Rear spoilers

Way out of my depth.

A I recall, race car suspension travel had to be changed to take advantage of the improved aeros. Too much travel would upset the wings "angle of attack" I believe that is something close to the correct term.
Reducing suspension travel on my car is something I do not want to do.
I keep hoping that proper spindles will magically appear soon!
Many people have run 17-18 wheels to get a stance that hopefully improves stability.






R
 
turtlevette said:
downforce.jpg


here's a graph i found. I would have thought the slope would have been greater. Its a squared function..............
Click to expand...

Welcome to the real world, Turd. We've been waiting for you.
 
Apples and oranges, huh?
On a road trip today I saw dozens of eighteen wheelers with multiple aero devices. Overcab wind deflectors, tractor side skirts, and even skirts on the trailers. Does anyone here disagree that these trucks are significantly slower than the speeds several of us push our Corvettes on the track? Perhaps another comparison: A Corvette weighs what (compared to an eighteen wheeler)? How wide are Corvette tires (compared to an 18 wheeler's tires)? How much horsepower does a Z06, ZR1, or my ZL1 have (compared to an 18 wheeler)?

And these comparisons mean what? The answer: Absolutely nothing. Air doesn't give a rat's ass how much horsepower a vehicle has. It also doesn't care how much the vehicle weighs or how much tire is on the vehicle.

Air only cares about coefficient of drag (or lift), frontal (or airfoil) area, and velocity.

Apples. Oranges. Lemons.[/QUOTE]

I see so what your saying is that great big wing on the roof of a winged sprint car is there to make the sprinter more aerodynamic but the side skirts on a semi trailer are there for downforce? I can`t wait to see your car with it`s World of Outlaws hydraulic roof wing, and please let us know how much it reduces your lap times...and when you win your first race in the Corvette...[/QUOTE]

Damn, Howard, do I gotta explain everything at an eighth grade level to you too?

Let's try it again. I was using a few examples of vehicles with aero add-ons to show that a vehicle does not have to be over 150 mph to feel the effects of the air. Eighteen wheelers at 65 mph gain fuel efficiency by using aero mods to reduce drag. (Is that clear?) Winged sprint cars, when running on quarter mile tracks probably peak out at 80 or 85 miles an hour. Plenty of aero downforce at those lowly speeds. (True?)

My point from the start has been that it is pure nonsense to claim that a vehicle (or wing) is immune to aero drag or lift until it is well over a hundred miles an hour. I've piloted airplanes that will leave the ground well below 100 miles per hour. For gosh sakes, look at a damn Prius. Does that thing look like a brick, or something that might have spent a moment or two in a wind tunnel?

Aero effects (drag and lift) occur at all speeds and affect all vehicles (even that silver Corvette you disparaged). What part of this concept are you still unclear about?
 
I think WC fields had you in mind when he said this,
"If you can`t dazzle them with your brilliance baffle them with your bullshit"
 
69427 said:
My point from the start has been that it is pure nonsense to claim that a vehicle (or wing) is immune to aero drag or lift until it is well over a hundred miles an hour. I've piloted airplanes that will leave the ground well below 100 miles per hour.
Click to expand...

just hold your hand out the window at 70mph and voila: there's the answer.....
 
phantomjock said:
Testing is always useful.
Gene has done some tuft testing as I recall, and another member was working testing on velocity change through a radiator.

Another approach; base a design on sound theory, set out a hypothesis, and then do some experimentation. Analyze results and repeat as necessary. (I'm sure someone can Google that series of steps and point out a few missed steps - BFD, you'll get the idea.)

If you are interested in some theory, I'll offer the following invaluable texts for low speed aerodynamics, theory and application - depending on the text:
Ing S.F. Hoerner - Fluid Dynamic Drag, and the companion book Fluid Dynamic Lift. Abbot and Doenhoff, Theory of Wing Sections; Geoffrey Howard, Automobile Aerodynamics; a translated Japanese text published by Car Styling, Automotive Aerodynamics, SAE Papers - Vehicle Aerodynamics (a collection of papers), New Directions in Race Car Aerodynamics: Designing for Speed by Joseph Katz, and Simon MacBeath, Competition Car Downforce: A Practical Handbook. These are all part of my growing Low Speed/Aero Library. I'm going to post a section from Simon MacBeath's Competition Car Downforce in the downloads - for those interested. It's a nice piece and useful for some of what you're looking for - if I read and understand your stated needs correctly.
Hopefully you'll find it interesting. It is a pdf and requires TT or BBShark to upload - so it will be a bit. Meanwhile, I offer a few jpgs of the appendix on WINGS (the correct name is WINGS, after all - spoilers are there to KILL lift! -- these WINGS just generate lift DOWN.):


thum_12695091ab92eb347.jpgthum_12695091aba107d25.jpgthum_12695091abb0dc5a4.jpgthum_12695091abbd9e0dd.jpgthum_12695091abcc0d3a2.jpg

