The wings of change
Of all the changes introduced by the 2011 technical regulations, perhaps the most exciting is the arrival of the adjustable rear wing, a device designed to generate better racing and improve the show for the fans. It's an interesting concept that presents the teams with a significant technical challenge and is likely to be one of the major talking points of the season.
A new approach
Along with the arrival of adjustable rear wings is the departure of adjustable front wings -- a concept that never really delivered what was expected of it, as Technical Director, James Allison, explains:
"The moveable front flap was brought in to try and assist with overtaking, but in practice it didn't really make a difference. Instead it was used as a device to optimise car balance as the tyres degraded and the fuel load reduced. That's why the teams voted to remove adjustable front wings and try a new initiative with the rear wings with the intention of generating better overtaking opportunities."
If adjustable front wings didn't help overtaking, why will adjustable rear wings fare any better? Well, it all comes down to the different way that changing the angle of the front and rear wings affects the overall drag of the car. If you change the angle of the front wing, you change the car balance, but the overall drag of the car remains about the same and hence straight-line speed is largely unaffected. However, changing the rear wing angle changes the drag of the car, and therefore the straight-line speed dramatically.
"If you allow the rear wing to reduce its angle, you lose drag, rather like an f-duct system last year," explains James. "So if two cars are racing each other, the car that has adjusted its rear wing angle will be able to go faster down a straight than the car that hasn't."
A precise set of regulations
Of course, if all the cars could adjust their rear wings at the same time, there would be no relative advantage. That's why great care has been taken devising regulations that will genuinely encourage more overtaking. The rules therefore describe a set of circumstances under which the wing angle can be altered.
"All the drivers will be free to reduce their rear wing angle during free practice and qualifying as often as they like, but in a race there will be restrictions on its use," says James. "The regulations will only allow it to be used when a chasing car is within one second of the car ahead. So if a driver can get within this threshold time, his car will be granted permission to use the moveable wing on one designated straight during the lap. Furthermore, the teams and the FIA have tried to design a system that only gives just enough assistance to a trailing car to make an overtaking manuvre just possible. Nobody wants to have a system that makes overtaking a formality."
In racing conditions the system will be policed electronically by the FIA. The default setting is for the system to be disabled, but after two laps of the Grand Prix, the system becomes potentially enabled, assuming the cars meet the criteria defined for its use. A light will appear automatically in the cockpit when the driver is eligible to adjust his rear wing, which can then be activated by pressing a button on the steering wheel.
The science of adjustable wings
As for the mechanics of moveable wings, the adjustments that can be made relate to the two elements of the wing: the main plane and the flap. While the main plane remains fixed, the rules allow the flap to rotate away from the main plane up to a maximum distance of 50mm. This creates a situation where the two elements of the wing stop acting in harmony and the airflow around the wing separates from the surface of the wing. This condition of separated flow is called a "stall" and it is accompanied by a large drop in both downforce and drag on the car. The overall effect on straight-line speed is a bit like an f-duct, but much more powerful.
-source: lotus renault