Internal Body Aerodynamics

[mfain]

Take a look at the aero on this Subaru.
http://www.thebaynet.com/articles/1220/pastrana-stunt-video-heats-up-the-internet.html
Active aero includes a spoiler on the rear wing that appears to be activated by the button on the top of the rear brake handle. He uses the spoiler (increased rear downforce) to control the car's pitch attitude during the long over-water jump. Equally impressive is Kirby Chambliss's ability to put the Red Bull aircraft in nearly 90 degrees of pitch - and probably 60+ degrees AOA - in less than 100' of altitude from initial takeoff. Both guys have great control of their respective machines. On another aero note, take a look at Brian Faessler's Mustang that won this years Ultimate Track Car Challenge at VIR, beating some exotic stuff like tube chassis Challengers with NASCAR motors and a couple of the Hendrick's Track Attack cars. It has a lexan strip horizontally across the hood just forward of the radiator "chimney" air outlets. The supports for the lexan strip also appear to be vortex generators that influence air that passes below the strip. Reminds me very much of the same type strips used on the old C-1 (1961-62) road race cars. The strip deflected the airflow over the hood so it did not hit the windshield at such a sharp angle - drag reduction. Also, on Faessler's car, the strip probably causes a low pressure area behind it and above the radiator chimney, probably increasing airflow through the radiator. He has a very small 17"X14"X2" radiator, but manages to cool a turbo, flat-crank, 600+ whp motor. He reached 181 mph at VIR! You can probably find info/videos regarding the car on the Grassroots Motorsports website. This stuff is a little more real world than a $10M, one-off supercar.

Pappy

 

[rtj]

Good stuff mfain. More links would be great too. I remember when every farmer had a bug deflector on their truck hood. The windshield would have a line showing where the air hit.

But, the high dollar cars show a lot of cutting edge stuff. Ideas that can be adapted.

Just trying to keep a discussion going when I see something that interests me. And, once you start watching a particular kind of video YouTube keeps offering them up.

It seems this site gets slower and slower. Which is too bad, there was always lots of good info before.

 

[COLE SWEAT]

Can any of this be applied to the c3?
Canards maybe? In front of the front wheels.

 

[rtj]

Wheel discs like on that Porsche a few pages back would likely work on grand sport rims.

Looks like cutting out the quarter panels is popular, but making it looks look good would take some effort.

Rear view cameras instead of mirrors.

Splitters work.

I’m seeing C7 widebody kits with the back of the flare cut out. It might be cosmetic, but some of these high end cars show that. So, could do that on a C3.

69427 has body panels under his car.

Yes, canards might even look good.

I guess it depends on how far you want to go.

Here is an example of the c7 widebody with the fender flares cut out. There is a better vid, just can’t find it.

[ame]https://www.youtube.com/watch?v=6-lDxscVgyo[/ame]


Am I going to do it ? Probably not, but I am interested in the topic.

 

[mfain]

Here are a couple of thoughts based on what others in the racing community are doing. A front splitter with diffuser tunnels produces good downforce. Air ducted into a narrow slot in the front fender well front lip creates a low pressure area outside of the front wheel (air curtain) for better brake cooling and promotes more laminar airflow down the side of the car. You see this on everything from late model Corvettes, Camaros, Vipers to pick-ups. Canards are pretty draggy, but if they are used to create a vortex outside of the front wheel they have the same brake cooling and airflow advantages as the "air curtain" described above. One of the best drag reducers is evacuating air from the front fender well. The Viper and Porsche GT2R have fender vents, and some like GSpeed with their C5 track car cut out the body panel behind the front tire. On a C-3, cleaning up the "parachute" at the back of the car with an effective, properly designed (not just cosmetic) diffuser helps a lot, as does a belly pan to clean up airflow under the car. Side skirts keep air from rolling under the car and causing lift. One of the best cooling/downforce aids is to route exhausted radiator air up through the hood (sometimes called a chimney) to reduce front drag and create better airflow up and around the cockpit. A lot of the design concepts rtj has been posting are all about managing airflow through the car, not just around it. In effect, they are reducing drag by reducing frontal cross-sectional area - creating areas where the air flows through the car without impacting blunt surfaces. They often use this "flow-through" air to interact with downforce devices or for cooling functions ala Formula 1.

Pappy

 

[phantomjock]

I'll second what Pappy said. And as I often do, add a few comments;
Splitter with Diffuser - these are awesome. By do that (as pappy described) you can effectively double the effectiveness of the splitter. So you can cut it back some - keep inside the "design box" constraints and garner heaps of DF.


Regarding air curtains - they are an easy build and can be effective in putting the flow where you want it. These two direct flow to the tunnels in the side pods of my SR. Garden-variety edging - literally. It bends easily enough and you can not worry about getting curb rash.

Hood and fender louvers - easy enough - and you can still get the fiberglass ones I bet from Ecklers (etc). But the best hood louvers I've seen are on Aaron's ride (Plastic-Fantastic). Add some smarts to them (and a motor) and - wow what an option. Work engine bay temps and flow through the hood.
Yes getting the radiator exhaust out the hood is the way to go. The Corvette team has demonstrated that a number of years - and with a setup like Arron has, could almost look stock when parked. Note - if you can do it to isolate the engine bay at the same time there would be a heap of drag saved - we've been over that before - but I need to repeat so I don't forget (getting to build again soon.)


