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Foil design idea

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tomtom
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Re: Foil design idea

Postby tomtom » Mon Mar 21, 2022 12:15 am

I like that he want to explore new possibilities. There is something about flex. I can made interface for more effcient energy transfer. PM me. I know a lot about flexible composite structures. But you need somebody with deep aero/hydro knowledge to execute this

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Re: Foil design idea

Postby Trent hink » Mon Mar 21, 2022 1:09 am

My comment might be a bit naive, but I have no doubt that there exists the possiblity for a great deal of improvement in our modern hydrofoils, so this idea is definitely worth pursuing.

One of the things I notice when I look at natural examples of wings and fins, is that not only does the shape often change, but also the angle of attack.

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Re: Foil design idea

Postby tomtom » Mon Mar 21, 2022 1:29 am

Trent hink wrote:
Mon Mar 21, 2022 1:09 am
My comment might be a bit naive, but I have no doubt that there exists the possiblity for a great deal of improvement in our modern hydrofoils, so this idea is definitely worth pursuing.

One of the things I notice when I look at natural examples of wings and fins, is that not only does the shape often change, but also the angle of attack.
What flex and other non rigid structures do in nature is equivalent of matching of impedance in electric circuits. It is there for better and more efficient energy transfer from muscles to media /air/water/.
To usefully utilize this is quite non trivial and will require many prototypes, metodical testing and preferably sort of generative design software support.

All of this had nature in disposition in evolution process.

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Re: Foil design idea

Postby fluidity » Wed Mar 23, 2022 8:43 am

yenice wrote:
Sun Mar 20, 2022 11:40 am
fluidity wrote:
Sun Mar 20, 2022 2:15 am
Yenice, you need to keep in mind that most of the development of flex in any flexible materials on the front wing when you are foiling will be from your own weight. The current pumping motion people employ is to push down on the board to lift themselves up, deweight the front first so that forward motion will then drive the foil up, then as you come down from your jump, land on the front first and glide down and forward.
I agree with your explanation above. Let us consider now that all your explained actions are transferred by means of board->mast to the foil as a whole. Then the foil system is like a whale doing these actions by his muscles and skeleton. Front-wing deflects somewhat as the forces of drive and drag change on it to a certain degree, but the deflection increases towards trailing edge of the wing and also towards the tips of the wing on both sides of the wing more. In order to facilitate this, I need to have a very stiff and solid area near the Mast-Wing connection section of the wing, but this stiffness needs to be decreased gradually towards the tips of the wing on both sides. In order to achieve it, I consider to build the front wing as follows:

Full fiberglass lamination on top and on bottom of the wing, keeping flexibility in mind.
Carbon lamination on top and also on the bottom of the wing ONLY near the center line of the wing with patches of decreasing area to the surface of the wing. That way the forces coming from the mast will be transferred uniformly without any local stress concentrations and they will also first meet a very stiff section of the wing, with stiffness decreasing uniformly as geometry gets further away from the center of the wing, increasing flexibility as distance from center increases.

http://nickflutter.blogspot.com/2011/01 ... t.html?m=1

This website shows a method to make the trailing edge of the foil wing flexible by means of a hinge. What if the trailing edge flexes without any hinge, because its core cross section gets progressively smaller in area (airfoil shape or a drop of water in free fall) and the glass lamination over that core is made flexible too.
fluidity wrote:
Sun Mar 20, 2022 2:15 am
Yenice, .. Learner foils are usually thick and slow, not super responsive any way. ...


My flexing-wing idea is an attempt to make these qualities of the learner foils improved. How much improvement is possible? I do not know.



fluidity wrote:
Sun Mar 20, 2022 2:15 am
Yenice, .. You can use a square 12mm Titanium section of about 400mm long to the stabiliser from a stub fuselage with about 200mm stronger, from the rear of the back of the mast if you like, this will give you small tail flex and pumping drive from just pulsing your back foot and not doing much else.
Thank you very much for those lines. I understand that your proposal is to make the fuselage between mast-joint and rear wing also flexible. This much I have not thought before. :idea: The rear wing would than act as if the tail of a whale indeed. But I did not understand the details you mentioned. Would you please make a simple sketch or something for me to grab the details? As English is not my mother language, I am having a hard time to grab your remarks fully. :roll:
tmcfarla wrote: 1.) since you mentioned “reduced cost” as a reason for building your own, be aware that you are probably going to spend more money for something that, at best, rides half as well as an off-the-shelf foil. Working with cf is hard, and you aren’t going to do it right the first time. Designing wings is hard, won’t do that right the first time either.
What I meant by reduced cost:
"Cost of full carbon wing" > "Cost of full glass wing with some local carbon patches"

The rest is the price I may be willing to pay for my DIY enjoyments. After 50 years of DIY, I know what that means.

