Kenworth Truck--air dam
 

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.

Some "moon eye" hubcaps would probably be good on all the outside wheels. If you can, switch to a more round front set of mirrors (assuming you have flat front ones now). If you have a "visor" on the outside of the cab, get rid of that if possible. When hauling around, move the goose neck hitch as close to the cab as is practical, to reduce the gap between truck and trailer. Put covers over the "bucket" headlights and other "holes" in the front bumper.

Some pics of the rig and trailer would help us see places that could use improvement. Also I'm sure most of us would be interested in seeing a gaslog (depressing, I'm sure, but interesting nonetheless)

How extreme are you willing to go? Is this your truck or a company owned one?

You could re-route the exhaust stacks to remain underneath the truck and exit by the (truck's) rear axles. Switch to "super singles" if you don't have them already. I'm sure that some kind of a "trailing edge" attachment for the back of the cab could be made, but I have no idea how to go about that or what shape they should be.

I know that driving a truck is very different from driving a car, but you could cruise with the engine below the powerband to consume less fuel. I'm not saying to lug it out of every gear, but when you aren't using much power (IE, cruising) you could keep the RPMs low.

Well, to help the mirror issue, you could use a camera setup. By eliminating your mirrors and installing cameras you would significantly reduce drag (I have a bus, and the mirrors are almost as much frontal area as most auto front windows). The advice of cleaning up the front end is good advice as well.
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With a diesel, turbo pressure increases efficiency. Dont lug the engine, but try being more patient on the road instead(i.e. sometimes we pass for no good reason).

As for the trailer, I dont know how much time you spend hauling a load, or not hauling, but it may be worth it to close up the wake of the truck. I am thinking of a wedge like device that goes from height A by the truck and decreases to deck height, or height B over some distance, C. Making it easily collapsible and storable would be the only thing that would be difficult. Good luck!

Don't forget you can go to super singles for the drives and trailer. The steer tires can go to 100psi and the drives to 105, if you are not in the habit of curb hopping you can go to 110 on the trailer to reduce rolling resistance if you are running duels. I had run as high as 120 in both drives and trailer before but it didn't seem to make any difference as far as mileage, but made a difference in ride so went back to 105 and 110. This was on Bridgestone 22 inch standard rubber. Guys running 22 and 24 inch low profile tires reported much the same results.

If you have side fairings on the tanks, look into adding another 4-6 inches of a flexible material to lower the sides.

To the flaps on the sides of the sleeper, add some more material until you are about 12 inches or so from the trailer.

If you have tarp loads, try to mold the tarps with the load to try to keep it as smooth as possible.

I have not driven trucks now for 10 years, so some of the tech on the tires may have changed since my time.

I have super singles on the tractor, can't get them for the trailer. I
don't have the budget/time to cut the axles and make drop axles, then
cut out the decking so the larger diameter tires would fit the
trailer. That is aside from the fact that doing so would cut up a
pretty new aluminum deck trailer, and limit some of the loads I could
haul. The trailer is basically a flatbed that drops down once it
leaves the tractor and the trailer uses ultra low profile tires. There
is little that can be done from a practical sense for aero mods to the
trailer and tractor/trailer interface as every load I haul is
different. If it was a box type trailer I would build some sort of gap
filler, round the upper edges, and skirt it, but this is a flat bed
type trailer. The exhaust is already routed under the cab, the sleeper
is mid-height which is too low for some loads, too high for others,
but practical on the inside. There are cab extenders on the sleeper
and I have considered extending these further. Mudflaps on the tractor
are drilled out just in case it makes a difference. They are also cut
down to the exact width of the super single tires. Homemade generator
(alternator running through inverter) provides standby power for
fridge, AC, sink, water supply, etc when parked. Up to about 85
degrees ambient I can used the electric AC (the one I installed for
night time/parking) in the sleeper to cool the cab as I drive, and
this lowers the engine intake air temp 8-15 degrees since the factory
AC condenser is mounted in front of the aftercooler. (When running
really really light, I can see the mpg drop slightly as the engine air
conditioner is engaged). Gearbox and differential oils are synthetic,
I am still using petroleum oil in the engine, which I change based on
analysis, typically every 40,000 miles. Flashing roof light for
oversize loads folds down behind the cab when not being used. Cruise
speed is 55 mph, 1100 rpm. (peak torque is 1200 rpm, general practice
is to gear 100-200 rpm above peak torque). Its a bit doggish at 1100
rpm, but not bad. 13 speed transmission splits the top gears in 200
rpm increments which makes the 1100 rpm feasible. Laptop monitors
engine ECM including intake air temp, fuel temp, atmospheric pressure,
tire pressure (Pressure Pro), etc. CB antenna is steel wire (smallest profile I can
find). Mirrors, hood, and cab are already "aero" though I have
wondered about trip wires at strategic locations. (I think DOT "requires" real mirrors, at least its not a fight I want to fight right now). Side winds seem to
be the absolute worst, and if you see pictures of the trailer, you
will probably instantly see why.

