Meet Grumpy the Rally Van

[ihatemybike]

I'm thinking homemade vortex generators. I have a couple non-operational TVs that could donate their cases. Where to locate them? I've read where people have them about 3" from the back edge on their wagons. Will my van be about the same?

[GasSavers_RoadWarrior]

If you've got a large dead TV, you might wanna see if the rear casing can be used as a grille blocker/nosecone. (Cut a 4-6 inch wedge off the top and stand it on the bumper...) typical TV vent sizes should aerodynamically block at highway speed.

I'm beginning to realise that modding minivans is a balance between reducing base drag and causing higher induced drag. At the moment the lift force generated by the van is probably perpendicular to a line drawn between the bottom of the front bumper and the top back corner of the tailgate. Now, adding turbulators to the roof will probably make the air "tuck in" a bit behind the van... but it will have altered the effective angle of attack, such that the lift vector is going to be perpendicular to a line from the front of the hood to the top back corner.. hence less forward component to the lift.... you can see that if you do a fully faired back on the vehicle, it may alter this line such that the lift force is exactly vertical, or even negative. This is why current cars are going for a clean edge separation higher up the rear of the car...

However putting vortex gens on the sides may have more benefit, since the top down profile of the vehicle is fairly square so there is minimal lift components to the sides to alter for the worse. At this point in time my thinking is that they could be dual purpose, encouraging upwash of the airflow across the sides of the vehicle to help the apparent angle of attack. Therefore I'd suggest delta shaped vortex generators be placed on the sides angled parallel to the line between front bumper and back corner... Also rear underbody treatment should be arranged to compliment this and angle air upward behind vehicle...

[ihatemybike]

Astro fanatic says, "My van aint mini!"

I'm such a noob, had to read through that many times.

So my current lift force is probably ok. Is there a way for me to check that? I'm thinking about making a few wool-tuft runs, will that show me?

How would I go about the rear underbody treatment?

[GasSavers_RoadWarrior]

Wool tufts will show you where you're getting separation and turbulence and the direction of flow on various surfaces, but it won't really tell you much about the angles for induced drag.

[Big Dave]

I have spent some time burning brain cells on the problems of vans. Vans are useful vehicles for certain missions but their truncated tails leave them with an enormous wake area. Grumpy could be the pioneer into the 'land of basjoos' for vans.

Imagine this: A fiberglass boattail attached to the back of the van. It could be either one piece, hinged at the top and raised by electric actuators, or a two piece split along the long axis and opened manually and laterally. How good a boattail it is depends on your tolerance for vehicle length. In both cases, the key is a set of strong hinges with very solid anchor points.

Because properly boattailling a 79 inch wide vehicle would require a minimum 72 inch long tail, you would probably want to truncate the boat tail at some point. Enter Dr. Kamm. The max angle before flow separation is about 29 degrees and the tangent of that angle is 0.554. 40 (half the width) divided by 0.554 is 72 and change. A six foot tail.

If you have done any fabricating you will come to appreciate 25 degrees which is a 6:12 pitch. Easy to lay out. Now your theoretical tail lengthens out to 80 inches ? as long as my pickup bed.

But if you truncated at 24 inches your wake area would be reduced by 54% and now would be roughly that of my faired pickup truck.

Nice thing about Grumpy is that you could weld on hinges and experiment with angles and find out just how much of a tail you can live with.

Basjoos started with a relatively small car and could go for a relatively pure boattail and still wind up with a reasonable-sized vehicle. With an 80 inch long tail, Grumpy would look like a brontosaurus. But I think you could find a happy medium somewhere in there.

[brucepick]

Wow - good luck in the run to Big Easy!

Definitely a basjoos-style front end would be the best front you could do. But it would be pretty big.
General wisdom is that on a square-backed beast (mine is a wagon) the aero losses at the rear are more significant than the other aero losses. So, if you have the nerve to build a good boattail that will probably help a LOT.
Pics of my pipedream boattail, which I'll likely never build.
http://i188.photobucket.com/albums/z...earView400.jpg
http://i188.photobucket.com/albums/z...ideView400.jpg

See the pic of my front grill panel to the left of this post.
It replaces all the headlight trim and the radiator grill.

Just recently I made a new one with Lexan (like plexiglass but hopefully more durable) covers over the headlight cutouts. Sorry, no pics yet - my camera went AWOL. It also has a simple rectangular cutout for radiator, with a center post. I have strips of different widths that I can slip in to block off part of the center opening. They press against the center post and at the sides, no fasteners needed. I use the biggest blocking strip that doesn't overheat the system.

Main panel attaches with four screws, one at each corner. It's cut oversize so it bows into shape when attached. Overall shape of panel is very similar to a windshield. It's a section of a cone. Mine is 2.7 mm. lauan plywood. Oil base house primer, then Duplicolor pickup bed liner over that, black textured stuff. The bed liner is very tough. Regular spray-can finish color didn't hold up.

[360ci]

Keep in mind going over a vehicle's size dimensions can have insurance consequences depending on your agency.

I'd add a homemade air intake (cone filter will run about $30 or so, plus another $15-20 in home depot pipe parts and clamps), and synthetic oil with new spark plugs. Total cost shouldn't be more than $115 and a few hours of your time.

Speed is the main killer of mpg, keep it at or under 65mph and you'll get at, if not above 16mpg for sure.

[red91sit]

Is this an off road rally? If not perhaps lock the center differential and drop out the extra driveshaft, differential, and axles. Definetly smooth up underside flow haha.

[ihatemybike]

Insurance is cheap, it insures and plates as a passenger car.

The air intake mod you describe has been reported to decrease mpg when done inside the cramped and hot engine compartment of the Astro. On my good Astro I installed a K&N filter than changed the intake routing to the drivers side drawing cold air from behind the left hand turn signal. Seems to work pretty good, but I have some off road plans from Grumpy after the rally and want to keep the intake in a higher location. Maybe I'l try to figure out some cowl induction.

I've been mostly keeping to 65 or under for my regular driving. I'm already able to get 16 mph pretty regularly. I'm working on my semi drafting technique. My current goal is mpg.

This is kind of a gimmick rally, speed is not important, but matching photos, spotting plates, and other various tasks to gain points is.

[korax123]

I would strip out the entire interior if you don't have to haul any people to save on a lot of weight. Heck it problably has 2 captains chairs and a 3rd row bench.

So you problably would save 150lbs or so. Even the sound proofing under the carpet is heavy. Save about 200lbs off the total of the van it will help out a lot.