Page 3 of 4

Re: Do the wings even need to be aerofoil shaped?

Posted: Sun Jan 19, 2014 5:33 am
by TPink
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.

Re: Do the wings even need to be aerofoil shaped?

Posted: Sun Jan 19, 2014 5:46 am
by Kamikuza
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?

Re: Do the wings even need to be aerofoil shaped?

Posted: Sun Jan 19, 2014 6:03 am
by Kamikuza

Re: Do the wings even need to be aerofoil shaped?

Posted: Tue Jan 21, 2014 9:18 pm
by Tiago1973
by other hand the video shows a streamlined body - the foil at zero angle attack - against a flat plate

for "ToneĀ“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

Re: Do the wings even need to be aerofoil shaped?

Posted: Wed Jan 22, 2014 7:19 am
by Kamikuza
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.

Re: Do the wings even need to be aerofoil shaped?

Posted: Wed Jan 22, 2014 10:13 pm
by davesails7
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.

Re: Do the wings even need to be aerofoil shaped?

Posted: Wed Jan 22, 2014 11:24 pm
by Arcsrule
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.

Re: Do the wings even need to be aerofoil shaped?

Posted: Thu Jan 23, 2014 3:04 am
by davesails7
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."

Re: Do the wings even need to be aerofoil shaped?

Posted: Wed Jan 29, 2014 1:38 am
by don pitcher
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

Re: Do the wings even need to be aerofoil shaped?

Posted: Mon Feb 03, 2014 2:50 pm
by dlprince69
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.