jmann

I think you ought to run them a low as you can, the less air underneath the better the downforce. Look at Nascar or the DP's in the Rolex series. The less air underneath the more downforce with proper aeroworks above. My only concern would be height for those off the track excursions. We don't have a unlimited budget and new noses sitting in the pitts, so that becomes a big part of the equation. As you know my aero up front os pretty low, I would guess somewhere in the 2" and change range and any off track excursions pretty much does it in everytime. Hard braking hasn't seemed to be an issue and I don't have 700# front springs, but high compression areas are and that is why I am going to a higher # springs this off season. Mainly The Ridge seems to have the worst after turn 7, mine rubs pretty bad there and as you know, we run there alot. The only other track I've had it rub at and I rubbed the first one through the bottom lip was at turn 7 at Pacific with its ripples. As you know I remove mine for loading as I would have to run a ramp probably 30 ft out and no thanks, you won't have that luxary with a splitter. So the moral of the story is make sure it sits level or with very little downward bias with you in the car and HIGH enough so hopefully everytime you go off you aren't having to drag it back to the pitts and remove it.

jmann

Plucas Really nice stuff. I am wondering how much trouble to run this setup on your program. I run with a air deflector from 949 racing, SuperMiata Air Dam NB1. It is very similar to nbr.4 in your pics., can I assume that it would be very close to that setup? Thanks

Vilko

Dont make too many comparisons to Nascar. I'm not sure about their splitters but a lot of their aero (such as rear spoiler) is set up to disrupt the car behind them and not optimum drag/downforce. Just something to consider.

jmann

I don't agree with that. I know a couple of guys that do Nascar and the aero is setup to go as fast as they can and keep the car planted. At 200 mph plus they aren't worried about the air on the car behind. Running the car on the bump stops up front so as to keep the splitter planted to the track without wearing it out along with side skirts is to keep the air from getting under the car, nothing to do with the car behind.

plucas

Not much trouble since I have everything already set up. Only thing that would need to be done is modeling the 949 racing product. It usually takes around 24 hours to run each setup.

That is incredibly false. Nobody in professional racing sets up cars to disrupt cars behind them. I can go into how they setup aero for each track, but that is off subject.

gtred

On a practical note, my splitter catches every time I back out off the trailer. It has caused the nose to rip along the top parting line at the front of the hood. I'm taking mine off.

1993ka24det

Thanks "plucas" I gave you props. I built #4 but it broke after hitting a puddle and a friend head smashed in to the dash. Keep up the good work, Love the data!!!!!!!

Leafy

iTrader: (1)

And you dont want to pull a coding paradox either, thats for sure.

GAMO

iTrader: (1)

I hope that #3 counts as having the R-package lip. :v

Seriously amazing information. Somebody needs to give this guy a rad custom title.

Vilko

Why yes, yes it is. A nascar reporter was saying it during the coverage of a race. I dont know nothing about Nascar and I made the mistake of thinking he did.

Anyway with your modelling do the splitters extend to the same point in model 4 and 6?

Midtenn

iTrader: (15)

With the different variations of tracks, there are probably different variations of aero packages. I know they vary the grill opening, the spoiler length, and spoiler angle depending on the tracks they are at, be it a super speedway, 1.5mi cookie cutter, or short track.

plucas

This. You normally run simulations to see what L/D value gives best track times and set aero package around that. Or... you set the aero package up for max downforce or least drag. It is all dependent on the track and goals.

jmann

As far as Nascar is concerned the spoiler size/height, angle and most anything else to do with aero is strictly controled by Nascar. The angle on the spoiler has to be right on what ever degree Nascar dictates, no room for adjustment. Other forms of racing you have alot more adjustability and design options.

plucas

This is very true. Nascar allow very little changes so teams spend a fortune on stupid things like battery box designs that will have the least amount of drag. The battery box sits towards the back of the car at the bottom. It was funny watching windtunnel test to improve this. This is one of many reasons Nascar is so lame.

M.Adamovits

Some of the best information I've seen on this forum.

plucas' post should be stickied.

ThePass

iTrader: (3)

Absolutely awesome contribution plucas. Thanks.
The big thing those models don't show is the benefit of covering the front tires - since they aren't spinning in those tests like you said. If they were, and the model was set up with wheel widths like a 15x9, we'd see much more drag on #1-3 compared to #4-6.
The differences between the different designs is really cool to see - stuff we all knew through common aero understanding and from testing, but probably most of us haven't seen actual numbers generated for the designs.

-Ryan

emilio700

iTrader: (3)

plucas,

Was there an undertray on any of the sim runs and if so how it shaped? There are a lot of HPDE and NASA drivers here. Both situations we are allowed a full coverage undertray forward of the front axle centerline. In practice, we can't run the tray to the lowermost extremity of a low airdam or it will get beat up and torn off. So it's often a few inches up. We have found, sort of by accident, that running the undertray up high like that makes downforce. Acting as a crude, separation prone diffuser probably but working nonetheless.

If config #6 doesn't have a full undertray, it might explain the odd low drag figure. Everything I think I understand about these things tells me #5 without splitter should be lower net drag than #6.

One variable not accounted for is a trunk mounted wing or spoiler and how that might effect net drag. We find that adding the airdam like #5 makes the wing have the same effect with a lower AOA than w/o the dam. The current set up on Crusher is the lowest drag we have come up with on our modest budget. The wing mounts, brackets and uprights are dirty but that will be addressed in a future iteration.

Thanks a ton for sharing this with the community.

miata_racer

#3 looks like my home depot setup

plucas

The undertray on the model is just a simple flat bottom. There is not any shaping at all. This is commonly done on cfd models for simplification. If I am visualizing this properly, I think I can explain this. The separation actually creates a deadwater region with low static pressure. This flow separation decreases the lift on the front of the car.

Configuration #6 also has a full undertray but it is not at the same height as the air dam.

I am working on a few analysis with wings also since I am designing a wing and mounting location for a friends miata. The airfoil profile is 100% finished and endplate design is going through final iterations. After that is done, prototype will be made. So I will be turning my analysis effort soon to wing location on the miata. It will be a swan neck mount and probably behind the rear bumper in the x-direction.

bbundy

I wounder how the lift numbers between 4 and 6 would compare if the splitter on 4 stuck as far forward of the furthest forward point of the nose as it does on 6. Im sure it would still have more drag but potentially even more downforce. I noticed a big differance when I doubled the length of my splitter to 6" in front of the furthest forward point on the nose. It works ok that long for autocross but Id probably be ripping it off all the time on a road course.

Bob