Rear spoilers

[SuperBuickGuy]

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.):




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.

Resurrect this thread, a bit, I bought Competition Car Aerodynamics, A practical handbook by Simon McBeath (2nd edition)... I can only read one section at a time so it will be awhile before it's done because it has a lot of information - with that said - thank you for the recommendation, it starts with the basics (which had a couple things I knew intuitively, but wasn't 100% correct in my thinking), then quickly builds to stuff that takes some time to digest... in short, I'd recommend this book too

 

[phantomjock]

Glad you like the book!
Katz is a good one too. But at one chapter at a time - finish Simon McBeath's first!

Here are a couple of areas to look at on the Tuft Test above - interesting - eh?

Cheers - Jim

 

[BrianE]

New to this thread, so back to the beginning. The Chrysler winged cars, wing was that tall so the trunk would open,it was also very effective. There were braces installed so at high speeds the downforce would not collapse the quarter panels.

 

[69427]

New to this thread, so back to the beginning. The Chrysler winged cars, wing was that tall so the trunk would open,it was also very effective. There were braces installed so at high speeds the downforce would not collapse the quarter panels.

You are correct. :thumbs:

Depending on which source you believe, the downforce numbers I've seen for those cars (Dodge Daytona and Plymouth Superbird) were 350 to 500 pounds. Not bad for a wing with such modest dimensions.

 

[SuperBuickGuy]

Glad you like the book!
Katz is a good one too. But at one chapter at a time - finish Simon McBeath's first!

Here are a couple of areas to look at on the Tuft Test above - interesting - eh?

Cheers - Jim

it'd look Bubba, but the best place for the spoiler would be on the targa panel. From reading the book, it wouldn't even necessarily need to be a spoiler, remove the rear window and put a lip on the back edge (with the t-tops removed, obviously) - might even satisfy the purists if it were made (the lip) removeable

 

[phantomjock]

Awww. Now look what you made me do - find a C3 "notch back" with a Wing:


Note the strakes on the T-Tops. :thumbs:
More pics and Specs over here:
http://www.race-cars.com/carsales/chevy/1166804889/1166804889ss.htm


Cheers - Jim

 

[SuperBuickGuy]

Awww. Now look what you made me do - find a C3 "notch back" with a Wing:


Note the strakes on the T-Tops. :thumbs:
More pics and Specs over here:
http://www.race-cars.com/carsales/chevy/1166804889/1166804889ss.htm


Cheers - Jim

Corvette notch.... I like it

I admit it - that's the first time I've seen strakes on a t-top Corvette

I also like how he used the front bumper bolt holes to mount the skirt on the front - looks like it'd easily be reversible....

Notice how he took the expensive wheels off the Corvette (the race picture) and put on steelies for the sale?
Still, I like the car, not $47,000 like, but like nonetheless

 

[Belgian1979vette]

Anyone know how much an original style Pacecar front -and rear spoiler are worth in terms of downforce.

I know that for the front it helps airflow for cooling the engine a lot, don't know about down force however.

 

[SuperBuickGuy]

Anyone know how much an original style Pacecar front -and rear spoiler are worth in terms of downforce.

I know that for the front it helps airflow for cooling the engine a lot, don't know about down force however.

Interesting coincidence. I'm reading the aerodynamic book recommended above; and I'm to that chapter which talks about that.... the answer is yes, by removing the air from under the car (creates low air pressure under the car, thereby giving it more force down - or probably more correct way of saying, less force resisting the downward pull of gravity)... unfortunately, I'm not to the end of the chapter yet, so I don't know how it ends (or how much it provides)

 

[Belgian1979vette]

Anyone know how much an original style Pacecar front -and rear spoiler are worth in terms of downforce.

I know that for the front it helps airflow for cooling the engine a lot, don't know about down force however.

Interesting coincidence. I'm reading the aerodynamic book recommended above; and I'm to that chapter which talks about that.... the answer is yes, by removing the air from under the car (creates low air pressure under the car, thereby giving it more force down - or probably more correct way of saying, less force resisting the downward pull of gravity)... unfortunately, I'm not to the end of the chapter yet, so I don't know how it ends (or how much it provides)

Not my field of expertise, but isn't it so that when the air below is less, that the air above gets to exert more downward force on the vehicle in question ?

 

[SuperBuickGuy]

Anyone know how much an original style Pacecar front -and rear spoiler are worth in terms of downforce.

I know that for the front it helps airflow for cooling the engine a lot, don't know about down force however.

