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Negative rocker TT?

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rynhardt
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Re: Negative rocker TT?

Postby rynhardt » Fri May 24, 2019 7:08 am

The lift pressure is dependent on the distance from the spray root, and the angle of attack (Tau in fig 2).
Qualitatively, if you have negative rocker in the middle of the board, the angle of attack will decrease for the red area, and increase for the orange/yellow areas.
Given that everything else stays the same, the area under the curve stays the same, but the peak moves more to the rear of the board.
I've drawn in a qualitative indication of what I expect the lift force distribution for a negative centre rocker looks like with the green line.

That's my story and I'm sticking to it :cool2:
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fig2-colour.png
fig2-colour.png (25.66 KiB) Viewed 138 times

AndersP
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Re: Negative rocker TT?

Postby AndersP » Fri May 24, 2019 8:05 am

If that is correct, how come you have more pressure on the back foot?

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rynhardt
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Kiting since: 2010
Local Beach: Leeupan
Favorite Beaches: Langebaan
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Gear: GK vSonic 6 & 11
Cloud C2 17
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Xelerator door
Hoff DD140
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Re: Negative rocker TT?

Postby rynhardt » Fri May 24, 2019 9:34 am

AndersP wrote:
Fri May 24, 2019 8:05 am
If that is correct, how come you have more pressure on the back foot?
I'm not saying it is correct per se :lol: But given my personal experience, knowledge and deductive reasoning I offered an explanation.
And within the scope of my explanation, the centre of water pressure (COWP) (red arrow) will be closer to the rear foot (we take the area under the pressure distribution curve to be equal on either side of the COWP, assuming board width remains constant).
And then assuming we have a net zero moment around the COWP, the rear foot, which is closer, needs to exert more force (big green arrow) to balance the front foot (small green arrow), which is further away from the COWP.

PS. I extended fig.2 with a purple line to indicate the front of the board more representatively.
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fig2 forces.png
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