F'ing fast.

[ray_]

https://www.epa.gov/sites/default/files/2016-10/documents/pb83211243.pdf

 

2002 Aerodynamics | The Tii Register

WWW.2002TII.ORG

---

2002 Aerodynamics In light of renewed economic and political interest in petrochemical conservation and an upswing in the popularity of aftermarket aerodynamic devices, let us take a look at our old friend the...

 

Edited February 20 by ray_

[visionaut]

23 minutes ago, ray_ said:

https://www.epa.gov/sites/default/files/2016-10/documents/pb83211243.pdf

 

2002 Aerodynamics | The Tii Register

WWW.2002TII.ORG

---

2002 Aerodynamics In light of renewed economic and political interest in petrochemical conservation and an upswing in the popularity of aftermarket aerodynamic devices, let us take a look at our old friend the...

 

Yeah- the Mulcahey article goes way back. A bit dated but good stuff.

 

I hadn’t seen the Kamei doc before - very cool. Thx Ray!

Tom

 

( I really should provide a little explanation along with my earlier diagram but I ran out of juice just finding it.. )

[visionaut]

18 hours ago, visionaut said:

( I really should provide a little explanation along with my earlier diagram but I ran out of juice just finding it.. )

 

Okay, so a semi-brief explanation…

 

This chart was used in a presentation on 2002 aero that I did more than a decade ago. The chart is both abstract and info dense, so I could use it to talk for half an hour. It’s a talk-to chart, not a read-it chart.

 

It’s basically a was/now take. The top representing a stock 2002 and the bottom an aero-modified version (very akin to my own car). The top introduces 3 of the most significant 2002 aerodynamic bugaboos - the upsloped fascia, the high ground clearance, and the notched rear deck. The bottom illustrates a set of added aero components and body orientation changes - and enabled me to discuss each of their aero effects to alter both drag and lift.

 

I used 2D calculations supported and supplemented by 3D wind tunnel testing results (and CFD analyses), plus my own speed flow pattern tests (taped strips of yarn) and observations. I made high leverage of the standard MIRA aero model, specifically the Notchback, which is amazingly close in dimensional features to a 2002. (See 2nd pic). MIRA standard models have been extensively analyzed (and tweaked) and wind tunnel tested (even full scale ones) for more than 20 years, so there’s a ton of useful available published data that’s not difficult to extrapolate to an 02.

 

The three charts in the graphic support discussion of the three 02 aero bugaboos, and how the different aero mods help to reduce their negative aero effects. Chart 1 shows the high drag penalty for having a -25deg effective slip angle to the 2002 aft body. Most folks don’t appreciate how much this factor contributes appreciably to the 02s poor drag coefficient. Chart 2 helps discuss the -60 deg slope to the front nose. It unsurprisingly has a significant effect on Lift, and it accelerates the underbody venturi effect, but luckily its effect on Drag reduces with speed. Chart 3 supports discussing the 2002 underbody flow, and explains how an airdam-less 02 ‘plants itself’ to the ground (negative lift) and how non-intuitively that flips to Lift as ground height (as alterable with an airdam) gets low. It also supports lead-in to talking about optimizing the airdam height..

 

The little numbers all around are dimensions in millimeters that I can reference. E.g. distance from top of headlight to ground -- 690 stock vs 644 me…

 

Clear as mud?

 

Tom

[Preyupy]

I think the most I have ever seen in a 2002 race car was just touching 140mph.  Stability was never an issue,  just trying to shove that much air out of the way with a brick takes a lot of HP.  I am sure there is a speed where aerodynamics will cause a straight line stability problem but it is going to take more than 300 hp to find it.  Turn 1 at Pacific Raceways at 135+ flat is doable with no spoilers or air dams.  An air dam does not seem to make it more stable just faster.  

[Dudeland]

On 2/20/2024 at 3:49 PM, visionaut said:

 

Okay, so a semi-brief explanation…

 

This chart was used in a presentation on 2002 aero that I did more than a decade ago. The chart is both abstract and info dense, so I could use it to talk for half an hour. It’s a talk-to chart, not a read-it chart.

