and more

 

Wow, this thread is pretty old and I had never scene it before. My brother was looking at the first few pages today and I got pretty wrapped up in it. Been studying it for the last few hours on and off.

trinydex, I don't know if my input makes a bit of difference or not and I'll gladly go away but there is something I don't agree with in here. In the thread I have going about this stuff a guy contacted me here at the shop who actually works at a wind tunnel. He did so trying to help me out. The guy is a wealth of knowledge since he is actually in the industry. I told him about the wickers I built under the car in front of the tires and that the EVO9 has them. At first he was against it but said if Mitsubishi was doing it then it probably is a good idea. In the picture above you can see how I have them built on my white RS. I was trying to keep the air OUT of the wheel wells. This aerodynamics expert told me the wheel wells are one of the worste places for drag on the car. Well after doing this wicker on my car and doing the "oil" test I called him again and told him what the results were. The wicker in front of the tire is apparently working to help keep that high speed air out of the wheel well area but he thinks I can do even better. I am going to make a new set up for my car and re-test it.

I am actually kind of confused on some of these undertrays pictured as it seems as though many of the manufacturers are attempting to cram air into the wheel well and from everything I am reading and getting from Jim (aero guy) that is not what you want to do, it creates a ton of drag. Now if brake cooling/tire cooling is the idea behind it then I get it. I think for 99% of us though it is for sure the wrong move.

I would like to see some of the front fenders from the back of the car, as Jim is telling me the fenders with the ducts in the rear are the best as they let all that high pressure air/drag out of there. An example of this for the EVO's are the wide front fenders offered with the vents built in.

Just some input and thoughts.

 

i'm not sure if you're asking me a question or not but i will tell you the answer.

the most basic way to say it is there's two ways to make downforce. 1 is to turn air. 2 is to bar air (create voids of air).

now you see some front undertrays, particularly the voltex that are tryinng to turn air into the wheel well. in order to turn air however you must have flow. the problem with trying to flow something on the UNDER side of the car is it usually has nowhere to go but back down after you turn it, UNLESS you go to the SIDE. the wheel wells are conveniently to the side of the bumper.

you are absolutely right when you say that the wheel wells are a trouble area for downforce. but it apparently has not been revealed to you why. as the wheel and tire turn they create one or more areas of high pressure (high pressure is bad when it's under the car). if we divide the tire into 4 quadrants labeling them 1 2 going horizontally in the top first row and then 3 4 for the bottom in a car moving to the right quadrant 4 is where the high pressure is produced.



so you see this undertray feeds right into that high pressure, this is bad, but it allows the air to turn and flow out of the wheel well which is good. this does not necessarily exacerbate the situation of high pressure in quadrant 4 of the tire!!!

so what do you do to remedy the situation of high pressure in quadrant 4 of the tire? you can do it in many ways but the way most common is to create a void of air on the outside of the wheel well near that quadrant. you can do this by creating wheel well spats for an air dam at that quadrant of the wheel well.



two seperate solutions to two seperate issues. one turns air and exhausts it into the wheel well. the other addresses some high pressure zones in the wheel wells, "tapping" the high pressure zones to reduce their pressure.

i hope that helps

 

I was simply looking for more conversation on the subject, which I got

I think the best thing that can be done is to try and eliminate the air from getting forced into the wheel well opening in the first place, would you agree? That is what Jim is trying to tell me to do. Getting it out of the wheel well can be done with the vents behind the tires as you see on most higher end vehicles built for high speed.

I would think the picture you have above of the green car would produce additional drag with that large flat area, correct? Maybe the effect from being able to drop the high pressure in the wheel well area overrides the drag from the flat spot.

Looking for more conversation

 

I went back and read your post a few more times....

Now I have a question. First, where did you pick up the knowledge you are passing along? Not making trouble, just curious.

