Not necessarily so. Just because a Nascar can take a certain corner at 150mph does not mean that the car is aerodynamicly optimized. Take that car, put a properly designed splitter/underpan/diffuser/wing on the car and it may be able to take the same corner at 170mph. Nascar (the sanctioning body) does not want that for safetly reasons. A Nascar car is not designed that way because it is BEST, it's that way to meet a very specific goal.

EVOlutionary

 

PM sent.

The current versions are 2 layers of carbon with a foam core. How much downforce it can hold is entirely dependent on the mounting to the chassis. If you tape it to your bumper it may hold 10 pounds. If you bolt it to your bumper it may hold 100 pounds. If you bolt it solidly to multiple hard points on the chassis it will probably hold over 1000 pounds. . .


EVOlutionary

 

David: thanks for posting up the pics. i see what you were saying about the trimming..should be just a little bit. Looks very sanitary. I'll pm you about more ideas on the full undertray.

This is a great thread and the aero pics of turbulent boundary air being used to separate the high speed air flow from the sides bring the point home.

The next question is threefold for this : First for full undertrays would drag be more of a problem across the flat surface bearing in mind the swept area of the undertray? Secondly do we want to keep the air under the car from spilling out the sides ( how ) ? third the high pressure area in the front is just above the splitter..low pressure just below..the car is raked at the front so ..to me this is acting just like 1/2 of a venturi..along the lines of a F1 ground effects tunnel ..would looking at the bottom of the car in this light be reasonable logic ?

Milburn

 

Lol I meant the construction of it, but you definately make your point clear . It would be bolted both to the bumper and somewhere on the frame. I would probably end up making some way to adjust how much splitter is sticking out in front, so I can match DF front and rear as much as possible. Next year is going to be a year full of trial and error, haha

 

I want to see what triny and evolutionary say about your other questions, but I can answer this. You basically want to keep as little air under the car as you can. This is not to say force the air thats under the car out to the side, but rather keep the air moving along the sides of the car from going under the car. the way to do this would be lower side skirts that stick out from the body more (I think I saw a carbon skirt kit for the new evos by chargespeed that sticks out from the stock skirts a few inches), along with correctly mounted canards.

 

Your train of thought is correct. Because you have high pressure on the sides of the car and low pressure under the car you want to keep the side air from coming in under the car.



If you save this and zoom in you can see the side-skirt extensions (grey) that stick down at the sides (a la Cyber EVO). Under compression of the suspension they actually scape on the ground. . .

I've seen AMod cars such as George Bowland's that have spring loaded side skirts so they are always in contact with the ground to keep every little bit of air out from under the car. Then there were the Chapparral race cars in the '70s that had side skirts that dragged the ground and sucker fans ducted to the underside of the car to suck the air out from under the car and make a low pressure zone. They were quickly outlawed.

EVOlutionary

 

man that's a lot of questions.

full undertrays... you're getting a lot of flow across a new surface area but i think that surface area is much less than that of the summed curved and otherwise not flat surface under the car untrayed.

do you want the air from the car to spill out... well... that depends. if the pressure if lower outside then yes, if the air on the outside is higher pressure you want to keep it out. this would be achieved by very strict ground effects. mainly in the front plowing the flow away and then the sides are sealed to the ground as much as they can be to keep it the way you set it up.

i don't understand the last part, please redescribe.

 

I remember seeing something about those chapparral cars with the fans, great idea, but pretty cheap trick at the same time, ha. Are the spring loaded sideskirts on that Amod car legal in scca competition? I dont know the rules above SM that well, so im not really sure. I have been friends with Evan Brauch and his dad Jeff Brauch for years, and I know they were having downforce issues with their Bmod car all year, switching around wings and setups. Im wondering if something like that might help them out a bit. Although Evan seems to have enough natural talent to overcome any issues they were having, as he took BM solo nats this year.

 

Agreed from what I am reading. You want to keep the low pressure air under the car and a simple side skirt can do this, although IMO they are ugly, but serve their purpose.

I also agree 100% with evolutionary on the fact that NASCAR's race cars are FAR from being optimized, they are built to limit their performance and keep speeds down to keep the racing safer. That is a well known fact.

 

this photo/example is much better than your intial pic/post.

this is reminiscent of the later toyota gtpgrp-c car & peugot, mazda's of the middle 90's & what is currently used today.

btw, i like davids undertray. if you really want to see how well it works, glue on some yarn ~3" long, below the license plate area & follow behind in another car & video tape. go around a few corners to & you'll see how the airflow changes relative to ride heoght.

or you can apply some liquid car wax to the underwing on both sides., go for a drive & see where the wax moves to. 1 thing nice about the wax, it dries, vs using a heavy weight oil that will still run once the car has stopped.

 

The liquid car wax is a great idea. The light oil I was told works best if you can drive somewhere dusty. I might put some liquid wax on the bottom on the trip to the track Saturday morning. Thanks for the compliment on the undertray.

 

you can buy pressure paints from places like mcmaster-carr

cb

and temp paints for brakes, if you care.

cb

 

Very interesting CBRD, I googled pressure paint, very interesting. I also looked into MSC and could not find it........crap. I just noticed you said McMaster..

 

CBRD, would you mind sending me a link to where that paint can be bought. I searched McMaster too and I can't seem to find it.

Thank you.

 

Evolutionary or I can help you with that.

The guy who makes the under tray and rear wing. I worked with on the FSAE car and we have been making carbon fiber parts with for a long time.

There is two sides of carbon with a 2 part epoxy. The parts are vacuum bagged for weight savings and strength. The core is a closed cell foam that will not allow epoxy past the surface. The mounting points are hard points put into the layup.

The rear wing is made different.