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4 Degrees up on the wing?

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NYKiter
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4 Degrees up on the wing?

Postby NYKiter » Sat Jun 03, 2017 12:56 pm

Someone mentioned this attack angle in relation to fuselage.
Is this up angle needed if the stab is 2 degrees down?
(may be over-simplifying things here of course)


Also - is eppler profile considered the go to profile?

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Re: 4 Degrees up on the wing?

Postby TomW » Sat Jun 03, 2017 4:23 pm

I'm interested too.
But I've been reading.
Basically a flat bottom foil will generate less lift when at zero AoA to flow, a foil with shape on bottom will have some lift at zero AoA. So you might need a constant AoA built into the design to generate a certain lift and a specific speed.
Foil designers call a flat bottom foil " symmetrical " and one with shape both sides " asymmetric ".

From what I understand, as you are starting to foil, you are moving slowly on surface of water and foil is not supporting all your weight.
As you gain speed, lift increases. Once you reach speed that lift equals your total weight you start flying. You don't have to lean back and increase your AoA to increase lift and get up. As you lift, drag is reduced and foil speed and lift goes up, now you have to put weight forward to counteract the increasing lift, reducing AoA and therefore the lift.

When you are more experienced, you get up to a minimum speed, and pop up into flying by momentarily increasing AoA and lift, and then once up quickly flying with lowered AoA and Higher speed. If you don't have that minimum speed needed you will porpoise

Now, imagine you have built in some AoA, you will build in more initial lift, your speed to start flying will be less, but you'll have to tilt down the nose more to not fly out of the water.

Really, I think what you want to achieve is having fuselage in most hydrodynamic position, with front wing at AoA and speed that generates lift for your total weight at a desired speed.
We are talking about + 10 degrees and - 3 AoA according to experts like T Speers.

So if you " think" you need 4 degrees AoA to fly at 20 knots then you would put your wing on so the fuselage is zero degrees to flow at 4 degrees AoA. Otherwise, you will end up tilting the wing and fuselage in flow, increasing drag. How much?? Who knows?

But I've also been reading about some of the dynamics, and perhaps attacks AoA is not that critical for Freeriding. The kite is lifting you and changing the load, not only vertically. The waves have water moving in circular motion, radically changing AoA as you pass waves. The foil is close to the surface and going through various density ( air bubbles) , causing changes in foil behavior that only scientists at Cal Tech can fathom. Even the density difference between salt and fresh water have effect.

My highly amateur conclusion is that due to all these variables, and the fact that kiter can easily change AoA, that almost anything that creates more lift than drag, will work.

Edit: I think there's a lot of good reasons to make your wings AoA adjustable on your home build.
Read this
hysecdes (1).pdf
(115.92 KiB) Downloaded 75 times

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NYKiter
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Re: 4 Degrees up on the wing?

Postby NYKiter » Sat Jun 03, 2017 5:34 pm

Good resource - thanks.

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Re: 4 Degrees up on the wing?

Postby juandesooka » Sat Jun 03, 2017 7:07 pm

TomW wrote:
Sat Jun 03, 2017 4:23 pm
My highly amateur conclusion is that due to all these variables, and the fact that kiter can easily change AoA, that almost anything that creates more lift than drag, will work.
The specs on foils boggle my mind. I have stringy wings, they are dead flat, no AoA adjustment seems to be needed....maybe because I am freeriding, going slow and turning constantly. I copied the stringy wings with g10, but left them thicker. Again, seems "balanced", no issues with porpoising, etc. If anything the ride feels more "cushioned" and maybe a little slower, but more stable. Now I have copied spitfire wings, so far the ride is not so stable, tendency to nose drop (though may just be not used to the different ride yet, not going fast enough to engage the wings). Anyways, I have a basic understanding of the concept of increasing AoA to either increase lift on front wing or increase drag on stab wing. But how to play with this when both wings are providing lift? Hmm. Going to take some playing around this summer, as I can't quite reason out which wing to raise or both.

