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My prediction.

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discojuggernaut
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Re: My prediction.

Postby discojuggernaut » Mon Sep 27, 2010 7:38 am

liquidlove wrote:I'm new to kiteing, and I'm just wondering if someone would tell me what pulleys do?
There are usually 3-4 attachment points (per side) for the bridle to support the Leading Edge, plus one more attachment point for the steering lines. The pulley usually sits between the attachment point closest to the steering lines (the tip) and the set of bridles (usually in a V form) closer over towards the center. Let my crude photoshop do the talking.

I don't care if a kite has pulleys as long as it flies well, and as long as the manufacturer uses good pulleys, the ones with hard plastic and bearings (ronstan).
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Re: My prediction.

Postby windmaker » Tue Sep 28, 2010 5:01 am

liquidlove wrote:I'm new to kiteing, and I'm just wondering if someone would tell me what pulleys do?
As far as I understand they can be used to do 2 things.

Help to shift the center of effort of the kite when located on the bridle (translates into tighter turns).

Lighten the bar feeling when placed on the kite or the bar by producing demultiplication .

This of course translates into some lost energy due to the sliding of the pulleys which sometimes translates into a blurry bar feeling but up to now they advantages outbalanced the disatvantages.

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Re: My prediction.

Postby Peter_Frank » Thu Sep 30, 2010 10:50 am

windmaker wrote:
liquidlove wrote:I'm new to kiteing, and I'm just wondering if someone would tell me what pulleys do?
As far as I understand they can be used to do 2 things.

Help to shift the center of effort of the kite when located on the bridle (translates into tighter turns).

Lighten the bar feeling when placed on the kite or the bar by producing demultiplication .

This of course translates into some lost energy due to the sliding of the pulleys which sometimes translates into a blurry bar feeling but up to now they advantages outbalanced the disatvantages.
I dont think this statement is correct at all:
This of course translates into some lost energy due to the sliding of the pulleys[
You DONT lose any energy because of the pulley principle :thumb:

(and I am 100% sure about that)

:D Peter
Last edited by Peter_Frank on Thu Sep 30, 2010 1:11 pm, edited 1 time in total.

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Re: My prediction.

Postby baller » Thu Sep 30, 2010 11:47 am

Peter - I think that you can argue that it is minimal, or not detectable, but certainly pulleys have some friction, therefore consume some energy. I'm 100% sure of that :D

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Re: My prediction.

Postby Peter_Frank » Thu Sep 30, 2010 12:37 pm

baller wrote:Peter - I think that you can argue that it is minimal, or not detectable, but certainly pulleys have some friction, therefore consume some energy. I'm 100% sure of that :D
Ha haa, I almost waited for that one, so you are right :thumb:

But would not complicate by taking this "not detectable" value into the discussion :D
(maybe simplified too much then....)

As we all know this is not the issue here :naughty:

It could be compared to saying that you got loss because of line stiffness, instead of having "infinite" soft lines :D
Where the answer to that would be NO, you dont have any loss because of line stiffness (because it is not detectable in any way).
But you could always argue that there would be a theoretical loss because of line stiffness, even though it does not make sense to take into any equation or view at things :roll:


The same goes for the pulleys - and the postulate was apparantly that the presence of "working" pulleys should make the kite less powerful, right ?
Which is not the case in any way (measurable ) :wink:

------------------------

Okay then, to be more precise:

The presence of pulleys, and the clean "sliding" action itself - DO NOT COST ENERGY !

The friction is of course a really small "heat" loss (energy loss) yes, but it will IMO not be detectable at all (which is a postulate, I know, but based on experience).


That was my point - just to clarify that the pulley principle do not cost energy :D
The FEEL when turning, can be influenced a lot, and both give the feel of having less power, as well as the opposite - depending on what principle used - but that is another issue...

Corrected my earlier posting, to "pulley principle" instead :thumb:

:D Peter

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Re: My prediction.

