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Pumping foil section/airfoil?

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jaros
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Pumping foil section/airfoil?

Postby jaros » Sat Apr 25, 2020 6:14 am

Hi,
Does anybody know what kind of airfoil is used on a current day pumping surf foil?
Thanx!

nixmatters
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Re: Pumping foil section/airfoil?

Postby nixmatters » Sun Jul 12, 2020 8:25 pm

I was just about to post a similar query, but had the patience to scroll through the search results till I ended up here.

Jaros, have you found any helpful info meanwhile? Thanks!

jaros
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Re: Pumping foil section/airfoil?

Postby jaros » Sun Jul 12, 2020 9:19 pm

No, nothing. Sorry. Still interested...

fluidity
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Re: Pumping foil section/airfoil?

Postby fluidity » Mon Jul 13, 2020 6:32 am

Jaros, There's a Gong video on line somewhere explaining regular pumping and some gull wing shaped new foil the designer says pumps better side to side(think ripstick or sketeboard)
He says that thin foils need slower pumping over more distance than thicker foils.
I think most of the foils are pretty traditional in having a longer curvier surface at the top. I designed one and I'm cladding the front and back wings at the moment after 3D printing. I suspect it's going to behave about as well as any other foil wing out there with matching aspect ratio and chord. It's all about pressure differential caused by faster flow over the top. This will be my first :-)

Erinhdisc
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Re: Pumping foil section/airfoil?

Postby Erinhdisc » Sun Sep 27, 2020 6:54 pm

It seems there is some dispute over the differential flow theory. Angle of attack and displacement are larger factors.

fluidity
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Posts: 278
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Local Beach: Ngati Toa, Plimmerton, Titahi Bay, Waikanae, Petone, Seatoun, Lyall Bay, Eastbourne, Lake Wairarapa
Favorite Beaches: Plimmerton
Style: Wave, jump
Gear: Late model Switch kites element and nitros,
DIY CAD ultra-concave wave twintips 1500 and 130mm with my own fin designs. Easy upwind, awesome carving. Switch Nitro 10m V7, Naish 5.3m Wing. Now focussing on Wingsurfing to rise to a new challenge. Building my own foils from my CAD design and 3D prints, built a CNC machine last year and now cutting designs with CNC as well as 3D printing.
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Re: Pumping foil section/airfoil?

Postby fluidity » Thu Oct 01, 2020 8:41 am

Erinhdisc wrote:
Sun Sep 27, 2020 6:54 pm
It seems there is some dispute over the differential flow theory. Angle of attack and displacement are larger factors.
I almost clicked on that video in another list on youtube last night.
It does do a nice quick summary of the history and thoughts on hydrofoils.
Airfoils are designed differently for supersonic.

In any case in both water and air, when people talk about low pressure, that pressure is totally reliant on atmospheric pressure from what gravity exerts on the air between any airborn wing and space. In water, you add the water pressure from the foil depth level to the air pressure at water level to get the total average working pressure. You can therefore theorise that a foil will be more cavitation resistant at lower altitudes and deeper under water.

When we slide a kiteboard sideways like a surface wing, we have mostly the effect of the inertia of water resisting moving down and in that water resisting that downward pressure for a moment, we get lift on our board.

I think for a submerged wing, the pressure above the wing has subtracted from it the force we impart by redirecting that water on top downwards also. In effect, approximately doubling our water mass displacement lift by working on both top and bottom surfaces at the same time. It's the combined atmospheric and water pressures AND gravity that cause the water not to simply separate and stay separated. This does align somewhat with what she said in the video near the end though I feel like she missed something in her explanation. However those two combined forces can't be telling the whole story unless hydrofoil manufacturers have it very wrong utilising similar wing shapes to air wings.


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