In recent weeks we have seen the first AC75s start to fly, but the engineering and sailing techniques needed to get these new monohulls to foil are very different to the catamarans of the previous Cup cyclesFlaps on the T-foils is a big change for this Cup. Photo: Harry KH \/ Ineos Team UKAmerica\u2019s Cup teams first flew in San Francisco in 2013. The use of hydrofoils to lift the AC72 catamarans out of the water was a Team New Zealand innovation, despite a class rule that was written to keep the boats in the water. This time around the AC75 rule definitely intends us to fly, and the foils will be a focus for the team right from the launch.
\n\u201cThe hydrofoils on a Cup boat work exactly as on an aircraft wing: you have the asymmetric flow around the wing or foil, which creates a pressure difference. That then generates a force that\u2019s trying to equalise the difference. The force lifts the plane off the ground \u2013 or the boat out of the water, in our case,\u201d explained Ben Ainslie.
\nThe central innovation in those early days was shaping the daggerboard into a foil that could provide both lift and leeway resistance. The problem was how to control the lift sufficiently well to enable stable flight.\u00a0The AC72 design rules forbid any part of the foil to move independently, so the Kiwis couldn\u2019t use flaps to control lift. These are the adjustable trailing edges, just as a pilot uses to control the lift generated by an aircraft wing.<\/p>\n
Trailing edge
\nThe design rule for the AC50s in Bermuda also forbade the use of flaps, but this time around, they\u2019re allowed. This is one of the biggest differences with the AC75 rule; it has ushered in a new era in foiling Cup-boats by specifically allowing flaps on the T-shaped foils.
\n\u201cWe will have direct control of the flap on the trailing edge of the T-foil,\u201d explained Ainslie. \u201cMoving the flap down will create more lift and more drag, but the lift is good for creating take-off. Moving the flap up to come more in line with the rest of the foil will reduce the lift and drag, which is then good for higher speed. It\u2019s finding that trade-off really.\u201d
\nThe flap is a much more efficient way to control lift than moving the whole foil, and it\u2019s no surprise that it\u2019s been allowed for the AC75. Now we\u2019re back to racing monohulls, which have a lot less stability at rest and slow speeds when the foils are not supplying any righting moment. The control systems will need to be more efficient to fly these boats compared to the AC50.
\n\u201cIt\u2019s [the AC75] got some form stability from the hull,\u201d said Ainslie, \u201cbut after that it\u2019s reliant on the lift from the wings and the foil arm to give the boat the righting moment. We think \u2013 we hope \u2013 we\u2019ve got a good idea of how this is going to play out and what sort of speed we need to create righting moment and ultimately to take-off.
\n\u201cWithout a lead keel you\u2019ve got to be very, very careful about how you power up the boat, how you create the speed, what angles you sail to create the speed.\u00a0The simulator has been really critical to developing the techniques, both for the designers and for the sailors,\u201d explains Ainslie.
\n\u201cWhat sorts of forces do we need to get the boat flying in the first place? What techniques do we employ? What settings do we employ? We can then incorporate that [information] into our test programme and flight programme for getting RB1, as we call the first AC75, out on the water and sailing and foiling.
\nArticle continues below\u2026<\/p>\n
\t\t\t\t\t\tRoad to the America\u2019s Cup podcast episode 1: Imagining the AC75<\/p>\n
\t\t\t\t\t\t\tThere is no doubt that the AC75 is a remarkable boat; a monohull designed to fly, engineered to reach speeds\u2026<\/p>\n
\t\t\t\t\t\tAmerica\u2019s Cup challenger Malta Altus withdraws as $1m fees deadline draws in<\/p>\n
\t\t\t\t\t\t\tAn America\u2019s Cup challenger from Malta has officially pulled out of the 2021 America\u2019s Cup in New Zealand. Malta Altus\u2026<\/p>\n
\u201cWe\u2019ve seen through simulation and the test boat that when you start off you\u2019re very gingerly trimming in the sails trying to get the right heel on the boat to create speed. Then as the righting moment kicks in you\u2019ve got the power, you trim on, you lift out of the water and then you\u2019re up to speed and the boat is more locked in.
\n\u201cIn that sense it will be quite a neat challenge for the sailors out on the water. Very similar to the high-performance dinghies you see.\u00a0I think our sailors are very well prepared for that. Obviously, time on the water will be critical, as will time in the simulator, so that we get as much time together as a group and really understand how we get maximum performance from these boats.\u201d
\n About the author
\nBen Ainslie is the most successful Olympic sailor of all time, and Team Principal of the British America\u2019s Cup challenger. INEOS Team UK will be challenging for the 36th America\u2019s Cup in New Zealand in 2021. Each month he\u2019ll be talking to Mark Chisnell\u00a0about the innovations and technology behind the new AC75 foiling monohulls.
\nThe post Road to the America\u2019s Cup podcast episode 2: How the AC75 will fly appeared first on Yachting World.<\/p>\n","protected":false},"excerpt":{"rendered":"
In recent weeks we have seen the first AC75s start to fly, but the engineering and sailing techniques needed to get these new monohulls to foil are very different to the catamarans of the previous Cup cyclesFlaps on the T-foils … <\/p>\n