Big Van airdam/side-skirt design suggestions

[mwilliamshs]

Planning my air dam and side-skirts. Ordered landscape edging for the lower portions and steel for some bracing. Going to look at aluminum Tuesday.



So with the very square and straight front end of my van and its mostly straight and square sides, I'm torn on what shape is best. In the pic below you can see that the grill slopes inward somewhat toward the bumper, likely creating a high-pressure point there. Ford put a pair of large grill openings there (see top picture), likely by design to take advantage of this high-pressure area for cooling air flow.



The questions for me are 1) should the airdam be straight across the bumper or be curved inward from the center toward the tire on each side? and 2) Should the side-skirts start inboard of the front tires' rear edge (closer to the centerline of the body) or be straight inline with the body itself? Inboard seems like it would keep the air stirred up by the tire from getting trapped underneath but inline seems like it would keep things more streamlined on the sides of the body, especially since my airdam will keep most of the air off the front tires and they now (thanks to new tires and wheels) sit nearly entirely inboard of the fender edges and finally 3) what should the skirts do behind the rear tires? I think they should probably pitch inboard from the rear inner finderwell toward the body's centerline but I'm not sure.

Any help here would be great! Looking forward to suggestions so I can start construction.

Here's a cropped image of my van if anyone needs it for some artwork. That'd be awesome BTW.



Here's another one somebody shared in another thread. The grille slope can be seen here. My van isn't exactly like the one pictured as my roofline is higher and my overall length is 20" longer.

[freebeard]

Looking at aerohead's drawing, it would obtain only if the body width is twice the height because you get a similar taper on both sides as well. With a square body the side tapers will meet in half the distance. Generally, for your purposes a Trailer-Tail™ type folding box cavity would serve well.

I think they should probably pitch inboard from the rear inner finderwell toward the body's centerline but I'm not sure.

I'm not seeing this. For the wheelwells on both ends, I think this makes sense:


In case it doesn't show, those deflectors are splayed out the width of the tire. In front the inner, the forward ends would need to be trimmed to allow the wheels to turn, then transition into a side skirt. aerocivic uses two side skirts making a tunnel between the front and rear tire. Here's the theoretical ideal:




This allows for front and rear departure angles. Notice the center angles to allow for high-centering.

I believe you don't want to increase the front overhang, but something like this would soften the front edge:



A good opportunity would be to ad a fillet from the top of the windshield to the front edge of the pop-top.

[mwilliamshs]

Originally Posted by freebeard

Looking at aerohead's drawing, it would obtain only if the body width is twice the height because you get a similar taper on both sides as well. With a square body the side tapers will meet in half the distance. Generally, for your purposes a Trailer-Tail™ type folding box cavity would serve well...

The first sentence of that completely evaded me. My overall height is about 90" and width is about 80". I agree about the tail but that's not at all what I'm working on at present, just the air dam and side-skirts for now. I know most of the potential for gain is in the tail but I drive 90% in the city where aero gains aren't very large to start with and where a tail adds complexity with most any mod (parking in parking garages, at my apartment, etc) whereas an air dam and skirts can be largely forgotten in every day driving.

Originally Posted by freebeard

...In case it doesn't show, those deflectors are splayed out the width of the tire...

I don't think they are. I'm pretty familiar with that body and its wedge shape (both vertical and horizontal) is likely just meeting up with a straight "deflector" by virtue of it narrowing aft of the rear wheel. I get what your saying though. Wouldn't splaying the skirts out like that increase the vehicle's wake?

Originally Posted by freebeard

...aerocivic uses two side skirts making a tunnel between the front and rear tire...

Nice but impractical unless your vehicle is suited to that design. My long axle beams (reach from wheel to opposite frame rail), solid rear axle, nearly identical track widths front and rear, and large underhanging frame rails, crossmembers, etc prevent such a tunnel.


Passenger's side^ Driver's Side \/

Originally Posted by freebeard

...This allows for front and rear departure angles. Notice the center angles to allow for high-centering...

My very minimal front overhang should make approach angles quite good and my departure angle is already quite terrible but I'll certainly keep those realistic. As for high-centering, I plan to drive over the biggest speed bump in my area and give it an inch or so of clearance to the bottom of the skirts. The landscape edging is of course used as a wearable edge.

Originally Posted by freebeard

...A good opportunity would be to ad a fillet from the top of the windshield to the front edge of the pop-top.

Plans include adding a roof-rack type cross bar at the fore-most edge of the rain gutters and affixing a wind deflector there. Crossbar and deflector would of course be far more streamlined than that tongue-in-cheek example. Solar panels are in the works (for cold drinks whilst camping, not vehicle propulsion) and must be sorted before other roof mods.

[freebeard]

The ideal Template is half-circular in section, and diameter is 2x the radius. Maybe you can infer it from this:

I don't think they are. I'm pretty familiar with that body...

Trust me, I was there and took the picture. The rear edge was in line with the outside of the tire. It makes what aerohead calls a divergent nozzle (I compare to an exponential horn loudspeaker). The inside faces act to slow down the air under the body, raising it's pressure.

Nice but impractical unless your vehicle is suited to that design.

Originally Posted by aerocivic

Side skirts made of coroplast (there are 2 side skirts on each side, one even with the inner edge of the tires, the other even with the outer edge of the tires).

http://ecomodder.com/forum/showthread.php/aerocivic-how-drop-your-cd-0-31-0-a-290.html#post2111

You're probably right about the high-centering, but that's a long wheelbase. I've seen an 18-wheeler that ran aground and was immobilized on a railroad crossing.

