Hi everyone,

I have been using a home made 1200 front wing with a angle of incidence (AOI) of 2 degrees for the past 6 months for both surf-foiling and kite-foiling and would like to build a new wing, dedicated to kite foiling (like this one below, around 850cm2). I could not find any info on AOI specifically, but believe these should be relatively low for our sport, maybe 0-1 degree?

What do you guys think?

Cheers, Moku

I've heard it said it's two degrees front and rear door suitability. So, +2 and -2?

I have seen these values around as well, especially for SUP and surf foils. However, my understanding was that small high aspect ratio wings had lower AOI, especially those built for speed (kite foiling, tow-in foiling...).

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Mokuleia said..
I have seen these values around as well, especially for SUP and surf foils. However, my understanding was that small high aspect ratio wings had lower AOI, especially those built for speed (kite foiling, tow-in foiling...).

I was surprised that the front wing had any at all.

Can you make your wing so that you can shim it?

No I cannot shim it, it is one of these system where the front wings fits into a "key", a la Armstrong.

No matter what angle you build into the front wing it will always align itself with the waterflow across it. But what will change is the angle of the fuselage, eg, shimming the front of the main wing will cause the fuselage to angle down towards the rear, and this then changes the angle of the rear stab to the waterflow pushing the stab up and the nose of the board down.
Through trial and error I found I could shim the rear stab to overcome too much nose down of the main wing, but at a point the mast is angled forward which seemed to make the foil very unstable.

When you say "the wing will align itself" you mean you as a rider will correct the angle of attack (AoA) to adjust for it I presume. This is where I think getting the AoI right in the first place is important to have a comfortable riding experience. Shimming the rear wing to fine tune lift/control is indeed the way to go (and less problematic mechanically speaking than shimming the front).

I would be very interested if someone had AoI values (or could measure it) to share on a given brand, for example a Armstrong kite (<1000cm2) vs surf/sup (>1500cm) front wings. I have contacted couple manufacturers. Not sure if any will share their data, but worth trying ;-)

The rider could align the wing but that would require either front or rear foot pressure to hold it there which gets tiresome quickly though some front foot pressure is preferable.
AOA will be difficult to measure due to the curve of the lower wing surface on many production wings, mine is 0.17 degrees nose down so pretty much zero with the fuselage, it has a flat lower surface the same as the older Naish surf wings and easy to measure.
I did run into issues when using thicker wings, I think the turbulence caused by the wing was impacting the stab which felt like riding on gravel. The fix was a 1 mm shim on the front main wing which moved the stab downwards out of the main wing turbulent flow.

Once you are moving up on foil, everything is centred around your main wing and the AOA it wants for the lift you seek out of it.
so at a slow speed you want to be foiling so there needs to be more AoA. Then less AoA as speed increases.
you control this by controlling pitch and the stabiliser wing helps with the effort needed to control the pitch.

As previously stated. For whatever starting angle you choose. What will change is operation is the angle the board runs at to horizontal.

Just to be sure we are all on the same page, here is how I define angles of incidence (AoI) and attack (AoA):
AoI: built-in angle of the wing with respect to the fuselage, which is fixed (except if you shim).
AoA: varies with pitch of the board (and your input as rider), and as such is variable.

A very simple way to measure the AoI is to use calipers with V-notches (can be done with a metal file) and a digital angle gauge. Alternatively, you can build the following contraption with only few parts (having a 3D printer helps). You can zero the gauge either on the fuselage to measure the AoI of the front wing or zero it on the rear wing to measure its angle with respect to the front wing.

If I agree that the wing AoA will vary based on operation, I can't imagine that AoI are not fine tuned by designers based on the optimum riding condition, that is high speed for racers, medium speeds for cruising and low speed for SUP...etc.

I have changed my mind a little and decided to go with a more "conventional" design based on Duotone's Spirit carve 700. Apparently, flat wings are harder to control than curved ones...

Cord length and wing span are identical to Duotone's. The profile is 1.75 cm thick and AoI -2 degrees.

I am a 6'1" 80kg rider. Not sure if 700cm2 is large enough. My current wing is identical in shape but 1200cm2. Maybe I should go with a little larger, like 850cm2?

Inputs from specialists more than welcome!

I can say for the Stringy foil that the angle of incidence on both front and back wings is exactly zero for both front and back wings.
That's to say, the lower surface of both front and rear wings is completely flat, and mounts on a completely flat fuselage (bottom upside down of course). So this is a working configuration.