How Hydrofoils Work: The physics of foils & how we might fly forever
HTML-код
- Опубликовано: 7 фев 2021
- FAVORITE FOILS
1 | Wake Thief Edition ($2,200)
tinyurl.com/2p9a6w48
2 | Slingshot Budget ($1,000)
tinyurl.com/yc6jeb92
3 | Waydoo Budget Electric ($5,400)
tinyurl.com/279b57p4
4 | Flite Performance Electric ($13,700)
tinyurl.com/yk4wjfyp
5 | Foil Drive Gen 2 ($8,400)
tinyurl.com/42uf42ed
6 | Beta Freefoil ($4,600)
tinyurl.com/44zpe8cp
Please use the "WAKETHIEF" coupon code & we will send you a hat.
Merch:
wakethief.myspreadshop.com
Donate:
/ wakethief
Affiliate Disclosure:
We’ve tried 300+ foils & have shared our experience in 100+ videos. Our recommendations are based on our desire to promote the best products. When viewers use our links and coupon code, we earn a commission. We have established a long list of affiliate partners. This allow us to earn a commission from the sale of nearly every brand. We believe this helps to eliminate any bias from our reviews and recommendations. We want to be transparent with our viewers, so we disclose our financial interests. Wake Thief has affiliate / financial arrangements with AXIS Foils, Takuma, Fliteboard, Beta Foils, Foil Drive, MACKiteboarding, REAL Watersports, Green Hat Kiteboarding, Bbtalkin, and Vibram. The above links are affiliate links, which mean we earn a commission if you purchase through our links. We thank you for your support of our channel and mission.
Safety Warning:
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 Wingtip vortices from Wikipedia: en.wikipedia.org/wiki/Wingtip...
Source of airfoil analysis:
airfoiltools.com 
Спорт
![[DEBUT STREAM] It's wind-up time!! #hololiveEnglish #holoJustice](http://i.ytimg.com/vi/p_ZQs-kgUKI/mqdefault.jpg)
Your breakdowns are solid! I really enjoy your scientific approach. Mad props to you and your neighbor.
Thanks, Serge. Justin has had a bunch of great breakthrough ideas and helps light the fire under me each day! Appreciate the comment.
Excellent work. Love the scientific approach!
Thank you, Ian. It's not perfect, but I'm doing my best. I keep finding better ways to do clearer/fairer comparisons and will embed in future videos. I appreciate the comment. Thank you.
Thank you for the physics breakdown this is really helpful
one of the best videos on youtube. Thank you!!!
Great work and very detailed
Thanks. Like most things, the more you dig the more complicated it gets and the less you realize you actually understood :) Thanks for the comment
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.
👍👍
Thank you! I'm 86kg and I think I could dock start the Infinity 99 if I were 10kg more, but don't think I could do if I were 20kg heavier. You will definitely need to run and jump onto it. You could bungee start it for sure, with a buoyant board. I tried 100 dock starts before I was able to do it, so keep practicing! If you ever have any questions, please don't hesitate to reach out.
You’re a genius creating a whole new sport. So inspiring!
Thanks, Nick. I'm not really creating the sport, but I can tell you that I'm obsessed in figuring out how to fly forever! This sport is truly amazing. I didn't even know it existed 3 years ago. Thanks so much for your comment.
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! 🙂
Thank you! If you ice break, please send a video! ... and dress warmly. 8/6 wetsuit highly recommended! Plus booties.
...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...
Thank you Leonardo. I appreciate your kind words.
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.
Thanks, Pete. I am amazed every time I'm pumping and look down in the water and see the "little" wing allowing me to fly. It is an experience like no other, and one that has to attract us all to clock more hours on our foils.
@@WakeThief The new saying should be, "It's all foiling now." Kite foiling, wake foiling, wing foiling, surf foiling, efoiling, even SUP foiling. I'm looking to start wing foiling.
Nice work! Keep it up
Thanks, Brendan. I appreciate the comment. Lots of learning still to do.
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
That's awesome! Thanks Geoffrey. With a
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..
That’s awesome! I remember those days well. Stay focused. There’s light at the end of the tunnel!
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.
Thanks Dr! I will certainly look this up!
