Foil design idea

[yenice]

I do not know if this has been discussed somewhere in this forum before, if so I apologize for the repetition.

I am thinking of building a beginner hydrofoil to learn wingfoiling. There will be no jumping. So, the front wing will be a large one.

Mast with carbon and as stiff as I can make,

Fuselage of carbon or aluminium and as stiff as it can be,

Front wing: carbon sandwich with epoxy lamination is an option most people use but I have another idea that can flex and therefore made of fiberglass lamination on a foam core material. Maybe the section of the wing that meets the fuselage will be of carbon patches made for stiffness but this carbon area will turn to glass as we move away from fuselage connection section of the wing, towards the tips on both sides. Therefore, most of the wing will actually be made of glass, and it will benefit:

Reduced cost and weight
Increased flexibility under increased loads, resulting in reduced drag and increased stability.

https://simpleflying.com/boeing-787-win ... -take-off/

I know the possibility of getting a damage if I hit a rock or debris in the water but let's consider this as a risk I can take.

I would like to get the opinions of members of this forum on this flexible wing idea.

[evan]

I doubt you can apply those aeroplane physics to a hydrofoil wing as they use the flex to curve the dyhedral (upward curved) wing into winglets. Main efficiency gains are coming from the weight savings, something you won't notice on a hydrofoil as those few grams diffence won't make a big impact on acceleration compared to the drag of water where a lighter aeroplane saves a lot of fuel on the climb to cruising altitude.

You don't want an upward curved main wing as you will run into problems with the wingtips penetrating the surface.

[yenice]

Foil flex movements

When the foil is pumped down, tips start moving less than the middle of the wing. The start of the wing tips depth is already below surface anyway. Tips do not reach the surface by this pump-down action.

When the foil is pumped up, tips move less than the middle towards water surface. Again, no risk of surfacing.

If a part of the wing would surface, that would be the middle section first.

If, on the other hand, the rider makes a turn in water, the foil tips are curved towards mast, so the surfacing could be possible or not, depending on the depth of the middle of the wing and magnitude of the forces in action, due to speed, weight and the radius of the turning action.

When I think of the slow motion of the fish and the birds in action, their bodies are not solid forms like our hydrofoils. Instead, their bodies change shape according to action and forces acting against them. And they are very efficient in flying and swimming, so I guess being not solid as a stone, is not a bad idea for these animals.

When I think of hydrofoils, I understand the mast needs to be solid as a stone can be, but the rest, especially the wings, why not to make them to bend according to the drag they receive a little? After all, the power of a tree withstanding of a storm comes from its fexing capabilities too, as well as the quality of its roots to grab the soil.

Please see the 2:35 of the following video. The tails of the whale is very similar to our foil forms and the flex of the tails is what I mean.



Of course it is not so easy to achieve the correct amount of the flex by construction. Too much flex and the foil looses power, too little flex and flex is not there to change anything.

Another detail I have in mind is not only the flex from middle to tips but also the flex from the front to back of the wings too. As the cross section of a wing gets smaller from front to back, this second type of flex is possible to be achieved by contruction. At least in concept.

[fluidity]

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. Learner foils are usually thick and slow, not super responsive any way. if you are making your mast and fuselage, make the big front wing connection very robust. 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.

[tmcfarla]

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.
2.) airplanes and hydrofoils are optimized for very different things, so trying to apply principles from one to the other is tricky. Airplanes are optimized for excellent lift to drag and stability, and they also get to change their wing shape during flight.
3.) Making a part out of carbon with reliable flex properties in you garage is really difficult. Most garage carbon builds just use enough carbon to be bomb-proof, and really stiff.

Not trying to talk you out of your project, just a dose of reality of what you are getting yourself into. It can be a really great hobby, but like any hobby, you spend money to participate in it, and the goal is the activity itself, not the result. You will not get a better and cheaper wing than what you can buy. It is totally worth the time and money if you will enjoy working with carbon and designing wings, but if your goal is to get out and ride, just buy something for a reputable manufacturer.

[Bille]

...

Please see the 2:35 of the following video. The tails of the whale is very similar to our foil forms and the flex of the tails is what I mean.

...Humpbacks dance...

Such Awesome creatures ; thanks for posting !!

Was surfing Blacks-Beach in San Diego , back in the 80's ; had
one of those beauties surface less that 20-M from myself, and
the buddy I was surfing with !!
It was a Glorious day ; Bottlenose dolphin's riding 12' waves
with us, and the Humpback surfacing so close ,(it don't get Better) !!!

The Beer & pot ; they hand No effect, later that day.

Bille

[Bille]

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

[yenice]

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.

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.

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. 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.

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.

Half of the wing

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 But of course, would consider the steps to make it better anyway even for the first prototype.

[yenice]

What I am worried about is the combination of glass and carbon. The following post in a German language forum has the translation:

"I am also critical of the combination of glass and carbon under high loads. The glass is much more elastic, it hardly bears any forces when combined with carbon."

https://oaseforum.de/showpost.php?p=144 ... stcount=38

Any ideas on how I can solve that problem?

[downunder]

^
It does not exist. Trust me, rather spend time on the water than time on this since the prices are not that high. For used gear, that is.

Almost no one is building anything any more because carbon is sooo expensive. Plus other bits and things. Sure it is great to use your own stuff because you can. Im all for it. But now we can buy almost new CF Raptor board for 400 AU$, complete. I cant build it for that money.

Up to you. Find something and replicate first. Than start tweaking it.

PS
And what does a tail do for fish or whale?
Its is the engine, correct? Why do we need it than when is not the engine?
So we really need an stingray