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Rocker Modification for early takeoff

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alex 1
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Rocker Modification for early takeoff

Postby alex 1 » Thu Nov 05, 2020 10:01 am

Hi,
in this small clip i show how i modified my Board with rounded Rockerkicktail for better release and Low-Wind properties...Paulownia Wood treated with epoxi and attached with double sided outdoor tape..



njoy

LXT
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Re: Rocker Modification for early takeoff

Postby gmb13 » Thu Nov 05, 2020 10:21 am

alex 1 wrote:
Thu Nov 05, 2020 10:01 am
Hi,
in this small clip i show how i modified my Board with rounded Rockerkicktail for better release and Low-Wind properties...Paulownia Wood treated with epoxi and attached with double sided outdoor tape..



njoy

LXT
Nice Video Alex,

It will work even better if you extend the block all the way to the back. In my testing it will give you about another knot lowend und 10 knots.

--
Gunnar

fluidity
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Re: Rocker Modification for early takeoff

Postby fluidity » Thu Nov 05, 2020 10:52 am

Inspiring.
It's breaking the Coanda effect which is the name for that drag you feel over that corner without the wedge you've added. A bit like the wind surf boards with recessed pockets at stern corners, it works to great effect with the shock loading transferred from the hand wing to the board to separate it from clinging water.

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Re: Rocker Modification for early takeoff

Postby Dave_H » Fri Nov 06, 2020 5:07 am

Very interesting subject. I was under the impression that a step up before the kicktail bevel would help break the attachment of the water flowing over the kicktail earlier as Alex is proposing in his modification. However, after looking up the Coanda effect on Wikipedia, it seems like it could have the opposite effect and cause the water to change direction more rapidly and stay attached to the kicktail due to a pocket of low pressure in the corner of the step. If air could enter the low pressure area created by the Coanda effect, this might enabling the water to breaking free from the kicktail surface earlier. However, I am not sure if there is an obvious way for air to get to to this area in the modification shown. It might be an interesting experiment to add a dedicated vent to allow air to be sucked into the step area.
In addition I have been very curious as to whether the kicktails provide real benefit to earlier foiling takeoffs on wing foil boards or whether a squared off tail would be better as Gunner suggests. There may be some dependence as to the take off style that the rider utilizes to get on foil, board speed to foil, vs board rocking/pumping to foil. Seems like SUP foil boards, prone foil boards, and wing foil boards are some of the few water craft currently utilizing kick tails.

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Re: Rocker Modification for early takeoff

Postby Dwight » Fri Nov 06, 2020 10:20 pm

You know how a short fuselage is easier to get it rocking.....same with tail kicks. It does actually feel easier to get it rocking.
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fluidity
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Re: Rocker Modification for early takeoff

Postby fluidity » Sat Nov 07, 2020 8:47 am

Dave_H, it's the rapid change on the squared off edge that disrupts the Coanda effect. Effectively it's atmospheric pressure holding the water around the curved surface until you get ventilation at the back edge. At that stage, the inertia of the water come into effect and if you have enough speed it peels off in a wake.
I haven't tried it yet but this is the simplest solution I can think of. A slightly stiff folded edge that should separate the flow from the gentle bends at the rear of the inflateable foil board.
Attachments
20201107_204818.jpg

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Re: Rocker Modification for early takeoff

Postby nixmatters » Sat Nov 07, 2020 4:24 pm

JP SUPs have such tail edge since 2 years I think. Few friends who tried my Allroundair did mention that if feels a bit faster for such a raft
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fluidity
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SUP Wedgies

Postby fluidity » Sat Nov 07, 2020 8:25 pm

I ran up a little test batch of 3D printed wedges last night and taped them on the back of my foil SUP instead of my tape only solution.
Wedges are here: https://pinshape.com/items/103157-3d-pr ... ng-wedgies

You can shorten them in slicing software to go around the bend on the sides as well.
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SUP wedgies.PNG
SUP wedgies.PNG (176.84 KiB) Viewed 1401 times

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Horst Sergio
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Re: Rocker Modification for early takeoff

Postby Horst Sergio » Thu Nov 12, 2020 12:57 am

@fluidity:
Looks also good and would be sure it will work quite suficient, think I will try also something similar like Alex, quick and dirty with some wood batten and tape.

Would be cool to find the material or even better one of the rubber profiles many manufacturers are using, to buy.

I think the effort to stick it could be very low with the right glue, not necessary need to use extra patches, as long it is just a simple semi professional solution.

fluidity
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Re: Rocker Modification for early takeoff

Postby fluidity » Thu Nov 12, 2020 8:14 am

Horst Sergio wrote:
Thu Nov 12, 2020 12:57 am
@fluidity:
Looks also good and would be sure it will work quite suficient, think I will try also something similar like Alex, quick and dirty with some wood batten and tape.

Would be cool to find the material or even better one of the rubber profiles many manufacturers are using, to buy.

I think the effort to stick it could be very low with the right glue, not necessary need to use extra patches, as long it is just a simple semi professional solution.
I attached a pic showing the profile if it helps...

In openscad the profile is:
difference(){
square([30,30]);
scale([1.3,1])
circle(r=30,$fn=180);


and wrapped like this:
translate([0,0,30])
rotate([-90,0,0])
linear_extrude(height=60){
difference(){
square([30,30]);
scale([1.3,1])
circle(r=30,$fn=180);
}
}


It forms a solid. Dimensions in mm.

I must dry my Ninjaflexx TPU filament reel and print, it's flexible and if I can get glue to stick, perfect as I can print hollow cored for lightness.
Attachments
HardAntiCoandaEdge.png


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