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 Post subject: Re: Do the wings even need to be aerofoil shaped?
PostPosted: Sun Jan 19, 2014 5:33 am 
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Kamikuza wrote:
For the small size of hydrofoils, flat vs curved would have negligible difference.


very inaccurate. All foils are curve shaped for a reason. Watch the vid above, proper foil is 4x less drag! Not Negligible.


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 Post subject: Re: Do the wings even need to be aerofoil shaped?
PostPosted: Sun Jan 19, 2014 5:46 am 
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TPink wrote:
Kamikuza wrote:
For the small size of hydrofoils, flat vs curved would have negligible difference.


very inaccurate. All foils are curve shaped for a reason. Watch the vid above, proper foil is 4x less drag! Not Negligible.

I read through a bunch of stuff the other day - it seemed to say for small scale and limited AoA, it doesn't make enough of a difference.

I'd still want proper shaped foil though :D I'll watch the video too.

Skimmed the video - did he ever say what the "units" were?


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 Post subject: Re: Do the wings even need to be aerofoil shaped?
PostPosted: Sun Jan 19, 2014 6:03 am 
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http://www.grc.nasa.gov/WWW/k-12/airplane/foil3.html

Does water too ;)


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 Post subject: Re: Do the wings even need to be aerofoil shaped?
PostPosted: Tue Jan 21, 2014 9:18 pm 
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by other hand the video shows a streamlined body - the foil at zero angle attack - against a flat plate

for "Tone´s foil" to create lift would need to have some angle of attack, but then at this point that body is no longer streamlined

also once there is lift there is extra drag due to lift generation (on top of the drag specifically linked with the physical shape, those shown in the video)

this to say that perhaps kamikuza reading has a point


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 Post subject: Re: Do the wings even need to be aerofoil shaped?
PostPosted: Wed Jan 22, 2014 7:19 am 
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Off the top of my head, the lift to drag of the shaped foil was 10:1 and the flat plate 6:1... for random selected shapes.


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 Post subject: Re: Do the wings even need to be aerofoil shaped?
PostPosted: Wed Jan 22, 2014 10:13 pm 
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Looks like these guys used just flat pieces of wood for their foils and works pretty good:
http://www.youtube.com/watch?v=pWNvY_8krWg

I plan on making a similar foil to the one in the video as soon as the weather warms up.

My 2 cents:
Making a foil shape will get you a better lift to drag ratio, but I think if you are just making a foil to learn on and mess around with for slow speeds a flat piece of wood should work. Trying to get the best lightwind performance, getting good speed, and for racing you need to refine the shape of the foil.


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 Post subject: Re: Do the wings even need to be aerofoil shaped?
PostPosted: Wed Jan 22, 2014 11:24 pm 
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I disagree with making a foil to learn on and mess around with for slow speeds a flat piece of wood should work. Learning will be much harder on a homemade , no shape board foil. You will never know what is wrong the reason you can't get up and foil. That's like learning to drive a car that you built, but you have never driven a car before. not something I would want to do. Maybe after learning to foil, then build one and have an understanding of what to do with it.


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 Post subject: Re: Do the wings even need to be aerofoil shaped?
PostPosted: Thu Jan 23, 2014 3:04 am 
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Arcsrule wrote:
I disagree with making a foil to learn on and mess around with for slow speeds a flat piece of wood should work. Learning will be much harder on a homemade , no shape board foil. You will never know what is wrong the reason you can't get up and foil. That's like learning to drive a car that you built, but you have never driven a car before. not something I would want to do. Maybe after learning to foil, then build one and have an understanding of what to do with it.


Yeah, could be. I'll let you know how it goes.

Before reading through this forum, I was under the impression that you need a meticulously designed wing shape to get this to work. However, the video I posted and the wood hydrofoil that Hawaiis built has shown that flat wood can work.

True, there is the risk that after a day or two of trying, I still won't be riding. I won't know if it is the board or me doing something stupid.

I don't think I'll be endangering myself. The only real risk is that I spend about $100 on a board that doesn't work. Either way I'll video the attempt and should be good for a laugh if I fail :lol:

Also, a youtube comment from the guy who made hydrofoil in the video I posted above:
"The foil is just a piece of plywood with some roughly shaped leading and trailing edges, but not a traditional wing shape at all. I was surprised at how well it worked considering the shape."


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 Post subject: Re: Do the wings even need to be aerofoil shaped?
PostPosted: Wed Jan 29, 2014 1:38 am 
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A flat piece of metal will work quite well. I have used 1/8" 7075-T6 and 6061-T6 aluminum.

One of the main differences between a foiled wing and a flat wing is the flat wing will be more sensitive to stalling. Since stalling in aircraft is catastrophic and structurally challenging, you don't see flat wings on airplanes. But this is not a big deal for a hydrofoil kite board.

Here is a graphic from an easy to read book, Understanding Flight by David Anderson.

Image


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 Post subject: Re: Do the wings even need to be aerofoil shaped?
PostPosted: Mon Feb 03, 2014 2:50 pm 
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The airfoil shape does assist in reducing drag by creating lift at lower angles of attack. However there are many aspects of the hydrofoil wing that are more important than going as fast as possible. Here are a few pictures of my test foils and a description of what I feel are the important factors.


Attachments:
Speedo_Wing_4.jpg
Speedo_Wing_4.jpg [ 538.47 KIB | Viewed 152 times ]
Speedo_Wing_3.jpg
Speedo_Wing_3.jpg [ 1.45 MIB | Viewed 152 times ]
Speedo_Wing_2.jpg
Speedo_Wing_2.jpg [ 2.2 MIB | Viewed 152 times ]
File comment: This was an experiment in stability over speed. The airfoil shape is the eppler 817 with an 8" root cord and 1.5" tip cord. The tips transition to a flat bottom instead of the eppler 817 lower profile. The tips also have a 2 degree nose down rotation for washout. The 3 inch wide center section transitions into drooped wings 15% down. The idea was to prevent ventilation by lowering the tips and a bonus of added stability with excellent rider feedback. This wing is by far better than the stock MHL wing for learning to foil. The same wing built with a thinner profile and covered in carbon is the next project.
Speedo_Wing_1.jpg
Speedo_Wing_1.jpg [ 524.3 KIB | Viewed 152 times ]
File comment: This was my first attempt to replace my stock MHL wing with a high aspect ratio speed wing. It uses an eppler 817 airfoil with a 5" root cord and a 1" tip cord. The core was cut at 50% thickness of the Eppler profile because glassing the core added thickness. The tips are rotated nose down 1 degree to add washout to help prevent tip stalls. This wing is very fast but a little twitchy as mounted in the picture. further testing has shown that mounting this wing in the most forward holes on the T-bar make it a great high speed wing.
Delta_Wing_1.jpg
Delta_Wing_1.jpg [ 968.54 KIB | Viewed 152 times ]
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