McLaren MP4-25 Boundry Layer Control System
Well looks like it's been confirmed, the weird vent on the rear of the MP4-25 is not just to vent air, it's an elaborate BLCS.
http://www.formula1.com/news/technical/2010/0/720.html
On the McLaren above the driver's helmet, the air inlet is separated into 2 sections, intake for the engine, and an air channel for what was speculated to be for the oil cooler, but is in fact for the gearbox radiator.
Rewind back to 2009, McLaren was struggling big time with high speed aero at the beginning of the year. They could not understand why their rear wing at high speeds was losing tons of downforce. Turns out, the way the original front wing was designed, the airflow was interfering with the rear wing in such a way that at a certain speed (basically high speed corners) the rear wing stalled and just lost downforce. In testing, they threw on the 2008 wing to try and figure out what was going on.
This was finally fixed by a new aero package for the German Grand Prix, where Lewis described the car as "switching on". McLaren had changed the airflow from the front wing to not interfere with the rear wing. Simple as that.
One of the effects of the stall was that aerodynamic drag was reduced along with downforce. McLaren decided to exploit this by blowing the proper higher pressure air around the wing, and is able to tune the speed in which the air was able to reattached better, thus creating a low drag zone at high speeds, basically on straights. This concept is used in glider planes for drag reduction.
Some aircrafts use this system (blown flap) to lower the stall speed of the wing so it can take off at lower speeds. This system allows for higher wing angles to be used without stalling. Basically, there's a point in the wing's angle of attack where it suddenly loses downforce and stalls (and creates a huge level of drag). By blowing high pressure air, you can increase the wing angle without stalling, thus creating more lift, or in a F1 car's case, downforce.
The MP4-25 has several access panels on the rear shark fin, which is speculated to be adjustable tuning devices to vary the pressure exiting the vent. This system should allow McLaren to tune the BCLS for each track, so it can get higher downforce (more wing angle) for the corners, but without the drag penalty on the straights, resulting in better fuel economy (a huge plus this year) as well as higher trap speeds.
Pretty cool stuff!
