SRW Advance to be used in Practice in Turkey

Force India will be using its own version of the F-duct in practice for the Turkish Grand Prix this weekend, called the SRW or switchable rear wing. But what is really? In a nutshell, the SRW is a device where a driver is able to manually alter the airflow over the rear wing and in doing so gain a speed advantage on long straights.

To fully understand the system and why they are so ingenious, first you must understand the technical regulation that states that all aerodynamic devices, eg. wings, flaps and so on, must be rigid and fixed to the car.

Article 3.15 of the technical regulations states:

3.15 Aerodynamic influence : With the exception of the cover described in Article 6.5.2 (when used in the pit lane), the driver adjustable bodywork described in Article 3.18 and the ducts described in Article 11.4, any specific part of the car influencing its aerodynamic
performance :

• Must comply with the rules relating to bodywork
  
• Must be rigidly secured to the entirely sprung part of the car (rigidly secured means not having any degree of freedom) ;
  
• Must remain immobile in relation to the sprung part of the car.

A wing generates downforce due to the way the air flows over its different profiles or elements. If an F1 wing is designed well, the air will flow faster over its lower surface than it does over the upper surface. The laws of physics are such that the higher the speed of the airflow, the lower the air pressure. Therefore the pressure under the wing will be lower than the pressure above the wing and this will create a downward force, generating more grip on the track. The disadvantage however of having a lot of elements and therefore downforce is that there will be a significant drag penalty, which will affect the ultimate top speed of the car on the straights.

In the past some teams had tried to create flexible wings that alter their performance when cornering or going down the straights, however these were banned by the FIA some time ago and article 3.15 of the technical regulations above clearly forbids any similar device.

If, however, a system could be found where the airflow is stopped or reduced while running over the wing, this would neatly circumvent this regulation as it’s just the wings that need to be fixed – the flow of air can be manipulated.

This is where the F-duct really comes into its own. It’s actually a very simple concept: there is a ‘vent’ in the cockpit that is either opened or closed manually by the driver’s limbs. Any moveable aerodynamic device is not permitted, but this clearly has no moving parts. Blocking the vent could direct enough airflow through the conduit to disrupt the flow over the rear flap and induce a stall. With less air pushing the car down, there’s also less drag, which means an increase in speed of anything from three to five kph on the straight.

Generally the driver will use only on a straight so it doesn't interfere with his normal operation of the car as the vents are closed by either an arm or a leg.

So far this year several teams have used the F-duct, although the name itself seems to have been created by media and the general public – McLaren has called their system the RW80, while Force India’s is codenamed the SRW (switchable rear wing).