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Canting on fins?

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Johnny Rotten
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Re: Canting on fins?

Postby Johnny Rotten » Mon Jun 18, 2012 1:14 am

lobodomar wrote:Wouldn't a 2dg (for example) V-shaped bottom at the front fins station have the same effect on the fins angle as canting them by 2dg at their base?


YES! Thank you! my reference frame was off, I was considering cant to be the angular measure of the fin from the flat board position. (effective cant) but in practice, the cant is established relative to the finbox. so a vee bottom board or a board built with the finboxes already canted would still get board lift with a FIN at 0 cant as the assembly would be canted when the board is ridden flat. . This is actually a much nicer design as it makes the fins interchangable from side to side and opens you (and the manufacturer) up to a world of off the shelf windsurfing fins

Space monkey: To answer your question (intelligently this time), I would eat my hat if the North design doesn't either have an angled bottom or have canted finboxes giving an effective cant angle of the fins when ridden flat.

wdric
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Re: Canting on fins?

Postby wdric » Mon Jun 18, 2012 10:31 am

Johnny Rotten wrote:
lobodomar wrote:Wouldn't a 2dg (for example) V-shaped bottom at the front fins station have the same effect on the fins angle as canting them by 2dg at their base?


YES! Thank you! my reference frame was off, I was considering cant to be the angular measure of the fin from the flat board position. (effective cant) but in practice, the cant is established relative to the finbox. so a vee bottom board or a board built with the finboxes already canted would still get board lift with a FIN at 0 cant as the assembly would be canted when the board is ridden flat. . This is actually a much nicer design as it makes the fins interchangable from side to side and opens you (and the manufacturer) up to a world of off the shelf windsurfing fins

Space monkey: To answer your question (intelligently this time), I would eat my hat if the North design doesn't either have an angled bottom or have canted finboxes giving an effective cant angle of the fins when ridden flat.


WE need a pic as proof for eating your hat
I have measured mine and their close enough to parrallel

ronnie
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Re: Canting on fins?

Postby ronnie » Mon Jun 18, 2012 11:44 am

Thing to remember too is that the fin bends, so it has various degrees of cant + or - depending on the loading and where its placed on the board.

See this thread
viewtopic.php?f=159&t=2374765&start=0

Windsurf boards generally are trying to plane off the rockerline of the board and want to keep the board in contact with the water at the fin base to reduce the likelyhood of spinout from air getting sucked down the low pressure side of the fin.

The less the kiteboard relies on cant instead of rocker and the smaller the total fin sizes the board can perform with, the more efficient the board will be by my guess.

You can see some of the windsurf ideas on tail shapes for the 2012 course race boards here.
The 2012 Starboard has a double concave at the front leading into a flat vee tail.
http://www.mobed.nl/2011_09_11_archive.html

ronnie
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Re: Canting on fins?

Postby ronnie » Mon Jun 18, 2012 1:27 pm

Interesting too that Airush built the Monaro V3 with a quad fin configuration with zero cant on the fins and asymmetrical front fins and now on the V4 have gone to a tri fin with 3.5 degree cant on the front fins.

Seems its hard to quantify the results?

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Re: Canting on fins?

Postby wdric » Mon Jun 18, 2012 1:41 pm

ronnie wrote:Thing to remember too is that the fin bends, so it has various degrees of cant + or - depending on the loading and where its placed on the board.

See this thread
viewtopic.php?f=159&t=2374765&start=0

Windsurf boards generally are trying to plane off the rockerline of the board and want to keep the board in contact with the water at the fin base to reduce the likelyhood of spinout from air getting sucked down the low pressure side of the fin.

The less the kiteboard relies on cant instead of rocker and the smaller the total fin sizes the board can perform with, the more efficient the board will be by my guess.

You can see some of the windsurf ideas on tail shapes for the 2012 course race boards here.
The 2012 Starboard has a double concave at the front leading into a flat vee tail.
http://www.mobed.nl/2011_09_11_archive.html


Check out the foot straps being spaced out off the board to give an effective wider board?
I wonder what those little trim tab looking devices are in one of those shots?

ronnie
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Re: Canting on fins?

