Streamline: Audi e-tron prototype at the Audi Wind Tunnel Center in Ingolstadt

Ready for the long-haul routes – every thousandth of aerodynamic drag counts

Why the aerodynamics are so important for electric cars

During the development of the Audi e-tron prototype, a special focus was put on the aerodynamics. Aerodynamics development manager Moni Islam explains why this is more important for the long-distance capability for electric cars than the actual weight.

Dr. Moni Islam
Moni Islam steers the aerodynamics development at Audi. Together with his team, he has reduced the aerodynamic drag of the brand’s first fully electric series model at the best possible rate.

How big a challenge did you and your team face when developing the aerodynamics of the first Audi electric vehicle?

It was a huge challenge. After all, the Audi e-tron prototype is our brand’s first fully electric production model. And that’s why we ourselves made a point of stating in the product specifications that it should be the most aerodynamic Audi model of all time in this vehicle class. As a team, we had to bring all our knowledge and skills into this project and put in one or two night shifts along the way.

Rethinking for electric mobility

In terms of aerodynamic development, how does an electric model differ from a vehicle with a combustion engine? Is there a different fundamental philosophy?

Our job becomes more challenging. Because good aerodynamics and low air resistance are even more important for electric cars. Essentially, you have significantly less energy available overall than you do with vehicles powered by a combustion engine. So we need to optimize efficiency in every area. And one area in particular is air resistance in constant driving conditions at constant speed, such as on freeways. We need to offer our customers an electric SUV suitable for long journeys.

Streamline: Audi e-tron prototype at the Audi Wind Tunnel Center in Ingolstadt
For the aerodynamics of an electric car, every detail counts: One thousandth of the cw-value represents around half a kilometer of reach in the customer’s everyday drive life.

Do aerodynamics engineers now have more influence generally on development?

Yes, I think they do, absolutely. And that’s because aerodynamics play a crucial role in determining the range of an electric car. After all, the energy used to overcome air resistance cannot be recovered – unlike with vehicle acceleration.
In town, a heavy electric car is also efficient because it can recover a large part of the energy, which it uses to accelerate, when running up to the next red traffic light. The situation is, however, totally different on long journeys where the Audi e-tron prototype is perfectly at home: Here from speeds of around 70 km/h (43.5 mph) the rolling resistance and the inertia take second place to aerodynamic drag irrespective of the type of car.
The energy required to overcome that drag is lost. That’s why clever aerodynamics measures are so important for the Audi e-tron prototype for ensuring high efficiency and thus a reach suitable for long-haul routes.

The underbody is covered by a 3.5-millimeter-thick aluminum plate. The fixing points at the high-voltage battery inside the body have indentations shaped like bowls. These “dimples” let the air flow even better.
The underbody is covered by a 3.5-millimeter-thick aluminum plate. The fixing points at the high-voltage battery inside the body have indentations shaped like bowls. These “dimples” let the air flow even better.

Which areas of an electric vehicle offer more design and development freedom compared to a conventional vehicle?

Thanks to their large battery, electric vehicles have an enclosed and very smooth underfloor. This is the dream of every aerodynamics engineer and a huge advantage for us in development. We could have just left it at that. But we didn’t. On the contrary: We’ve done all we can to make the shape of the body as streamlined as possible. And we’ve also incorporated a new feature. The Audi e-tron prototype is the first Audi production model with an enclosed air flow which is guided through the entire front end and back out through the underfloor. No combustion-engined model has that yet.

Clever aerodynamics measures

For you personally, what’s the most important component for the aerodynamics of the Audi e-tron prototype?

For me it’s the virtual exterior mirror – without a doubt. And not just because it helps to improve the aerodynamics significantly, but because it’s also symbolic. It heralds a new generation of vehicle development – one with completely different approaches.

Let’s be honest now. Who had the idea – was it your team or your colleagues from design?

For years, aerodynamics engineers have looked forward to the day when it would be possible to dispense with exterior mirrors. The virtual exterior mirror concept for the Audi e-tron prototype was decided on relatively early on in the process. But who ultimately had the final idea, I can’t say. But it’s not important. What is important is that this design detail brings a 5-point advantage in terms of cd and extends the range by around 2.5 kilometers (1.6 mi).

Die virtuellen Außenspiegel reduzieren den Luftwiderstand um weitere 5 cw-Punkte im Vergleich zu den bereits strömungsoptimierten, serienmäßigen Außenspiegeln und sind ein aerodynamisches sowie optisches Highlight zugleich.

For the first time ever, virtual exterior mirrors will be used in the Audi e-tron prototype. They reduce the drag by another 5 cw and are both an aerodynamic and optical highlight.

Thanks to the sophisticated aerodynamics measures the Audi e-tron prototype has a top cd-value. How does this benefit the customer?

With electric cars, the cd-value plays a vital role in determining the range. That’s a crucial factor for our customers. The Audi e-tron prototype is better than a conventional SUV of comparable size by just under 70 cd points – in terms of range, that’s a gain of around 35 kilometers (21.7 mi).

When did you and your team start development work on the aerodynamics of the Audi e-tron prototype?

Very early on – back in 2013. We were involved right from the initial concept, analyzing the initial drafts alongside the designers and testing the first models in the wind tunnel.
The result will soon be visible: The Audi e-tron prototype will be presented in 2018 and will soon be represent the electric segment of Audi on the streets and highways.

The e-tron prototype in the wind tunnel

With a drag coefficient of 0.28, the Audi e-tron prototype achieves even with conventional exterior mirrors a top rating in the SUV Segment . The highly developed aerodynamics provide a big of the car’s areas.

Due to sophisticated aerodynamics measures, the Audi e-tron prototype offers high efficiency for a long-distance reach. It reaches more than 400 kilometers with one battery charge In the WLTP cycle.

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To achieve a cw value of 0.28, the Audi engineers brought various aerodynamics measures into play. Some of those technical solutions are visible at first sight, while others do their work more covertly.

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The first fully electric Audi will celebrate its world premiere in 2018. Until then, the prototype of the sporty electric SUV will travel its last few test kilometers with a special apparel, since the camouflage design of the Audi prototype has become a designer piece itself.

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Audi e-tron prototype
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Audi e-tron prototype

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matthew boyd

12. September 2018 um 23:52
Nice to know such high-level work went into the drag coefficient of the e-tron Quattro. Good work Audi. I worked for an Audi dealer network for three years, left the company in 2017 to continue my graduate studies. Very excited to see this car.
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