Wind tunnel testings

[jeff_alexander]

Some interesting Stuff I found on fastestlaps.com regarding aerodynamics and lift/downforce on cars.

http://www.fastestlaps.com/forum/vie...er=asc&start=0

Originally Posted by Georg

because at the GT-R datasheet discussion ot factory claimed cd of 0.27 and sportauto clocked 0.31 on one of the most modern windtunnels in the world I thought it would be interesting to compare the sportauto results to manufactor claims..

Important... not cd is important.. the airdragindex is the important number... the combination of cd and the size of the vehicle.. the lower cd x A the better is the aerodynamic of a car...
a other sidenote... many "noseheavy" cars can become nearly weightblance neutral at higher speeds if the lift at the front axle is greater than it is at the rear

BMW X6 M

frontal surface area (A) 2.85m²
cw (cd) 0.38
airdragindex (cd x A) 1.07
at 200km/h (125mph)
lift front axle 69kg
lift rear axle 48kg



Audi R8 V10 5.2
(A) 2.024m²
(cd) 0.36
(cd x A) 0.72
at 200km/h
lift front 23kg
downforce rear 3kg



Mercedes SL 65 AMG Black Series
(A) 2.17 m²
(cd) 0.37
(cd × A) 0.80
at 200km/h
lift front 56kg
downforce rear 22kg



Corvette ZR1
(A) 2.059 m²
(cd) 0.32
(cd × A) 0.66
at 200km/h
lift front 39kg
lift rear 14kg



Ford GT
(A) 1.92 m²
(cd) 0.35
(cd × A) 0.67
at 200km/h
downforce front 44kg
lift rear 2kg



Mini Cooper S John Cooper Works
(A) 2.05 m²
(cd) 0.36
(cd × A) 0.73
at 200km/h
lift front 17kg
lift rear 20kg



Lexus IS-F
(A) 2.22 m²
(cd) 0.30
(cd × A) 0.67
at 200km/h
lift front 31kg
lift rear 7kg



Ford Focus RS
(A) 2,35 m²
(cd) 0,36
(cd × A) 0,86
at 200km/h
downforce front 8kg
lift rear 4kg



Nissan GT-R
(A) 2,30 m²
(cd) 0,31
(cd × A) 0,71
at 200km/h
lift front 3kg
downforce rear 8kg



Porsche GT3 facelift
(A) 2.04 m²
(cd) 0.32
(cd × A) 0.66
at 200km/h
downforce front 15kg
downforce rear 19kg



Audi TT-S
(A) 2.10 m²
(cd) 0.32
(cd × A) 0.68
at 200km/h
lift front 42kg
lift rear 17kg



Lamborghini Gallardo LP 560-4
(A) 1.93 m²
(cd) 0.35
(cd × A) 0.67
at 200km/h
downforce front 4kg
lift rear 37kg



Alpina B3 Coupe
(A): 2.14 m²
(cd): 0.29
(cd × A): 0.63
at 200km/h
lift front 12kg
lift rear 13kg



Aston Martin DBS
(A): 2.11 m²
(cd): 0.36
(cd × A): 0.76
at 200km/h
lift front 11kg
lift rear 10kg



Abarth Grande Punto esseesse
(A): 2.21 m²
(cd): 0.34
(cd × A): 0.75
at 200km/h
lift front 26kg
lift rear 31kg



Mercedes C 63 AMG
(A): 2.18 m²
(cd): 0.32
(cd × A): 0.69
at 200km/h
lift front 35kg
lift rear 42kg



BMW Z4 3.0si Coupé
(A): 1.94 m²
(cd): 0.33
(cd × A): 0.64
at 200km/h
lift front 28kg
lift rear 43kg



Lotus Exige S
(A): 1.62 m²
(cd): 0.44
(cd × A): 0.71
at 200km/h
downforce front 5kg
downforce rear 24kg




Porsche 997 Carrera S facelift
(A): 2.02 m²
(cd): 0.29
(cd × A): 0.59
at 200km/h
lift front 24kg
lift rear 14kg



Ferrari 430 Scuderia
(A): 2.02 m²
(cd): 0.33
(cd × A): 0.66
at 200km/h
lift rear 4kg



Audi S5
(A): 2.18 m²
(cd): 0.31
(cd × A): 0.67
at 200km/h
lift front 52kg
lift rear 34kg



Lamborghini Murcielago LP 640
(A): 2.04 m²
(cd): 0.35
(cd × A): 0.71
at 200km/h
downforce front 30kg
downforce rear 11kg



from a other planet were the Gumpert Apollo numbers..