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Re: 4 Degrees up on the wing?

Postby tahoedirk » Tue Jun 06, 2017 4:32 pm

4 degrees is the difference between wing and stab. It might be 1 degree or 5 degrees but it is the difference . The angle relative to the fuselage will affect the angle that the fuse and board travel . I go with 0 degrees on the front because I like the pitch of my board while foiling. I think 3 degrees up would make the fuse perfect for the direction of travel but angle my nose down 3 degrees also. I have not discovered a go to profile yet

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Re: 4 Degrees up on the wing?

Postby alexrider » Sun Jun 11, 2017 6:45 pm

tahoedirk wrote:
Tue Jun 06, 2017 4:32 pm
4 degrees is the difference between wing and stab. It might be 1 degree or 5 degrees but it is the difference . The angle relative to the fuselage will affect the angle that the fuse and board travel . I go with 0 degrees on the front because I like the pitch of my board while foiling. I think 3 degrees up would make the fuse perfect for the direction of travel but angle my nose down 3 degrees also. I have not discovered a go to profile yet
I wish I could increase the angle of attack of my Zeeko White & Green main wing (without affecting the difference with the stab) by a few degrees to prevent the board's attitude to point upwards (see attached picture) in order to make the stance more comfortable as I was used to with the Cab DA I learned with. At the moment, I'm forced to ride front leg bent and back leg straight, and only in the jibes I don't find it an issue. It had to be the designer (Nico) deliberate goal to have it as it is, perhaps to have softer landings (the tail touching water first), but I'd like to find a way to alter (increas by 4 to 8 degrees) the wings' angle of attack relative to the board. Side theoretical benefit, foiling should occur at a lower speed. I see three ways to achieve that:
- changing the whole foil assemblage's (mast, fuse and wings) angle by inserting a wedge between the mast plate and the board
- changing only the fuselage and wings assemblage by inserting a wedge between the mast and the fuse. I'm afraid the rigidity of the connection would suffer in that case
- changing the angle of attack of both winds with wedges between them and the fuse.
Thoughts welcome on how I should proceed.
Incidentally (sic), a decreased AoA of the stab relative to the main wing is equivalent IMO as having bigger rocker on a surf board. It make jibes and carves easier at the cost of decreasing speed in straight line.
To illustrate, this is a screen grab from a Zeeko clip.
ZEEKO FOIL ALLOY SERIES.mp4_snapshot_03.00_[2017.02.21_05.17.42].jpg

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Re: 4 Degrees up on the wing?

Postby Peter_Frank » Mon Jun 12, 2017 3:35 pm

I dont like the "board pitch up" attitude either, it both looks wrong and feels wrong having to bend your front leg :wink:

I have seen when relatively new riders get a racefoil instead of the typical "learning" foil, then they often balance on the verge to stalling (as not used to riding fast, they try "not to"), and the board points ridiculously upwards now :rollgrin:

Boards pointing up is practical as it can recover from touchdowns quite well, but making loads of nosekick is way better IMO as it does not look wrong, and you dont have to bend your front leg :thumb:

8) PF

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Re: 4 Degrees up on the wing?

Postby TomW » Mon Jun 12, 2017 5:09 pm

I'm not an expert, but Is this really the neutral angle of the strut? It's hard to believe. Seems like it's in angle that would lead to launching out of water.
I would think the strut should be near vertical when flying at neutral altitude.
But if indeed then something else seems wrong. The fuselage must be dragging at that angle too.
Before making shim between board and strut, I'd try changing AoA of the wing. Front edge up. That way you are getting lift with less tilt back on strut, keeping board more horizontal.

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Re: 4 Degrees up on the wing?

Postby Cdog » Wed Dec 06, 2017 5:31 pm

Not sure this helps
https://youtu.be/mVdSx5eNdUA


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