Front aerodynamics... need help!
 

I need some input from anyone who's got some expertise on aerodynamics.

I've been looking at various bodykits with the goal of increasing front downforce in mind. Want something functionally-minded, but as this is my daily driver I don't want something *too* race-track ready (i.e. a big front-diffuser jutting out, getting caught on curbs and speedbumps and driveways).

So I was excited when I saw the Vertex Japan kit, as it seemed to be clean, not over-the-top, but still provide surface area to affect downforce. Then I noticed the middle section of the front-lip...
http://i1255.photobucket.com/albums/...an/Vertex2.jpg
http://i1255.photobucket.com/albums/...man/Vertex.jpg

Now, is it just me, or does it seem like that section will cause the front end to lift, rather than hunker down? That was my thinking, anyway... so I dismissed it as just another kit that was putting style ahead of substance.

But then I started noticing other kits with that same sort of upturned middle section, notably the Garage Vary kit...
http://i584.photobucket.com/albums/s...3/1bedited.jpg

...and the Rocket Bunny kit...
http://i584.photobucket.com/albums/s...97887454_o.jpg

So here's my question: is there some secret to the aerodynamics on the FR-S/ 86 body that makes this upward-deflection area a good idea? And if so, can somebody explain it to me why? Best I can come up with is that it might speed up air flowing under the car, therefore creating low-pressure and drawing the entire vehicle down. But if that's the case, would our cars need the under-panels that are present on the JDM model GT-Limiteds to make this effective? :iono:

Thanks in advance for any help...

Do some research on flat underbody panels. It may yield valuable information for you that will help you with this.

So you're saying that these, err... plow-sections? (don't know what else to call them)... on the front-lip kits smoothen out the air flowing under the car?

Garage Revolution has a functional front lip for the 86. Given their presence in the WTAC, I don't doubt their claim that it actually works.

http://revo-tune.jp/catalogue/detail.php?id=303

Okay, so that's a fourth one using that sort of style, so there's got to be some very important reason behind it. Now, can anybody explain to me what that is? Cause my brain keeps trying to tell me that's just going to result in front-end lift. :(

Just buy some canards :)

Your best bet is going to be getting a front splitter with some canards. After that I would recommend a flat underbody - I believe you can now get that imported from Japan. Lastly, look into getting a diffuser. For all intensive purposes, the front splitter would be your best best on getting more downforce.

Additionally, lowering the car also gives you more downforce, though it is not that substantial.

http://en.wikipedia.org/wiki/Diffuser_(automotive) ...so yes...it looks as if the part in question acts just like an upside down airplanes wing to create downforce...

Edit: http://www.rapid-racer.com/aerodynamic-upgrades.php BTW i hate this thread its 30 minutes later and im still researching this info just because...

As you assumed earlier, air will be moving faster underneath the car with correctly designed front lips and under body panels. Think of an airplane wing, or airfoil. Air moves faster on top of the wing and slower below. Slower air below, means higher pressure under the wing, thus causing lift. The intentions of the front lip and under panels is the exact opposite, thus creating higher pressure on top of the car which is your desired downforce.

LOL... well, you've been helpful enough that I can turn this into another "Umm... should I buy this car now, or wait?" or "I think the FR-S can beat the Veyron on a curvy enough track!" threads, if it'll make you feel better! :happy0180:

Okay... so it really isn't just a case of weird aesthetics; the folks designing these front lips actually DO know what they're doing, and its just the 86's particular aerodynamics that mean its more effective to have that little upturned center on the lip. Thanks for taking the time to explain all that! So you'd reckon that, for maximum effectiveness of the front-lip, I should go ahead and order the under-panels as well? :thanks:

Thanks guys! A million threads on suspension and exhaust mods, but aero gets treated like some sort of voodoo black magic on here.

as far as ordering the under panels...i plan on getting some sintra board or similar and making my own under trays...should be cheaper and work exactly the same...

No problem :), BUT i'm assuming not all aftermarket companies actually test their prototypes in wind tunnels, which can mean some may be purely aesthetic.

IIRC, lengthening a body behind it's leading edge reduces the separation (of air flow) and should help with creating a more slip stream body.. So, by adding under body panels this should lengthen the surface of usable area behind the lip to prevent this phenomena from occuring. The Less turbulent air under the car means lower pressure underneath the car meaning your additional downforce. :thumbup:

All of that air under the car looks like a bad idea to me.

Air is going under there whether you like it or not. There is only so much air you can block/deflect. But, if you can speed it up you can use the air more effectively.

I'm in no way an expert, hell, I can't make a paper airplane that flies straight, but watched a great, two hour long, aerodynamics video a few years ago, fasinating and informative. James May would've loved it. Could I find it in a google search?? Nope... Grrrrr. Sorry, I tried

Check out most supercars, lots of them have it too. The McLaren F1 was born in the wind tunnel. Gordon Murray wanted air to go down the middle.

Ever seen an F1 car? High nose yea?

Air under the car is not necessarily bad if the underbody is smooth and shaped correctly. Because the ground acts as a barrier for airflow (ground effects), channeling more air under the car gives you more downforce because the air will be forced to speed up where the body is closer to the ground. With the disastrous aerodynamics of most cars this won't work very well though, and that's why when it comes to diffusers and splitters you really have to pay attention to what they're actually doing, it's not like a wing where you just raise it really high, give it a big angle of attack, and have some kind of result that is at least partially desirable.

Spot on. A splitter/diffuser is not about keeping air from under the car. The purpose is to split the air smoothly around the car and reattach it with as little turbulence as possible. The smoother the air under the car, the cleaner a proper diffuser can reattach it creating a low pressure area and thus downforce. Unfortunately aero is not really a cookie cutter science and every car will have different requirements and different methods will work.

Surprisingly the splitter also has a large effect on the rear of car. But without having a flat bottom (like any race car) I don't there would be any gain with a nose like that.

But here is an example of a DP car with that type of splitter:
http://www.carfani.com/wp-content/pi...r-exterior.jpg

Your worry is a legitimate one, but one that can be solved.

When do you want downforce the most? Corners.
When do you want a lower drag coefficient? Straights.

When you're about to take a corner your car will dive some. This will reduce the angle of the center part of the lip and most likely end up being pretty parallel to the ground, not having to worry about lift. In addition, downforce will be added directly to the corners (where the wheels are) to increase downforce sufficiently.

When you are in a straight, the car's front will inevitably lift a bit, letting some are under the car. Since air is hitting the center mass of the car, it will create drag and probably a bit of lift. But having the lip come up in the center will let air flow through the bottom of the car easier, resulting in less drag. The design offers a good compromise between downforce through corners, and less drag on the straights.