Just a thought.....is that the reason the Grand Sports have holes about the size of the tail lights accross the rear panel?

 

I just went back to look at that funny car and flapping tailights better. There is a blonde in a yellow top backing the funny car up. How did I miss that earlier. Yowsa!
Bee Jay

 

I'm looking at a pic of the LeMans car. It had a sheetmetal cowcatcher about 12" long w/60* from vert, boxed on the sides. More aero than downforce? Very close to the ground, There must not have been any dips?
The rear only had a small lip like 69, but it did have 2 slots in the rear near the exhausts. Which also came out the rear cover, not hanging below. I'm sure the car was very clean aero by the stndards of that day.
Quote:
"The 580 hp L88 routinely saw 212 on the Mulsanne"
CORVETTE
Fifty Years
Randy Leffingwell

 

if it is a latter C3, with a rear rubber bumper, couldn't 'louvers' (really nothing-more than 'slats') be cut into the area on either side of the license plate, below the tail-lights, above the exhaust outlets?

If you wanted to get real-serious, take .032" sheet-aluminum, form it to match the contours of that area, cut-out that piece of the fascia, and replicate the F/C tail-lights, hinged at the top:
is it possible the hinge could be located 'inside' the fascia, so that the hinge itself wouldn't be seen, with only the rivets (fascia-to-hinge/flap-to-hinge) visible?


I'm jes' sayin'.....

I don't know, but I believe they flap-open during the burnout procedure itself, but this could-be from the body-twisting, or from tire-shake:
the picture above shows the slicks still fairly-round, so I am guessing it is down-low, maybe 300', so it isn't above 200 MPH yet

 

Check out this article for some hard data of all models of Corvettes. http://www.corvettefever.com/techart...ing/index.html

For the rear under the bumper it needs a diffuser that is blended from around the differential that slopes to the bottom lip of the bumper.

BeeJay, I like your PC airdam undertray. That is pretty nice and a good start.

Taijutsu, what is your goal? Reduce lift or reduce drag? And further, reduced total drag, Cd or CdA? Also, you are using terms confusingly. Aero or aerodynamics has a definition but you seem to use it when you mean drag or perhaps efficiency, I'm not sure. Angle of attack is used for airfoils/wing sections but you are referring to the entire car(?), as in the rake? or something else?

Lowering the car as much as practical is a good start to reducing frontal area and therefore drag. It will also reduce lift by reducing the amount of air under the front of the car.

 

Burners: You found me out, I'm not an engineer. lol
I use aeros as a catch all term for aerodynamics. You are correct about my intentions. Angle of attack is for the airfoils and rake is the angle of the body. Got it.
Yes, I want better cda "I just learned that them" and less lift and less drag if such a thing is possible? I think I can have a little of both.
I'm guessing that a car lowered at both ends has better cda and a car that is raked has less lift? I would say that less drag is more important right now, not to say lift is unimportant.
Am I making any sense yet?

 

I thought stepping away from the technical details for a minute or two here might help bring a little focus onto the big picture for you, and viewers alike, and submit this offering to that end...

The tipping point between reducing lift (or increasing downforce) vs. drag being the higher priority depends very much on one's purposes. This is a tremendous consideration in road racing (on some circuits every bit as much, if not more, critical than damper settings), and it shouldn't take a rocket scientist to understand why I've run radically different wing settings on various courses. Road America vs. Lime Rock is as good a case in point as any; the former being a place where very much wing at all carrys just too much drag penalty on the long straights unless you've great gobs of HP; and the latter being a place where you pretty much want all the wing you can crank in shy of stalling them to stay stuck down in the turns.

With that in mind, FWIW, since we're not talking about a scale of literally tons of available adjustment coming from the kind of tweeks we can most readily adapt onto our sharks as compared to a winged formula car, IMCO for most of us I'd think improving the lift/downforce picture would almost always be the priority more worthy of pursuit (unless you're only in it for max mpg), as that's going to pay off in better stability and handling at speed; which, in turn, promotes higher confidence in a car, allowing one to more comfortably approach its true terminal velocity limits without fear of flight. (OMG, was that sentance long enough?)

There's obviously more to it than simply tacking on a front air dam (something I'd never recommend without balancing that with an appropriate rear spoiler), but the neat thing about working to reduce the amount of air going beneath the C3 body is that (to a point) such measures can serve to improve both lift/downforce and drag characteristics. Win/win! So, IMHO a good dam/splitter should probably be highly considered as a sound cornerstone from which to build better aeros, to use your term.

It can be taken as my testimony (whether you value it as being from an "expert" of sorts or not) that the difference between many a stock C3 with poor/no thought given to aero and those with a little well thought out and executed work can be substantial - even staggering - in true high speed sweepers (>100mph). Bottom line (finally, get on with it man): my take is that splitters, trays/pans, diffusers, vents and etc. are all well and good, but installing and properly securing/bracing a good dam & spoiler, lowering ride heights without going bonkers on rake, and improving the suspension (including stiffening) are prerequisites which one cannot afford to overlook in the matter of pursuing honest-to-goodness high speed performance.

That's my $.02 (maybe that's $.03), at no charge. Hope it's worth more to someone than any of you paid.

