just another one

 

I saw the post and was thinking the same thing.

 

Just a guess here, but it probably causes a lot of turbulance due to the hot (low density) air meeting the cold (higher density) air, and rapidly cooling. The rapid cooling would cause the cold air to try to fill the pressure gap left by the previously hot air. It would probably throw off laminar flow a bit.

Somebody will have a better answer shortly.......

 

I read that most of the higher end Japanese tuners do wind tunnel test their products (something that attributes to their price for this stuff), mazdaspeed, mugen, all the big dollar ones do. I also "heard" (no flames please) that feed does too.

 

Minimizing lift is probably the first place to start. Look at nearly every production-based race car and they have very low front bodywork, even if it's something as crude as a lip extension. This prevents air from flowing under the car and creating upward pressure as it slows down due to the irregular-shaped underbody. A flat underbody panel is helpful, adding rake will aid in minimizing lift (look at Nascar, they are very limited in the aero department, they use suspension settings to induce rake in the underbody).

I'm not sure how effective it would be on our cars, but many LeMans prototypes use vented /louvred front wheelwells to create downforce. Take the Audi R8 for example: http://www.mulsannescorner.com/audir8-01-5.html

I think the most effective thing in terms of actual downforce would be a front channel, similar to the ones pictured above. One thing could be improved is the relative flatness of the front edge of the car below the headlights; angle it further downward like Ferrarri's.

What type of racing is this for?
-s-

 

If that was the case, then supersonic aircraft (the friction of the airflow over the skin of the aircraft heats both to high temps) would have some serious problems with aerodynamic drag...
The heated air is less dense, reducing the effects of any aerodynamic downforce designs.

 

OK, that makes sense. So, along the same lines: Will my car be less stable at high speeds on a hot day, on a hot surface. I plan on competing in the Texas Mile, a one mile standing start land speed race, and I'm now concerned with the high speed aerodynamics of my car. The race is about 75 miles SW of Houston, and if I attend a summer race you can figure on at least low 90's for local temperature, and the runway will be much, much hotter.......

Or, is it such a small difference that I shouldn't be concerned with it.

 

I doubt the difference would be noticeable, for a couple reasons:

1. The effect mentioned by Kento is caused by only some of the air being heated, the air that has passed through the radiator. An increase in ambient temperature would make all the air less dense, for a somewhat uniform decrease in both lift and downforce.

2. A 60 degree day vs. a 90 degree day is only 30 degrees difference, while the surface of the radiator should be nearly 200 degrees, that's a good 100 degrees difference at the least. I'm guessing you wouldn't notice the difference in stability between summer and winter. When is the last time you heard of people avoiding racing in the summer due for fear that their cars aren't as stable at high speeds? Sounds a bit silly to me.

-s-

 

No, it won't make a difference, because the general atmospheric conditions are "hot", not just the airflow traveling over the top of the car.

 

I'd just like to cover all my bases. Thanks, Kento.

 

I should probably take that advice. Aerodynamics is a non-obvious science. Instead of testing and measuring and trying to understand what is happening, people just slap stuff on hoping it works.

Example: What do you think happens to all that air that goes though the radiator? It does just disappear. (It vanishes into thin air!) No, it gets dumped underneath the car and generates alot of lift. This is why most race cars have massive hood venting. (look at a C5R.) It's not just to help cool, it's to prevent all that enters the nose from going underneath the car. Now look at all the aftermarket body kits with the huge radiator opening. More air though the radiator means more air pushed underneath the car which means more lift. Take a hint from nascar and use the smallest radiator opening you can get away without overheating.

Another example: You've heard stories of headlght covers flying off FDs at speed. That right there should tell you that there is a low pressure area over the head light cover (or a high pressure area underneath it). But for some reason, some people think that the headlight cover is a good place for air intake.

 

Actually that happens because the plastic tabs at the front of the cover through which the mounting screws pass crack. The cover flutters a little at the front until it catches enough air to rip it off the car. About the same as driving around with your hood popped and no auxilary latch to ensure it can't open further; it would eventually fly open when you went fast enough.

As for high speed aero on the FD it is already very good for a street car. I don't think there's any use in sweating these things unless you really are driving it 150 mph on a track all the time.

Downforce on a car is especially tricky. You'll hear teams talk about the center of pressure on a car (the center of pressure is to aero what the center of gravity is to mass of the car). If your center of pressure moves around at different speeds the chassis is not consistent as speeds vary. It's very difficult to make the front and rear of the car equally efficient so that the chassis doesn't exhibit different handling characteristics at different speeds. Sometimes you hear teams talk about pitch or yaw sensitivity. This normally is a result of the center of pressure moving around as speed, pitch and yaw varies. This is why you'll see an F1 car for instance make a front wing change and then the redesign the barge boards and the rear wing as well. It all has to work together.

 

nix that