Mercedes rear wing wobble, might be a TMD!

YeahOuch

First off, are there any engineers here who can put some maths to all of this?

I saw the discussion on the F1 thread and wanted to spin it off to a new thread to avoid it being mixed up with the usual gossip and chat. Plus, this is a wordy post by definition because the specifics of this are pretty subtle and I’m going to need you to visualise what I’m describing to show you what I’m implying here, so that’s going to need a lot of words too.

At first I dismissed the rear wing wobble as a nothing story, most likely the usual Mercedes bashing from Italian media in the lead up to Monza to gee up the tifosi. Plus, intuitively, having a destabilised wing should be counter-productive, right? But the deeper I’ve thought about this, there’s a compelling argument to be made here that Mercedes is pushing right past the boundaries of what’s intended by the rules.

Note, I’m not making accusations of cheating but mainly because I don’t think there are regs focusing on what they might be doing here. If what I describe below is close to the truth, then, from an aero-philosophy viewpoint, Mercedes has made their rear wing & suspension interact in a way that can be considered to be a Tuned Mass Damper! But with the added benefit that instead of having an actual TMD device, such as mid-2000’s Renault, Mercedes has tuned their aero/suspension interactions to mimic the affect of having a TMD device.

So, this needs some background before I go into what they’re doing and then drawing conclusions:

- background: are Mercedes capable of this? Yes, for a number of reasons. Not just to do with money or an innate willingness to push the boundaries of the regs way beyond the “spirit” of the regs but also do they have the materials knowledge to produce an intentionally-wobbly rear wing while also demonstrating that they clearly have the expertise to fine tune a suspension setup to extract subtle-yet-influential gains? All of those are easily proven: Mercedes are the richest team on the grid, so money and materials’ expertise is a given. And they’ve been caught red handed pushing the limits of what’s legal so many times it’s impressive: notably, the oil burning scandal and their trick suspension.

It’s this last one that also implies that they’ve got the expertise to fine tune a suspension far beyond what us lay people consider. The trick suspension was doing way more than the usual springs/shocks tuning, which is why it was banned in 2017. Pre-season rumors back in February 2018 hinted that not only had they revamped their trick suspension to be a totally compliant suspension setup for 2018, but that it outperforms their previous architecture.

So that’s the suspension background, what’s that got to do with a wobbly rear wing? We are all taught that the best performing rear wing, from an aero point of view, will be absolutely horizontal at all points throughout a corner. And to achieve that, suspension needs to be tuned to counteract the centripetal forces that both push a car away from an apex but also, and importantly here, those forces also induce body roll that rotates the car around its center of mass such that the inside tries to rotate up, off the ground. This is usually counteracted by the suspension being tuned to allow for a certain amount of body roll. And the rules assert that the only way that body roll is allowed to be counteracted is by tuning the suspension springs & shocks. That very assertion is why Renault’s TMD and Mercedes’ trick suspension were banned.

Body roll and it’s suspension is a huge factor in rear wing design too: taking the aero-philosophy that “we want our rear wing to be as horizontal as possible throughout the apex” also mandates that you need to put extra emphasis and effort into stiffening the rear wing side walls because rear wings do not have suspensions to counteract body roll, they are just flapping about in the breeze, so to speak. Ferrari & Red Bull have clearly gone to great effort to stiffen their rear wings, according to the video evidence.

So a flat horizontal rear wing is theoretically ideal and that is the design philosophy expected by the current F1 regs; but we all know that ideal is never achievable. What if we flip that paradigm and embrace that idea, and design our car, not with the philosophy that it’ll corner with a rear wing that is as horizontal as possible: what if we design a car that is tuned from the ground up to not just expect that body roll will happen but to thrive in that condition?

At first the intuitive reaction to this is: why? We’ll need to deal with harmonics from a wobbly rear wing that are just not present when we stiffen it. Also, and more pertinent: what benefits will we get? All intuition points to a horizontal rear wing having the optimal performance anyway, one that pushes straight down perpendicular to the track, and therefore straight through the tires. But is that true?

If we fine tune our suspension to account for a rear wing that is built to embrace body roll: we can use that to pivot the rear wing around the center of the car ensuring that the aerodynamic force generated by the wing doesn’t push straight down but pushes at an angle, straight through the center of mass of the car.

Now you’re thinking: “WTF, why would I want that? I need downforce, not slightlyoffsetatanangleforce”. And I was too until I realised that such a setup would provide not just downforce but also would provide a force parallel to the corner literally pushing the car into the apex.

Why should we care about that? It’ll counter the centripetal force pushing the car away from the track, making it easier for the car to hit the apex and thus shorten the track. Plus it’s affect is directly proportional to the amount of centripetal force pushing your car away from the apex. And best of all, it works no matter which direction you turn! It’s a win-win if you can get this philosophy to work.

