure is maintained on a wider range of conditions than a fixed bridle which is optimized and locked around a given set of AOA and windspeed.
But of course pulley and bridle are only one set of parameters in the design of a kite, how well the profile is locked in place at the various windspeeds and AOA will be critical for that. From what I understand, the center of lift on a deep profile tends to shift backwards as the windspeed increases whereas a thinner profile won't do that as much, as the drag component isn't increasing as much. So designing a kite with a thick profile without pullies might be a harder task than a thin profiled one. Or there would be substantial changes in the bar pressure.

But in practical usage, when you reach the top of the windrange or when depowered more, is it actually beneficial to keep an optimal profile? If your profile starts fluttering and with that killing some of the lift, this can help keeping the things slow and manageable, and be perceived as an advantage. Similarly, an increased bar pressure is not necessarily a bad thing for some segments of the market. So it's just one parameter in the design, along with profile distortion, and that's just for flying in straight line. Because how a kite turns matters a lot for riders, this is also to be combined with twist, and all... Complex shit, compromises everywhere!

Now from experience, I never experienced pulley failure, I've had to replace worn bridles on a kite that had obscene amounts of hours of use, but that's totally expected, took 1 hour and $20. Main factor for me is to have short bridles that cannot get anywhere to wrapping around the wingtip cause this is bad, really bad! And for a while fixed bridles where typically longer than pulleyed bridles. (There were also long pulleyed ones, by the way :roll: ...). What I liked the most on my pulleyed kites, (GK Trix, short bridle, 2 pulleys per side), was the retained responsive steering wherever in the window, even with barely tensioned lines/ drifting. What I didn't like that much was the way the kite rocks back and forth on its pulleys when lit on choppy/waves conditions, with pulleys doing their job at every change in tension, and with resulting feedback in the bar/harness. Typically a sign that it's time for a smaller one though.
On my fixed bridle Enduros, despite a big wind range, I find that when maxed out, the profile flaps a fair bit, which is not necessarily a bad thing in itself, and there's also a tendency to backstall when too low in the window heading towards it... On the other hand, that's why it can backwards relaunch too... so not necessarily a bad thing either within its design brief.

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Re: Pulleys on kites

Postby alexeyga » Tue Jan 02, 2018 2:28 am

marlboroughman wrote:
Tue Jan 02, 2018 1:16 am
To understand how pulleyless system give you less bar pressure do this exercise.
Look at the five line kite from the side. Front lines are behind fifth line, right, so they hold certain amount of load even before you touch the back lines.
Look at the side of the pulleyless bridle. Do you see how the bridle does basically the same.
Put the pulley on it and what do you think that holds? It is all on back lines, now.
Dude where from do you come up with that stuff? Bar pressure has no relation to pulleys what so ever, only to the overall kite design. There are pulley-less kites what will rip our you forearms just as there are kites with pulleys that you can ride all day long without any of your pinkies getting cramped up - and the other way around. One of the reasons why I dumped C4-s, was the fact that as of 2012 Ozone has increased the bar pressure beyond any sense.


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