Postby bay surfer » Thu Sep 30, 2010 3:47 pm

Hmmmmmm, Interesting discussion here...... I have a 08 RRD type 8, damn thing turns too fast for predictable 720s hate when your half way into the second rotation and the kite kiteloop/F-16 with the high speed body slam!!! No slower attachment points. I just may remove the pullys all together, because of the info on this post, and see what happens.

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Re: My prediction.

Postby jedi1 » Thu Sep 30, 2010 4:03 pm

windmaker wrote:
Bigdog wrote:Cabrinha seems to be going the other way and those kites fly VERY well with very clean canopy tension.

I think there will be lots of kites with pulleys and at least 5 struts in our future.

my2c

Stan
Cabrinha is not going the other way. Just like all the other brands they have had kites with pulleys for at least 5 years , so nothing has changed.

I might be wrong, but the need for innovation (and market shares) will bring us cheaper, simpler, lighter and more reliable kites without pulleys.
Hmm from what I know 2011 Crossbow is the same design as 2010. The only difference is the bridle, which actually has one more pulley. They've put the pulley on the wingtip, just like many 07 kites. Kinda strange design strategy I guess, when most companies want to get rid of pulleys.

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Re: My prediction.

Postby windmaker » Thu Sep 30, 2010 4:57 pm

Peter_Frank wrote:
baller wrote:Peter - I think that you can argue that it is minimal, or not detectable, but certainly pulleys have some friction, therefore consume some energy. I'm 100% sure of that :D
Ha haa, I almost waited for that one, so you are right :thumb:

But would not complicate by taking this "not detectable" value into the discussion :D
(maybe simplified too much then....)

As we all know this is not the issue here :naughty:

It could be compared to saying that you got loss because of line stiffness, instead of having "infinite" soft lines :D
Where the answer to that would be NO, you dont have any loss because of line stiffness (because it is not detectable in any way).
But you could always argue that there would be a theoretical loss because of line stiffness, even though it does not make sense to take into any equation or view at things :roll:


The same goes for the pulleys - and the postulate was apparantly that the presence of "working" pulleys should make the kite less powerful, right ?
Which is not the case in any way (measurable ) :wink:



------------------------

Okay then, to be more precise:

The presence of pulleys, and the clean "sliding" action itself - DO NOT COST ENERGY !

The friction is of course a really small "heat" loss (energy loss) yes, but it will IMO not be detectable at all (which is a postulate, I know, but based on experience).


That was my point - just to clarify that the pulley principle do not cost energy :D
The FEEL when turning, can be influenced a lot, and both give the feel of having less power, as well as the opposite - depending on what principle used - but that is another issue...

Corrected my earlier posting, to "pulley principle" instead :thumb:

:D Peter
For sure the energy absorbed by the pulleys is so minimal that irrelevant.

Anyway what I really meant was not lost energy but lost motion.

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Re: My prediction.

Postby experienced1 » Thu Sep 30, 2010 6:01 pm

Jedi1:
I believe the center section of the bridle has been changed...shorter, and the front and rear pulley circuits are now attached similar to '09
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Re: My prediction.

Postby Hansen Design » Thu Sep 30, 2010 6:13 pm

Before discounting pulleys, one should consider their function and loading as they are used in two very different ways:

1) Pulley(s) on the bridle - provide a movable front towpoint and variable bridle geometry allowing the kite to 'tip' reducing AOA and de-power.
2) Pulley(s) on the kite - support the wingtip area between the front and rear lines while allowing the kite to 'tip' reducing AOA and de-power.

In (1) the pulley is highly loaded and must withstand the force of the kite (or a portion of it depending on number of pulleys.) A failed pulley can result in loss of control and be dangerous. Pulleys on the bridle move independently giving a less connected more 'sloppy' feel.

In (2) the pulley allows the structure to be smaller and lighter with less MOI. Pulleys on the kite are lightly loaded and failure will not cause a loss of control. They connect the front and rear lines giving a smoother, more consistent feel.

Many small aircraft utilize pulleys in their control systems.


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