Swept by constant winds, caught between the steep mountainsides and accelerated by a venturi-like effect – the northern end of Lake Garda, between Torbole and Malcesine, is a hotspot for windsurfers. But what happens when the southerly wind, known as the Ora, subsides as evening falls? That’s when Franz Hofmann and his Audi e-foil take over.
The word “foil” is part of a sailing megatrend. Racing craft have been flying across the water for years on nothing but a narrow blade. The same goes for the Olympic Nacra 17 catamaran class competed in by the Audi e-tron sailing team of Johannes Polgar and Carolina Werner. Kite surfers and windsurfers use foils, too. The principle is always the same: as soon as the boat or board reaches a certain speed, the foil generates sufficient upward force to lift the hull out of the water. This causes a massive drop in drag, enabling extremely high speeds from very little wind.
Franz Hofmann is an expert in lightweight engineering
33-year-old Audi engineer Franz Hofmann loves the thrill of kite surfing with a foil. In his day job he develops hydrogen tanks made from carbon-fiber reinforced polymer (CFRP) in Ingolstadt and is an expert in lightweight engineering. No surprise then that he didn’t rate the first kite foils when they appeared in stores several years ago – too heavy.
Hofmann got in touch with Christian Rößler, whom he knew from his youth in the Upper Franconia region of southern Germany. Rößler works in the aerospace systems faculty at the Technische Universität München and knows just about all there is to know about fluid dynamics. He built initial computational models and simulations and used them to create his very own hydrofoil. Hofmann and Rößler cut molds at the TU, sanded and smoothed them to the correct shape at home in their living rooms and then laminated the first CFRP foil in the basement. The kite foil was finished in 2015. “From a fluid dynamics standpoint, data comparisons tell us that it was one of the best and most efficient foils out there,” says Hofmann with a certain degree of pride.