All about aero

While much has been said about the importance of correctly managing energy and power in Formula E, there is still a performance to be gained by tweaking the Spark-Renault’s aerodynamic balance. Technical guru Craig Scarborough explains how.

Formula E is purely a street racing category and is designed to develop electric powertrains. The absence of high-speed running and the championship’s focus on battery and motor tech means that aerodynamic design hasn’t been the talking point that it is in other series, such as F1.

However, the shape of the bodywork and its resultant downforce is what keeps the car’s four wheels on the tarmac. This can help or hinder lap times, affecting grid positions and even whether drivers make it to the end of the race. Despite the simple-looking surfaces of the Spark-Renault, aero balance is still critical to race day performance.

“What’s needed in qualifying is different from what’s needed in the race,” says Marc Priestly, ITV’s technical analyst for Formula E and a former chief mechanic at the McLaren F1 team. “When you go for a fast qualifying lap, you want a high downforce car – it gives you all the grip you need to stick it to the road. You don’t worry about energy management and, in this series, you don’t need to worry about tyres. In the race, you want the slipperiest car you can get: low downforce means less drag and increased range. You have less grip, but if the driver can manage that, the advantage is that you can go much longer.”

Tuning the Spark-Renault’s aero set up is only possible with the front and rear wing angles. The rest of the bodywork is not adjustable and teams are not able to develop their own aerodynamic upgrades through the season. The surfaces that the car comes with are what the engineers have to play with.

Here are the main aerodynamic features of the Spark-Renault, and how they can affect performance.

High nose

The Spark-Renault has an aerodynamically-beneficial high nose chassis design. To make best use of the feature, the front suspension utilises a single keel, whereby a pillar below the front of the chassis is used to mount the front lower wishbone. This allows for the ideal front suspension geometry while retaining the high nose. The design also forces the use of a pair of pillars to mount the front wing assembly.

Current E Buenos Aires 2014 Trulli nose cone and front fairings

Fenders

A pair of curved fenders sit ahead of the front tyres, at either end of the front wing. While these will aid aerodynamics, their primary focus is to minimise wheel to wheel contact, a high risk in a tightly packed grid around a street circuit. Similar fenders are mounted to the rear wing, behind the rear tyres.

Current E Buenos Aires Mahindra front fairings

Canards and short sidepods

The short sidepods house the radiators for the battery and drivetrain and help prevent wheel to wheel contact. They are widest just ahead of the rear tyres. This approach differs from the orthodox “Coke bottle” shape, where a single seater’s sidepods start wide at the cockpit before tucking in tightly between the rear wheels.

Current E Punta del Este 2014 testing Alguersuari on track

The short sidepod design exposes the side impact structures on either side of the Spark-Renault’s cockpit. These are therefore shrouded in aerofoil shaped fairings, which add little to the aerodynamics but which do add visual excitement.

Current E Putrajaya 2014 Renault candards and sidepods

Underbody

The Spark-Renault’s underbody is a very important component aerodynamically, as it creates downforce with very little drag. It is made up of a short floor and a diffuser that is long by modern conventions. Starting ahead of the rear tyres and extending backwards to finish behind them, the diffuser accelerates the air moving under the car, which reduces air pressure and sucks the vehicle to the track.

Current E Scarbs Spark-Renault underbody illustration

The car also gets a near-universal stepped floor, where the centre is protected by a wooden skid block (plank) and the outer sections are some 50mm higher. This arrangement prevents the teams running ultra-low ride heights in an attempt to gain more downforce from the underside.

Current E Beijing 2014 e.dams-Renault underbodyCurrent E Beijing 2014 e.dams-Renault underbody

Here’s the underbody from another angle (and with far less car around it!):

Current E Punta del Este 2014 contoured underbody

The short underbody creates its peak downforce at both its leading edge and the kick line between the floor and diffuser, which biases the downforce towards the rear. This matches the car’s weight distribution – it’s heavier at the back, largely due to the mass and location of the batteries at the back of the car.

Current E Punta del Este 2014 Trulli rear diffuser

Wings

Current E Scarbs wings illustration

With a reasonable amount of downforce produced by the contoured underbody, the Spark-Renault’s rear wing can be relatively small. The rear wing adds a lot of drag, so while it can be tuned to balance grip with top speed, teams will want to trim it to be a shallow as possible to maintain aerodynamic and therefore energy efficiency.

