Fairing Well,NASA truck aerodynamics

[some_other_dave]

Don't some drag numbers go up with the square of speed, and some with the cube? It could be that in cars, the squared term is dominant, but in aircraft the cubed term is.

-soD

[RedDevil]

Drag force goes up with the square, power usage with the cube.
Power is force times distance.
At higher speeds you cover more distance in the same time.

To double your speed you need 8 times as much power to pull 4 times the drag over twice the distance.

[freebeard]

Well put.

[slowmover]

OA good read. Eighty pages.

As to truck drivers being resistant. This is more the truck company owners shifting blame highlighted by a few stories. A conventional tractor also tends to have a better ride (VERY important) as well as better handling. Built better, and can be specd over a far wider range. And part of that is having serious power unhindered by restrictions in the engine air intake or exhaust path. Giant radiator. No slowdowns due to op temps.

An owner operator can make a net income of $100k or more, but that is dependent on loads, not overhead. At 5-mpg planning average. It was a lot of years before I drove a holy grail truck with 500-HP and a thirteen speed. A truck like that gives choices to the driver a lesser truck is incapable of. And, frankly, the net loss of income isn't overwhelming. What makes a truck driver is tied to how well a truck can do work. In the right hands. Big power and long life. A great ride. And always high resale value. A better tool. Can't run out of gears or horsepower.

A truck with over 2,000-TQ is a world away from the fleet aero trucks. Especially as all of them get older. The sheer variety of types of truck driving is overshadowed by the assumption of warehouse to warehouse by most folks. Or what they might see at a truckstop. There are legions of trucks never at a warehouse, and many never at a truck stop except to buy fuel.

The pride and polish is its own little subgroup. It's hard as hell to keep a big truck clean ($70 week for one wash in 2-3000 miles doesn't cut it), so they're to be respected for their dedication. And never going off-road. Another way of demeaning the man behind the wheel who may be home 1-2 days monthly and who will statistically lead a shorter life. I'm just as likely to laugh at the circus wagons as anyone else. It's like the old hotrod saying of if its slow, chrome it. On a big truck they add more chicken lights and chrome.

Back to topic. Nice to read the change on the van re radiused edges. Says it all in the world of RVs. Horsepower demand.

More importantly, with low ground clearance, the ability to handle crosswinds. Hard to test that, though, with repeatable results. It's easily as important as FE as it can turn over the vehicles, trucks or RVs. And it's a good thing to have in mind in reading this.

[aerohead]

Here are NASA's mods in order of execution.
Altogether,they allowed a crosswind-averaged drag reduction of 67%,and they left some fruit on the tree.

If you look carefully,the lowest two images are red-lined underneath to depict full tractor-trailer belly-panning.