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February 20th
ACEA/Guilan Grenier

ACEA/Guilan Grenier

“Platform aerodynamics, I think, made the difference between the American boat and the Kiwi boat.” Tom Speer, wing designer, Oracle Racing

By Kimball Livingston

We could have titled this, Six Extra Feet of Wing, But Do You Know How to Use It?

The way “Fresh” Burns tells the story, and he should know, having been head of performance for Oracle Team USA, there were multiple turning points in Oracle’s desperate, early losing days of the San Francisco America’s Cup. The American boat was losing on every tack, every gybe. Then the Mere Grinders came to the Mighty Chiefs and said something like, “Look, we can tell when the boards are loaded and when they’re not loaded. Why don’t we try moving them when they’re not loaded?”

Boink.

And if you’ve been around even a little while, you’ve heard someone on deck wisecrack, “You just keep grinding, and if I need any sheet, I’ll take it.”

Well, sonny, that’s pretty much how the Oracle crew was sailing USA-17—with hydraulic pressure always on tap—on those upwind legs where the comeback finally kicked in. Nonstop pumping. No-delay trimming. That was the context when Ben Ainslie yelled, “This is it! This is it! Work your arses off!”

Skiff stuff, translated. Advanced Sailing 101.

And then the dazzled Kiwi press went to spinning stories about a “Herbie,” a Boeing-built gyroscopic stabilizing contraption that made quite a good story, if you needed a story. My headline ran, “Bigfoot Sighted on Grassy Knoll.”

These days, Burns commutes between his home in the California wine country and 201 Shipyward Way, Suite B, Newport Beach, CA. That’s the street address of Morrelli & Melvin, where the next design rule is taking shape. If you’re paying attention, you already know the basics: 60-65 feet long, certain components made one-design in the hope of achieving cost savings, fewer restrictions on control surfaces to make the boats, in turn, easier to design, safer to sail, and faster per foot of LOA. Oracle Racing CEO Russell Coutts has gone public with that much, and in my too-cool-for-school fashion I assumed that 60-65 feet was merely a gloss of an already established overall length, to hold something back for the press conference at the release of the next Protocol, presumably in March. Maybe. But when I threw that at Oracle wing designer Tom Speer—returning for 2017— Spear allowed as how, “Actually, I think they’re still working on it.”

Maybe. Tom Speer is a straight shooter when he can be. I think we can take it for granted that it’s a welterish job down at M&M, trying to sort through the gamut of the possibilities for a 2017 AC generation in the wake of all the unintended consequences of the 2013 generation.

ACEA/Guilain Grenier

ACEA/Guilain Grenier

Speer spoke on Wednesday at a noontime gathering on the San Francisco cityfront, addressing wing development over the decades and, inevitably, in Q&A, the comeback. He went so far as to say, “Platform aerodynamics, I think, made the difference between the American boat and the Kiwi boat. We had that pod [below trampoline level] that effectively extended our wingspan two meters. That gave us the potential for the upwind speed that we eventually developed, and platform aerodynamics is the area in which we perhaps can make the biggest performance difference going forward.”

With that potential waiting to be exploited, and New Zealand close to clinching the win in spite of it, another key turning point in the 34th match came, gradually, as Oracle studied how to retrim to add more load to the back of the wing. “The boat had lee helm,” Speer said. “You know that kills upwind speed. It was clear that we needed to retrim, so we raked the wing aft—and no, that didn’t work. It turned out that when we powered-off the upper elements—when we added twist aloft—the center of effort shifted down and forward. There was no relief in that. So instead we opened the slot. That gave us less lift on the main element and more lift on the flap [which funnels air aft]. Over the course of the regatta we increased the traveler load by 50 percent. That eliminated lee helm, helped the boat point, and simply made us faster upwind.

“So, it was a bunch of boat-tune things that turned it around for us. Look at any one-design fleet, and the difference between the front and the back is huge. Most of that is fine tuning.”

Before we leave the subject of “slot,” we should listen to Tom Spear describe the effect of the slot from an engineer’s point of view. Here goes: “The slot allows you to go to a higher maximum lift because of the behavior of the boundary layer, which is where all your skin-friction losses occur. The boundary layer is thin, but it wants to get stuck to the wing and not move. Meanwhile, at the leading edge of the wing, the pressure is very low. Toward the trailing edge, pressure increases. There is a tendency to push the boundary layer toward lower pressure—push it forward on the wing—and that’s where you get flow separating from the surface and a big dropoff in lift. With a slot-and-flap arrangement, you are basically dumping slow air from the lead element into high-velocity air around the flap. Or, let’s say that you are taking one bottom layer and handing it off to a fresh bottom layer on the flap.”

Wings have been a fascination in this space for years, but in Spear’s figuring, “Wing development has hit a plateau. [in only one AC cycle, after decades in C-cats and A-cats!]. Given the motivation to control costs, it’s likely the next design rule will constrain the design of the wing so that teams don’t have to spend so much in that area.” Again, if you’ve been paying attention, you’ve heard the talk in high places about making all or, more likely, parts of the wing one design.

NEXT:
Control. Control. Control. Another just-in-time for Oracle, and the hydro that bit New Zealand.

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This article was syndicated from BLUE PLANET TIMES

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