Mike Stevens | Aug 29, 2008

Something I've always fantasised about - in the engineering skunkworks that is my brain - is active aerodynamics. Aerodynamics, it would seem, has always been a trade-off between drag and downforce. When race teams set up their cars for maximum aerodynamic performance it becomes a matter of "more grip, or more speed?"

More of one means less of the other; but why can't you have what you need only when you need it? While my total aircraft-like vision of active aero-based yaw control has yet to go anywhere beyond the space between my ears, a company in the US, Aeromotions, is developing a downforce-generating rear wing with active adjustment.

Porsche Active Rear Spoiler - UpIn some ways, the basic principle of this 'new' rear wing is no different to any electronically controlled rear wing already on the market, most famously found on the old Porsche 911s and a headline act on the Bugatti Veyron and Mercedes Mclaren SLR.

Old news, in other words.

The "new and shiny" part of Aeromotions' system is that the airfoil is in two parts - an active split rear wing with sensor inputs - and independently adjustable.

The original design, conceived in MIT's wind tunnel, used a clay model on a pendulum with the wing affixed. The mounting point between the pendulum and model was set so the model would not lean if left to its own devices. When the tunnel's turbine was turned on and air flowed over the model, the wing adjusted itself and levelled the car out.

The settings and control logic developed in this wind tunnel, were then applied to a full-scale test car.

In some ways it would be like your standard active rear wing. At low speeds in a 'normal car', there is little aerodynamic benefit from air-effect devices (aerodynamic forces increase with the square of velocity - in other words, you have to be travelling at a certain minimum velocity for a 'wing' to work).

At low speeds in a 'normal car', you want as little drag as possible, so you don't want an aggressive wing setting. (At Formula 1 'low speeds', it's a little different. Hammond, on Top Gear, struggled to drive a Formula 1 car fast enough to generate sufficient downforce - and grip - to get the car to turn.)

Car and Airfoil - SilhouetteHowever, as speed rise, airflow over the car increases, generating both turbulance and lift - notice how the basic 'curved top/flat bottom' profile of a car is similar to that of an aircraft's wing. (And remember Mark Webber's experience at Le Mans when the aerodynamics on the team's Mercedes-Benz CLRs failed?)

Thus, as speeds rise, to counter lift and assist airflow, the wing will need to operate more aggressively to generate downforce. But since top speed is now the aim (and downforce increases drag), and because the downforce produced by the wing increases as the velocity of the air passing over it increases, the ideal wing is one that can respond by adjusting to the downforce needs of the car.

Of course, in a straight line, that aerodynamic load should be distributed evenly across both sides of the car. When cornering it's a different proposition. The load on the suspension and at the wheels (and tyres) is uneven, with centrifugal force 'pressing' mass away from the inside wheels as you turn: thus, applying more downforce to the inside of the car is one way of reducing this effect (provided the car is travelling fast enough). You may also remember Formula 1 teams experimenting with 'active suspension' as a counter to this effect.

Aeromotions' wing, with its airfoil split in the middle, lets you run more downforce to the side of the car that needs it most while cornering (while slightly decreasing drag because only half the wing is aggressive).

Aeromotions are using a BMW 3 Series coupe as the test vehicle, competing in autocross competitions, an entry level motorsport similar in principle to what Australians call motorkhana. Autocross however reaches speeds we wouldn't see in a local 'khana.

Aeromotions have provided some videos of the system in action.

As you can see, the actuators move quite quickly, and while there's no footage of the car without a wing to compare you can see how stable the rear of the car is on a relatively tight course. If used on a proper track, where the speeds are higher, I can imagine this wing is better again.

Despite all the hard parkers you see cruising your local entertainment district on a Friday night, a rear wing is actually useful for more than just a place to rest your cup of Coke if you're driving your modified car at the track, not just to McDonald's. This wing appears to be the next step in aerodynamics for motorsport enthusiasts.

By the way, if anyone from Aeromotions is reading this and needs someone in Australia to test their product and to sponsor, contact me. Please.

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