Now, here's a little inspiration for those of us who can't get enough of this kind of thing...




TSW


PS: Bee Jay, I don't guess I noticed the funny car in that pic of that rather nice looking woman in the yellow top until you pointed it out.

 

Web sites that cover the Open Road Races (Big Bend, Silver State, etc) should be good sources for pics of experiments.....

 

Heck, they should have produced this body style, it rocks, esp the rear fenders.


Who's looking at the rear facia of the car?

 

1.There is netting in the windows, so maybe it was a race car only design.
2. I hate to admit it, but I was. I'm such a nerd.
Bee Jay

 

R
Here's Greenwood ZL1

 

I've been trying to figure out some kind of rear diffuser that is functional with my rear exhaust. I have a picture of a nice one at home.

My Bud and I were at this year 2009 Monterey historic car races. Me working up a sweat and him showing off his car and checking out the ladies!

 

If I remember correctly Vanacor used to offer a fiberglass panel that filled in the area under the rear of the car - it had openings for the tailpipe to emerge and went all teh way back to the back of the rear wheel well openings.

 

 

I'm the good looking one, tall, dark, and handsome.
Bee Jay

 

SW: You put it all into a nice pkg even I can grasp. Of course there is the issue of balance if we change either spoiler,splitter, rake or wing.
Since I don't have the resources for testing, I think the PC kit might be the best way to get started. The problem is that the PC kit was designed for a glass back car that has same size tires. What about a 17/18 combo that has some rake? If the front is lowered 2" and the front tire is 1" smaller, that comes to 3" lower than the rear. That should get an effect, but how does it change things?
Would the extra downforce change the balance of the PC kit?
After seeing the 212mph LeMans brick, I'm thinking this:
Other than the PC kit, I want to take a look at my undercarrage to see what is hanging and flapping in the breeze. lol
Does anyone have a better idea?

R

 

Taijutsu, glad you thought that was helpful to some degree. Don't recall if you took part in it, but there's a fair amount of good aero chat in the old thread below which might provide you with still more insight into this. I'd suggest paying attention to those posts of Blue71vette, as he has a lot deeper background in this aerodynamics stuff than do I...

http://forums.corvetteforum.com/c3-t...ics-et-al.html

The main thought I have at the moment on rake is that of "diminishing returns". The higher the angle of attack (and larger any gaps from the body to the ground) the larger becomes the problem of keeping "new" higher pressure air from migrating in from the sides to "fill" any lower pressure area there may be underneath (hence the need for ground effects skirts rises); panning the belly to smooth out irregularities becoming a secondary concern in relation. Yes, this can also prove detrimental to achieving balance.




BTW, Bee Jay, the flat bottom ahead of the diffuser on the otherwise carbon-fiber Reynard in my avatar is of plywood (aka: "nature's composite material").

 

Plywood=Natures composite. I like it.
Bee Jay

 

I agree that TheSkunkWorks did a fine job of summing up many points. My further questions for Taijutsu are;
What is the operating speed range that you hope to realize improvements?
How radical of a configuration are you willing to go with? (big wings, extremely lowered, body mods, etc)
Are you looking for bolt-on solutions or will you build some of this yourself?

I also wanted to address your concern about the rake no the car blanking the front air dam. That would not be possible without a very large and possibly unobtainable rake angle. Additionally, reducing the front wheel size by running a 17" versus an 18" on the back will only lower the front by 1/2". Let me state a few things in point format.

Drag reduction
*Reduce Cd
-remove appendages the protrude into the air flow
-fix areas that cause turbulent flow such as the rough underside of the chassis or the wake at the rear of the car.
-minimize the amount of air flowing under the car

*Reduce frontal area
-trim the car for minimum rake
-lower the car

Lift reduction or adding downforce
*Increase downforce (this is usually were you trade off drag for downforce)
-increase rake angle
-airdam/splitter on front
-spoiler/wing and diffuser on rear (often times a small spoiler and proper diffuser can reduce drag)

I want to comment on the diffuser on the widebody Vette that Gkull posted. The back half of it has an angle that is way too steep. You should not exceed about 9 degrees otherwise you will get flow separation (which causes drag).

Honestly, if you are looking for a simple solution you have pretty much suggested it already. A PC front airdam with an 80-82 rear bumper cover gets you a long way there.

 

Burners: I remember seeing the Camero that Jim Sietlow, I think that's his name, built and coined the term Pro Touring. If I had to give it a name, that will do.
I want a solid car that is ment to drive fast, safe and comfortable.
Along w/that I have had the Silver State on my list of things to do for years. I am looking for bolt ons that can be massaged as needed.
I have eliminated the pop up headlights for the recessed and will get covers to streamline things soon. I have to find something I like first.
I am considering extra rubber skirting on the air dam if needed and extending the rear spoiler a little and lowering the front end.
That and the 17/18 wheels for a little rake is about all I can think of.
I want to keep my luggage rack by moving it forward about 6" so I can run a rear spoiler. My 74 has nothing.
Cleaning up the undercarrige is a good idea. I saw a few hoses hanging lower than they should.
As usual the magic bullet does not exist. Thank you for sharing your time and experience.

R