Up or Down... Finally Answered

jeff

Moderator
Here's one for all of you high mileage truck drivers... Found this online by mistake the other day and thought it might benefit some of you that run with the tailgate down. I used to but gave it up when I didn't see any difference in mileage.

Start here ---->

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
 

Kritter

Krittro Campbell
They ran something similar on the news a few years ago. I never understood why people would do it anyways...whenveer I had to have my tailgate down it would come up and slam down on every bump...and the nets...those are in the same category as hot pink shock boots.

something else to remember is that drag force is cubely (is that a word? third power) proportional to velocity (speed in our case) so those bumpers with garage door angled skidplates create a huge amount of drag.

Cubely proportional meaning double your speed and the drag force increases 8X!

Kris
<A target="_blank" HREF=http://www.dmsrace.com>www.dmsrace.com</A>
"Jesus loves you, everybody else thinks you're an A-hole"
 

SDranger

Well-Known Member
According to dictionary.com cubley is not a word, i think you mean: "cubicly- adv. Of the third power, order, or degree." But i still got what you were saying, no wonder my truck got slower with full glass. lol


97 Ranger 4x4
02 CR125
 

Timberwlf

Well-Known Member
Hey Now ......

Hot Pink shock boots are wayyyyyyy Bling Bling. ond so are the neon green ones =)

Ahhhh hhhhhhhhhhhhhaaaaahahahhhahhhahhaaa

Brandon
avprerunners.com


94 Ranger X-Cab 4x4 5.0 H.O. v-8 Pre-Runner/ Chase Truck
 

ntsqd

Well-Known Member
Hey now !!! My Yoter came to me with a Hot Pink net gate. It was the first thing to come off.....

TS

"It only seems kinky the first time"
-- Bumpersticker seen in Lost Wages
 
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