Regarding side skirts. First there are a lot of "odd things" you could see/say about this car. But he's got the radiator exit on hood, side exits ahead of front wheels, cut out front fenders, side splitter, etc.


He has the side skirts figured out, I believe. Sharp corners tend to not let air wrap around and get back underneath the car. Also if you are not concerned with sanctioning rules, or ride height restrictions, you could add PVC verticals reaching to almost ground level. They will make the car ride like on rails when matched with a full belly pan. I ran that on the SR (illegal in my class - then pulled to race) and the difference was night and day. Wish I had the data to prove it - we bought the data boxes later that season.

Here is pic from a guy I spent some time chatting with about some interesting areo approaches (as he had done some tunnel testing full scale during his build). For his radiators:
he split them; left and right and exhausted outside in front of the tires. Got 2 biirds with one stone. He runs/ran in SPO and set several track records in NE. Car sometimes on RacingJunk - still for sale. (Not a Corvette--but may be a useful approach.)

Not a vette - but a few ideas here from my SR:

The hood exhaust the laydown radiator that is augmented with 2 fans. The louvers were pulled to baseline the DF without louvers, then with. The tire diffuser/spoiler/spats cover the wheels that are "exposed" when turning, but the aft wheel cut out is a do-able mod in a C3 (I think). I'll try a CAD look on a C3 this weekend - time permitting.

Mirrors will remain draggy until sanctioning bodies let cameras do that job.

ENOUGH! I hear you say.
I say, Cheers - Jim

 

[rtj]

Good stuff mfain, Phantomjock.

Another C3 option is the Greenwood trick, running a convertible hardtop. Just an hour or two with the sawzall if you have a hardtop.

The silver C3 from Europe posted at the beginning of the thread has some aero. Those photos were 10 years ago. I think racers started the technique of supporting the rear wing on the top/pressure surface more recently, it is possible that would benefit a c3 wing (same downforce less drag as the suction surface isn’t disturbed).

Found this looking for the silver C3.



Not for me, but it worked on the Dodge. Probably would work best on a big rear window car (78).

 

[rtj]

This shows the cutouts on the back of the flares better. Not sure if they did any testing, but there are other cars with that feature.

[ame]https://www.youtube.com/watch?v=Kaj4RUp5xPo[/ame]

 

[rtj]

[ame]https://www.youtube.com/watch?v=DdZIkFSz0iI[/ame]

YouTube picks these, this one was worth sharing.

 

[mfain]

These Time Attack Cars take things to the extreme, but if you look through the photos you will see examples of some of the things we have been discussing - waterfall hood openings, cut-outs behind the front and rear tires, extreme side skirts, etc.

https://www.bing.com/images/search?...13730D&selectedIndex=6&FORM=IRPRST&ajaxhist=0

In rtj's video above - smart guy! Interesting concern for "wheel wake".

 

[rtj]

That’s really cool, all the things we’ve discussed. Their track times are their “wind tunnel tests.”

I guess searching for time attack corvette or time attack c3 might yield some great information.

 

[69427]

I'll second what Pappy said. And as I often do, add a few comments;
...................

He has the side skirts figured out, I believe. Sharp corners tend to not let air wrap around and get back underneath the car. Also if you are not concerned with sanctioning rules, or ride height restrictions, you could add PVC verticals reaching to almost ground level. They will make the car ride like on rails when matched with a full belly pan. I ran that on the SR (illegal in my class - then pulled to race) and the difference was night and day. Wish I had the data to prove it - we bought the data boxes later that season.

..............
ENOUGH! I hear you say.
I say, Cheers - Jim

I've often wondered about the sharp edge shape there. I hope you're correct, as that's an easy piece/shape to fabricate. Years ago I replaced my short height rocker panels with longer (lower) pieces of Lexan (painted black), as I hated the side view with the transmission crossmember visible under the rockers. I like the looks of the rocker panels now, but I'm often scratching my head trying to figure out if I'm reducing external airflow from getting under the car, or if I'm trapping undercar air from getting out sideways. I've kicked around putting a scoop or two inboard of the rockers to scoop out undercar air and vent it out through some blacked out screens in the rocker panel. I'd like to do some actual differential pressure measurements in that area, but I haven't completely worked out how to get an accurate reading there given the moving/fast/turbulent air in those areas.

Just something for me to figure out over the winter.

 

[BBShark]

Wheel discs like on that Porsche a few pages back would likely work on grand sport rims.

Looks like cutting out the quarter panels is popular, but making it looks look good would take some effort.

Rear view cameras instead of mirrors.

Splitters work.

I’m seeing C7 widebody kits with the back of the flare cut out. It might be cosmetic, but some of these high end cars show that. So, could do that on a C3.

69427 has body panels under his car.

Yes, canards might even look good.

I guess it depends on how far you want to go.

