Contact   Imprint   Advertising   Guidelines

roll stability of foils?

A forum dedicated to Hydrofoil riders
User avatar
lovethepirk
Very Frequent Poster
Posts: 583
Joined: Sun May 10, 2015 7:04 am
Style: Almost air tacking on hydrofoil...
Gear: Delta Race Hydrofoil, 15m SS Turbine, 12m Switchblade, 9m Switchblade
Brand Affiliation: None
Location: Naples, FL
Has thanked: 0
Been thanked: 10 times

Re: roll stability of foils?

Postby lovethepirk » 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.

User avatar
alexrider
Very Frequent Poster
Posts: 1477
Joined: Thu Jun 05, 2008 1:52 am
Gear: foils and foils
Has thanked: 1 time
Been thanked: 3 times

Re: roll stability of foils?

Postby alexrider » Wed Aug 16, 2017 7:28 am

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.

User avatar
gmb13
Very Frequent Poster
Posts: 1934
Joined: Wed Sep 12, 2007 10:19 am
Kiting since: 1998
Local Beach: Flag Beach, Fuerteventura
Style: Everything
Gear: Indiana, Sailmon
Brand Affiliation: Indiana, Sailmon
Location: Fuerteventura
Has thanked: 36 times
Been thanked: 294 times

Re: roll stability of foils?

Postby gmb13 » Wed Aug 16, 2017 12:28 pm

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

Blackrat
Frequent Poster
Posts: 252
Joined: Thu Mar 12, 2015 4:55 pm
Local Beach: Jeffreys Bay , South Africa
Gear: old
Brand Affiliation: None
Location: Jeffreys Bay South Africa
Has thanked: 0
Been thanked: 0

Re: roll stability of foils?

Postby Blackrat » Wed Aug 16, 2017 3:10 pm

Gunnar , I think you got pitch and roll switched

User avatar
Horst Sergio
Very Frequent Poster
Posts: 772
Joined: Thu Oct 29, 2015 10:57 pm
Kiting since: 1999
Gear: -
Brand Affiliation: kitejunkie.com

Account abandoned
Has thanked: 91 times
Been thanked: 147 times

Re: roll stability of foils?

Postby Horst Sergio » Wed Aug 16, 2017 3:26 pm

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:

User avatar
gmb13
Very Frequent Poster
Posts: 1934
Joined: Wed Sep 12, 2007 10:19 am
Kiting since: 1998
Local Beach: Flag Beach, Fuerteventura
Style: Everything
Gear: Indiana, Sailmon
Brand Affiliation: Indiana, Sailmon
Location: Fuerteventura
Has thanked: 36 times
Been thanked: 294 times

Re: roll stability of foils?

Postby gmb13 » 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

User avatar
abel
Very Frequent Poster
Posts: 1585
Joined: Thu Dec 25, 2003 11:32 pm
Kiting since: 2003
Favorite Beaches: Naxos, Kos, Rodos (prasonisi), Red sea, Cumbuco, Kalpitia (Sri Lanka)
Style: freeride, very light winds
Gear: Peak4, Airush Ultra, hydrofoil Moses 633
Location: Small village
Has thanked: 19 times
Been thanked: 13 times

Re: roll stability of foils?

Postby abel » Wed Aug 16, 2017 4:18 pm

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?

User avatar
gmb13
Very Frequent Poster
Posts: 1934
Joined: Wed Sep 12, 2007 10:19 am
Kiting since: 1998
Local Beach: Flag Beach, Fuerteventura
Style: Everything
Gear: Indiana, Sailmon
Brand Affiliation: Indiana, Sailmon
Location: Fuerteventura
Has thanked: 36 times
Been thanked: 294 times

Re: roll stability of foils?

Postby gmb13 » Wed Aug 16, 2017 6:28 pm

Yes. You are misestimating here.

User avatar
gmb13
Very Frequent Poster
Posts: 1934
Joined: Wed Sep 12, 2007 10:19 am
Kiting since: 1998
Local Beach: Flag Beach, Fuerteventura
Style: Everything
Gear: Indiana, Sailmon
Brand Affiliation: Indiana, Sailmon
Location: Fuerteventura
Has thanked: 36 times
Been thanked: 294 times

Re: roll stability of foils?

Postby gmb13 » Wed Aug 16, 2017 6:38 pm

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

plummet
Very Frequent Poster
Posts: 6819
Joined: Sat Aug 29, 2009 11:25 pm
Local Beach: EE
Favorite Beaches: NZ
Style: Terrain riding
Gear: Old wornout ozone.
Plummet hydrofoil and mutant
Brand Affiliation: None
Has thanked: 11 times
Been thanked: 224 times

Re: roll stability of foils?

Postby plummet » Wed Aug 16, 2017 7:37 pm

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!


Return to “Hydrofoil”

Who is online

Users browsing this forum: alekbelia, fleetrico, kajuk and 209 guests