Has anyone seen aerodynamic data on the FD - especially lift at front and rear at various speeds with base model vs. various chin spoilers/splitters and rear deck spoilers/wings? I see this sort of info fairly frequently on modern high performance cars, but haven't been able to find it for the FD.

I have a base model '93 with the R1 chin spoiler. I am going to need to paint the car before long, and am considering whether or not to add a rear spoiler. I like the clean deck look, and am not looking to add a lot of downforce to the car, but would like to know whether or not to expect some rear end lift in awkward places - like the uphill esses at VIR - without some help.

 

Here are the coefficients of lift and drag for a base and R1. You can use these coefficients to calculate the actual lift and drag forces at various speeds. I have a lot more data on this, but I'm at work right now, so I can't really help you out. Maybe sometime this weekend I can throw a quick spreadsheet together regarding this.

RX-7 base model (no spoilers)
drag coefficient (Cd) - 0.29
lift coefficient, front (Clf) - 0.16
lift coefficient, rear (Clf) - 0.08

RX-7 R-model (front and rear spoilers)
drag coefficient (Cd) - 0.31
lift coefficient, front (Clf) - 0.10
lift coefficient, rear (Clf) - 0.08


Also notice that the stock (93 style) spoiler does very little to alter lift. If you are considering a rear wing with the intent of adding downforce, I would suggest a 99spec or similar.

Hope that helps a little,
Rob

 

I did some quick a dirty calcs when I installed a '99 rear wing:
http://www.negative-camber.org/crispyrx7/99wing.htm
Please ignore bullet hole stickers....since removed.

FWIW
Crispy

PS Mmmmm uphill esses at VIR...YUMMY!

 

Very nice write-up as usual. Like the "test vehicle" decal!

Gene

 

thats a pretty low drag coefficiency isn't it?

 

yeah .29 is very good. Mustangs are .36 and Camaros are .35 just for comparo. I wonder what the drag coefficient is on an F1 car...

 

An F1 car would be pretty high because of all the wings and spoilers used to generate downforce.

 

Yes at least 1300lbs of downforce. So much in fact that at some set speed (100mph?) an F1 car could drive on the ceiling without falling down ...if there were upsidedown racetracks
Crispy
-my meaningless post for the day

 

Nice write up, as usual.

BTW, coefficient of drag (Cd) is not the only factor which affects aerodynamics. The frontal area (A), which is the size of the proverbial "barn door" you're trying to push through the air, must also be taken into consideration. Frontal area is the surface area of everything visible from the front of the car. For the FD, that's 19.2 sq. ft., IIRC.

The Lexus LS430 has a Cd of 0.25-0.26, but that doesn't necessarily mean it's as aerodynamic as an FD, because it has more frontal area. How much more? Good question. Most manufacturers conveniently don't publish frontal area. At most, they'll usually say something like "frontal area was reduced" in their ads or brochures, because they want you to focus on Cd... which is only half of the story.

Anyway, here are a few examples...

FD base model CdA = 0.29 x 19.2 sq. ft. = 5.568 sq. ft.
FD R1 model CdA = 0.31 x 19.2 sq. ft. = 5.952 sq. ft.
Z06 Corvette CdA = 0.28 x 21.3 sq. ft. = 5.964 sq. ft.

See what I mean by not just focusing on the Cd? The Z06 is not more aerodynamic than either FD, despite having a lower coefficient of drag.

 

maybe im just stupid, but how, exactly, is cd calculated?

 

excellent thread, always good to have these everyonce and a while. I imagine that they are tested in a wind tunnel and by that they find the Cd but what kinda CdA or just Cd numbers do you need to have in order to be safe at high speeds, 200+mph for example. I think i've seen it posted that the Corvettes have been tested to simulated speeds of over 200mph and is "built" for it. I'm not sure how much of that my memory is recalling correctly but it issomething along those lines. But what over all what number do some of the "exotic" cars have that enable them to be more stable and/or safe at higher speeds?

 

A low CD number has very little to do with how stable a car will be at high speed. At speeds of over 120 MPH, some cars experience lift ...... too much air going under the car, making it lighter, and less stable. A good example of such a car is the 1st gen RX7. It has a low CD (something close to .30 IIRC). However, in a stock configuration, the car experiences significant lift of the rear end at speeds over 110 mph. I suspect that a Suburban would be more stable at that speed, with a terrible CD.

 

Coefficient of drag merely defines how efficient the shape is at cutting through the air. A vehicle with poor aerodynamics requires more power to attain and maintain the same speed as one with less drag. That is why hybrid and electric cars require very aerodynamic designs to make up for their lack of power.

Downforce defines how stable a car is at high speed.

 

Most of the "exotic" cars have a combination of things. The significant difference is a lot of them have underbody (venturi) channels and a much lower overall ride height and much less suspension travel (making it much easier to setup proper underbody aero). For brief blurbs on different aerodynamic things you can do to a car: http://aerodyn.org/Annexes/Racing/hlifts.html

 

This thread is outta my league, BUT I got another fact like yours Crispy...

Only 2 production cars were ever able to generate that kind of downforce, to actually drive upsidedown...

1) The Vector
2) Porsche 959

(This is old info, there may be more from the past decade)

 

Does anyone know the #'s for a rear c/f rear diffuser?Or a stock R1 wing with it combined?Maybe it stablelizes the car from left -to right.

 

Yeah, I neglected to mention this is my initial post. I didn't have the frontal area number with me at work. Jim is correct though, the FD's frontal area (stock) is 19.2 sqft. Also, be aware that the frontal area will change if the height of the car is altered. If you lower the car, area (A) will also decrease, providing for even better aerodynamics.


Mods: Can we move this thread to the Advanced Tech section? It has some really great technical info in it.


Rob

 

Very interesting. Good info!

X...

 

The diffuser function varies greatly depending on the height above ground - i.e. if your car is stock height vs lowered, and if you corner hard so it leans. What it does is reduce lift and does it without greatly increasing drag (compared to a wing). On a street car (suspension soft enough that you retain fillings in your teeth and high enough that you can enter and leave the road) it looks great.

 

since this might be moved to Advanced Tech, heres a link to a thread on NP that i replied to. Involves underbody diffusers and venturi tunnels: http://www.nopistons.com/forums/inde...howtopic=40746

there was a better thread from a while back, but it fell off the forum

-Zach

 

Thanx, guys - exactly what I was looking for.

 

The Saleen S7 was designed to be able to perform that feat at 160mph + I've also heard rumors of the F60 Ferrari being capable of this.

 

The Saleen S7 was designed to be able to perform that feat at 160mph + I've also heard rumors of the F60 Ferrari being capable of this.

 

Yea my old first gen would float and be pretty uncontrollable at the near top speeds....my second gen was better but so much steering play over 120... FD rides like it is on rails...very nice