Martin Witmarsh said today that the competition at first did not know what their rear wing slot was, and then they did not know if it was legal, and now they don't know how long it will take to replicate the wing on their own cars. Funny, but true.
The wing slot is the barely discernable curvy black line seen on the upper element (between the green ovals). The seperation between the lower element and the upper element is easily seen: there is daylight showing through it. The rules limit the number of rear elements to two, so the slot is an effort to create the effects of multiple elements, but without circumventing the rules. But there is more....
Originally it was thought that the slot was being fed high speed air via the engine airbox intake. The intake has a seperation that creates two paths. The larger one is the engine air intake. The purpose of the smaller upper air path was unknown. Some thought that this was ducted to the rear of the car to concentrate air on the rear wing.
My original thoughts were that the second intake was to facilitate cooling of the oil tank. It is believed that the tank was relocated from in front of the engine to the area around the gearbox. They may have included the oil tank inside the gearbox casing as was common in the '90s. This relocation was done to open up some space for the large fuel tank. The electronics were also believed to have been moved from the side pods for the same reason. The extra cooling was required to keep everything functioning properly. I think this is still the best explanation. But, I don't really know.
Recent photos have shown another interesting development. There is a scoop located on the monocoque that apparently is another route for air into the interior of the car. This may, in fact, be ducting that routes air through the chassis to the rear wing slot. The theory is that the ducting passes through the cockpit and provides cooling air for the driver via a hole located near the foot rest. However, it is also believed that the ducting continues rearward and exits the car via an opening and is directed toward the rear wing, specifically the slot.
Apparently the additional air influences the "shape" of the flow around the rear wing at high speed and reduces the drag, thus allowing a higher top speed. Some believe that the driver can place his foot on the in-cockpit outlet in the duct to allow some control over the flow to the rear wing. Foot-on at high speed to stall the rear wing, and foot off at slow speed to allow max downforce. Instead of the flow going to the wing, it now escapes into the cockpit. Very interesting.
It all sounds a bit Rube Goldberg to me, but who knows. Do you remember the extra rear-only brake pedal that McLaren employed in 1997? We would have never known about that except that Darren Heath snapped a pic after Mika's car retired and was abandoned near the wall at Luxembourg!