PHYSICS Aero. I believe I can fly…

Wings? Where we going we don't need any wings...
In original AC we could simulate as many wings a we wanted. So you wanted to simulate the body aerodynamics? Put a wing and apply proper values. You had a splitter? Add a wing with different values. Rear spoiler? Add a wing. Diffuser? Vertical fins? Side boards? Buffets. Add a wing. Each wing could have a specific area, lift coefficients, drag coefficients, sensitivity to ride height, yaw sensitivity… even active telemetry inputs that could modify the angle in real time and simulate all those active wings moving around… pretty impressive stuff, many industry firsts and so on. We were quite proud of the aero system in AC…

Great, scratch that and let’s build something completely new.
The aerodynamic model for ACC is completely rewritten from Stefano and Fernando. It doesn’t use an unlimited amount of wings anymore, but takes aeromap data from wind tunnels or CFD and uses them in way that everything in the car body, influences everything.
Ok let’s take a step back and analyze what is happening in real life and why such a development was needed. In real life an object, a racing car in our case, travels through air which is a fluid. Flow and turbulence is created and the shape, size and speed of them is relative to the shape of the object. Now comes the “obvious” but interesting part, a change in the shape of the object, changes the flow and the turbulence. A racing car is a big object and features on the body of the car, change the flow and create turbulences that affect a different feature in a different place of the body. A different front splitter, will not only change the aerodynamic characteristics on the front of the car but will also change the flow at the rear wing and rear diffuser, changing the aerodynamic forces of those features. A diffuser of a different shape or working in a different angle, will also change the flow behind of the rear wing and so the air approaching it, again changing the forces of the wing. A different rear wing shape or angle, can create pressures that change the flow from the front of the car, actively modifying the forces at the front.
Nothing of the above would be possible to simulate with the old system, at least not without some nasty workarounds and side effects that could be taken advantage by players in order to produce unrealistic end results.

The new aerodynamic modelling does exactly what we need. The rear wing can affect the front downforce, the front splitter can affect the rear wing and diffuser, but most importantly the ride heights now become the most important part of car setup. Modern cars that generate big amounts of downforce by the use of splitter and diffusers, are very, let me repeat that, VERY ride height and pitch sensitive.
The difference between front and rear ride height is of massive importance. Changing the front e rear ride height, moves forwards or backwards the aerodynamic pressure point, or to say it in a more simple way, how much of downforce goes to the front or to the rear of the car. Why is this so important? 1mm of ride height change at the front, can move the aerodynamic balance forward or backwards by 0.5% to over 2% depending on the car and rear wing setting. Let me say that again. 1mm of ride height, equals up and over to 2% of aero balance shift. You think it’s not much? 10mm can mean way over 20% aero shift. Good drivers will easily understand changes of 1%. Average drivers might not, but they will have big instability problems with a change of over 5%. Remember, these cars generate way above 500kg of downforce at medium speeds, so that’s a lot of force shifting around.
Furthermore we are talking about static balance. While driving, the car also pitch and rolls. Lifting off from the accelerator at a high speed turn or braking hard while turning in, can have catastrophic results in car stability if the aero “platform” is not setup properly.
It’s not over yet. With speed, the pressure created in front and under the front splitter might change the flow to the rear diffuser or make the front splitter more efficient, thus moving the aero shift even more forwards. This means the car might change balance going faster.
It is clear that splitters and diffuser are very sensitive to ride height. Finding the correct ride height and trying to maintain it in a acceptable range under all conditions is what we call “maintaining the aero platform stable”. One big aid comes from the rear wing. The wing doesn’t travel close to the ground and the flow it receives is relatively clean so its aerodynamic characteristics remain stable. The more rear wing you use, the more you average the pitch and roll sensitivity and you stabilize the car in various conditions. The balance shifts less forward and backwards under pitch and squat. Unfortunately the rear wing adds a lot of drag and of course shifts the whole balance to the rear which brings understeer. So again it’s a compromise but a much more complex one than before. You can use less rear wing angle, but then the car becomes unstable. You can use more rear wing angle but the car becomes understeery as balance, but gains grip because the whole downforce raises.
We’re not done yet. Normally in sims, a change in a wings angle, roll, speed will instantly translate in an equivalent change in aerodynamic effect. For example let’s say we brake hard for a turn and this translates in a pitch of an extra 1° of angle. All the aerodynamic wings will instantly start to generate downforce and drag for an extra 1° of angle. But that’s not what happens in reality. The air can be compressed, the flow can get slower or faster, or can create “pumps” from pockets of air that get compressed and uncompressed. All of this takes tiny bit of time. It acts as if there’s some small amount of lag in the results and, yes you guessed it, it is now simulated in ACC. Sometimes this effect can be your friend, like when you start braking from high speeds it might take a fraction of a second before the balance shifts way forward and by that time your speed is slower. Sometimes it can caught you off guard, like when you’re jumping in a kerb and you think you cleared the first part, only for the aero instability to hit you hard in the second part!

By now it is pretty clear that the aero model is advanced and complex, but how we control the aero platform in an efficient way, except from adding tons of rear right wing? That was the same question I asked myself when for the first time I configured the values and went for a first ride. I’m famous for my self control so my exact words have been: “WTF what have we done?!?!!?”.
Right. It was evident that we needed a much more stiff front suspension to limit pitch. Again remember, we’re talking that we are trying to avoid mere millimetres of ride height change, let alone macroscopic movements! So we’re gonna use bumpstops right? But nobody likes bumpstops, they make you car understeery and they make your car jump on kerbs.. bliah! So we simulated variable stiffness for bumpstops. And more precise bumpstop range. And better control of their placement when you change ride height. And then we had to control the suspension from this all, so in goes a more advanced damping system… and then we realized that we had to do something to help people setup this whole thing… Remember? In AC you can change a bit of ride height, or fuel load and then you need to change again all the alignment to bring it back to your original chosen values. Nightmare.
But that needs a different post, something regarding suspensions and setup…

I told you we worked a lot. I’m starting to realize it from the amount of stuff I need to write for every damn post!

 

I think you are confusing the static aeromap data that you can easily input in AC as all the cars have. You can also go deep into such simulations as many different cars in AC have, and I suppose various modders have achieved good levels with their cars.
The difference is that the whole model is not taking into account of how a wing can influence another wing, before or behind it. You can be VERY specific for a static model with AC, but when the car starts moving, there is only so much you can do. Some scenarios are either not possible, or can be taken advantage from aliens in the setup, or go simply outside what the real car is doing in real life.

Well, real life GT3 teams do not get that much of aero data from the manufacturer and some times the data doesn't translate 100% with real life performance either... heck not even F1 can do it and predict everything 100%. But as I said, we're working to offer a easy to work with setup page.

 

I probably didn't explain myself properly. I was mentioning original AC bumpstops that have 1 fixed stiffness, so when you go on them they create quite a jump in stiffness.

 

Obviously we're doing the end result and effect. We are not simulating proper CFD in real time. Just to be clear, we are not selling miracles and marketing