Porpoising – The Inevitable Consequence of Ground Effect

A porpoise is an aquatic animal, similar to a dolphin. Porpoises can usually be seen at the surface of the sea, jumping over the water and then going back into it. They repeat this in a cyclic rhythm that resembles an oscillation. The key word here is oscillation. Ever since the first day of testing in Barcelona for the current (2022) F1 season, where the cars in participation were all brand new and built from the ground up, F1 fans noticed a weird phenomenon. Some of the cars going down a straight were literally bouncing up and down at the rear. However, this bouncing was rhythmic and oscillatory in motion. Hence the name “porpoising” was given to this strange phenomenon. The word has been on the lips of all Formula 1 fans throughout every single session at every Grand Prix. 

In this article, the definition and causes of “porpoising” are discussed, along with its history in the field of motorsports. Also listed are a set of solutions, desired by some teams, to tackle the issue.

Ground Effect
Porpoising in itself is a complex phenomenon that occurs above certain speeds, as discussed further in the article. However, as a concept, porpoising can be easily understood by understanding the term “ground effect”. This is because cars that do experience porpoising are designed on the principle of ground effect.

The “venturi effect” states that if a liquid is passed through a constricted section (“choke”), the velocity of the fluid will be greater at the constriction due to the reduction in pressure, than at the wider end. Planes use the same principle to lift into the air. Formula 1 cars just use the inversion of this principle to make sure the vehicle sticks to the ground. The floor of the car is designed in such a way that it forces the air through a narrow passage which increases its speed, thus reducing the pressure underneath the car which pulls the car down, creating downforce. This phenomenon is called the ground effect.

Ground effect was not a concept that was used in early racing history. Take the 1960s for example. The cars then were as streamlined as possible so that they could “slip through the air” with the least drag. Although this, in my opinion, created some of the most beautiful cars in history (Jaguar D-Type, Ford GT40 MKII, Ferrari 330 P3), these vehicles struggled to turn to tackle high-speed corners without downforce. Due to the instability of these cars at speeds greater than 150 mph, fatal accidents were a common sight.

To make motorsports safer, manufacturers started to add wings or spoilers to the back of their cars to generate downforce at high speeds. There were similar attempts to increase downforce by using inverted wings and even fans! Perhaps one of the most iconic cars of F1 history is the Brabham BT46b or “The Fan Car”. Designed by a legend of the automotive world, Gordon Murray; the same man who designed the McLaren F1. The fan car also used the same principle: use a fan to lower the pressure at the back of the car to create downforce.

After the death of Jochen Rind in 1970 and the infamous Niki Lauda flaming inferno in 1976, the FIA decided to bring in more safety in the form of downforce. Manufacturers tried various methods but it was the late Colin Chapman at Lotus who created the first competitive ground effect F1 car in 1978 and aptly named it the Lotus 78. The underbody of the car was shaped in such a way that it increased the airflow through those tunnels and thus reduced pressure under the car. Consequently, it sucked the car down and increased downforce. In the Lotus 78, Mario Andretti won the 1978 West GP in Long Beach, California and  explained that ground effects made the race car “…feel like it’s planted to the road…”.

Gordon Murray’s BT49 was one of the most successful “ground effect” cars, winning the championship with Nelson Piquet behind the wheel in 1981.

Porpoising
Although teams tried to increase ground effect as much as possible by sealing the floor using skirts and underbody structures, the satisfactory wind tunnel results did not translate into real life. What happened in real life were “disturbances”. On the race track, the winds were not as “controlled” as produced in the wind tunnel testing scenarios. These “disturbances” were attributed to varying wind speeds, air density, gusts and wind direction. These scenarios were hard to simulate in the wind tunnel. If a car had the airflow under it “disturbed”, the low-pressure area would move unpredictably (i.e. stall) and the downforce would never be constant. An F1 car ‘stalls’ when the vehicle suddenly loses the lower air pressure underneath it, causing it to lift. This movement of the low-pressure area would cause the car to dip and heave, resulting in the phenomenon called “porpoising”. The FIA banned “ground effect” cars in 1983 as the unpredictability of the low-pressure area during high-speed corners would put the driver’s life in a massively risky situation.

