Big Van airdam/side-skirt design suggestions

[mwilliamshs]

Originally Posted by Goofy1

Wow, something I have a tiny bit of experience with!!...2. I blocked off the grill...

Originally Posted by Varn

I drive a 2005 Econoline and had a 1990 before that. One thing that has helped the economy is to put three layers of metal window screen behind the grill work....

My grill blocking^ (far right column is blocked) from here: Big Van trashcan grille block

Originally Posted by Varn

...Running the tires at max pressure helps.

^Not exactly original advice but valid all the same

[deejaaa]

Originally Posted by Angib

The real textbook on how to make a van more aerodynamic was done by NASA Dryden back in the 1970s/80s:

A Reassessment of Heavy-Duty Truck Aerodynamic Design Features and Priorities
(Oops, first post, so can't link to file - google 88628main_H-2283.pdf and it will get you to their report.)

This has lots of scientific testing of real-world(-ish) aero mods which will teach anyone something - for example they tested a full boat-tail and a truncated one with precious little difference (Cd=0.242 v Cd=0.238).

looks like a good read. here's the link:
http://www.nasa.gov/centers/dryden/p...ain_H-2283.pdf
from the Abstract:
"The demonstrated increase in base drag associated with forebody refinement indicates that the goal of a 0.25 drag coefficient will not be achieved without also reducing afterbody drag. A third configuration of the test van had a truncated boattail to reduce afterbody drag and achieved a drag coefficient of 0.242.
These results are included here and references are identified for other means of reducing afterbody drag."

[aerohead]

This image is online,but there's no discussion.
The car is a modified 1983 GM Aero 2002,which was originally Cd 0.14.
New skirts use a lower flow fence to sequester the air above the belly line,while allowing sectional density control between the wheels.
The flow fence is continued behind the wheels.
It would have been beneficial had someone with GM mention why they chose this streamlining path.

Here's link to the original '83 Aero 2002
http://deansgarage.com/wp-content/ga...hcenter650.jpg
Here is the '84 Citation IV, Cd 0.18
http://storkli.com/wp-content/upload...on-IV-1984.jpg
The car at the top is referred to as the GM Aero.With full skirts,it's more refined than any of the 'published' cars.

[Varn]

Looks remarkably like Tony's (arcosine) saturn

[freebeard]

The doors are at the maximum body width and have a high step-over height on ingress/egress. Maybe it's to pull the bottom of the door inward while maintaining a beneficial bottom edge.

[Varn]

You might try putting in about 3-4 layers of window screen in your grill. When I drive my econoline it is usually loaded (unfortunately) and getting about 18 mpg. If I can't fill it I drive something economical.

Originally Posted by mwilliamshs

My grill blocking^ (far right column is blocked) from here: Big Van trashcan grille block



^Not exactly original advice but valid all the same

[aerohead]

I added links to the original Aero 2002 and '84 Chevy Citation IV concept, Cd 0.18,at #33 permalink.

[Sven7]

With that shark nose, depending how much time and money you want to spend, you might want to try to make your way toward something like this:



Or this (taller, of course):



It is generally said around here that you want a low stagnation point, something the semi truck doesn't have. Do this by angling the front surface on your vehicle backward to let air flow over and around the body instead of over it.

As for the air dam, I made mine slightly curved and I have the same front bumper as your van. I don't know if it really matters that much, but you may as well put a sublte curve in it if you can.

As was said earlier, you might consider a box cavity on the rear. We haven't had many EM'ers try them, and I never got a good chance to test mine on the Probe. Will you be the first? Otherwise, boat tail!

[fbov]

My $0.02 - don't forget crosswind stability.

At issue is the tendency of a car in a cross wind to steer into the wind (stable) or away from the wind (unstable). Those familiar with Hucho know that a square-cornered box is stable, and a sleek teardrop is not. There's a reason Porsche 911's all have wings.

Looking at the trailer lead edge treatment, I'll wager the open end has the beneficial property of increasing drag in crosswinds. That's the trick; you can get stability from a low drag body by increasing drag in crosswinds.

This isn't something you want to learn on the road...

HAve fun,
Frank

[aerohead]

Originally Posted by fbov

My $0.02 - don't forget crosswind stability.

At issue is the tendency of a car in a cross wind to steer into the wind (stable) or away from the wind (unstable). Those familiar with Hucho know that a square-cornered box is stable, and a sleek teardrop is not. There's a reason Porsche 911's all have wings.

Looking at the trailer lead edge treatment, I'll wager the open end has the beneficial property of increasing drag in crosswinds. That's the trick; you can get stability from a low drag body by increasing drag in crosswinds.

This isn't something you want to learn on the road...

HAve fun,
Frank

I think that crosswind stability issues for teardrops is a dead issue since 1976,after Morelli's CNR work with Pininfarina.
Center-of-pressure issues were resolved with fin area behind the rear wheels,also acting as fairings.
I don't have issues with the truck and she's zero-lift also.Goro Tamai at MIT considered them extremely stable platforms.
Porsche 911s are pseudo fastbacks,with significant rear lift due to separation over the aft-body.They are not proper teardrops.