Instability of Ferrari SF-23: technical factor that alters aerodynamic map of floor

The eighteenth F1 weekend in Qatar didn’t provide any surprising results. It was known that Red Bull and McLaren’s performance would be very high, with Mercedes, Ferrari, and Aston Martin chasing this duo. Instead of dwelling on almost unchanged on-track values, which have already been extensively analyzed through our usual on-board, performance, and telemetric analyses, it can be useful to take a closer look at the challenging conditions that the drivers had to face on the Losail circuit.

We’re talking about aggressive curbs, very strict track limits, reduced grip due to sand, but above all, a lot of wind. It is this last point that we will focus on to understand how the air can affect the performance of an F1 car, making it extremely challenging to drive. We will also refer to simple physical concepts to better understand the situation.

Let’s start with the basics: Formula 1 cars utilize various components to generate downforce, a force directed downward that pushes the car towards the asphalt, increasing the tire contact area and, consequently, grip. The main downforce-producing surfaces are the wings and the underbody. Regarding the wings and their function, there is a “simple” physical relationship: L = 0.5 * ρ * A * v^2 * CL.

“ρ” (from the Greek “rho”) is the air density, a parameter that mainly varies with temperature, pressure, and to a lesser extent, humidity. By convention, the attributed value is 1.225 kg/m^3, evaluated at 15°C at sea level. In the specific case of Qatar, where various sessions take place at different times of the day, the value of ρ can fluctuate from a minimum of 1.164 kg/m^3 (e.g., night qualifying with an air temperature of 30°C) to a maximum of 1.127 kg/m^3 when the outside temperature reaches 40°C.

These variations are relatively small and do not significantly impact the downforce values produced. However, with the same downforce produced, it is possible to use lighter wings during night sessions. “A” is the frontal area, i.e., the value expressed in m^2 that represents the wing when viewed from the front. Its value primarily changes with the angle of attack of the flap: the wider the angle, the larger the frontal area. Specific configurations designed for greater load will provide higher A values.

“CL” is a dimensionless coefficient with no unit of measurement that depends on the shape of the aerodynamic profile. It also varies with the angle of attack. While “v” is, of course, the velocity expressed in m/s. It is the primary parameter that determines downforce, as it has a quadratic relationship with it. This means that if the speed doubles, the “L” produced will be four times greater, if it triples, it becomes nine times larger, and so on. This close relationship with speed helps us understand how the wind can disrupt performance.

Windy motion is nothing more than moving air with varying speed and direction, never constant, from a point A of high pressure to a point B of low pressure. The greater the pressure difference between A and B, the more significant the gradient that moves the air mass. A larger pressure difference allows the air to move more rapidly but for shorter distances, creating so-called wind gusts, as they are called in the UK.

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More than the intensity, the real problem that disorients the drivers is its inconsistency. Knowing the wind direction allows drivers to adapt their driving to the conditions: a tailwind will lengthen the braking phase and reduce the load produced by the wings. In contrast, a headwind allows slightly later braking and provides more confidence in fast corners. Crosswinds are the most “troublesome,” so to speak.

When the wind direction is uncertain, you often find yourself taking jumps into the unknown in corners. It’s easy to understand why. We’ve mentioned that downforce is mainly related to speed. Now imagine a corner of any track where the wind is blowing into the face of the driver. If in that turn you usually enter at a speed with a hypothetical value V1, the load produced will be determined by the previously mentioned formula and will have a value L1.

However, if an unexpected gust of wind (with a direction concordant to the wind and of constant value) arrives in the same corner, the relative airspeed will not be V1 as before but rather V1 + ΔV (with ΔV being the m/s value of the wind gust). As a result, the wing will produce more downforce, and the driver can achieve a higher speed in the corner compared to the previous lap.

To put this into context, think about the last weekend. In Qatar, on Friday afternoon, wind gusts reached speeds close to 35 km/h (approximately 10 m/s), causing load shifts of up to 10 percentage points. If the gust was in the opposite direction, the term ΔV would subtract from the initial speed V1, resulting in a decrease in the total load on the analyzed car.

Both examples are highly simplified to convey the idea. A key factor in real conditions would be the constant speed of the gust and its direction consistently aligned with the wind. However, this explains the drivers’ difficulty in dealing with the wind, as they need to have extreme sensitivity to aerodynamic grip to adapt their handling to different conditions.

