Active aero for a sedan, A3 Clubsport Quattro
 

...active rear wing, not just for road-hugging downforce but also for warning-lights & air-braking!

https://www.youtube.com/watch?v=5JbJHaBlYhY

active wing
 

Mercedes-Benz had a 1950s racer with active wing.
Chrysler followed later in the 50s with it on a concept car.
Bugatti's Veyron does this.
It's a good idea.

Demmit. I need a test track! Well and good. I would think it is fairly easy to increase drag on a sedan. Those look like they were using linear actuators with some kind of linkage. You could link these to steering position sensors/encoders and ECU and would automatically deploy when they sense steering activity or brake pedal being pressed. But I would question the benefit in low speed corners especially anything below 100km/h (63mph). Linear actuators don't come cheap.

This company serves the active-wing aftermarket. They have patent-pending wing computer/controllers that monitors acceleration, braking, speed and lateral G’s to determine the aggressive/optimal angles of wing. Fast-response actuators move the low-drag profile blade to any angle, giving your car the right aerodynamics for every situation; variable & split downforce, air-braking or low drag/0-angle. Videos - aeromotions

Aero actuators for my 1960 chevy P/U
 

This is so Cool! This is exactly what I need to finish the active aero and braking functions I have added to my 1960 Chevy P/U:eek:

This is the "Breaking Wind Position"


http://i855.photobucket.com/albums/a...ps35c8560a.jpg


And here is the "I didn't see that coming position"


http://i855.photobucket.com/albums/a...ps0c209435.jpg

I will admit this project has some more bugs to work out, but at least I know there are some off the shelve actuators available,;)

Experimental Air Brakes
 

Racers experimented with their aftermarket wings and added headlight or wiper motors; cheap, quick response and reliable. It was either triggered by the brake lights with a SPDT relay or manually deployed by a steering wheel-installed switch. It shows one-and-done, full stall deployment or flat. They are also working on prototype wings with brake pressure transducers hooked up to arduino controllers for intermediate wing angles. The potential dangers are in top speed racing conditions, where there are quick handling transitions and also have to take account to different driver/driving styles. But the simplicity of this on-off system; easier to make, easy to adjust and easy to test and easy to operate.

https://www.youtube.com/watch?v=7VHDfn_rHAk#t=31

https://www.youtube.com/watch?v=MuBmUr2qG3g

the benefit
 

I suspect that Audi is anticipating those who have access to the unlimited-speed portions of the Autobahn and Autostrada,where they might operate the car near its terminal velocity,or near the limit of adhesion through s-curves 'n such.
Traffic fatalities can be a black mark on an automaker.With no control over how their products will be used,they probably attempt to keep customers away from Darwinian moments.

determine
 

It's smart use of off-the-shelf technology.Perspicacity in action.:)

The use of aero surfaces for increasing traction is well known. Formula 1's DRS is a case in point. I do think however that in chasing efficiency, ecomodders would like to see Active Aerodynamics being used to actually reduce fuel consumption by minimizing drag. These would enable air to stick to the length of the car body or even extend the flow. Instead of boat-tailing, aero surfaces could react as active deflectors; to force air departing from the rear of the car in such a way, it would reduce the wake or create vortices. Boat tailing may be the best solution in terms of design, but it would only appeal to a very very niche market.

Active aeros on the other hand is relatively small and can even be a bit of a bling feature for the young. IF the price is right which it is not at the moment. I also fully understand the production cost issue but its the market that they are targeting; it would not get the Critical Mass of reducing fuel consumption.

A pneumatic tail can 'wag the dog'. Englar's paper seems to have gone behind a paywall.

Development of Pneumatic Aerodynamic Concepts for Control of Lift, Drag and Moments plus Lateral/Directional Stability of Automotive Vehicles

I won't repost it but I can answer questions about the copy I may or may not have on file.