E-foil Foil Wing Design Discussion

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Max Maker   1 µW

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E-foil Foil Wing Design Discussion

Post by Max Maker » Nov 15 2017 7:30pm

Please point out if the following logic is right or wrong.

I am not convinced that E-foils should use the same wing geometry that Kiteboards, Wakeboards or Surfboards use. In those three cases, the propelling force acts high above the board. This generates a moment that wants to push the nose down into the water. Therfore, the back wing is inverted and creates downward lift. This counteracts the moment generated by the Kite, Cable or Sail. Remember, they are acting on the exactly oposite end as the motor.

On an E-foil, the propulsion happens very close to the wing, the generated moment is much smaller here and in the opposite direction. So I belive that the back wing is not optimal. I saw a low of videos where the surfer has to lean forward a lot to keep the nose down. So the surfer is acting against the back wing which can only cause drag and wasted energy. The Wings should rather be like on an airplane and going both in the same direction.

I hope this is uplifting news. (Sorry for the pun.)

I think we could push the e-foils development much further if we could create the optimal wing first. An open source design would be amazing, so people could compare their results. Unfortunatley, I don´t know much about flow analysis.

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Re: E-foil Foil Wing Design Discussion

Post by CobraJet » May 13 2018 9:11am

I just moved onto a lake that requires no gas engines.

It will be very interesting to see your results.

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Re: E-foil Foil Wing Design Discussion

Post by LockH » May 13 2018 11:26am

Hehe... Had to look up watt yer tapping about. As seen here?:
http://efoil.builders/about
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Re: E-foil Foil Wing Design Discussion

Post by Chalo » May 13 2018 11:46am

Max Maker wrote:
Nov 15 2017 7:30pm
The Wings should rather be like on an airplane and going both in the same direction.
An airplane's horizontal stabilizer is not set at the same angle of incidence as the wing. It is designed to cause a downward force on the aircraft's tail. But it is often able to be trimmed to different angles for different loading conditions.

I think you're right that the angle of incidence of the rear foil should change if the propulsion exerts a much smaller pitching moment than usual. But that's not the same as having the front and rear foils set to the same angle of incidence.

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Re: E-foil Foil Wing Design Discussion

Post by classicalgas » Oct 13 2018 1:03pm

RE: Both wings lifting. *Some* airplanes generate lift at both ends, using a small wing ahead of the main wing ("canard") and no tail surface, and they are efficient designs, but tht's not typical. Canard layouts depend on stalling the front, smaller wing, before the main wing for dynamic stability, so the front wing runs at a less efficient, higher angle of attack than the main wing.

That's arguably better than running the tail at at negative lift, in order to keep the main wing at a lift generating angle of attack.

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Re: E-foil Foil Wing Design Discussion

Post by Voltron » Oct 13 2018 1:21pm

From my fast sailing experience, when you're not driving the sails hard enough you can feel a flutter in the rudder from the disturbed flow off the daggerboards ( or keel, or centerboard, whatevs) hitting the rudder, so keeping your rear foil out of the wake of the first one is a consideration and intentionally trimming the rig to where the rudders are running at a slightly higher incidence angle is normal than the forward foil(s). It creates way more effective lift. You could feel it on my hydrofoil trimaran too... if things were set so the tail foil wasn't lifting too it was really really hard to lift off and get foiling...

One gigantic difference between water based foilers and airplanes is that with aircraft, its essential that it wants to naturally dive a little, otherwise it can lock into stalls and never recover. On the water, you pretty much always want to go up. You might limit the lift a little when you're really cooking, but its a whole different thing if you stall the tail a little even if you wipe out compared to control recovery in the air.

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Re: E-foil Foil Wing Design Discussion

Post by Voltron » Oct 13 2018 1:40pm

Its great seeing the mixing of ideas that sends you off on a google search for foilers without the drive force acting from high above the water and you find something like this,,,lol


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Re: E-foil Foil Wing Design Discussion

Post by classicalgas » Nov 25 2018 1:52am

"...On the water, you pretty much always want to go up. "...Don't you get "porpoising" if a foil breaks the surface?

Somewhere I've seen surface skimming linkages that auto trim the front fol to prevent that.

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Re: E-foil Foil Wing Design Discussion

Post by Voltron » Nov 25 2018 5:12pm

You definitely don't want to be breaking the surface...I did that on my front foils right into a wave at top speed and went farther underwater than I ever have in a boat.

