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North launches a foil kite

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gwicke
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Re: North launches a foil kite

Postby gwicke » Mon Feb 20, 2017 2:50 am

Regis-de-giens wrote:Your table is really great. How did you obtain the values for projected areas ? It is hard to find this.
For the kites that don't have the data published I looked for photos from the rider's perspective (straight below). Then I used a photo editor (Gimp) to cut out the kite outline & measured kite span and area in pixels. Projected AR is span² / area. Accuracy seems to be decent, as I got closely matching results from several different photos of the same kites.

Regis-de-giens
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Re: North launches a foil kite

Postby Regis-de-giens » Mon Feb 20, 2017 4:36 am

Nice work !

rtz
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Re: North launches a foil kite

Postby rtz » Mon Feb 20, 2017 6:38 am


Mossy 757
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Re: North launches a foil kite

Postby Mossy 757 » Mon Feb 20, 2017 12:38 pm

Priced higher than chrono v2... Interesting

evan
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Re: North launches a foil kite

Postby evan » Mon Feb 20, 2017 1:48 pm

gwicke wrote: For the kites that don't have the data published I looked for photos from the rider's perspective (straight below). Then I used a photo editor (Gimp) to cut out the kite outline & measured kite span and area in pixels. Projected AR is span² / area. Accuracy seems to be decent, as I got closely matching results from several different photos of the same kites.
Your Measurement of the projected AR of the 11.5 Ace is 5.43 while North states it to be 4.90, that is quite a difference! Or is the North-data faulty?

https://www.northkiteboarding.com/products/kites/ace/

Size - AR flat - AR projected - S flat in m² - S projected in m²
8,5 - 6,70 - 4,80 - 8,50 - 7,10
11,5 - 6,70 - 4,90 - 11,50 - 9,50
14,5 - 6,90 - 5,00 - 14,50 - 11,90
17,5 - 7,00 - 5,00 - 17,50 - 14,30

Size Cells - Longest Rib in m - Smallest Rib in m - Weight in kg
8,5 - 53 - 1,36 - 0,35 - 1,90
11,5 - 53 - 1,57 - 0,44 - 2,28
14,5 - 53 - 1,75 - 0,44 - 2,70
17,5 - 53 - 1,90 - 0,49 - 2,88

gwicke
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Re: North launches a foil kite

Postby gwicke » Mon Feb 20, 2017 5:39 pm

evan wrote:
gwicke wrote: For the kites that don't have the data published I looked for photos from the rider's perspective (straight below). Then I used a photo editor (Gimp) to cut out the kite outline & measured kite span and area in pixels. Projected AR is span² / area. Accuracy seems to be decent, as I got closely matching results from several different photos of the same kites.
Your Measurement of the projected AR of the 11.5 Ace is 5.43 while North states it to be 4.90, that is quite a difference! Or is the North-data faulty?
Overall, measured ARs are likely to be slightly higher than theoretic published values for the following two reasons:

- Perspective: Ideally, a photo would be taken from far away to avoid any distortion from perspective. Compared to that ideal, the more easily available photos from the rider's perspective tend to add 0.1-0.2 to the aspect ratio. To get consistent relative data I used that perspective throughout, so perspective shouldn't introduce much error for the relative comparison.
- Design software vs. reality: Listed projected ARs are often based on the output of the design software, which does not necessarily match reality 100%. Most wings have some degree of wash-in near the tips to reduce tucking. The higher AoA near the tips causes a higher aerodynamic load than at the center of the kite, which causes them to pull the bridle slightly outward, opening up the arc a bit & increasing projected AR.

In any case, for all interesting kites I consistently used photos since I'm interested in a comparison. I expect the relative values to be accurate to roughly +- 0.1, which is good enough for my purposes.

Edit: Removed bit about measurement being based on 17.5m² after verifying that the video was actually about the 11.5m².

gwicke
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Re: North launches a foil kite

Postby gwicke » Mon Feb 20, 2017 7:55 pm

FWIW, the following photo of the 11.5m² shows an AR of 5.0, despite a) not being taken from the riders perspective & at moderate distance, and b) having the kite not quite perpendicular to the photo axis. Both factors would cause an under-estimation of AR, so I think it's pretty clear that North's projected AR specs are slightly too low.

Image

dr511
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Re: North launches a foil kite

Postby dr511 » Tue Feb 21, 2017 8:14 pm

Mossy 757 wrote:Priced higher than chrono v2... Interesting
These prices are in pounds... so it would be half the price in euro's :remybussi:

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Re: North launches a foil kite

Postby socommk23 » Tue Feb 21, 2017 10:15 pm

dr511 wrote:
Mossy 757 wrote:Priced higher than chrono v2... Interesting
These prices are in pounds... so it would be half the price in euro's :remybussi:
Not quite. Exchange rate isnt that good sadly. 1.18 euros to the pound.

Mossy 757
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Re: North launches a foil kite

Postby Mossy 757 » Tue Feb 21, 2017 10:28 pm

dr511 wrote:
Mossy 757 wrote:Priced higher than chrono v2... Interesting
These prices are in pounds... so it would be half the price in euro's :remybussi:
Yeah, I did the conversion to USD before I posted that...


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