Wing half.jpg

Bille wrote: For the spar in your wing :
I recommend No core on the spar itself ; I would use Uni
on both sides of +-45 glass instead , or the core will
just break down after 20,000 cycles of bending.

The foam core can go in front, and behind the spar though .

Bille
I wish I could be so near to a whale myself, without disturbing their living. You are lucky to be one of a few to have done it. Such an occasion would be a very happy memory for me too.

What do you mean by "spar" I do not get. If my first foil experiment would survive 20k cycles, I would consider it a very successful first prototype :lol: But of course, would consider the steps to make it better anyway even for the first prototype.
It's my belief that your idea lacks the refinements to achieve your goal. Consider that a distorted wing of your concept looses it's designed foil shape and efficiency.
Wakethief did a semi hinged tail which is one solution, I don't think he felt it was efficient enough though. My solution with a flex rear end fuselage in 12mm titainum square rod would give you Wakethief's effect but in a more flowing design. You need to consider that a good wing shape is critical to efficiency and a front wing is designed as a best effort for the designer to fit a particular use case range. The pumping motion that experienced foiler use employs a wing's designed shape to very good effect, I think you're trying to provide a solution to a problem that doesn't exist without sufficient time considering wing eficiency vs wing distortion and rider load deformation of your solution.

However, personally I really value my ideas that didn't work, I learn something each time and if you have a vision, try it out! Best case it works, worst case you wasted some materials but gained a lot of knowlege that you'd be unlikely to learn any other way. Holding something in your hands, having it under your feet, that will give you practical understandings and intuitions that I can't pass on to you with the same authority you will get by trying your self! Importantly though, keep your end foiling goal in sight, it's worth it!

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Re: Foil design idea

Postby fluidity » Wed Mar 23, 2022 8:50 am

tomtom wrote:
Mon Mar 21, 2022 12:15 am
I like that he want to explore new possibilities. There is something about flex. I can made interface for more effcient energy transfer. PM me. I know a lot about flexible composite structures. But you need somebody with deep aero/hydro knowledge to execute this
You're right and personally I've found flex with composites interesting too. Fibre layup is critical to flex characteristics as is the compression and tension fibre selection. Do keep in mind that at the flexure extremes the foil will be highly distorted or so non-high-aspect ratio that it might resemble a flipper more than a hydrofoil. Speed and pumping frequency change with ability and foil type, our thread author is at the start of his journey and will benefit from getting away from the drawing board and in the water above a foil... :)

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Re: Foil design idea

Postby Schietwedder » Wed Mar 23, 2022 4:31 pm

I know that there exists some engineers in americas cup that did a lot of research with fluid structure interaction (FSI) on foils. Hard to get insights there and also the calculations are nowadays often fully automised optimisation algorithms or VPP simulators. The design/optimisation goals differ as well probably.

Also in scientiffic wind energy and sailplane literature you find some papers about flexible wings and fluid structure interaction.
Flutter has to do with it as well. A lot has been written there!

Good luck and looking forward to see some results!
Guess there is two main optimisation directions for a flexible foil.... flexible on bending or flexible on torsion, both interesting aspects with totaly different design outcomes.
Torsional stiffness is probably based on profile moment of the airfoil as well as center of torsional stiffnes/location of shear web in chord percentage
Bending stiffness more a question of overall fibre layup with as less unidirectional fibres in span direction as possible but large enough torsional stiffness.

Interesting!

In terms of Simulation what you describe sounds highly non-linear and dynamic as well plus the fact that fluid structure interaction is one of the most expensive and time consuming fields in simulation/numerical modelling.
So probably such complex tasks have to be reduced so far in the modelling stage that the outcome might not have to do anything with the reality. Let alone parametric studies to understand more about it.
So if something is gonna be found out its only possible by practical trial and error as you plan to do is my guess!
Never the less a good research can save numerous prototypes.

