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Are Pulley bridles more tolerant to stretch/shrink?

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Greenturtle
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Re: Are Pulley bridles more tolerant to stretch/shrink?

Postby Greenturtle » Sun May 06, 2018 7:47 pm

I think because the LE is quite flexible as a whole, even pumped up hard, none of the bridle lines are going to slack out when sheeted to different angles. The sheeting changes are not that extreme, and the LE just flexes a bit and bridle stays taught.

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Re: Are Pulley bridles more tolerant to stretch/shrink?

Postby GregK » Sun May 06, 2018 8:21 pm

And that front view of the Ozone Reo is a frontal projection of the bridle geometry, not a true-view of the A1/A2/AL1 plane, so the angles shown in that frontal projection are not true, but rather projections onto the front view plane.

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Re: Are Pulley bridles more tolerant to stretch/shrink?

Postby Peert » Sun May 06, 2018 8:24 pm

Greenturtle wrote:
Sun May 06, 2018 7:47 pm
I think because the LE is quite flexible as a whole, even pumped up hard, none of the bridle lines are going to slack out when sheeted to different angles. The sheeting changes are not that extreme, and the LE just flexes a bit and bridle stays taught.
No one mentions that the tow point (where front line is attached to bridle) is not a fixed point.
Not even a point in a single plane. It can shift closer or further away from center axis of kite. I would say you will never get slack lines (in a reasonable well designed kite) since as soon as the kite lowers AOA and pressure is released from outer branch of the bridle the tow point shifts closer to the longitudinal axis of the kite.

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Re: Are Pulley bridles more tolerant to stretch/shrink?

Postby Sandras » Sun May 06, 2018 8:49 pm

GregK wrote:
Sun May 06, 2018 8:21 pm
And that front view of the Ozone Reo is a frontal projection of the bridle geometry, not a true-view of the A1/A2/AL1 plane, so the angles shown in that frontal projection are not true, but rather projections onto the front view plane.
Still if you add all vectors in a (non accelerating) node they should equal zero in the 3d space AND in every 2d projection of it.
No?

Yes, a line will never go slack because LE will adapt and tension this line, but this structural load is peanuts compared to the front lines pulling.

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Re: Are Pulley bridles more tolerant to stretch/shrink?

Postby Bushflyr » Sun May 06, 2018 9:40 pm

^Dude. You obviously just want to argue.

That's not how kites work. Go tie your kite to a solid object, fully power it up near the ground, go ping the lines. You'll see that they're pretty equally tensioned. Then come back and whine about how the experiment is invalid.

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Re: Are Pulley bridles more tolerant to stretch/shrink?

Postby Sandras » Sun May 06, 2018 10:10 pm

Bushflyr wrote:
Sun May 06, 2018 9:40 pm
^Dude. You obviously just want to argue.

That's not how kites work. Go tie your kite to a solid object, fully power it up near the ground, go ping the lines. You'll see that they're pretty equally tensioned. Then come back and whine about how the experiment is invalid.
Well, I just want to learn and I do so by challenging the things that don't seem logical to me and get convinced from those that give me a better understanding

It seems that you are not a good sparing partner here (contrary to everybody else in this thread ! :thumb: ),

first you axiomatically say just no - no explanation whatsover
then you say "go do the vector analysis" , like there was a fully defined system and the only thing remaining was to solve it. Anyway, I explained you why this is wrong by focusing on a part that proves your idea wrong (Reo drawing).
and now you propose an experiment that's simply not practical to do... What about the back lines? Pinging the lines will measure the forces or that there is "some" tension?

Anyway, in this thread, you are the only one who believes that the lines in a fixed bridle are "pretty equally tensioned"...
In a very specific angle of attack maybe, overall definitely not.

Here is the designer of a legendary kite, after many years of experience showing how the line of the tip gets loose when sheeting in... :bye:
phpBB [video]

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Re: Are Pulley bridles more tolerant to stretch/shrink?

Postby foilholio » Mon May 07, 2018 5:54 am

If you know the factory lengths, then with measurements of a used bridle you can compare shrink. Lines with more shrink have less load or maybe better said less duty.

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Re: Are Pulley bridles more tolerant to stretch/shrink?

Postby GregK » Mon May 07, 2018 7:36 am

Sandras wrote:
Sun May 06, 2018 8:49 pm
... if you add all vectors in a (non accelerating) node they should equal zero in the 3d space AND in every 2d projection of it.
No?
Yes, agree with you there, but have you considered the possibility that the Reo bridle diagram isn't a true front-view projection of a 3D CAD model of LE and bridle, but instead a sketch or schematic of the bridle, arranged for easy interpretation but far from the real geometry? The wingtip / steering line has definitely been altered from true geometry.

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Re: Are Pulley bridles more tolerant to stretch/shrink?

Postby Sandras » Mon May 07, 2018 9:50 am

20180507_104910.png
Vector analysis on real picture /experiment show that a2 does not carry load, because if it would a1 and al1 would not be parallel!

And off course if "equally loaded" a1 would have the same angle as a2 compared to AL1.
Now one is parallel and the other at right angle!

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Re: Are Pulley bridles more tolerant to stretch/shrink?

Postby abel » Mon May 07, 2018 6:21 pm

Sandras wrote:
Sat May 05, 2018 7:58 pm
reo.JPG

My understanding may be wrong and I welcome you to correct it.
I paste the bridle of Reo as an example of a non pulley kite.

1) For pulley less kites only one of the A1,A2,A3,A4 carries the load of the front lines (the rest have a very small load that just keeps the shape of the kite)
A1 (and the back lines) is carry the load at the maximum sheet in and A4 carries the load when fully de-powered.

2) A bridle with pulleys, because it can move it divides the load in the bridle lines.

My though is that a bridle with pulleys is less sensitive to stretch/shrinking exactly because the pulley can move and redistribute the load. That is that even if +/- a bit it would still work better than a pulley less bridle.

Is this thinking correct? If not, what's wrong?
Your thinking is correct. But...
But you have to consider "hidden" parameters when you compare kite features.
The top for Ave Joe are "personal feeling and fun factor" which is very tricky to determine as it difficult to quantify, and its almost impossible to carry out statistical testing under controlled conditions.
Even if you would like to check by yourself, you"ll have to carry the test with same kite and two different bridles (with and w/o pulleys), right? :roll:

Back to your question, the angle between the front lines and the leading edge cord (segment between front tips) determines the "loosness" of bridal segments.
By chance, just a couple of days ago I was wondering about the same question and I played with the front line to see which and when the bridle segments get loose.
I concluded that for practical riding the angle variation is relative small and most of the time all bridle segments are under tension (more or less).
So in theory you are correct, but practically it has a less significant impact on stretching than in steer feeling (if those two can be compared :wink: ).


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