Kenworth Truck--air dam

[DonR]

Somewhere I read about mounting a turning vane (what was essentially a cut section of pipe) at the cab roof top & at the edged of the windshield/door junction. This is supposed to turn the air so it runs down the sides of the cab & box trailer, which you don't have, more smoothly.

Here is a link to a manufacturer of "low drag" flaps. Also supposed to help rearward visibility in the rain.
Eco-Flaps

An outfit called AT Dynamics makes wheel covers & trailer skirts. The skirts wouldn't fit your trailer, but may give you some ideas if you don't use toolboxes.

Let us know what works for you. I need to work on my Inlaws & their grain truck.

Good luck
Don

[davidgrey50]

This link covers, at least in a general way, most of your questions. Freightliner unveils big rig concept showcasing future technology — Autoblog Green
Good luck!

[usergone]

Hey guys, I went and found some pics of the truck, so we can see what he's working with.




From the looks of things IMO you could help with an air dam (like you had in mind) and skirt the side of the truck from the end of the black step area all the way to the mudflaps. For the mirror on the passenger's side on the hood, maybe a parabolic "wind break" would help a bit.

Also, there seems to be a lot of ground clearance under the truck. How about an impact-safe skirt on the side that goes as low as possible/legal. Impact safe, meaning that you can high center without tearing it up, like some kind of rubber sheet or coroplast.

[euromodder]

Originally Posted by DonR

Somewhere I read about mounting a turning vane (what was essentially a cut section of pipe) at the cab roof top & at the edged of the windshield/door junction. This is supposed to turn the air so it runs down the sides of the cab & box trailer, which you don't have, more smoothly.

European truck often have a vane at the lower corners of the cab (which are mostly cab-over-engines)

In the picture below they're visible on both sides of the top grill, in this Volvo pic, they're most obvious on the right side of the cab.



The sunshade at the top of the windshield performs the same task. While not always visible, they're open at the aft end where they are attached.

[euromodder]

How about Air Tabs ?
They're designed and sized for trucks after all ...

(Test on passenger cars didn't show an improvement in mpg though.)

[aerohead]

Originally Posted by KWTrucker

Greetings,

I run a KW T600 truck and step deck trailer. It is not practical to skin the underbody of the truck, though perhaps it might be for the trailer. I would like to pursue an air dam for the truck and have continuous tool boxes to install down each side of the trailer to provide storage and skirting.

The issues raised in "Aerodynamics of Road Vehicles" conclude that an air dam will help up to a certain "height" (they discuss the height in relation to how far it hangs down from the bumper) but after it exceeds that height (i.e. gets too close to the ground) the effect becomes detrimental.

Further, there is reference to the work of W. H. Hucho, et al, where it was demonstrated that an air dam by itself (properly designed) reduced drag by 2%. They then added sort of a mustache dropping down just slightly from the from lip of the hood. This also achieved a 2% drag reduction. However, when these two mods were combined, a total dray reduction of 8% was achieved. (Lift was also reduced, though this is little concern for my truck).

Is anyone familiar with this combination or concept? The references in the book include 4 basic drawings (dimensionless) and sort of a fleeting reference to "properly designed" being necessary.

Any help in reducing the learning curve would be appreciated.

Fiat's Auto Wind Tunnel Dept. researched the airdam in the above cited paper.
For 'low-drag' cars the dam created a shielding effect good for delta-Cd 0.025,but it also caused a concomitant growth of both upperbody drag ( 0.054 ),and engine-cooling-system drag ( 0.008 ).
At some point for 'dirty' underbodies,drag reduction is nullified by the braking effect of a Cd 1.11 flat plate correspondent of an airdam.
Everything has to be taken on a case-specific basis.
I would recommend you maintain standard ground clearance.And I'll get in trouble for saying it.

[SvdM]

Originally Posted by davidgrey50

Freightliner unveils big rig concept showcasing future technology — Autoblog Green

Originally Posted by aerohead

At some point for 'dirty' underbodies,drag reduction is nullified by the braking effect of a Cd 1.11 flat plate correspondent of an airdam.
Everything has to be taken on a case-specific basis.
I would recommend you maintain standard ground clearance. And I'll get in trouble for saying it.

No trouble from me Aerohead. I agree; you take something away and it gets added somewhere else - or so it seems with aerodynamics - hehe.

The link shows us how the pro's do it One can see that they still let a lot of air in underneath the truck, but it's nice to see how the front air-dam then drops in front of the wheels to get air going around-, rather than 'stuck' in the wheel-wells. Hence, the designers and engineers try to get the airflow over, around and under as smooth as possible whilst trying to increase the total frontal area as little as possible in the process.

[Patrick]

What's with the giant holes in the drive wheel skirts?

[3-Wheeler]

Thanks for the pictures! That helps allot to have something to look at.

The mirrors could be cleaned up by the following:

http://ecomodder.com/forum/showthrea...pes-11183.html

See figure 12.

The shape should be "closing" to reduce the mirror wake size.

The shape could easily be carved from foam, but will need to be covered or painted to keep the UV from degrading the foam. Latex paint works good for this.

Hope this helps.

Jim.

[Patrick]

Originally Posted by 3-Wheeler

The shape should be "closing" to reduce the mirror wake size.

If you use the same mirror and the shape is closing then you have made the fairing larger than necessary and therefore increased the drag.

In other words, the Cd may be lower, but the frontal area has increased.

I wonder how a larger-than-mirror-crossection fairing that closes somewhat toward the rear would compare to a same-size-as-mirror-crossection fairing that was just straight back where it met the mirror?