I own the truck and the trailer. I don't mind going pretty radical,
though I am pretty limited by time. Ground clearance is an issue,
especially RR tracks. I am planning to hang the side tool boxes so
they can both flex and lift as I high center them. Engine is
Caterpillar ACERT 15 Liter, 435 hp, 1650 ft-lb torque @ 1200 rpm,
compounded turbo intercooled and aftercooled. Average mpg over the
last year is 8.5 mpg. Industry average for this type of truck/freight
is 6.0 and some are getting as low as 4.5. The money I save in fuel
makes it practical for me to make a living doing this and leaves a bit
left over to experiment with, though time is really a bigger factor.
Whatever mods I made MUST be easily removed/hinged away, etc to
service the truck on a daily/weekly basis. The area I am trying to
focus on at this time is the lower parts of the truck, wheels on down.
I was pondering some sort of air dam, increased tractor skirting
possibly covering the super singles as they sit in just slightly as
compared to the duals, and then "skirting" the trailer with continuous
tool boxes.

Other mods in the long term are lift axle on the trailer, convert the
tractor to single drive with liftable idler. Also working on some sort
of retractable tarp for the upper deck/front part of the trailer that
would act as a gap filler for many of my loads. Also have considered
cutting up the hood to vent the air through the top, removing factory
AC and adding electric on the cab roof, and filling in the step areas.

Bottom line, it makes money now, and needs to continue to do so in the future.

How do I post pictures? thanks for the reply

Myron

PS, for the time being, you can see some pictures of the truck, some typical loads, and ponder my daily experiences at my infrequently updated blog. Hmm, won't let me put in the link. It is bigtruckthoughts-dot-blogspot with all the correct front and end stuff.

thanks again,
Myron

Myron,
I know that I am not a trucker, but if it were my setup, I would try to avoid mounting the tool boxes any lower than the frame. If you want extensions further down, use some flexible plastic or rubber. As for a gap filler, chase the huge one between the trailer and truck (lower portion behind super singles and above wheels below trailer).

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Just some ideas.

Awesome to see a trucker looking at Aero mods- its something that's been sorely overlooked regarding fuel efficiency.

Kudos to you for making the truck work- 8.5mpg is better than most European trucks..

autoteach seems to have a pretty good idea regarding the aero mods, but is it also woth considering rshutting off some cylinders when you're up to cruising speed?

shutting off cylinders would not be a good option. I would leave engine modifications alone, and for good reason. Who wants to take out a second mortgage on an engine? Anyone? Just work on the aero, where things are cheap to do and cheap to discard or repair.

Shutting down cylinders in a diesel engine doesn't do much, really... the way a diesel works, the other cylinders will just "pick up the slack" and injectors will toss in some more fuel to make up for the loss of power.

Especially while hauling, this wouldn't be effective in most situations, because unlike most cars, which produce wayyyyy too much power, most larger trucks are "just right".