F1 / Mercedes, problems of heights – Carlo Platella

The Frecce d’Argento are experiencing the most difficult technical moment since the debut of hybrid engines in Formula 1. The reigning world champions currently hold the role of third force on the grid, but the performance gap from Ferrari and Red Bull appears decidedly wide and not easily bridged. However, Brackley’s technicians believe in recovery and in the possibility of returning soon to compete for pole position and victory. First, however, it will be necessary to fully understand the origin of the numerous problems that grip the W13, not attributable exclusively to the distinctive conformation of the bellies characterized by an extreme tapering. As always happens, the answers can only be given by Mercedes itself, but from the external observations and from the statements of the key figures of the team, the main criticalities that are currently slowing down the Anglo-German car emerge.

One of Mercedes’ great weaknesses at the start of the season is the lack of speed on the straight, a shortcoming also closely related to the lack of grip when cornering. The first suspect traditionally looked at when there is a lack of competitiveness in the draw is the engine. The Mercedes power unit does not appear at the same level as Ferrari and Red Bull / Honda, suffering a drop in power due in part to a less than excellent adaptation to the new fuels composed of 10% ethanol, but not only. At the end of last season the Brixworth engines had shown an inconsistency of performance as the accumulated mileage increased, with a progressive decline in performance. It is therefore not excluded that the modifications made to the 2022 engine have partially sacrificed power in favor of reliability and constant performance. However, according to what Mercedes recently leaked on several fronts, the gaps in the engine would have a marginal role in the gap currently accumulated by the W13s towards the F1-75 and the RB18.

Hence, to provide an explanation at low top speeds, aerodynamic drag takes over, of which three main sources can be identified. The first is the cooling drag, i.e. the resistance associated with the passage of flows inside the engine hood, through the cooling system. According to what recently declared by Pat Symonds, Mercedes in 2022 uses an intercooler developed by the aerospace company Reaction Engines, which among the advantages disclosed by the company itself boasts a reduction in aerodynamic resistance compared to a traditional intercooler. However, it is difficult to quantify how the compact packing of all the radiant masses on the W13 affects the cooling drag total. The second contribution is represented by the aerodynamic drag associated with the car body and wheels. As mentioned, the Silver Arrows have the smallest bellies of the entire grid, with shapes and a front section that, instinctively, would lead one to think that they also generate a low resistance to advancement. However, the compact sides leave the rear wheels completely exposed to the flow, partially shielded on the Ferrari by the bulky bellies of the F1-75, helping to increase the overall drag of the W13. On the previous generation of cars the tapering of the bellies was one of the main design guidelines, but the regulation also allowed the use of bargeboards, boomerangs and other appendages on board the car that allowed the turbulent flows coming from the front to be diverted externally.

The third macro-source of aerodynamic drag is embodied by the wing appendages, in particular the rear wing, which according to the technical director James Allison represents the main reason for the slowness of the Mercedes on the straight: I think it’s largely due to the size of our rear wing. With a little luck in the next races we will quickly improve our car and this will allow us to resize the rear wing and as a consequence to improve the speed on the straight ”. The Brackley team is in fact forced to resort to a generous rear wing, from which the low top speeds derive, to compensate for the lack of aerodynamic load generated by the underbody. This shows how the lack of competitiveness in length and cornering are strictly interconnected. The bottom represents the main source of downforce on the 2022 single-seaters, as well as the main determinant of performance. Its lateral Venturi channels follow a profile with a wide section at the entrance to the sides of the passenger compartment, followed by a narrowing that accelerates the flow, thus decreasing the pressure and accentuating the “sucking” effect at the base of the aerodynamic load. The lower the car is relative to the ground, the narrower the central section of the Venturi channel is compared to the inlet, the more the flow is accelerated and the underbody generates load. One of the problems that Mercedes is facing is the need to ride at a higher ground clearance than the opponents to control porpoising, thus sacrificing bottom load and trying to compensate for the loss with a larger rear wing.

