Aerodynamics acording to Myth Busters!

It is more fuel efficient to drive a pick-up truck with its tailgate
down, rather than up.

Busted

Driving with the tailgate down actually increased drag on the pick-up
and caused it to consume fuel faster than the identical truck driven
with the tailgate up. It was later revealed that the closed tailgate
creates a locked vortex flow that created a smoother flow of air over
the truck. With the tailgate down, the trapped vortex was dissipated and
the drag increased.




http://en.wikipedia.org/wiki/MythBus...%29#Blown_Away

"cavelamb himself" wrote in message
link.net...

It is more fuel efficient to drive a pick-up truck with its tailgate
down, rather than up.

Busted

Driving with the tailgate down actually increased drag on the pick-up
and caused it to consume fuel faster than the identical truck driven
with the tailgate up. It was later revealed that the closed tailgate
creates a locked vortex flow that created a smoother flow of air over
the truck. With the tailgate down, the trapped vortex was dissipated and
the drag increased.




http://en.wikipedia.org/wiki/MythBus...%29#Blown_Away

Somehow, that is even harder to accept, as a general statement, than the
original assertion.

It has not been proven either way, from my experience.
When I had a 1977 Toyota pick-up, I tried it and could not prove any
difference at all; so I went back to driving with the gate closed--because I
felt that leaving it open defeated that purpose of having a rear bumper.
OTOH, a know two owners of late 1990s full sized Chevy pick-up
trucks who both swear that it adds between 1 and 2 mpg. One of them, who
only occasionally loads cargo in the bed, simply leaves the tailgate at home
when not in use.

I must suggest that different trucks may have different results, even when
tested at the same speed, and that the biggest improvement of all might be
from driving the other car when there is nothing to haul. Then again, if
you have only one vehicle, there is a damned good case to be made in favor
of the truck!

Peter

Peter Dohm wrote:

"cavelamb himself" wrote in message
link.net...

It is more fuel efficient to drive a pick-up truck with its tailgate
down, rather than up.

Busted

Driving with the tailgate down actually increased drag on the pick-up
and caused it to consume fuel faster than the identical truck driven
with the tailgate up. It was later revealed that the closed tailgate
creates a locked vortex flow that created a smoother flow of air over
the truck. With the tailgate down, the trapped vortex was dissipated and
the drag increased.




http://en.wikipedia.org/wiki/MythBus...%29#Blown_Away


Somehow, that is even harder to accept, as a general statement, than the
original assertion.

It has not been proven either way, from my experience.
When I had a 1977 Toyota pick-up, I tried it and could not prove any
difference at all; so I went back to driving with the gate closed--because I
felt that leaving it open defeated that purpose of having a rear bumper.
OTOH, a know two owners of late 1990s full sized Chevy pick-up
trucks who both swear that it adds between 1 and 2 mpg. One of them, who
only occasionally loads cargo in the bed, simply leaves the tailgate at home
when not in use.

I must suggest that different trucks may have different results, even when
tested at the same speed, and that the biggest improvement of all might be
from driving the other car when there is nothing to haul. Then again, if
you have only one vehicle, there is a damned good case to be made in favor
of the truck!

Peter



I personaly can't argue either way.

Both answers seem to have merit - and then not...

But those webbed tailgate thingies have GOT to increase drag.

Don't they???

Richard

In article .net,
cavelamb himself wrote:

I personaly can't argue either way.

Both answers seem to have merit - and then not...

But those webbed tailgate thingies have GOT to increase drag.

Don't they???

They re-visited the tailgate issue in a later episode, and re-busted
tail gate down being more efficient, but found that the mesh thingie
increased mileage. Still questionable since they were doing the
tests on public roads with traffic.

http://en.wikipedia.org/wiki/MythBus...ailgat e_Down


Necessary aviation content: They also tested the 'jealous wife
shredded the plane with a chain saw' myth.

http://kwc.org/resources/2006/mbnew/sp.photo.jpg

http://en.wikipedia.org/wiki/MythBus...Shredded_Plane

John
--
John Clear - http://www.clear-prop.org/

On Jul 23, 6:42 pm, (John Clear) wrote:
In article .net,
cavelamb himself wrote:



I personaly can't argue either way.

Both answers seem to have merit - and then not...

But those webbed tailgate thingies have GOT to increase drag.

Don't they???

They re-visited the tailgate issue in a later episode, and re-busted
tail gate down being more efficient, but found that the mesh thingie
increased mileage. Still questionable since they were doing the
tests on public roads with traffic.

http://en.wikipedia.org/wiki/MythBus...#Tailgate_Up_v...