Second, don't you feel the picture of the red EVO you have above is making the problem worse? You have air coming from the front of the car, it appears to me as though the air is being directed up into the wheel well area rather than trying to keep it out?

The wickers I built on the undertray for the black car and my RS both caused the air to swirl before it got the wheel well area. I was told this is better than the high speed air being jammed up into the wheel well but it would be best if I could direct the air out from under the car and past the wheel well before it gets in there. Do you agree with this?

Thanks,

 

I like mine..

 

crap i forgot to address that part.

so the wickers you have on your tray. what they're doing is instead of immitating the wrc car's air dam on teh bumper and creating void on the SIDE of the car to "tap" the high pressure zone and bleed out the high pressure in the wheel well, you're doing the SAME thing from UNDER the car. this is perfectly acceptable, BUT it doesn't allow you to have the TURNING of air from under the car like the voltex style "underwing" does.

i think the ideal case is to do both but that requires a new bumper and a complex undertray with upward moving vents (i still can't figure out what to call those things, wings, vents, ducts but basically the thing we've been talkin' about). whereas your solution only does one of the two possible engineered downforce mechanisms but is drastically simpler.

the swirl you talk about... which direction is it going as this is of great interest to me. the high pressure zone that the tire makes also has a swirl and if you can make both swirl the same way while making a low pressure zone that would probably expidite the evacuation of the high pressure zone in the wheel well. but like i said... exhausting the underwing flow into the wheel well doesn't necessarily have to increase the high pressure zone in the wheel well ESPECIALLY if you have the air dam on teh bumper tapping the high pressure zone for flow.

 

here's some pictures to try to illustrate what i'm saying

so as you can see by the two pictures of the blue car. the high pressure zone spins as to peel off the tire and then it swirls.

there are two possibilities of the wicker making vortices. if the gurney flap twin vortices theory holds here then it should be the first picture of the blue car.

 

here are pictures of what Voltex front lower diffuser look like.. very well thought out.

 

pics don't work

 

Fixed!

 

making a full underbody?

 

trinydex,

I will try to get a picture of the air flow and how the oil moves on the tray, sometime in the near future. I am swamped right now with all the new crap we have going on and the shootout this week.

I will attempt to explain it though. The wicker I put on the bottom of the undertray is right at the edge of the tray, before the front tire. You can see it in the pictures of our trays. The swirling actually appears to be taking place in front of the wicker. You can see the oil going straight towards the wicker and then you can see it either seperate or swirl, hard to see it with the clear oil (WD40) I was using. I'll do it again when I get a chance.

 

I believe Voltex is making a full underbody as we speak..

The pix above were from their blogs because I was too lazy to take pix of the same bumper we got from them.

 

I think the difference we are seeing is downforce improving drag times vs. downforce for road racing.

Downforce = Drag (but controlled to do what you want it to, rather than just random drag).

For drag racing you want to eliminate all the drag you can. So in that instance, David's setup is perfect because you're smoothing the airflow across the turbulent underside and directing it where to go.

For road racing, that's not nearly enough because in general our Evos have more rear downforce (especially the MR) than they do front downforce. Downforce is much more important in road racing where you're not looking for top speed but you need cornering ability. This is why you always see drag cars having minimum drag with only downforce additions on the rear to keep it planted for best power distribution (and some small additions in the front just to keep the front end from flipping on top fuel cars). Compare that to F1 or LeMans Prototypes and you will see there's a huge difference.

I think that's where the "discussion" is coming from. David's pieces are great for a drag racer who's looking to eek the last 10th from his time. But a road racer just needs more than that.

Like I pointed out earlier in the thread, I have Beatrushes under tray which is nearly the exact same thing as David's undertray but in steel, and when I raced with it, it didn't provide nearly enough downforce in the front vs. my APR GTC-300 rear wing . It smoothed the air going under the front which helped the car at high speeds, but it didn't bring the front down at all.

With that in mind we're looking at two different applications with two totally different needs.

- Patrick