Will Gray

Tech Talk: The importance of ride height stability

Will Gray

The FIA's ban on ride-height stability systems could have interesting consequences for teams that had been developing it for 2012 — but why is ride height such a vital area of aerodynamics?

The innovative suspension system, initially developed by Lotus, was designed to ensure stable ride heights throughout the lap, much like the aims of the electronic active suspension systems run but subsequently banned in the early 1990s.

In this case, rather than being electronic inputs that controlled the position of the suspension wishbones and the car body relative to the wheels and the track, it was a mechanical system of hydraulic cylinders and actuators.

Due to its completely mechanical operation - which involved brake torque activating hydraulic devices to maintain a level ride height - it was seen by the FIA as not an aerodynamic device and not governed by the regulations that stipulate no moving aerodynamic parts.

And while it was effectively driver-operated - because the action of pushing the brake pedal activated the system - the primary reason for the driver braking is clearly to slow the car down, not to specifically activate this system, as had been the case with the banned f-duct.

However, further investigation led the FIA to ban the system as they determined it did constitute a movable aerodynamic device.

But why would it have been so effective?

The system was designed to fundamentally limit yaw and roll in the suspension, particularly during braking.

Such are the forces in F1 that despite extremely stiff suspension the forward pitch of braking still pushes the nose down towards the track under braking. Cars are also subjected to yaw (the left/right forces trying to twist the car on its centre — like twisting your shoulders) in cornering.

The front wing (and the floor — but we shall just focus on the front wing) benefits from ground effect. The shape of the wing, even away from the ground, leads to air flowing faster below and slower above, creating a net downward pressure, but when close to the ground the narrow gap between the underside of the wing and the track forces air to travel even faster, creating an even greater pressure difference and more downforce. Moreover, by lowering the endplate as close to the ground as possible, it creates an effective skirt that increases downforce even further.

Red Bull have developed an aggressive rake (setting up the car with a high rear end and lower front end) to bring the front wing closer to the ground (while also beneficially raising the height of the rear diffuser). They and several other teams also use flexible wings that bend under certain conditions and bring them closer to the ground.

Too much flexibility, combined with too big a rake and too much pitch and yaw in braking can lead to the front wing end plates scraping the ground — which is not good for the airflow or the bodywork.

The minimum wing height is measured statically but it is limited by the car's on-track dynamics — basically the combination of tyre pressures and downforce as well as how much the wing flexes and how much the car dives in the heaviest braking zone.

The front suspension already includes geometric anti-dive design to limit pitch movement — but the ride-height stability system would have virtually eliminated forward pitch, allowing teams to run their wing lower, gaining a reported benefit of up to half a second per lap.

Aerodynamics is very sensitive in this area, however, and a wing will easily stall if it experiences a different flow regime than it is designed to run in.

So any team that built their 2012 concept around such a system will likely have to re-work their front wing to optimise it for the flow regime it must now work in, and that itself can affect how the air flows over the rest of the car.

All that takes valuable corrective time, which would otherwise have been spent on moving forwards.

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