With the advancement of technology and increase in competitiveness within the sport, “ground effect” was brought back for the 2021 season, although it was pushed forward a year due to the Coronavirus pandemic. The 2022 cars are supposed to be a lot cleaner: both aesthetically and aerodynamically. This allows for closer racing due to the car in front creating less wake which allows the car in behind to follow much closely. Wake is the turbulent air created by the car in front. Driving through this wake does not only affect the aerodynamics of the car behind but also the engine temperatures, as the wake is less dense and provides less airflow to cool the car.  The 2022 cars have been fitted with a wooden plank at the bottom so that the large venturi tunnels formed by strakes and veins stay intact even if the car runs over bumps and potholes.

Craig Scarborough, one of F1’s best technical journalists and illustrators, defines “porpoising” as the following: “As speed increases the downforce increases too. This compresses the tyres and suspension. As the underfloor gets closer to the ground, it works even better creating even more downforce (this is ground effect). Ride height continues to reduce with the aero load. This reaches a critical stage, where the ride height is too low and the airflow in the underfloor stalls. This suddenly reduces downforce, the reduction in load uncompresses the tyre/suspension, lifting the car back up to a higher ride height. This sets off a cycle, called porpoising. As normal ride height returns, the airflow reattaches and downforce is created again, again compressing the suspension. The car will bounce until its speed changes. Not every car will porpoise, some designs are more prone to it.”

The evidence of some teams struggling more than others can clearly be seen during the race. Porpoising not only affects the speed of the car in long straights, but it also affects the driver physically. Carlos Sainz claimed that the bouncing of the car at high speeds made him feel ill. Lewis Hamilton experienced some of the worst porpoising seen this season in the Azerbaijan Grand Prix and he even claimed that his lower back was hurting immensely. 

Porpoising also depends on the track surface, the wind, and many more factors. Therefore, if a car does well on one circuit, it does not mean that it will do equally better on another.

Take the Mercedes W13 for example. In the Spanish GP in Barcelona, it looked like they had solved their porpoising issues and left their troubles behind. However, a few races later in Baku they again displayed more porposing than any other team.

From the graphs above, it is clearly evident that the Mercedes W13 struggled immensely in Baku even though they finished just behind the Red Bulls. So how do you even solve this issue? Or do you just mitigate it?

Solutions

We’ve learned so far that porpoising is caused due to the stalling and un-stalling underneath the car. If the floor of the F1 car could be made stiff enough, it would stop the car from being sucked into the ground as much. However, the geometry of the floor makes it impossible to make it that stiff. Another method to stop the floor from collapsing would be to use a tie-rod but that wouldn’t be a long-term solution.

The simplest ‘solution’ would be to lift the car at the back. This would reduce the porpoising drastically. However, it could also be detrimental to the performance of the car. Lifting the car would reduce the ground effect drastically and thus also reduce downforce even though it would stop the porpoising.

The length of the gearbox casing and its packaging could also be an important factor. The cars that porpoise the least, i.e. the Ferrari and the Red Bull have a tear drop like shape whereas the Mercedes power unit cars are boxier.

As stated by Mark Hughes in a Tech Tuesday article for www.Formula1.com, the “boxier” cars have a wider design at the back and this could possibly contribute to the restriction of airflow in the underbody. Also, the centre of gravity for the more tear-drop-shaped cars is really in an awkward position relative to the stall point and this creates a leverage effect which stops it from stalling underneath.

Obviously, these solutions are legal ones from a technical perspective. But teams such as Mercedes that have been struggling have urged the FIA to consider solutions beyond the technical regulations. These solutions are Active Suspension and Tuned Mass Dampers.

Active Suspension:

The movement of an F1 car on its vertical axis is called heave and this movement is highly exaggerated during porpoising. Currently, the effect of heave is mitigated by a purely mechanical spring which is a passive element. This spring is quite large and adds weight to the front end of the vehicle. Since this spring is passive, it can only be adjusted while the car is in the pits, and changing the stiffness of this spring also changes the front-end characteristics of the car.

