Every area of the F1 car comes under renewed scrutiny at some point, for many years the sidepods have been a relatively stagnant area, especially at their fronts. Numerous rules fix various aspects of the sidepod-front design and this set up works well, but some free thinking always helps shake things up. Ferrari did exactly this last year with their high-top sidepod design, visually its very different to the traditional design and creates a number of benefits. Perhaps not the key reason for Ferrari’s renewed competitiveness in 2017, but certainly a factor. Over the winter most teams have reviewed their sidepod philosophy and many have switched over to the Ferrari style high-top sidepod. But what’s so special about this set up and why is so beneficial in 2018?
It seems the majority of the new cars this season will adopt this high-top sidepod concept, the benefit is primarily aero, but perhaps not where everyone is looking. Many of people will see the inlet and point to it as the key gain, yes the inlet is higher and the plethora of aero vanes directing the airflow towards it may well give an improvement in flow to the sidepod, but there’s more to it. As it’s not the gain in the cooling inlet, but the increased space underneath it that is used to create a larger undercut in the sidepod shape. What’s not immediately clear, but it’s not just the inlet that’s higher on Ferrari’s 2017 sidepod, but the entire sidepod front is higher than everyone else’s. This added height is only possible with the structural changes inside the sidepod and can’t be achieved with a conventional set up.
This added space is used to create a deeper undercut to the sidepod front, this shape collects airflow approaching the sidepod and diverts it downwards around the sidepod. From there, this downwash is used to create higher pressure over the floor at the rear of the car. This improves the sealing between the tyre\diffuser and the diffuser performance itself, both by having high pressure above it and also by driving low pressure aft of the trailing edge created by the flaps and vanes around the diffuser exit’s perimeter. If you can make the diffuser more effective without creating penalties in the process, the car’s overall aero efficiency is improved. As the draggy rear wing can be backed off for a given downforce level, creating less drag for more top speed.
Firstly, let’s think about what a sidepod does, it houses the various radiators for the power unit, as well the electronic boxes used to control everything. To do this it needs an inlet and outlet for the air that passes through the radiators, as well as form the outer bodywork shape to direct the air around the car. Additionally, the front of the sidepod needs to house crash structure spars to protect the driver in the event of a side impact, these are known as SIPS. With this the sidepods then present a problem to the car’s aerodynamicists, they are a huge obstruction to the airflow, as the team want the nice clean airflow to go straight to the diffuser to create downforce. Over recent years, the sidepods have been slimmed, the overall shape much more tightly packed against the internal hardware and sculpted to try to direct more of that airflow towards the rear of the car.
Ferrari's sidepod (right) meets the same rules as a conventional side (left) for maximum height and SIPS positioning
Rules that dominate this area are largely the maximum height for the sidepod bodywork (600mm) and the height of the SIPS alongside the cockpit.
Each SIPS shape is fixed by regulation, they are made by the teams, but to a specification set out by the FIA back in 2014. The design of the spar was initially a Marussia part, with additional development put in by Red Bull Technologies to optimise the design, under the FIA’s management. One spar typically mounts low down at floor level, although rules give a vertical spacing of 120mm to position it relative to the floor. Then, the upper spar has a similar 120mm vertical window to fit to the chassis side, this is between 400-520mm above the reference plane at the bottom of the car.
The 2017 rules allow more sidepod width than most teams use, instead the resulting sidepods tend to be as narrow at the front as they were before 2017. Further detail rules also come into play, the front section of the sidepod is free from shape restrictions, whereas the bulk of the sidepod going back towards the tail is bound by minimum curvature rules, preventing fins and flicks being added to the surface. An interesting side point, this free area at the front of the sidepods was originally going to be as severely restricted as the rest of the sidepods as part of the Overtaking Working Group (OWG) ideas put into the 2009 rules. But, Paddy Lowe, with McLaren at the time, argued a small area of free design would still be good for differentiation and innovation between the teams. Post 2017 there were also demands the sidepod front slanted backwards when viewed from above and the front upper surface had to have bodywork present.
A typical sidepod front has a mid-inlet, that is the inlet sits between the upper and lower SIPS. With this set up, the upper SIPS sits as high as the rules allow and the inlet sits below it. Due to the height limitation of the Upper SIPS, the sidepod cannot usefully be made any higher to fill the space up to the maximum bodywork height of 600mm. This leaves free space above the inlet\upper SIPS, this space is often filled with vertical fins or horizontal vanes to direct airflow over the rest of the sidepod.
A large proportion of the flow hitting the sidepod passes over the top and less directed to the undercut
One problem here is the top edge of the sidepod above the inlet is quite thick as it houses the upper SIPS, while there’s high pressure formed on the sidepod front it creates lift back along the sidepod top as the airflow speeds over it. But more importantly the space for the undercut is limited by the space available below the upper SIPS and inlet.
HIGH TOP SIDEPOD
The design Ferrari pioneered with in 2017 and many are taking inspiration from in 2018 is the so-called high top sidepod. Here the upper SIPS sits lower and the inlet sits above it, what is critical here is that this allows the inlet to be as high as the 600mm bodywork height limit, some 80mm higher than a mid-inlet. This places the upper SIPS and the same size inlet much higher, creating an equally taller space for an undercut below.
With this larger undercut more air can be directed towards the rear of the car to drive the diffuser’s performance. Additionally, the thick lift inducing sidepod top is slimmed further aiding aero performance.
While the weight of the upper SIPS being lower is a small but useful reduction in CofG height, there may be a small weight penalty with the upper SIPS being mounted lower down the tub and needing reinforcement to transfer the crash loads into the chassis structure.
IS IT A MUST-HAVE?
There are some good aero and some other smaller benefits for the high top set up, but the importance of this design probably isn’t massive in terms of overall car performance. Teams without this design in 2018 will not be massively handicapped, the aero teams were bound to have tested the high-top solution and felt that their current mid inlet design works well enough. If the high-top solution is good enough, like other good ideas in F1, eventually everyone will follow them. For this year it’s likely to be front wing and bargeboard design that dominates the car’s aero performance, rather than sidepods alone.