TECH TUESDAY: The key developments that allowed Mercedes to come from behind to win its 8th constructors’ title


Mercedes faced its biggest hybrid-era challenge in 2021 from both a power-up Red Bull-Honda and a regulatory change that disproportionately impacted Merc’s low-lean aero philosophy. .

In the first part of the season, Mercedes most often played second behind Red Bull, winning just three of the first nine races, with Red Bull winning the remaining six, including five successively from Monaco to Austria.

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The turning point came at Silverstone, in many ways other than the infamous Lewis Hamilton / Max Verstappen crash. The British Grand Prix also marked the technical Mercedes’ season pivot as well, as a powerful upgrade allowed them to maximize the benefits still inherent in the low-lean concept, but which regulatory changes had made difficult to access.

From Silverstone, Mercedes was in the ascendant and, in its purest form, really should have won more than six of the remaining 13 races. Qualifying told a more representative story, with Mercedes on pole for eight of Silverstone’s 13 races, Red Bull just four times.

So here is the Mercedes technical story of ’21 …

MERCEDES’S RESPONSE TO THE RULE CHANGE

In terms of basic design, the team’s response to the floor / diffuser / rear brake duct regulatory restrictions while maintaining the same chassis was:

  • A new rear suspension revised to create even more air volume around the exterior of the diffuser.

  • The introduction of the Z-floor edge which would come to be widely copied.

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The development token spending allowed between the 2020 car and the ’21 car was around the nose of the car, but was for a feature that was never used, the assumption being that it provided no benefit.

Significant improvements were also made to the power unit, although they were not related to any regulatory changes.


Mercedes struggled more than Red Bull with regulatory change

Rear suspension

In 2020 Mercedes found big aerodynamic gains by sweeping the rear suspension far back, mounting the front lower wishbone in the crash structure rather than the gearbox, as is conventional. It was a feature copied by Red Bull on their ’21 car. Mercedes took it a step further with its own 21 car, the W12.

The lower links of the triangle were no longer contiguous but separated. This allowed the rear linkage to be mounted even further back and slightly higher, less disrupting airflow through the body coke cylinder section. It helped to try to recover the rear downforce lost due to regulation.



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In yellow above are the lower control arms of the rear suspension, now separate and not restricting airflow through the profile of the coke bottle (blue arrow)

Z-floor

To compensate for the ban on 21 louvers and slits in the floors that had previously helped seal the sub-floor by inducing vortices on its outer edges, Mercedes proposed a Z-shaped cutout along part of the length of the sub-floor. floor. which gave up some floor space in exchange for triggering air to create the desired vortices.

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The yellow section shows the floor area surrendered when creating the Z-floor

This and the waveforms immediately in front of the Z worked together to trigger the air by spinning and turning under the edge of the ground. The Z-floor ended up being present on all cars, but it appeared first on the Mercedes.

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On the W12 it was not enough to fully recover what the slots had done, and for the first few races the Merc had a significant rear downforce deficit, at its most evident in the opening race in Bahrain, where the car just doesn’t have the rear cornering entry stability traditionally seen in this team’s cars.

The changes were thought to have hurt the Mercedes’ low-tilt concept more than rival high-tilt designs, especially since the diffuser and rear brake ducts – both of which had been limited in the length of their vanes. – were physically more distant. on a low-tilt car. On a steep slope car, the diffuser rises with the car on its suspension to get closer to the brake ducts.



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The W12 lacked the rear stability characteristic of Mercedes in Bahrain

The airflow link between the two components was a powerful tool to energize the airflow around the diffuser and therefore the downforce created by the sub-floor.

For the remaining races between Bahrain and Silverstone, the team made detail changes to the barge panels and diffuser edges to bypass the basic rear limitation and new configurations were developed around the lack to make the more maneuverable car.

Behind the scenes though, work was underway on the planned big upgrade, which would debut at Silverstone.

THE SILVERSTONE UPGRADE

Obviously, the Silverstone upgrade was less dramatic than its effect. There was a reworked barge board, reshaped floor edge, and re-bevelled deflectors around the entire lower area in front of the pontoons.

Their goal was to divert some of the airflow to the underbody around the lower flanks. Why would an aero team seek to reduce the mass of airflow to the underbody, when underbody downforce is about four times more effective in drag than rear wing downforce? Because it was all about getting the diffuser to stall more fully at high speed when the car collapsed on its rear suspension.

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All teams use the diffuser stall to some extent. As the speed of a car increases, the downforce acting on it increases by the square of the increase in speed. As the rear of the car is pushed down on its suspension by downforce, a point is reached where the angle of expansion of the diffuser is small enough that there is no longer enough difference. pressure between the air under the flat part of the floor and that under the diffuser to keep the diffuser operating.

It actually stalls, losing a lot of downforce to the car but also the associated drag. The speed at which it does this can be adjusted with the rear ride height and suspension settings.

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It can also be adjusted according to the amount of air mass injected into the soil. The stall point will be easier to reach the less the mass of airflow passes through the ground. Hence the Silverstone upgrade diverting some of the airflow from the ground.

With a rear suspension geometry that locks in a lower position once beyond a predefined load threshold and only unlocks once a different (lower) threshold is reached, the car can be brought in lose a lot of drag at high speeds but still have good downforce at the speeds required for cornering. This is what Mercedes had.



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Mercedes got Red Bull licked in straight-line speed after Silverstone

The suspension system had been in place for a long time, but the Silverstone upgrade made the diffuser stall more efficient. This allowed Mercedes to use larger fenders and more lean to create more downforce, knowing that the usual drag penalties for this would be overcome by the diffuser stall and associated suspension sink.

For the remainder of the season, Red Bull couldn’t approach Mercedes’ straight-line speeds, as their cornering advantage was significantly reduced. This was the essence of the different competitive image between the two cars before and after Silverstone, which was only improved between Mexico and Brazil, as Mercedes found a much better setup which allowed Hamilton to ‘get more out of the car.

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The trellis around the planks of the barge (above) has been modified, as has the shape of the edge of the floor, especially around its leading edge. The purpose of these combined changes was to reduce the mass of air to the floor and divert some of it around the exterior body. This would normally be counterintuitive to achieve more effective downforce, but was done to facilitate greater diffuser stall in straight lines.

Overall, these changes were enough to allow Mercedes to win an unprecedented eighth consecutive Manufacturers’ Crown – and at times it seemed unlikely.


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