Ajaaaah
miren lo que encontre:
http://www.awtrucks.com/tailgateup.htm
Dear Tom and Ray:
I'm an aerodynamics engineer. When I was in the U.S. Air Force a few years back, I worked with folks from the Lockheed low-speed wind tunnel.
In the 1970s aircraft production went into a slump, and Lockheed started looking.for other customers for its wind-tunnel services.
Prime candidates were automakers, and Lockheed was successful in convincing Ford, among others, that the wind tunnel wouId help them reduce drag and wind noise on their vehicles.
Needless to say, in the past 15 to 20 years, Lockheed has learned a lot about car and truck aerodynamics.
Anyway, they actually performed drag tests on pickups with the tailgate both up and down, and found that drag was actually LOWER with the tailgate CLOSED!
This ran counter to their intuition (and yours). The reason is that a closed tailgate sets up a large "bubble" of stagnant air that slowly circulates around the bed of the truck (we aero types call this a ("separated bubble"). When air approaches the truck, it "sees" the bubble as part of the truck. So to the air, the truck looks like it has a nice, flat covering over the bed, and the air doesn't "slam" into the vertical tailgate.
If the tailgate is open, or replaced by one of those "air gate" nets, however, that nice, separate bubble in the truck bed does not form (it "bursts").
Then the air approaching the truck "sees" a truck with a flat bed on the back of a tall cab. This is a very nonaerodynamc shape with a very LARGE drag.
So, believe it or not, it's best for gas mileage to keep the tailgate CLOSED. Hope this information is helpful.
Ed Fitzgerald
Research Assistant
Department of Aero/Mechanical Engineering
University of Notre Dame
En palabras simples, las camionetas tienen mejor coeficiente aerodinamico
con la tapa que con la malla.