2022 cars 'porpoising' at high speed

[djos]

Agreed, they aren’t ground effect vehicles using Venturi tunnels like the Pikes Peak Tacoma I posted earlier.

It has a flat floor and a diffuser. Any CART and Group C or LMP (etc.) with a third spring from the past thirty years would have been equally relevant. Venturi typically means to imply and hourglass profile beneath the car. The silhouette Tacoma is a ground effect vehicle in so far as any car with ground proximal aero devices is a ground effect vehicle; in the classic F1 sense it doesn't fit the description; no skirts, no venturi tunnels, no known instances of porpoising (on the mountain).

Did you even watch the video?

The Pikes Peak Tacoma has giant Venturi tunnels (shown in the video) and Rod Millen even says (in the video) that the 3rd spring setup was specifically to stop the car from bottoming out and choking the flow to the Venturi tunnels.

[Hoffman900]

Agreed, they aren’t ground effect vehicles using Venturi tunnels like the Pikes Peak Tacoma I posted earlier.

It has a flat floor and a diffuser. Any CART and Group C or LMP (etc.) with a third spring from the past thirty years would have been equally relevant. Venturi typically means to imply and hourglass profile beneath the car. The silhouette Tacoma is a ground effect vehicle in so far as any car with ground proximal aero devices is a ground effect vehicle; in the classic F1 sense it doesn't fit the description; no skirts, no venturi tunnels, no known instances of porpoising (on the mountain).

Did you even watch the video?

The Pikes Peak Tacoma has giant Venturi tunnels (shown in the video) and Rod Millen even says (in the video) that the 3rd spring setup was specifically to stop the car from bottoming out and choking the flow to the Venturi tunnels.

As someone who lives within eyesight of Pikes Peak, those vehicles do not go up it anywhere near the speed of a F1 car, the road is rough due to horrendous freeze / thaw conditions, and wings / tunnels are outsized due to the 1) lower speed 2) lower air density.

None of it is relevant to F1 or their porpoising phenemon.

Indy Car is interesting because they have been averaging north of 220mph around ovals for decades now.

[djos]

Did you even watch the video?

The Pikes Peak Tacoma has giant Venturi tunnels (shown in the video) and Rod Millen even says (in the video) that the 3rd spring setup was specifically to stop the car from bottoming out and choking the flow to the Venturi tunnels.

As someone who lives within eyesight of Pikes Peak, those vehicles do not go up it anywhere near the speed of a F1 car, the road is rough due to horrendous freeze / thaw conditions, and wings / tunnels are outsized due to the 1) lower speed 2) lower air density.

None of it is relevant to F1 or their porpoising phenemon.

Indy Car is interesting because they have been averaging north of 220mph around ovals for decades now.

That's completely incorrect, any vehicle with Venturi tunnels needs to control its minimum ride height or risk porposing, that's just a fact. It doesn't matter if you are doing 100mph or 200mph, porposing needs to be prevented if you want a stable and fast car.

[Hoffman900]

Did you even watch the video?

The Pikes Peak Tacoma has giant Venturi tunnels (shown in the video) and Rod Millen even says (in the video) that the 3rd spring setup was specifically to stop the car from bottoming out and choking the flow to the Venturi tunnels.

As someone who lives within eyesight of Pikes Peak, those vehicles do not go up it anywhere near the speed of a F1 car, the road is rough due to horrendous freeze / thaw conditions, and wings / tunnels are outsized due to the 1) lower speed 2) lower air density.

None of it is relevant to F1 or their porpoising phenemon.

Indy Car is interesting because they have been averaging north of 220mph around ovals for decades now.

That's completely incorrect, any vehicle with Venturi tunnels needs to control its minimum ride height or risk porposing, that's just a fact. It doesn't matter if you are doing 100mph or 200mph, porposing needs to be prevented if you want a stable and fast car.

Your assumption is that porpoising is caused by choked flow. If this is true, then the squatting of the previous generation of cars to reduce drag would have caused porpoising, and they didn’t.

It’s pretty much been said by all those who actually have a clue and spoken publicly; Jean-Claude Migeot, Peter Wright, and James Allison that choke flow is NOT the issue. I am not sure why people are yammering on about it still. Every single person in the media talking about this have no idea. They are journalists and pundits, not aerodynamicists, not engineers, and none have designed even something as simple as a Formula Ford.

As for the ride height, you need to control it on everything, from NASCAR, vintage Trans Am cars, to rally cars, to flat bottomed formula cars, to venturi F1 cars. It’s part of the go fast equation.

The heave spring set up came to be to control vertical downforce load while still being able to run a soft enough suspension for mechanical grip.

[djos]

As someone who lives within eyesight of Pikes Peak, those vehicles do not go up it anywhere near the speed of a F1 car, the road is rough due to horrendous freeze / thaw conditions, and wings / tunnels are outsized due to the 1) lower speed 2) lower air density.

None of it is relevant to F1 or their porpoising phenemon.

Indy Car is interesting because they have been averaging north of 220mph around ovals for decades now.

