Author Topic: Wing lift or AOA lift?  (Read 11952 times)

SURFFOILS

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Re: Wing lift or AOA lift?
« Reply #15 on: July 29, 2017, 05:06:57 PM »
heres some other foils . not mine , in South Africa where theyre doing a bit of AOA and foil

surfcowboy

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Re: Wing lift or AOA lift?
« Reply #16 on: July 29, 2017, 08:51:03 PM »
What a cool design. But do you have info on why such a large foil on a small board?

Seems almost like a stepped hull board where you ride up on another surface once at speed but in this case the sq. inches are really similar.

SURFFOILS

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Re: Wing lift or AOA lift?
« Reply #17 on: July 30, 2017, 03:23:38 AM »
I'm not sure about the why's of this design, l it does seem big but it might be more of a full planing foil rather than when a submerged or surface piercing. I thought it was. A cool design tho.

surfcowboy

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Re: Wing lift or AOA lift?
« Reply #18 on: July 31, 2017, 07:21:19 PM »
Yes, I checked the thread and he's doing some cool stuff. Wild all the paipo stuff that's out there.

SURFFOILS

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Re: Wing lift or AOA lift?
« Reply #19 on: August 05, 2017, 04:15:39 AM »
Is there any theory on zero AOA or do you need foil for lift.
 Here's one from a guy named Bruno in France.
« Last Edit: August 05, 2017, 04:33:19 AM by SURFFOILS »

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Re: Wing lift or AOA lift?
« Reply #20 on: August 05, 2017, 04:44:19 AM »
duno about theory but my old foil had so much lift you would end up flying at negative aoa to keep the thing in the water. the problem was it had too much lift so there was a huge wave drag hump to over come at sub foiling speed, ended up cutting the trailing edges straight across and removing 10+mm of material from the underside going to a semi symmetrical airfoil with no big concave 'hook' in the aft sections. that got rid of heaps of drag while only sacrificing maybe half a knot of take off speed. last pic is what it looked like in the end

SURFFOILS

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Re: Wing lift or AOA lift?
« Reply #21 on: August 05, 2017, 04:56:54 AM »
While lift is the goal, too much or constant high lift requires so much effort to counteract it. Similar to what you've done Container, less lift may result in slower initial lift but will result in a more manageable ride.

Beasho

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Re: Wing lift or AOA lift?
« Reply #22 on: August 05, 2017, 08:23:55 AM »
Is there any theory on zero AOA or do you need foil for lift.

The theory was settled nearly 100 years ago.

A Cambered Airfoil, Flat Bottom Curved Top, generates lift at 0 degrees angle of attack.  A symmetric foil, Double Foil, generates Zero Lift at Zero degrees.  The lift profiles are otherwise identical - See the blue lines in the first diagram.  The Camber induces lift, through "Circulation", approximately 8 degrees sooner (to keep it simple).  A cambered foil also has the benefit of generating through a larger range of Angles of Attack before stall for equivalent speed.

For example: High Cambered Airfoil generates lift from -8 degrees to +12 degrees: Spanning 20 degrees - ORANGE ARROW

 vs. a Symmetric Foil that will generate lift from 0 degrees to +16 degrees.  Spanning just 16 degrees - PURPLE ARROW.  This is the distance from where the blue line crosses the X-Axis to the Stall Angle. 

I am now convincing myself why the thick Cambered Go-Foil works so well in the surf: 

Because we wobble up and down and the angle of attack (called pitch) changes so much when dropping down a face, carving down the line or pumping to make a section - We need a heavily Cambered foil.  This produces the greatest 1) Potential Lift  2) Range of Pitch before Stall   

Here are some pictures describing what is going on.
« Last Edit: August 05, 2017, 09:05:25 AM by Beasho »

surfcowboy

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Re: Wing lift or AOA lift?
« Reply #23 on: August 05, 2017, 12:04:31 PM »
Beasho, I love you. Thank you for this post.

So in the end, basically anything works, but the more cambered the foil, within limits, the more flexibility you have with angle. And yes, of course it makes sense that on a big long keel/mast where you can wildly vary the AOA by your movements, you'd want a thick, cambered foil.

When U.K. told me to start at 1 1/2" for a thickness I was surprised but as I see more of these types, I get why you'd want that.

I have a feeeling that once I get one made, I'll start messing around and seeing where you can go. I think there are many solutions to foiling yet to be seen.

Again, thank you for the science, it's sadly so rare these days.

SURFFOILS

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Re: Wing lift or AOA lift?
« Reply #24 on: August 06, 2017, 04:15:12 AM »
Is there any theory on zero AOA or do you need foil for lift.

The theory was settled nearly 100 years ago.

But that theory was based on static air and not moving water wasn't it ?

Beasho

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Re: Wing lift or AOA lift?
« Reply #25 on: August 06, 2017, 05:08:40 AM »
In engineering terms it's all called fluid.   Water, air... effectively the same. 

Lift = 1/2 Density x Velocity^2

Density of water is 800 X that of air which is why the tiny wings work.

There's a slight difference due to incompressibilty of water or when nearing the speed of sound and scaling (called Reynolds number think a bee flying vs 747) but otherwise for LIFT start with this stuff. 

Otherwise for what you/we are doing zig zagging starting and stopping on a wave I agree no one knows what works best yet. 


surfcowboy

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Re: Wing lift or AOA lift?
« Reply #26 on: August 06, 2017, 08:00:30 AM »
Surffoils, I also verified this with an aerospace engineer buddy of mine here as well. There are differences in practices for sure when you get into the water (speed, lift per sq inches etc, but the ideas are the same.

I think that clearly there are many ways to solve the problem here but the best way to find out is to do a few wings and vary the angles.

I've also got some weird ideas that I'll try to draw while I'm traveling and send you. Some of the paipo ideas I think will translate pretty well to standing up. The low drag ideas are interesting for paddle in foiling.

SURFFOILS

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Re: Wing lift or AOA lift?
« Reply #27 on: August 06, 2017, 07:13:54 PM »
There doesn't seem to be a lack of lift , we've got so much lift we're literally standing on it to hold it down, I think control is the goal to aim for ?

surfcowboy

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Re: Wing lift or AOA lift?
« Reply #28 on: August 07, 2017, 07:13:44 PM »
That's the part I have to get into the water to see, but yes, control is key. We need to get UK to talk about his Tacuma vs his home built foil. That's why I'm considering starting with a flat wing and a curved one to feel the difference. Then add in a flat foil with no foil profile and we will learn a lot in a short time.

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Re: Wing lift or AOA lift?
« Reply #29 on: August 07, 2017, 09:12:22 PM »
i have tried both go foil models and i found the feel to be very similar to my various foils, the maliko in my opinion is unstable in the roll axis but super stable in pitch and a great L/D ratio, like a slipperier version of my current foil. the kai foil rolls easily but has alot of reserve stability thanks to the crescent shape and needs a fair bit more speed than mine and the maliko to fly. its also interesting to note the foil section differences between the two. i'll try do a sketch from memory comparing them

 


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