drag from wind for a ute

[Conn]

hey guys,

was just wondering if people can clarify this for me as i have heard both sides, if i drive my ute with no cover on it what so ever does wind enter into the tub a cause drag? cheers.

Con

[CANYONERO]

i would say so, when i had my ute i had the tonneau on with no bracing in the middle it used to get a massive sag at higher speeds wicked for cornering! but i later had the hard top.

[Joey_21]

well myth busters proved that by having the drop down tray at the back up actually works better then leaving it down less drag when its up so having the cover on wanted make that much difference

[TVR-190]

i think they would be designed to be relatively the same with or without it

[commsirac]

hey guys,

was just wondering if people can clarify this for me as i have heard both sides, if i drive my ute with no cover on it what so ever does wind enter into the tub a cause drag? cheers.

Con

Its more the flow around the cabin wont be as smooth, rather than air being trapped by the back. Its not only the shape of the front of the object that affects aerodynamics but that of the rear surfaces as well. My best guess would be that the cover would achieve a smoother flow than the open area.

If the difference is signficant, you should be able to see the difference, ie top speed the vehicle gets to, which might not be practical to test.
A more practical test might be to get it up to 140km/h or so, take your foot of the gas and see how long it takes to slow down to 120km/h.

[minux]

Its more the flow around the cabin wont be as smooth, rather than air being trapped by the back. Its not only the shape of the front of the object that affects aerodynamics but that of the rear surfaces as well. My best guess would be that the cover would achieve a smoother flow than the open area.

If the difference is signficant, you should be able to see the difference, ie top speed the vehicle gets to, which might not be practical to test.
A more practical test might be to get it up to 140km/h or so, take your foot of the gas and see how long it takes to slow down to 120km/h.

Every method was tested on mythbusters...it was proven that the best fuel economy is no cover and tail gate up.

[Not_An_Abba_Fan]

The area behind the vehicle is a low pressure area. The air flow over the cab and into the tub is a high pressure area. High pressure areas flow into low pressure areas. Any "parachute" effect caused by the tailgate will be canceled out by the air movement from the high pressure area in the tub to the low pressure area behind the vehicle. The faster you go, the faster this movement is, you can't outrun fluid dynamics. The low pressure area behind the vehicle is greater than the high pressure in the tub. So the movement of this air actually creates less resistance.

You have to get over what your eyes tell you, just because there is a physical barrier there doesn't mean it creates a resistance.

[commsirac]

Every method was tested on mythbusters...it was proven that the best fuel economy is no cover and tail gate up.

??, ok, so most likely no cover is the go.

But they did this test with commodore utes?

or brick like aerodynamics on a pickup truck,
Have looked it up, the tailgate findings make sense and I am in agreement with the theory, but couldnt find much about the cover findings?
All the same, the testing method was simplistic, driving two vehicles until they run out of gas, good television but good testing procedure?(using ~200L of fuel to get a finding is not a very smart way of doing it, and 3-4hours of driving), did they do any controls here, like drive both vehicles with the tailgates up and establish that they both run out of fuel at the same time? (whch would have used another 200L of fuel...if they did it)


Regardless, it would be a big call to apply their findings to every vehicle, it doesnt take much visually to get a big change, which is why I suggested actually doing a very basic test to find out with the vehicle at hand( and it wouldnt need 200L of fuel either)

[commsirac]

The area behind the vehicle is a low pressure area. The air flow over the cab and into the tub is a high pressure area. High pressure areas flow into low pressure areas. Any "parachute" effect caused by the tailgate will be canceled out by the air movement from the high pressure area in the tub to the low pressure area behind the vehicle. The faster you go, the faster this movement is, you can't outrun fluid dynamics. The low pressure area behind the vehicle is greater than the high pressure in the tub. So the movement of this air actually creates less resistance.

You have to get over what your eyes tell you, just because there is a physical barrier there doesn't mean it creates a resistance.

Yeah, nice theory/rhetoric, but was is your prediction on whether the cover will slow it down or not?

[Not_An_Abba_Fan]

If I had access to a wind tunnel I would test my "theory/rhetoric", but as I only have my limited knowledge of fluid mechanics and aerodynamics to go by, I stand by it.

In "theory", the cover will only deflect airflow and not create the low pressure area inside the tub. The low pressure area behind the vehicle will then, in fact, act as a parachute in itself. You will need to have some sort of flow interrupters on the rear of the cover to create turbulence to lessen the low pressure behind the vehicle.

Bernoulli's principle states that an increase in speed of a fluid occurs at the same time as a decrease in pressure. Applying this principle to a vehicle in motion is what brought me to the conclusion that the tail gate up is the best for economy.

[TVR-190]

get a cover with a spoiler if you're worried.

[Jesterarts]

Umm.. we all do realize that in the end we are talking about very very small margins right??

I think in the end having a hard lid or not wouldn't have much of an effect.

In the end the biggest motivator woudl probably be... do I like the look of a hard cover, a soft cover or open tray...

And to answer the original questions in brief...

No, it will not cause any EXTRA drag...

Cheers

[commsirac]

Umm.. we all do realize that in the end we are talking about very very small margins right??

I think in the end having a hard lid or not wouldn't have much of an effect.

In the end the biggest motivator woudl probably be... do I like the look of a hard cover, a soft cover or open tray...

And to answer the original questions in brief...

No, it will not cause any EXTRA drag...

Cheers

Im in the not sure camp.....Its not totally clear from the person posting the enquiry whether they have a cover already, but my initial thoughts were yes and that's why I suggest doing a very basic test to find out. To state categorically that the difference will be small or that there is no difference solely based on speculation is incredulous.

[VH commodore]

if theres no extra drag from having no lid then do that cuz it be alot lighter than a hard cover.

[Not_An_Abba_Fan]

To answer the OP's question specifically, no, it will not cause drag.

Here you go, http://ecow.engr.wisc.edu/cgi-bin/ge...hi1/pickup.pdf an actual test that proves it. Sorry about the file size.