The stall stability issue is usually compensated for by making the horizontal stabilizer (front wing) stall before the main wing, which then lowers the pitching force, so that the main wing effectively *can't* stall.
wow solved my question
Веома занимљиво 👍. Нисам знала да овако нешто постоји.
Nice work!! A foil may reduce induced drag using "winglets"
Excellent point! Since the 1150 isn't perfectly elliptical (there's still some chord length at the tips), it makes sense that this could help.
Epic video!
I think the most intuitive way to understand aspect ratio is as the foil's area compared to the foil's max possible area. The max possible area being the shape of a square with side lengths equal to the wingspan.
What do you think about the bicycle foils that are coming out? For example, Manta.
Thanks, Matthew. I haven't looked into Manta. I will now! Appreciate the comment.
Excellent explanation. I would like to know your thoughts on wingtip shape and washout to reduce tip loss.
I have found winglets have helped enhanced carving capability for the very high wingspan wings. I don't have any experience in washout tips and how they affect performance.
AGAIN, this video is amazing! Best channel about how to learn/understand foiling and how to pump!
What do you think about the effect that the board could have in the equation' Bigger Boards, will reduce speed, and you will nedd more power to lift them, and them will be go "nose down" easier due to its weight? right?
Thank you, Jose! I think boards make a big difference. The swing weight of the board while pumping is a energy suck, the drag in the air is a smaller, but real factor, and the weight of course. Thanks for the comment.
Great video! No mention of the stabiliser and it’s effect in the pumping though? How to angle it and what airfoil to use should make a big difference to drag and pump efficiency
All good points. I will add these to the list of topics to cover & dig into. Thanks for the suggestions.
Fantastic video again. Is there any chance you may be able to do a comparative HA Wing from different brands? I am similar to you in that I have been learning to foil on our local Dam and the small wakes from the wake boats across the Dam would be fun to ride. I am keen to see how the Naish HA would compare as this is what I was able to get second hand to start with. I am looking to move to the Jet 1800HA as its compatible with the 2018 set up we have.
Keep up the great work and thanks for your time and effort.
Thank you! Yes. Naish is on my list for when the lake thaws. I appreciate the comment
Thanks
You're Welcome!
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!
Blaine! I can’t thank you enough for this. One of my hopes was that this video would gain the attention of folks like you who could take this to the next level. This is great guidance and I understand the points you made. Thank you! So kind of you to take the time to educate me. Best wishes. Devon
People study aeronautics for this kind of stuff! Respect!
I am amateur (I should probably include that disclaimer!). Appreciate the comment. Thank you.
Thanks for that awesome video. I am looking for a very slow wing. Currently I am testing the gong curve xxl with a wing span of 120cm. That's the biggest wing I have ever pumped and it feels like that I can go very slow but long on this one.
Hi Olaf! Thanks for sharing. That wing is way larger (area) than anything I've flown! at 2800sqcm and 120cm span, it's (120x120 divided by 2800) 5.1 aspect ratio which is pretty similar to the 1020 I showed in this video. I don't know the Gong foil section so hard to really compare, but I would expect that you can fly slower than me, but that you'll have more induced drag (lower aspect ratio and much higher area) and more viscous drag (much higher area). If they could keep that area and go to a 2m wing (while keeping rigidity) I'd guess it would pump longer than anything I've tried. Did you say you can go slow but NOT very long? Please clarify. Thanks for your comment!!!
ruclips.net/video/dIvBT4Jn-Iw/видео.html
@@s2oooo this is great. Thanks for sharing
@@WakeThief my xL isn't wobbly gong improved using a bolt the other side. I've also got the M pro my favourite foil with a kite. I suspect the XL Pro will be my natural upgrade when i finally get around to polishing my skills.
Thanks again for sharing
Hi, Great stuff and solid math. Just for what we're battling against, I'm curious how much drag just the mast and water releasing is. All I can think of is when I SUP and practice bringing my paddle blade through the water, not lifting it out, and repeat. Of course I can rarely do it very straight or smooth, the drag feels extremely small. You mentioned how drag increases with speed, so perhaps when we reduce the pump speed on the larger HA foils you suggest, perhaps there's another efficiency advantage. For my own interests I sure would like to know what the mast and water releasing 'costs' us.
It's likely costing us more than we appreciated. It's hard to know for sure, we can only estimate.
This is so cool. Thank you..