The retractable trailer tail may be too much trouble. Here's a stepped box:



This could be mounted on the rear doors and hinge with them.

[oldtamiyaphile]

Here's and image you might find interesting.

The naked van scores 0.44Cd

The small pop top increases that to 0.45

The large pop top increases that to 0.51

The big high roof reduces CD to 0.40

and the big camper surprises with a 0.46



As for the airdam, I'd curve it if possible. All the new Euro vans have quite a curved front end in plan view.

[freebeard]

Cd is only part of the story, there's also A(rea). Those numbers are:

• 1.35
• 1.40
• 1.62
• 1.44
• 2.38.

I didn't remember the slide-on camper as being part of the sequence, so thank's for that.

The large pop-up increases the frontal area 'unnecessarily' (it's a stowage bin). Drawing a curve from the slope of the windshield to the top front edge of the pop-up would be most like the high roof.

With this body the stagnation point is at the front edge of the hood. Everything below that is going under the body. I'd make it straight and push it out to the hood-line.

The other problem is the square corner; look at the later models. The air dam, by my estimation, is only 1/7th the height of the front fender. That's why I'd suggest adding a 1/4-round outside the headlight.
_______

Lot's of room on the pop-up for solar panels.

[mwilliamshs]

Originally Posted by freebeard

...diameter is 2x the radius...

Yeah, I think I've read that somewhere before.

Originally Posted by freebeard

...With this body the stagnation point is at the front edge of the hood. Everything below that is going under the body. I'd make it straight and push it out to the hood-line...

Interesting. Very interesting. I know my stagnation point is different due to the difference in body shapes and because my van has an open grille in the front with a large engine-driven fan creating a low pressure area behind it, which the vanagon does not. IF I went with a straight dam, what should I do with its ends, the edges nearest the tires?

I'm curious why some vans shown above do and some do not have airdams or at least they have different varieties. Anybody know?

Originally Posted by freebeard

...The other problem is the square corner; look at the later models. The air dam, by my estimation, is only 1/7th the height of the front fender. That's why I'd suggest adding a 1/4-round outside the headlight...

What's a 1/4 round? I get that it's a 90* radius (one-fourth of a circle) but as related to a car body, I'm at a loss. How big are we talking? Some proportion of the body's size?

Originally Posted by freebeard

...Lot's of room on the pop-up for solar panels.

Not as much as I'd like lol. I think about 400w is all I'll be able to fit.

Picked up my edging today. 60ft of Pro-grade Royal Diamond for $20 off Craigslist. A guy here in town just bought too much and the box had been rained on so the store wouldn't take it back. It's $47 on Amazon, $35 at Home Depot.

[mwilliamshs]

Originally Posted by freebeard

...Trust me, I was there and took the picture. The rear edge was in line with the outside of the tire...

The shadows of the rear tire and skirting don't align. Not trying to be argumentative and I appreciate all the input, just saying it's tough to tell from the picture.

[freebeard]

The shadows of the rear tire and skirting don't align. Not trying to be argumentative and I appreciate all the input, just saying it's tough to tell from the picture.

Shadows on the ground is what had people calling 'hoax' on the Moon landing. Compare the rear edge to the corner of the body.

What's a 1/4 round? I get that it's a 90* radius (one-fourth of a circle) but as related to a car body, I'm at a loss. How big are we talking? Some proportion of the body's size?

The 3D rendering of the camper shows a half-round. I said quarter because of the headlights. You could go half-round with a cut-out or recess for the headlight. The rule of thumb is 4% of gross body width, minimum, so 4 inches or less.

The cooling air is a fraction of the air moving over the body (water-pumper Vanagons do have a front radiator). The fan is to overcome internal air friction.

I'm curious why some vans shown above do and some do not have airdams or at least they have different varieties. Anybody know?

They're from different sources. Different strokes for different folks. As for the outer ends, ultimately you'd want an air-curtain for the front wheelwell. Here's a rendering that is indecipherable (I had a system crash and never retraced the steps).



Sort of an anti-spat. Radiusing the edge and aircurtaining is probably nit-picking. Keep in mind that I'm speculating way beyond my direct experience.

[kach22i]

I had a 1976 short box Ford van back in 1983-84.

I installed a deep sheet metal chin spoiler with a garage door bottom edge rubber, and I recall being able to get a nice broad arc to it.

I had the same problem back then as I had a few years ago on my S-10 when I tried lawn edge material, people kept bumping it with their low car bumpers while parking.

The sheet metal would dent, the lawn edging eventually would crack.

I now use conveyor belt material, much more expensive, but will last more than a few years.

I've found that the greatest attribute of a deep chin spoiler is better control and near immunity to cross winds on the highway.

As for the rear where most of the drag happens, something like the baffles currently retrofitted to large semi truck trailers, or something like the below may help.

http://ecomodder.com/forum/showthrea...uck-26367.html





Mesilla Valley to put Aerodynamic Tails on 4,000 Semi Trucks


Someone mentioned curved leading edge corners.

Custom Trailer Aerodynamics | Freight Wing


I recently saw a semi-truck on the hi-way with the rear baffles installed, but not deployed, they were still stuck flat against the back. You can lead a horse to water.............

Your other choice for front corners?

http://ecomodder.com/forum/showthrea...ces-21242.html