Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Making a "Kammback" with the Sunroof and Rear Window

Cd · 09-07-2013, 10:39 PM

I ran some quick and sloppy tests of the Cd ( or cD ) and in both cases the drag went way up. More so with both windows down versus just the sunroof ( around 21% with both windows open )

I would guess that the airflow is creating some major turbulence in the area right before it enters the low pressure zone ( the open windows ) as well .

Look at the ( virtual ) increased frontal area that the airflow is causing. This test only took into account the drag coefficient and not the total drag including the frontal area.

So, no apparently this test will not show any benefits in drag reduction.

If you have the free time, and are willing to buy a battery powered carbon monoxide alarm, I say go for it ! A real world test is always nice to have in the archive here, even just to prove that it doesn't work.
It can be referenced to when the question gets asked again.

http://www.hardwareworld.com/Carbon-...d-pYB7HRK.aspx

If I did such a test, I would make sure that the air had as smooth a passage as possible to the back. If the seats in the rear fold down, this would be a good time to do it. Also i would add tufts at the rear of the vehicle ( inside the vehicle ) to show the direction of the airflow.

As far as deciphering the images, I'm clueless and would have to point you to Aerohead.

I can tell that there is a major disturbance in the force ...er of the air entering the open windows / sunroof but that's all i can decipher. I'm puzzled at the change in pressure at the front of the vehicle once the windows are opened.
I suspect this software has some bugginess. ( But hey its FREE ! so no complaints here ! )

If i have time i will try the open window as well as sunroof idea as well. Perhaps tomorrow.

09-07-2013, 10:39 PM	#12 (permalink)
Cd Ultimate Fail Join Date: Feb 2008 Location: Austin,Texas Posts: 3,585 Thanks: 2,872 Thanked 1,121 Times in 679 Posts	I ran some quick and sloppy tests of the Cd ( or cD ) and in both cases the drag went way up. More so with both windows down versus just the sunroof ( around 21% with both windows open ) I would guess that the airflow is creating some major turbulence in the area right before it enters the low pressure zone ( the open windows ) as well . Look at the ( virtual ) increased frontal area that the airflow is causing. This test only took into account the drag coefficient and not the total drag including the frontal area. So, no apparently this test will not show any benefits in drag reduction. If you have the free time, and are willing to buy a battery powered carbon monoxide alarm, I say go for it ! A real world test is always nice to have in the archive here, even just to prove that it doesn't work. It can be referenced to when the question gets asked again. http://www.hardwareworld.com/Carbon-...d-pYB7HRK.aspx If I did such a test, I would make sure that the air had as smooth a passage as possible to the back. If the seats in the rear fold down, this would be a good time to do it. Also i would add tufts at the rear of the vehicle ( inside the vehicle ) to show the direction of the airflow. As far as deciphering the images, I'm clueless and would have to point you to Aerohead. I can tell that there is a major disturbance in the force ...er of the air entering the open windows / sunroof but that's all i can decipher. I'm puzzled at the change in pressure at the front of the vehicle once the windows are opened. I suspect this software has some bugginess. ( But hey its FREE ! so no complaints here ! ) If i have time i will try the open window as well as sunroof idea as well. Perhaps tomorrow.