An “active suspension” can be used to combat porpoising by having measuring and control systems on each wheel. According to www.flowracers.com: “Active suspension in F1 is an electro-mechanical system that can actively adjust the stiffness and position of the suspension connection to each wheel. This is able to adjust the ride height of the car to ensure an aerodynamically efficient position despite the different conditions around a circuit.” An active suspension has multiple sensors, servo motors, and an ECU to actively adjust the stiffness of the suspension on each tire depending on the pressure feedback received from the tires. An active suspension can also adjust the ride height of the car and thus becomes one of the solutions to porpoising.

Since this form of suspension uses sensors and computers, the ride height is adjusted in real-time – hence the term, active suspension. A few of the control devices used include ride-height sensors, pressure sensors, ECUs, and servo motors. The sensors sense the vertical load change during porpoising and feed the data to the ECU. The computer then calculates the appropriate counter-measure required and feeds the servo motors/actuators with those results. The final control elements (servo motors) receive those commands and adjust the suspension accordingly. This process in its entirety happens almost instantly and thus provides a smoother ride, eliminating porpoising.

Unfortunately, the 2022 regulations state that the suspension has to be purely mechanical. There can not be any electrical or hydraulic assistance. This means that the heave has to be fully controlled only using a large mechanical spring that manages the vertical load of the vehicle. This spring has no sensors or actuators, therefore doesn’t have a feedback element, and can only stop the heave up to a certain point without affecting the driving characteristics of the car. The FIA also banned a couple of other tricks to prevent teams from finding loopholes (for example, the DAS system used by Mercedes in 2021).

Many individuals in the F1 paddock are in support of allowing cars to run active suspension. However, the teams that have reduced porpoising without compromising performance are, as expected, against it.

Mass Damper:

Mass Dampers and Inerters are another solution that can be considered to reduce porpoising. However, they are often confused with each other. A mass damper is a passive element and is connected to the chassis of the vehicle. An inerter is an active element and it is connected to the suspension (and also driven by it). Currently, both inerters and mass dampers are banned in Formula 1 as they both are “movable aerodynamic devices” and they violate Article 3.15 of the FIA Technical Regulations.

In the 2005 season, teams were required to have the front spring excessively stiff so that the front wing could be planted as close as possible to the ground. The idea was to increase the downforce at the front of the car with a simple solution. However, the stiffness of the front spring meant that it would not absorb as much of the vibrations which resulted in the front of the cars bouncing when they were in pitch. Renault found an ingenuous solution to the bouncing. They needed to install ballast in the car to help reach the minimum weight anyways so they installed a free-moving weight which was suspended in a cylinder. This was essentially a mass damper which counteracted the vertical movements of the front of the car. This not only reduced the bouncing but also allowed the drivers to be a lot more aggressive without compromising stability or aerodynamic grip. Renault also installed a mass damper at the rear of the car later in the season, and other teams also jumped on the bandwagon. However, movable aerodynamic devices were soon banned by the FIA and still are to this day.

Conclusion

Porpoising is not a new phenomenon. It has been around for a while and is an inevitable consequence of “ground effect” cars. It has more disadvantages than advantages, and is definitely a hindrance. Although solving the issue of porpoising is not an impossible task, doing it while still adhering to the technical regulations provided by the FIA and staying within the budget allocated, is what is stopping teams from getting rid of the issue. Some solutions were provided in the article that may help teams in the short-term while compromising some performance. Other solutions were also provided that go beyond the technical regulations but would definitely solve the issue with no drawbacks.

Key Words:
Porpoising, Ground effect, Mass Dampers, Inerters, Venturi Effect, Strakes, Active Suspension, Stall, Oscillations, FIA, Airflow, Formula 1.

References: 

• https://cdn-1.motorsport.com/images/amp/0qXjGQg6/s1000/formula-1-saudi-arabian-gp-202-2.webp 
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• https://www.formula1.com/en/latest/article.tech-tuesday-why-the-gearbox-layout-could-be-key-to-solving-the-porpoising.70jyq6WLn2OpvXsoXdlwQE.html
• https://www.formula1-dictionary.net/motions_of_f1_car.html
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The following blog post has been written by Aamir Ghare. An Instrumentation Engineer deeply engaged in cars all his life. Aamir loves watching motorsport and hopes to be involved in it in the near future.

This post has been edited for grammar and other inconsistencies. To learn how you can contribute to content creation at Formula Bharat, visit www.formulabharat.com/careers.

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