greeenteeee

okay more corrugated plastic used.

outline of what i have. up front only 18x24" piece is corrugated plastic, i've a cutout for the front jack point and a door/flap for the oil drain bolt. used both successfully this wknd without having to remove it.

rear initially was 24x36" down the middle, added 15x36" sheets on each side, overlapping ~1" above the center panel, with cut outs for the tire. I could have gone closer to the wheel but oh well.

@#$%@#$%@#$%@#$%23452435

this is what i had initially. i have to remove the diffuser to jack up the car.
but i can jack up the diff as is.



crawling around under there I couldn't help but think that gap can't be good.



came up with this. sides are added 15x36" sheets, cut out to 11" wide (instead of 15") for the 22" span of the tire (not the complete OD of tire because it's not in line with the largest OD of the tire).



have not done any drilling into the chassis yet, was avoiding doing so as this will inevitably be changed somehow in the future, maybe complete it with a mid-chassis belly pan, but it's not too high on my list. last i checked miata challenge doesn't assign points to a mid-body undertray anyway.

@#$%@#$%@#$%@#$%@#

so hopefully as the photos show, i'm basically trying to seal up everything after the bottom floor in the middle of the car.

here's what it looks like under the pax door looking back:



only concern with the current iteration is the plastic between the pinch and the frame rail. it's not mounted in anyway, and is just hanging there. the leading edge can catch air = bad. without doing rivets, i'm considering like RTV silicone to make it stick to the frame, and/or maybe plasti-dip on top of it so it seals off the holes of the corrugated plastic and holds it up. this way it is temporary.

any suggestions welcome and would be highly appreciated.

here's a complete picture with drawings of what i added to get a better idea.

ChrisGriffin

Please someone put their gopro under the car with all that plastic and zipties. Then post. I need to laugh today.

greeenteeee

It's not a go pro, but check the previous page. Then tell me what's so funny so I can make it even funnier or what not. Ideally, I'd want you to tell me what I'm doing wrong if anything, or what I'm doing right.

edit here's another video for you.

ChrisGriffin

Alright in a bit of insanity I will give you some info. I appreciate your desire to learn. There is noway that your plastic and zipties will hold up to the downforce a flat floor can produce. The more you lower the car and as speed increases those panels will fail. Think of the force associated with pulling the car down to the road surface, that is what the flat floor has to withstand. Also have you ever seen someones undertray flapping on the highway? Those panel will make good template material but I would convert to something more rigid. And if you are going to run in a class with minimum weight I would put your ballast in those panels.

vehicular

iTrader: (3)

In what possible interaction between a flat panel and air flowing parallel to said panel could there be force produced in any direction other than friction between the air and the panel?

Flat floors produce absolutely no downforce on their own. They reduce drag, and provide clean air to the diffuser.

nitrodann

Shut up chris. Dont pretend you know heaps of secret info and then say stupid things.

Dann

UrbanSoot

iTrader: (24)

Equalized pressure difference, 'nuff said.

pusha

iTrader: (5)

subbed for future bro ownage

ChrisGriffin

http://scarbsf1.wordpress.com/2011/0...ics-explained/

240_to_miata

iTrader: (2)

This.

Seefo

iTrader: (5)

"A purely flat floor would probably produce lift rather downforce, so the rules have allowed a diffuser to be fitted to the rear of the underbody since 1983. "

vehicular

iTrader: (3)

Hyper lolz.

Seefo

iTrader: (5)

yea, I am not really sure what this guys is talking about. I was a little surprised with the first message, but I didn't respond in-case I was having a "bad English comprehension" day.

Anyways, Party kitteh for everyone!!

I said I would post some undertray info about 3 weeks ago and have been lazy. I hope to finish up the sides this weekend and I will post it all then.

mx5autoxer

iTrader: (1)

I'm pretty sure that downforce created by an undertray pushes down on the top of the car. Think about an airplane wing. The bottom side of the wing recieves the force to lift the aircraft, not the inside of the top surface.

vehicular

iTrader: (3)

Yes, do think about an airplane wing. It is shaped like a car.





As air flows over the top of the car, it has to speed up in order to catch up with the air travelling under the car. This increase in velocity causes a drop in pressure over the car (thanks ideal gas law!), which subsequently causes lift. As such, the flat floor on it's own provides no downforce. It reduces drag by smoothing airflow, and subsequently provides clean air to the diffuser, which DOES make downforce.

18psi

iTrader: (76)

1st thing I popped into my head too

Savington

iTrader: (31)

This is completely false. Flatbottoms work the same as splitters - by eliminating the myriad of sharp edges and protrusions under the car, they accelerate the airflow and reduce the pressure under the car, which results in decreased lift/increased downforce.

The interaction between air and a flat panel is not exactly hard to prove - hold the short end of a piece of printer paper under your lower lip, pinch it at the two edges, and then blow out across the paper. If you blow hard enough, the paper will lift up and extend straight out, because you've increased the velocity on top of the paper enough to create a pressure differential between the top of the paper and the bottom (aka lift). It's that same interaction, except with way more air and way more surface area that makes a flatbottom produce downforce.

vehicular

iTrader: (3)

That's an inappropriate analogy. There's no associated air movement on the underside of the paper. When you blow over the paper held under your lip a venturi effect causes air to flow over the underside of the paper causing the lift.

Holding your hand out a car window would be a more appropriate illustration. If you give it angle of attack and will push itself around in your hand, but as long as it stays parallel with airflow there won't be any appreciable lift or downforce.

ChrisGriffin

Dont forget about ground-effect in this discussion.

Faeflora

iTrader: (2)

Do you mean gravity?