Crosswinds are undoubtedly more challenging to explain and manage. F1 teams spend a significant portion of their allotted time in the wind tunnel studying the car’s behavior at different yaw or sideslip angles, which occur when the car rotates around its vertical axis. Essentially, in these tests, the car is rotated by a certain angle, making it transverse to the airflow in the wind tunnel.

It’s easy to understand that if the car were struck laterally by the air, some surfaces (the ones most exposed to the airflow) would produce more load than their symmetric counterparts, creating an aerodynamic imbalance, and thus a loss of proper balance. This can translate into understeer or oversteer issues depending on the track’s morphology.

Furthermore, with increasing yaw angles, the car body tends to behave like a sail: it is now known that air moves by pressure differences, and when it hits a surface, it generates a force called “pressure force.” It is evaluated as follows: F = p * S. It’s evident that this force is directly proportional to the exposed surface, which in turn varies with the yaw angle, making critical the corners and sections where the car is placed more perpendicular to the wind.

The underbody can also be affected by crosswinds because it alters the so-called aerodynamic map of the car’s floor, i.e., the values of pressure at every point on the underbody. Maintaining this map intact is of vital importance, as it is thanks to this factor that efficient load is produced and the car remains balanced.

This is not a perfect recipe for combating the adverse effects of wind and gusts due to their sudden and unpredictable nature. Nonetheless, engineers spend many hours simulating at the CFD and in the wind tunnel. The goal is clear: to experience what happens when exposed to the wind to “engineer” the cars and try to make them as insensitive as possible to gusts. It’s an aspect on which Ferrari, as we know, has shown a lack of expertise.

Ferrari SF-23: The Critical Aspects
Since the first outing on the track during the pre-season tests in Bahrain last February, the engineers at Scuderia Ferrari received certain confirmations regarding suspicions already held during the design phase: the vortex structure of the SF-23 was not performing on the track as expected through computer simulations. This is a fundamental problem that is not easily solvable in general, and even less so within a regulatory framework that restricts track testing as much as possible.

Apart from the outdated concept of various aerodynamic concepts that don’t offer significant advantages in current wing cars, it should be considered that the aerodynamics of the SF-23 continue to suffer from specific environmental conditions that worsen an already imperfect situation. As mentioned, given the budget cap, it’s not possible to completely overhaul certain design philosophies. This is because many of the visible shapes are tied to the car’s underlying structures “hidden” under the bodywork, such as the chassis and impact structure.

It’s clear that the technical team at Scuderia Ferrari, led by Enrico Cardile, could only partially modify the aerodynamics of the SF-23. Although the results obtained have improved the car’s airflow management, some problems continue to be present. This is why, for example, in Japan, they introduced yet another specific underbody (the fourth of the season), which was later approved in Qatar.

Fred Vasseur, along with the “two Carlos,” has often mentioned the wind as Ferrari’s number one enemy. Many have commented and labeled these words as a “simple excuse” to justify poor performances, considering that these conditions exist not only for Ferrari but for all teams. This is all true logically, until we consider a fact confirmed by the team management itself: the SF-23, compared to other F1 cars, is significantly more sensitive to the wind.

As we come to the end of this article, a question naturally arises: why does Maranello’s car show a higher level of discomfort compared to other cars? Assuming the answer is certainly not straightforward, especially without working within the GES and having access to the Italian engineers’ simulations, we can say that the “inherent uncertainty” related to the vortex structure produced by the SF-23 at certain speed ranges underlies this puzzle.

We know that medium-speed corners are difficult for the red car to handle. We received confirmation of this just a few days ago. Observing the on-board footage, it was clear that the SF-23 had a certain propensity to lose downforce in the high-speed sections of Losail. We are talking about a certain instability that Charles Leclerc himself commented on the radio repeatedly, considering himself fortunate not to have lost control of the car and ended up against the barriers.

The aerodynamic map of the Ferrari loses a lot of efficiency when it is hit by crosswinds, and as a result, localized downforce losses give rise to this sudden instability. This is a condition that is hardly manageable by the drivers. The various updates have allowed for the use of more suitable ride heights. In this sense, being able to set smaller heights relative to the reference plane (the asphalt) when defining the car’s setup helps shield the wind gusts that tend to slip under the car’s floor.

However, for all the reasons discussed earlier, the vortex structure of the Maranello car continues to suffer greatly from this context. For this reason, in certain layouts, the only useful solution is to minimize this limiting status. At the moment, there’s not much more that can be done.

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