Rain Gutter Side Skirts
 

Hello -

The wonders of Saturn plastic paneling helped me again. I took a rain gutter and attached it as a side skirt to my SW2 :

http://ecomodder.com/forum/member-cf...-installed.jpg

This has been bubbling around in the back of my head for a few years. I can't believe how easy it was to do. I just :

1 - Removed the plastic rocker panel, held on with the plastic push bolt thingys :

http://ecomodder.com/forum/member-cf...emove-only.jpg

2 - Figured out that I had a lot of "interior volume" to work with :
http://ecomodder.com/forum/member-cf...rior-holes.jpg
The holes for the drop-down bolts were drilled in the "cavity" area (the round interior volume). There was a problem in that if I remove the wingnut, the bolt could "fall up" into the cavity. I solved that by gluing pipe insulation above the bolt. This way the bolt will stay in place.

3 - Attached with 3 bolts :
http://ecomodder.com/forum/member-cf...s-bottom-i.jpg
The wingnut attaches at the bottom. I just unscrew three winguts and the side skirt comes off. I dremeled the "curvy" part of the rain gutter off because it made it harder to get at the plastic pushpin thingys. Now I guess I could have left it on, but I am still happy with the current result.

I deliberatly chose the location of the holes on the theory that the weight of the vertical part would "pull down" the gutter and keep the horizontal portion "pushed up" against the bottom of the rocker panel. If I had centered it, I think the vertical part might have a tendency to pull down the gutter and "sag", if you know what I mean.

Here is how the "attachment sandwich" looks

Benefits :
1 - Cheap. $7 for the rain gutter. I don't count the bolts, washers, and wingnuts. because I can reuse them for other things. Bolts n' stuff are always good.
2 - Easy to make.
3 - Easy to remove. I need to take it off when the car is going into the shop.
3 - 100% reversible. It only cost me three drilled holes where nobody can see. There is already a hole in the rocker panel that I think is for drainage, so I could argue that I am just adding a few more "drain points".

Problems :
1 - The rain gutter plastic is that kind that is "brittle", so it will be interesting to see what will happen when I bottom out and hit something. lawn edging would be more durable to impact, but I wanted the "L shape" to maintain rigidity and have a connection point to the rocker panel.
2 - White. Not really a problem, because it matches the car. If I wanted to be steatlhy, I could paint it black.
3 - In order to keep the bolt in place I used pipe insulation. If water gets into the rocker panel, it could swish around. But that could be solved with ... a few more holes!

In general, I am not a fan of "ground effects" on cars. However, I am happy that this is such an easy "exploit", and I do like how it looks on my car. If it turns out that it doesn't help or is problematic to maintain, no big loss.

I only made one for now to see how well it takes punishment. So far no bottom-outs, and I am not babying it (because I forget about it).

CarloSW2

Not bad at all! Do you have plans to do testing?

Nice!

I wish I could remove my rocker panels that easily!

Daox -

I guess I could, but I don't feel like there is a place in Los Angeles that I could do a reliable test. All paths are beaten (to a pulp) in LA. The good part is that it is so easy to take on/off that it wouldn't be hard to try to do the test.

CarloSW2

Why didn't you leave it a c? It would have helped to keep under car flow from contacting the tires, too... (basjoos-style)

Christ -

Very good point. It wouldn't have been a C shape per se, but it would probably have worked anyway. I cut it for clearance initially, and I was also worried about the inner side leading to sagging over time. By the time I thought about leaving it, it was already cut. My Dremel out-thought my brain.

To have a *symmetrical* inner panel, I could cut another one that I install on the inside. That could also get me closer to the actual tire width (not sure how important that is).

CarloSW2

I don't think I can postulate as to the importance of them being tire-width, but I did notice those pinch-welds would also be a great place to hang an inner skirt, if you were so inclined. They appear to be just inside of the tire's inner surface, which might be close to ideal. Of course, you probably won't want drill the pinch weld, but if you could mount the inners to the original rocker cover as well, you could use the pinch point as a guide, and mount your angle right into the angle created by it. You could also put some kind of sealant on the piece before you put it on, so that water/dirt don't get up in there. Silicone would work fine for this, even if silicone doesn't adhere to the plastic very well, since it will harden and work as a gasket without falling out. For no real good reason, other than myself having been a professional caulker, make sure you slick it down good so it's not all bumpy and stuff. :)

Very nice, cfg83!
My rockers aren't flat, they taper down at either end, so I had to do some fancy cutting and tucking.

http://i337.photobucket.com/albums/n...e/100_4190.jpg

You can paint them with Krylon Fusion spray paint.

http://i337.photobucket.com/albums/n...strakes004.jpg

Oh, and I have dragged them over a sharp hump. They're tougher than you may think. :thumbup:

Tango Charlie -

I just *knew* someone had already done this besides basjoos, but I forgot it was you (or were you the first?!?!? stupid brain, never helps when I need it)! Verrrrrry clean execution.

