Mercedes has dumped the previous sidepod undercut for a new narrow cross-section with small cooling intakes
An updated Mercedes W13 with radically narrow sidepod inlets broke cover in Bahrain testing. It created a considerable stir.
There is something very ‘stealth fighter’ in the way the Merc’s bodywork deflects into different planes in this region, with odd unresolved-looking angles. But in this case it isn’t evading radar; rather it’s cheating the air, tricking it into providing downforce and cooling but at less expense in drag. Furthermore, that tall, narrow inlet has allowed the regulation upper impact structure to be exposed and sheathed in a cover which directs airflow from above down to the outer floor area.
Traditionally, this part of the leading edge of the sidepod will feature a big undercut in its lower regions with which to create a low pressure to hurry the air around that obstructive corner. That’s how it was on the original Merc W13 which ran in the Barcelona shakedown a week earlier. The new layout pretty much inverts that tradition, a narrow top and wider bottom visually recalling some of the ‘triangular’ monocoque shapes of the mid-1970s such as the Brabham BT42/44 and BRM P201. But in those cases the triangular section ran the length of the tub and was about minimising the centre of gravity height, when full, of the fuel tanks which were housed in there. This time it’s nothing to do with centre of gravity, but of finding a new optimised trade-off between the demands of downforce, drag and cooling under the new venturi floor regulations introduced this year.
The wide bottom of that section of bodywork around the radiator inlet also allows maximum aerodynamic use to be made of the exposed upper side impact structure – through a dimensional ‘shadow’ requirement in the regulations. It allows that contoured impact structure to extend further outwards. If the bottom bodywork was narrower there, that side impact ‘wing’ would be obliged to be similarly narrower.
Barcelona test
Bahrain test
Getting the best combination of airflow through the tunnels and around the sidepods is the key to maximising downforce. There’s only so much airflow mass to work with and how much goes around and how much goes through is crucial because the two flows then meet up again at the rear of the car. The two flows can be thought of as one which is initially split then later re-connected. Getting the best overall performance from that combined flow is what the aerodynamicists are striving to do.
The airflow going around the sidepods exits over the top of the venturi tunnel diffuser and beam wing and in that way draws on the underbody flow, effectively scavenging it out of there faster. On its way around the sidepods that airflow is also enhancing the underbody’s performance by sealing the floor with vortices. The pressure they create around them keeps the airflow through the tunnel from leaking from the sides and stops the floor’s low pressure drawing in turbulent air from outside. This all helps to maximise the underfloor air speed – and the greater that speed, the greater the downforce.
Mercedes’ ‘no sidepod’ concept made waves at the Bahrain test, amid suggestions that it might not be legal. Kyle Forster explains why it does comply with the rules and how it works
The sidepod shape is very much part of determining the split between the air going around the sides and that going through the tunnels. The small size of the radiator inlet opens up more real estate for the airflow to go around the sidepods, feeding the wide channels in the Merc floor’s outer edge. The remaining flow in that part of the car as it travels from between the front wheels to the floor can be fed to the venturi tunnels where it can be accelerated harder by the enhanced energy of the airflow travelling down the sides.
That outer floor airflow has been energised not only by the new sidepod corner shape but also by the air redirected from above by the impact structure ‘wing’.
The gains made from changing the flow in this way have evidently overcome the loss of the undercut to speed up the flow there. But how has it been possible to make the sidepods so narrow as to create this wide outer floor channel and expose the side impact beam? It implies a smaller radiator area needing to be cooled – or more efficient cooling. A significant part of that is almost certainly the new capillary radiator technology being used for the water/air intercooler used by Mercedes. This has been developed with Reaction Engines, which supplies cooling systems for rocket-powered spacecraft. Capillary motion concerns how liquid in a tube can be induced to move against gravity and this phenomenon is believed to be incorporated in a pre-cooler within the intercooler which allows the whole component to be shrunk in size.
Intercoolers are not considered part of the power unit within the regulations and even customer engine teams tend to source or make their own. So the intercooler on the W13 is almost certainly not shared with the Mercedes customer teams.
