Uncovered: The Secrets of Red Bull RB19 F1, part III - Underfloor Magic

Part I - here!

Part II - here!

Red Bull RB19 is 6/6 this season, winning every race so far. Luckily for us, we had a chance to "look up its skirt" as TP Horner said. Gracias Checo! We already knew that Red Bull has their own way of floor design in this "ground effect" era of F1, seeing the thing for the first time also in Monaco last year - and also thanks to Sergio Perez.

It was clear even then that Red Bull is doing things very differently. Usually, the ground effect floor is designed as a giant underside of a wing, having a smooth profile shape to provide a specific throat section (where the profile is closest to the ground) and form a Venturi channel, with throat section being the source of suction and therefore downforce. However, Red Bull seemed to design the floor with the throat moved way to the back and forming an almost discreet kick - this acute shape was in fact smooth, but the overall philosophy is the same.

The other specific of their design was a relatively high front part of the floor with an arched roof section. It became clear quickly the intention here is to allow the vortex shedding off the front strakes to develop fully and give it room to keep spinning along the roof all the way to the kick.The question remains - how does this compare to the typical Venturi floor design? Well, if things were this simple - it would be a very bad floor indeed!

While the numbers on these diagrams are irrelevant (as they depend on chosen surface Area), their nature and behaviour of two bodies is important. Both depend on gap to the ground to provide optimal performance, or when it comes to actual car - ride height. So, if there is a sweet spot and you want to go as low as possible, why did Red Bull chose to go high? And, more importantly, how did they claw back this raw, ride-height-dependant downforce they gave up on? Let's keep things up to date and take a look at RB19 floor now.

Needless to say, I do not own the original photos and you can find all of these and much more on f1technical.net/forum. As can be seen, RB19 floor is further developed and features much more details than last year. One thing that stands out from 2022 is an introduction of another kick, this time at the front. Both kicks provide local load for the floor, since they now form an elongated throat section in a way. But, we most definitely cannot make a 100% certain conclusion on the geometry based on the photos, no matter how many of them we look. With so many kicks, flicks and pockets, it is indeed very hard to distinguish individual forms and overall geometry - making it virtually impossible to give any guaranteed conclusion on what's actually going on and where.

With that said, we can continue our quest towards unravelling this aerodynamic engineering marvel. Another thing that seems to have changed from 2022 design is the lack of fully developed arch roof, going all the way to the diffuser kick. Yes, there is a section of some length with this arch (which has a much greater radii than R25 required by rules) but it's not as long as last year. There is a new feature instead, a very curios transition surface changing the profile to the diffuser kick along the floor section, both in longitudinal X-axis and lateral Y-axis. We'll come back to that later and let's see how the roof height compares to other competitors.

While my illustration and assumption of roof geometry may not be 100% accurate, the difference in roof height is clear and almost shocking. Ferrari utilises a typical Venturi floor, by its very definition. There is a single throat section, very low to the ground and reference plane (the one where the plank meets the floor) and the shape seems to be fairly smooth. Contrary to it, RB19 floor is still very high, has two big kicks and seemingly undefined throat section. If we return to the diagrams by prof. J. Katz above, we would have to assume Ferrari is generating much more downforce with their floor than Red Bull. However, Red Bull won every race so far and a few more podiums along the way, while Ferrari has just one single podium in 6 races this season and it's a general consensus that RB19 has the most downforce on the grid. So, where and how did RB19 find this extra downforce?

Let's digress a bit and ask a different question - why did Red Bull even chose a floor design like this in the first place? Those who followed F1 long enough, know the important thing is to win races and gather points. Being fast over a single lap is good, but not necessarily an indicator of strong performance in the race. It wasn't always like this, but since refuelling was banned in the race, setup changes between Qualification and Race also got outlawed and F1 switched to Pirelli tyres - it became the most important thing to pursue. Last year, we started the season with many cars bouncing all over the track due to the new floor regulations and it took some time for teams to get things sorted. Many got surprised by this phenomena, but not Red Bull, whose RB18 was almost always the car with the least visible amount of bouncing (or porpoising, the term that references to aerodynamic bouncing).

This bouncing was caused by excess downforce, to put things simply. With too much floor downforce, the cars started experiencing wild bouncing due to unstable aerodynamic load. As the car accelerates, downforce compresses the springs up to one point. Usually, the floors stall when they get too close to the ground (again, clearly seen on diagrams above) which leads to unloading of the floor, leading to spring decompression and an increase in ride height. This leads to flow reattachment and the whole cycle starts again and the frequency often keeps increasing with speed - as does the amplitude. While many believed this is what happened to F1 cars, it was also reported no teams found any initial stall to happen on the floor that caused the bouncing. In fact, it seems many teams had their cars bumping too hard when the springs compressed fully, leading to rebound suspension reaction, which is what often triggered the stall to complete the porpoising phenomena cycle. This is a curiosity and was not official confirmed, to the best of my knowledge.