By the way, can you pump the foil with both stance, meaning starboard or port side stance?... For me, it is seems harder for me to balance on the port side during the wake foiling (being towed by the boat) 😵🤨
Thank you for the kind comment. I cannot pump both ways, only the one way. I have tried to ride the foil the other way and it’s really hard for me.
@@WakeThief So, I am NOT the only one! I feel better now!! 🥰😘🤣😂
Definitely not!
Since drag is such a big deal then the surface of the foil is critical. Smooth surface with something that allows it to slip thru the water would help. Most of us surf on our foils so we use the wave energy for our power source. The other thing I notice is when the foil is closer to the surface it is easier.
Great to hear from you, Steve. Only recently did I receive that suggestion and intend to do a comparison once my lake thaws. I was told it might add 20s to my 2min 30s pump. That's certainly worth a try! I've also noticed that keeping the wing near the surface helps. In this video, I didn't do a very good job of that. I believe and have been told that less mast under the water reduced drag when wing near surface. If you think there are other surface-related phenomena driving this feeling of reduced drag, I'd love to hear your thoughts! Thanks for the comment.
Nice vid. Im thinking about picking this water sport up. I live a near a tidal lock where the water gets forced through at some speed. So my question is, how does moving water effect the foil? I imagine it is different than wave motion but not sure. Hope you can shed some light on the physics.
It definitely works. I’m friend with a guy on Facebook who uses a bungee attached to a bridge and lets the moving river stretch the bungee out and launch him. It’s amazing. Check out my foil bungee launch video. It will show you a bungee in action.
@@WakeThief Thx for the reply. But i was wondering if water flow it self would create any lift and if so how much? Could you glide in place like a glider in a strong enough head wind?
Yes. We’d need 7mph of water to lift me at 190lb on this wing
I have a question about board/foil design. Since I have a structural analysis background, I have to ask if the design of the "airplane" (actually waterplane in this case) has a reason for the placement of the mast. OR... is it simply the first person put it there and everyone else is following the motto, "That's the way it has always been done."
As everyone that has designed an airplane (even flying model (RC) planes) knows, the center of lift is approximately 25% of the chord back from the leading edge. IF... the mast were put at this location, the forces on fuselage due to the up/down-forces of the rear wing are near negligible. The fuselage could be made far smaller and lighter. I see some vendors go so far as to having titanium inserts at the conventional mast to fuselage design. The very high stress concentration point in the conventional fuselage is eliminated and so could these inserts.
Even the mast could be made somewhat lighter as it would have near zero moments. Compressive strength and Euler column buckling is greatly reduced if the moments are reduced. Using clever design, the same set of bolts could fasten the fuselage, wing and mast at the same joint.
As the mast is further forward on the "plane", it would need to be moved further forward on the board as well. This would reduce the cantilever requirements on the board and thus, even the board could be made somewhat lighter.
I doubt these weight savings would be that significant to most riders, but someone like you looking for that 2% improvement, it might be. I guess the point being... is there some fluid-dynamic reason for the conventional placement of the mast? There certainly isn't any good structural reason.
Fascinating!!! Curious if Hydrodynamic cavitation has an impact on your pursuit? I would guess not as the speeds you are pumping are not likely to create enough of the affect for it to deleterious relative to your performance. It’s interesting watching the AC75s as the American’s (unlike the other teams that solved for it) really struggled with it causing such extreme impacts that wheel of the boat was at times hard to control. As foil discussions are usually discussed relative to airplanes, hydrodynamic cavitation is unique to water.
I loved the video you shared with me on Facebook. Those folks are deep. The stakes are much higher for America's cup than our pursuits on the lake, so I bet there's a lot we can learn. I have noticed that when I'm pumping, the rear wing sometimes triggers a noise that sounds like cavitation. It tends to happen at slower speeds and with very low chord rear wings. I'm not sure what it is, but would love to find out. Perhaps I'm stalling the rear wing while I'm pumping?
@@WakeThief Have you thought of using a GoPro underwater at high frame rate to capture the motions and possible cavitation bubbles during pumping. Maybe rig up a bracket and foil mast as mount for GoPro and drive close by as you foil…
I’ve tried to pump while holding the go pro underwater. I need to try it again. Thanks for the suggestion.