Here is an example of the c7 widebody with the fender flares cut out. There is a better vid, just can’t find it.

Am I going to do it ? Probably not, but I am interested in the topic.

"Rear view cameras instead of mirrors". Great idea. The mirrors on a C3 are pretty useless.

I did a search to see if these exist. Unfortunately Google confuses this with a rear view mirror and there looks to be 100's of option. I think I'm seeing that the manufacturers want to do this but there are DOT requirements to have physical mirrors on the doors.

 

[rtj]

Wheel discs like on that Porsche a few pages back would likely work on grand sport rims.

Looks like cutting out the quarter panels is popular, but making it looks look good would take some effort.

Rear view cameras instead of mirrors. [/B.

"Rear view cameras instead of mirrors". Great idea. The mirrors on a C3 are pretty useless.

I did a search to see if these exist. Unfortunately Google confuses this with a rear view mirror and there looks to be 100's of option. I think I'm seeing that the manufacturers want to do this but there are DOT requirements to have physical mirrors on the doors.

I have a bunch old iPhones and was planning to use one for a speedometer. I think the gps still works, maybe not. But, you could also make the side mirror displays with them and a couple of Bluetooth cameras. Yes, I’m cheap.

But, camera display kits are probably available for reasonable prices.


I was looking for these and realized I had posted them before (they were in myimages).







I’ve always admired this car. He made a thread on DC a long time ago. Maybe if I step up my engine game a lot....

 

[phantomjock]

I've often wondered about the sharp edge shape there. I hope you're correct, as that's an easy piece/shape to fabricate.

Yes the edge does keep the flow from "wrapping around". Here you can see the CFD streamlines over the fenders "wrap" (also pushed by the windscreen) - but note they are "tripped by the A-Pillar. You's want to keep the low pressure under the car from filling and losing the downforce you'd generate. Ignore the text on the slide - recycling a pic for the streamlines...


I'm doing that on my car and will extend the side "box" to the rear fenders, and blend it in with an upward sweep. I want to send the flow over the top of the rear wheels through the fenders. [need to start building those soon] An advantage to that design is you can use the box for side pipes (cleaning up underneath for a belly pan) or from an aero perspective make the interior volume into its own tunnel. Small but every bit helps. And, it is at the mid-point on the body so helps keep the aero-balance.

There is a lot going on in that picture of a formula car - but you'll get the idea of using the side "pod" to aero advantage. If a "box" like on the purple car - fill and shape the interior like a tunnel/diffuser. Or build it lower in front so it has a natural rake. Remember to add the side skirts inside and out. Again, easy to build and replace -- like your rockers. Easy to test with a few pressure taps too.

Years ago I replaced my short height rocker panels with longer (lower) pieces of Lexan (painted black), as I hated the side view with the transmission cross-member visible under the rockers. I like the looks of the rocker panels now, but I'm often scratching my head trying to figure out if I'm reducing external airflow from getting under the car, or if I'm trapping undercar air from getting out sideways.

Yes - and Yes. Keeping the outside air from flowing in - and reducing the low pressure you're created (with the side skirts and chassis rake). Also, keeping the underneath flow in as long as possible to get the low pressure region back to the rear of the car to exit (hopefully) through a diffuser. As an example of the effort - you've seen semi-trailers with the side skirts. They hit up to 25% reduction in drag when used with the boat-tail plastic panels.

I've kicked around putting a scoop or two inboard of the rockers to scoop out undercar air and vent it out through some blacked out screens in the rocker panel. I'd like to do some actual differential pressure measurements in that area, but I haven't completely worked out how to get an accurate reading there given the moving/fast/turbulent air in those areas.

With some vanes to direct flow from aft of the wheel well into that region could be useful. The flow could then exit through the screens. Not likely to get much flow that is further aft under the body to move forward to those. It might reduce the overall low pressure region created though.
Testing would be a very good idea! Would really like to see some numbers before/after. Quite a simple setup I'd think too. Use 2 sets of rockers (with/without screens). I wouldn't try one each side - afraid the data would be corrupted. Here is an idea like I understand you are suggesting:

He has the side pipes in the forward area and the louvers for cooling(?). Note the exit of the exhaust mid-length.

Cheers - Jim

BTW - I'm putting together a compendium of C3 ideas for aero - I hope it makes some sense. This Thread and others bring out a lot of good examples to pick from.

 

[rtj]

I thought this was kind of interesting. It is just a concept not a working prototype.

[ame]https://www.youtube.com/watch?v=EpCLiL3HkfM[/ame]

 

[rtj]

[ame]https://www.youtube.com/watch?v=iE30AQ2_UvQ&t=371s[/ame]

 

[mfain]

^^^^^^^

While I like the looks of the "bowl", I suspect that the aerodynamics would be better if it was covered with a flat disk.

 

[phantomjock]

A lot of effort that hearkens back to post #317!
Interesting paddle-wheel effect to get the air out, as opposed to making it more like a "screw" aligned web.

Cheers - Jim

 

[BBShark]

I'm not understanding how the straight vanes "pump" air through the wheel?