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Wings for Garbage Winds

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NYKiter
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Wings for Garbage Winds

Postby NYKiter » Mon Nov 18, 2019 2:01 pm

Not for the coasties who have relatively steady winds....

After a few years of riding Im seeing roll stability being a key factor for foiling in frontal-driven winds (wide-range, punchy, gusty, garbage winds)

Obviously the 633 type surf wings with anhedral offer the best roll stability, but Im seeing the Armstrong (CF800) as having even more anhedral....

Any comments on wings that have the most anhedral?

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Re: Wings for Garbage Winds

Postby Herman » Mon Nov 18, 2019 2:21 pm

On an aircraft anhedral is used to make it more manoeuvrable and less roll stable. If you want more roll stability you use dihedral. I am scratching my head to think why it should be any different for hydrofoils. Am I missing something?

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Re: Wings for Garbage Winds

Postby tomtom » Mon Nov 18, 2019 3:25 pm

Very interesting thoughts. Do you guys consider 633 roll stable? Because for me it is roll - quite lively. I would like it more roll stable and less stable in pitch.

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Re: Wings for Garbage Winds

Postby NYKiter » Mon Nov 18, 2019 3:43 pm

The 633 is lively to me...and banks well....but at the same time it doesnt appear overly-sensitive to shotgun blast gusts on the kite and harness...could be the thickness....

I have found flat wings like the spitfire ( XL also) to have extreme roll instability....obviously they want folks to bank turn a lot...but when the wind is crappy it easily throws me off when there are spikes in strong gusts.....


makes sense that dihedaral would make it more roll stable but probably pop out of the water.....so they go with anhederal instead? The anhederal stab seems to help as well....so my line of thinking is that more of this could be better for those who contend with garbage winds all the time.....I could be wrong....

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Re: Wings for Garbage Winds

Postby grigorib » Mon Nov 18, 2019 4:13 pm

633 is lively, 683s is even more lively, 720 is way more roll stable than any of these, and when ridden with 450 stabilizer - it’s quite lightwindish wing despite 740 sq.cm area

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Re: Wings for Garbage Winds

Postby Herman » Mon Nov 18, 2019 6:30 pm

Having scratched my head I suspect that the wing in a hydrofoil situation is not subjected to the levels of sideslip seen by wings in aviation. Therefore both the effect of anhedral and dihedral will be reduced with respect to roll stability. This coupled with the c of g being forward and way above makes it an interesting problem to design in roll stability. Possibly one of the reasons you can't just look at a wing and say whether the designer.was going for stability or manoeuvrability.

No doubt there will be somebody out there that has done the math but unfortunately I am not Adrian Newey! A quick look suggests there is surprisingly little info readily available on the subject.

I had wondered myself why beginner foils did not run a fair degree of dihedral!

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Re: Wings for Garbage Winds

Postby plummet » Mon Nov 18, 2019 11:37 pm

I'm not sure its garbage winds that need different wings. You sort the power output for any given day by kite selection. Select the correct kite and there should be no change to the foil.

BUT.

Washing machine sea conditions (typically associated with garbage frontal winds) is another thing entirely.

I find the more tumultuous the sea the harder it is to ride. I have some pretty darn flat wings on my foil. Similar to spitfire wings and in clean conditions they are sweet. The more crap the sea conditions the harder they come to ride.

I will be making some wings with more anhedral shortly. I'll report back with my findings.

Ps. The reason kites have anhedral is to give them additional stability with varying wind angles

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Re: Wings for Garbage Winds

Postby BWD » Mon Nov 18, 2019 11:56 pm

Herman wrote:
Mon Nov 18, 2019 2:21 pm
On an aircraft anhedral is used to make it more manoeuvrable and less roll stable. If you want more roll stability you use dihedral. I am scratching my head to think why it should be any different for hydrofoils. Am I missing something?
It works nearly opposite on hydrofoils, mainly because the center of gravity is the rider, typically 2+ wingspans above the wing. The dynamics are just wrong, and the issue of wingtips surfacing makes it worse.

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Re: Wings for Garbage Winds

Postby jumptheshark » Tue Nov 19, 2019 12:14 am

Aren’t all the newer slingshot wings dihedral through the centre with anhedral at the tips?

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Re: Wings for Garbage Winds

Postby Herman » Tue Nov 19, 2019 12:37 am

The high c of g makes it unstable but does not effect the fluid dynamics of the wing. Dihedral on the aviation wing produces a stabilizing roll moment because the aircraft side slips in the turn. The side slip results in a change in the angle of attack between port and stbd wings. It seems to me that you do not get this side slip in the hydrofoil and so it no longer matters much if you have anhedral or dihedral in this respect.

Therefore if you want a curve you may as well have anhedral because it looks punchy and it is less likely to breach etc

Note: there are a couple of reasonable vids available on how side slip is needed to make dihedral stabilizing. This is taking me way back so if there is a designer who wants to correct any of that feel free!


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