How Hydrofoils Work 

"We talked to aerospace engineers and we watched University lectures on fluid mechanics"... you guys are truly next level!

Nice work. As an engineering analyst I didn't expect you to explain this so well. We can't even agree on how it works! Luckily there has been significant empirical data gathered for our home shaped hydrofoils to be developed from. I'm enjoying putting my work into my pleasure, shaping boards and foils to work that much better. In 1996 I was flying a home built personal hydrofoil on Lake Tapps outside of Seattle while working as an analyst to Boeing. My lovely family put me off for 25 years, but I'm back at it, kite foiling and wing foiling with an amazing crew down here in NZ! Woo-Hoo!

This video confirms what I have thought about lift for about 50 years. I never believed the first explanations, and this seems to me to be so obvious. Thanks! I feel vindicated.

Holy cow! You guys are raising the bar for all other kiting channels!! I didn’t expect to be taken back to my chemical engineering fluid flow class but enjoyed your academic explanation nonetheless!!! Nice work and keep the educational videos coming. The technical aspect of this sport can be intimidating at times but it’s also what makes it so cool! Thanks so much for your work on your channel.

Fascinating, well presented. And to think, I put a kayak up on a submerged foil around 1960, but I could not paddle so fast for long. I still remember tying a line to the kayak and having a person tow me onto the foil for a sustained ride. As soon as the kayak popped up on the foil, he went head over heels as the foil abruptly reduced the load on the tow rope as it lifted the kayak above the water. I went on to fly possibly the first of what is called the Rogallo Wing and it"s motorized form, the trike. I could have stayed with the hydrofoil!

Thanks for the comparison of the different explanations/factors for lift. One thing not mentioned is the general shape of a wing: it is a stretched teardrop (teardrop is the most aerodynamic shape). A straight "stretched teardrop" that has the trailing edge lower in the airstream would get lift because of the angle of attack alone (1) (like sticking your hand out the car window, due to molecular collisions, pressure differential, or whathaveyou). A flat board would also receive such lift, but it wouldn't slide through the wind as well as the straight-stretched teardrop shape. We don't often see such zero angle-of-attack straight "stretched teardrop wings, though. ... Stretching the top side of the teardrop while keeping the bottom straight and while keeping the angle-of-attack at zero degrees (2) would also provide lift (due to the Bernoulli effect), but we don't see this alone often either. Combining 1 and 2 gives more lift than either one alone. ... You can also see from the blades of a household electric fan that the local angle of attack increases as air moves over the blade. The inside of the curve of the blade gradually pushes harder and harder on the air molecules as the airflow gets pushed more and more. I don't know if this is force (3) from my above analysis or just an aspect of (1) and (2) twisting together. ... And when an airplane flies upside down, the angle-of-attack has to be increased enough to overcome the downward "lift" caused by Bernouli effect of the longer bottom side of the wing (and the curved shape, I guess). This is why such flights are slower and require more engine power to execute. They're inefficient and always at near-stall.

And in the end, I am always blown away at the thought that the relatively small main and rear wings can generate enough lift to push not only the board but the weight of my body up and out of the water. Fascinating!

I never knew what was under those cool floating surfboards. Always thought it was a motor. Great physics lesson.

Laurie went HARD on hydrodynamics, and I love it. I knew most of these principles already - and BTW the full explanation for lift is all of the above (to varying degrees in different flight regimes) plus compression lift at trans/supersonic speeds - but it's really cool to hear it from a kiteboarding expert's perspective.

that was the most complete explanation of dynamic lift I've ever experienced. Excellent work!

I was extremely impressed with the quality, presentation style, editing, and thoroughness of the video. You guys are going to have hundreds of thousands of subs one day, and honestly ya'll could broaden the target audience and you'd 100% succeed.

I was thinking about designing a mini hydrofoil for a project, but needed info on how exactly they worked so that I would make one that was effective. This video was 100% perfect and did a phenomenal job answering all of my questions, and some I didn't know I had! Bravo, great stuff all around!

You could be a great professor!! 😅. Remember studying this during Wind design for buildings. Awesome content.

Excellent video. I'm not an engineer, but understood a good amount of this. It's really refreshing to see people make the effort to understand and explain, kudos.

great video! re: planes flying upside down, fwiw, when flying an RC model plane upside down, you typically have to add a bit of elevator angle to counteract the 'downward' lift being generated by the inverted wing. Probably similar in real life.

