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@NineLivesJohnny

Anyone have Aero questions?

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That's awesome.

 

It reminds me of the pic where they pit bags on manure on the open wheel car to simulate downforce.

 

 

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I've actually made a mistake. In my math to convert a change in ride height to an amount of downforce, I factored in the springs wrong. I had divided the whole equation by two to calculate for there being two springs, but I needed to actually multiply by two. This made for much larger numbers, and after doing some tests with people sitting on the car, it's more believable. 

 

277721171_RideHeightSpreadsheet2.thumb.PNG.bde983953f947acc3a0b6d04513c11fe.PNG

 

This makes a bit more of an impact to most of the numbers shown above but it also highlights how little of a pressure difference is actually being created by the splitter. At the most, there would be a 0.35 psi difference from the top to the bottom of the splitter(a little more than 0.02 atmospheres). That is where the large surface area comes into play as it all adds up eventually. 

 

Based off of this data, I'd say the easiest way to increase downforce on a splitter is to just increase its surface area. Less messing around with the heights and angle of attack and more surface area. Of course those heights and angles are going to help that pressure difference, but the surface area is going to be a big factor in overall downforce. 

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Interesting, I guess that explains some of the splitters that used to look like a beaver tail sticking out front.

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Small potatoes, gonna build a Chaperal 2J sucker on my c3 Corvette 🥴 that would be kind of insane but it could be designed. As many problems as they had with the original it would probably be impossible to make it last for 8 hours. Where is the green font???

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Edit: Wasn't very clear in my first attempt to ask my question.

 

How critical is it to maintain proper laminar flow over the whole vehicle? Does it require smooth, non-disjointed surfaces from the start, or can the air flow reconnect and still be useful in producing downforce? In other words, if you experience turbulence over the hood, does that disruption impact the benefits you would normally get over the rest of the hood, roof, vehicle? Obviously there is new clean air coming into contact with the windshield, so perhaps it's negligible. Same question for underneath the car.

 

 

Edited by EngEtan

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Hey folks,  

 

at the risk of subjecting myself to the scrutiny of some folks that know what the hell they're doing I thought I'd share the analysis I did on adding Aero to our Neon.  

 

Here is a link to the analysis I did which tried to predict the impact on lift and drag to various Aero strategies. I used a purchased CAD model of our Neon combined with Fusion360's CFD package (the old Blue Ridge Numeric's CDDesign).  

 

I am NOT an aero engineer so caveat emptor.  I suspect Johnny C will find some deep flaws.  

 

https://drive.google.com/open?id=1SJUoOjb7sRXu9ehfUWbrHwP6xpzpRUxr

 

As for the impact - it's hard to say since we were changing other things on the car at the same time. I've tried running without the wing and the car seems quite a bit less stable but it's possible that's subjective and my butt-dyno at work.  Conversely - at Gingerman we ripped the chin off the car and went on to run our fastest lap without it - but again it's hard to say.  

 

Hope this adds value to someone.  I built the wing and splitter myself so if anyone want's plans let me know. 

 

Please be gentle with your analytical pitchforks!


Dave 

 

 

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I think the rear diffuser looks a bit ineffective. The chart at the bottom shows the car with and without the diffuser, with the same setup otherwise. There is almost no change and I think this is due to the fact that there is no under body or side skirts. If you wanted to increase the usefulness of the diffuser, you could add a flat bottom and side skirts. Basically, if you looked underneath the splitter at the front all you should see is a rectangle that exits at the back through the diffuser. An under body without side skirts is better than nothing but I don't think its worth it because of the cooling problems. I saw a miata at the last race I went to that had a flat bottom. The entire bottom of the car was flat, and it led into a diffuser at the back. They faced overheating problems with the transmission, differential, and gas tank. Be careful.

 

If I were you, I'd just take the diffuser off and run with the wing and splitter.

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On 9/12/2019 at 3:41 PM, Davef_dci said:

Hey folks,  

 

at the risk of subjecting myself to the scrutiny of some folks that know what the hell they're doing I thought I'd share the analysis I did on adding Aero to our Neon.  

 

Here is a link to the analysis I did which tried to predict the impact on lift and drag to various Aero strategies. I used a purchased CAD model of our Neon combined with Fusion360's CFD package (the old Blue Ridge Numeric's CDDesign).  

 

I am NOT an aero engineer so caveat emptor.  I suspect Johnny C will find some deep flaws.  

 

https://drive.google.com/open?id=1SJUoOjb7sRXu9ehfUWbrHwP6xpzpRUxr

 

As for the impact - it's hard to say since we were changing other things on the car at the same time. I've tried running without the wing and the car seems quite a bit less stable but it's possible that's subjective and my butt-dyno at work.  Conversely - at Gingerman we ripped the chin off the car and went on to run our fastest lap without it - but again it's hard to say.  

