Let's Talk Aero

[cornercarvin]

This is what im running from Kohr, and it fits the conversation at hand (in the s550 applications anyway). Designed by kohr for "increased downforce, and engine cooling" as this conversation explains. Just trying to help a little by providing another example. By the way....its on sale

 

[RES_22]

All other things being equal (basic balance, tire temps, pressures, damping set properly)....static balance mechanics applies while the chassis is settled at speed...irrespective of speed. Is the condition worse (when settled) at 120? Can you test that - hard to find a corner where you can really settle (4 or 5 seconds) at 120+. Or is the condition more impacted by tipping into the throttle?

Sounds like a combined effect...bias shifts to rear balance with speed (aero - rear wing or front lift) AND power bias shift - lose front grip when you tip into throttle (similar to too much front rebound or not enough rear bump damping).

If you love the front-end feel everywhere else and you want to try something super-easy...just add a couple of turns of rear spring preload (or go up 50# at the back)... then go beat on it. IF the tip-in-induced rear bias shift disappears...then take a bit of wing out and try again...might fix neutral throttle rear bias shift and the slightly higher rear spring rate coupled with a bit less wing might let you drive it with the throttle a bit easier...might.

Alternatively....IF you want to mess with the front ( not me)...believe that front aero-induced lift above 100mph is the culprit...then try to block off the grill a bit OR duct the rad to get more air out of the bottom/back of the engine compartment. Could solve neutral push issue but prob won't completely cure tip in- induced bias shift AND might cause multiple front bias/handling changes .

Check these articles if you can lay your paws on them...practical classroom with worked examples. Really good reading.

 

[VoodooBoss]

AJ's car, click on the photos to enlarge them.



@moto R at Fontana. Note the hood venting and smaller grille opening on the R

 

[ArizonaBOSS]

AJ will probably chime in on this later this week. I’ll take a detailed read later today

 

[antman450]

I am going to be making some ducting for behind the radiator to direct air upwards in addition to what I said earlier. I am sure with a bit more front aero changes this would be resolved. Neutral to on-throttle causes understeer. Weight bias is certainly in play here, but for example at Fontana, turn 1 and 2 are 130 MPH corners with little weight bias changes. They are long corners on a banked oval and it happens there too. It is quite simple, the front gets light at speed. The vents and splitter are simply not enough. I am sure it would not take much more to fix my issues. Plus, I took the wing off one session and it went away, albeit I was 3 seconds slower a lap at Buttonwillow. And my wing is not ideal. It is from a friend who wrecked his Vette and didn''t need it. When I buy a proper 2D wing, it would probably exacerbate what I am experiencing with more rear downforce.

Having said that, I made this thread to have a nice discussion about aero, since my engineering type brain likes it. Fixing my issue was not so much the purpose as much as a brainstorming, knowledge transfer thread.

 

[ArizonaBOSS]

The ducting up to the hood is a good idea but tough to accomplish with all the hoses and FEAD stuff in the way with the Coyote engine.
Adding a wickerbill to the Trackspec louvers would be pretty simple, especially if you are already cutting the hood. You may want to consider doing two banks of louvers on the hood similar to what @Fabman has done on his car. I probably would have gone this route if something this "plug-and-play" (not to mention relatively inexpensive) was available when I was doing my stuff.

It sounds like at this point, if your issue is really aero-caused or aero-related, that it's probably more of a balance issue.
You could reduce rear wing effect by reducing the angle of attack. This will also start to affect the speed at which the wing will generate downforce as well.
To add more front aero effectiveness, you could install a splitter spacer to make the front splitter lower to the ground at static ride height, add canards, or add front wheel-well spats to help move air around the tires/fenderwells at-speed. You could also consider adding some rake to your static ride height, either by lowering the front of the car or raising the rear--this will have other side effects, however.

It could be possible that your rear spring package is not stiff enough for the DF being generated by the wing and the rear of the car is getting too low (thus raising the front somewhat) at speed. This is purely bench-racing stuff but with the total aero package you need to comprehend the static and loaded cases, as well as how it affects the overall vehicle center of pressure. That being said--I've basically just been winging it on my application (all puns intended) and haven't taken the time to approach it academically from a free-body-diagram or dynamic state perspective.

 

[antman450]

@ArizonaBOSS These are all things I am looking at. I will do, spats, air dam, fender vents, ducting, canards and all other tricks I can think of. With respect to the louvers, I wish someone made an off the shelf setup with more ducting and a wickerbill. You can probably make the stock hood as effective, or at least close, for reasonably cheap.

