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Old 10-03-2010, 10:10 AM   #1 (permalink)
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Kenworth Truck revisited, considering belly skirt?

Kenworth T600 tractor, 53 ft Step Deck trailer.

Earlier I had posted about installing an air dam as I thought belly skirting impractical, but am revisiting belly skirting instead. The basic issues to deal with are maintenance (mostly greasing the drive line, clutch, brakes, etc, and checking fluids in transmission, rear ends), and heat rejection from the engine, transmission, and brakes. Under the truck there is some grease spin off from the drive line. The trailer presents no real issues of either maintenance or heat rejection. The truck gets quite hot under the cab/sleeper area. There is heat from the radiator that flows here, heat from the transmission (it gets up to 200 Deg F) and the exhaust system runs under here. A leaking exhaust once melted once of the DOT plastic air hoses (the hose was about 30 inches from the exhaust)

I have purchased tool boxes that will run the length of the trailer that will be hung from the structural cross members that hold up the floor of the trailer. This will provide badly needed storage and also provide a modestly smooth side skirting for much of the trailer. The main beams of the trailer are curved on the bottom, so ground clearance varies depending on which part of the trailer is being considered. The tool boxes would be approximately the same distance off the ground as the lowest part of the trailer. Additional side skirting below the boxes may be beneficial, I don't really know.



I have considered three basic under/side skirting materials and am curious as to what other may think or what I maybe should consider instead. Weight is a major consideration of anything I do. Ease of sourcing materials is also important. As usual, cost must also be considered.

Option 1. Custom made tarp that would attach to a cable system and be able to roll up similar to a garage door. This would be suspended between two firmly anchored "rails" such as 80/20 or something similar. The tarp would include sewn in battens to reduce the chance of flutter. This would work under the trailer, but I think it would not work well near the exhaust and under the tractor.

Option 2. Polycarbonate roofing. This is very lightweight, affordable, easily available, easy to work with, and very durable. It is available in 26"x12' sections at Home Depot, Lowes, etc. This seems like it would work well under the trailer and also a skirting to cover the rear sides of the tractor over the drive tires. My main concern with this is that the material is not flat. It is either smooth curved "semi-circles" or "half-hexgon", both running parallel to the length. This does add significant rigidity to the material and keeps it nice and light. MAIN CONCERN: What am I likely to give up in aero benefits by having some sort of light "ribbing" running parallel to the air flow. This would increase the surface area, which in theory may reduce the surface pressure, I don't really know. Being under the trailer, would this even be much of a concern? The skirting under the trailer would be approximately 10-12 inches off the ground. While I don't particularly like the looks of this material for filling in gaps in side skirting, it seems like it would work well and be easy to work with for the sides as well. Thoughts?

Option 3: For under the cab area, either flattened expanded aluminum or perforated aluminum. "Expanded" is sort of the diamond shape holes, available in various sizes. Perforated is round holes simply punched in the sheeting. Expanded is cheaper than perforated and according to the manufacturer, is it stronger and/or stiffer than the original sheet. "Flattened" is where it gets run through a roller or press and makes is smoother again after the "punching/elongating" process does the "expanding". I am still researching whether this material would be flexible enough in one direction to roll into a roll, but am working on some sort of accordion/hinge/slider system that would allow the skirting to be easily slid out of the way, probably using a cable system. The holes/perforations would allow for some heat rejection and also a modest amount of self cleaning of the spun off grease. My basic thought is that small holes/perforations, while not ideal, would not be much of a hindrance to air flow. This would be the choice for under the cab/sleeper/engine area as I need some sort of non-combustible product to deal with the heat.

Any thoughts, input would be appreciated
Myron

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