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Re: roll stability of foils?

Posted: Wed Aug 16, 2017 4:18 am
by lovethepirk
alexrider wrote:
Wed Aug 16, 2017 4:01 am
Sorry pirk, I know what you mean, but in order to avoid misunderstanding, I suggest you use proper terminology.
I edit the post to reflect your suggestions.

Re: roll stability of foils?

Posted: Wed Aug 16, 2017 7:28 am
by alexrider
Now I can concentrate on your post, Pirk. :P
Yes, the theory is correct, but I sometime hear that anhedral improves stability of foils, something I don't believe myself.
Recently, I've swapped the Freeride (which has anhedral) wing for the Carver (flat) of my Zeeko foil. Didn't really notice roll stability improvement. Should actually compare with the earlier B&W Freeride wing, which is flat.
I got this from I cannot remember where (probably Zeeko's site):
Zeeko Black&White vs Blue&White Alloy 2016:
- Black&White has more roll stability, due to straight/flat frontwing its better for beginners and freeriders, easier to learn new manoeuvres
- Blue&White is due to anhydral frontwing more agile but a bit less roll stability, harder to learn new manoeuvres

Incidentally, with the Carver wing, the pitch stability seems improved and, surprisingly, I'm not so scared of speed as much. I guess its angle of attack is probably not the same relative the the stabiliser. Need to measure precisely. I love the Carver btw.
2016-06-30_210446c.jpg
lovethepirk wrote:
Wed Aug 16, 2017 4:18 am
alexrider wrote:
Wed Aug 16, 2017 4:01 am
Sorry pirk, I know what you mean, but in order to avoid misunderstanding, I suggest you use proper terminology.
I edit the post to reflect your suggestions.

Re: roll stability of foils?

Posted: Wed Aug 16, 2017 12:28 pm
by gmb13
The Front wing has only a small part to play in roll stability. Also I prefer to differentiate between Roll Stability and Roll Resistance/Sensitivity.

Roll Stability judges how easy unwanted roll happens without pilot/rider input. This can be caused by turbulence or cross currents in the water.

Roll Resistance is how the Foil resists your rider input to roll the board/foil.

That aside, the stability and resistance are controlled more thought the back wing than the front. You will notice how a more active back wing (higher angle of attack or size) will give you more roll resistance.

The only thing that makes a front wing more roll resistant is span. eg. The higer the span, the slower the wing will roll, but this is not as apparent compared to the back wing.

--
Gunnar

Re: roll stability of foils?

Posted: Wed Aug 16, 2017 3:10 pm
by Blackrat
Gunnar , I think you got pitch and roll switched

Re: roll stability of foils?

Posted: Wed Aug 16, 2017 3:26 pm
by Horst Sergio
Blackrat wrote:
Wed Aug 16, 2017 3:10 pm
Gunnar , I think you got pitch and roll switched
I don't think so, but think he is right. :wink:

Re: roll stability of foils?

Posted: Wed Aug 16, 2017 3:29 pm
by gmb13
Blackrat wrote:
Wed Aug 16, 2017 3:10 pm
Gunnar , I think you got pitch and roll switched
Nope. I mean roll. Both roll and pitch stability are controlled by the "stabiliser" or back wing.

--
Gunnar

Re: roll stability of foils?

Posted: Wed Aug 16, 2017 4:18 pm
by abel
gmb13 wrote:
Wed Aug 16, 2017 3:29 pm
Blackrat wrote:
Wed Aug 16, 2017 3:10 pm
Gunnar , I think you got pitch and roll switched
Nope. I mean roll. Both roll and pitch stability are controlled by the "stabiliser" or back wing.

--
Gunnar
Aren't we neglecting the mast here?
I assume that a deeper the mast in the water will increase roll resistance, while a mast higher in the air will ease rolling.
It has lot of perpendicular flat surface at quite a rotational length opposing the rolling direction (in addition to the total wings area).
Now given a high mast above water surface, then the next significant influence on rolling characteristics would be the FRONT wing's, size, aspect and section.
I don't understand why the rear wings can have more effect on the roll than the front one.
The rear wing does have has some effect, but secondary to the front wing. Am I misestimating here?

Re: roll stability of foils?

Posted: Wed Aug 16, 2017 6:28 pm
by gmb13
Yes. You are misestimating here.

Re: roll stability of foils?

Posted: Wed Aug 16, 2017 6:38 pm
by gmb13
What most people forget is that the foil is not sitting still in the water. It is flying at speed, and the pull of the kite is trying to pitch the foil forward. This makes the tailplane or stabiliser more important than on a plane driven by engines. The Tailplane is preventing the Front Wing from pitching forward and also resisting the yaw (especially on back wings without a yaw stab fin) and roll. If you get the chance try small and larger back wings back to back, and you will see the difference. When you switch out front wings (for example Zeeko Freeride wing to Speed wing) you will notice no huge amount of change in roll stability. But if you reduce the angle of the tailplane (shim) you will have a major change.

But hey. What do I know about foils? ;-)

--
Gunnar

Re: roll stability of foils?

Posted: Wed Aug 16, 2017 7:37 pm
by plummet
I agree with Gunnar. I've been playing with my aoa lately to try and find the optimal angle between stability and reduced roll resistance. For wave riding I want a lively fast to react foil. But that makes so I back the aoa off and get a lively beast that will roll easily. But man its twitchy. Still trying to find that magic spot. I think i'm almost there.

So note. For my testing I'm shimming using ducttape. 2 slithers of ducttape makes a huge difference!