The DOWNFORCE Thread!

[zeitgeist]

Curious about effective angles for diffusers/canards/spoilers. Looks like everyone just puts stuff on without thinking about this

[Sleepy_Steve]

Ya'll need to go to an ALMS (now Tudor) race and just snap ungodly amounts of pics of the prototyles and their dive planes / diffusers / splitters / belly pans if you can see them..... Just figure they've scienced most of this out, so its a good pool to pull ideas from and learn from.

[Otto347]

Lol I've been doing stuff like that for years. Photograph suspension and all kinds of things to get ideas. They have money to burn for r&d on that stuff.

[crzsteveo]

Originally Posted by zeitgeist

Curious about effective angles for diffusers/canards/spoilers. Looks like everyone just puts stuff on without thinking about this

they have definitely put some effort into scientifically testing all aspects of it.

There are ssssooo much articles and websites online explaining about the size, angles etc and how much it affects air pressure around the vehicle. ive been researching more along the lines of time attack cars to see if I can tie those designs into a road car, for like high way speeds.

Its sucks because its all a balancing act. you lower your car and increase the angle of your front splitter towards the ground more, by doing so you increase down force creating more grip but increase the drag and change the air pressure around your vehicle.

what I want to accomplish with my car is creating that balance of air moving around my vehicle and kill that turbulent air that sits behind my hatch.

if you have a smokey car you can see this just by driving. the smoke curls and spins around the taillights and continues to do so without going anywhere.

I think that's because the low pressure going under my car and the high pressure going over my car and around, are moving at different speeds or created turbulence somewhere else along my car causing a whole mumbo jumbo type shit.?????

[Z_Spool]

Originally Posted by crzsteveo

...causing a whole mumbo jumbo type shit.?????

Yup... that's pretty much the long and short of it.

[ehhhregartless]

RE style diffuser with some strakes might get you in the right direction

[Bushido]

[crzsteveo]

Bushido thank you!!!

[Def]

Originally Posted by Bushido

The guys on ecomodder don't know near as much about aerodynamics as they think they do. Although every once in a while they do some interesting stuff.


3 degrees is NOT the ideal diffuser angle, especially when you have a compound divergent upper surface (a boat tail), that is working the airflow as hard as it can. Which BTW, flow is NOT attached to the rear hatch window on a stock S13. It separates 1/3-1/2 of the roofline back from the front windshield. Boundary layer is around 3/8" at the start of the rear hatch, and grows quite a lot from there. Vortex generators will reattach it, at the expense of drag. Your rear aero determines if attached flow is worth it.

So to sum it up, they're working the air over the top of the car extremely hard, with really aggressive divergent angles, and then say 3 degrees is the ideal rear diffuser angle? That's completely crazy. You can easily go to 6-8 degrees and ensure you won't have separation in a diffuser if you're expelling to a low presssure area (i.e. the rear bumper), and probably even if you completely boat tail the rear (higher pressure at the diffuser exit). But really, even diffuser angles of 10-12 degrees can work when pumping to a low pressure area, but at that point, you probably need to start considering the 3D effects of the flow like how it's coming in from the side skirts and around the rear suspension area.

For the average car here, you could easily do a 7 degree diffuser and be fine. But I would not even think of bothering for a street car. You probably won't feel much of a difference unless you get a big splitter, flat bottom leading to the diffuser, and wing. The splitter and wing do most of the work, the splitter pumps more air out the underside of the car and makes the splitter and underbody produce more downforce. Just putting a diffuser on the rear doesn't really help much just because there's not a nice large area of attached flow to accelerate and get a benefit of.

And BTW - the stock S13 gas tank actually makes a halfway decent diffuser, but the angle is a bit steep at the end, bordering on 12-15 deg by my measurements.

[ehhhregartless]

^Ideally, sector times should change on a given track between the turns and straights. Turns should be faster because you're able to put down all the power that you make with max grip. And straight line speed would go down a bit. But not enough to negate the gains from the turns. Yes, overall your gains would eventually become less and less after which you'd adjust and add power.

[OBEEWON]

^^^

[ehhhregartless]

At 4:35 is what i was trying to explain. The whole video is definite worth the watch.

http://youtu.be/v_767VQBFi0

[ehhhregartless]

[ehhhregartless]

[ehhhregartless]

[kognition]

Looks great!

Originally Posted by Imarvin240

So I have been looking around on here trying to find proper info on wing angle, wing stand types, front splitters, diffusers, canard info, and other downforce aero related info...but didn't find much, if anything. I figured we should have a thread to post up questions/info/photos on our wing, splitter, canard, diffuser setups. I think this will help some of the future aspiring track guys on here.

Rules: Only post info, pictures, questions regarding downforce aero.



Here's mine to get it started.

It's a 70" Kognition Designs carbon fiber chassis mounted quick disconnect wing.





It's an extremely well made product and it's a well proven product on the track. The quick disconnect is just a few pins on each side that get pulled out to remove the wing, which then allows the hatch to open easily. The whole kit is super easy and simple to put together. The only tough part would be cutting the hatch in the correct spot lol. Touge Factory will be doing a full carbon fiber underbody diffuser, front splitter, and canards on the car, which I will post up later.


Looking forward to seeing some of the other setups on here and hopefully learning a few things as well.

[kognition]

GST Motorsports driver Jeff Westphal reset the all time track record at ButtonWillow at the recent GTA/SLB time attack event this past November. They use our 76" span chassis mount kit for the GC8.

[Xplat]

Figured this video belongs here.

https://www.youtube.com/watch?v=quDLzxmJl5I

[ehhhregartless]

That's a very informative vid, definitely learned a lot from it. Looks like I'll couple that with this DIY for aero testing/development in the spring

http://www.autospeed.com/cms/article.html?&A=108656

[crzsteveo]

^same here. that's definitely the best alternative to a wind tunnel

[crzsteveo]

I love time attack cars.

http://www.youtube.com/watch?x-yt-cl...-ts=1422411861

[ehhhregartless]

[voiddweller]

Originally Posted by Sleepy_Steve

+1 you probably want to move this to the tech section.....

Thank you!

The summary you put together pretty much sums up all the research I've been doing over the past several months and should definitely be 'stuck' for the benefit of the community.

[ehhhregartless]

[ehhhregartless]

[NISSeAN]

I generally don't like body kits but the GP sports looks awesome and functional

[ehhhregartless]

^2nd, one of my favs

[ehhhregartless]

[silviasandbeer]

cliff notes.. add canards
cool vid ehhhhhregardlessssss

https://www.youtube.com/watch?v=Pgpawejpi6o

[voiddweller]

Interesting video!