Barcelona F1 test day two
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The aero rake mounted to the Red Bull is in front of the rear tyre. Now the Red Bull is an interesting case because it has a different sidepod philosophy to its rivals. Nearly all the others have an undercut sidepod leading into the 'Coke bottle' area but the Red bull has a tight, limpet-style engine cover.
There's an undercut at the front, which you need for the bargeboards to have an 'exhaust' area because the airflow is being pulled by the low pressure behind the car. But the rest of the sidepod is very tight. This means Red Bull is trying to get a lot of airflow off the top of the sidepod down into the Coke bottle.
This rake is about management of the airflow onto and inside the rear tyres. It's very high as well, to measure the airflow down the side of the engine cover. Any knowledge above that is of limited use as there's not much you can do about the air above the car.
As Red Bull is out on a limb, the key is that it needs to have the airflow over the top of the sidepods to be as useful as possible – as useful as what you'd pull around the sidepod with a conventional undercut.
By measuring what's happening here, it can check the correlation between real world and its CFD model.
Bottas: Now at speed (Sutton Images)
When you steer the wheel, you might have between three and six degrees of lock in a faster corner and that changes how the tyre influences the airflow. As you close the wheel across the front wing the airflow spills over completely differently.
The challenge for the aerodynamicists is deciding whether you want it perfect at a certain angle, or a compromise across a range. That's what makes a difference between one car and another, it's all about your priorities.
What you need is stable aerodynamics. The driver never complains on the straight that it's unstable, but you get a lot of complaints in the high-speed corners.
In the slow corners the driver can hustle the car more, but in fast corners the car dictates what you can do. So when it comes to aero management, you want to bias it more towards the faster corners.
Like all teams, McLaren has sometimes sent its car out with pitot tube arrays such as this one.
We talk a lot about these outer-corner vertical turning vanes on the sidepods being key to controlling the wake coming off the front tyre. And to control it, you need to know what it's doing.
These sensors are located halfway between the front wheel and the leading edge of the sidepod and you want to learn how fast the air is travelling and in what direction. Direction is tricky as all you get is a snapshot, but the speed the air is travelling at is clearer.
What McLaren will want to do with this data is correlate the real world with its CFD model. Modelling a rotating wheel with a constantly changing steering angle is a very difficult task so you have to validate your model with real-world data.
Once you have that model as accurate as you can, and you'll never get it perfect, you can optimise the parts to manage the airflow.
Sirotkin 17; Bottas 16; Leclerc 9; Vandoorne 9; Sainz 8; Gasly 5; Vettel 5; Ocon 5; Magnussen 1; Verstappen 1
By: Geoff Creighton