Gumpert Apollo Sport
(A): 1,99 m²
(cd): 0,57
(cd × A): 1,14
the very bad cd is because of the giant rear wing and the million cooling openings all over the car ... but they are there for one reason downforce..
at 200km/h
downforce front 20kg
downforce rear 176kg




Honda NSX-R (2002)
(A): 1.7800 m²
(cd): 0.34
(cd × A): 0.60
at 200km/h
downforce front 32kg
downforce rear 5kg



Porsche Carrera GT
(A): 1.95 m²
(cd): 0.37
(cd × A): 0.72
at 200km/h
downforce front 49kg
downforce rear 40g



Mitubishi Evo VII
(A): 2.12 m²
(cd): 0.37
(cd × A): 0.79
at 200km/h
downforce front 37kg
downforce rear 8kg



Pagani Zonda F
(A): 2,08 m²
(cd): 0,36
(cd × A): 0,74
at 200km/h
downforce front 1kg
downforce rear 25kg



Koenigsegg CCR
(A): 1,86 m²
(cd): 0,35
(cd × A): 0,64
at 200km/h
downforce front 13kg
lift rear 11kg



Porsche 997 Turbo old
(A): 2.04 m²
(cd): 0.29
(cd × A): 0.59
at 200km/h
lift front 9kg
downforce rear 12kg



Mercedes SLR
(A): 2.07 m²
(cd): 0.37
(cd × A): 0.77
at 200km/h
downforce front 19kg
downforce rear 35kg



Maserati Coupé Cambiocorsa
(A): 2.016 m²
(cd): 0.34
(cd × A): 0.68
at 200km/h
downforce front 55kg
downforce rear 45kg


no windtunnel picture avaible online

Ferrari 575 M Maranello
(A): 2.09 m²
(cd): 0.32
(cd × A): 0.66
at 200km/h
lift front 61kg
lift rear 40kg



Porsche 996 GT3 RS
(A): 1.94 m²
(cd): 0.30
(cd × A): 0.58
at 200km/h
lift front 19kg
downforce rear 26kg



Ferrari Challenge Stradale
(A): 2.0 m²
(cd): 0.31
(cd × A): 0.62
at 200km/h
downforce front 10kg
lift rear 21kg




Mercedes CLK DTM AMG
(A): 2.15 m²
(cd): 0.34
(cd × A): 0.73
at 200km/h
lift front 37kg
downforce rear 12kg



Mercedes SL 65 AMG
(A): 2.1 m²
(cd): 0.31
(cd × A): 0.65
at 200km/h
lift front 29kg
lift rear 33kg



Mercedes SLK 55 AMG
(A): 1.95 m²
(cw): 0.32
(cw × A): 0.625
at 200km/h
lift front 23kg
lift rear 31kg




Corvette C6 Coupe
(A): 2.0 m²
(cd): 0.29
(cd × A): 0.59
at 200km/h
lift front 54kg
lift rear 28kg



Lotus Exige (Mk I)
(A) 1,631 m²
(cd) 0.43
(cd x A) 0.70
at 200km/h
downforce front 20kg
downforce rear 58kg


no windtunnel picture online

Opel Speedster Turbo
(A): 1.61 m²
(cd): 0.38
(cd × A): 0.61
at 200km/h
downforce front 23kg
lift rear 19kg


no windtunnel pitcure online

Ferrari 599 GTB Fiorano
(A): 2.23 m²
(cd): 0.33
(cd × A): 0.73
at 200km/h
lift front 41kg
lift rear 24 kg



BMW e92 M3
(A): 2.17 m²
(cd): 0.33
(cd × A): 0.71
at 200km/h
lift front 10kg
lift rear 23kg



Corvette C6 Z06
(A): 2.1 m²
(cd): 0.308
(cd × A): 0.647
at 200km/h
lift front 49kg
lift rear 22kg



Opel Corsa OPC
(A): 2.15 m²
(cd): 0.36
(cd × A): 0.78
at 200km/h
downforce front 23kg
lift rear 22kg


no windtunnel picture online

Ferarri F430
(A): 2.04 m²
(cd): 0.34
(cd × A): 0.70
at 200km/h
lift front 11kg
lift rear 6kg




RUF RT12
(A): 2.04 m²
(cd): 0.33
(cd × A): 0.67
at 200km/h
lift front 11kg
downforce rear 34kg



Honda Civic Type R
(A): 1.93 m²
(cd): 0.326
(cd × A): 0.63
at 200km/h
downforce front 19kg
lift rear 44kg

[slammer111]

AWESOME post.

Cd CAN (and normally does) change depending on wind speed though, so using 200km/h may not reflect real-world situations.

In any case, they should've used N for force instead of kg.

To calculate the total drag (ie backwards-acting) force on the car at any given moment, use the formula Fd = (1/2)(rho)(U^2)(Cd)(A)

rho = air density, which is 1.2 kg/m^3 @ 15C, sea level
U = airspeed in m/s
CdA = that drag index thingy.

One thing to keep in mind about the lift/downforce numbers is that in this test the floor is not also moving at 200km/h relative to the car. That is going to induce a ton of turbulence and mess up the results. So I'd take the numbers with a grain of salt.

[FN-2199]

Damn, that NSX is slick.

[hk20000]

The most surprising result is probably that EVO7 where it's basically a sedan with wing yet it can generate downforce at 200km/h on both ends of the car.

good job Mitsubishi

[Volvoman]

I love each one of those cars

[AzNightmare]

Don't really understand those numbers, but some of those pics were pretty cool...

