RACING

TECH TUESDAY: The smart Red Bull subfloor that made porpoising less of a problem on the RB18

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Mark Hughes examines how the Red Bull subfloor design could have made the team less prone to porpoising in Azerbaijan, with technical illustrations by Giorgio Piola.

Baku has revealed how much porpoising is still suffered by many cars, but it is clear that the winning Red Bull was not significantly compromised by the phenomenon, as it has been since the start of the season.

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As such, the RB18’s subfloor design – which is notably different in concept and detail to that of its main Ferrari rivals – is attracting a lot of attention now that it has been revealed further after the crash. by Sergio Perez during qualifying in Monaco.

Before looking at specific floor details, perhaps the most significant aspect of its design is how its tunnel roof appears to be taller and more arched than those on other floors. Potentially, this should make it inherently less prone to stalling.


The Red Bull subfloor keel is less pear-shaped than other cars, with specific contours (1, 2 and 3). It would seem that the Red Bull tunnels therefore allow for greater variability in pressure as the ride height decreases and increases with the speed of the car. The tunnels also vary along their length, suggesting that they are carefully matched to the roof of the tunnel to equalize the pressure in this front part of the tunnel. The ‘ice skate’ element (4) is a metal wing under the floor.

As the car’s speed increases, it gets closer to the ground and ground effect – which is derived from air rushing through the small gap in the lowest part of the tunnel to fill the upper low-pressure area behind – becomes more powerful. As the gap narrows to the last millimeters, the airflow velocity – and therefore downforce – increases exponentially.

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The danger is that it can get so close to the ground that the airflow stops, triggering porpoising. A taller roof should make downforce less sensitive to height, even if its theoretical maximum downforce is lower. It is the expansion of air into the larger volume behind the small gap (between the tunnel and the track surface) that creates the lower pressure behind the gap that the air rushes to fill.

As the car lowers, this roof seems to allow for more air expansion and therefore less chance of the space being blocked by overpressure.


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Ferrari’s flat center keel is uniformly pear-shaped and less complex than that of the Red Bull.

But even within this general layout, there are several very distinctive characteristics of the Red Bull floor.

Adrian Newey pointed out that there are many different airflows under the ground and the key is to make them work together. The entry strakes at the front of the floor have a variable geometry along their length, probably adapted to the shape of the tunnel and thus helping to equalize the pressure, giving the airflow more energy as it travels through the tunnel. A lot of effort seems to have gone into matching the lateral and vertical shapes to keep the resulting volume as consistent as possible at different ride heights.

Likewise, the flat central keel is not uniformly pear-shaped as in other cars (see the Ferrari for comparison) and appears to be shaped in conjunction with the varying height of the tunnel along its length. The volume of the tunnel available for air obviously decreases as the ride height decreases. This shaping would make the change in tunnel volume at different ride heights more even throughout the length.

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Sergio Perez’s RB18 released in Monaco, with ‘ice skate’ location circled

There are also at least two distinct “mini-venturis” in the tunnel – where the height changes to form diffusers to reinvigorate the airflow. Red Bull is not unique in this area, but it is another detail that adds to the effectiveness of the Red Bull subfloor.

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Finally, just at the point where the ground begins to taper inward in front of the rear wheels, there’s what’s been called an ‘ice skate’ (above). The regulations allow a mini-wing on the ground in front of the rear wheels, but do not specify that it must be above the ground. Red Bull interpreted this to form an additional strake – metal to make it less vulnerable – on the subfloor there to help channel air more aggressively towards the tunnel exit.

The Red Bull floor is obviously of a more complex and sophisticated design than those of other cars. It’s probably no coincidence that he’s relatively immune to porpoising while still creating good downforce.

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