Awesome video! Great to see a Justin cameo ;-). This video got me thinking. You didn't really talk about how to reduce the induced drag coefficient. Why don't foils have the little winglets like modern planes do now to reduce the induced drag, especially since you pointed out it's more than double the viscous drag? Also, since you were talking theory, it got me wondering if you put a marathon runner on the board, with the same pumping skill that you have, would they have the power to weight ratio to keep the board going well beyond the 3min mark? I wonder how this could be calculated using the power and lift force equations you mention.
I think that the Go Foil NL series has the winglets you're talking about. They supposedly help with the induced drag.
Once your achilles is back to normal, you can be our "learn to pump" test subject in summer 2021? :) Looking at the induced drag coefficient equation, the ways to reduce are reduce AR and reduce e (wing efficiency factor). I thought I covered those, but I need to go deeper there. As Bohdan mentions, the NL wings from Go Foil have it. I can't tell if they reduced induced drag in my test, but I could certainly feel the nice cut / line I could create while pumping in a circle. Those winglets really dug in nicely. ruclips.net/video/AIpY3VUlWro/видео.html
Thanks, bogdan. I liked how the wingtips cut in on the NL series. ruclips.net/video/AIpY3VUlWro/видео.html
So, the next step is to introduce flapping wing theory, and I'm just starting to roll up my sleeves. This is currently way over my head. One of the new terms is propulsion efficiency, in addition to the strouhal number and reduced frequency (two new dimensionless terms to me). Birds can be quite efficient, but given the rigid setup here we might be limited to 50% propulsion efficiency. I think of this way. When I pump it perfectly I'm at 50%, but guessing I'm 30-50% range from pump to pump. I now believe this is less about fitness and more about technique. I'm in ok shape, but not amazing shape. I could run a mile in 7.5min, as an example, not 5min. Lots of learning still to do. Thanks for the comment.
@@WakeThief this is where dynamic lift and drag come into play too. Look up Theodorsen's eqn./unsteady aero-hydrodynamics.
The tail surface is there to give static stability; same as an aircraft, you need the tail to be on to make sure as you pitch up there's a natural tendency to develop a pitch down moment. Otherwise it would be statically unstable and likely impossible to fly (as a human)!
Very detailed info! I’m building a hydrofoil and I’m worried that the trailing edge of my wings are too thick, does this matter a lot? Will a flat trailing edge add a significant amount of induced drag?
The trailing edge will matter to drag ... I've seen the trailing edge 1-2mm on most foils I've tried.
@@WakeThief I made the modifications 👍🏄🚀
@@WakeThief what about the leading edge, is that ok to be rounded or also needs to come to a point?
Leading edge has to be rounded.
Have you considered polishing the foils with compound or 2000 grit sand paper? What kind of improvements could you see?
I think it's a great idea. Thank you. Someone shared this idea with me a couple of months ago and I intend to a side by side once my lake thaws. I'll keep you posted. Thank you! I was told I might see 20s added to my 2min 30s pump. We will see.
Any thing past 800g doesn't seem to make a,big difference , however the trailing edge shape can
Split that in two and make two for each feet then connect both together and start running or stepping. Just a thought !
Interesting! Never thought of that before!
I have a question , What if the foils used in the high water current like the river etc..?
It's all about the relative speed of the water relative to the wing, so if you're pumping upstream you won't be moving very fast relative to the ground. If you're pumping downstream, you'll be moving very fast relative to ground.
Good work on the video. But man, I’m glad I’m not stuck foiling in a dead calm lake.
You’re lucky to have access to the ocean ... for the rest of us, we make the most on the lake! But it is still a blast on a lake.
Awesome video. I wish University classes were as interesting as this.
It has been a while since I took up Aerodynamics, so I might get this wrong. We already know that one single foil can never do all things great. It is going to be a jack-of-all trades, but master of none, or a master of one aspect, but at severe limits to all other qualities, or somewhere in between, depending on design.
In most other foil activities, you are propelled forward through a kite, wing or the waves themselves, and you do not need the wing to help you build speed, just keep the speed and be stable.
So my question: Yes, lift and drag matters alot, but the pumping motion itself is a different application of the wing, a different primary quality needed than all the other foil activities. It is not just about keeping speed and stability, but you also need to "catch" the water to build speed, which is a completely other thing. Or is it?
