I agree, it is there to help with flow under the windscreen and to help reduce turbulence behind the screen. In all likelihood, without it you would get a low pressure vortex up under there. I had a long day at work and my engineering brain is shot at the moment. I'll be having some beers with some old college buddies who did aerospace engineering with me later tonight. Perhaps we can hash this out and come up with only a mildly beer influenced psuedo scientific answer.
You crazy engineer guys. Way to catch up with your buddies VFRBulldawg - I can see the scene at the pub tonight:
VFRBulldawg: "Okay guys, really great to catch up, it's my shout so I'll get the beers. While I'm gone John I want you to start deriving the formula for lift from first principles, paying particular attention to verifying the coefficient of lift."
John: "Can do Bulldawg, can't wait to get my teeth into it - and some hot chicken wings "
VFRBulldawg: "Fred I want you to consider the profile drag for a 5th Gen ZG windscreen, let's review at all speed gates in 10mph increments from zero to supersonic, that should give us enough data to reach some decent conclusions"
Fred: "Check - no problems buddy"
VFRBulldawg: "Bobby, you weren't an honors student so you're the scribe, write everything down on the back of these 50 beer coasters I've collected."
Bobby: "But Bulldawg, can't I do some calculations?"
VFRBulldawg: "Bobby, we've been through this before, you should've studied harder at college, now enough of these complaints, remember there's no I in team"
Fred: "Dawg, are we going to think about any 7th Gen Aerodynamics tonight?"
VFRBulldawg: "Let's not get ahead of ourselves boyz - one VFR generation at a time"
Fred: "Copied all brother"
VFRBulldawg: "Righto, so has everybody got their calculators, a thirst for good aerospace engineering, and a thirst for beer?"
All: "Sure have, you bet, can't wait" <hi-5s all round>
And so the evening progresses in a fog of beer, applied algebra, and good times with some old mates ... :beer:
And you guessed it right - I'm the "Bobby" in this story - although I didn't study engineering! :happy: