AC72 wing sail design
For the America’s Cup in San Francisco, the AC72 catamarans have to be able to race in winds from 5 to 33 knots (6-38 mph). Since they can race in 5 knots, in strong wind they will be seriously overpowered.
Controlling the power
The AC72 wing sail control systems allow the wing to be depowered by adjusting the flaps and the camber.
To make things more complex, the windspeed can vary by over 10 knots from the water to the top of the AC72’s 40 meter (130 feet) tall wing sail. There are multiple flaps on the trailing element of the AC72 wing. These can be trimmed separately, putting “twist” into to the wing’s shape. It appears that New Zealand and Luna Rossa (who shared the same design in the first phase of development) can also twist their wing sail’s leading element.
Artemis took a different approach with their first wing, with a with a wider forward element and narrower flaps. Their second wing is much closer to the other teams’ with wider flaps.
Trading off control and complexity
Emirates Team New Zealand designed their wing with a twist control for the forward element. As of 21 March 2013, we have not seen whether Artemis‘s forward element twists. USA 17, Oracle Team USA’s boat, does not have a twisting forward element, but, like Artemis, it does have a movable “tab” on the leading element.
We’ll get into more details of each team’s wing as time goes by.
Background on aerodynamics
A.M.O. Smith “Wright Brothers Lecture” – a classic in the science of high lift aerrodynamics. Don’t let all the greek letters and formulas put you off – skim through this and you’ll understand wings (and hydrofoils) better.
Updated 22 March 2013 by Jack Griffin