The mechanics behind porpoising in F1 - and how to fix it

If you look at Google’s trend graph for ‘porpoising’, there’s a very steep incline between the past week and the week before. Nobody was interested in the car-bouncing phenomenon named after the dolphin-like marine mammal until Formula 1’s 2022 cars broke cover – thus turning the Circuit de Barcelona-Catalunya's main straight into a bigger porpoise exhibition than SeaWorld.

Like the DAS and the “Pink Mercedes” in previous years, porpoising courted the column inches during the first week of pre-season testing at Barcelona. As the cars began to drop down towards the first corner, the cars began to shake up and down visibly, pacified only by the application of DRS or by the driver lifting off the throttle.

The appearance of porpoising appeared to catch many by surprise – even the teams, who had not encountered the sudden onset of an oscillating heave motion during their simulations. It was unclear what the root cause was, with many (ourselves included in this one) suggesting that it was a cyclical stall-and-reattachment of airflow under the car which was producing the lifting and rising motion.

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But that’s not quite right, explains Jean-Claude Migeot, the former chief aerodynamicist of Tyrrell and Ferrari in F1. He contends that stall cannot be the cause, firstly as detached flow can’t interact with the dynamics of the car, and also because the point at which the car begins to porpoise on the straights is long before the ideal point selected by F1 designers for the floor to stall and find extra speed under acceleration.

“The car started porpoising by the end of the pitlane, not far after that, which is not that high speed,” Migeot explains. “So if people design and set up their car to go into stall at that stage, it'd be massively wrong. So of course, the stall will happen, but much later; it depends how the underbody is designed. But it can't provoke this kind of thing because stall cannot interact with the mechanics, because it's detached, it's too late.

“It's like when a plane is stalling, it's falling like a stone because it cannot hang onto something. [Porpoising] is a very dynamic phenomenon. There's elastic forces in that process that change very quickly with ride height and that happens when the flow is attached both sides, on the body and on the ground.

F1 teams were taken aback by the level of porpoising seen during Barcelona testing

Photo by: Carl Bingham / Motorsport Images

“Stall is often helpful in a straight line because it stops the car sinking more, which means you can set it to lower on medium and high-speed corners. We are in a passive suspension era, so the car is sinking from zero speed up to the maximum speed it reaches, and stall is sort of limiting factor which help to set the car near to the optimum for the fastest corners.”

Instead, the cause of porpoising lies in studying the harmonic motion of the car, and the interaction between the aerodynamic forces and the suspension. At its absolute simplest, the aerodynamic forces produced by the underbody – now featuring Venturi tunnels – is very high, bringing the car down towards the ground and creating a nearly closed system underneath.

This leaves the car susceptible to resonance, the car in a position where it is effectively undamped. Since the undertray resembles a wing body, the long chord length means that it can produce resonance at low frequencies.

"When you look at the Ferrari, you see the rear moving up and the front a little bit. That’s because it's much stiffer on the front than the back. The movement is not parallel to the ground, but it's sort of rising back much more. That's the natural heave movement of the car" Jean-Claude Migeot

Migeot explains that, with the strength of the downward forces produced by the Venturi tunnels, the derivatives of those forces begin to produce a “very annoying” amplitude which then affects the dynamics of the car.

“When the car is shaking up and down quickly it can generate other forces,” he says. “It’s the same for an aeroplane when it’s climbing. When the pilot is pulling the stick there is an oscillation of incidence and there is a first link to the speed of pitch. But this coefficient is stabilising so in fact, the movement of the aeroplane is completely stable.

“For a Formula 1 car, it's destabilising because it increases the downforce when the car goes down and it's diminishing it when the car is moving up. That's the first step. The second step is these forces are big only in certain circumstances. Actually, up to last year, they were ridiculous; they were so low, that it was not even worth measuring them because they had no influence.

“But when you have a system which is almost a closed channel, which used to be the case with skirts, which looks like the case now when the perimeter of the floor is very close to the ground, the amplitude [of the forces] start to be annoying, really annoying. And this happens because there is an interaction.

Low floors contribute to increased movement

Photo by: Mark Sutton / Motorsport Images

“This starts because we're talking about long chord [floor] - we're talking about a length of several metres, which is in the same frequency range than the natural frequency of the car. The car has two natural frequencies – actually, there are four, but let's put the wheels bouncing outside of the picture because that's where they're controlled by the dampers. The body has two natural frequencies - the heave frequency, which is the movement you see at Barcelona, and the pitch frequency.

“When you look at the Ferrari, you see the rear moving up and the front a little bit. That’s because it's much stiffer on the front than the back. The movement is not parallel to the ground, but it's sort of rising back much more. That's the natural heave movement of the car.”

For clarity, every object has a natural frequency, at which it begins to vibrate. You might have even felt it yourself with motion sickness; your body is subjected to a frequency that induces nausea. Close to that value is a resonance frequency, at which the oscillations are at their greatest.

All structures are developed with that resonance frequency in mind, and numerous steps are taken to either avoid that frequency being driven into the structure by winds or seismic action – or tune it out. For example, the Taipei 101 tower in Taiwan makes uses a mass damper system to offset any resonant movements.