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Re: Foil design idea

Postby Trent hink » Thu Mar 24, 2022 12:13 am

tomtom wrote:
Mon Mar 21, 2022 1:29 am
Trent hink wrote:
Mon Mar 21, 2022 1:09 am
My comment might be a bit naive, but I have no doubt that there exists the possiblity for a great deal of improvement in our modern hydrofoils, so this idea is definitely worth pursuing.

One of the things I notice when I look at natural examples of wings and fins, is that not only does the shape often change, but also the angle of attack.
What flex and other non rigid structures do in nature is equivalent of matching of impedance in electric circuits. It is there for better and more efficient energy transfer from muscles to media /air/water/.
To usefully utilize this is quite non trivial and will require many prototypes, metodical testing and preferably sort of generative design software support.

All of this had nature in disposition in evolution process.
Ok, my comment is totally naive... And I completely agree about what I am dreaming about being non trivial!

In evolutionary terms the modern kite hydrofoil has only just arrived. What is it... 10-15 years old at best? There were very early examples in the 90's, but it took a long time to even imagine that they might work for kiting, and a long time to make them actually work for the common user.

So maybe, eventually, the machines we use can evolve just like nature...

This does not mean that there is no point thinking about it now, and perhaps... Quite the opposite....

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Re: Foil design idea

Postby tomtom » Thu Mar 24, 2022 12:12 pm

Just to be sure we are all on same boat. I do think that pumping a foil will benefit from flexible interface. I do not think that externally powered foil /i.e. kite/ will benefit from it.
I want to write PM, for OP but maybe we start discussion here.

I see two point where flex can be beneficial to pumpable foil.

A. Main wing for energy store and gradually release. Think about that in this way. Same energy - the longer and slower stroke to pump the more efficient transfer will be. So pump - load the wing and wing will release loaded energy on longer stroke.
B. Stabilizer AOA. While pumping stab is often in AOA position where it cause a lot of drag. Auto adjustable stab AOA will imo help.

Now about execution. of A.

We pump at some frequency let says 1hz. The resonant frequency FS with your weight in this flex mode in water should be close to this - because you need to be close to resonance to achieve best efficiency. /max amplitude at lowest force/
Same as jumping to trampoline. If trampoline FS is too high you will not be able to use it for jumping higher. Other thing is this resonance Q, which will describe how broad or narrow resonance peak IS. Dampened resonance /low Q/ will have lower amplitude resonance but at broader range of frequencies - So it somehow work even in some range above and bellow FS but it not so prominent at FS. Undampened /hiqh Q/ resonance is exact opposite. There is optimum for this for most efficient pumping and you can aim for this optimum by composite layout.

High aspect long span wing are good candidate for such energies store and release.

I can help with design composite layout do achieve desired parameters.

Unfortunately i cannot design wing itself - we need hydro aero specialist here. But to act as spring wing must be preferably long span and thin. Also not foam cored.

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Re: Foil design idea

Postby Schietwedder » Thu Mar 24, 2022 12:47 pm

Not a fluid mechanics expert, but naval architect...
When computing this resonance problem not only the structural mass is to be taken into account but also the hydrodynamic added mass (and damping)of the foil hast to be calculated.
An excerpt from ship vibration course for a underwater tidal turbine:
added mass.JPG
added mass2.JPG
added mass2.JPG (13.87 KiB) Viewed 1433 times
With rudder height AR is ment (because chord length is 1)

Hydrodynamic damping:
https://ntnuopen.ntnu.no/ntnu-xmlui/han ... 50/2596883
https://iopscience.iop.org/article/10.1 ... 032044/pdf

both saying that damping is linear to velocity. At the low velocities on a pumping hydrofoil, I would neglect damping to start simple.

Maybe that helps, on stiffness matrix you´re the expert @tomtom

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Re: Foil design idea

Postby yenice » Thu Mar 24, 2022 9:43 pm

Screenshot_2022-03-24-23-24-15.png
Fluke flexibility of a whale
Source research downloadable from:

https://www.researchgate.net/figure/Suc ... _239905938


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