Rebound fight
The Frecce d’Argento are among the cars that most of all suffer from porpoising, the uncontrolled rebound of the car body caused by the aerodynamic imbalances of the bottom. “The mechanisms that cause porpoising are not yet fully known”, James Allison explains“But they are quite different from the explanations commentators are providing on TV and on the web. The amount of porpoising on our car, especially when we introduced the evolution package during testing in Bahrain, was quite extreme“. According to the interpretation traditionally given so far to the porpoising phenomenon, as speeds increase, the aerodynamic load crushes the car to the ground. The height from the ground is thus reduced to a critical threshold beyond which the flow is interrupted, the bottom stalls and the loss of load causes the car body to rise. As the distance from the ground increases, the bottom starts to generate load again, triggering the entire cycle from scratch and giving life to the repeated oscillations. According to what Allison said, however, the phenomenon is much more complex and its accentuation with the arrival of the new bellies to the tests in Bahrain is proof of this. The package of updates introduced on the W13 has in fact changed the aerodynamic structure of the flows, the pressure fields and the vortices, thus increasing the sensitivity of the underbody to pressure imbalances. The fact that at the first race in Bahrain a new fund was tested, which however did not give the desired effects, confirms that the problem cannot be solved by intervening only on the fund itself.

Pending the arrival of further updates, the team is forced to increase the distance from the ground, thus sacrificing the load generated by the most important component of all, the bottom. In fact, the W13 is the car that is currently forced to run with the greatest ground clearance. “We are starting to keep porpoising under control “, comments Andrew Shovlin, chief engineer of runway operations, “But the moment we do it we are throwing away the basis of our car’s performancewhich is a minor problem, to keep the main criticality under control, that is the uncontrolled rebound “. As mentioned, porpoising was sharpened by the aerodynamic package introduced in Bahrain, but Mercedes’ refusal to return to the original version testifies to how the team believes in the possibility of solving the problem and above all in the potential of tapered bellies to improve extraction. of the rear speaker.

A sensitive car
In Saudi Arabia the gap of the W13 from Ferrari and Red Bull was wider than in Bahrain. On the one hand, the long straights highlighted the car’s shortcomings in lengthening, on the other hand the high-speed curves forced the ground clearance to be raised even more, sacrificing performance, to postpone porpoising and prevent it. triggering when cornering. The main criticality, however, lies in the difficulty not too hidden by the team in fully understanding the origin of the car’s problems, as stated by Shovlin: We still don’t understand the car as well as at the end of last year. This is why we always do set-up experiments with Lewis, trying to find a direction that gives us performance ”. The experimentation aspect was particularly emphasized: “We have a bit of a margin on the midfield, which we can use for experiment on the weekendtry solutions to improve the competitiveness of the car ”. A situation emerges in which Mercedes has yet to fully understand the behavior of the car and the direction to be imposed on development. “Honestly we are struggling to understand the car at the momentcommented Russell after qualifying, “We have a very small window and we have to adapt to this”.

However, experimentation always presents risks, which materialized on Saturday in Jeddah. Lewis Hamilton had found a right direction for the set-up on the night between Friday and Saturday, emphasized between FP3 and qualifying, but these last small corrections were enough to compromise the competitiveness of the car again, leading to exclusion in Q1 . The W13 also turns out to be a particularly nervous car and sensitive to set-up variations, limiting flexibility with the set-up, as confirmed by the words of Toto Wolf in the commentary on qualifying in Gedda: “We didn’t make huge set-up changes, but big enough to have dramatic consequences on machine performance”. In this aspect the difference emerges with Ferrari, which has made the flexibility of the set-up one of the design guidelines of the F1-75: For our part, we tried to design a car that was as flexible as possible with regards to set-up choiceswith the aim of not being bound to specific assets and not being able to move from one side to the other”, Explained Binotto during the presentation. “This is because we are convinced that in the initial phase, when we learn about the car and how to set it up, maybe we will have to make choices that we have not yet seen today, but that we must be sure that the car, from the point of view of the project, can grant “.

In conclusion, the current priority for Mercedes is the development of updates that allow to keep the porpoising phenomenon under control, so as to bring the car back to the optimal ground clearance and generate the necessary load from the bottom. The increase in the efficiency of the underbody will also be sought in the perspective of a new smaller rear wing, with which to reduce aerodynamic drag and improve travel in extension. Whether this will be enough to bring Mercedes back to Ferrari and Red Bull level only time will tell, also because in the meantime the competition will also progress. For the Brackley team, however, even more important of all will be improving understanding of the car, an essential tool for directing development and reducing set-up experiments, while defining more and more targeted set-ups.

FP | Carlo Platella


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