It is a simple two element design. The top rear wing is the obvious structure that stands proud of the rear of the car. It is sits above and is supported by the lower rear wing, known as a beam wing, which joins up the airflows from the top rear wing and diffuser for more downforce. This bolts to the top of the rear crash structure and extends past the rear wing endplates to mount the rear tyre fenders.

Current E Beijing 2014 rear wing assembly

“I’ve been told that no one has yet been able to quantify what the rear wing does, but the car can be balanced using the front aero surfaces,” says Marc Priestley.

The front wing is used to balance the downforce created by the rear end’s aerodynamics, and to help match the car’s weight distribution. As the car is rear end heavy, the front wing only requires a simple main plane and small adjustable flaps to achieve this.

Current E Beijing 2014 Venturi front aero surfaces

Track evidence

That’s how the theory looks. When we look at what’s happened to date at the races, we can see evolving strategies, says Ross Ringham.

Consider first e.dams-Renault. The French team was quickest through most of preseason testing, has secured two pole positions (almost three, had it not been for Prost’s grid penalty in Malaysia) and is one of the four race winning teams to date. 

In Beijing, both drivers ran high-downforce settings in the race itself. In this picture of Nico Prost, who secured pole and who very nearly won the race, note how high both the rear and front aero surfaces are set:

Current E Beijing 2014 Nico Prost in the race

It’s a very similar story for his team mate, Sebastien Buemi:

Current E Beijing 2014 Sebastien Buemi in the race

We can see different decisions taken in subsequent races. Buemi won the third round, Punta del Este, using a similarly aggressive approach in quali but far flatter angles in the race (the difference in angles makes it much easier to read “Renault” on the rear wing in the first picture, taken during quali, than in the second, taken during the race):

Current E Punta del Este 2014 Sebastien Buemi in qualifying

Current E Punta del Este 2014 Sebastien Buemi in the race

It’s an approach that seems to have worked, for the team repeated it in Buenos Aires, where Buemi was the fastest man by far in quali (note the difference of angles again between the first pic, taken at the end of quali, and the second, taken during the race):

Current E Buenos Aires 2015 Sebastien Buemi in qualifying

Current E Buenos Aires 2015 Sebastien Buemi in the race

What’s intriguing is that, despite all using the same car, the teams do not have cookie cutter approaches to aero set up. Look at this picture of Nelson Piquet being followed by Jean-Eric Vergne in the Punta del Este race. You can clearly see the China Racing car has almost completely flat surfaces whereas the Andretti man has his rear wing set similarly to an e.dams-Renault in quali trim:

Current E Punta del Este 2014 Nelson Piquet followed by Jean-Eric Vergne

That almost totally horizontal surface setting of Piquet is seen too in Buenos Aires:

Current E Buenos Aires 2015 Nelson Piquet in the race

Another driver who favours the ultra-low downforce set up is Antonio Felix da Costa. Here he is on the way to victory in Buenos Aires, and those surfaces might as well not even be there:

Current E Buenos Aires 2015 Antonio Felix da Costa in the race

Elsewhere, Sam Bird’s performance in Putrajaya was utterly remarkable, where he left his competitors for dust during the race. But the following two pictures show that he made virtually no changes to his aero setting between quali (first picture) and the race (second picture):

Current E Putrajaya 2014 Sam Bird in quali

Current E Putrajaya 2014 Sam Bird in the race

The approach is repeated in Buenos Aires. Look at how similar Jaime Alguersuari’s surface settings are (leading car) to Bird’s:

Current E Buenos Aires 2015 Jaime Alguersuari and Sam Bird in the race

By contrast, Nick Heidfeld seems to run a relatively high downforce set up during the race, which may explain how he was able to outbrake Alguersuari down into turn one:

Current E Buenos Aires 2015 Nick Heidfeld in the race

Current E Buenos Aires 2015 Sebastien Buemi, Nick Heidfeld and Jaime Alguersuari in the race

What does all this tell us in conclusion? We can see that the aero balance really does have a part to play in the set up of the Spark-Renault, despite relatively low speed tracks. There are other factors at work too, such as the driver’s style and the team’s power maps. But it does seem that the leading teams have found what works best for them, and they’re sticking to it.

Current E Buenos Aires 2014 adjusting the rear wing

 

 

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