My Analysis of the Aachen Eace05 Formula Student Car

Hello there!

So, when walking around the paddock at Formula Student (FS) 2016, a number of cars court my eye, mainly due to the quality and professionalism they had. While most people look around Delft or Munich, the RWTH Aachen team showed up with a very professional car, that was somewhat overlooked.

The 2016 car, deemed the eace05 is a clear evolution from the eace04 model. Team manager Marcel Eckert says “It is the first time that the team built a four wheel driven electric formula student racecar. So we are proud that we managed the challenge to build up a new car from scratch with this drive concept.” He also confirmed the 2017 car from RWTH Aachen will be an ‘evolution’ from the current model.

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When I was around the car at Silverstone Formula Student event, the team’s members all had their own individual tasks and got on with them. The car was well looked after, and never really ran into problems. The tasks where Aachen looked at most on the eace05 was to “save weight by optimisation of all parts, and guarantee a production without any faults” says Eckert. Although the team had the odd glitch at Hockenheim, the eace05 is one of the quickest and reliable overall racecars. 

Chassis

Pic: Stefan Ruitenberg

The age old question in Formula Student is space frame or monocoque. While the latter is much more expensive, the performance gain is somewhat advantageous. If your team does use a space frame, a good solution is to use bonded panels to increase the overall structural integrity. For the RWTH Aachen team, they opted for a monocoque, as they were able to find the sponsorship to do so. This is something that teams don’t try hard enough in currently, I find.

For the chassis, the team has used two materials to make the monocoque. The inner honeycomb structure is aluminium, with outer carbon bodywork. This concept has slashed the manufacturing time, while not losing out on the structural integrity of the chassis. The design is Prepeg sandwich structure, which is used by all other monocoque users in Formula Student.

The design has been made in-house at the team's base in Aachen. The design is a blend of neat approaches undertaken by the team: such as the battery position, spacious peddle box and unique side pods. Due to these innovative ideas, the team has created an all-around solid package.

The biggest compromise with the chassis is the battery housing. Chassis engineer Christopher Schob says “the way we designed it, it has only a minor impact on overall stiffness of the monocoque. For us, it was a fair tradeoff in terms of maintenance and stiffness.”

One area where the car really stands out is the one-piece alloys. Like TU Graz, RWTH Aachen had produced its own lightweight carbon alloys for its eace05 car. This is an idea quite new to Formula Student, and one which will sure catch on.

Powertrain

Pic: Stefan Ruitenberg

For the power train, the car uses hub motors, which are from German based company AMK. These are placed in specially designed uprights for the car. While they never went for the inboard motors as seen on the Karlsruhe Institute of Technology (KIT) car, which saw them mounted horizontally under the carbon monocoque chassis.

Speaking at the team's base Janek Jurasch said “In our opinion, the ‘AMK - Racing Kit’ is the best buyable system of motors and inverters for Formula Student cars. We did research right at the beginning of the development of the eace05 and found the supporter AMK with their motors and inverters as the lightest components with a very high performance compared to other manufacturers. Only a self-developed motor or inverter could increase the performance on the one hand, but on the other hand, there is a high risk in the reliability of the car if we would develop these complex components by our own. So we decided to buy the AMK system” who is head of powertrain solutions at Ecurie Aix.

Another neat feature, a simple one, is the battery pack, which has a special housing fight at the back of the chassis. This easy to use concept, has the battery, diffuser and twin cooling fans as one object. This creates a quick process if the battery has to be changed quickly. Some teams in Formula Student have battery packs that drop out under the chassis, so this is a neat feature on the Eace05 racer.

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Janek Jurasch adds “the position of our battery container - right behind the driver - as low as possible inside the car has been chosen because of the centre of gravity and for packaging reasons. To get the maximum performance out of the battery pack, it is necessary to cool the cells. We realised that with an air stream, which starts at intakes below the driver’s seat and ends its way through our battery container in the fans installed at the rear of the car.”

Suspension system

Pic: Stefan Ruitenberg

As highlighted in my previous article looking at the technical trends in Formula Student, suspension systems are one area which saw big gains from the previous year.  The gains with a system which can isolate each chassis movements are key. That’s roll, pitch, heave, warp and hump motions is much bigger than it once was.

The front suspension on eace05 is pushrod arms which are mounted on top of the uprights. This set up is used all round, with twin wishbones from the tub to the uprights. The rear also sees it laid horizontally on top of the tub.