Necessary aviation content: They also tested the 'jealous wife
shredded the plane with a chain saw' myth.

http://kwc.org/resources/2006/mbnew/sp.photo.jpg

http://en.wikipedia.org/wiki/MythBus...Shredded_Plane

John
--
John Clear - http://www.clear-prop.org/

Yes, it has been proven more than once that tailgate up is better but
IIANM the difference is too small to worry about. Minor change in
driving behavior from one day to the next would wipe it out.

Harry K

On Tue, 24 Jul 2007 01:42:48 +0000 (UTC),
(John Clear) wrote:


Necessary aviation content: They also tested the 'jealous wife
shredded the plane with a chain saw' myth.

http://kwc.org/resources/2006/mbnew/sp.photo.jpg

that photo is of an aircraft parked on parafield in south australia.
a chap with a flat battery in another aircraft hand propped the
aircraft, engine started and roared into life, the aircraft jumped the
chocks and graunched along the fuselage of the twin until the meatier
parts around the wing stopped the engine.
photo taken after the aircraft were pulled apart.

Stealth Pilot

On Jul 24, 3:46 am, Stealth Pilot
wrote:
On Tue, 24 Jul 2007 01:42:48 +0000 (UTC),

I tested this one on my own after reading a NASA report about that
locked vortex thingie. Using cruise control only, at 70 mph, out
accross I-70 in western Kansas, both ways to account for headwinds,
etc., ad-infinitum, my 2002 Dakota 4-door averages 1/2 mpg better with
the tailgate up. woohoo. big deal.

The vortex is not a myth though. Wanna guess what happens when a house
painter opens the sliding rear window of his Chevy and then flicks his
butt out of the driver's window? Non-smoker's revenge! Yep, that so-
called vortex grabbed hold of the forest-fire inducing, bar polluting
cancer stick and shot it back inside the truck, under the seat. Where
it did its thing and set his truck on fire a few minutes later in the
parking lot of the local strip joint.

Now here's the real question. If Jamie was using an "aircraft" fuel-
flow meter and it had been "calibrated" to his truck (also a Dodge
Dakota, but a 2-door and I'm guessing a 3.9L V-6), why did it show
something like 5.4. ...5.4 what? They never did say how many mpg
they got with either method. And I've never been able to work out the
math on that number. If its gph, then at 55 mph, thats 5.4 gallons,
devided by 55 miles, equals 9.163 mpg? In a Dak? Only if he's towing a
5k trailer into a 30mph headwind uphill. The 3.9L Dakota should be
somewhere around 18-21 mpg at 55 mph. I can get 19-20 with my V-8.
Could it be pounds per hour? That doesn't sound right either. A gallon
of unleaded is roughly 6 lbs according to BP, or so sez the internet
page I just Googled. So Jamie's truck is getting nearly 60 mpg at 55
mph?

Anyone have any more insight on this?

Harry "saws arm off and hands to gas station clerk" Frey
'02 Dak pusher

"John Clear" wrote in message
...
In article .net,
cavelamb himself wrote:

I personaly can't argue either way.

Both answers seem to have merit - and then not...

But those webbed tailgate thingies have GOT to increase drag.

Don't they???

They re-visited the tailgate issue in a later episode, and re-busted
tail gate down being more efficient, but found that the mesh thingie
increased mileage. Still questionable since they were doing the
tests on public roads with traffic.


It's hard to measure small differences in fuel economy even when you are
running a vehicle over the same cycle on a chassis dyno with a million
dollars worth of analyzers- trust me on that one - I've looked at the
results of thousands of emission tests over the years.

Trying to see the difference on public roads in traffic? You might as well
throw some dice for anything less than 10 or 20 percent.

Doing coast-downs is a much better method - it gives a reasonably reliable
results for finding changes in aero drag.


--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote in message
It's hard to measure small differences in fuel economy even when you are
running a vehicle over the same cycle on a chassis dyno with a million
dollars worth of analyzers- trust me on that one - I've looked at the
results of thousands of emission tests over the years.

Trying to see the difference on public roads in traffic? You might as well
throw some dice for anything less than 10 or 20 percent.

Doing coast-downs is a much better method - it gives a reasonably reliable
results for finding changes in aero drag.


--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.


Exdellent point.

Peter

I personaly can't argue either way.

Both answers seem to have merit - and then not...

But those webbed tailgate thingies have GOT to increase drag.

Don't they???

Richard

My feeling about the web tailgates is the same as yours; but I really don't
know.

Peter