Aerodynamic Pros/Cons with Roof Spoiler on 180SX?

[Howie Felter Snatch]

Could someone shine some light about the aerodynamic advantages or disadvantages (IF ANY) in regards to having a Roof Spoiler on a 180SX?

I know the 180SX is known for having a low Cd (Coefficient of Drag), would adding a roof spoiler add more drag/increase downforce or does it only help in smoothing out the air flowing over the roof/hatch area?

Thanks!

[PoorMans180SX]

Roof spoilers cause the airflow to detach from the rear glass area, creating a low pressure zone and increasing drag.

[Silverbullet]

^ that is assuming air even stays attached going down the glass. If it detaches from the roof to begin with, the rear window visor spoiler would keep it attached for slightly longer.

Its hard to tell without actual testing. You can easily do a tuft testing (http://sites.google.com/site/601cgzdc/Home/Tuft-testing--vortex-generators) and drip test (forgot actual name), where you apply a few drips of oil, drive and watch where the oil/fluid trails to.

[PoorMans180SX]

I can tell you right now that the air will stay more attached without the roof spoiler, and that there will be a much larger low pressure zone behind the roof spoiler than if there wasn't one there.

If you're looking for an aerodynamic improvement, look into airtab vortex generators.

http://domofactor.com/wp-content/uploads/2010/06/180sxvortex.jpg

[Pandapants]

I thought those were only good if you paired them with a large rear/trunk spoiler, like on the wrx?

[PoorMans180SX]

I thought those were only good if you paired them with a large rear/trunk spoiler, like on the wrx?

No sir, they work regardless. The reason they put them on STi's and Evo's is because their roofs drop off rather abruptly, and they help more airflow stick to the glass and therefore flow over the wing.

The fastback profile is much more aerodynamic, but it can't hurt.

[delado]

I can tell you right now that the air will stay more attached without the roof spoiler, and that there will be a much larger low pressure zone behind the roof spoiler than if there wasn't one there.

If you're looking for an aerodynamic improvement, look into airtab vortex generators.

http://domofactor.com/wp-content/uploads/2010/06/180sxvortex.jpg

Where do I find these?!

[Silverbullet]

^That S13 post above has them more for styling rather than function.
The purpose of those is to keep air attached as they detach from the body. It reduce the drag. In the STi and Evo case, they are used for that and to direct the trailing vortecies to the wings.
Vortex generators are also common in the form of a dive plane or canard (aka, the ricey looking fins on the sides of some front bumpers). The plane itself helps with some front down force, but also the edges create vortecies along either teh side or top of the wheels to reduce the amount of air getting caught in the hairiness of the rotating wheel.

//edit. got damn u guys type fast.

[Silverbullet]

and they help more airflow stick to the glass and therefore flow over the wing.



Air flow can not make that turn on an Evo coupe body to stay attached to the glass. The air flow leaves as trailing vorteces.

//edit
http://image.motortrend.com/f/8523433/112_0512_wrx_evo_18z+2006_mitsubishi_lancer_evo_ix _mr+vortex_generators_action_view.jpg
nvm. I wasn't too faimilar with the shape of the shape and wing height until i looked it up. Im impressed.
That is a tufts test btw.

[PoorMans180SX]

Yup yup, the fastback doesn't need much help, but it can't really hurt.

And yes, a properly shaped canard helps reduce drag and underbody airflow as well.

Airtab.com

[Howie Felter Snatch]

Excellent replies guys, thanks!

So basically the Roof Spoiler does NOT help in smoothing out the trailing air flowing over the roof/hatch area (Origin-Labs explanation) and instead creates a low pressure zone right at the top of the hatch and thus increases drag.. So its safe to assume that a roof spoiler is just for LOOKS and not for FUNCTION? If that is the case, then I don't want it.. :facepalm:


That airtab Vortex generator thing looks quite interesting, I've seen them on Evo 8/9's with that very steep rear window design.. I don't know if a 180SX would really gain much advantages with it but know knows.. Cool stuff regardless.

[AeroDesigns]

The basic roof spoilers dont do much other then add visuals to your car.

But like the others say, vortex generators do improve drag but only if you have a large wing in the back. The use of a vortex generator is to keep the air from dispersing and in a consistent flow.

[duffman1278]

Roof spoilers cause the airflow to detach from the rear glass area, creating a low pressure zone and increasing drag.

I believe it creates high pressure (bernoulli's principle) and usually after the rear window it goes from laminar to turbulent flow which is drag as u said.

I do highly agree that a vortex generator is a much better investment as it will transfer the energy of the fluid and keep it going instead of slowing it down because if the fluid slows down then you get increased pressure regions. But incase anyone ask there is drag from the generator, it's just a different form (induced drag) but it is a way better option.

OP, there's many factors you need to consider when discussing aerodynamics, there's plenty of pros and cons but they come from your setup as well. Some people tend to believe that the greater the angle of attack your wing has, the more down force you get. And this is simply NOT true.

The design of the wing(s) also have major influences on the wings performance