Mercedes W13

[Hoffman900]

So someone who has no F1 experience then?

Are we going to hang our hat on what someone who has no F1 experience, did some rudimentary Cfd work on a random forum says?

He worked on projects that had budgets of the entire F1 field combined and the issues if not resolved would have resulted in death. The physics are the same.

Likely the issue is Mercedes had a high peak downforce with a steep C_l curve, that as the car got sucked down, the velocity of it caused it bounce off the ground. This bouncing introduced von karmen vortex street components (ie: flutter) that it could never drive out of. Stiffening the car to keep it from bouncing off the floor only goes so far unless the forces involve overpower the sidewall, which they did. They're undampened.

I forgot how pedantic this place is and how much it's not about learning but a **** measuring contest of purported knowledge.

None of this has to do with personal knowledge. I've only presented to you Adrian Newey's comment on the matter. I am not a source of reference. I can only gather what other's have said and access their credibility.

When it comes down to it, your PHd friend has no race car experience while Adrian Newey just won the championship.

And I presented to you three other F1 aerodynamics, two of which have also won championships. In Merc's case, it's likely what I presented. Just stop and you're out of your depth, so not sure why you even waded into this in the first place. Flutter on an airliner flap is the same as a the rear wing bouncing up and down. It's the same physics and the negative feedback loops it presents are the same.

[henry]

Disagree Vanja, and I base that on talking to a PhD aero friend and hearing Peter Wright, James Allison, and Jean-Claude Migeot’s take. Lewis Hamilton also parroted the sidewall issue which would have come from his engineers.

If stall caused this, the collapsing rear suspensions of years pass would have also caused this, and they didn’t.

All cars have the same tires and some of them didn't porpoise. Yes, the tire sidewall has deflection under load, but sidewall deflection is simply a lowering of the car, triggering the aero induced porpoising, which is a matter of a poor approach to a ground effect floor design.

It has to do with peak downforce. Merc was making so much that a stiffer rear suspension pushed the loads into the sidewall and over powered it. This is a big part of why this didn’t scale to the wind tunnel model and the CFD didn’t pick it up because they don’t have accurate or the ability to use accurate tire models (tires are incredibly hard to model) and why their monster of a downforce making design failed in the real world.

The tyre sidewalls are springs in series with the mechanical suspension. They see the same loads.

[Vanja #66]

Well the issue is when it bounces off the floor from bottoming out, you've now introduced the Von Karmen Vortex street component (ie: flutter) and it can be self perpetuating. Model the car bouncing hard off the floor. This is the same reason hitting a bump for Mercedes would also introduce it.

A PhD Aerodynamicist friends who worked for one of the major aerospace companies, in a very high up level, gave me examples of this, but I can't share them.

Agreed, an aerodynamic phenomenon coupled with suspension travel that leads to separation

Flutter on an airliner flap is the same as a the rear wing bouncing up and down. It's the same physics and the negative feedback loops it presents are the same.

No, they are not really the same in any sense at all other than being aero foils that have some z-axis movement.

[AR3-GP]

Are we going to hang our hat on what someone who has no F1 experience, did some rudimentary Cfd work on a random forum says?

He worked on projects that had budgets of the entire F1 field combined and the issues if not resolved would have resulted in death. The physics are the same.

Likely the issue is Mercedes had a high peak downforce with a steep C_l curve, that as the car got sucked down, the velocity of it caused it bounce off the ground. This bouncing introduced von karmen vortex street components (ie: flutter) that it could never drive out of. Stiffening the car to keep it from bouncing off the floor only goes so far unless the forces involve overpower the sidewall, which they did. They're undampened.

I forgot how pedantic this place is and how much it's not about learning but a **** measuring contest of purported knowledge.

None of this has to do with personal knowledge. I've only presented to you Adrian Newey's comment on the matter. I am not a source of reference. I can only gather what other's have said and access their credibility.

When it comes down to it, your PHd friend has no race car experience while Adrian Newey just won the championship.

And I presented to you three other F1 aerodynamics, two of which have also won championships. In Merc's case, it's likely what I presented. Just stop and you're out of your depth, so not sure why you even waded into this in the first place. Flutter on an airliner flap is the same as a the rear wing bouncing up and down. It's the same physics and the negative feedback loops it presents are the same.

Adrian Newey built the car that did not porpoise and won the championship. One can presume that he knows more than the rest of your sources.

I never said that flutter does not exist. In fact I explained that flutter can be a forcing function acting upon a sprung mass, but highlighted that Adrian Newey does not point to it as the root cause. Adrian Newey points to the loss of downforce at very low ride heights.

You have a personal theory which seems to only apply to "Mercedes" prodigal levels of downforce superior to RB, but then fails to explain why backmarkers also porpoised.

