Aero mods for chumps...

[Vanquizor]

Given the information above I'd say its mighty unfortunate that the stock rear window angle is somewhere between 30-35 degrees...

I could have guessed it wasen't optimal as on my drive to work this morning the layer of frost and a dusting of lighter snow gave me a bit of real world wind tunnel visualization. The outer 1/4 to 1/3 of the read window clearly is turbulent right from top to bottom as both the snow and heavier frost were blasted off almost immediately in waht appeared to be random directions (some floating off the trunk some crossing the trunk some levitating before falling to the ground, some floating across to the other side of the road, ect.). I would guess the center top of the window has flow separation within about 2 inches of the top as the snow in this area was swept off and the frost peeled it self from front to back flying cleanly off the car a couple feet above the trunk. The center base of the windshield was kinda fun to watch as it showed it has a recirculating bubble that goes almost 1/2 way up. For about 6 blocks till I came to a traffic light the initial dusting of snow tumbled round and round in the same spot. The final point of interest is the patch of frost with a small patch of snow in its center which sat in the center of the rear window spanning from a few inches fron the top down to almost the center of the rear window. This was never removed on my 14 block drive to work, although I was able to blow the snow off it with a quick puff like you would blow candels on a bithday cake out with. I couldn't remove the frost with breath alone but brushed it off easily with my glove.

I think have officially had WAY too much fun on my drive to work.

[aerohead]

Originally Posted by Vanquizor

Not sold on the wheel covers... our 4 tire change was under a minute last time we practiced, it would be tough to convince me the aero gained would make up for the time it took to peel off the covers and re-install them.

I've been eyeballing the back of the car, and I wonder what gains there would be going to a fastback. I thought I read somewhere that if you end up with an angle between 15 and 30 degrees it was worse for drag then cutting a steeper angle and letting the air seperate.

On account of safety concerns from one of our team members the roof is staying on and we'll put lexan in where the glass we need to remove was.

In Hucho's book and the papers which became part of it,the researchers say,stay away from 28-degrees.It's the angle from Hell!

[botsapper]

Ahh, fun anecdotal 'snow' visual observations...many have chimed in on that ,especially in the snow zones. The snow flurry/water droplets/dust vortices does give good sense of flow movements. Taped-on yarn tufts are always good to study general/specific areas of your vehicle aerodynamics (with requisite CCD cameras at critical areas). But it is the proven modding that gives real results. Example of a three-box (sedan), thanks from a fellow eco-modder study.

http://www.youtube.com/watch?v=by0sanLNf3Q

Most have done it for extreme aero/best fuel economy, very different criteria from your racing modes. Some important downforce may be required for safe handling performance at top speeds. A scenario of a wide hi-speed decreasing-radius turn, you may need some rear downforce (some trim tab) to tidy up your rear. Neon's fwd, inherently an under-steering dog. Your suspension setup needs to be tweaked in a low-drag profile.

Most will recommend a fastback modification (top-speed numbers), the 'most bang for the penny' budget that you have. Study the templates and many comments from eco-modding practitioners with their own real-life 'test' vehicles.

Very interested what you will implement and eager to follow your tests/races/performances. Good luck.

[euromodder]

Originally Posted by Vanquizor

Given the information above I'd say its mighty unfortunate that the stock rear window angle is somewhere between 30-35 degrees...

Make it 12 degrees with lexan and taper in the sides aft of the C-pillaras well - essentially making a boattail over the trunk area.

Getting the lexan to conform to a compound curvature rear window will likely be tough anyway.

[Vanquizor]

Assuming I'm going with a 4 section flat bottom, section 1 being the splitter to front rad support, section 2 the bottom of the engine bay, section 3 the main underbody, and section 4 the diffuser. what kind of angles should I be shooting for with respect to the ground?

I'd kinda pictured the first 3 as parallel to ground and the 4th at about a 5 drgree angle, but not set on that. If I pitched the whole underside at 2 or 3 degrees it would allow me to get a gentler slope on the rear fastback...

[dennyt]

This post has some interesting plots.

3 degrees for minimum drag, and more is better (the graph only goes up to 12 degrees) for downforce.

[botsapper]

...if you are installing a deep front air dam & deep perimeter skirts, are there a substantial gains from a full belly pan & diffuser. Unless you intentionally an underside center channel and create an effective venturi tub/rear diffuser, the low air dam/side skirt combo mainly divert over & side air flows and greatly minimize underside flow.
Anyone, any prior/comparative results?

[Vanquizor]

Originally Posted by dennyt

This post has some interesting plots.

3 degrees for minimum drag, and more is better (the graph only goes up to 12 degrees) for downforce.

I saw thoese, its partly the reason I was envisioning about a 5 degree angle on the 4th (diffuser) section. What I haven't seen is anythign saying if its better to have the sections in front of that parallel to the ground or pitched in one way or another.

Right now for simplicity sake the plan is to have a flat bottom from front to back. Here's a bit of construction detail for section 3 (the main underbody & side skirts)

[Vanquizor]

And so it begins....








Any thoughts on how tough it would be to build an effective venturi tunnel into the underbody given I'm working with used furnace ducting?

[Vanquizor]

still pondering full smooth underbody vs. venturi, but the side skirting is on (28g furnace ducting)




And then I got to work on the fastback... a little 2x2, some painters tape and duct tape...


A little fiberglass, a little bondo...



Add an adjustable spoiler for good measure... CHUMPTASTIC!


The fastback itself sits at an 18 degree angle with respect to the roof, by adjusting the height of the rear spoile I can tweak the effective angle between the roof an the tip of the spoiler from the 18 degree starting point down to as shallow as 12 degrees. Right now the plan is to run the spoiler high an proud, then keep lowering it till we no longer see a measurable increase in speed on the front straight. Any bets on where we'll stop?

I wish I had a rear shot showing the inward taper of the fastback, but at its termination point it is 50% the width of the rear of the vehicle.

Given the work to date- comments? suggestions? Quit cluttering the forum nobody cares about your crap can?