Perhaps one of the simplest and most misunderstood aerodynamic devices on a modern F1 car is the sharkfin. These large, sail like panels work great as billboards, but they also have a significant contribution to the lateral forces on the car when it is in a corner, and benefits in yaw stability.
The shark fin on the W08 progressively grew over the year from being non existent to completely full size.
The first misconception about the shark fin is that it has come about as a result of the low wings and the need to clear up airflow to them. This is patently untrue, Mercedes found in a study that the presence of the shark fin takes about 3% of your rear wing downforce in a straight line (I found a similar trend in the video at the bottom, but it was less as 2017 cars have wider wings, and I was using a truncated fin). There's a lot of talk about cleaning up airflow, but in a straight line the airflow is symmetric across the car (apart from transient fluctuations), so the shark fin does nothing except produce it's own boundary layer, drag and wake. In yaw, the fin does help the endplate separation, but these effects are very minor.
So, what are they for? Well, as Adrian Newey called it, it's like a weather vane. If you imagine a car taking a corner, the tyres have a slip angle, for an F1 car this is in the region of 2-4 degrees. As the rear axle is fixed as perpendicular to your car, you can see that for an infinite radius corner (strange to comprehend I know) 4 degrees of rear tyre slip angle means your car is effectively yawed 4 degrees into the corner. As your car gets under yaw, aerodynamic side forces will start to be applied through virtue of the whole car being at an angle. These side forces can help the car pull more lateral G, as they essentially push the car into the corner. For stability reasons, we want this sideforce to be behind the centre of gravity, much like the reason an arrow has feathers. The presence of the sharkfin both increases the amount of total sideforce we have available, and by virtue of being rearward, shifts the centre of pressure of the aero forces rearwards. This aids in our total lateral G, and our yaw stability, so it's win-win.
Shark fins aren't without cons though, while in a straight line the drag penalty is minimal, it does still exist. Again, while minimal, they add weight to the car, which is worse when you consider how high up it is. And in a straight line they compromise rear wing performance, which may have been why Mercedes was so reluctant to run them at the start of the year. They also increase side loads due to crosswinds, however this is somewhat offset by the yaw stability improvement in crosswind.
So, why are they getting banned next year? Well, halfway through the 2017 the rules for 2018 were changed to ban the fin on aesthetic grounds. However, soon after plans were set in motion for the fins to return, and teams started designing around the fins being there. That brings us to recently where McLaren decided to veto the rules change, reverting the rules back to the previous shark fin ban. The official story is that McLaren executive Zak Brown thinks they are ruining the commercial aspect of the rear wing, which seems a bit odd given the advertising space that the fins offer. As such, it may be likely that either a) McLaren was planning on using a last minute rules change to disrupt other teams rear wing designs, or b) They currently have a clever solution and total aero package in the works that functions effectively without the shark fin. I'll let you form your own opinion on what is the real case there, but hopefully we get to find out what they had planned in 2018.
Check out the video for a more detailed analysis of how shark fins work!
Kyle Forster is a qualified Aerodynamicist, race car engineer, and the man behind JKF Aero, a firm that offers a variety of aerodynamic consultancy services for racing purposes. If you have any questions for Kyle or have any suggestions for future videos, drop them in the comments below!