That's completely incorrect, any vehicle with Venturi tunnels needs to control its minimum ride height or risk porposing, that's just a fact. It doesn't matter if you are doing 100mph or 200mph, porposing needs to be prevented if you want a stable and fast car.

Your assumption is that porpoising is caused by choked flow. If this is true, then the squatting of the previous generation of cars to reduce drag would have caused porpoising, and they didn’t.

It’s pretty much been said by all those who actually have a clue and spoken publicly; Jean-Claude Migeot, Peter Wright, and James Allison that choke flow is NOT the issue. I am not sure why people are yammering on about it still. Every single person in the media talking about this have no idea. They are journalists and pundits, not aerodynamicists, not engineers, and none have designed even something as simple as a Formula Ford.

As for the ride height, you need to control it on everything, from NASCAR, vintage Trans Am cars, to rally cars, to flat bottomed formula cars, to venturi F1 cars. It’s part of the go fast equation.

You can't mix and match examples from Last gen and current gen F1 cars, last gen did not have Venturi tunnels and did not have flat bottoms either.

Perhaps you should take your argument up with the engineers who designed Rod Millens Tacoma, they clearly do not agree with your POV.

[Hoffman900]

That's completely incorrect, any vehicle with Venturi tunnels needs to control its minimum ride height or risk porposing, that's just a fact. It doesn't matter if you are doing 100mph or 200mph, porposing needs to be prevented if you want a stable and fast car.

Your assumption is that porpoising is caused by choked flow. If this is true, then the squatting of the previous generation of cars to reduce drag would have caused porpoising, and they didn’t.

It’s pretty much been said by all those who actually have a clue and spoken publicly; Jean-Claude Migeot, Peter Wright, and James Allison that choke flow is NOT the issue. I am not sure why people are yammering on about it still. Every single person in the media talking about this have no idea. They are journalists and pundits, not aerodynamicists, not engineers, and none have designed even something as simple as a Formula Ford.

As for the ride height, you need to control it on everything, from NASCAR, vintage Trans Am cars, to rally cars, to flat bottomed formula cars, to venturi F1 cars. It’s part of the go fast equation.

You can't mix and match examples from Last gen and current gen F1 cars, last gen did not have Venturi tunnels and did not have flat bottoms either.

Perhaps you should take your argument up with the engineers who designed Rod Millens Tacoma, they clearly do not agree with your POV.

I can definitely do that. The idea works the same. By choking the floor you reduce drag / downforce. It is the same issue. When that occurs, by your logic, the car should have rebounded, but they didn’t.

While I don’t know them, I do know others who build race cars at a high level and I know aerodynamicists. None of them, that I talked to, buy this stall induced porpoising phenomenon.

NASCAR doesn’t have tunnels and they have lived and died by this controlling ride height issue for decades. They do it with the shocks though. Controlling ride height is always important on a race car.

[djos]

The idea works the same. By choking the floor you reduce drag / downforce. It is the same issue.

While I don’t know them, I do know others who build race cars at a high level and I know aerodynamicists. None of them, that I talked to, buy this stall induced porpoising phenomenon.

On a Venturi tunnel car, choking the floor causes you to lose downforce - that much we agree on. I'm not an Aero engineer (ex IT Server Engineer / Electronics Engineer) so I have to rely on the experts like Aero Gandalf and those who build an operate race cars with Venturi tunnels.

[vorticism]

The Pikes Peak Tacoma has giant Venturi tunnels (shown in the video) and Rod Millen even says (in the video) that the 3rd spring setup was specifically to stop the car from bottoming out and choking the flow to the Venturi tunnels.

It's a diffuser, just larger than you're used to seeing maybe; flat floor in front of it. Tunnel alone doesn't imply venturi geometry (images below). The tunnel shape on the Tacoma is due to available free space within the chassis. See note on venturi nomenclature. Some might say any diffuser is a venturi or at least exhibits a venturi effect, although for specificity people usually say diffuser and reserve venturi tunnel for hourglass or wing profile shape as with a venturi tube. Third springs are for heave forces, yes, the building of aero forces. Not strictly to address porpoising.

[djos]

The Pikes Peak Tacoma has giant Venturi tunnels (shown in the video) and Rod Millen even says (in the video) that the 3rd spring setup was specifically to stop the car from bottoming out and choking the flow to the Venturi tunnels.

It's a diffuser, just larger than you're used to seeing maybe; flat floor in front of it. Tunnel alone doesn't imply venturi geometry (images below). The tunnel shape on the Tacoma is due to available free space within the chassis. See note on venturi nomenclature. Some might say any diffuser is a venturi or at least exhibits a venturi effect, although for specificity people usually say diffuser and reserve venturi tunnel for hourglass or wing profile shape as with a venturi tube. Third springs are for heave forces, yes, the building of aero forces. Not strictly to address porpoising.


http://www.mulsannescorner.com/ToytaEagleMkIII-RH6.jpg

https://cdn-6.motorsport.com/static/img ... aero-d.jpg

Take a closer look, the tunnels on the Tacoma actually start with the front under-wing which compresses the air ahead of the large expansion tunnels. Rod Millen specifically says the result is the downforce is generated at the centre of the car. If it was just a "normal" big diffuser setup that would not be the case, it would be rear biased.

