Car & Driver Aerodynamics Test

[oldtamiyaphile]

Originally Posted by aerohead

.I'm not sure what Nissan's claim to fame is.
If you have some technical information from NISSAN it would be most appreciated.Hopefully it is not from the same tunnel that their 280-ZX was developed in.

The GT-R has a 0.26CD which is great for what it is.

The aero section starts about 10mins in:

https://www.youtube.com/watch?v=52Yyo5s9HgQ

And of course Mercedes have a rolling road wind tunnel, nothing 1930's about it:

https://www.youtube.com/watch?v=AH-vZrpBxus

[NeilBlanchard]

The Mercedes video shows rollers under the wheels, which is part of it - they get the wheels spinning. But having the whole "road" surface rolling past the car sets up things under the car that cannot be accounted for otherwise.

[oldtamiyaphile]

Originally Posted by NeilBlanchard

But having the whole "road" surface rolling past the car sets up things under the car that cannot be accounted for otherwise.

Actually there is a 5 belt system to simulate the interaction with the ground plane.

The whole thing can be pivoted for cross wind testing too.

[freebeard]

...it must be nice...

[whatmaycome14]

The video of the Merc didn't get to show the really important stuff. Who cares about what's happening 2ft above you... what about closer to the ground???

[UltArc]

I find that .26 very hard to believe. The down force of the GTR is IMMENSE. Formula 1 cars (per wiki) range from .7 to over 1, how can it have such an incredible Cd, yet be held down so powerfully?

This article is exactly what I mean: 2009 Nissan GT-R - First Drive Review - Car Reviews - Car and Driver

"Nissan claims the GT-R generates more than 176 pounds of downforce at 186 mph. At both ends. According to wind-tunnel tests by the German magazine Sport Auto, few production cars are better, and those few—the Bugatti Veyron, the Mercedes SLR McLaren, and the Porsche Carrera GT—cost a lot more than the $70,475 base price the GT-R will command when it reaches the U.S. this spring."

So which is it, Datsun? ( I do love the GTR, but these two claims together don't pan out. Is there something more to this?)

[oldtamiyaphile]

Let's stick to road cars, not sure what F1 has to do with anything.

A McLaren P1 produces 1323 pounds of downforce at 161mph. Is the GT-R's 186 at 186mph still immense? If you build a car with low drag, it won't have much lift, add a good under tray and diffuser and you should have modest downforce with no drag penalty (compared to an unclad underside at least).

[gone-ot]

ANALOGY - imagine this airplane WING airfoil as a car (lefthand pix):




...or, think about this being UPSIDE down, and think what the inverse of LIFT-INDUCED drag would be (DOWN-FORCE drag!):

[UltArc]

Sure, let's stick to road cars. So you know, the purpose of bringing up the F1 car was the correlation between downforce and drag. So the drag of a stationary F1 car may not be much, but when air is forcing it down (part of the GTRs superb handling, stability, and track performance) it increases it's grip (downforce). That's the point. More force pushing down takes more force to accelerate or maintain speed.

About road cars, can we stick with reasonable road cars and not multimillion dollar hyper car hybrids with fluctuating aerodynamics that change depending on speeds and conditions? Especially since at certain speeds, the downforce lets up because it will destroy the rear suspension. Or it's used as a rear brake. Either way, factors the Insight and GTR do not deal with.

Unfortunately, I can't find anything on the downforce of a G1 Insight.

Oh, and comparing to somewhat ordinary cars: Corvette Wind-Tunnel Testing - Is Corvette Styling Just For Looks? - Corvette Fever Magazine - View All Page

Only the C3 was able to actually create downforce. The rest all created lift. Now the Corvette is no GTR (although Car and Driver rates the Vette #1, and GTR #5) it also isn't a Focus. I compared the 2009 model GTR to a 2009 model Corvette, because after the "Black" (or is it a V Spec? I forget what they name them) GTR came out, it started getting more and more downforce. Then the regular GTR essentially was as good as the previous year "Black."

[oldtamiyaphile]

Originally Posted by UltArc

Only the C3 was able to actually create downforce. The rest all created lift. Now the Corvette is no GTR (although Car and Driver rates the Vette #1, and GTR #5) it also isn't a Focus. I compared the 2009 model GTR to a 2009 model Corvette, because after the "Black" (or is it a V Spec? I forget what they name them) GTR came out, it started getting more and more downforce.

The reason Corvettes create lift is that in profile, they're basically an aerofoil.

Squared off cars don't have this problem.

Honda Quoted the 1981 City as having zero lift (written just under the blue car):



If you start with zero lift, you won't have to induce much drag to create the modest downforce that the GT-R has. That's part of it's genius, staying away from swoopy high lift curves.