What I meant was, if you stall the tail in a boat, it just noses up, loses speed, and settles back down into the water as you get things going again. You're also not usually foiling in shallow water where settling will crash you or kill a bunch of passengers.

With aircraft if you stall the tail you can go into deep stalls that can be unrecoverable, esp while coming in for landing... It just can't be allowed to happen or terrible things ensue, where with a recreational boat you don't need to design the foils around positive passive stall recovery.

And yes, surface sensing wands that are mechanicaly linked to the foils are a common control method. Moth class boats also have a linkage in the rudder so when you twist the tiller it moves the trim tab on that foil while the wand does the front.

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Re: E-foil Foil Wing Design Discussion

Post by ecycler » Dec 24 2018 1:30am

Max Maker wrote:
Nov 15 2017 7:30pm
Please point out if the following logic is right or wrong.

I am not convinced that E-foils should use the same wing geometry that Kiteboards, Wakeboards or Surfboards use. In those three cases, the propelling force acts high above the board. This generates a moment that wants to push the nose down into the water. Therfore, the back wing is inverted and creates downward lift. This counteracts the moment generated by the Kite, Cable or Sail. Remember, they are acting on the exactly oposite end as the motor.

On an E-foil, the propulsion happens very close to the wing, the generated moment is much smaller here and in the opposite direction. So I belive that the back wing is not optimal. I saw a low of videos where the surfer has to lean forward a lot to keep the nose down. So the surfer is acting against the back wing which can only cause drag and wasted energy. The Wings should rather be like on an airplane and going both in the same direction.

I hope this is uplifting news. (Sorry for the pun.)

I think we could push the e-foils development much further if we could create the optimal wing first. An open source design would be amazing, so people could compare their results. Unfortunatley, I don´t know much about flow analysis.
I think you are putting too much thought into this. On an efficient, high aspect ratio wing the amount of propulsion it actually takes is surprisingly low to maintain lift and speed. I would much rather worry about designing my foil for the dynamic handling characteristics for the given type of riding. It is quite easy to change your stance, F/R weight bias, or both to negate the effects of the pull/push moment on the system. Regardless, some very small shims to change the AOA of either wing is all it should take. Riding style and personal preference are most likely going to matter more than theory.

I say all of this having only been towed on foil (and yet to be pushed, since I have not built or bought an efoil yet) but the range in angle of pulls I have experienced is very large - from a few inches off the surface of the water when I tied a short wake-surf rope to the transom of an inflatable dinghy thus having the line actually pulling me downward as I am riding on a 36 inch foil mast to having a 45 degree angle of pull from above. It is very easy to adapt once you get the hang of it... just think about kiting where you have to constantly adjust for the angle from which the kite is pulling. Most of the guys who get into foiling do it for the light wind days where there is quite a bite of sine waving the kite for maximum pull.

Note: All this is much easier said than done. After trying to teach more than 10 people, only one of my friends is able to ride on foil for more than 30 seconds. My advice before building an efoil board is to spend a great deal of time riding foils behind boats, kites, and waves to make sure you even like doing it.
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Re: E-foil Foil Wing Design Discussion

Post by brantfredrickson » Jan 27 2020 5:26pm

Max Maker wrote:
Nov 15 2017 7:30pm
Please point out if the following logic is right or wrong.

I am not convinced that E-foils should use the same wing geometry that Kiteboards, Wakeboards or Surfboards use. In those three cases, the propelling force acts high above the board. This generates a moment that wants to push the nose down into the water. Therfore, the back wing is inverted and creates downward lift. This counteracts the moment generated by the Kite, Cable or Sail. Remember, they are acting on the exactly oposite end as the motor.

I think we could push the e-foils development much further if we could create the optimal wing first. An open source design would be amazing, so people could compare their results. Unfortunatley, I don´t know much about flow analysis.
I'm a beginner wind foiler will 11 sessions and about 17 minutes up on the foil. The power of the sail is used to get the board up on a plane. Then and only then will the foil lift you and the board up. You need about 6 to 8 mph of board speed before the foil will lift you out of the water. Once your out of the water you sheet out the sail and the power of the sail is reduced by about 75 percent. That is why old guys like myself love foiling. You can go just as fast as your windsurfing buddies with 25 percent of the effort.