Basically: If you want the ultimate pumping foil, will this require producers to design for only this purpose, or will you get to the same design eventually if you simply just maximize lift and minimize drag? Intuitively, I am thinking a pure pumping foil would require another approach, but I might be mistaken.
To do a bird analogue, the peregrine falcon looks to be the fastest bird both by top speed ie straight vertical drop and self-propelled horizontal flying. I am not sure this is a fully applicable analogue, though. Not sure which bird is most accurate to reflect what you are looking for, either.
I am sure if you get to the ultimate speed design, it is going to be so taxing that you can only run it for about 30 seconds. I guess that is what you figured out when testing the 1300. Unless it was more about bodyweight or any other factor...
Looking forward to more of these!
Sven - Thanks for writing this. Very thoughtful. Please check out the latest video: ruclips.net/video/hpTU0nam8aE/видео.html. On Monday we will share what we've learned. You're exactly right. The video you reference is just steady flight, and I needed someone smarter than me to help. Luckily, I found two people! I've learned that we basically need to calculate lift and drag in each frame during a "pump" and integrate it. I took aerodynamics nearly 20 years ago, and I never learned about flapping flight ... reduced frequency, propulsive efficiency, etc were all new concepts to me. I am quite confident we are going to realize what you just said, and that will be the holygrail for wake thieving! Thanks again for the comment.
@@WakeThief Bøckmann is a fellow countryman. Looking forward to the conclusion. I got aware of foiling last year and have since bought an Efoil and wingfoil kit. Still a giant rookie, but it is my go-to activity for summer.
Fixed wing poses new challenges, as they are not flexible like bird wings. That is why I was not sure how applicable the bird analogue was, but it has to be a little bit at least.
Intuitively it makes alot of sense for a wing like this to have a slightly anhedral, slighty backward swept wing, fixed profile/chord length from mast, almost all the way to the tips. Then change the wings to give at least some control to carving, stability and retaining some of the lift that is lost at the end. Basically describes the 1150. Looking forward to seeing if you can get closer to the ultimate design aspects and ratios.
Would also be interesting to know how to best scale the best wing for heavier or lighter individuals. Basically shrink/enlarge everything 1:1, or just increase wingspan, redesign the whole thing?
Naish looks to simply add alot of chord length on their setup, like on the S25 HA series with almost fixed wingspan on all sizes. This is not to say this is not high quality, I got the 1800HA and the quality, performance and materials is superb.
On the other hand Armstrong seems to have a redesigned, not just scale, the entire wing in the high aspect series, though with lots of similarities. I have the cf2400 myself. I know armstrong takes alot from sailing and what is happening with foiling sailboats.
Lots to learn.
Thank for the thorough comments. We have some basic models to size up/down the foils based on weight. Please check this out if you're looking for rules of thumb: ruclips.net/video/jzM7ocflVXQ/видео.html
Second thought. Are you building your own wings or have the ear of a builder?
I use JavaFoil to do this type of analysis. I plugged in your Reynolds number (350,000) for 7 mph and aspect ratio of 7.7 to get an approximation. For the NACA 4412 you used in the example at Cl=0.63, I got a Cd=0.029. Although far higher than your 0.007, I'd assume that is because of aspect ratio and surface finish which I assume also takes into account viscous drag.
Anyway, have you considered taking a page from the P-51 Mustang and the supercritical laminar flow airfoils? Using the same Re and AR and using a NACA 07-512, I was able to get Cd=0.025. A 14% reduction in drag.
Even better... at some points in your stroke (top of stroke semi-weightless) your induced drag is greatly reduced. For the NACA 4412, the minimum Cd=0.01294, while the NACA 07-512 is Cd=0.0085. A 34% reduction in drag.
I'm sure there have been even better foils created since WW2 :)
Eppler 817 in the same conditions
Flying drag - Cl=0.63, Cd=0.022 => 24% less drag
Minimum drag - Cd=0.00675 => 48% less drag
Awesomeness!
Any insights as to how you manage to avoid touching down on the one hand and broaching on the other hand all the while getting impressively close to either limit...... ?
