PERFECT FOILS

What goes into a set of AC50 foils?

Reaching speeds of up to 50 knots, it’s widely expected that the high-tech AC50S in this 35th iteration of the America’s Cup will spend more time ‘out’ of the water than in it. Riding high on their foils, these cats are airborne even during tacks and gybes. All of which puts enormous loads on the foils, rudders and elevators. So it’s understandable that the teams have put enormous R&D and precision engineering into the design and construction of these appendages.

For ETNZ, transforming those designs into reality fell to Auckland’s Jackson Industries, a company specialising in composite engineering and precision machining for the marine industry. It’s been a highly collaborative relationship – one which saw part of ETNZ’S engineering and construction team move on to the company’s Onehunga site nearly two years ago.

Over that period the combined teams have produced dozens of parts including foils, rudders, elevators and other AC50 components. To begin to understand the magnitude of that feat, you need to delve into the construction of a one of these foils. As with most of an AC50’S components, the foils are carbon fibre. Each is built from hundreds of layers of 0.2mm Pre-preg material. To create the right structural and mechanical properties, the layers are introduced in stages, going through many ‘curing’ phases in ovens and auto-claves.

Which means each daggerboard foil takes around three months to build and yes, you read right – they built many of these – each an evolutionary progression from its predecessor, based on real-time testing.

Preparing the female moulds for each of the appendages – and ‘finishing’ it to within 0.2mm of the original design specification – demands precision machining. This is where Jackson’s expertise comes into the equation.

There are two critical processes to building a foil to the required accuracy, says the company’s Project Manager, Paul Flett. “The first is producing the tooling – the female mould – and the second is machining the foil’s upper surface.

TOOLING

“The foils have a 90-degree shape and their overall length is about six metres. Machining a one-piece mould for each foil not only demands a large ‘bed’, but also a facility that guarantees a high degree of accuracy over a very large area. Fortunately, we have a number of large five-axis machining centres able to tackle the foils’ complex geometry.

“Given the high-precision requirements, using a thermally-stable material for the moulds is vital,” he adds. “Even the best, most accurately-machined mould is useless if it expands and contracts wildly during the curing stages. The specified 0.2mm tolerance becomes a pipe-dream if the mould – and therefore the foil – expands or contracts by even a few millimetres during the curing process.”

To eliminate this problem the same high-end, ceramicbased tooling substrate favoured by the Formula 1 and aerospace industries is used.

MACHINING

While the lower surface of the foil is perfectly smooth thanks to the finish and accuracy of the mould, the upper surface must be machined into the required geometry after curing.

The foil – still sitting in its mould, is returned to the five-axis machining centre and precisely relocated into its original position.

“Machining carbon fibre accurately isn’t easy, and it demanded considerable up-skilling on our part to get it right”, says Jackson’s Project Manager Cameron Walker. “For a start carbon is very hard, brittle and abrasive which mean conventional cutters and machining strategies aren’t suitable. You can’t afford the risk of a conventional cutting head ripping the fibre apart or splintering the surface.

“Instead, we had to source specialist, diamond-coated cutting heads equipped with a unique geometry. They’re used in the aerospace industry, and while they’re not cheap, they leave a superb finish.”

The many foils, including rudders and elevators were all successfully manufactured at the Jackson Industries Onehunga facility. Managing the processes and deadlines,

says Flett, demanded enormous flexibility and long hours from the company’s skilled team.

“Each foil takes three months of intensive work from everyone in the team – and we were all acutely conscious of the need to avoid errors. One stuff-up means you’d have to start all over again, and in context of ETNZ’S campaign schedule, we didn’t have that luxury.”

Flett and his crew also machined a range of carbon fibre components used in the cat’s ‘wing’. These were mostly structural and mechanical items for the wing’s control systems. They included carbon fibre cross-arms and brackets for the very complex system – all used to manipulate the wing’s camber and twist.

ETNZ’S radical pedal-power bikes, too, were created from Jackson-machined moulds.

“Post-machining these units proved particularly demanding,” says Flett, “not only because of the complex geometry, but because we needed to accommodate the housings for items such as high-accuracy bearings.”

ENGINEERING EXPERTISE

The company operates seven five-axis machining centres of various sizes – the biggest measuring 10m x 4m x 2.5m. Complex, high-accuracy projects end up on one of these centres, while smaller or simpler jobs are tackled on three-axis machines.

“Jackson Industries has been yet another of the unsung heroes of this campaign. They have operated to a fantastic level of quality over two years under constant pressure to deliver what could turn out to be some of the most important components to helping us win the America’s Cup.” GRANT DALTON: CEO, Emirates Team New Zealand

Material used for the moulds varies according to the design specification. High-accuracy, composite jobs will typically use a high-tech, thermally-stable material. Depending on the requirement, other jobs might use polystyrene, MDF or polyurethane foam.

“Selecting a material for a mould,” says Walker, “is usually a compromise – a balance between cost, accuracy and stability. For the vast majority of our clients, we assist with making a material choice and design of the tooling itself.”

Panels for each job – whether fibreglass or carbon fibre – are prepared on a large CNC plotter-cutter. Computer programming provides ‘nesting’ – a technique which optimises the use of the raw panels.

Creating the 3D models for each mould is tackled with Solidworks, and translated into G-code for the machining centres with Mastercam.

ETNZ’S AC50 project, says Flett, demanded enormous challenges and plenty of rapid-fire R&D on Jackson Industries’ part. “It’s fair to say that much of this was facilitated by a grant from Callaghan Innovation – their support has been invaluable.”