Milling the foil .

That's all the milling done to reference points .The rest I do by hand . 1 kg at this point . Thinking 900 gm when finished.

Looks great!

How will the weight compare with the G10 version?

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fangman said..
How will the weight compare with the G10 version?

Kinda the same.

Not 100% sure what the plastic is . The guy selling it said it was food grade nylon . But it's not . It's not LD , LLD PE , Copolymer , Random Copolymer , Polycarbonate ( wish it was ), Acrylics or glass filled plastics . This I know , ( ex injection moulder ). It has the distinctive smell of PVC pipe but it's not brittle . It's a plastic that I haven't dealt with. I'm just presuming it is a grade of PVC. It could be styrene. I could find out if necessary.

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fangman said..
Pressure drag on fins exponentially increases with velocity.

The drag formulas I have seen usually talk about a square relation, not an exponential relation. What am I missing?

If you limit the speed differences between starting to plane and top speed to a factor of 4, the differences between square and exponential increase are small enough to be ignored (25%). But if you go just a bit further, the differences get bigger quickly, e.g. to more than 2-fold for 5x.

Com'n in a bit late to this but though better respond re spinouts. Did a lot of testing on the fin spinner about 6 months ago and meant to post 2 vids on this but got distracted by some really unusual results that still doing my head in, sailing buddy Reg passing, sail rocket2 model builds, sailing injuries and other projects.

Saw this thread and inspired to post what I found. For sure I have no clue to all this, just what I've seen:-

A) Spinouts almost always occur from ventilation when the surface turbulence propagates to the tip vortex. (i.e. air from surface finds a path to the tip vortex (bottom) of fin). Have literally hrs of repeatable video evidence of this so pretty sure is fact.
B) Spinout from cavitation is much harder to induce but appears to flash the trailing edge vortex/surface vortex instantly to leading edge (only got one shot of this so this is very flakey evidence so probably best ignore)

There was quite a few learning from this:-
1) On regular fins going through chop makes it easier for the surface turbulence to get to the tip and spinout.
2) The deeper the fin the harder it is for surface turbulence to reach the tip (probably why cutouts work??)
3) Increasing AOA/speed makes the surface turbulence greater and more likely to connect to tip vortex
4) Once the fin tip connects with surface it never lets go until speed is reduced to nearly zero (i.e. once in spinout you are screwed)
5) The low pressure side of fin can be dry as long as surface air doesn't get to tip (or leading edge) and fin won't be in spinout

In contrast a fin of exact same profile with a bulb on it seems almost immune to spinout. Even though the surface turbulence seems to touch the bulb it does not propagate around to the tip. The bulb appears as some sort of barrier. Maybe the bulb moves the tip vortex further aft making it way harder for the surface to connect?? If a bulbed fin does spin out then it can recover by itself without a reduction in speed and just a small decrease in AOA (Angle of Attack). I think this is exactly how Fangman describes the real world bulb fin that it is more forgiving. i.e. less likely to spinout and more likely to recover with AOA reduction if do spinout.

The bulb fin showed more drag at no AOA over a non bulb fin but no measurable increase in drag for any AOA over 4deg. I believe most real world fin AOA's are greater than 8deg so the only detriment to a bulbed fin is injury to sailor and added complexity to make.

My main video showing/explaining all this has a bunch of missing links to clips thanks to my delay to post so will take some time to repair. This video in meantime shows most of the effects but in a more artistic manner. I meant to post both together so this alone might look weird. Or just hallucination from watching something spin for so long. The really weird effects that caused the initial delay in posting all this will have to wait.


PS Above video was primarily meant as challenge to Valentina Lisitsa performance of Ave Maria Schubert Liszt suggesting there are no visuals that can match the music.

Great vid and tech Flex2.

It still amazes me how a massive fin can go through water totally sideways with virtually no resistance . I understand a lot of air is involved and a fin goes through air easily. But there is still the fact that a huge amount of water has been displaced for the air to get there. Where is the energy involved to do this ? I don't feel this when going sideways. Does that energy push the fin directly up , is that why the board tends to fly until my ass hits the water ? Still it doesn't feel like that amount of energy is pushing anything like the amount of water being displaced.

In the above vid it shows a ton of air involved , that's pushing a huge amount of water out of the way to do so. Like a wheelbarrow load each lap . How can that much water be moved with almost no energy. The pool water level would have to go up . That's a big ring of air where water once was.

This is where my pea brain gives up.

ya, it is weird and gets weirder the more you look. The only thing I can see is a spunout fin is fully encased in an air pocket, i.e. on high pressure side as well as low pressure side. How the air gets to the high pressure side appears in most cases (filmed in the fin spinner) to require travelling over the tip of the fin which it does instantly the tip vortex connects to surface. A bulb seems to make it much more difficult for this to happen as does cutouts, cav plates/fences and probably bunch of other stuff all with their own side effects.

I wish Leonardo was still around, he was great with vortexes, or is that vortie

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boardsurfr said..

The drag formulas I have seen usually talk about a square relation, not an exponential relation. What am I missing?

An exponential equation takes the form a^x = b. x can be any real number. A square relation is a subset of the exponential form. However, in this case, you are correct that drag equations have the value of x=2.