All wings have lift and drag. In addition they have a pitch down moment. The stabilizer is there to counteract the that moment. It's not there to handle the pitching down moment of a fully load sail.

High aspect ratio, high speed, low drag performance oriented foils for racing are designed to get the most velocity made good upwind. My Slingshot foil is a low aspect ratio, high lift foil that does a whole different job. It is best at gliding, like a high performance sailplane. It is much more user friendly when compare to a racing foil.

Slingshot make boards and foils for kite foiling, wind foiling, SUP foiling, surf foiling, and wake foiling. All their big wings work in all those applications. But in each application where you stand to operate the kite, the sail, the wave, or the tow rope is different. What is the same is that your center of gravity has to be just ahead of the neutral point to achieve longitudinal stability. And very small movements are necessary to maintain the balance. Hope this helps.

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Re: E-foil Foil Wing Design Discussion

Post by John in CR » Feb 21 2020 3:23am

Why hasn't someone come up with a set of surface piercing foils like hydrofoils on boats available commercially just smaller and mounted on a board that is stable and easily ride?

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Re: E-foil Foil Wing Design Discussion

Post by Voltron » Feb 21 2020 12:29pm

Surface piercing foils are usually designed for a narrower speed range, and flatish water conditions, which on say a powered ferry on a river is fine. Then you get major wake reduction, and relatively simple construction. They're usually are designed to self limit the ride height, with ever smaller foil sections down low, so there's less lift the higher it goes out of the water.

For the varying speed of say a kiteboard, and rougher water, fully submerged L or T foils are better... Then they're under the wave tops all the time, where surface piercing doesn't like random waves hitting the upper sections that are out of the water at speed.
But then you need some kind of active system to control the ride height, which could be as simple as a foilboard where the weight shifting the whole fixed assembly changes the angle of attack. On bigger boats, it's usually a wand that droops down to feel the water surface, connected thru a linkage to a trim tab, or maybe rocking the entire foil.
Last edited by Voltron on Feb 21 2020 1:05pm, edited 1 time in total.

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Re: E-foil Foil Wing Design Discussion

Post by Voltron » Feb 21 2020 12:42pm

Here's some pics of some test boats for the next Americas Cup.... When they change directions, all three are temporarily swung down, then back to two most of the time.

T foils rock 👍
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My old boat... So insane driving a 16ft boat at over 30... It had foot steering, so your hands were free for the sails and foils. So once it was up to speed and trimmed out, you could drive around with a drink in one hand and waving with the other at all the boats you were passing 👍
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You can see the wands, the more one is pushed up, it knows that side of the boat is low, and increases the lift. The other side starts drooping, and that starts limiting the lift on the foil that is too close to the water surface, with sensitivity adjusters in the cockpit. Then there's a joystick next to the driver that manually sets the rudder trim tab, that has enough area to basically change the trim angle of the entire boat a ridiculous amount, with adjustable stops for ones normal liftoff vs speed settings.

That's a stock image btw... My beards not that white yet... Lol.

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Re: E-foil Foil Wing Design Discussion

Post by John in CR » Feb 21 2020 1:56pm

I'm sure that was a blast to sail. Would it turn somewhat when the sides were at uneven heights? I'm convinced that a more stable foil board is possible. All that's needed is less sensitivity to fore and aft COG changes, but leave the left/right changes making it carve turns. Let the pros have their super sensitive foils, and give us regular people the ability to cruise smoothly above the water with so much less drag, and we'll see an explosion of popularity.

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Re: E-foil Foil Wing Design Discussion

Post by Voltron » Feb 21 2020 2:13pm

It turned like it was on rails regardless of tilt... You could feel the g forces trying to fling you out of the boat in high speed 180s.

Edit...
But if you meant did heeling induce a turn, not noticably, esp compared to a regular keelboat, where when you heel there's a big offset between the drag of the keel and the drive from the sails when leaned over. This one self corrected instantly in a gust, and turned it all into forward acceleration...

And for a smooth water, steady speed situation like a recreational e-foilboard on a smooth lake or bay, simple self limiting ladder foils might work just fine. But when you want smooth swoopy motion left and right, you kind of need it to be one center foil and one tail foil... As soon as it's three at once, it turns into a go cart like, flat cornering machine, much like the feel of bike vs trike. With two, you're back to not every body will have the ability to lean into the turns right, but you could def make it a lot less pitch sensitive, esp with the motor driving it at a fairly constant speed.

