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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:
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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. |
Damn, that NSX is slick. |
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 |
I love each one of those cars |
Don't really understand those numbers, but some of those pics were pretty cool... |
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? |
nice man, interesting facts there |
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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. |
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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. |
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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. |
wow interesting |
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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! |
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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. |
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Nope, looks like the side profile of a 911 to me. |
^ 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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