So, how do you get rid of the bouncing? You can stiffen the suspension a lot, but this leads to great losses of mechanical grip and limits setup options - which can also lead to poor tyre treatment, short tyre life and loss of lap time since you can't ride the kerbs. Instead, many teams had to raise the roofs of their floors significantly and give up on raw ground-effect downforce in the process. If you have the car bouncing wildly, something might break and you end up with a DNF in the race. Even worse, the drivers can and did get hurt because of this, so you also lose driver performance in the process. RB18 had a raised roof from the start and this allowed the team to have two things:

• softer suspension and
• lowest possible ride height in medium and high-speed corners

Soft suspension is always welcome for mechanical traction and RB18 never had problems with that. Low ride height in corners makes up for high tunnel roof design, while it also provides better mechanical floor sealing, meaning you have less losses on the floor edges since their gap to the ground is as small as possible. In short, it's better to have a high tunnel roof and low ride height than to have low tunnel roof and high ride height. In fact, Ferrari SF-23 is reported to be very sensitive to ride height variations, especially since going faster in Qualifying makes the car ride lower than in the race - where Ferrari seems to be very weak so far. Overall, we can conclude it is very likely that Red Bull knowingly gave up on raw ground-effect downforce and chose to explore other phenomena to claw back the downforce it gave up on.

Red Bull has used transition zone between the boat section of the floor to include many small kicks that generate some local load. This is clear to conclude, since their local geometry forms mini diffusers. Many believe they are also vortex generators, however in my view they lack the discrete edge transition needed for that - they must be rounded by R25 per rules. This might not be their only function, but we will get back to that. Let's also take a more detailed look at RB19 diffuser design.

The diffuser has a complex curvature, after the kick there is a concave surface where there is some pressure recovery due to a drop in expansion. At the edge and under the beam wing, there is a specific flick on the floor, introducing another area of low pressure, which especially works together with beam wing to further drive the whole floor by generating big suction zone. When you have a big suction zone here, the whole mass of air under the floor also speeds up to reach this low pressure zone. However, these two points (underfloor kicks and diffuser design) are not the only secret. Coming back to three points now - front strake vortex, underfloor kick and also several specific transition areas on the floor. We will examine a small part of amazing work by Latios on F1Technical forum (more here).

Suction and downforce areas are painted in shades of blue and the peak is painted in purple. By my estimate, the peak equals to Cp=-1. The biggest load zones here are the diffuser kick, tunnel roof and rear corner of the floor. Tunnel roof and rear corner are loaded by two strong vortices and tunnel roof is interesting to observe. The vortex moves around and changes in strength (vorticity) along the tunnel. The rear corner vortex (incidentally, formed at the very place where RB19 floor has a pocket in its diffuser kick) continues going into the diffuser, where two vortices meet and form one typical diffuser fence vortex. Playing around with the geometry of the tunnel roof can have a big influence on how the strake vortex moves around and how strong it is. Helping it and feeding it with more air and guiding it in the right way can further improve the performance of the floor and claw back the raw downforce that you gave up on in the first place. Another important thing here is the rear tyre squirt management, which can have a big negative influence on diffuser performance if turbulent tyre squirt is sucked into it mid-corner.

Now that all of this comes together, it's not so strange to see Red Bull so focused on flow behaviour on top of the floor and right ahead of the mouse hole. It is clear great attention is paid to this area, meaning it must be a performance-critical zone. Indeed, it points to a complex interaction of several flow structures, both on top and under the floor. All of these must work in unison all the time at all ride heights - and Red Bull engineers have mastered this extraordinary task perfectly!

Honourable mention to RB19 Suspension

It was mentioned before that working the tyres in the right way (well, window is the right expression) is the most important thing for success in the race. After all, all the forces of acceleration, braking and downforce are transferred to the ground via 4 contact patches on the 4 tyres of the car. Suspension design is of course critical for this, however it is now also very important for aerodynamic performance. Don't get me wrong, ever since Lotus cars started featuring wings many decades ago, engineers understood this extra load must be transferred with proper suspension design. Later, it also became obvious you can lose a lot of downforce if the car is moving too much during the lap, leading to introduction of active suspension and other special suspension designs.

RB18 and RB19 feature a decent amount of anti-dive on the front suspension. As a non-expert in suspension, I will keep it simple and say only this - anti dive allows the car to move very little during any braking or other deceleration phase of the lap. Anti-squat in the rear does the same during acceleration. With ground effect floors, ride height is an absolutely essential performance driver and keeping the car stable over the entire lap, during braking and acceleration, in roll and over bumps and kerbs can lead to a big improvement in lap time. This is where suspension design is critical and Red Bull have shown to be the masters!

Final point for the amazing RB19 car. As it was also mentioned earlier, during the race the cars go slower through the corners than during qualifying. Since speed squared increases the downforce, this means you have less loading on the suspension springs during the race, especially at the start. This also leads to less spring compression, which leads to higher ride heights. Higher ride height means you lose floor performance, while you would actually want to drop the car even if you go slower. How do you do that? You can take a softer suspension setup and allow the car to compress at slower speeds. It is believed this is where RB19's amazing pace in the race comes from - they are able to ride lower even during the early laps and, when cars are heavy and centrifugal forces lead to lower cornering speeds. It also explains why Ferrari in particular suffers so much in the race - their suspension might be too stiff and their car too high in early stages, so they can't reach the optimal ride height window for their floor design. This could mean Red Bull purposefully gives up some raw downforce in peak performance to make sure the car behaves better in different conditions and, especially, during the race!

A big Thank You!

Yes, thank you for sticking around all the way through this text and taking interest in my thoughts. I hope you found it interesting and for students among you - I hope you found many topics to study further and unravel the wonderful science of Race Car Aerodynamics!

Ciao!