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ultimate lowend: fixed bridle wins over depower foils. why?

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herculon
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ultimate lowend: fixed bridle wins over depower foils. why?

Postby herculon » Tue Jan 12, 2010 5:31 pm

it is generally agreed on that fixed bridle high performance kites like the
ozone yakuza or the peter lynn vapor are the ultimate low wind machines, that get you moving on snow or ice in 4 knots, and on water in 5 or 6 knots. here are some videos with a yakuza:

kitesurfing: 4-7 knots:
http://www.youtube.com/watch?v=xc7mQhj5-hg

720° in slow walking speed:
http://www.youtube.com/watch?v=3SvVc8L1_1I

and this is with a relatively small foil of 10sqm !!!

while all known depower foils (flysurfer speed deluxe; ozone manta) need at least 6 knots, better 8-10 knots to get you moving.

is there any good explanation? i just cant get it. all kites are high aspect high performance kites (yakuza, manta, flysurfer speed).

* material cant be the reason. the deluxe cloth of flysurfer is probably lighter than yakuza cloth.
* the little additional weight of the pulleys or bridle cant be the reason.
* angle of attack cant be the reason (you can adjust it on the depower foils as flat or flatter than the fixed AoA is on the yakuza)

is it the even higher aspect ratio and more agressive (whatever that is) profile of the yakuza ?
maybe the yakuza maximises power on the cost of stability? is it that flysurfers and manta are much more stable at the cost of performance?

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Re: ultimate lowend: fixed bridle wins over depower foils. why?

Postby marshall10488 » Tue Jan 12, 2010 5:44 pm

all down to the profile. there is a little from the wieght of pullys and from drag due to the addition of more bridle lines. (most bridle drag comes from wave harmonics, so it doesn't matter that you put tiny lines on s they will still form waves.)

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funalex
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Re: ultimate lowend: fixed bridle wins over depower foils. why?

Postby funalex » Tue Jan 12, 2010 7:34 pm

more AOA possible, because of a more powerfull profile. the reflex profile used on depowerable foil are not good for the best low end.

And very big AR is a good thing for low wind machine too.

They are very very flat too ! and they are light.

But as you can see it, you have a lot of power, but not a lot of manoeuvrability, and if you can't move quickly in the wind window, you can't really take advantage of this extra power.

bye.

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Re: ultimate lowend: fixed bridle wins over depower foils. why?

Postby Tone » Tue Jan 12, 2010 7:52 pm

err, there was no kitesurfing that first vid.

herculon
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Re: ultimate lowend: fixed bridle wins over depower foils. why?

Postby herculon » Tue Jan 12, 2010 8:11 pm

@funalex: i thougt the yakuza & co. have a very low AoA ? and why cant there be a yakuza profile with depower pulley bridle? not stable enough?

what about your naiboo morphine? can you think of a lightwind version ? or is it already much more lightwind than PL arcs? can you think of a morphine made out of 20g ripstop nylon, very thin carbon spars, more bridle on the leading edge to support the carbon spars ? what weight have your current morphine kites ? i would like to add them to the weight per proj. squaremeter list (i think and hope your morphine will be way up in the list, near the c-quad!!!):
viewtopic.php?f=1&t=2360753
i just watched today your vids again - and its fantastic. no more prefill!

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Peter_Frank
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Re: ultimate lowend: fixed bridle wins over depower foils. why?

Postby Peter_Frank » Tue Jan 12, 2010 9:32 pm

funalex wrote:more AOA possible, because of a more powerfull profile. the reflex profile used on depowerable foil are not good for the best low end.

And very big AR is a good thing for low wind machine too.

They are very very flat too ! and they are light.

But as you can see it, you have a lot of power, but not a lot of manoeuvrability, and if you can't move quickly in the wind window, you can't really take advantage of this extra power.

bye.
What you mean is more LIFT (=power) possible.

Would just correct, as the term AOA (angle of attack) can be very misleading if comparing airfoils :o

If you take a totally flat profile, that means no camber at all, it will actually have somewhat higher AOA than a curved profile (like a seagull wing or kite) when flown with max power 8)

Many are surprised by this, but it comes from the fact, that the "high lift" profile, which is curved like a seagull wing - has a high value of lift even at zero degree angle of attack.