 

Hope this adds value to someone.  I built the wing and splitter myself so if anyone want's plans let me know. 

 

Please be gentle with your analytical pitchforks!


Dave 

 

 

Can you model it with the rear bumper cover removed?

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On 9/12/2019 at 1:41 PM, Davef_dci said:

Hey folks,  

 

at the risk of subjecting myself to the scrutiny of some folks that know what the hell they're doing I thought I'd share the analysis I did on adding Aero to our Neon.  

 

Here is a link to the analysis I did which tried to predict the impact on lift and drag to various Aero strategies. I used a purchased CAD model of our Neon combined with Fusion360's CFD package (the old Blue Ridge Numeric's CDDesign).  

 

I am NOT an aero engineer so caveat emptor.  I suspect Johnny C will find some deep flaws.  

 

https://drive.google.com/open?id=1SJUoOjb7sRXu9ehfUWbrHwP6xpzpRUxr

 

As for the impact - it's hard to say since we were changing other things on the car at the same time. I've tried running without the wing and the car seems quite a bit less stable but it's possible that's subjective and my butt-dyno at work.  Conversely - at Gingerman we ripped the chin off the car and went on to run our fastest lap without it - but again it's hard to say.  

 

Hope this adds value to someone.  I built the wing and splitter myself so if anyone want's plans let me know. 

 

Please be gentle with your analytical pitchforks!


Dave 

 

 

 

A few questions about the analysis:

 

Was the road stationary or setup as a moving wall? 

 

How was the grid made? Automated in Fusion360? 

 

Do you know what the y+ is for the grid? Target/average/whatever

 

Euler or full Navier-Stokes? 

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Interested to hear thoughts about the Fastback hatch I made for our Miata. Specifically where I designed the rear open to allow the cabin air to escape and its effects as it hits the spoiler. Some have said that may create more drag than downforce. I know nothing about everything so any and all comments are welcome.

 

 

 

20190919_221718.jpg

20190907_192726.jpg

20190908_100516.jpg

20190920_163147.jpg

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Marc , a spoiler reduces lift by  spoiling the smooth flow that is acting like a wing..regular positive lift wing..the additional air through the cockpit should make the reverse bubble behind the spoiler larger...so drag should be increased...bet you could not  tell a performance difference in the real champ car world though...I am not an expert in these matters  but did sleep a a holiday inn express a few years ago...

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Hey, I've got some questions:

1) From an aero perspective, how dumb is it to remove the windshield and roof from an NC Miata?

cmpA5PhGw4yrT1eOlXbXCom4kxrZkRilhPlKaejs1e66JYiu8fT5ZZo6XfpwTJZtzhx_GStoyeDBSawH9HuM8_zVwP5TbXAIxtUgUcf10BgXZ8vh2uDw_igl5fv7EnYJgskQ7QmmsryC_vJQPJffhOEpBYFDt6VUXf7m5A3Ty4SYVdT7YVroFaUZ9RRDtiblx7jPdDQeMnnWdx_kgL2-vkf0Y7KNwNaZ6B3i7Wq-erOyyrw-SGTmzksgStkaaXmKuvH94sE3Afc5jMwuGyV6SoR2jaDW7haa3NT5nASu7s_1g-v6FfvVkA3yIP3nhmDb1EJhisRqUT-Ru2I3K14ZyVmf-fgV2E2o-6AcWc191ocv37ZgDFKewxSS4rAdY6xIKLLDCqBP90qMjR0jUPEI0vedlIgC54iniROIGDomxHOMHhGLJhwo15vPE8UQOkPGSbuV_-9_fR1FwbGhXsuHM579NpO7DoUS--mZhzWos2bw-y13Thefui_oCtbR7aIY9sqon-mO_fWlVmOapimCVkebkO9KIokS1FcZ1RpOeH7nbUyQHnhhFeBUfGaKMf77uoQkFCkfOZDT-FXeO0Q5O_ANqqSpowj7DDKzJnExgEAhM1bkUqRJUZucf4QXRpljjHpJcmqnhe96Bgf46Z08QgeFXDHjvUKPl4U0zvzJRMmvGg2ZUNx0Ask=w2597-h1947-no

We tried to keep the bars in-line with each other, so nothing extra is hanging out in the air stream.

2) We were thinking of 3D-printing a wing to go over the top part of the main hoop. Does this sound like it's worth doing?

3) Could you guys scan our car and set us up with OpenFOAM? I'm a software engineer and have never messed with CFD or even much in the way of CAD. I'm not sure where to start, but I'd love to get set up to do my own testing and tweaking with CFD.

Thanks!

