Stabaliser wing - which way up

JB can you advise, I have Naish medium thrust.

Things change a lot when you start adding in different angles.

Angles (usually down) help with constant turning like with SUP and Surfing. However flat is actually more efficient and great for straight line lift like with Kiting or Windsurfing.

Kiting and Windsurfing you use a power source like your sail to deliver the power and speed you need to hydrofoil, where as a surf foil requires forces and gravity to create the equation.

I have had a lot of time between the Naish WS and the Naish Surf Windfoiling in waves and it is very apparent the differences.

Naish Thrust Surf

Naish Thrust Windsurf.

The Naish Surf tends to lift very early and with a lot of stability at low speeds. It also continues this stability when you do turns, even at super low speeds. However the Surf foils do have a limited top end, and will reach a point where you are learning so far forward (seemingly) to control the lift.

The Naish Thrust WS1 is very smooth and constant with it's lift. It is not far behind the Surf with it's foiling speed, but it tends to want to go faster, and it naturally does go faster. Now when you go to turn the WS1, that's when you'll notice the different. Large open turns are fine, and the foil feels naturally stiffer, but when you try to tighten up your turns like achievable on the Surf, smoothness and lift is compromised.

When I have used the WS1 rear wing on the Thrust Surf Foil, I notice similar to the WS1 Foil characteristics, which shows that the rear wing really does influence the turn-ability of the foil.

When I change up the rear wing on the Thrust Surf XL is also interesting. The XL Rear wing king of makes the foil feel like the Thrust Surf Large does with the WS1 rear wing. It is more efficient and great for pumping, but tight turn are difficult and stiffer. By simply changing the rear wing to the Surf rear STD, I can get a lot more mobility in the XL.

I think that when a flat wing is leaned over the combined forces change (please be kind on my tech diagram ;) ). The reason a surf wing keeps consistence in lift though turns is because the lift co-efficient remains similar, where as the flatter wing changes. This feels fine on the wind wings because generally you are riding in a straight line with a lineal power souce, but surfing your power source if not so constant and directional.





Anyway I am sure there is a much more technical reason behind much of this, but there is definitely a different, especially with aggressive turns.

I'll speak with the engineers and see if I can get a better response.

Ride safe,

JB

Good info tonhelp my understanding.
Look forward to more from JB.
I will do some on water testing and this information helps my understanding of what is happening and why.

And here's the more technical answer I received from Nils Rosenblad Naish Engineer and Thrust Designer. Although he is mainly describing the front wing, the theory is the same. Again, not to dis-similar to my thoughts above.

Hi JB
The simplest and clearest explanation is that kite (and WS) foils are primarily optimized for steady state flight - you want to get up and go, and then keep going in a roughly linear direction - whereas surf foils are primarily optimized for turning, with steady state flight being secondary. Think of the difference between a glider and a stunt plane.
Interestingly enough, even downwind SUP foiling is much closer to surfing than kiting - we tried both, and the flatter wings were a disaster because they simply didn't respond to the constant rider input (which of course is the opposite of steady kite foiling). I was initially imagining that scenario to be closer to steady state, and turned out to be completely wrong.
The reason the geometries are very different is also quite simple.
Kite foils cant (to windward) to shave off excess lift and increase lateral resistance at speed. The higher aspect ratio, flatter wings have much better L/D ratios (especially at the higher Reynolds number/speed regime kites operate at) and have a normal elliptical load distribution that results in efficient, steady, controllable flight. Any wingtip treatment (winglets etc) is solely there to mitigate tip vortices (drag).
Surf foils are designed to generate most of their lift in the center section, and the large down-turned wingtip sections are there to both keep the lift fairly constant through a wide range of cant angles (the speed range is relatively narrow once you are on a wave), and to minimize side slip thru a carving turn. They are also shaped to make the transition from one extreme cant angle to another - think 'S' turn - as smooth as possible.
An easy way to look at it is to imagine that the center part of the foil wing is the tail of a surfboard, except fully submerged - the tip sections are the thruster fins.Hope this helps, and that you are doing well and having fun!
Best Regards

Nils Rosenblad

Here is a link to the definition of the Reynolds numbers - en.wikipedia.org/wiki/Reynolds_number

I hope this all helps.

Ride safe,

JB

Slingshot Foil Designer Tony Logosz discusses the basic concepts and function of a foil's stabilizer rear wing.

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Windgenuity said..
In my opinion, the smaller rear/stab is no where near as affective as a larger one for pumping and the smaller rear/stab is far better for turning. I have tried many combo's with big front wings and I basically put it down to;

I am not a pumping expert, but all the good pumpers I know (the ones able to pump back to the lineup and catch a 2nd wave still flying) told me that a smaller stab helps a lot for pumping, as it is less stable it frees the rider to perform all the small movements needed for efficient long distance pumping.

Basically what helps turning helps pumping. Just like with surfboards, actually.

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7-Nation Aust said..

Windgenuity said..
I'm a little confused about the rear/stab concepts discussed at 2:15.

In my opinion, the smaller rear/stab is no where near as affective as a larger one for pumping and the smaller rear/stab is far better for turning. I have tried many combo's with big front wings and I basically put it down to;

- Non breaking waves, fat and lots of pumping = XL rear/Stab.
- good walls and great for carving and turning = Std Rear/Stab.

Now, obviously I am referring to the Naish Thrust Set up, and it may be different on the SS.

The larger rear does however offer up a lot more stability. Makes your glide ridiculously stable.

Great vid though, and appreciate the time getting info out, just wanted to share my thoughts there as to me, the message seems a little odd.

Ride safe,

JB

Hey JB

I think the technique used to pump the Naish foils is to use a bit weight to push off the rear wing?

While with the Slingshot foils the pumping technique is a little different and using much more weight on the front wing

We have definitely found it easier to pump the smaller rear wing than our larger one, no matter the wing size. Meaning you can use the smaller better turning rear wing for almost all conditions.

The one exception was our Spaceskate (H4) wing which because of the accentuated delta outline and a dihedral underside, which makes it super lively from side to side, with sharp carving, tight turning, and agile handling. (The shortboard of wings) You can pump it in the turns, like a skateboard with loose trucks. It's a wing that advanced riders will use to create speed in the turns.

This wing actually was easier to pump with the larger rear wing as you were using that to push off as well.

It's an interesting theory, I have done a lot of pumping on both. and agree that pumping on the smaller rear is good. I change back and forth all the time until I need to cover a long distance pumping, then the XL rear wins every time. It you keep your speed up and can maintain your speed the std rears work fine, and you'll likely travel faster with the std then the XL rear (I think my GPS reading are around 3-5km/h slower on the XL rear for the same day pumping). But I find with the std rear if I am going to link more than 2 or 3 waves or cover a lot of distance I absolutely have to keep my speed up, whereas the XL rear I can afford to ride a little slower and actually work a little less, slower cadence and conserve energy. I agree with you that the STD rear makes the foil feel free'er but just not "better" for pumping (I guess we need to define what better is). Also if I am paddling up onto the foil without a decent wave or swell on SUP, the XL rear makes a huge difference (like for down winding).

Interesting, and makes me want to play more :)

Ride safe,

JB