Pardon me if I'm hijacking a thread but I was chastised by a forum sheriff for giving this post one of its own. IMHO, it's a distinct and separate topic, but I seem to have been overruled.
I was having a great deal of difficulty getting my head around the aerodynamics of this ...until I realised it has nothing to do with stalling. I suppose whomever elected to call it a 'stall' preferred to use that oversimplification rather than having to explain what really is happening, which is rather more complex. And truth be told, calling it "an oversimplification" is being generous because, if I'm right (always a risky proposition), "stall" is nowhere near the truth.
The lack of detail in the photos and diagrams I previously had seen online didn't tip me off but this morning I was looking at online articles about Ferrari's new F-duct at Shanghai when it occurred to me.
This article on Ferrari's ducting system referred to,
"...the known rearward slots in the upper deck...." That was when it struck me.
They're not stalling the wing, they simply are reducing the (inverted) lift it generates by blowing ducted air through slots that increase the velocity of the air flowing rearward over the wing's (high pressure) top surface.
>velocity = <dynamic pressure
Lift (downforce) comes from having differing air pressures on the two sides of the wing. Reducing air pressure over top of the (inverted) wing while pressure underneath remains the same reduces the resulting level of downforce.
<downforce = <drag
<drag = >trap speed
Now it makes sense. They effectively are reducing the wing's angle of attack (or increasing its lower camber) by manipulating the energy of the air flowing over its different surfaces. I know McLaren's system is driver-controlled but, apart that detail, I'll wager the basic function of their F-duct is the same as the Ferraris'. I'll wager it doesn't "stall" anything either, rather it just redirects airflow to reduce the strength of the Bernoulli effect.