Interesting coincidence. I'm reading the aerodynamic book recommended above; and I'm to that chapter which talks about that.... the answer is yes, by removing the air from under the car (creates low air pressure under the car, thereby giving it more force down - or probably more correct way of saying, less force resisting the downward pull of gravity)... unfortunately, I'm not to the end of the chapter yet, so I don't know how it ends (or how much it provides)

Not my field of expertise, but isn't it so that when the air below is less, that the air above gets to exert more downward force on the vehicle in question ?

mine either (which is why I said "read in a book" numerous times).... but I suppose, technically speaking, the air squishes better under the car when there's less of it

(I can just hear the true aero experts admiring my technical expertise and quick grasp of the complexities) :rofl:

 

[phantomjock]

So we are all finding ways to occupy our time, Ive been on the SR getting it ready for a few final races before passing it on to another person.

Meanwhile, I've been revisiting some interesting Aero books I've added to my collection. Turns out I have 2 of these [AIAA SECOND SYMPOSIUM AERODYNAMICS AND RACING CARS, May 1974]

Some real good info there and I'll offer one of them for sale. But meanwhile I'll address this slide:



One of the papers addressed this very problem! Title - TRAPPED VORTEX FLOW CONTROL FOR AUTOMOBILES. I've lifted 6 images and posted in the Downloads section for those interested.

At about 100 mph, you'd need around 4000 cfm fan for the suction - but should be doable with 12 volts. I can scan the maths if desired too.


It will be in DOWNLOADS once approved (Chassis and Suspension - Title; C3 Rear Deck Aero.)


Cheers - Jim

 

[phantomjock]

I'll add 2 images from the pdf as a teaser. The first shows the "baseline" of flow which is not too unlike the tuft test shown previously.



The second shows the flow "modified" using the techniques presented in the pdf.


You'll note the flow aft of the car is very streamlined, and an added bonus is the air over the rear deck provides much needed downforce. No spoiler, no wing. Just some suction.

If anyone is interested in the book - let me know via pm.

Cheers - Jim

 

[vette427sbc]

Jim- very interesting method, especially applied specifically to our cars!

Does the book go into more detail than what you posted in the downloads section?

I also wonder at what speeds that is valid until?

Thanks for posting!

 

[phantomjock]

Chris -

They used a model in the tunnel (typical approach), and they tested the effort at 100 feet per second. Just over 68 mph. So, the effectiveness is a good speed range. The article in the book includes the calculations for amount of suction needed and I ran it to about 100 mph to estimate the 4000 cfm requirement. Go faster, might need more suck. Once the vortex is "trapped" it would need to be sustained.

The book (if interested) includes 18 similar topics; land speed design, Can-AM cars and aero, effect of aero downforce on handling, coast-down testing discussion, some high speed motorcycles an even one article on drag reduction on trucks! I'll load the TOC and cover in the classifieds in a bit.

Unfortunately, the author of the article passed in 2012, and would have been a fantastically interesting man to spend some time with. https://www.legacy.com/obituaries/atlanta/obituary.aspx?n=joseph-cornish&pid=155461905

No, it wasn't CCP-Virus!

Cheers - Jim

 

[phantomjock]

This seemed like the right place to add this.




I was looking at wings on cars, following SBG's addition and did a "dive. Came up with some interesting notes to pass along. Most notable (stock car - not Can-Am/F-1) was theh Daytona Dodge and Super-Bird series wing cars.

The first problem area was the Charger’s recessed grill, which was creating a tremendous amount of drag and lift at the front end. The other problem was the rear window area, which appeared from the side to be an aerodynamically efficient fastback design, but was in fact two hollow C-pillars flowing to the back with a near-vertical back window nested in the center.
Aero Warrior—1969 Dodge Charger Daytona https://vintageracecar.com/aero-warrior-1969-dodge-charger-daytona/4/

Sound like a '68-78 C3?

...John Pointer began sketching cures for the aerodynamic deficiencies. These cures included a narrowed-and-sealed grill insert to deflect air around the car’s nose, as well as a sheet metal cover over the C-pillars to create a true fastback design at the rear. These changes were tested at the Wichita State University wind tunnel and proved to be a significant improvement over the previous design.

So who was this guy, John Pointer?

The man who first conceived of the wing—and the nosecone as well—was John Pointer. Pointer was a rocket scientist who came over from Chrysler's missile division and was asked to make the 1968 Dodge Charger "go faster."

When told he could do anything he wanted, he drew a crude outline of a car and plastered a nosecone on the front. Over the decklid, he placed a giant wing—the top of which was roughly at the roofline of the car.- Steve Lehto Road & Track Jun 2016

So given rules set by the several racing associations, the size and height of a rear wing may be limited. Other modifications could "fit" under some classes. For a "stock 68-78 C3, a suitible rear "filler could be fabricated (fiberglass and lexan) to fasten and potentially get similar reductions in drag as shown here:



The above image was part of a paper presented at the Automotive Engineering Congress, Detroit, Mich., January 12-16, 1970.. WHy didn't GM/CHevy incorporate this information into the C3? Most likely because of they're "Not in Racing" policy? Doesn't mean we cant "VetteMod" today!

Cheers - Jim​