How Hydrofoils Work: The physics of foils & how we might fly forever

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This sport is dangerous. Please be safe. We’d encourage you to thoroughly review all product safety material prior to trying. If you don’t feel safe, do not proceed. This sport is not as easy as it looks. It took us many hours of practice, but we enjoyed the journey. Please use a CGA life vest. Please wear a helmet to protect your head. Please wear a wetsuit to protect from cuts from any sharp edges. Please proceed at your own risk. We review products and share our own personal experience. If you rely on the information in this video, you assume responsibility for results. Wake Thief, LLC.

We're trying to figure out how to fly forever. Like an airplane, a hydrofoil experienced drag that slows it down. Figuring out how to reduce drag is the key to flying forever. We've done plenty of product review and have played around with different front wings, rear wings, mast lengths and fuselage lengths and we've found a setup that we really like, but we need to go deeper if we want to fly farther. We need to go back into the classroom, open some aerodynamics and physics textbooks to learn about flight, and how we can unlock longer human powered flight on a hydrofoil. Our current pumping record is 2.5 minutes, but we want to go further, and "pump" the foil for longer.

Source of airfoil analysis:

[sergemann]

Your breakdowns are solid! I really enjoy your scientific approach. Mad props to you and your neighbor.

[leonardodausa]

...finally some science...bravo...
...thank you very much for your effort...
...the most important thing-you aren't just talking but walking as well...respect...
...stay safe...all the best...keep pumping...
...bravo one more time...

[andreatopcat]

one of the best videos on youtube. Thank you!!!

[danielreitermusic]

Another thing that may be worth considering is the configuration of the wings & stabilizer. The canard configuration puts the lifting wing in back and stabilizer in front, for example. This allows both wings to produce lift and can in theory provide a much more efficient foil with regards to drag. There's been a few canard style foils out there you could look too, like the Zeeko Spitfire kitefoil. Canards have stability issues when recovering from a stall which has serious safety concerns for aircraft, but for foils it may work fine.

[Pete_R]

The science is wonderful and I am always amazed that the hydrodynamics of those (relatively) little wings can generate enough force to lift the board and its rider up and out of the water. Fantastic.

[nicksowles]

You’re a genius creating a whole new sport. So inspiring!

[ianravera]

Excellent work. Love the scientific approach!

[geoffreyyoste]

Slow and steady like my retirement plan. I’m determined to learn how to hydrofoil, I live in Mississippi so getting good waves is out of the question. I am totally digging your videos. My twin brother and I started looking for Jetske last night

[heliboyfly]

Brilliant work. Thank you for posting.
I’ve been trying to figure out the forces at work using the lift equation in air and you’ve put me right with the fluid dynamics and the difference between air and water.
I have the infinity 99 but at 105 kgs I doubt I would ever be able to dock start but the bungee could be a go. I’ve managed 10 pumps on my wing so far but it’s completely alien technique and I feel the wasted energy slowing me down with each pump.

Please keep the videos coming.

👍👍

[jordangarrison]

Thank you for the physics breakdown this is really helpful

[jonathanreinke]

This was educational and entertaining, thanks for making!

I think we are gong to get snow and very cold temps in the next couple of days here in WA, I am motivated to also try Ice breaking Windfoiling at Lake Ballinger. Hope it gets cold enough for some freeze over.

Have a great one! 🙂

[albericsarrazin]

Awesome work it is very complete and will help me to finish my school project (if i may oc) awesome chanel by the way!! helps me as an engineer student to not loose motivation in my long school jounrney..

[zurraspa]

Nice work!! A foil may reduce induced drag using "winglets"

[ic]

Веома занимљиво 👍. Нисам знала да овако нешто постоји.

[scor]

A very useful info. Thank you very much

[JaretCa]

I have a question, What if the foils used in the high water current like the river etc..?

[blainerawdon]

Thank you for your beautiful and interesting series of videos. This one is a useful analysis of the design problem - thank you. The following comments are intended to help you refine your design progress and reach your goal of sustained foiling. This is feasible and is amenable to analytic design methods - that is, you can figure out what is best on paper and that should get you close much more quickly than pure experimentation. You ran the numbers approximately correctly. It is correct that power is the product of total drag and speed. It is noteworthy that your wing induced drag far exceeds your wing viscous drag. It would be worthwhile in this estimate to include the viscous drag of the mast, fuselage and stabilizer. To achieve minimum drag force, you should aim for a speed at which total viscous drag and induced drag are equal. However, _power_ is minimized when CL^3/2 / CDtotal is maximized. This means foiling at a greater lift coefficient. A few key points: 1) Using aspect ratio to estimate induced drag can be misleading since the formula you have is for induced drag _coefficient_, not induced drag _force_ which is what you want to reduce. What determines induced drag force is water density, speed, lift, and wingspan. Aspect ratio falls out of the calculation. Given a selected span and a target speed, you then want to select an airfoil chord that provides the minimum viscous drag _force_. Reduced chord leads to reduced Reynolds number and higher lift coefficient, and probably a greater viscous drag coefficient. This is multiplied with the area, so you have to experiment (on paper) to see what aspect ratio is best for a given span, speed and lift. 2) What you are doing here is similar to the human powered airplane (HPA) problem. Paul MacCready made a big jump in HPA performance in 1976 by using a huge span in combination with extreme light weight and large chord to get airspeed down. This reduced power so that sustained flight was possible. I think you need to think about much bigger wingspans - perhaps two meters or more to drop your optimum speed to a lower value while avoiding large induced drag forces. 3) You have to be a bit careful in estimating induced drag force because the wing is operating close to the water surface. The wing is not engaging only water as assumed by your e value - it is also working on much lower density of air. The result is a considerably lower e value, maybe 0.6 - 0.7 (wild guess) depending on depth to span ratio. You don't want to go too deep or the mast drag hurts. But you don't want to be too high or the e drops a lot. You can see in your video the effect of induced drag creating a wake on the water surface behind your wing. This will diminish with a longer wingspan. 4) Another factor affecting induced drag is the lift from the stabilizer. My firm impression is that the center of gravity (CG) of the rider and board system is well ahead of the wing quarter chord. This means that the stabilizer provides a substantial downforce. This puts a big dent in the lift distribution that further reduces e. A possible measure to address this is to increase increase chord in the wing in the region ahead of the stabilizer, in a tapered way. Extra lift from this extra chord offsets the download from the tail to preserve an efficient lift distribution. Most airliners use this method to offset tail download. You can see this in the tapered extend trailing edge chord region ("Yehudi") and sometimes in a tapered, extended leading edge region ("glove"). A good tool to address this is Prof. Mark Drela's Athena Vortex Lattice (AVL) free software. Powerful but hard to learn, . OK. Enough for now. I hope this is helpful. Please keep up the beautiful videos!

[Sanguen]

I started the video as a surfer, and finished it with a Phd in physics.
10/10 would watch again!
great info <3

[StandUpMagazin]

People study aeronautics for this kind of stuff! Respect!

[terrywells]

Excellent explanation. I would like to know your thoughts on wingtip shape and washout to reduce tip loss.