America's Cup: Look, Ma - No hands! Flying the AC40 explained
by Richard Gladwell 5 Sep 2023 06:30 PDT
6 September 2023
American Magic - LEQ12 - Day 46 - July 27, 2023 - Barcelona © Paul Todd/America's Cup
Occasionally, we see the AC40s jumping clear of the water - often followed by a spectacular nosedive at some quite acute angles.
It makes great viewing and takes the America's Cup into a different area. It's certainly not your Father's America's Cup.
Cup aficionados know that an automated flight/foiling control system is in place, and it is hard for those watching to understand how such high-speed acrobatics occur.
"Any foiling boat is hard to control in an inconsistent sea state. These conditions are obviously more challenging for the autopilot, too," the AC40 design team told Cup Spy in response to several written questions on flight control systems.
"The sailors are responsible for setting target parameters - the pitch and immersion and heel angles they want to maintain - and they set the autopilot to operate within these ranges."
The AC40 can be sailed in auto or manual modes.
The sailors onboard set the trim (pitch of the boat) for the autopilot to target. They also can control the immersion of the foil in the water, which the flight control system gives the sailors a range to adjust within.
The flight controller can also adjust the cant angle, which isn't linked to the autopilot but is on their control panel.
The crew can also raise and lower the boards from this panel.
Co-helmsman for Emirates Team New Zealand, Nathan Outteridge, explained the controls for flight control and sail-trim during the commissioning phase of the first AC40 in Auckland.
The autopilot system functions well in a flat or even sea state, which is a good match for the foiling geometry of the AC40. The issues arise when the pre-set limits are incorrect, or there is an unexpected change in the sea state, and the co-helmsman needs to react quickly.
On the AC40, the co-helmsmen sitting on each side's front bucket seats control the flight control functions. The two sail trimmers sit behind, with the windward one controlling the mainsail and the leeward trimmer handling the jib.
Unlike the AC40, automated flight control is prohibited on the AC75's sailed in the 2024 America's Cup. Only a manual system is permitted. Sensor inputs to the manual flight control system are restricted.
Five of the teams have gone in two directions in developing their custom-designed manual flight control systems.
Three teams (American Magic, Emirates Team New Zealand and Alinghi Red Bull Racing) are sailing AC75s from the 2021 America's Cup cycle - and can develop their flight control systems on those boats.
Two teams (INEOS Britannia and Luna Rossa Prada Pirelli) developed their own 12-metre-long test boats - LEQ12s - to test their flight control and other systems to be ported to the AC75.
As a starting point, they both have legacy systems developed for the 2021 America's Cup.
It is not known what the French Orient Express Racing Team will do for the development of their flight control system. But they have at least two options: one is to test on their AC75 race boat, which is currently under construction. Or they can take their AC40 out of one-design configuration and test a team-developed flight control system.
All teams must put their AC40s back into strict one-design mode and pass a measurement check before being raced in a Preliminary Event.
Even the top teams are not immune from the occasional AC40 aerobatic performance. We can expect to see some spectacular incidents similar to the ones above during the first Preliminary Regatta from September 15-17, 2023 in Vilanora.