I enjoyed this sentence.

also, teh Z was designed with a pretty flat bottom. most components are tucked above the floorboard level.

 

That's the part I don't understand There's got to be a reason why those "exotics" all have a floor to go with the diffuser.

Same case on a race car; they all have floors.

edit: editted the previous post for errrr english brainfart

 

it's just the most efficient... but it's also expensive, illogical for a road car and probably impossible to package the car with it on the cheap.

you can have a diffuser at the front and rear work independently of each other.

just like the stock diffuser (yes we have a stock front diffuser) has the concave area, that is where the downforce is created. as you all discussed already.

there will still be airflow over the rear that can be used to create downforce by a diffuser, it just will not be as optimal as perfectly straight airflow.

 

A lot of it wasn't too hard to understand... at least the math part. That said, the tire/suspension chapters had me rereading them for quite a while. Hell even SAE said it wasn't the most complicated book in the world.

You'll want a flat bottom and a diffuser without too steep an exit angle, otherwise seperation will occur.

 

what do they mention in that book about maximum ride height before loss of any aero benefits to lips and diffusers? Isn't it a few inches?

 

In Indy Lights back in the late 90s, it was 20 thou.

I'd imagine flat bottomed cars being quite tricky to drive due to the increased pitch sensitivity.

 

The idea is that if you lower your car too low, the boundary layer underneath teh car will essentially block air from flowing underneath it, and you will pretty much lose all downforce (V = 0). That is why you see stepped underbodies in F1 these days, and this was also recently introduced into sportscars (FIA GT, LMS, etc) - to prevent too low of a car. This is also taken into account once it starts raining.

I would think that the splitter design on the Nismo 350Z (raised middle portion) would combat pitch sensitivity, as well as provide an inlet to the underbody.

 

that is not what I meant.

they say splitters, underbody trays and diffusers loose a large % of thier effect and effeciency at over a certain maximum height. I forgot what the quoted distance is.

 

I didn't get too far in that book, but there wasn't too much in the aero department. But I thought you'd want the car low to the point that it isn't bottoming out or if the boundary layer started messing with the car. Not for ultimate downforce figures but to keep the car predictable at the limit.

 

i thought it wasn't more so height (although that is important due to airflow speed) it was the angle due to flow separation.

for rear it was like the diffuser's effectiveness decreases as the angle of attack increases over 6 degrees.. (which is what the stock muffler is at)

there's supposedly this really good SAE journal/whitepaper written by a Japanese student/researcher on car aerodynamics and their work, but i could never find it.. i tried poking around teh interwebs ,but never found out. i think i was on http://www.eng-tips.com/ when i first heard about it.

 

God I love it when I stumble onto these super informitive threads, you guys are answering every question that I've been searching for. Reminds me of the RX-7 forums! Keep it up.

On a side note, Chebosto what diffusor set up are you running, front/rear/side/wing? IIRC you track test and alter your set up frequently.

 

Ride height shouldn't really affect splitter effectiveness; after all, a splitter only relies on stagnant pressure across where it is attached to. As a means of providing an underbody inlet, again height would be adjusted according to meeting regulations, and making sure that the underbody isn't choking.

As for angle of attack for the diffuser (alpha), usually you would want to keep it small such that the flow doesn't detach.

http://www.mulsannescorner.com/techarticle1.htm

http://www.mulsannescorner.com/benzCLR1.html

These articles are interesting...

 

+1. Thanks guys.

 

there is a really interesting picture in the 6th issue of the japanese Z magazine. (i got mine off Amazon.co.jp)

there was a CFD model of the new Nismo edition Z; color coded for high (red) and low (blue) pressure zones. they actually had a shot of the underside of the car.

in the stock form, there was naturally high pressure right at the front tire, but deep(er) blue zones immediately following the end of the front undertray (which acts as a front diffuser) and a deep blue zone immediately following the stock exhaust. what i thought was interesting was that there were blue zones (although not as dark) where the front underside framing/catalyst converters sat, and turning green (slightly higher pressure) right before the rear sub frame. true this car isnt completly flat underbody like a ferrari, but it's pretty good, and i do think you would be able to feel the effects of underbody enhancements at high speeds. that nismo kit really looks good on a design standpoint.

i'll try to scan that image when i get home...

 

so if you have a diffuser, would "speed holes" still have any benefit in realeasing any pressure from some of the air that gets stuck between the diffuser and the underside of the car? or would speed holes disturb the air flow from the diffusers?

 

You should check if air is actually getting trapped in there first. Like that one on the revolvfe or something. I can't see a significant amount of air going in there in the first place.

 

the scanned image of the under and over airflow analysis Nismo did on the Nismo Ed Z.

simulated or actual windtunnel tests, i gotta get a translator. but here it is:

i'm assuming red is high pressure, since the front of the wheel and nose areas are red.

 

^ interesting...

 

here is a cool article: http://www.clarkson.edu/honors/resea...an-Michael.doc

there is a term called 'critical ride height', that I see people referencing about aero efficiency at ride heights. Just like you can be too low from the CRH, when you increase the ride height over the CRH it does the same, and lowers the effect the undertrays have on the downforce produced.

 

too much air flowing under the car is undesirable. i.e. increase ride height or increased pitch angle of the leading edge. I am only considering static arguments and not related to suspension compression or squash.

Really, there is a large wealth of information on how ride height is a hugely important part of the downforce equation. They say that aero trays on most road cars are wholly ineffective because our static ride heights are far to tall. on a car like Chestons, which is basically a race car ride height from the pictures on this site!, they will be very effective.

how high do you think the average Z's front bumper is off the ground? 35mm? 50mm?