CarloSW2

I never would have thought those were rain gutters... go you!

Thanks, cfg83. No, I wasn't the first. I was inspired by Xringer. I'm not sure what basjoos used.

Now I need to get that belly paneled in...

My gutters have been on for over a year now (painted w/black Krylon as well). No problems from the few times I've scrapped them.

Hi folks,

Can I ask what is the intended aerodynamic function of these side skirts?

Personally, it feels a bit counterintuitive -- I would think that you want to have air "escape" out from under the car; and not to trap it under the car. And none of the ultra-low Cd cars that I am aware of have anything like this.

The Loremo has side skirts. Some high performance vehicles extend their bodywork down lower than the lowest point on the suspension.
I think the idea is that air wake generated by the tires does not propagate and further disturb the air flow underneath the car.

NeilBlanchard -

My (ever so flawed?) thinking is that I am separating the "clean airstream" from the "bad airstream", but I don't really know. With this mod I think I should create a "snow-plow" air dam to minimize the amount of air flowing under the car. If nothing else, in tandem with an air dam, I think this could be a form of "virtual lowering".

I did some flow simulation YouTubes and found something interesting. The imaging is a top view and is problematic, because none of the "objects" actually touch the ground, they only interfere with the air stream. I was trying to simulate the engine, transmission, suspension, and exhaust piping :

http://www.youtube.com/watch?v=WcCE7bYvUmE
http://www.youtube.com/watch?v=SQ3uZw-oUgw
If the above is showing a valid result, then the rear ( non-moving!!! - :o ) tires seem to have less turbulence associated with them.

CarloSW2

Rain gutter material also makes a nice front air dam...

I thought about trying side skirts but attaching isn't near as friendly as that Saturn. I'd have to fab something up, and would probably use more lawn edging. I got a bunch of it from spring cleanup piles earlier this year, some of it still brand new.

instarx -

Oh yeah, I remember yours. Fantastic work because it's so OEM-ish.

CarloSW2

Hello -

Based on this comment from aerohead :

I modified my side skirts to taper-in at the front *and* taper-out at the back. It was super-easy to do because there are only 3 wing nuts holding it up. I left the center wing nut the same and drilled new holes in the rain gutter on each end. The new holes were offset 1/2" from the original holes. That leads to this look from below :

http://ecomodder.com/forum/member-cf...kirt-below.jpg

And from the side :

http://ecomodder.com/forum/member-cf...-side-view.jpg

I don't think the taper-out at the back matters because the side skirt and rear front mudflap are already sticking out. It's probably a better compromise.

I doubt it will make a measurable difference, but I like the idea of copying the "trucker side skirt" model.

CarloSW2

Thanks for bumping up the thread. Ingenious idea.

Looks like a neat and cheap project. Did you notice a gain in fuel economy and or more stability going down the road?

intended function
 

They're borrowed from racing where they segregate the flow between sides and bottom (as pickups are using step rails today),making a 'flush' pathway for the air across the tires.Sometimes,air fence flow straighteners are added to keep the air moving longitudinally,not transversly).
The John Shinella' Trans Am Firebird units were shown in the Lockheed tunnel to cut drag.
Lower skirts have been used in ground-effects cars,but I don't think there's a drag advantage.
IMHO I would not have them lower than the belly.I used them on the CRX
http://i1271.photobucket.com/albums/...itled310-1.jpg

I'm listening

straighteners
 

The 1987 Olds AEROTECH would be an example
http://deansgarage.com/wp-content/ga...n_at_speed.jpg
A bunch of Pontiacs had these as styling features.

I want one

are the straighteners the horizontal surfaces (and the transition to such) at the rear of the skirts?

are the
 

Yes.They intrude into the airstream and create a physical boundary which directs the flow and helps isolate it from hostile pressure gradient across the 'border' which might otherwise induce a span-wise flow,spinning up into power-robbing vortices.
Once the flow is aligned with the fence,it builds momentum which tends to keep it moving in that direction.

i got most of that...
 

the horizontal fins on the side skirts...

is that about right?

spanwise flow
 

Yep,you've got a good handle on it.
For the spanwise flow,here's a better explanation:

If the pressure below the car was higher than the pressure besides the car,the high pressure air would bleed up into the lower pressure air alongside the car,moving transversly,or,sideways (spanwise if on a wing).
This transverse flow spins up into vortices,as a fast-moving tributary meeting a slow-moving river,or as the jet stream spins warm,rising,moist gulf air over Colorado into supercell tornadoes.
The vortices lockup kinetic energy which can never be converted to pressure,ultimately raising the pressure drag.
If the fence can keep the two pressure regimes apart,we can skip the vorticity.
Winglets on commercial airliner wingtips are a form of exaggerated fence which helps spanwise vorticity from forming.