The theories proposed by Adrian, Kyle, and Migeot are much more plausible and apply to all teams. It's nothing to do with overall downforce, but entirely due to the shape of the downforce curve as a function of ride height, and where you are operating the car in terms of ride height.

[Hoffman900]

Well the issue is when it bounces off the floor from bottoming out, you've now introduced the Von Karmen Vortex street component (ie: flutter) and it can be self perpetuating. Model the car bouncing hard off the floor. This is the same reason hitting a bump for Mercedes would also introduce it.

A PhD Aerodynamicist friends who worked for one of the major aerospace companies, in a very high up level, gave me examples of this, but I can't share them.

Agreed, an aerodynamic phenomenon coupled with suspension travel that leads to separation

Flutter on an airliner flap is the same as a the rear wing bouncing up and down. It's the same physics and the negative feedback loops it presents are the same.

No, they are not really the same in any sense at all other than being aero foils that have some z-axis movement.

A wing is a fixed flap that introduces those time forces into the chassis as opposed to the airplane wing or overpowers the hydraulics controlling the flap.

The tyre sidewalls are springs in series with the mechanical suspension. They see the same loads.

You put ever increasing stiffness springs on it to where the tires do most of the work. That's how they use to be and the inerters manage the undampened sidewalls in a way. That's why inerters are fantastic on large soft sidewall designs like the rear end of a drag car. This is also what tuned mass dampers control as well.

[Hoffman900]

None of this has to do with personal knowledge. I've only presented to you Adrian Newey's comment on the matter. I am not a source of reference. I can only gather what other's have said and access their credibility.

When it comes down to it, your PHd friend has no race car experience while Adrian Newey just won the championship.

And I presented to you three other F1 aerodynamics, two of which have also won championships. In Merc's case, it's likely what I presented. Just stop and you're out of your depth, so not sure why you even waded into this in the first place. Flutter on an airliner flap is the same as a the rear wing bouncing up and down. It's the same physics and the negative feedback loops it presents are the same.

Adrian Newey built the car that did not porpoise and won the championship. One can presume that he knows more than the rest of your sources.

I never said that flutter does not exist. In fact I explained that flutter can be a forcing function acting upon a sprung mass, but highlighted that Adrian Newey does not point to it as the root cause. Adrian Newey points to the loss of downforce at very low ride heights.

You have a personal theory which seems to only apply to "Mercedes" prodigal levels of downforce superior to RB, but then fails to explain why backmarkers also porpoised.

The theories proposed by Adrian, Kyle, and Migeot are much more plausible and apply to all teams. It's nothing to do with overall downforce, but entirely due to the shape of the downforce curve as a function of ride height, and where you are operating the car in terms of ride height.

There are multiple mechanisms at play. Yeah, stall/choke flow might be at play on them, but this is the W-13 thread and James Allison specifically called out that theory as wrong.

I was originally commenting on Vanja proposing that the it's choke flow in the W-13 thread, about the W-13.

[AR3-GP]

And I presented to you three other F1 aerodynamics, two of which have also won championships. In Merc's case, it's likely what I presented. Just stop and you're out of your depth, so not sure why you even waded into this in the first place. Flutter on an airliner flap is the same as a the rear wing bouncing up and down. It's the same physics and the negative feedback loops it presents are the same.

Adrian Newey built the car that did not porpoise and won the championship. One can presume that he knows more than the rest of your sources.

I never said that flutter does not exist. In fact I explained that flutter can be a forcing function acting upon a sprung mass, but highlighted that Adrian Newey does not point to it as the root cause. Adrian Newey points to the loss of downforce at very low ride heights.

You have a personal theory which seems to only apply to "Mercedes" prodigal levels of downforce superior to RB, but then fails to explain why backmarkers also porpoised.

The theories proposed by Adrian, Kyle, and Migeot are much more plausible and apply to all teams. It's nothing to do with overall downforce, but entirely due to the shape of the downforce curve as a function of ride height, and where you are operating the car in terms of ride height.

There are multiple mechanisms at play. Yeah, stall/choke flow might be at play on them, but this is the W-13 thread and James Allison specifically called out that theory as wrong.

I was originally commenting on Vanja proposing that the it's choke flow in the W-13 thread, about the W-13.

I understand your reference to James Allison but the problem is well...the W13. The W13 points to a general lack of understanding at Mercedes. James Allison's comments come from Bahrain. Mercedes did not understand much of anything at that point.

I acknowledge that there are always going to be multiple theories to explain a phenomenon. This is apparent looking at academic journals. What one can do to identify which theories are more likely to be accurate is to look at the pudding. The RB18 vs the W13.