Great video Yuri and Laurie! I’m sure a ton of research and work went into this one. Great comparisons of the 3 theories (with great visuals) which provide a good understanding of the aero/hydrodynamics associated with foil lift. So, should we anticipate the next step will be about the impact foil shape has on lift, drag and speed? Well put together guys, keep them coming! 👍👍👍😀

Thank you, I have never quite understood hydrofoils. I can only learn by seeing, so descriptions are just words that mean things to everyone else. You taught someone something today

Keep in mind that streamlines do not reach the end of airfoil at the same time. Look for Holger Babisnky's explanation on how airfoils generate lift, for more knowledge. PS: airfoils work virtually the same way as hidrofoils.

This video was clearer than any fluid mechanics textbook in the world

Very refreshing to not just hear the canned explanation with no thought behind it if it actually makes sense. Great job!

I love how easy it is to just randomly stumble upon a great video.

This video reminds me studying for my professional license of Engineering. Solving problems using the Bernoulli equation to find pressure head.

OMG! The first video I've seen that actually get's the physics of wings correctly! Well done!

Keep going guys! At this rate you'll be the number one kite channel in no time... Thumbs up! Great video.

Much, much, more information then I set out to look for... but I watched it all because it was engaging, informative and well put together. 👏🏻

I've been working with wings since the late 80's. We talk about this constantly, and i've never seen a better, clearer explanation. I kept wait for you to leave something out like AOA, but nope, covered, not only covered but gave the ratio's as well. Will be bookmarking and sharing this as the number one best explanation for how wings work, especially when thicker skulls insist on arguing. Brilliant.

Cool cameo by Rod Parmenter of Foil Buzz at 1:27! (His '87 classic VHS "Hard Winds a Blowin" drew me to the left coast in search of nuking winds decades ago).

Your explanation is compensative. I was just looking for an explication on this subject after viewing the America's Cups yacht races. Thank you.

If you ever try wakeboarding, on the take off, it's best to point the board to the side a bit or you will be fighting the high pressure force from under the board when pointing towards to boat. The shape of a wing can exaggerate this effect to generate lift. Nice video on this topic! In science I think air and water are considered fluids.

Love your videos! Thanks for taking the time to dig into topics with method and persistence. Great fun watching and learning.

I'm an engineer and I learned something by this video - very impressive

Excellent video! I'm about to move to a beach town with a small season for surfing, windsurfing and kite boarding, so I've been looking into wing surfing. This video is very informative and clear. Subscribed!

Nice to see the Bell and Baldwin HD experiments getting a shout out. In fact they did a ton of experiments with kites as well that led them to form the AEA and become some of the first humans to fly. Happy to report, some generations later their great grandkids are still flying kites and riding foils, often at the same time. I think if my great grandfather was alive today (F.W.Baldwin) he would be a kite-foiling nut for sure.

Thoughtful, intelligent, complete. Thank you!

Excellent narrative and explanation. Really well done. Would love to see a 2nd part dealing in more detail with upside down wings and flat wings.

Science geeks! I love it! :-) By the way, before using the term "geek", I searched the web and attended university lectures. I found three definitions, but most experts agree, a "geek" is "a knowledgeable and obsessive enthusiast". I think the definition fits.

As a fluid mechanics PhD and Aerospace engineer I went into this video with trepidation that you’d point to an incomplete/flawed explanation like Bernoulli’s equation which is a specific simplification of the energy equation that can be made under very specific circumstances. I was extremely relieved to see that your explanation focused on conservation of momentum an generally agree with almost everything you said, well done! My only concern is the assertion of a lack of understanding or consensus among scientists and engineers-the bottom line is you need at least all 5 Navier Stokes equations-conservation of mass, conservation of x, y & z momentum and conservation of energy-to fully describe real fluid flow around 3D foils. It’s very complicated and usually impossible to solve with pencil & paper but there is a general understanding.

This is the best explanation on youtubue of hydrofoils, thank you.

Thank you for the video!!! Was really searching for a good explanation and you did it. Can’t appreciate it enough

A really great explanation of how this works!

For any Fluid Dynamics expert The vorticity generated by the boundary layer deflects downward the flow and for the conservation of momentum the wing is pushed upwards NO DEBATE

As a mechanical engineer, I just wanted to say…great video!!!!

I was thoroughly excited watching this.

Finally, I found an explanation! Thank u.

Excellent content. So valuable and well researched. Thank you

Great video; I appreciate the fact that you took us through the different explanations and research points. Thank you.

Well done. Great summary. It's like myth busters for kiters. Often wondered if it was angle of attack forcing water down or shape of wing for lift ... Or a combination of a bit of both.

