GTS Wing's Aerodynamics

[tsk94]

Originally Posted by b4hand

With no engine in the front, gt3's have pretty good front aero. I don't think its as simple as "big splitter" with 911 gt3 based cars.

Exactly. It's not as simple as rhyary makes it out to be. The GT3 Cup cars have very good underbody aero up front due to the rear engine design. Also, due to the rear engine design, the rear diffuser on a cup car is very minimal and thus not very effective - hence large rear wing and relative lack of front splitter.

However, just because a cup car has a very minimal front splitter and a large rear wing that doesn't mean the same approach is as effective on a the E92. I wouldn't suggest looking at a rear engine race car for inspiration on how to setup aero for your front engine car.

That said it depends on how aggressive you run your wing. Running a full size wing at 0 AOA I don't think calls for a splitter upgrade from a GT4 style one. Also depends on your track. Like I mentioned, I run my wing at an aggressive AOA and only have a GT4 splitter. That being said, most of the benefits I'm getting from the wing are in braking stability. My home track is slow and most corners are slow enough speeds that the high AOA of the wing isn't creating an aero imbalance. At higher speed tracks I dial back the AOA otherwise the front understeers way more in high speed turns and creates too much drag on longer straights.

[rhyary]

My goal has always been to run a wing at its most efficient AOA which is typically 0. Initially I wanted to do this with the GTS. Which let to a discussion about a wing and a spoiler.

But even 0 AOA is not simple. That is 0 AOA is in relationship to the air flow. And air flow is not necessarily relative to the track surface. You can't see 0 AOA.

This means that even running 0 AOA requires experimenting and adjusting the angle. Not easy without access to wind tunnel.

But it can be done, and it will be done.

The 2021 goal is to see if 0 AOA on an efficient wing can help lower lap times.

[admranger]

I see big splitter.

[Bartledoo]

[tsk94]

Originally Posted by Bartledoo

Is that what happens when you run a wing with no splitter????

[Bartledoo]

Originally Posted by tsk94

Is that what happens when you run a wing with no splitter????

That turn in though...

[admranger]

Originally Posted by Bartledoo

Auberlin has an amazing story about that crash. Said he'd seen the LeMans flips and thought "well, if that ever happens to me I'll just hit the brakes like I did on my motocross bike to use the inertia to bring the front back down." He then went on to talk about the data review which showed 100% throttle the whole time. He laughed at himself. "So much for planning".

[Navman56]

Popping back into this thread…

I like that OP is making a good effort to figure out this aerodynamics/vehicle dynamics business. It’s not easy stuff.

However, I agree with other comments of ‘analysis paralysis’. OP, I wouldn’t try to extrapolate too much from a limited dataset. The best thing you can do is experiment with a few small changes on track one at a time, build a better understanding of what each does, and slowly work towards improving your racecar.

With any complex system, a ‘1 shot 1 kill’ approach rarely works. In racing, teams will do sophisticated simulations to establish a car setup before they ever even get to the track. By the end of first practice, the race setup is typically not what you unloaded off the truck with. Even with all the analysis resources in the world, you still just need to try some things out.

In regard to ‘balancing a car’ with aero, the rule of thumb is you want the fore/aft center of pressure to fall a little bit behind the fore/aft center of mass. This ensures stability and is as much true for cars as it is for rockets. So, if you have a massive rear weight bias (like in a 911), you want a ton of rear downforce, definitely more than if the car was 50/50 weight distribution.

A brief note on splitters…

I would be extremely conservative when trying to make an assessment as to how much front downforce a car is making by looking at an exterior picture. Splitter overhang isn’t actually all that important, and often times it’s the geometry you don’t see that’s way more important.

This is the Toyota GT-One. Looks inconspicuous from the outside right?



However, this front ‘splitter’ is doing way more than most of the massive planks you often see bolted to time attack cars.

[rhyary]

I visited my car at ACM yesterday and took it for a drive to test the GPS09. So now I have two options as input to the AIM profiles. Specifically, and related to this thread, are the oversteer and understeer profiles.

The US and OS profile calculate the steering angel at the wheel (STEER_ANGLE/12.5) and a mathematic calculation of what the arc should be based on LatAcc and LongAcc.

My EVO5 has the 10hz Lat and Long (inline) accelerometers and my GPS09 have the new ones @ 25Hz.

