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 Post subject: AC72 foil
PostPosted: Wed Sep 25, 2013 7:07 am 
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It's called a J-foil, there efficient enough because Sail-Rocked used one.
Does Anyone know what airfoil they use on the wing part of the AC72 ?

Bille


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 Post subject: Re: AC72 foil
PostPosted: Wed Sep 25, 2013 9:21 am 
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It is not a conventional J foil sin the foil section attachment to the board is almost at a 90 degree angle. It is an acute L foil based on this http://carbonicboats.blogspot.dk/2013/0 ... -soup.html

From the on-board footage it looks to be a fairly high aspect ratio foil with a shallow profile. The outline is a bit special and I think I have seen two different on the Oracle boat.


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 Post subject: Re: AC72 foil
PostPosted: Wed Sep 25, 2013 7:18 pm 
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It's very different to the foil sail rocket uses. The AC72 foil is made so the the tip points "up" when the board is down and canted. When the tip pierces the surface it reduces the lift, and cavitates the top of the L/V on the foil. Sail rockets foils are all about preventing cavitation which happens at around 50 knots. You can see it happening here The water starts to boil on the high pressure side and it's game over.


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 Post subject: Re: AC72 foil
PostPosted: Sat Sep 28, 2013 4:50 am 
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ozchrisb wrote:
Sail rockets foils are all about preventing cavitation which happens at around 50 knots.

The water starts to boil on the high pressure side and it's game over.


Cavitation is from low pressure, not high pressure. The top of a hydrofoil is the low pressure side. High pressure stops water from boiling.

This is the second time I've seen someone state that cavitation happens at 50 knots. Are you saying that the particular foil on sailrocket cavitates at 50 knots? There is a speed when cavitation will happen for a particular foil at a particular angle of attack, but there is no single speed where all foils will cavitate.


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 Post subject: Re: AC72 foil
PostPosted: Sat Sep 28, 2013 2:13 pm 
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Maybe they get that from Spithill at a press conference. Spithill said something like that the rudder foil, being fixed, cavitates around 50mph. He said if they could adjust the rudder angle on the fly, they could hit 60mph in the AC72

But yeah, that is a particular foil at particular speed, not a general rule.

- Stafford


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