Wing lift or AOA lift?

[jondrums]

the maliko in my opinion is unstable in the roll axis

Do you think that's because of the negative dihedral of the tail stabilizer and the fact that that main wing has no dihedral?  I guess the downside of positive dihedral is that the wing might pierce the surface, but it seems like it would make it more stable in roll.  Come to think of it, I suppose the stabilizer needs negative dihedral to initiate a turn, but I think just a little positive dihedral on the main wing would go a long way.

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 because the main wing is flat so has zero reserve stability. my foil has dihedral and its slightly more stable than the maliko but still less so than the kai foil. the tips poking out thru the waves is also a fairly big problem.
it seems counter intuitive but anhedral is more stable. my tail foil can go in either way, lifting with dihedral or downforce with anhedral and that makes a huge difference to all round control but thats more cause of the lift/downforce than what way the wings are angled.
the downforce just steadies up the whole operation because of a sort of 'triangulation' of forces whereas with it also providing lift you really are just balanced on top of the mast trying to keep the thing level. i reckon its alot faster and less drag though so i prefer it this way

[Beasho]

Keep testing: Aeronautic theory states


• Dihedral is More Stable in flight.
• A dead Flat Wing is Most Efficient from a lift to drag ratio: Maliko
• Anhedral, curved down wings like a gull, is inherently UNSTABLE.  Unstable is coincident with and produces maneuverability. Go-Foil KAI Model

Fighter aircraft can be so unstable that a human can no longer fly them.  BUT a computer can fly them.  This combination gives the benefit of flight with wacky maneuverability.  With our "Go-Foil" wings we are the computer starting from Kai's processing power and moving down from there. 

However modern theory doesn't play on the boundary between Air and Water that is 800X denser and foam which is somewhere inbetween.
 Watching the videos you will see why Dihedral doesn't work.  When the rider is turning, as suggested, the tips get exposed.  The primary benefit of Anhedral with underwater wings is (maybe) that the entire wing stays submerged during maneuvers.

https://en.wikipedia.org/wiki/Dihedral_(aeronautics)

Anhedral:
Military fighter aircraft often have near zero or even anhedral angle reducing dihedral effect and hence reducing the stability of the spiral mode. This increases manoeuvrability which is desirable in fighter-type aircraft.[/list][/list]

[SURFFOILS]

Beasho, I think it's the degree of dihedral or upturn thats too great.
 From a flat foil there's reduced lift as the foil is tilted. By adding an upturned tip of 9 degrees to 50% of the each wing length you get a greater spread of lift as the foil tilts out to about 40 deg.

[Beasho]

From a flat foil there's reduced lift as the foil is tilted.

TRUE

But a Flat Foil still has more horizontal lifting force than a Dihedral foil of equal area, hence more vertical lift, when tilted at the same angle.   

A bit about my background: I have an Aeronautical Engineering Degree from Cornell '92.  Same school as Bill Nye the Science guy except he was just a Mechanical Engineering.  So while I never played engineer on TV I did get my arse kicked and was graded on this stuff.

I was a pretty good designer.  From an original design perspective I would never have spec'd a Kai Go-Foil. 

The beauty of Design was that the original
 Theory almost NEVER, EVER, EVER, NEVER plays out in the real world.  Nature always throws you a curve ball. 

This is why every Chuck Yeager has his Jack Ridley https://en.wikipedia.org/wiki/Jack_Ridley_(pilot), and Kai Lenny has his Alex Aguera.

I wax on about the theory because to break the rules you have to understand them first. 

PS:  When you stumble upon something that REALLY doesn't make sense but your theory fits reality you get to name your discovery like Bernoulli.  Because it is NOT common sense.   

As Feynman said:  "If you think you understand quantum mechanics, you don't understand quantum mechanics."

[Beasho]

Here is an example of the Go-Foil on the edge. 

Note Keahi turning hard but the foil is still engaged, producing lift and not stalling.  The Right Wing Tip appears to be at its limit.  The tip appears to be cavitating, on the verge of stall or all of the above.

The Anhedral is keeping the tip in the water, which otherwise would have breached and caused all sorts of chaos.

Note too:  When we turn, and turn hard, the speed of the outside tip can be MUCH, MUCH greater than the inside of the turn (Maybe 2X??).  Airplanes DO NOT have as great a speed differential, and yet they crash when flying on the verge of stall and turn too hard.  We had 2 people die in Half Moon Bay this April turning downwind and not realizing how slow they were flying relative to the column of air. 

This may be another advantage that the Go-Foils have over airplane wings and why the thick wing is necessary to keep the inside wing from stalling during turns. 

https://youtu.be/3WzVKy-tP8M?t=107

[Beasho]

Light Bulb Moment:

"Pumping a Board Left to Right should produce Lift and Forward motion similar to Pumping the Board up and Down."
- Beasho

You heard it here first.

Like a skateboard generating forward thrust from pumping left to right the foil board should be able to achieve the same forward thrust from pumping left to right.  The harmonics, or resonant frequency, favors up and down motion but should work left to right if you can turn fast enough. 

There is a gravity kick from up/down but the physics are the same.

A Few Quick Searches Later and OMG!     This guy figured it out.  He explains Pumping on a Skateboard and unknowingly explains Pumping on a Surfboard, Accelerating down the line, and explains Pumping on a Foil board.  Its all about reducing the Radius of Curvature by pumping your legs.