Where a noncambered (flat) profile has exactly zero lift at zero AOA.

The curved profile has much higher max lift, correct, but still not so much that the AOA is higher than the flat profile at its max lift.
On the contrary - the flat profile would have max lift AOA at about 3-5 degree higher AOA than the curved (kite) profile, or something like that :thumb:
The magnitude depends on the specific airfoil, as there are differences, but the tendency is clear.

Of course it is not the absolute max lift I am talking about, but the max USEABLE lift angle, where the drag is not rising by a huge factor so it just stops instead of flying.

This is a surprise for some - but if you look at the curved profiles trailing edge - one can easily understand this, as it will act as a "brake" much earlier than if flat, because it is directing the wind downwards even at zero degree AOA.

And wind tunnel tests shows, that even with the higher max lift for the curved profile, the AOA is lower than the flat profile - when max lift/drag or max "power" is obtained (two different AOA's, but not that far from each other).

Would just comment as I noticed this post.

And can agree - that the profile and somewhat the AR of the kite is by far the most determining factor regarding power.
But I dont know these specific kites that well...

So Herculon might be very right, that the very powerful Yakuza has lower AOA than other less powerful kites 8)

Kindly, Peter Frank

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funalex
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Re: ultimate lowend: fixed bridle wins over depower foils. why?

Postby funalex » Tue Jan 12, 2010 10:04 pm

Totally OK with Peter !
herculon wrote:and why cant there be a yakuza profile with depower pulley bridle? not stable enough?
That's it. It could, but it would be a little too dangerous, and a dangerous kite can't be sold.
herculon wrote:can you think of a morphine made out of 20g ripstop nylon, very thin carbon spars, more bridle on the leading edge to support the carbon spars ? what weight have your current morphine kites ?
lol...we have tested everything you can imagine in this concept...carbon is definitly bad, even titanium ! 7075 alloy is very good. And light. We can't go too light, because we need a solid kite.

Maybe 2 kg for the 8,5m², I don't know...of course a big size (18m²) could be very good for light winds...but even if the kite is really really stable, the power is just the same as another tube kite. So you can go earlier on land, but not on water, it doesn't change a lot. Because you need a lot of power to keep you on the water.

Then, the truth is that Niaboo don't have money anymore, that's the reason why we decided to publish one of our work, we hope a brand will help them to push a lot of different design further.

We are working on another concept, lighter than everything !

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grantman54
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Re: ultimate lowend: fixed bridle wins over depower foils. why?

Postby grantman54 » Wed Jan 13, 2010 4:16 am

There is definately more wind than 7knots in that video. At least 9-11knots. I rode in conditions like that just like he did with my 12m SLE recently and the wind was 11knots.
Judging by the feedback on the mic, and the fetch (wind over the water) there is no way that is only 4-7 knots

herculon
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Re: ultimate lowend: fixed bridle wins over depower foils. why?

Postby herculon » Wed Jan 13, 2010 4:41 pm

thanks for all the high level input here! i need to study airfoil profiles in depth to understand that magic better !
any opinion on cooper kites here? are they equal to yakuzas in power? i already heart that built quality is not on par with ozone yakuzas, but if the power is, one could get the same power for half the price... and there is this special cooper ultralight:
Cooper 10,2 Ultra Light is made out of Skytex 27

and 22% lighter than a normal Cooper 10,2.
10,2 UL 1565 gram incl bag
10,2 2042 gram incl bag
Image
Image

looks like the perfect low end kite to me... "just" 650 euro..

crash&burn
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Re: ultimate lowend: fixed bridle wins over depower foils. why?

Postby crash&burn » Wed Jan 13, 2010 5:23 pm

sorry to flame up a topic but.....

I can't believe that people have enough time to contemplate the mechanics of kiting in under 10 knots.

Its a cliche but life is far too short to kite or try to kite in wind that has less power than a fart.


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