So after playing around on NJ's RT-208 going on the exit and entry ramps I looked at the data and indeed it looks like the GPS09 is taking at least twice the data points per second than the EVO5 (evo5 and the GPS08 accelerators were the same)

Armed with better OS and US profiles, it will be easier to understand what the car is doing with the new 71" wing and hopefully able to see differences in the OS and US between different AOA.

While there, I saw a 1 series white car that was built to the gills for time attack. 67" APR-250, huge splitter, huge diffuser. It looked mean and balanced as advised on the thread.

It was so visually unappealing that I would never pursue such a "correctly balanced" car. Just not my cap of tea. I rather go slower than look at this CFD looking car.

But not by any means criticizing any one who does.

[leftfootbr8king]

It's interesting to me that you have such a desire to go faster through data acquisition and analysis, but only to the point it still looks visually appealing to you. So what happens if/when you find out you actually need some front downforce to balance that wing?

[rhyary]

Originally Posted by leftfootbr8king

It's interesting to me that you have such a desire to go faster through data acquisition and analysis, but only to the point it still looks visually appealing to you. So what happens if/when you find out you actually need some front downforce to balance that wing?

Speed is like money, you justify it then...

At some point you have to consider other cars. This project has to do both opposing objectives.

It needs to be as fast as it can with full interior, looking good and drive to the park and track.

Everything I am doing and learning can be transferred to another project - a dedicated track car.

[DRLane]

Originally Posted by rhyary

Speed is like money, you justify it then...

At some point you have to consider other cars. This project has to do both opposing objectives.

It needs to be as fast as it can with full interior, looking good and drive to the park and track.

Everything I am doing and learning can be transferred to another project - a dedicated track car.

This took an unexpected turn. 😂

[rhyary]

Originally Posted by DRLane

This took an unexpected turn. 😂

In theory only.
I have no interests in other projects.

[Bartledoo]

If the aesthetic is important you may not like a big GT250 wing. It's not gonna be pretty, especially with the front looking relatively empty. I have only a 67" and feel a bit like a clown driving it around.

[rhyary]

Originally Posted by Bartledoo

If the aesthetic is important you may not like a big GT250 wing. It's not gonna be pretty, especially with the front looking relatively empty. I have only a 67" and feel a bit like a clown driving it around.

I am putting it on a spare trunk.
I can't tell you how lucky I got.
We found a Jerez trunk 10 min from Autocouture. It was wrapped in black vinyl.

Yesterday we put it under a heating lamp and peeled off the vinyl.

Perfect Jerez black trunk.

I already feel like a clown with the M stripes.

[Bartledoo]

Originally Posted by rhyary

I am putting it on a spare trunk.
I can't tell you how lucky I got.
We found a Jerez trunk 10 min from Autocouture. It was wrapped in black vinyl.

Yesterday we put it under a heating lamp and peeled off the vinyl.

Perfect Jerez black trunk.

I already feel like a clown with the M stripes.

Yea that is lucky. I need to find a black e90 trunk so I can take it off in the off season. Miss driving it in low key fashion.

[gmx]

Wonder how anal/OCD you guys get... Big ticket to knowing local cars are crashed/repaired/suspicious history is socket marks on the bolts that attach things like bonnets, bootlids, fenders etc. You guys do anything to prevent that or give zero F's and send it?

[leftfootbr8king]

Prevent what? Socket marks on body fastener hardware?

[admranger]

Originally Posted by gmx

Wonder how anal/OCD you guys get... Big ticket to knowing local cars are crashed/repaired/suspicious history is socket marks on the bolts that attach things like bonnets, bootlids, fenders etc. You guys do anything to prevent that or give zero F's and send it?

Send it. Take pics of what you're doing if you're worried about people asking about those when you sell the car.

[Bartledoo]

Originally Posted by gmx

Wonder how anal/OCD you guys get... Big ticket to knowing local cars are crashed/repaired/suspicious history is socket marks on the bolts that attach things like bonnets, bootlids, fenders etc. You guys do anything to prevent that or give zero F's and send it?

My car has a weld in roll bar. It's a permanent known track car at this point.

[Vybz]

^ Same. Car will never go back to being a street car, so zero f*cks given I guess.

[roastbeef]

Originally Posted by gmx

Wonder how anal/OCD you guys get... Big ticket to knowing local cars are crashed/repaired/suspicious history is socket marks on the bolts that attach things like bonnets, bootlids, fenders etc. You guys do anything to prevent that or give zero F's and send it?

They are in for a bigger surprise. This car has been completely molested.