This is the strangest idea I've heard in a number of years. And stranger still, it may also be one of the best I've heard in a number of years.
A magazine is fair game for any crackpot or snake-oil salesman with a “revolutionary” invention, and normally a recent email would have had my credibility alarm ringing loud and long. A team of researchers claimed that it's come up with a way to cut tractor-trailer fuel consumption a whopping 12% by blowing compressed air through slots spread around the trailer.
If the fuel savings isn't outlandish enough, the researchers say this “pneumatic system” can also help control jackknifing and trailer sway, improve vehicle stability in ice and rain, shorten stopping distances, increase tire life and reduce wheel spray. Does it also make coffee and unload the freight?
I probably wouldn't have given the note a second glance if it wasn't for the source — it's the highly reputable Georgia Tech Research Institute (GTRI), which received funding for this particular project from the equally reputable Dept. of Energy's (DOE) Office of Heavy Vehicle Technologies. Even more impressive was the email's attachment, a formal paper presenting the group's research, experimental results and conclusions in great detail to their peers at SAE.
Borrowing from patented pneumatic systems developed in the 1970s to boost lift for airplanes, the GTRI team used a wind tunnel to test the concept on a tractor-trailer model. They found that blowing lightly compressed air over a curved surface on top of the trailer decreases drag by 35 to 50%, while also decreasing rolling resistance by lifting a portion of the vehicle's weight off the tires. A 35% drag reduction would translate into a 12% fuel savings by their calculations, or about 1.2 billion gallons of diesel a year in the U.S. The 50% number would raise the annual savings to 1.7 billion gallons.
Blowing air through a slot, or plenum, under the trailer had the opposite effect, increasing downward force on the tires for better brake performance and traction. Air pushed through slots on the trailer side could counter cross-winds as well as function as an aerodynamic brake, and air blown through slots at the rear of the trailer greatly reduced turbulence and spray behind the vehicle.
Yes, that's in a wind-tunnel with a model, but before you dismiss the idea as just another interesting but irrelevant experiment, consider that DOE was so impressed that they've decided to fund some real-world testing. As we go to press, DOE and GTRI engineers were planning to meet with truck and engine manufacturers, ATA and the Dept. of Transportation to work out the details for a road test before the year is out.
We'll keep you posted on this particular crazy idea as they move ahead with the tests. In the meantime, if you'd like all the technical details, you can order “Advanced Aerodynamic Devices to Improve Performance, Economics, Handling and Safety of Heavy Vehicles” (SAE Paper 2001-01-2072) at the organization's web site www.sae.org.