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Flex2 said..

That is outrageously good Flex. Gonna take me a while to unpack all that info.

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Flex2 said..
Com'n in a bit late to this but though better respond re spinouts. Did a lot of testing on the fin spinner about 6 months ago and meant to post 2 vids on this but got distracted by some really unusual results that still doing my head in, sailing buddy Reg passing, sail rocket2 model builds, sailing injuries and other projects.

Saw this thread and inspired to post what I found. For sure I have no clue to all this, just what I've seen:-

A) Spinouts almost always occur from ventilation when the surface turbulence propagates to the tip vortex. (i.e. air from surface finds a path to the tip vortex (bottom) of fin). Have literally hrs of repeatable video evidence of this so pretty sure is fact.
B) Spinout from cavitation is much harder to induce but appears to flash the trailing edge vortex/surface vortex instantly to leading edge (only got one shot of this so this is very flakey evidence so probably best ignore)

There was quite a few learning from this:-
1) On regular fins going through chop makes it easier for the surface turbulence to get to the tip and spinout.
2) The deeper the fin the harder it is for surface turbulence to reach the tip (probably why cutouts work??)
3) Increasing AOA/speed makes the surface turbulence greater and more likely to connect to tip vortex
4) Once the fin tip connects with surface it never lets go until speed is reduced to nearly zero (i.e. once in spinout you are screwed)
5) The low pressure side of fin can be dry as long as surface air doesn't get to tip (or leading edge) and fin won't be in spinout

In contrast a fin of exact same profile with a bulb on it seems almost immune to spinout. Even though the surface turbulence seems to touch the bulb it does not propagate around to the tip. The bulb appears as some sort of barrier. Maybe the bulb moves the tip vortex further aft making it way harder for the surface to connect?? If a bulbed fin does spin out then it can recover by itself without a reduction in speed and just a small decrease in AOA (Angle of Attack). I think this is exactly how Fangman describes the real world bulb fin that it is more forgiving. i.e. less likely to spinout and more likely to recover with AOA reduction if do spinout.

The bulb fin showed more drag at no AOA over a non bulb fin but no measurable increase in drag for any AOA over 4deg. I believe most real world fin AOA's are greater than 8deg so the only detriment to a bulbed fin is injury to sailor and added complexity to make.

My main video showing/explaining all this has a bunch of missing links to clips thanks to my delay to post so will take some time to repair. This video in meantime shows most of the effects but in a more artistic manner. I meant to post both together so this alone might look weird. Or just hallucination from watching something spin for so long. The really weird effects that caused the initial delay in posting all this will have to wait.

PS Above video was primarily meant as challenge to Valentina Lisitsa performance of Ave Maria Schubert Liszt suggesting there are no visuals that can match the music.

could rake the fin forward so turbulence is directed towards the board and not the tip as is done with some aeroplanes.

Methinks that unfortunately the weed here and a forward rake fin will be an arrestor hook in disguise. Probs gotta leave that one for you mob in the weed free water.

Impressive Flex but I question if your fin spinner is a true representation of what is happening with a windsurf fin. From what I can see and correct me if I am wrong the fin in not attached to a plate which represents it being attached to a board. In reality a fin has an end plate which is in the water, the board, which prevents air being sucked down until the point that the vortex is large enough to move beyond the tail of the board and create a path. What you are showing seems more relevant to foil masts... am I missing something?

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could rake the fin forward so turbulence is directed towards the board and not the tip as is done with some aeroplanes.

Justin....
You mean like this.......slightly forward swept stabilizer...works a treat.

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mr love said..
Impressive Flex but I question if your fin spinner is a true representation of what is happening with a windsurf fin. From what I can see and correct me if I am wrong the fin in not attached to a plate which represents it being attached to a board. In reality a fin has an end plate which is in the water, the board, which prevents air being sucked down until the point that the vortex is large enough to move beyond the tail of the board and create a path. What you are showing seems more relevant to foil masts... am I missing something?

You correct mr love that it is not a true representation however I think it is still relevant. If you saw the original fin spin videos it started with a board system. However there are so many variables trying to spin a board and fin around consistently to be able to compare so I decided to eliminate the board entirely and just focus on small differences in fins. The original plan was to spin the fins then 3D print a small board and repeat the experiment but there have been so many weird things occurred I haven't got to that.

The reason why I think it is still relevant is that when you watch really fast sailors their board is barely or not touching the water, I think called flying the fin. For the rest of us mortals just hitting chop makes the board leave the water at times. There is a bunch of air at any speed being pushed from the front of the board to the rear and some of this hits the fin but this really doesn't seem to effect the fin at all otherwise we would spin out all the time. Finally for the current wind powered water speed record holder Paul Larsen's SailRocket 2 the fin/foil is identical to the fin spinner arrangement. Paul had many issues with ventilation and he finally resolved it for his record run with a fence. You can see pics of it on his YT.

Hopefully I can repair the main video so it is clearer how this ventilation is happening which will show surface turbulence from board/fin or chop hitting the tip vortex is the main reason for spinout.

Yep, spot on.....Plenty of times when you are fanging that the board is not in the water.