I’ve never heard of aero being used in this way before but if this is what Mercedes are doing its so impressive. And totally legal too!

This philosophy is bonkers, I know, and I understand how ridiculous it is that I’ve written such a detailed post but I’d love to see what engineers on here think about the implications here because as far as I can see, such a philosophy is totally counterintuitive at first glance yet totally plausible on F1 cars.

PS: while I’m at it, thinking on this last night I hit on some reinforcements backing up this idea that are too juicy not to share: an aero-philosophy such as this also implies a lot of other known quantities about Mercedes cars that we all know of: particularly low rake & low performance in dirty air!

Why low rake? Well the high rake philosophy preferred by Ferrari and Red Bull (and pretty much everyone else) derives it’s performance advantage by generating downforce from under the floor, which overwhelmingly favors as horizontal a pitch as possible because any body roll will raise one side of the car and thus ruin the air pressure differentials built up by the floor. They need the car to be perfectly parallel to the track, that is critical to optimizing their performance and also implies why they’d put such effort into stiffening the rear wing.

And dirty air? How does that make any difference? Well, the potential-Mercedes philosophy would by its nature depend on untouched airflow to maximise the gains brought by the rear wing. If you visualise just the rear wing itself, unconnected to anything and surrounded by nothing but air: if that air is natural and perfect, it’ll produce its usual amount of downforce. But if that air is coming off the back of a horizontal wing: the air is not only turbulent but it’s turbulent at a slightly different angle to our wing, inducing even more turbulence that is also not evenly spread across the wing. Leading to a situation where stalling is much more likely.

Also the wing performs its tricks when it’s tilted and suspension is tuned for each track, this means the car has to be going as fast as possible to induce the wing tilt angle that is needed to get the suspension to do its magic. If you’re slowed down by a car in front of you, your wing produces less tilt which kicks your suspension out of tune.

Downsides to this are many: notably mucking up your suspension setup. But Mercedes are experts at this and usually nail it. However, we have all seen weekends where they’re just “off” as a team, right? This could totally be explained by this idea, if, for whatever reason, they just don’t nail the suspension setup then the car will be out of balance for the whole track and thus underperform. At least the high take cars just need to nail a horizontal setup, Mercedes are dealing with both 1st & 2nd harmonics and resonances and all sorts of headaches derived from having many more movable parts than the high take teams.

Another backup to this idea is driving style: (the term smoothness is up for debate so I’m going to define it here and, for this particular point, use “smoothness” as a term to describe a driver who is gentle around corners and is also smooth on the throttle around corners.) So, this aero-philosophy would best be driven by a smooth driver who does not tend to smash the kerbs. Smashing the kerbs or even applying the throttle in a janky way will, as we saw in that Sky Italia video, induce the wobbly rear wing to oscillate violently (which will also reduce performance), much more than the stiff rear wings of the high rake teams. Coincidentally, Mercedes happen to have two of the absolute smoothest drivers on the grid. Apart from Alonso, is any other driver as smooth? And even more coincidentally, the Mercedes up and comer, Ocon, is also an exceptionally smooth driver.

So TL;DR: Mercedes are intentionally building a wobbly rear wing and that has been the secret to their exceptional chassis performance. They’ve been caught out and the clock is now counting down to a ban.

Conclusion: All of the above points to this being a moveable aerodynamic device and it’ll be banned ASAP because to compete on this front will cost the high take teams a fortune. (And, funnily enough, it’s literally a moveable aerodynamic device because it moved when it wobbles!).

I’d love to see what everyone else thinks of this. I don’t know the specifics detailed by the regs here, I’m sue they have some sort of mandate for rear wing sidewall stiffness and I’m sure that the stiffness test can be gamed by a team that knows what they’re doing which would make this innovation “technically legal”. If this is what Mercedes are doing, I cannot express how happy I am. Crazy **** like this is one of the best advertisements for why F1 is the pinnacle of motorsport!

Also if this is banned and Mercedes has got to totally revamp their aero- or suspension philosophy/architecture for 2019, that either bodes for a Ferrari dominant season or yet another tight battle. Either way it’ll make for drama!

YeahOuch

vectra wrote: »

Was there any investigation into Mercedes flexy rear wing last Sunday?

twitter. com/Vetteleclerc/status/1033791752216473605

This is the video, I can’t post urls but just take out the spaces.

vectra

Not an engineer nor am I anything close to it,
But on that said discussion it was stated that the reason the merc wing appeared to be so wobbly was because of how Lewis hit the kerb.
Well, strangely enough at one point today Lewis mounted the kerb in a very similar manner and the wing looked very stable compared to last week.
Coincidence?


https://twitter.com/Vetteleclerc/status/1033791752216473605