Btw, here is Rod Millen Talking specifically about the 3rd Spring (20:18):



EDIT: and here is Rod Millen talking about the Venturi Tunnels and Aero design (12:16):

[vorticism]

Take a closer look, the tunnels on the Tacoma actually start with the front under-wing which compresses the air ahead of the large expansion tunnels. Rod Millen specifically says the result is the downforce is generated at the centre of the car. If it was just a "normal" big diffuser setup that would not be the case, it would be rear biased.

Btw, here is Rod Millen Talking specifically about the 3rd Spring (20:18):

https://youtu.be/SsB5RyQ5yqQ?t=1218

In the vid link you just posted you can see it's a flat bottom w diffuser. Similar to Group C etc. Not that this details matters too much to the current discussion.

Your initial claim was that suspension tuning for reaction to low Hz repetitive similar amplitude inputs was less relevant. It's too early to say if modern F1's porpoising is predominantly a suspension issue or an aero issue. There will be washboard or sawtooth or sine wave profiles to an F1 car's plotted vertical forces; just as with the road profile beneath the desert trucks. To Hoffman900's point: bottoming out on the Tacoma may be more like the concern with bottoming out on flat undertray cars (80s/90s F1, 80s/90s prototypes), not that it necessarily leads to porpoising. The downforce loss when transitioning to zero ride height might be more gradual than the flow structures breaking down on modern F1 cars, which can't fully bottom out; as such perhaps not instigating porpoising. Thus the role of the third spring might be looked at in a different light. As a ride height limiter/static heave spring force vs tuned to react to cyclical heave forces.

[vorticism]

[The] assumption is that porpoising is caused by choked flow. If this is true, then the squatting of the previous generation of cars to reduce drag would have caused porpoising, and they didn’t.

I think the same applies to the both the flat floor cars and the step plane cars. Basically, their floor generated downforce gradually reduces as ride height is lost, eventually to nil. All the while the other downforce providers are still contributing at their normal level. Hence, no spring back, as the wings continue providing downforce while the floor can only gradually increase from zero. The flat floor cars would just drive with the underfloor scrapping the ground not springing back up; pinned by the wings and a floor which couldn't suddenly start producing more downforce.

One of the mods recently said those cars could porpoise, and perhaps they could in certain circumstances, although I have never heard of them spoken about in that context. Contrast to current F1 cars. They produce more downforce the closer they get to the ground (note opposite trend vs. flat floor cars) up until a certain point, where there is a suddne downforce loss combined with a potential energy return from the suspension springs and tires. aka the onset of porpoising.

[vorticism]

It may follow then that one aerodynamic solution to porpoising on the 2022 cars would be to tune the maximum floor generated downforce to occur well before zero ride height (plank on ground), and ideally have zero ride height concur with as little floor downforce as possible. Tricky because the tunnels can't bottom out and will probably always be producing downforce regardless of ride height.

Some further mechanisms I'm considering:

-Bumps in the track initiate porpoising by causing the otherwise low riding car to suddenly rise; this rise re-intensifies the vortexes under the car causing a sudden low pressure increase pulling the car back down, which the suspension/tires can't cope with, leading to the cyclical phenomenon

-Front floor strake proximity near zero ride height causes a spike in front floor inlet high pressure; essentially if the strakes are too restrictive at near zero ride height they will cause the front floor to gain too much positive lift, pushing it up. Once it raises back up, pressure drops back to a normal level and overall vehicle downforce then pushes it back down, repeating. Essentially riding on a transient cyclical high pressure bubble under the front floor.

[humble sabot]

I don’t think quick movements from the body “re-intensify” underfloor vortexes so much as destabilize any flow structures.
I think the whole suspension angle must be some kind of red herring because the baseline for body control in F1 is already amongst the highest for short travel vehicles with high downforce.

Maybe the idea that it’s a “choking” specifically is a gross over simplification but not off base. I also think that the pedantry around “venturi” vs “diffuser” here is absurd.

It seems to me that the plank, being a linear surface, adjoining rather more sophisticated shaping probably has a very strong interaction with the stability of the flow structures under the car, be they inward flow, outward flow, or vortical. The fact that all the teams are extremely aggressively forcing most of the throat flow directly outwards as soon as possible seems like a very strong source as well of height sensitivity.

[vorticism]

To your first point: I suppose it depends on how compliant the suspension is. Bumps leading to either a loss of ride height or a gain. How does this relate to the onset mode? Is the onset defined by downforce loss or downforce gain?

[atanatizante]

Could someone explain to a novice why for F1-75 car :

1. porpoising is occurring at a higher speed than W13
2. this phenomenon is stopping when the car is approaching a slow, medium and medium-to-fast corner or just putting in other words why is occurring only on the straights?