From a letter to Tom and Ray Magliozzi (click and clack) in their October
1997 files:
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 the
auto makers, and Lockheed was successful in convincing Ford, among others,
that the wind tunnel would help them reduce drag and wind noise on their
vehicles. Needless to say, in the past 15-20 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 nonaerodynamic
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, Dept. of Aero/Mechanical Engineering, U.
of Notre Dame
Tom: Sounds pretty convincing, Ed. Thanks. We also heard from none other
than Bob Stempel, the former GM president, who wrote us to say that
aerodynamically it doesn't make that much difference. But, he says, a pickup
truck is structurally much SAFER with the tailgate up.
Ray: So for that reason alone, we suggest you throw away those tailgate
nets, folks. And as your flight attendant might say, please return your
tailgate to the upright and locked position.
Thanks,
Gary
-----Original Message-----
From: HP-3000 Systems Discussion [mailto:[log in to unmask]] On Behalf
Of Art
Sent: Monday, May 26, 2008 6:14 PM
To: [log in to unmask]
Subject: [HP3000-L] OT: Realistic Gas Saving Questions
Hi All :)
Ok... being that I now have to commute (albeit only 4 miles each way ) I
have some dumb questions for how to get the best milage possible while I
wait for my company provided Bus Pass at the new company...
Which is better on the engine and saving of gas:
1. Higher RPM's in a lower gear (sayh 2200 in 3rd)
2. Lower RPM's in a higher gear (say 1600 in 4th)
Can the fluids in the transmission make a difference?
Since the vehicles kick the compressor on all the time now - not just
when using the air conditioner... does running the A/C make a true
difference?
Now I drive a 2005 Ford Ranger 4x4 with a Leer Canopy (cap for you
Southern Folk hehehe) and it has a 4.2l V-6 engine with a 5 speed manual
transmission which I know how to drive fairly well (NASCAR skill level I
ain't! hehehe)
Art "Questioning once again" Bahrs
=========================================
Art Bahrs, CISSP
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