Flex , have you tried the experiment with the pool the right way up ?

On another note , talking foiling , do the speed guys spin out or do strange stuff ? Can air get sucked down the mast and along the fuselage to a wing ? What about after breaching ?

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mr love said..

could rake the fin forward so turbulence is directed towards the board and not the tip as is done with some aeroplanes.

Justin....
You mean like this.......slightly forward swept stabilizer...works a treat.

Nice! Yep that's the go.

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Imax1 said..
On another note , talking foiling , do the speed guys spin out or do strange stuff ? Can air get sucked down the mast and along the fuselage to a wing ? What about after breaching ?

Yep the mast can and does ventilate at times. Also you can get wing ventilation if you fly too high or if you get a tip breach

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mr love said..

Imax1 said..
On another note , talking foiling , do the speed guys spin out or do strange stuff ? Can air get sucked down the mast and along the fuselage to a wing ? What about after breaching ?

Yep the mast can and does ventilate at times. Also you can get wing ventilation if you fly too high or if you get a tip breach

I've had spinouts, I don't think I have videos of those going just down the mast but I did catch a few ventilating the whole foil.

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fangman said..
An exponential equation takes the form a^x = b. x can be any real number. A square relation is a subset of the exponential form. However, in this case, you are correct that drag equations have the value of x=2.

Fangy, you're taking originality a bit too far. There's a predefined meaning of a and x in these formulas. The typical writing of a square formula is f(x) = ax^2 + b. The x input value (in this case, speed) is squared.

The exponential function has the x in the exponent: f(x) = a^x, or f(x) = a * exp(x). That leads to much faster increases for larger x values - here is an example for a 5-fold range:


For fins, the distinction is quite relevant. Exponential increase in drag would set a very hard upper limit due to drag. The actual square increase in drag matches the square increase in power from the foils used (sail, fin, foil). Seems the limits encountered for record speeds are the amount of power a sailor can hold, and (according to Vestas 2) cavitation.

Finished

Tuttle just over , Powerbox just under 800 gm.
They have flex so it will be interesting to see what happens . It looks kinda right but there is nothing to compare to .It moves about 5 mm with 5 kg at the tip. About 30 mm with 20 kg. After that it doesn't want to move much more with more weight . Ps , my measurements are rough , real rough . With the 5 kg I pushed the kitchen scales against it . The 20 kg is just a guess by feel.

Now I need 12 - 15 kts and choppy water to test .

Work of art

looks good iMax. Thanks to you I managed to turn the pool right ways up and repair the edit that was supposed to come before previous vid. I've cut 100% of the weird stuff out, hopefully will get around to editing that but it really makes you feel like you are on heavy narcotics.

Anyone interested in exploring the paranormal or just saving hallucinogenic drug costs can replicate by doing what I did by mistake. I had left the retainer nut off the indexing angle of attack (aoa) arm bolt to make it easier to change angles quickly. During my ever enthusiastic attempts at creating chop to spin out fins at various aoa, (will make more sense in video below), I knocked the indexing arm clean off.

This meant the fin was free to spin at its preferred angle which I assumed (turns out I think incorrectly) was angle of least drag. As per Fangman's suggestion this is something of use to allow calculation of lift matrix for a fin and thus be able to quantify the original intention of project to determine if fin A is better than fin B. Then I put a bulb fin in and it really went pear shaped.

Suffice to say I spent an entire week spinn'n, getting more and more confused and lost more and more interest trying to edit a video that made the slightest sense...in the end I gave up and went on to other projects....this vid up to the point where it went pear shaped. (sorry, its a bit long so only the deluded will watch)

Wow that was fast Imax! I particularly like the look of the fillet radius reduction in the mid chord. Very keen to hear what happens when on the water when compared to the predecessor.

Flex, interesting as always for me. There is a fair bit of data there for me to get my head around, and I reckon quite a few more questions about some of those 'unexpected' results.

1st test report.
It feels great .
NP V8 8.7m. Just planing up to medium powered. Flat water.
Testing against my G10 version. It was short test of about 15km before the wind ran out.
Neither came close to even thinking about spinning out. Both go upwind with ease. I'm sure it creates more lift because it was a smoother softer ride. Another thing I did notice is that it sits the board flatter side to side. The problem going from a pointer to a shallow water fin is the foot straps are too far outboard with the shorter fin and I tend to sink the windward rail more and catch my heel in the water at low speeds. This has improved but not to where a pointer is. I'm too lazy to change my straps every time I change fins. At today's speeds ,21kts max, reaching, there is no way I could tell which was faster. At this speed, I think I like the new plastic one more, purely for comfort.
I'm keen to see what happens when properly powered up, when sinking the rail and dragging a heel doesn't happen. Jibing felt the same, but the water was flat and easy. I need to test when its rough and I'm on the edge. It may do strange things going over 25kts.? Another thought, does the new plastic fin bend enough to work soften itself over time?
So far, I'm very happy. I'll get others to take it for a spin, see what happens. I'm probably sailing with rose colored glasses. Or I've just assed it again.
If I can get it close to 30kts and it doesn't try to kill me, I'll be very happy.