Bionic Van

[Big Van]

I'm sure everyone on this forum has heard of the Mercedes "Bionic car" based on the boxfish... I'm wondering if I could apply any of its principles to modding my 15 passenger van, as suggested here:

Fuel Efficient Vehicles Now! - Bionic Vans Trucks & Buses

Or maybe something like this:

AeroTruck 1

The boxfish car claims a Cd of .19. I know the enormous area of a passenger van would blunt the effects of a slippery shape, but I figure anything's worth a shot.

Can anyone enlighten me as to why the Mercedes's shape is so much more efficient than a normal van's? Could I work some kind of cloroplast wizardry to emulate it on my own vehicle? Thanks!

[Daox]

Well, the overall shape is quite a bit more aerodynamic than a conventional van. You could definitly work on rear wheel skirts and an under belly pan.

[aerohead]

Conventional vans are for hauling,and are optimized for useful interior volume.So you get a lot of floor area you can stack stuff,right up to the ceiling.Its a cubist's dream come true! The down side,is that vans tend to be slab-sided,with very little plan- curvature ( curvature to the sides when viewed from above),and a relatively flat roofline.--------------------------------------------- This means that the van is basically a "full wake" vehicle.The cross-sectional area of the van,from the windshield back,is constant,at full projected frontal area,until the very back of the van.This means that the wake of the van is also the size of the full cross-sectional area of the van.Really big!!!!!!!!!!!!!!!!!!!!!!!!! ------------------------------ With the "bionic" car,you'll notice that the roofline curves gently down as it projects towards the rear of the car.Also,if you were above the car,looking down,you'd see also,that it was growing ever so slightly more narrow from front to back.This is where the Cd0.19 comes from.--------------------------------------- For your van,the air is disturbed from it's "rest" position,knocked out of place and accelerated to about 1.3-times the velocity of your speedometer,and since there is no narrowing of the body,the air stays completely out of equilibrium,until the van passes,where it tumbles into the void left behind the van,creating an enormous wake of turbulent air which cannot convert itself from its state of kinetic energy,to the calm,atmospheric pressure air it was before you came along.This in essense is your aerodynamic drag.--------------------------------------- And for your van there is no easy remedy,as the only way to get the air re-organized without turbulence,requires a lengthy tail.You could do all the mods you see for the Fed Ex concept truck.This would reduce the forebody drag,when combined with a full bellypan.You might see Cd 0.20.------------------------------------------- If your at say, Cd 0.38 now,and you could cut drag to 0.20,that's a 48% drag reduction,and would be good for about 24% better mpg at 55-mph,a little better at 70-mph,I don't think you could do better unless you cut into the roof and sides,and re- designed the rear 1/3rd of the vehicle.All your time trouble and material expense would have to be recouped in fuel savings.And you'd be losing interior space.--------------------------------------- A boat-tail will give you some savings,but the extra length can be a real issue when parking.-------------------------- you may want to do a ecomodder search for aero-mods # 11(aftbody streamlining/boat tails),there is some empirical data for you to peruse and may be of benefit to you.

[Big Van]

Thanks, Aerohead, your explanation was really helpful. So I guess the best thing to do is to try to go from "rough brick" to "smooth brick" with a belly pan, wheel skirts, etc. I might also try something like this for long hauls where parallel parking isn't an issue:

Green Car Congress: New Boat Tail Design Could Improve Class 8 Truck Fuel Economy by 10%

I don't think I'm ready to invest in the ultimate solution:

AeroTruck E-38096: Air flow testing on aerodynamic truck

[NeilBlanchard]

I think the comparison between the van and the Bionic "Boxfish" car is reaching.

[aerohead]

Originally Posted by Big Van

Thanks, Aerohead, your explanation was really helpful. So I guess the best thing to do is to try to go from "rough brick" to "smooth brick" with a belly pan, wheel skirts, etc. I might also try something like this for long hauls where parallel parking isn't an issue:

Green Car Congress: New Boat Tail Design Could Improve Class 8 Truck Fuel Economy by 10%

I don't think I'm ready to invest in the ultimate solution:

AeroTruck E-38096: Air flow testing on aerodynamic truck

What NASA did is what I did to my VW van in college.Rear skirts,full bellypan,and 18-inch long boat tail.She could hit 35 mpg on a good day.You can make the bottom more horizontal than NASA did.If you can deal with the extra length,they're money in the bank!

[Big Van]

Whoa, that's encouraging! Since the thing's already as big as a whale, an extra 18 inches isn't terrible... Maybe I can make it so it folds flat against the sides of the van when not in use.

[aerohead]

That's the trick.And the jury is still out,with respect to the "best" solution.I did a fan-powered inflated tail also and it worked well.It was a crude proof of concept and I'll probably re-visit that one.If you look carefully at the NASA link photo,you'll notice that the tail starts out with very little curvature.The further it goes,the steeper it gets,to a point where it follows basically a constant angle from there back.If you start too steep,the flow will separate,with little benefit to your wallet.Scale that photo to your van,and you ought to be good to go!

[dadag]

just for fun

[aerohead]

I don't think the World is ready for Luigi Colani.I think the atmosphere is though.