Appreciating your hard work!

amazing description, I really like this kind of video. good job to the team who made this. thanks

The best and informative kite channel in the world.

The best explanation for wind over wing.

Bell didn't invent the telephone, he just marketed it, Antonio Meucci was the inventor

Ilmu fisika yg dipelajari ketika SMA. Orang kreatif yang menerapkan di dalam kehidupan

Thanks for this great explanation. The Bernoulli explanation I was fed at Engg school caused a lot of confusion as it is a complete abstraction from intuition and every day experience and a very inadequate explanation as you point out in your examples which could also include canvas wings. The top of the wing induces suction which in the extreme case in a liquid medium results in Cavitation . This explanation links lift and Cavitation. Great Job and thank you.

New video!!! How much am I waiting for these videos

i absolutely love this channel! So much info in a easy way to learn.

This is the first solid presentation explaining lift in its various theories and finally a solid visual and clear theoretical explanation of it. You guys are amazing! Thank you!

Our Kite Life and OK Kiteboarder are the most amazing RU-vid kite channels.

Best explanation so far .

Im Building a hydrofoil rn and this vedeo helped me a lot, thanks : Ofc I subscribed👍

Great explanation. Did not expect that!

Love watching your videos!!

Many thanks for this explanation video. Have a nice day.

This is great. I think I've done most of the same research you guys did to make this video, and this is probably the best simple-ish explanation I've seen. Everything else is either so simple as to be wrong (usually covering just the first "equal time" idea from this video) or requires a math degree to understand. You guys did a great job with this. Also, you got my friend Rod downwind foiling here in the Gorge in there, which is cool, too. :)

Great video. Also reminds me why I like maths more. There is no such thing as a better explanation. Things work or they don’t.

This is well done! Entertaining and educative. Thank you

nice presentation made it easy for old guys to understand

Nice video. Must point out that the ones well described here are not “different theories of lift” instead they are individual explanations of the various forces acting on a wing all together creating lift.

Well, that was enjoyable. I follow a lot of science explanation videos on RU-vid, and not any kite surfers, so it's interesting that RU-vid knew to recommend me this video.

Brilliantly explained.

Wow that was comprehensive great job

Very interesting technology. It does look like a surfer is defying the laws of density when raising above water while using these wings.

best ever explaination ❤️ thank you so much for wounderful information 👍🏻💐

Wow you really did your homework...Wonderful.👏 Thank you !!

I feel shortchanged by my physics professors! But I never went too deep into fluid dynamics.

Nicely done!

Amazing knowledge shared. Thanks 🙏

Thanks for sharing!

Great job.

wonderfully researched. Great explanation!

Thanks for educating us.

Well produced video I was looking for something that explained hydrofoil but I kinda think the airplane lead was unnecessary. There are major differences with the interactions of rudders, ailerons & wings. I get that they are wing like and provide lift. I would have liked to hear what some challenges that builders had to overcome before finished products. But it still helps me understand more

EXCELLENT EXPLANATION.

Very cool, thanks!!

the (4th) angle of attack explanation is the correct answer as it explains how planes fly upside down,how symmetrical aerofoils work,and also how propellers (air and water screws ) , wind turbines and sails work- And it is also the correct explanation of Newtons 3rd law a wing weather it is in air or water is producing thrust, just like a rocket, by accelerating a mass downwards , All aerofoils do is increase the efficiency of this process by reducing drag , (they also have an important effect on controllability of the craft) The confusion is caused my the imaginary 'lift force' when in reality its just Thrust

Awesome video. You guys are the best. ;)

great work! you guys are amazing!

No discussion of circulation theory and starting vortices? After all, it is the explanation that ties in with the magnus effect (lift generated by a spinning cylinder or sphere). It is also the theory of lift presented by Whidden and Levitt in the 2016 edition of "The Art and Science of Sails" published by North Sails Group LLC.

mark Zuckerberg july 4th video post brought me here 😅

Thanks from my heart. Very knowledgeable information 🙏

Representation great choice of words

This gives me ideas. Thanka

Nice explanation. Well done.

I appreciate this video. I LOVE the science.

Interesting, I wasn't aware their were multiple theories on lift. thanks

Much love to you guys. ❤

Loved video, helped alot💪

Awesome video - love your channel!

I think that is best explanation for foil.

I loved the the video and, I need to say, what a beutiful tiny eyes girl! She is mesmerizing! :) Hope this channel grows a lot!