Speaking on the concept “the suspension design all in all is quite good. Due to the small rim, we had some issues with A-Arms that collide with the rim at some setups, so we were not able to run all setups we want. Furthermore, the tie rod of the rear axle has too much compliance which has to be fixed for next year” exclaims Marcel Eckert.

One other area the suspension is optimised up front is the addition of an anti-roll bar, which is integrated within the two front heave springs mounted on top of the tub. As the team has a special place for its front set up, which is deeper in the chassis, the team has created a neat little cover for them. “The front cover is a huge step forward from the old layout with uncovered suspension. It reduces the positive lift of the monocoque and gives an overall benefit of 5% in downforce. I’d like to highlight the cover at the rear end of the car because it has an especially positive influence on the overall performance. The intentional idea was reducing drag by improving the airflow around the rear. But during development, it turned out that the cover had a much more positive effect on rear wing and diffuser than actually reducing overall drag. Lift on these parts were increased by about 30% without any overall drag penalty” says Marius Reiter, head of aerodynamics.

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Due to the sensible changes, the suspension packaging has been able to reduce drag levels, while not interfering with the tyre set up and contact patch.

Aerodynamics

Pic: Stefan Ruitenberg

The overall aerodynamic packages in Formula Student are of big interest. The overhaul at Munich saw an all new layout which gave them huge side wings. For Aachen at least, it was a subtle evolution from the car before.

Starting with the front wing, it’s a two element design, with an inboard fence, and curved end plates. “We use an aerofoil configuration based on last year’s development, which is optimised for using the small available space of up to 250mm above ground level (defined by the rules) most effectively. It was relatively easy to create the required amount of downforce based on this already good configuration, so the development focused on optimising the airflow to other parts of the car. We were able to gain 40% more Downforce on side wings and underbody by optimising the end plates and the step-shaped main wing element” says Marius.

Talking on side wings, RWTH Aachen was able to create a small side pod intercooler, as well as apply quite sizeable side wings on the car. This concept proved to be quite popular for 2016, as It was used by a number of top teams, such as Eindhoven University of technology and Delft.

The design sees lots of carbon used in the two element side wings which are mounted on the floor of the car. An end plate has been added to counter out the vortex produced on the wing tips. Speaking on the design, Marius Reiter says “One main design goal of the side covers beside creating the required airflow through the radiator was having no negative effect on the side wings. The strategy to leave a slot between these parts turned out to work really well. In fact, if you left out the side cover, it would result in an overall loss of downforce of nearly 10%, so it has even a positive effect on overall performance.”

Pic: Stefan Ruitenberg

He adds “We know from our lap time simulation that downforce is much more important than low drag, so we’ll focus on creating as much downforce as possible in the development for 2017.”

One area where the RWTH Aachen does stand out is the rear wing set up. A pair of curved end plates is bolted on the back of the tub, with triple main planes places between them, all with trailing edge gurney flaps. These differ to conventional end places which are normally swan neck pylons.

Team aerodynamicist Marius says “The biggest disadvantage of mounting the wing on the elements themselves, be it from the bottom via posts or rods, or better from the top via swan neck, is, that the flow close to the wing and in the boundary layer is disturbed by these devices, which causes flow separation. So consequently, we decided to mount the wing only on the end plates.”

He later adds “The characteristic curved S-shape is caused by the fact that the frame, where the end plates are mounted, is much smaller than the maximum width of the wing. In Addition, we were able to save weight compared to swan neck pylons, because the system of rear wing with structural end plates is lighter than a rear wing with swan neck and non-structural end plates.”

With weight being saved, and good downforce figures coming from the CFD process, the team has built a car which produces a lot of downforce. Marius adds “The influence of the side wings on the rear wing has always been a challenge. A part of the upwash of the side wings is hitting the rear wing, which has a negative effect on its lift. The challenge is to find a solution which creates the most overall lift, and this is the point where we have a great opportunity to improve in the next year”.

While the radiators are packaged in their housing, the team has applied turning vanes behind the intercooler to help combat the turbulent air. As Marius states, the interaction of the air from the radiators to the rear wing set up is difficult, not only for Aachen but any other team who has a similar philosophy here.

Conclusion

Pic: Stefan Ruitenberg

To conclude this feature, the eace05 car is the first to run hub motors all round, and what a first attempt. The car came in at 16th place out of 111 FS entries at Silverstone, as well as winning the best engineering award by Schaeffler at Hockenheim shows the team has many bright heads, and while they don’t have the biggest budget in the world, they are certainly a team to watch out for in 2017 beyond.