To say Nuna6 is merely more efficient than a Nissan Leaf or Chevrolet Volt is an understatement. If the hot favorite for the World Solar Challenge, a 1,865-mile economy dash across Australia held every other October, were to start a journey from its native Amsterdam equipped with a 18.5-gallon gas tank instead of its standard 1,690 solar panels, lithium-ion battery pack and 5kW electric motor, it would finally run out of fuel in New Delhi, India, some 5,600 miles later. Meanwhile, the Leaf would still be looking for a charging point in Belgium and the Volt's 9.2-gallon fuel tank would have needed filling just west of Berlin.
Nuna6 is the work of 13 students from the Delft University of Technology in the Netherlands. The carbon fiber-bodied three-wheeler, which has taken 18 months to build, is 12 times more aerodynamically efficient than a Honda Civic and weighs just 320lbs.
The Dutch squad's fearsome reputation in the World Solar Challenge, to be contested in 2011 by 42 teams from 21 countries, is not without historical justification. Four of Nuna6's five predecessors have taken victory in the race and Nuna5's disappointing second place in 2009 was put down to a crash in testing, which harmed the team's preparations, rather than a flawed design.
The rules of the challenge are simple. Teams start on Oct. 16 in Darwin, in Australia's Northern Territory, and the winner will be the first car to reach Adelaide, South Australia, around four days later, having been on public roads through the barren Australian Outback for nine hours each day. The course record is the 64mph average speed achieved by Nuna3 in 2005 – the last year of competition in which drivers were able to lay flat, rather than sit up, for even greater aerodynamic efficiency.
After signing off the aerodynamics package in DNW's Marknesse wind tunnel last month, the Nuna6 team will imminently set off to Australia to focus on important reliability tests. As the team says: “If we're not moving, everyone else is.”
So what are Nuna6's speed secrets?
Nuna6 is body-on-frame. The 0.4-0.8in-thick structural cell weighs just 88lbs and is of sandwich construction, featuring carbon fiber and lightweight foam. Kevlar is also used in key crash structures for added strength. A titanium roll bar sits above the driver's head for safety, too. The body is made of carbon fiber, with a special weave featuring a unique resin from Dutch maker DSM. This makes the carbon fiber flatter (and lighter) and therefore more aerodynamic. Nuna6 weighs just 320lbs in total, 33lbs lighter than 2009's Nuna5 and 298lbs lighter than the original 2001 Nuna1.
SUSPENSION, BRAKES AND WHEELS
The F1-style double wishbone suspension features a single upright at the front; the rear gets a single trailing arm setup. Most teams adopt a double arm at the rear but a single arm is lighter and allows for quicker wheel changes. An electrical brake is used in the rear motor – although regenerative braking can only be used below 9mph – and mechanical brakes are used for the front wheels. The 16in. wheels wear Michelin tires designed for solar cars.
A 5kW electric motor is mounted in the rear wheel to provide direct drive. When the sun is shining, the 1,690 silicone solar panels, which are spread as thinly as possible across the top of Nuna6's body, send power to the rear wheel. Spare power is stored in a front-mounted 5kWh lithium-ion battery pack, weighing 46lbs. This feeds the electric motor if the sun stops shining, or if extra power is needed to climb hills or pass other cars.
This is Nuna6's most crucial design element, because 70 percent of total energy consumption is determined by drag. Its slippery shape is the result of hours of advanced computer design, wind tunnel tests and lessons from previous Nuna entries. Nuna6 is 10 percent more aerodynamically efficient than its Nuna5 predecessor. The team claims Nuna6 has as much wind resistance as a truck's wing mirror when traveling at the same speed.
Although maximum power is 5kW, the electric motor typically produces around 1.5kW. It is running at its most efficient at 1.2kW. If Nuna6 travels at 56mph, the motor is producing around 1kW – about the same as a vacuum cleaner. Nuna6 can crack 0-62mph in about 10sec and its top speed is around 95mph. Driving at this speed is ineffective, however, because the battery charge would quickly deplete, forcing the team to stop and receive sufficient charge from the sun to carry on.
“It's a good job I'm not claustrophobic,” says one of Nuna6's three drivers, Javier Sint Jago (RIGHT), as he contemplates one of his three-hour stints in the cockpit. Nuna6 isn't built for MPV-style interior space, so the cockpit can be unforgiving. “You need to be flexible to get in,” says Javier, “and your field of vision is only around 120 degrees with the helmet on.”
All Nuna6's controls – including the throttle and braking – are operated using the steering wheel, which also houses a computer screen for real-time info about the car's functions.
Javier says it can be easy to get distracted on the long Australian roads – especially in an interior that can reach up to 122 degrees Fahrenheit. “You really have to concentrate as things can go wrong in a split second," he says. "You have to listen to every sound when you're driving and monitor the screen for any problems. But it's such a cool car to drive; you always feel a part of it.”