 

[JAJ]

There's a famous low-pressure area at the base of the windscreen, and it's been a feature of race-car design for fifty years or more. What happens if you gap the back of the hood? Someone must have worked this out by now - I'm just curious.

 

[ChrisM]

The undertray on my 07 is basically a square that's only as wide as the radiator. It doesn't fill in the corners or go back to the axle. What might be the effect of adding a full undertray without a corresponding splitter (not a complete underbody, just the front undertray)? And what exactly do the aero tunnels do that I see on high performance cars?

If I had to venture a guess I'd say that they may reduce drag for a higher top speed but not necessarily increase downforce? Or maybe they would, but not as well as a splitter. And I'd guess the tunnels direct air towards the brakes but also reduce turbulence from air shed into the wheel wells.

I get these random questions staring at pictures of cars...

 

[LERCH]

There's a famous low-pressure area at the base of the windscreen, and it's been a feature of race-car design for fifty years or more. What happens if you gap the back of the hood? Someone must have worked this out by now - I'm just curious.

I thought at the base of the windshield was high pressure. That's why the old carburated racecars had their intakes sealed to the hood on the front/sides, and were open at the rear.

Sent from my SM-G950U using Tapatalk

 

[VoodooBoss]

Porsche does a nice job of aero on their cars.

 

[JAJ]

Porsche does a nice job of aero on their cars.

Were you awake when you wrote that?

 

[VoodooBoss]

Barely. The photo above is a 911 GT3 I believe. I've seen a GT3 up on a rack at my local Porsche dealer and it's impressive.

 

[ChrisM]

Barely. The photo above is a 911 GT3 I believe. I've seen a GT3 up on a rack at my local Porsche dealer and it's impressive.

It is. I like to look at undercarriages

 

[Grant 302]

Great thread idea antman! Just picked up a Dwyer 2004C Magnadoohickey gauge and a bunch of tubing for more nerdy fun! Planning on picking up a few more gauges and a pitot tube or two. Wool tuft and water droplet testing only takes you so far. Pressure and speed data can be much more telling.

Read this years ago, but finally decided to pick up one of the gauges mentioned here:
http://www.autospeed.com/cms/articl...tomotive-Modification-ToolKit-Part-3&A=111111
The author mentions using a 0-1" gauge for aero work, but he was only testing to 60km/h or 37 mph. I got more for testing in 'Mexico'.

Anyway, before I mention any other front aero mods...have you considered a little more rear spring rate? Have you confirmed the aero push by using a smaller AoA on the wing?

I think you've got your work cut out for you in trying to balance the front downforce with the rear wing at 100 mph+. Your list of mods will certainly help reduce the imbalance, but it might be tough considering that most front end mods are single and double digit lbf. and the wing is easily in the 300-600 lbf. range at that speed. The splitter drop will probably be the most effective. Underbody work might help too, if possible. For upper surfaces, I'd suggest making sure that everything planned works together. Like the splitter/canard(s)/spats/fences. Better sealing at the hood perimeter might help too.

The lip around the vents of the Tiger hood create a pressure difference that actively draws air out (not sure if that's the correct description), whereas the Trackspec louvers lack that.

Sounds familiar.

And IIRC, that type of louver works a bit better if it has a wicker bill at its leading edge. Not unlike the raised front/perimeter area on the Tiger Racing design.

 

[antman450]

Thanks @Grant 302 . I tried a session where I took the rear wing off. It balanced the car at speed again, but this time I was 3 seconds a lap slower at Buttonwillow. So, yes I will try to mix all those things together and see where it gets me. I think even some double digits increase in downforce/decrease in lift will fix it right up. Splitter drop, canards, wheel well splates, and some more venting should really do it.

 

[ArizonaBOSS]

Regarding the radiator-to-hood ducting, I forgot that Vorshlag was able to accomplish this on their "Big Red" Mustang--you can probably pore through their blog and find the photos of how they laid everything out to clear stuff. It looked great but also very labor-intensive (read: expensive).

 

[RES_22]

Fabricated these out of screen and 100mph tape. Can tweak to manage airflow...easily.

Got to integrate my engineering background with my arts'n'crafts side .

 

[antman450]

View attachment 2544

Fabricated these out of screen and 100mph tape. Can tweak to manage airflow...easily.

Got to integrate my engineering background with my arts'n'crafts side .

Interesting. What tape did you use?

 

[RES_22]

ISC racer's tape from HRP (Hoerr). Tough.

The grill inserts sit outboard and are held in place by couple additional pieces of tape.