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Re: E-foil Foil Wing Design Discussion

Post by Voltron » Feb 22 2020 12:39am

Some surface piercing type.... For a while Hydroptere held the outright sailing speed record and the measured mile speed record.
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That was an incredible feat, as most drag race sailboats are tiny and fragile, but this was designed for open ocean crossings.

But, they did run into development problems...
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It's ok though.. They were already working on Hydroptere 2, which is the black trimmed one in the second pic.

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Re: E-foil Foil Wing Design Discussion

Post by The fingers » Feb 22 2020 7:35am

What about the risk posed by floating timber/utility poles?
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Re: E-foil Foil Wing Design Discussion

Post by John in CR » Feb 22 2020 4:15pm

Voltron wrote:
Feb 21 2020 2:13pm
It turned like it was on rails regardless of tilt... You could feel the g forces trying to fling you out of the boat in high speed 180s.

Edit...
But if you meant did heeling induce a turn, not noticably, esp compared to a regular keelboat, where when you heel there's a big offset between the drag of the keel and the drive from the sails when leaned over. This one self corrected instantly in a gust, and turned it all into forward acceleration...

And for a smooth water, steady speed situation like a recreational e-foilboard on a smooth lake or bay, simple self limiting ladder foils might work just fine. But when you want smooth swoopy motion left and right, you kind of need it to be one center foil and one tail foil... As soon as it's three at once, it turns into a go cart like, flat cornering machine, much like the feel of bike vs trike. With two, you're back to not every body will have the ability to lean into the turns right, but you could def make it a lot less pitch sensitive, esp with the motor driving it at a fairly constant speed.
Ok, so only a rudder turns those, but I gotta believe there's something somewhere in the middle between the overly sensitive foils it takes an expert to ride vs water piercing foil front and rear that are like riding on rails, so no carving a turn. Everything maritime related is sorely missing the single best innovative concept of the younger generation, and that is OpenSource. Just like with ducted prop design, anything involving the water means every new idea is treated like a "state secret". That's a big reason why the maritime industry is so slow to change...a real pity on a planet where 70% of the surface is water.

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Re: E-foil Foil Wing Design Discussion

Post by John in CR » Feb 22 2020 4:21pm

Maybe the solution is a relatively small underwater wing for lean induced turning combined with surface piercing foils fore and aft for stable lift (just reach the speed threshold and you're airborne and stable).

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Re: E-foil Foil Wing Design Discussion

Post by spinningmagnets » Feb 22 2020 4:37pm

This is the first I've seen of this thread. If I retired to a lake-front property, I'd definitely want to build something these. Not necessarily to achieve the greatest top-speed, but reducing drag can provide adequate propulsion from a very light wind, which would dramatically expand the conditions where sailing is possible.

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Re: E-foil Foil Wing Design Discussion

Post by Voltron » Feb 23 2020 12:07pm

It is an amazing feeling when you start sailing faster than the wind speed in smooth water... Magical. Some of the new boats can do 2.5 times the wind speed in perfect conditions... Going 20kts in 8kts of wind creates this weird sensory field that makes your brain reel.


Just watch out for stumps and sandbars! The very first time I sailed one I went to San Diego with a guy for a demo day... While I'm talking to the rep who's looking at me with his back to the bay, I see the other guy cruising at speed on the foils... And he suddenly yanks to a stop, and the boat stands nearly vertical on the bows with the tail in the air 12ft or so. Then it flops back down and starts going again. I was pretty proud of my poker face right then... 😶
That's when I realized how strong the foils are. The body is rotomolded plastic, and one outer float hit so hard it was bent and wrinkled... Then by the next day had straightened out in the sun!

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Re: E-foil Foil Wing Design Discussion

Post by Voltron » Feb 23 2020 12:12pm

The Hobie version they made for a while.. The yellow L foils flip under the boat in use... You did NOT want to run that one aground!
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Re: E-foil Foil Wing Design Discussion

Post by Voltron » Feb 26 2020 7:03pm

Nothing new under the sun as the saying goes...
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Basic aftermarket surface piercing set up.

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Re: E-foil Foil Wing Design Discussion

Post by Voltron » Feb 26 2020 7:11pm

This guy, Kotaro Horiuchi, pretty much perfected the submerged two foil power setup, where well designed alignment of the thrust makes it naturally lean into the turns.
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