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jeff_alexander 01-14-2010 01:59 AM

Wind tunnel testings
 
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

Quote:

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

http://img3.sportauto-online.de/BMW-...f48-279843.jpg

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

http://img2.sportauto-online.de/Audi...f26-260889.jpg

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

http://img2.sportauto-online.de/Merc...16a-242538.jpg

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

http://img3.sportauto-online.de/Corv...6b9-267910.jpg

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

http://img3.sportauto-online.de/Ford...9dc-219808.jpg

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

http://img2.sportauto-online.de/Mini...388-232969.jpg

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

http://img2.sportauto-online.de/r498...b9b-162751.jpg

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

http://img4.sportauto-online.de/Ford...44e-255719.jpg

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

http://img3.sportauto-online.de/Niss...081-250214.jpg

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

http://img4.sportauto-online.de/r498...d28-245985.jpg

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

http://img1.sportauto-online.de/r498...ab4-162580.jpg

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

http://img3.sportauto-online.de/r498...850-164900.jpg

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

http://img2.sportauto-online.de/r498...973-159560.jpg

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

http://img4.sportauto-online.de/r498...84f-159394.jpg

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

http://img2.sportauto-online.de/r498...e02-160595.jpg

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

http://img3.sportauto-online.de/r498...9bf-161808.jpg

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

http://img1.sportauto-online.de/r498...61a-220061.jpg

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

http://img3.sportauto-online.de/r498...354-170963.jpg


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

http://img4.sportauto-online.de/r498...0f5-165853.jpg

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

http://img2.sportauto-online.de/r498...5db-171339.jpg

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

http://img3.sportauto-online.de/r498...99e-191026.jpg

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

http://img4.sportauto-online.de/Lamb...9ab-191384.jpg

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


http://img3.sportauto-online.de/Gump...f55-279758.jpg

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

http://img2.sportauto-online.de/r498...9d1-165539.jpg

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

http://img3.sportauto-online.de/Pors...258-238806.jpg

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

http://img3.sportauto-online.de/r498...eca-187021.jpg

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

http://img4.sportauto-online.de/Paga...041-219874.jpg

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

http://img3.sportauto-online.de/Koen...8f8-219828.jpg

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

http://img2.sportauto-online.de/Pors...6e8-191706.jpg

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

http://img3.sportauto-online.de/Merc...9d6-243286.jpg

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

http://img4.sportauto-online.de/r498...ada-174210.jpg
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

http://img3.sportauto-online.de/r498...c8b-187029.jpg

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

http://img2.sportauto-online.de/r498...0ea-238772.jpg

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

http://img2.sportauto-online.de/r498...dc9-181483.jpg


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

http://img2.sportauto-online.de/r498...4ed-158083.jpg

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

http://img2.sportauto-online.de/Merc...354-220157.jpg

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

http://img3.sportauto-online.de/r498...e26-158130.jpg


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

http://img1.sportauto-online.de/r498...718-188162.jpg

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

http://img2.sportauto-online.de/Lotu...f6e-181166.jpg
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

http://img1.sportauto-online.de/Opel...67e-187262.jpg
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

http://img3.sportauto-online.de/r498...8fd-191814.jpg

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

http://img3.sportauto-online.de/BMW-...011-219515.jpg

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

http://img2.sportauto-online.de/Corv...e6c-191745.jpg

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

http://img1.sportauto-online.de/Opel...4e4-191065.jpg
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

http://img3.sportauto-online.de/Ferr...3a8-219791.jpg


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

http://img2.sportauto-online.de/Ruf-...91c-191044.jpg

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

http://img3.sportauto-online.de/r498...f16-186952.jpg


slammer111 01-14-2010 03:10 AM

AWESOME post. :thumbsup:

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 01-14-2010 03:17 AM

Damn, that NSX is slick.

hk20000 01-14-2010 03:46 AM

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 01-14-2010 09:59 AM

I love each one of those cars

AzNightmare 01-14-2010 10:21 AM

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

TOPEC 01-14-2010 11:57 AM

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 01-14-2010 12:17 PM

nice man, interesting facts there

Rich Sandor 01-14-2010 01:39 PM

Quote:

Originally Posted by slammer111 (Post 6769539)

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 01-14-2010 01:45 PM

Quote:

Originally Posted by RX_Renesis (Post 6769919)
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 01-14-2010 01:54 PM

Quote:

Originally Posted by hk20000 (Post 6769557)
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 01-14-2010 06:26 PM

wow interesting

TOPEC 01-14-2010 07:35 PM

Quote:

Originally Posted by Rich Sandor (Post 6770050)
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 01-14-2010 08:25 PM

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 01-14-2010 08:37 PM

Quote:

Originally Posted by Meister1982 (Post 6770706)
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 01-14-2010 09:36 PM

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 01-14-2010 09:45 PM

Quote:

Originally Posted by Rich Sandor (Post 6770826)
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 01-14-2010 10:43 PM

Quote:

Originally Posted by RX_Renesis (Post 6770847)
u mean an upside down air plane wing?

http://warp.povusers.org/grrr/images..._incorrect.png

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

Rich Sandor 01-14-2010 10:50 PM

^ 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.


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