Postby ronnie » Mon Jun 18, 2012 2:19 pm

As you can see, Starboard have brought out two boards, both of maximum width, but one with a narrower tail than the other.

Alex Aguera has done something similar with a narrower tail version for higher winds.

On canting of fins, Erika Heineken said at the Lord of the Winds that she was using Johnny's MikesLab board from last year and was using 4 degree cant front fins on it. Its the one that seemed to have cutouts at either side of the tail like the windsurf formula boards, but anytime I could make out the detail, they seemed to be blanked off.

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JS
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Re: Canting on fins?

Postby JS » Sat Jun 30, 2012 8:53 am

A pair of fins, canted equally in opposite directions, generate the same net vertical lift as two uncanted fins. The canted ones have slightly more surface and drag relative to useful lateral lift though, so may be slightly slower.

However, canting can affect handling. With fins canted outward, the leeward rail will get 'sucked' downward somewhat while the windward rail will get a bit of vertical lift, compared to uncanted fins, all other things being equal. In other words, outward canting causes more heeling moment, which must be overcome by the rider. Inward canting does the opposite.

Cheers,
James

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davesails7
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Re: Canting on fins?

Postby davesails7 » Sat Jun 30, 2012 4:53 pm

JS wrote:A pair of fins, canted equally in opposite directions, generate the same net vertical lift as two uncanted fins.


I guess once you get heeled over to leeward, that's when the fins really start lifting. The leeward side of the fin is the high pressure side of the foil, so if you heel to windward the board gets sucked down, if you heel to leeward the board gets lifted up.

I see what your saying about the lift of the two canted fins cancelling eachother out. I guess the leeward heeling moment gets the board into a position where it can lift out of the water.

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Re: Canting on fins?

Postby Johnny Rotten » Sun Jul 01, 2012 9:36 pm

JS wrote:A pair of fins, canted equally in opposite directions, generate the same net vertical lift as two uncanted fins. The canted ones have slightly more surface and drag relative to useful lateral lift though, so may be slightly slower.

However, canting can affect handling. With fins canted outward, the leeward rail will get 'sucked' downward somewhat while the windward rail will get a bit of vertical lift, compared to uncanted fins, all other things being equal. In other words, outward canting causes more heeling moment, which must be overcome by the rider. Inward canting does the opposite.

Cheers,
James



Yes I was dead wrong :duh:
I was (incorrectly) thinking 90 degree cant = airplane wings = vertical lift and so I incorrectly assumed (heavily influenced by rista video) that any angle less than 90 would simply have a component of vertical lift

Not the case. The PRESSURE is what matters and due to the drift angle, all three fins will have positive pressure on the leeward side. making the "lift" of the 2 canted fins oppose one another....

Now I'm really confused though.
This provides a balancing moment to the riders weight by lifting the heel side, and sucking down the toe side which would tend to flatten out the board. The lateral "upwind" lift still produces a moment in this same direction (albeit with a slightly smaller lever arm located at the CP of fin rather than the 1 board width away.) but still I can't imagine 2-4 degrees of cant really has a significant effect.

For "stability" somehow I intuitively expect that as the board rolled from flat, the cant would create a self righting moment keeping the board flat, but looking at a free body diagram this doesn't appear to be the case either. Boardlift (buoyancy and planing forces) are the only self righting mechanism as it rolls due to parts of the board losing contact with the water.
(ONE of the reasons a big fat board is beneficial)

Guys who ride this stuff, what do you "FEEL" with canted vs uncanted fins. !!??

any other ideas?
Am I missing something?

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lobodomar
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Re: Canting on fins?

Postby lobodomar » Wed Jul 18, 2012 12:54 pm

Johnny,

I share your questions, would be really nice if someone with more knowledge/experience could bring on more info.

My take for now is that canting is more useful at low speeds, when the heeling moment generated by the lateral force component is not enough to keep the board flat. In this case, the vertical component provided by canting helps in providing enough heeling moment.

As the speed increases to the point where canting is no longer necessary to keep the board flat, I would say that 0 canted fins would be better, since they are able to provide more upwind drive for a given fin size.

I would really like to experiment with fins (for example have 2 pairs of the exact same fin, one pair canted and the other not), but good fins are so expensive :cry:


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