 

It’s basically a was/now take. The top representing a stock 2002 and the bottom an aero-modified version (very akin to my own car). The top introduces 3 of the most significant 2002 aerodynamic bugaboos - the upsloped fascia, the high ground clearance, and the notched rear deck. The bottom illustrates a set of added aero components and body orientation changes - and enabled me to discuss each of their aero effects to alter both drag and lift.

 

I used 2D calculations supported and supplemented by 3D wind tunnel testing results (and CFD analyses), plus my own speed flow pattern tests (taped strips of yarn) and observations. I made high leverage of the standard MIRA aero model, specifically the Notchback, which is amazingly close in dimensional features to a 2002. (See 2nd pic). MIRA standard models have been extensively analyzed (and tweaked) and wind tunnel tested (even full scale ones) for more than 20 years, so there’s a ton of useful available published data that’s not difficult to extrapolate to an 02.

 

The three charts in the graphic support discussion of the three 02 aero bugaboos, and how the different aero mods help to reduce their negative aero effects. Chart 1 shows the high drag penalty for having a -25deg effective slip angle to the 2002 aft body. Most folks don’t appreciate how much this factor contributes appreciably to the 02s poor drag coefficient. Chart 2 helps discuss the -60 deg slope to the front nose. It unsurprisingly has a significant effect on Lift, and it accelerates the underbody venturi effect, but luckily its effect on Drag reduces with speed. Chart 3 supports discussing the 2002 underbody flow, and explains how an airdam-less 02 ‘plants itself’ to the ground (negative lift) and how non-intuitively that flips to Lift as ground height (as alterable with an airdam) gets low. It also supports lead-in to talking about optimizing the airdam height..

 

The little numbers all around are dimensions in millimeters that I can reference. E.g. distance from top of headlight to ground -- 690 stock vs 644 me…

 

Clear as mud?

 

Tom

So the air dam actually causes lift at a specific height. ?  The bottom two graphs have no scale/speed, so we don't know when these things begin to happen. 

 

I guess I am getting a spoiler.  I wonder if we go with a Zender replica like the one @Ireland Engineeringsells.  Or do we get something more radical like Koogleworks. 

 

 

[visionaut]

1 hour ago, Dudeland said:

So the air dam actually causes lift at a specific height. ?  The bottom two graphs have no scale/speed, so we don't know when these things begin to happen. 

Yes - when you close the gap too much, all the air flows over the car. Even an 02 creates a top airflow shape that’s like the upper surface of a wing. A wing works on differences n air speed above and below. When you begin to cut off the below airflow on a car - you get a wing. It goes up = lift.

 

Graphs - yes, by design. The basic shapes in the graphs hold for a range.  In chart 2, the transition points velocity varies based upon a given cars aero. In chart 3, where the greatest venturi effect and the lift transition point occur vary with velocity, and underbody roughness coefficient.

 

The purpose of a spoiler is to reduce the amount of air flowing under the car, reducing the air pressure under the car. Like the low pressure air that’s behind the car. When racing and you’re drafting a car it’s about getting into that low pressure wake…

 

1 hour ago, Dudeland said:

I guess I am getting a spoiler.  I wonder if we go with a Zender replica like the one @Ireland Engineeringsells.  Or do we get something more radical like Koogleworks. 

 

If it’s the duckbill, it won’t have the best

aero. Proven long ago - they look rad but a vertical spoiler is more effective. Just say-in’. 
 

On 2/20/2024 at 3:30 PM, Preyupy said:

Turn 1 at Pacific Raceways at 135+ flat is doable with no spoilers or air dams.  An air dam does not seem to make it more stable just faster. 

Agree - with that well sorted race 02 suspension, ride height and tires that many mentioned upfront. That’s why folks love these cars. But a spoiler can make it the cars aero effects more consistent across the speed range.

 

135 in a bare body a) means it’s a beast, and b) means the owner favors a simpler style and doesn’t mind leaving an additional 15mph out there from good aero...