Yes, when I first starting pumping I thought mast height helped me make longer strokes which would help me pump. I think realized that the efficient stroke only needs a small amplitude (
ruclips.net/video/jzM7ocflVXQ/видео.html&lc=Ugw0BMIRDy7dU8numMt4AaABAg
@@WakeThief Thanks for the quick response. I guess that you can just 'sense' the foil height, ie: looking where you are going rather than looking down.
And thanks in general for making all these videos. Informative, high quality, and truly inspirational.
Thank you! I cannot sense it. It's funny you ask that. I realized recently when it's dark outside of water completely calm, I struggle. I have to see the water to pump. I wish I didn't! Thanks for the comment!
I started the video as a surfer, and finished it with a Phd in physics.
10/10 would watch again!
great info
Thank you!
Thinking more about it, I firmly believe the key to your breaking the 3min. barrier will require a new board. You are hitting the limits of what a fiberglass board can afford you in terms of performance. Further, the drawfcraft board is uniquely thin thus increasing the flex coefficient and wasting that much more energy. Given your weight, the thin board, the fiberglass construction, and fiberglass to carbon connection to the mast - you are losing SO much energy that needs to be directed to the foil (particularly on the down stroke of the pump). At your level. you really need to commission a carbon board + longer shank at the top of the mast connecting to the board which will drive the energy into foil vs. lost on the flex of the board and connection to the mast. Might make a fun video as you and "other" Justin are masters in the shop - connect the dwarf to a vice and have you pump up and down - immediately showing how much flex and energy you are losing as not translated to the foil. Further, when you build your carbon board I'd wager you want a bit more volume (same 6 lb weight, but carbon will allow for more volume at same weight) which will aid in creating greater stiffness as well as little more volume for the rope tow, etc. This is coming from an economics major w/an MBA so laugh at me rather than with me as I provide physics and mechanical engineering "council" - but strikes me you have to change your board to change the game and break the 3min mark. '21 is the year of the 4 min. pump run!!!
Justin! Ha! Love the comment. Degrees aside, it's a great suggestion. It's been so long since I was a real engineer, I really don't consider myself qualified! This makes sense and is a great idea. I'll be sure to have a new board for the start of my 2021 season. Got a lot of great suggestions! I hope you're right about the year of the 4min pump! I would've never thought 2.5min was even possible if you asked me one year ago. Thanks for the comment.
Great point, in sup paddle shafts there is a suitable stiffness to max out a stroke , its not rigid stiff though , there is a bit of flex, i expect enough flex to unleash the full energy before the stroke is complete, it also lowers fatigue to have a tiny bit of flex still.
How does Salt water vs Fresh water affect your result?
Not too much different because salt water is a bit more dense (3%) and slight higher viscosity.
Hello! Do you can recommend me a model to print it in 3d? I want make me one to surf
I’d recommend you check out winghopper. It’s a software program with pre build wing designs.
@@WakeThief Hello! Thanks you for the awnser. I saw this page, but I dont know how calculate the dimensions and I should desing the fuselage connection.
Why are wings sooo expensive? It sems to me to just cur a NACA like profile out of styrodur, fiberglass and epoxy the surfaces and maybe insert some polyamid or carbonfibers on the underside to counteract the pulling forces of the weight of the driver. 800$ vs 50$ material + some hours of work. Or did i miss something?
Interesting stuff. Why is it called "flying" though?
It’s a loose definition of flying :)
@@WakeThief That goes without saying. I mean, why is it not called something like Sailing?... I assume that would only be applicable if a Sail was used? So flying because you generate Lift via thrust or "Pump" as you've called it?
@@silver_m009 super well said. Thank you
SPM 2021 Physics Essay Question
😂 let me know if I can help. I’ll try but can’t promise anything!
I think you have a problem. 99% of the market is trying to go faster and you want to go slower. Who will make the foil you look for? Haha. In my amateur opinion, for both, faster and slower, you always want to reduce drag because it is lost energy. But to go slower, which requieres more lift, you just need a different airfoil profile. The Axis 1150 has quiet a lot of lift but is still designed to ride at a decent speed to not get boring for the market that buys it. But the market wants even more speed, so they made the black series not only higher aspect, but a different profile, opposite of what you look for.
Super well said! I think that’s my dilemma. Need more people who want to go a bit slower to go a lot farther :)
Reminds me that surfing went through the 30 rough years of following high performance trends until it re-found a fish type board (low profile) that was better for 90 percent of surfers. Lesson- be careful what get served up to us by the manufacturers combined with marketing designed to sell more units fast. Watching you guys closely. Good luck.