Edited by Grant

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2 hours ago, Grant said:

Hey, I've got some questions:

1) From an aero perspective, how dumb is it to do this to an NC Miata?

cmpA5PhGw4yrT1eOlXbXCom4kxrZkRilhPlKaejs1e66JYiu8fT5ZZo6XfpwTJZtzhx_GStoyeDBSawH9HuM8_zVwP5TbXAIxtUgUcf10BgXZ8vh2uDw_igl5fv7EnYJgskQ7QmmsryC_vJQPJffhOEpBYFDt6VUXf7m5A3Ty4SYVdT7YVroFaUZ9RRDtiblx7jPdDQeMnnWdx_kgL2-vkf0Y7KNwNaZ6B3i7Wq-erOyyrw-SGTmzksgStkaaXmKuvH94sE3Afc5jMwuGyV6SoR2jaDW7haa3NT5nASu7s_1g-v6FfvVkA3yIP3nhmDb1EJhisRqUT-Ru2I3K14ZyVmf-fgV2E2o-6AcWc191ocv37ZgDFKewxSS4rAdY6xIKLLDCqBP90qMjR0jUPEI0vedlIgC54iniROIGDomxHOMHhGLJhwo15vPE8UQOkPGSbuV_-9_fR1FwbGhXsuHM579NpO7DoUS--mZhzWos2bw-y13Thefui_oCtbR7aIY9sqon-mO_fWlVmOapimCVkebkO9KIokS1FcZ1RpOeH7nbUyQHnhhFeBUfGaKMf77uoQkFCkfOZDT-FXeO0Q5O_ANqqSpowj7DDKzJnExgEAhM1bkUqRJUZucf4QXRpljjHpJcmqnhe96Bgf46Z08QgeFXDHjvUKPl4U0zvzJRMmvGg2ZUNx0Ask=w2597-h1947-no

We tried to keep the bars in-line with each other, so nothing extra is hanging out in the air stream.

2) We were thinking of 3D-printing a wing to go over the top part of the main hoop. Does this sound like it's worth doing?

3) Could you guys scan our car and set us up with OpenFOAM? I'm a software engineer and have never messed with CFD or even much in the way of CAD. I'm not sure where to start, but I'd love to get set up to do my own testing and tweaking with CFD.

Thanks!

While you still have forward visibility through the gap, keeping the hood up like that will greatly increase your drag. Engine cooling may be improved though. 

Also, removing the doors may sound good for weight, but that created a big drag pocket and will probably slow you down as well. 

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Is the intention to run without doors or are we looking at something else here?

 

"9.5.3. Doors cannot be removed. All cars must have a door or “OEM equivalent” body panel."

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On 7/15/2019 at 12:03 PM, E. Tyler Pedersen said:

 

I would say top place in their class....Jacky Ickx and Premium Dudes took the top spot on Saturday and Sunday

 

On 10/13/2019 at 8:22 AM, Mazmarc said:

Interested to hear thoughts about the Fastback hatch I made for our Miata. Specifically where I designed the rear open to allow the cabin air to escape and its effects as it hits the spoiler. Some have said that may create more drag than downforce. I know nothing about everything so any and all comments are welcome.

 

 

 

20190919_221718.jpg

20190907_192726.jpg

20190908_100516.jpg

20190920_163147.jpg

Looks fantastic.  should dramatically reduce drag. 

i would seal the area by the spoiler.  if your looking to vent the car... you want the vents where the air is moving the fastest. this helps it "pull" the Tourbilant and slow moving air thats inside the cabin.  those fast moving areas would be on top of the roof, or the back "glass" area. putting a gap in a "seam" (aka where a part of the body meets another part of the body.) is where air is moving slowly. if it's moving slowly it has a better chance to changing direction, and entering the cabin. 

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8 minutes ago, ross2004 said:

Is the intention to run without doors or are we looking at something else here?

 

"9.5.3. Doors cannot be removed. All cars must have a door or “OEM equivalent” body panel."


No, of course not, door skins are very light and an aerodynamic aid. They simply aren't on the car while the cage is being worked on. My post meant to refer to windshield and roof removal.

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3 hours ago, @NineLivesJohnny said:

 

Looks fantastic.  should dramatically reduce drag. 

i would seal the area by the spoiler.  if your looking to vent the car... you want the vents where the air is moving the fastest. this helps it "pull" the Tourbilant and slow moving air thats inside the cabin.  those fast moving areas would be on top of the roof, or the back "glass" area. putting a gap in a "seam" (aka where a part of the body meets another part of the body.) is where air is moving slowly. if it's moving slowly it has a better chance to changing direction, and entering the cabin. 

Thanks for the kind words. I will come up with some way to seal the back of the hatch.

 

So maybe two small NACA ducts reversed toward the rear of the "glass" for cabin flow?

 

Thanks for all the responses guys. Very much appreciated.

 

 

 

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