Another approach you see more these days is the Cellular Wing -- witness the posted A-Mod Autocross/Hillclimb car (which is so cool I want to build one next.) I did MS work using Cellular Wing Theory it and a presentation at AIAA regionals - back in the very early 70s. It was also a key to our Uni study for a Man Powered Aircraft. No, we didn't build it - but would have been a player! McCreedy had the funds - we were poor students - and could only afford to build a HG instead - 50 bucks - and it flew.


Hope you enjoy.

Cheers - Jim
Class adjourned.
Click to expand...

I have either the 1st or 2nd of those books - and now a friend has it and has been working through it.

and I think you just answered one of my questions "why not simply slap a later 80 up spoiler on the back?" let's see if I'm getting this, it wouldn't work because the airflow prior to the flap hasn't been (I know this is the wrong word, but don't know the right one) conditioned prior to hitting the flap to provide downforce... on an 80 up vette the window would act as the foil surface prior to the flap....
 
LOL! I like you choice of words there - "Properly Conditioned!" It's added to my vocabulary - very useful - thanks.

The Gurney Flap is another approach and it takes advantage of just that. WRT the rear wings of the 78 Pace Car and the 80s -up lip, there is some prior conditioning as the fast back allows the flow to be a bit more uniform than a notch back. I've got a few pages on the Gurney flap I'll drop in later.
Cheers - Jim
BTW - if you have any of the Sig Hoerner books - they are GOLD - try and find one for less than a couple of hundred bucks. And a great collection to just browse through.

Cheers - Jim
 




The wing is made for Porsche 911 GT-2, it gives reasonable downforce.

The suspension consists of a complete set from VB&P with bilstein shocks extremes at the rear. Dual mount rear spring, no rear sway bar!

Jeep steering Box.

12Bolt Internals 4,11:1 and 4"Halfshafts

Brakes are Wilwood W6A Radial mount with 14"x1,25" Gt rotors at all four corners. There is also Wilwood setup for the Balancebar and Cluch.

Transmission is Autogear M22X with Tilton Magnesium Bellhousing and TIlton tripple plate 7.25" hydraulic cluch.

358 Engine Consist of Rodeck Aluminum Block 4,130 bore , Bryant crank 3,34 stroke, H-Beam rods, 13,5:1 Je pistons, GM 18 degree 364 heads Ti valves, Comp Special Grind 305 311 Duration@ 0.020 and 0.732 0,692 lift With Jesel 1,85 175 Rockers, Verdi 4 stage drysump and jesel beltdrive. 550 wheel horsepower on Mustang MD 1100 Chassis Dyno, 500 lb/ft on flywheel in engine dyno.

In my last race i was a tad quicker than a 996 GT3 Super Cup on Michelin Slicks. I was on Hoosier P-Metric.



This what the owner of the grey car posted years ago.
 
My only effort EVER at any yarn test was done due to a conversation concerning my open BB scoop on my '72 and the lack of a hood gasket in the rear, so I taped a few pieces of yarn over the back/rear opening which is several inches forward of the rear hood edge......and went for a drive up to 100 mph, no significant yard movement....not sucking into the openings, and certainly not blowing out indicating LIFT from under the hood,

now that hood WILL lift super quickly off the car at about 30 mph, and please don't ask how I know this......:suicide: all the up force is forward of the radiator support in that triangle, just like all that air pushing through the radiator, it's being compressed in front, which necessarily created lift in that area.....if anyone curious, go to my sites below, where a couple shot of the front end are shown, an you note the whole front end is opened up for breathing.....I noted the removal of front tag crap from up north, greatly aided the freeway summer cooling here in 130f road temp FLORIDA.....

:lol:
 
Critique this rear.
My hypothesis is it doesn't work at all
vemp_0603_07_z+black_1969_corvette_coupe+rear_view.jpg

Here's my amateur view:
the spoiler is mounted too low to be effective. Where it's at the air would be tumbling off the rear window and play all sorts of havoc with clean air flow

the deck spoiler is for nothing but show, and would create huge turbulence behind the car

there's no belly pan or defusers

the mirrors are useless (okay, not spoiler related but curious if you could see around the widebody kit)


That said, I do like the look of that rear profile - reminds me of the Shelby Daytona coupes....
 
