Is this to Extreme?

[ttoyoda]

I don't think you need the shark fin. But be on the lookout for the car showing an instabilty at higher speeds, i.e. it wants to wander left and right. If you see this then the center of mass is not in front of the center of drag and you are getting a lot of lift. On your front engine car I would think it would be OK, as long as you keep the tail weight low. Also try sharp jerks of the steering at low speed. Does the weight (or moment of inertia) of the tail make the car oscillate from side to side after you straighten the wheel? This would be bad also in a panic accident avoidance event.

The crosswind problem is a different one. This problem will be caused by the long tail behind the rear wheels, i.e. the wind can push on the tail sideways and try to rotate the car around the back wheels. Even if you do not have a shark fin.

The shark fin makes the cross wind problem worse, not better. And the fin only helps the stability at high speeds.

[ebacherville]

Originally Posted by ttoyoda

For computational fluid dynamics modeling :
http://www.fluent.com/solutions/automotive/aero.htm
Big money unless you get it free at school. Not the eaisest to learn. Pitfalls for the unskeptical, i.e. you make an error in setting up the model or test conditions (true for any modeling software) you might get wrong answers and not realize it. I used to use it years ago, to model air flow thru heat sinks and air distribution ducts, and it was easy to spend weeks making models, running the simulation, interpreting the results. In the end, the PCB layout guys put components where THEY wanted, and we would make ducts and heatsinks so the product would not catch fire.
If you have no training in modeling with it, it will take you less time and you will have more fun just making the real thing. If you have the software free and someone can show you how to use it, then make models.

Yeah as I suspected.. ill just do what i can learning from others and companies that have spent millions in the area of study.. far simpler.. and probably more reliable..

[ihatejoefitz]

Originally Posted by ebacherville

How would I model this? software or something?

I'll see if I can get some models made. I'm not a school, so finding the software may take a while.

[ebacherville]

Originally Posted by ihatejoefitz

I'll see if I can get some models made. I'm not a school, so finding the software may take a while.

Don't bother on my behalf.. if you want to for your own research go right ahead.. . Ill probably have this thing built before you find the software ....lol

[i_am_socket]

Let's see... Blender + OpenFOAM = software, but time to learn to use and develop models and run tests, understand test results, modify tests to achieve desired data, remodel, retest, etc... unless you're planning on putting your mod into full production

Or doodle and compare and use fuzzy logic until your home-brew 1 off is good enough.

I think it's a bit extreme for all the issues mentioned by ttoyoda. I'd clip it off at a point where it's close enough, but thats me.

[ebacherville]

Originally Posted by i_am_socket

Let's see... Blender + OpenFOAM = software, but time to learn to use and develop models and run tests, understand test results, modify tests to achieve desired data, remodel, retest, etc... unless you're planning on putting your mod into full production

Or doodle and compare and use fuzzy logic until your home-brew 1 off is good enough.

I think it's a bit extreme for all the issues mentioned by ttoyoda. I'd clip it off at a point where it's close enough, but thats me.

Most of that could be achieved by a simple Kamback for the entire rear of the car.. make it out of polycarbonate and it will be totally clear and I can see through it... however it makes a huge hole in the rear of the car for air to spin around and create a draft... however it would be fairly simple to make.. a sheet of it and some bracing etc. and your set..

[zjrog]

Uh, how steep is your driveway? Doesn't look that steep, but... Interesting work. What material is that framework?

[Cd]

Originally Posted by i_am_socket

Let's see... Blender + OpenFOAM = software, but time to learn to use and develop models and run tests, understand test results, modify tests to achieve desired data, remodel, retest, etc... unless you're planning on putting your mod into full production

Or doodle and compare and use fuzzy logic until your home-brew 1 off is good enough.

I think it's a bit extreme for all the issues mentioned by ttoyoda. I'd clip it off at a point where it's close enough, but thats me.

I'm not trying to divert this thread , but I looked at OPENFOAM, and I think it is just for Linux. Also, it apparently takes a knowledge of math to use it - so that leaves me out.

I have a model of this very car. ( an early model CRX )
I'm not sure if it is in a correct format for me to use though ( it is a .DWG )


I was also modeling a VW Jetta for use in some CFD testing.

Perhaps I could post the model of the CRX here, and one of you guys with the brains could figure out OPENFOAM.

[Cd]

I have like five or so 3D programs ... and only one will open this file.

It's a save disabled DEMO.

Crap ! Can anyone here convert a .DWG file for me ?? ( To .Obj , .3ds etc )

Right now ... it's useless. Aint that a bi#ch !

[JV-Tuga]

Pale Melanesian said:

Originally Posted by PaleMelanesian

I think that tail ^ is a bit short / steep. You might get flow separation somewhere along the way. I'd go with something in between the two.

Regarding:

What if you added some vortex generators at the top of the back window? I think that might make this work, from what I've read around here.