Progression of the Bi-Directional Hydrofoil

[don pitcher]

Hats off to Hawaiis for progressing the bi-directional hydrofoil and improving the ease and cost of do-it-yourself.

Some have said,

Why would one want to make a TT hydrofoil? It will always be inferior (less efficient) compared directional hydrofoils

A bi-directional hydrofoil will never be as efficient as a directional, but there is a significant negative aspect to conventional hydrofoils, jibing. Some people find surfboards fun, while the majority of kite surfers are annoyed by having to jibe them and don't have the time, skill, or patience to learn how to jibe, so they use a twin tip.

I think the same is true with hydrofoils. Yes, there is an efficiency trade-off, but if the trade-off can be minimized thru continual development, then there will be a market for people that want to ride over the chop instead of thru it and have good lightwind ability, while not having to learn how to jibe or get wet every tack.

I think Hawaiis progression will help make this a product that will eventually come to market, especially if the cost is much less than current hydrofoils.

Here is my understanding of the history of bi-directional hydrofoil kite board (please correct me if I miss something).


chemosavi surfacing bi-directional hydrofoil (~2005)
viewtopic.php?f=1&t=2361561&start=11




Barney Townsend surfacing bi-directional hydrofoil (~2008)
viewtopic.php?f=1&t=2361561




don pitcher low cost bi-directional hydrofoil attempt (2008)




Wavy 2013 Hydrofoil




SURFFOILS
viewtopic.php?f=1&t=2361561&start=73




Hawaiis low cost bi-directional hydrofoil (2013)


http://vimeo.com/81259824



I find this exciting. I hope this progression continues. I Hope more people jump into progressing this idea and low cost hydrofoils in general.

[Bille]

...

A bi-directional hydrofoil will never be as efficient as a directional, but there is a significant negative aspect to conventional hydrofoils, jibing. Some people find surfboards fun, while the majority of kite surfers are annoyed by having to jibe them and don't have the time, skill, or patience to learn how to jibe, so they use a twin tip.
...

Thumb's Up on That one !!!

It would be a pretty Sad world, if Everyone was into the same thing. Like with a HG, most
people are Just into XC and racing around turn-points ; I HATE it, and all i wanna do is ACRO.

Same goes for kiting ; some like Racing, other people are into Free-style. Personally, i thought
learning to ride a surfboard on a lake, was a pain in the Butt, but i did it so i could go on a hydrofoil.

It kinda looks like with this bi-directional Hydrofoil, i won't need to jibe any longer, and that sounds
just FINE to Me !!!

Seriously , if this Bi-directional thing works out, it's gonna add an entire new
dimension to Free-style , with a jump-ramp that's always Under your board !!!

Bille

[Hawaiis]

Don:
Thank you for providing the useful information leading to this point.
Could not have done it without the help of all you guys

Mahalo

[Hawaiis]

Here is another missing link

[Peter_Frank]

Awesome to see all the "stages" and different ways of doing it (and also those not really working maybe)

Great creativity, and impossible to see where we "end up".

See also this post: viewtopic.php?f=1&t=2361561

Peter

[TopLine]

From what I am seeing and hearing around the place - foils are a hot subject. I have just ordered my first Directional foil and board from a reputable dealer/maker and am very keen to hit the water. I would consider myself like most seasoned kiter's, happy to purchase products and hand over my hard earned cash if the product is already working and appealing to the user for the conditions it is designed for.

I like the feeds you guys have put on here regarding the twin tip foil, I think it has merit and would be a product people would want if as I stated before it can be proven to a certain degree that for "most of us" we are happy to hand over our fun tickets and get it out on the water.

For now with myself and my other racing mates, we are all about going fast either just on the water and more so around the race course. Directional style race boards are obviously the most popular for course racing and even more so with the IKA ruling and Olympic race style potential. Twin tip foil style boards would open up the potential for as mentioned before the market of kiter's that are not into gybing or have trouble with foot switch moves on the moving board. It can definitely make the foil experience able for all to enjoy. Biggest factor as I mentioned before is cost $$$$ It's currently a big investment from your pocket and time on the water to get into it.

[ronnie]

This is an interesting study of elliptical aerofoils and the influence of angle of attack, thickness to chord ratio, Reynolds Number etc.

The most interesting stuff seemed to start about page 73. it seems to show that a thickness/chord ratio of about 0.09 while giving better lift up to about 7 degrees has a stall angle below 8 degrees angle of attack, whereas a t/c ratio of from 0.18 and up has a stall angle of 17 degrees.
It might also allow for using this info to adapt the foil to higher speeds, so some of the foil would produce high lift at low angles of attack and maybe other parts produce low lift at low angles of attack (such as a flat plate).

They are also showing the effect of 'tripping' the flow (or tripped flow), which seems to affect the turbulence produced at the downstream end of the ellipse.

It may be relevant to the twintip foil because it is a bi-directional aerofoil.

https://mospace.umsystem.edu/xmlui/bits ... sequence=1

[ronnie]

This shows the lift/drag for a flat plate at various angles of attack.

What I'm thinking is that maybe a flat plate with an ellipse moulded onto the top an bottom surfaces over part of the width would give a combination of lifts that would be efficient at low angles of attack and high speed, but compensate for the more sudden stall of the 0.12 t/c elliptical aerofoil (which seems to have the highest lift) because the plate is going to be providing a higher portion of the lift as the angle increases.

http://www.atkinsopht.com/row/liftdrag.htm

[cglazier]

It is good to see people trying things... Have fun with your twin tip experiments.

Some people find surfboards fun, while the majority of kite surfers are annoyed by having to jibe them and don't have the time, skill, or patience to learn how to jibe, so they use a twin tip.

I have been riding a directional hydrofoil for several years and you do NOT need to gybe them. It is not difficult to simply turn and then ride toe side (while staying up on the foil). By simply riding heel side and then toe side you can go back and forth while staying up on the foil indefinitely.

I suggest that you will enjoy doing transitions this way on your "twin tip" hydrofoil so your foil will always go in one direction and this will allow you to use a more efficient directional hydrofoil design.

Of course the gybe and tack are good to learn eventually.

CG

[TopLine]

Gybing and tacking a directional is a must for the race course. It's difficult but not impossible.. The challenge of learning and mastering new board types and styles of riding has motivated me so much in the last couple of years.

I would be interested to see a really good Twin tip foil design come through onto the market??