Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Drag penalty for having a shallow rear window angle, and using spoiler to re-attach ?

tomi_k · 09-18-2021, 10:08 PM

Thanks, Vman455 ! Totally understood. I am not looking direct association to my vehicle, just trying to get what type of improvements people doing mods are generally achieving with spoilers (if any) and magnitude of them (like 0.1%, 1%, 10% etc.)... And if I have understood correctly, e.g. using your spoiler as an example, the wake area increased a bit but gained pressure reduction on larger rear window area and then based on experiments, sounded like drag reduction happened based on your measurements and analysis. Earlier Aerohead indicated regarding the wake area, that's it's not the area but the pressure... in what magnitude, i have no idea nor data and that's what I try to understand....

Specifically related to spoiler, I am build one with adjustment of height and angle and planning to run series of tests to see what happens on my vehicle. My questions earlier were (and still are) something what I am curious to understand as if there is clear evidence that rear window / area pressures or change of them with help of a spoiler (or a wing) targeting to reduce overall drag can NOT be achieved due to basic aerodynamics, then it gives me some kind of baseline that IF I do not see improvements on results, then I have some idea why that's not happening. I have read few books, articles and searched info about overall drag reduction of road vehicles (not interested to increase downforce at the moment). Then run into spoilers / wings which put me thinking while targeting to reduce wake area drastically, would it be possible to "tweak" the airflow over the rear window area with spoilers while reducing overall drag.
I am just trying to form an generic idea how rear window / area angle vs. overall drag vs. wake area is behaving and how they correlate / associate.

If I would ask that what happens putting a 10sq.ft. flat plate on top of my vehicle and nobody would be saying that it does increase drag, don't do it and if I couldn't figure that out using any generic theories - I would not have much other options than head out and test it... lol.

09-18-2021, 10:08 PM	#24 (permalink)
tomi_k EcoModding Lurker Join Date: Jan 2021 Location: Ontario, Canada Posts: 68 Thanks: 54 Thanked 50 Times in 35 Posts	Thanks, Vman455 ! Totally understood. I am not looking direct association to my vehicle, just trying to get what type of improvements people doing mods are generally achieving with spoilers (if any) and magnitude of them (like 0.1%, 1%, 10% etc.)... And if I have understood correctly, e.g. using your spoiler as an example, the wake area increased a bit but gained pressure reduction on larger rear window area and then based on experiments, sounded like drag reduction happened based on your measurements and analysis. Earlier Aerohead indicated regarding the wake area, that's it's not the area but the pressure... in what magnitude, i have no idea nor data and that's what I try to understand.... Specifically related to spoiler, I am build one with adjustment of height and angle and planning to run series of tests to see what happens on my vehicle. My questions earlier were (and still are) something what I am curious to understand as if there is clear evidence that rear window / area pressures or change of them with help of a spoiler (or a wing) targeting to reduce overall drag can NOT be achieved due to basic aerodynamics, then it gives me some kind of baseline that IF I do not see improvements on results, then I have some idea why that's not happening. I have read few books, articles and searched info about overall drag reduction of road vehicles (not interested to increase downforce at the moment). Then run into spoilers / wings which put me thinking while targeting to reduce wake area drastically, would it be possible to "tweak" the airflow over the rear window area with spoilers while reducing overall drag. I am just trying to form an generic idea how rear window / area angle vs. overall drag vs. wake area is behaving and how they correlate / associate. If I would ask that what happens putting a 10sq.ft. flat plate on top of my vehicle and nobody would be saying that it does increase drag, don't do it and if I couldn't figure that out using any generic theories - I would not have much other options than head out and test it... lol. Last edited by tomi_k; 09-18-2021 at 10:27 PM..