 

[TobyB]

Thanks for that!  Especially the explanation of the lift with reduced underbody flow.  

 

Quote

doesn’t mind leaving an additional 15mph out there from good aero.

 

-or from rules restriction. 

With race cars competing in restricted classes, many aero 'common sense'

mods (like closing your windows) are specifically prohibited... even in relatively

free classes like GT.

 

t

 

[Ian]

Thanks for the nice explanation and figures!

[visionaut]

Glad you liked it. Wanna really know more about wings and lift? (Lots of explanations you heard in school are likely wrong.) Here’s a good one:

 

https://aerospaceengineeringblog.com/how-do-wings-work/

 

 

[Dudeland]

On 2/22/2024 at 8:43 PM, visionaut said:

Yes - when you close the gap too much, all the air flows over the car. Even an 02 creates a top airflow shape that’s like the upper surface of a wing. A wing works on differences n air speed above and below. When you begin to cut off the below airflow on a car - you get a wing. It goes up = lift.

 

Graphs - yes, by design. The basic shapes in the graphs hold for a range.  In chart 2, the transition points velocity varies based upon a given cars aero. In chart 3, where the greatest venturi effect and the lift transition point occur vary with velocity, and underbody roughness coefficient.

 

The purpose of a spoiler is to reduce the amount of air flowing under the car, reducing the air pressure under the car. Like the low pressure air that’s behind the car. When racing and you’re drafting a car it’s about getting into that low pressure wake…

 

 

If it’s the duckbill, it won’t have the best

aero. Proven long ago - they look rad but a vertical spoiler is more effective. Just say-in’. 
 

Agree - with that well sorted race 02 suspension, ride height and tires that many mentioned upfront. That’s why folks love these cars. But a spoiler can make it the cars aero effects more consistent across the speed range.

 

135 in a bare body a) means it’s a beast, and b) means the owner favors a simpler style and doesn’t mind leaving an additional 15mph out there from good aero...

 

Is under body aero a good idea for the 02? Does anybody sell a rear splitter for our cars? 

[tzei]

Idk but i'm in a process of making (almost) flat underbody.

[visionaut]

4 hours ago, Dudeland said:

Is under body aero a good idea for the 02? Does anybody sell a rear splitter for our cars? 

I don’t think it’s worth the effort to tackle 02 underbody aero. A proper underbody aero design would need a splitter upfront, engine bay venting, tire aero-spats, side skirts, a rising to the rear smoothed underside with a diffuser in the back. That’s a lot of complexity to design right. It’s simpler and quite effective to just use a big airdam to aerodynamically ‘hide’ the underbody from a lot of the airflow.

 

Splitters go at the front - and are generally large ‘plates’ that extend forward of the bumper and run parallel & close to the ground mounted to a vertical airdam. Perhaps you mean something else?

 

3 hours ago, tzei said:

i'm in a process of making (almost) flat underbody

Be careful — it’s too easy with a flat-bottom to generate lift that can mimic hydroplaning.  Smooth air over the top, smooth air under the bottom. That's a wing…

 

Flatbottom generally aren’t very effective without accompanying aero mods (splitter/skirts/diffuser).

 

[Ian]

I like the idea of a functional diffuser in the rear if it could replace a wing.  I don't care for the looks of a wing on the trunk, and currently have a turbo-style deck lid spoiler for the Kamm effect.  But I'd love to get more downforce at the rear to match a spoiler+splitter in the front.

[uai]

2 hours ago, Ian said:

I like the idea of a functional diffuser in the rear if it could replace a wing.  I don't care for the looks of a wing on the trunk, and currently have a turbo-style deck lid spoiler for the Kamm effect.  But I'd love to get more downforce at the rear to match a spoiler+splitter in the front.

side exhaust

trunk mounted tank

no spare tire well

try googling for zynki

 

Edited February 24 by uai

[66m10]

6 minutes ago, uai said:

 

try googling for zynki 

Hans-Jochen Zychlinski aka Zynki Power that is