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"Foil Effect": A team Rista video on race dev't in Maui

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"Foil Effect": A team Rista video on race dev't in Maui

Postby radam » Wed Mar 07, 2012 6:04 am


Séb
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Re: "Foil Effect": A team Rista video on race dev't in Maui

Postby Séb » Thu Mar 08, 2012 1:09 pm

Nice video :thumb:

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davesails7
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Re: "Foil Effect": A team Rista video on race dev't in Maui

Postby davesails7 » Thu Mar 08, 2012 2:09 pm

Is that a little too much of a "foil effect"?

On my board it seems like when I get too much out of the water and pushing hard on the fins, the fins airate or stall or something. I thought you wanted where the board meets the top of the fin to stay in the water at all times. Is this not an issue with larger fins like these? (I'm riding the stock fins on the 2011 Cabrinha 183 board)

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Re: "Foil Effect": A team Rista video on race dev't in Maui

Postby ronnie » Thu Mar 08, 2012 4:14 pm

I thought that was the most impressive thing about the video. I'm used on my windsurf board when going fast over chop and the board leaves the water that I have to turn the board slightly downwind when it lands to avoid the fin stalling and make sure it will re-establish the flow.

Paolo must have done a good job on those fins for them to be able to come in and out of the water so much and keep the flow attached. Usually when a fin comes out of the water like that, the low pressure side of the fin can suck air down that side and lose the lift, which is why keeping the board on the water was so important because it kept the low pressure side of the fin away from the air.

One thing I would like him to explain is why the kite raceboard has 3 forty cm fins but a windsurf formula board has one 70cm fin and both are holding the same power?

This shows both the bend on a windsurf formula fin and the flow detaching during spinout.
Attachments
spinout2.jpg

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Re: "Foil Effect": A team Rista video on race dev't in Maui

Postby swell » Thu Mar 08, 2012 7:04 pm

A modern 3fin kite-raceboard has never a spinout, I think because of 3 fins... at least not in that way that it comes in windsurfing.
A windsurfboard needs only one fin because of power development right on the deck of the board and not above that like in kitesurfing where all the power from the kite is transmitted trough the rider only (his legs).
I realy doubt that on this pfoto is a formula fin - do they bend sooo much???

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Re: "Foil Effect": A team Rista video on race dev't in Maui

Postby zerogee_ca » Thu Mar 08, 2012 8:03 pm

Formula windsurf fin flex



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Re: "Foil Effect": A team Rista video on race dev't in Maui

Postby swell » Thu Mar 08, 2012 8:43 pm

OK, I realise the board in photo is on it's rail so than this bending of a fin is possible.

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Re: "Foil Effect": A team Rista video on race dev't in Maui

Postby JS » Sun Mar 11, 2012 1:42 am

ronnie wrote:Paolo must have done a good job on those fins for them to be able to come in and out of the water so much and keep the flow attached. Usually when a fin comes out of the water like that, the low pressure side of the fin can suck air down that side and lose the lift, which is why keeping the board on the water was so important because it kept the low pressure side of the fin away from the air.

One thing I would like him to explain is why the kite raceboard has 3 forty cm fins but a windsurf formula board has one 70cm fin and both are holding the same power?

The second paragraph responds to the first, and vice versa.

Also, yaw and roll stability are more challenging with a kiteboard, due to less length and mass, including lack of an attached rig. Notwithstanding, don't be surprised to see kite racing boards evolve with fewer fins.

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Re: "Foil Effect": A team Rista video on race dev't in Maui

Postby davesails7 » Sun Mar 11, 2012 2:32 pm

Do kite race fins bend like that also?

I had heard that if the fins bend, it makes the board really difficult to ride downwind.

Is there a benefit to a bending fin? It seems like keeping the fin straight would give you the most lift in the direction you want it (upwind).

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Re: "Foil Effect": A team Rista video on race dev't in Maui

Postby Gebi » Sun Mar 11, 2012 5:09 pm

We are not loading the fins like on a windsurf board on a kite race board. Yes we are maxed out on pushing the fins, but it is a fine line not to put to much pressure on the fins. A lot of the pressure is in the harness.

Keep in mind we do not have a mast and rig loading the board through a universal joint. We do not make the fins go through the water with as high of an angle of attack as a windsurf (as on a formula windsurfer) We need 3 fins to keep the board railed up. If the windward rail goes down, then you tend to spin out or get thrown over the front of the board.

Its about the fine line of keeping just the right amount of load on the fins. Thats why you have to ride a race board with a custom adjustable trim system and you have to adjust the depower for almost every puff, which you can see of the better videos of the boys riding here.

Watch the video starting at the 1:10 minute mark and you can see that Adam is always holding the trim line and using it to keep his body constantly hiked out. This is the main point that people just getting into kiteracing do not understand. You are not loading the board the same as riding a twin tip. A race board does not flex.

The race fins flex a little, but not much. The Body position of hiking out and counterbalancing against just the right amount of load against the fins is the trick, and the tricky part. If you are riding a race board and someone is riding a twin tip, you would be one or 2 kite sizes smaller on the race board, as you rely on the power of the fins as much as the power of the kite. Its a fine tuned balance game.

http://vimeo.com/25127199

If a puff hits and you have to sheet out and get pulled up over the board, you are not loading the fins anymore and lose control of the board. The exact proper "Hiked out to the max" body position has to be kept all the times, which you can see in the videos.

There is flex in the Rista fins but not nearly as much as say a formula fin. Thats why Rista is making the best fins, tons of testing, in template outline, proper rake, proper cant, flex thickness and the foil shape....he's super into the details (hey Paolo I need some speed fins for Rob, really!!)

By the way Paolo "Really" Rista was once one of the top 10 Pro PWA windsurfers in the world and has a background in Marine applications of engineering, he's a pretty sharp and talented guy. You should of seen him ripping Hookipa on a wave windsurf board back in the day...he is talented, minka...


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