@sajhkg lovely comment. Thank you. I’d love to hear your thoughts on what you think this sport might need?
How did you manage to calculate for CL of .63 I can't get the math to math correctly 😂
What about a wave wing with rebound springs providing the 8lb of reverse energy to counter your push. In theory the push is launching you up. If maintenance is equal to gravity +-1. The struggle is to fight gravity. The best way to fight gravity is to extend gravity to the infinite. Basically think of a bamboo mat; shaped into an aerodynamic tear drop, where each piece of bamboo is tensioned against the next. Water will build its own design to match optimum wave variables. The wing could be adjustable horizontally as well as vertically so the length is manufactured based on the travel input calculations. Lmfao. Just a thought. The Idea Man?
Thanks for this. Love this thinking! Don’t know if it will work. There’s so much potential to be had!
Saving this for tomorrow since my dad keeps thinking its magic and there's a motor somewhere
LOL ... It still seems like magic to me!
@@WakeThief Lol here I am again because he talked about buying a hydrofoil thinking it was an electric surfboard and he forgot about what a hydrofoil is
What is C in your equation??
Lift or drag coefficient
working on the rider weight part of the equation :)
Lol! I totally hear you. I will have three months of no foiling, and no doubt will have to pump a bit faster to accommodate my winter weight! love the comment. Thanks, Seb!
Hi nice video! I think you explained the lift and drag equations very nicely with good examples.
I've got a few questions and idea's:
- Why did you look at the minimum drag in your calculation example and not at the minimum lift-over-drag-ratio?
- The rear wing is there for stability and often does not create lift but downforce. If the foil remains rideable, it might be a good idea to remove the rear wing. This video shows a guy kitefoiling with just a front wing: ruclips.net/video/yn_2a1zl9pQ/видео.html. Maybe gain some inspiration from flying wing planes?
- Creating a wing that glides with very low drag is one goal. But creating a wing that pumps efficiently might be a completely different thing. If you compare the wings of a hummingbird and a soaring type of bird. They look completely different and are used in a different way. This might also be the case for hydrofoils. What do you think the differences in shape between a perfect pumping hydrofoil and a pumping hydrofoil are.
- The human body is made to make certain movements. In you video's you often mention that a wing pumps easier/harder. I can imagine that this has to do with the size and frequency of the strokes that you have to make to pump the foil and how well our body is made to make certain movements. Maybe there is an optimum design for the human body. I like to make the comparison with cyclists. Some like to pedal in a high gear, some like to pedal in a low gear. Maybe there is a biomechanics student living near you that finds foiling interesting? Might be fun to discuss this problem with him/her.
I would love to hear what you think of these ideas.
Keep up the great work. I love to watch your video's!
Webwolf! Where have you been all my life. These are great questions:
(1) Max CL/CD is good too, and will play into it during the periods I'm recoiling the foil to max elevation. I think this is a next level concept beyond just smooth flying at constant AoA. Yes, it needs more attention.
(2) I've tried foiling without rear-wing. It's doable and requires a lot of focus, but I wasn't able to pump. We need the rear wing to increase our elevation when we recoil to max elevation at the top of the pump.
(3) There is no doubt you're right. I can probably learn more by watching birds or tails of dolphins than an airplane. That's where I'm going next.
(4) You're exactly right. I learned about the Strouhal number. This is a dimensionless number that's a function of the frequency of pump, amplitude of pump and the speed I'm moving . Turns out I'm 0.08, which is a bit lower than most flapping/thrusting animals, but my body seems to think it's ideal. I have a more to learn here. I also have learned that there's a propulsive efficiency factor that I need to consider. Thank you for taking the time to comment! You suggest some good paths for me to take next.
@@WakeThief thanks for your reply. Looking forward to the developments. Are you actually planning to build your own foil? That would be epic.
I don’t have the skills to do it, but I’m hoping these learnings can help those who do have the skills.
@@webwolf4 Not until my wife lets me squeeze a CNC machine between the pile of foils in our basement :) Thanks again for the chat. Nice to meet you!
Facebook owner 💯😂
They used a fresh girl board wow
Fresh = 1996 model :) was my last skateboard