[Hoffman900]

Adrian Newey built the car that did not porpoise and won the championship. One can presume that he knows more than the rest of your sources.

I never said that flutter does not exist. In fact I explained that flutter can be a forcing function acting upon a sprung mass, but highlighted that Adrian Newey does not point to it as the root cause. Adrian Newey points to the loss of downforce at very low ride heights.

You have a personal theory which seems to only apply to "Mercedes" prodigal levels of downforce superior to RB, but then fails to explain why backmarkers also porpoised.

The theories proposed by Adrian, Kyle, and Migeot are much more plausible and apply to all teams. It's nothing to do with overall downforce, but entirely due to the shape of the downforce curve as a function of ride height, and where you are operating the car in terms of ride height.

There are multiple mechanisms at play. Yeah, stall/choke flow might be at play on them, but this is the W-13 thread and James Allison specifically called out that theory as wrong.

I was originally commenting on Vanja proposing that the it's choke flow in the W-13 thread, about the W-13.

I understand your reference to James Allison but the problem is well...the W13. The W13 points to a general lack of understanding at Mercedes. James Allison's comments come from Bahrain. Mercedes did not understand much of anything at that point.

I acknowledge that there are always going to be multiple theories to explain a phenomenon. This is apparent looking at academic journals. What one can do to identify which theories are more likely to be accurate is to look at the pudding. The RB18 vs the W13.

Choke flow is the easiest thing to understand and would have been something they looked at from the get go. They actually purposely introduced this in the flat floor era on the straightaways and flat floors are also subjective to this phenomenon and also work best at low ride heights. This is a big reason why the cars in 1994 were a handful to drive. To paraphrase Frank Dernie, they're a mess at extremely low ride heights and specifically what the plank solved... kept the floor height to some rules mandated minimum.

What they didn't have was the ability to produce as much peak df as they have with the floor.

You can see that here:



From: https://viterbik12.usc.edu/wp-content/u ... namics.pdf

Notice how much less peaky a flat floor is? My guess is RB's floor has a flatter curve than the Merc which went for a narrow range / high peak df design.

The cited SAE paper:
https://www.researchgate.net/publicatio ... Components

[Vanja #66]

I was originally commenting on Vanja proposing that the it's choke flow in the W-13 thread, about the W-13.

I really hate it when posters here turn out to be arguing semantics over technical topics, which is why I wrote choke/stall later... I only use choke because this term is made closer to most users by the media. Oh well, at least this time in the end we came to an agreement.

[Hoffman900]

I was originally commenting on Vanja proposing that the it's choke flow in the W-13 thread, about the W-13.

I really hate it when posters here turn out to be arguing semantics over technical topics, which is why I wrote choke/stall later... I only use choke because this term is made closer to most users by the media. Oh well, at least this time in the end we came to an agreement.

That's fair. I mean, at the end, this just results in a bunch of technical-y data on the site. Better than the usual non-technical data.

[AR3-GP]

There are multiple mechanisms at play. Yeah, stall/choke flow might be at play on them, but this is the W-13 thread and James Allison specifically called out that theory as wrong.

I was originally commenting on Vanja proposing that the it's choke flow in the W-13 thread, about the W-13.

I understand your reference to James Allison but the problem is well...the W13. The W13 points to a general lack of understanding at Mercedes. James Allison's comments come from Bahrain. Mercedes did not understand much of anything at that point.

I acknowledge that there are always going to be multiple theories to explain a phenomenon. This is apparent looking at academic journals. What one can do to identify which theories are more likely to be accurate is to look at the pudding. The RB18 vs the W13.

Choke flow is the easiest thing to understand and would have been something they looked at from the get go. They actually purposely introduced this in the flat floor era on the straightaways and flat floors are also subjective to this phenomenon and also work best at low ride heights. This is a big reason why the cars in 1994 were a handful to drive. To paraphrase Frank Dernie, they're a mess at extremely low ride heights and specifically what the plank solved... kept the floor height to some rules mandated minimum.

What they didn't have was the ability to produce as much peak df as they have with the floor.

You can see that here:
https://live.staticflickr.com/65535/525 ... aa10_z.jpg
https://live.staticflickr.com/65535/525 ... 45d1_z.jpg

From: https://viterbik12.usc.edu/wp-content/u ... namics.pdf

Notice how much less peaky a flat floor is? My guess is RB's floor has a flatter curve than the Merc which went for a narrow range / high peak df design.

No car has anything near a "flat floor". Not the W13 or the other cars.

What Adrian and the others proposed is visible in your photo. If the shape of this downforce vs RH curve is like a bell at low ride heights, then you are going to be in for a bit of grief unless you operate far away from the bell.

