With the wind against the wind
A hand just barely fits between the asphalt and the race car. The gap shows that this is all about aerodynamics. And weight. The racer that’s largely made of carbon fiber tips the scales at a mere 171.7 kilograms (379 lbs). Its four wheels are as thin as those of a road bike, but its most conspicuous characteristics are the two rotors above the cockpit. The rotor blades are the race car’s engine – and the wind is its fuel.
Welcome to Racing Aeolus, a unique kind of race. It doesn’t feature a field of roaring twelve-cylinders but so-called headwind vehicles aka wind cars. Essentially, they’re wind turbines on wheels. The race is held at Den Helder in the Netherlands. The race track is an asphalted dyke, 500 meters (0.31 mi) in length. A little more than a dozen university teams from all over the world compete in the event. The objective of the race is to drive faster than the wind. That’s why it’s difficult to state the actual speeds driven – they decisively depend on the prevailing wind speed. In good conditions, it’s 40 km/h (25 mph). The race is unique because the cars drive directly into the wind instead of being propelled by tailwind. Amazingly, the faster the vehicle moves, the stronger the apparent wind blows, in other words the sum of the actual wind force and the airflow aboard the vehicle – which increases the propulsive force.
Efficiency leads to victory
Michael Liebl explains how driving against the wind works: “The aggregate of all frictional forces – from the rotor blades to the gearbox to the wheels – must be less than the propulsive force gained from the wind.” Liebl is one of the three team principals of the InVentus race team from the University of Stuttgart supported by Schaeffler, where the “Ventomobil” was developed and built.
The idea of being able to driver faster than the wind was purely theoretical for a long time. It wasn’t until 2016 that the Danish team DTU proved that it’s possible by reaching 101.76 percent of the wind speed prevailing at the time with their vehicle. In 2017, the Canadians from the Chinook ETS team took the lead by achieving 102.45 percent. In 2019, the same team even recorded 113.97 percent – a world record!
faster than the wind that served as the only source of propulsion energy was the speed at which the world record holder drove in the 2019 Aeolus Race – not with tailwind but straight into the wind. The record set by the Canadian Chinook ETS team means that at a wind speed of 40 km/h (25 mph) the highly efficient vehicle would achieve 45.588 km/h (28.327 mph).
The blades of the Ventomobil spin at a rate of up to 1,500 revolutions per minute. “We don’t even need half of the acceleration distance to achieve our target speed,” says Liebl. In addition to the percentage-wise speed in relation to the wind, acceleration and innovation are rated in the competition.
Ingenuity and creativity are essential
The commitment of the Stuttgart squad began in 2007 when two students started constructing the first Ventomobil. It was their final project for earning their degrees. The vehicle consisted of a carbon fiber chassis and a rotor that propelled the wheels directly. The effort paid off: in 2008, they won the Boysen Award for the best thesis in the field of environmental engineering. “A project such as InVentus poses a challenge to the budding engineers because knowledge of theory as well as ingenuity and creativity are essential there. You don’t learn these skills for your future profession in the lecture hall but in the field,” says Professor Po Wen Cheng, PhD, Head of Wind Energy Institute of Aircraft Design at the University of Stuttgart.
The idea behind Racing Aeolus is to design and build cars, i.e., wind powered vehicles that generate energy while driving against the wind and competing with teams from all over the world. It is a real challenge for the student teams. It requires steadfastness, co-operation, perseverance and fearlessness. They learn how to handle renewable energy. Some of them are really motivated and manage to find a job in this fieldHans Verhoef,
Chairman of Racing Aeolus
Over the years, the Stuttgart-based team developed three different vehicles. The latest generation is a hybrid with two rotors trapping the wind. One of them supplies its torque directly to the rear wheels while the other one drives a generator powering two electric motors on the front axle. With this design, the team exploited the maximum permitted rotor area of four square meters (43 sq.ft), with the maximum rotor diameter being limited to two meters (6.6 feet). Although the hybrid approach entails conversion losses it facilitates the transmission of power from the two rotors. Instead of complex shafts and gearboxes the electrical part of the drive train just requires a cable.
Even so, the team did not claim victory in their last race participation in 2018. “Our purpose-developed power electronics unit was finished just shortly before the race, so we were able to test it only for functionality but not for efficiency,” says the then team principal Julian Fial. That’s why the squad from Stuttgart raced only with the mechanical drive unit and achieved just 95.6 percent of the wind speed. However, due to having won the innovation award for their hybrid drive, they finished in second place overall anyhow.
Due to the Covid-19 pandemic, there were no races held in 2020 and 2021. “The team, though, did not spin its wheels but used the time to design a number of innovations and improvements some of which still need to be integrated into the vehicle,” says co-team principal Liebl. They include a new rotor hub with torque measurement, a new rotor with a triple-blade geometry, a new drive train including new bearings from the team’s sponsor Schaeffler, and the new aerodynamic cover of the entire rear end of the vehicle based on a wound flax fiber structure.
Michael Liebl and his teammates are optimistic about the next race: “That’s when we’re going to show the capabilities of our hybrid drive.”