It is really, really PURDY!
Seriously - it looks nice.

The wing does appear low - as you've commented. But it would be coupled with the rear oversized Gurney-style "flap," and yes a diffuser would - REALLY benefit here too. So, there is some flow change and appears to be in the correct direction for increasing Downforce.

Rear turbulence is not necessarily a BAD Thing. You can reduce overall Drag - with a bit of that - note the KAMM-effect:
If a body is not properly conditioning flow on exit - cut it off and end the skin friction and Boundary build up and pay the penalty elsewhere. (my version)​

Some folks can't get over "Mud-Flap" flares - but I'm pretty sure they would be useful for flow considerations as well. - For BOTH front and rear -- at least that's where I'm heading on my mods.

Any more pics or a reference for this car? It would be nice to see the front end treatments too.

Cheers - Jim
 
Custom Front End?

Anyone know about the exotic front end?
Except for the wing, that is almost perfect!

The tucked in rear w/spoiler is nice, the stick out behind is
not.

Since my 74 body is very rough. It might be easier in the long run to graft on some new custom glass? Any thoughts on this?

That big plastic spoiler on the 76 might do some good, if it was doubled?

Since I don't have a wind tunnel handy, coast down testing and yarn action is about all we can do. Hopefully someone, somewhere is curious and has too much time on their hands.

R
 
rtj said:
SuperBuickGuy said:
Yep... not my tastes, but boy did this owner do a lot of work
http://www.vetteweb.com/features/vemp_0603_black_1969_corvette_coupe/photo_01.html
Click to expand...

Super BG,

Check out the APR gallery pages. The lotus on pg 1 is somewhat C3 like. Also, nearly every install has the wing at roof level or slightly below. They may have tech recommendations, I'll check.

If you are real serious make you car a hardtop convertible.
Click to expand...

I did briefly consider filling the space with plexiglass (or whatever), but decided that would be the point that I go to a Miata :wink:
 
phantomjock said:
Back to the issue at hand...
What about a high mounted rear foil on a C3?
I offer the following:
thum_1269509176b22d479.jpg

This image was lifted from a VetteWeb article on 1980s Kevlar bodys for Greg Picket. This particular image was identified as being one of, "A wide variety of "aero" devices were evaluated in order to determine the optimum shape for the 1980 race car. Courtesy of Dr. Kevin Cooper, NRC."

It appears not to be fastback (mirrors don't look right, not a 78 escutchion - so maybe a 76?) - so if it is a 'notch-back - it answers the original postings.
Unfortunately I find no details (lift/drag/downforce/velocity/etc)- but what you see. Kevin Cooper has done a lot of research in aero devices, he is an award winner at SAE, and has worked on "near surface (ground) flow." Most recent work appears to be in the area of rear diffusers.

Nice splitter too.

Cheers - Jim
Click to expand...

My wife used to work with Kevin Cooper, wonder if he's still around the nrc

Sent from my Transformer Prime TF201 using Tapatalk 2
 
Ricisan said:
SBG: Someone on CF has done some yarn testing. I believe it was to do some Mythbuster type testing on a hood/windshield. They were trying to prove or dis the low pressure area at the base of the windshield being of benifit to performance.

The evidence was interesting, but by no means conclusive.

If your testing can really prove the wing is significantly better for downforce w/o big increase in cda, I'm happy to consider it.
I'm waiting for George to jump in.

R
Click to expand...

See my photo album, "Stringray." Page 2, starting toward the bottom and page 3.
Along with just general air flow patterns info, I was looking to prove the high pressure at the base of the windshield, why a back facing cowl scoop works so well for carb induction. And to verify the gills do extract air from the engine compartment, thus relieving under car turbulence & air pressure a bit. The pics won't help with wing or spoiler design, but they are interesting to study.
(Oh, and that's my friend Wes driving, not me. I was behind the camera.)
 
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very helpful
66481b8b2855b98.jpg

the low pressure behind the window and the rear spoiler are pretty amazing. I'll have to see what the airflow looks like with mine (75) since it's a different angle
 
Don't assume that airflow, pressures, turbulence, airfoil dynamics, etc are all so simple. Yarn tests vs. turbulence vs. magnahelic(?) guages vs. all the rest of it are only contributing factors. Which in the end, I have decided, don't really matter on a street car where .10 second lap time differences aren't critical.
Fun to play with, but of no real importance in the real world.
But fun to think about and play with, yes!
 
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