Ahhhhhhhhhh!  Creek and all those Crazy wiggle-waggle pumpers have been vindicated by some Khan Academy YouTube guy with fluorescent chalk. 

https://youtu.be/YgUmAwq1WG4?t=299

[surfcowboy]

Beasho, as a guy who translates complex things (computer code) into simple ones that can be sold, I'm going to keep this going and try to lay out some testing concepts here with input from more of the guys who are testing in the real world as well.

If everyone will indulge us and continue to pitch in while also remembering that sometimes what we feel as humans can be affected by a lot of factors including conditions and our physical and mental perceptions.

One of the things I love about surffoils and container is that they didn't worry as much about theory and just built stuff to try. I'm trying to set a jumping off point for my own build/s using not the dogma of the commercial foils, but the engineering wisdom that's magically here (crazy how many creative and smart folks are on this forum) as well as the "let's try it" side as well.

So. For the fuselage foils, I offer these. Copy and correct please, where you see inaccuracies.

1. Flat wing, with a foil might be a place to start. Might suffer from issues turning, but should have good lift and be relatively stable compared to anhedral.

2. Flat wing, no foil, should be tested just for testing to solve arguments and for curiosity. Predicting similar results to above, but we can see. I believe this is the Clearwater design, can someone with a kit confirm?

3. Wing with foil and anhedral, should be less stable but should perform better in turns and waves. Thick profile tapering to ends should help with lift when tilted.

4. Wing with foil and dihedral, should be most stable and have good lift, but there are concerns about tip exposure during turns. (Should this even be tried? Worth the effort?)

5. Downward curved wing with foil but dihedral tips, are we hitting a sweet spot here or over-thinking things into a mess?

I don't think I could survive making 5 wings but I'm curious about this and would like to try to make a few over time or split the load with someone else in easy shipping/swap range. Considering a keel and fuselage that could accept these for testing, nothing crazy but glass, plywood, and carbon so it'd be cheap and relatively fast to build and bolt on to.

Then... we get into the surffoils discs and other alternative shapes that I think could really be cool as well lol. Maybe I won't build a new board this year, just lam up wings all winter?

Hope this inspires thought, feel free to use the numbers and comment and we will aggregate the results.

[surfcowboy]

And then Beasho tossed another grenade into the pool lol. I love that idea! But man, who's got those chops? (Kai?)

[Beasho]

I'm going to keep this going and try to lay out some testing concepts here with input from more of the guys who are testing in the real world as well.

I agree with everything.  How about trying adding the possibility of moving from GREEN to BLUE. 

Figure out how we can take off in the Green profile, at low speed, and then retract the flap to shift to Blue profile with lower Coefficient of Lift but with less drag and therefore a HIGHER Speed profile.  Effectively a 2 gear foil.

LIFT must stay constant.  The foil has to lift ~ 200 lbs of board and rider whether going 10 mph or 20 mph.  The only way to modulate this is to Change Angle of Attack.  Otherwise lift increases 4X and you fly out of the water.  A flap would massively expand the speed envelope. 

I want to surf big waves and the Flap may be necessary. 

[Beasho]

Here's another one. 

Who ever heard of a Gurney Flap?

This could be a cheap way to modify an existing foil for low speed or learning conditions.  Just bolt a vertical Fence off the trailing edge.   

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this site just got real interesting real quick! what about a flexi foil? super massive camber in the aft sections that loads up and straightens out when you are flying?

[supuk]

Love how everyone is thinking now this stuf has been going through my mind a lot. Yet to prove the 3D printed/composite wings but think it could be a way way for a group of us to do a lot of testing and prototypes of the same design and then make everything work on a universal Ali mast and fuz. Maybe we set up a group on fusion if a few of you are now playing with it.


I think a form of altitude management similar to the moths is going to be the next big step as the hole breaching thing is one of the largest problems with sustaining flight for beginners at least.

[jondrums]

This could be a cheap way to modify an existing foil for low speed or learning conditions.  Just bolt a vertical Fence off the trailing edge.

How about having a hole in the front of the rig that passively diverts a small amount of water through a manifold and out of holes spread across the back of the foil?  Not sure if they should be pointed downward or upward for the effect to work.  It might be possible design a proportional valve in the manifold that modulated orifice size based on flow rate, and thus at high speeds it effectively "spoils" the lift.  I am not sure, but I think it would only take a very small flow rate of liquid to make a pronounced effect on the lift.

I could imagine a totally passive system that is tuned to provide something closer to constant lift across a wider speed range without the need for angle of attack and drag at low speeds.

Maybe this has been demonstrated already and named - I don't have the background to know what to search for.

[SURFFOILS]

This could be a cheap way to modify an existing foil for low speed or learning conditions.  Just bolt a vertical Fence off the trailing edge.

How about having a hole in the front of the rig that passively diverts a small amount of water through a manifold and out of holes spread across the back of the foil?  Not sure if they should be pointed downward or upward for the effect to work.  It might be possible design a proportional valve in the manifold that modulated orifice size based on flow rate, and thus at high speeds it effectively "spoils" the lift.  I am not sure, but I think it would only take a very small flow rate of liquid to make a pronounced effect on the lift.

I could imagine a totally passive system that is tuned to provide something closer to constant lift across a wider speed range without the need for angle of attack and drag at low speeds.

Maybe this has been demonstrated already and named - I don't have the background to know what to search for.

Oh you mean like a hoop foil ?