Many things can get you into trouble with the bell. A random bump or compression in the circuit? A static rideheight that is already too low or if your floor literally flexes downwards and reduces the ground clearance.. Cars have "hit the deck" in years past to no ill effect. As suggested in the photo you linked. The flat floor doesn't have a bell. The flat floor drives to the ground and stays there because the downforce doesn't weaken causing the springs to raise the car again.

It's apparent that the W13 was designed to operate in a very unstable window and they presumed the suspension would keep the car on one side of the curve without regard for what happened as a result of perturbations near the bottom.

[Hoffman900]

I understand your reference to James Allison but the problem is well...the W13. The W13 points to a general lack of understanding at Mercedes. James Allison's comments come from Bahrain. Mercedes did not understand much of anything at that point.

I acknowledge that there are always going to be multiple theories to explain a phenomenon. This is apparent looking at academic journals. What one can do to identify which theories are more likely to be accurate is to look at the pudding. The RB18 vs the W13.

Choke flow is the easiest thing to understand and would have been something they looked at from the get go. They actually purposely introduced this in the flat floor era on the straightaways and flat floors are also subjective to this phenomenon and also work best at low ride heights. This is a big reason why the cars in 1994 were a handful to drive. To paraphrase Frank Dernie, they're a mess at extremely low ride heights and specifically what the plank solved... kept the floor height to some rules mandated minimum.

What they didn't have was the ability to produce as much peak df as they have with the floor.

You can see that here:
https://live.staticflickr.com/65535/525 ... aa10_z.jpg
https://live.staticflickr.com/65535/525 ... 45d1_z.jpg

From: https://viterbik12.usc.edu/wp-content/u ... namics.pdf

Notice how much less peaky a flat floor is? My guess is RB's floor has a flatter curve than the Merc which went for a narrow range / high peak df design.

No car has anything near a "flat floor". Not the W13 or the other cars.

What Adrian and the others proposed is visible in your photo. If the shape of this downforce vs RH curve is like a bell at low ride heights, then you are going to be in for a bit of grief unless you operate far away from the bell.

Many things can get you into trouble with the bell. A random bump or compression in the circuit? A static rideheight that is already too low or if your floor literally flexes downwards and reduces the ground clearance.. Cars have "hit the deck" in years past to no ill effect. As suggested in the photo you linked. The flat floor doesn't have a bell. The flat floor drives to the ground and stays there because the downforce doesn't weaken causing the springs to raise the car again.

It's apparent that the W13 was designed to operate in a very unstable window and they presumed the suspension would keep the car on one side of the curve without regard for what happened as a result of perturbations near the bottom.

Not sure why they would design a floor that breaks down with the plank height at zero. That ultimately dictates your "too low". Remember, the plank height and tunnel dimensions are dictated such that choke flow shouldn't occur, the dimensions are known in advance. If you look at a C_l curve, the part where it drops back down should occur at a ride height at some point lower than the plank will let you, this way you never theoretically reach that point on track. That is the whole point of the plank to begin with, flat floor or venturi tunnel, and why it came into existence (dictate aerodynamic stability of the floor by having some minimum)

[maxxer]

So if you design the venturi inlets so that when the car is almost bottoming out they let less air in the problem would be solved?

The only time that happens is when the throat is choked - and that's how bouncing starts

Oops we just revealed the problem then

[e30ernest]

Adrian Newey built the car that did not porpoise and won the championship. One can presume that he knows more than the rest of your sources.

While I don't disagree with your point about Newey probably being among the few who actually knows what's going on, I'd also take whatever he says with a massive grain of salt. The same for James Allison really.

There is a massive competitive advantage to be had by understanding this phenomenon. Neither of them are going to give straight out explanations on what is causing the porpoising. It is possible both Newey and Allison are telling part truths, or they can be misdirecting totally.

I do love this discussion on the Merc's floor though. Been learning a lot from Vanja #66 and Hoffman900.

[VacuousFlamboyant]

So if you design the venturi inlets so that when the car is almost bottoming out they let less air in the problem would be solved?

The only time that happens is when the throat is choked - and that's how bouncing starts

Oops we just revealed the problem then

The key issue is how to mitigate it, on top of avoiding it. I suspect the placement of side vortex generators in the throat section, where air velocity is higher and would be more prone to leak or choke the inlet if it has nowhere to go, helps in this regard. Many teams have moved them to the middle of the floor.

That's why one of the things I expect Merc to do next year is a small cutout that leads to this area, to extract the excess mass flow that could choke the floor. (A new chassi, with slightly wider sidopods for better colling management, increased coke bottle effect and lower COG due to the radiators, so more air goes into a smaller rear wing, you get the idea... hidden mirrors I posted here and a large soda. Please!)