Cars have their own natural frequencies in heave (the up and down motion of the car) and pitch (the front-to-back rotation around the transverse axis where the car rocks backwards and forwards). Migeot says “this frequency in my time was typically 5Hz and 8Hz - five for the heave, eight for the pitch. Now with the stiffer tyres, I guess it's gone up a little bit but not that much because we’re talking about a stiff suspension.

“If the floor is on a very short chord like a wing, the phenomenon could be the same under the front wing, for instance, when it's very low [to the ground]. But the chord being so short, it's exciting frequency (the point at which the wing begins to oscillate dramatically) is much higher than the car frequency. So it's completely filtered.”

The next thing to note is that frequency is equal to one divided by the time period. Assuming that the heave frequency of the car is 5Hz, which is one complete oscillation, then the airspeed passing under the car would need to pass from the front to the back of the floor in a tenth of a second (or within a similar ballpark) to produce one half of that oscillation – so either the car lifting up or moving down.

Migeot, pictured with Jean Alesi aboard the Tyrrell 019, was an influential F1 aero guru before starting his own Fondtech consultancy

Photo by: Ercole Colombo

Migeot adds that if the airspeed is much lower than that – or much higher – then there’s no interference from the forces produced by the airflow. That’s why the previous example of the front wing won’t produce the same phenomenon, as the chord length is much shorter and thus takes much less time for the airflow to pass under it.

"If the time is similar; actually, this kind of speed may have half a tenth when the time for the air to go under from the leading edge to trailing edge is of a similar order - maybe twice or half as fast - that's an interaction,” he says. “And because of that interaction, the phase of the aero forces changes. That's mechanical engineering. To look at the dynamic mass damper system, the force is not synchronous with the movement - it's delayed.

“So it creates what I call an anti-damping which makes the dampers inefficient, because of the force which is opposed to the aero force. That's why you see the car bouncing like the damper was broken, because with increasing speed the damping is less and less and less effective.”

"The solution is in the windtunnel. The solution is looking at these forces and optimising them together with static forces" Jean-Claude Migeot

With porpoising proving to be a problem for the current generation of Formula 1 cars, the teams will have to enact a fix to alleviate the heave oscillations along the straight at high speeds. Although in testing it largely caused discomfort for the drivers, it could prove to be a problem in races with all 20 cars on track, as the motion could resurface in the wake of another car and cause instability under braking.

If not fixed in time, the porpoising effect could prove to be worse on other circuits where the bumpiness of the road can also contribute to driving further motion through the wheels as the suspension damping proves to be ineffective. Migeot says that owing to the restrictions on modern-day suspension, fixes will most likely have to be pursued in the windtunnel.

“The remedies on the mechanical side, knowing that active is verboten, the number of things that are not there [means] you are left with very little freedom or parameters to play with,” says Migeot, who in 1993 founded aerodynamic consultancy Fondtech, which today has three windtunnels across two sites. “You cannot ignore the optimisation of the static forces that put the car in the best position for whatever corner you choose. That is strategic.

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“On the suspension side, unless you’re making some invention; like at the time of the skirts, an inerter could be there and maybe that can help, but it's forbidden again. So the solution is in the windtunnel. The solution is looking at these forces and optimising them together with static forces.

Engineers have precious little time to understand and remedy the porpoising effect

Photo by: Mark Sutton / Motorsport Images

“I had a couple of years with porpoising at Renault in the last years of skirts, but the basic windtunnel technology was still in its infancy. It was also a big problem in Le Mans from the straight, high speed and also in the DTM - when we introduced this front undertray which were huge surfaces, it was porpoising like hell. But these were very heavy cars, so the driver could cope because it had much more inertia.

“But in a formula car, it's terrible. It's something you can do in the winter, but you need to have a model support, which is designed for dynamic testing. We had it on our windtunnels and we used them intensively for Le Mans, but after that they put the big plank on in Le Mans. So again, the problem got away. But it was still there on the front undertray; when we went to the open front on the Audi (R8), [we went] short on the front undertray and used a flap after it. That was mainly to get a smaller blown system at the front to tune the car without entering in instability. That's standard now.”

Migeot also suggests that F1 could also order a quick fix by re-introducing a stepped floor system to raise the height of the skirts – which would cut porpoising by limiting the ground effect, but also slash the speeds significantly. It would also lay waste to the optimisation work undertaken by the teams back at the factory during the design phase and thus be particularly unpopular.

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He also warns that, if teams aren’t able to get the porpoising and the reaction to the dynamic forces under control, that there could be “tragic” consequences owing to any destabilisation under braking, but that he “hopes to be wrong”. Some of the teams are finding their way around the problem, however, and are currently exploring options with regards to set-up and aerodynamics to counter the porpoising effect.

Just as the new F1 regulations have brought new tools and opportunities for the engineers to develop their solutions, they also bring their own troubles. The teams are confident that they can eliminate the porpoising problem – it just might take a little bit of time to iron out.

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Photo by: Mark Sutton / Motorsport Images