[TOPEC]

so in laymens terms, cars with very little downforce at the rear end when compared to the front end will snap oversteer very easily at speed?

[Mugen EvOlutioN]

nice man, interesting facts there

[Rich Sandor]

Originally Posted by slammer111

In any case, they should've used N for force instead of kg.

One thing to keep in mind about the lift/downforce numbers is that in this test the floor is not also moving at 200km/h relative to the car. That is going to induce a ton of turbulence and mess up the results. So I'd take the numbers with a grain of salt.

The reason they use kg instead of N in this example, is to quantify the handling in relation to the vehicle's weight. For example if you know the vehicle weighs 1500kgs, then looking at 100kg downforce is far more useful than seeing XX newtons of downforce.

Moving floor windtunnels really only help make numbers more accurate for cars with extremely low floorpans, and those with groundeffects or/and rear diffusers. On a stock 911 carrera or mini cooper, it won't make any difference.

[Rich Sandor]

Originally Posted by RX_Renesis

so in laymens terms, cars with very little downforce at the rear end when compared to the front end will snap oversteer very easily at speed?

Not necessarily. You cannot make any firm statements based on these numbers alone. Aerodynamics and downforce are only a fraction of the factors that define how a car handles.

Alignment setup, weight (mass) distribution, and tire choices can have more drastic effects on oversteer/understeer, especially on 2500+lbs cars running below 200kph.

... I say 'mass' because for example, a porsche 944 and a porsche 914 both have nearly perfect 50/50 weight distribution. However, the 944 has an 500lbs engine up front, and a 500lbs transaxle in the rear, whereas the 914 has the engine and tranny right in the middle. Where the 'mass' is has more influence on snap oversteer. (ask any mr2 owner)

... although yea, if you take an F1 car, and rip off the rear wing, you're gonna have crazy snap oversteer going into every corner.

[Rich Sandor]

Originally Posted by hk20000

The most surprising result is probably that EVO7 where it's basically a sedan with wing yet it can generate downforce at 200km/h on both ends of the car.

good job Mitsubishi

The fact that it's a sedan has nothing to do with an ability or inability to generate downforce. You can put a front splitter and a huge rear wing on a BRICK and it will generate downforce at both ends at speed.

The fact is a sedan is going to have a larger frontal surface area and will have more surface drag, and therefore will require more power to overcome that surface drag at higher speeds.

One of the things ya'll might not know, is that induced drag (drag created by wings) increases EXPONENTIALLY as speed increases. Not only that, but there are optimum speeds for any given airfoil, beyond which it acts more like a giant airbrake than a downforce generating wing.

Most of these cars have aerodynamics suited to a specific application - note the difference between the 911 GT3 and the 911 carrera. There is a reason why the carrera does not have or need the aero of a GT3.

[AVS_Racing]

wow interesting

[TOPEC]

Originally Posted by Rich Sandor

Not necessarily. You cannot make any firm statements based on these numbers alone. Aerodynamics and downforce are only a fraction of the factors that define how a car handles.

Alignment setup, weight (mass) distribution, and tire choices can have more drastic effects on oversteer/understeer, especially on 2500+lbs cars running below 200kph.

... I say 'mass' because for example, a porsche 944 and a porsche 914 both have nearly perfect 50/50 weight distribution. However, the 944 has an 500lbs engine up front, and a 500lbs transaxle in the rear, whereas the 914 has the engine and tranny right in the middle. Where the 'mass' is has more influence on snap oversteer. (ask any mr2 owner)

... although yea, if you take an F1 car, and rip off the rear wing, you're gonna have crazy snap oversteer going into every corner.

i would give u a thanks but my thanks button is missing, i think i'd given out all my thanks for today.

[Meister1982]

I didn't know there are so much lift at 200km/h on these cars. I always thought that because of the front windshield there's always downforce and no lift at all.

thanks for the info!

[some_punk]

Originally Posted by Meister1982

I didn't know there are so much lift at 200km/h on these cars. I always thought that because of the front windshield there's always downforce and no lift at all.

thanks for the info!

You also have to look at the underside of the car too. some cars use the air flowing underneath to breath.

[Rich Sandor]

99% of cars are basically an airplane wing when viewed from the side, which means they want to 'take-off' as they go faster. Actually very few cars have downforce at an axle, let alone both axles. You can see from the list above that most only the performance oriented cars have any actual downforce.

[TOPEC]

Originally Posted by Rich Sandor

99% of cars are basically an airplane wing when viewed from the side, which means they want to 'take-off' as they go faster. Actually very few cars have downforce at an axle, let alone both axles. You can see from the list above that most only the performance oriented cars have any actual downforce.

u mean an upside down air plane wing?

[jeff_alexander]

Originally Posted by RX_Renesis

u mean an upside down air plane wing?

Nope, looks like the side profile of a 911 to me.

[Rich Sandor]

^ exactly.

The cross-section of an average car is just like the cross section of an airplane wing. That's why most everyday cars tend to get light and floaty as they get faster.

an upside-down airplane wing is what you put on the back of a race car to get downforce.