I was just wondering if the RX-8 spoiler actually does anything for the Drag Coefficient or not.

Prompted by a discussion in this thread @ RX7Club: http://www.rx7club.com/showthread.php?t=650877

Cheers,
Cody

 

Minimally. You'd need something big and obnoxious like the Evo or STI wind to really make any difference. Even then, just putting a big wing on isn't going to do much without wind tunnel testing and people with a very good understanding of physics and vehicle dynamics helping with the design.

 

I figured it'd be minimal. Someone said that the stock wing I have on my RX-7 reduces the Cd to 0.29. All the numbers I've found for stock RX-7s say Cd is 0.30.

So that's a VERY minimal difference. But interesting nonetheless. My wing is actually... "functional". :-P

Cheers,
Cody

 

well, the little euro lip spoiler reduces the coefficient of drag and is required for fuel economy reasons...so i hear?

 

Yea, the beer opener OEM wing is ridiculous. Not functional at all IMO.

 

An effective wing will increase downforce and reduce lift. However, I think adding even the best designed wing will still increase drag by a little so I don't see how it could "reduce" your Cd. Hopefully someone who knows more about aerodynamics will confirm or deny this.

 

Hmm... interesting. I wish I could find more numbers for stock RX-7s / 8s.

Cheers,
Cody

 

My spoiler adds 15 hp...

 

If it could keep some of the air from becoming turbulent, then yes it could reduce the drag coefficient, but my guess would be this isn't the case.

 

This is generally true for a wing, but the "duckbill" he has on his RX-7 is a spoiler. Spoilers can help maintain laminar flow and delay separation. They can also minimize turbulence behind the vehicle, reducing "boattail" drag. So yes, it's not uncommon to hear of spoilers that reduce the Cd (albeit by a small amount). This is why I find it annoying when people criticize spoilers on FWD cars.

 

The duckbill spoiler on the S4 RX-7s did infact lower the CoD.

 

They are Look Coefficient.

 

you are brilliant!

i wish companies who made spoilers actually did some aero testing it would help me decide on which to buy.

 

This is the one I bought. http://cgi.ebay.com/ebaymotors/MAZDA...spagenameZWDVW

 

The stock one on the 8 is for looks only.

 

And don't it look good!

 

I prefer the spoiler look. But that is just opinion.

 

The stock spoiler just adds needless weight. The Euro lip spoiler is much more functional and subtle.

 

Most of the "euro lip" spoilers that are actually functional and necessary are found on cars with abnormally large low pressure areas over the rear deck lid behind the rear windshield. The Audi TT is one of those cars that gets a little evil at high speeds without it. The vast majority though are for appearance purposes only.

 

I was under the impression that a true "spoiler" (not a wing) is supposed to be curved on the bottom, and flat on top. Much like an upside-down airplane wing. As an airplane wing passes through air, lift is created. As the spoiler passes through air, downforce is created since the curved side is on the bottom instead of the top. Look at the OEM spoiler - curved on the bottom, flat on top.

I would assume that this would only have any noticable effect at extremely high speeds, though. I may be wrong, but it always seemed to make sense to me.

 

Maybe if you were going mach 1. I sincerely doubt that it would have any impact even on the track. There are few production cars with wings that actually do anything really productive in terms of downforce. As mentioned before the EVO and STI have them, and they are enourmous and high. Some cars like the tt and beetle need a little lip as their shape is conducive to creating alot of lift around the back of the car without one. Those are unique and stupid shapes for cars IMO. The rx8 wing is merely a convenient horizontal surface for you to rest your detailing product of choice. Maybe a beverage.

As far as the difference between spoiler and wing, I don't think they are really distinct and are pretty interchangeable.

 

Are there decent diffusers for the RX-8 out in the market? For real, tested and confirmed aerodynamically? I want to branch out from AX next year (saving for so much else at the moment) into track days and I know that the real front lip spoilers can create a serious amount of useful front-end downforce and would love to be able to balance that at the rear without a giganto wing.

I could also see these reducing Cd as well...

 

Aero testing is amazingly expensive (it is still really pricey even if you own the wind tunnel). Most companies are not going to worry about engineering a perfect wing because the gains are so little compared to spending time developing the aero on different parts of the car.

 

Audi was prompted by customer complaints and accidents to add the little lip on the tt. So not much testing going on there! Apparently a 1:1 scale wind tunnel is stupid expensive. One of the reasons BMW bought Sauber was to get a freebie wind tunnel thrown in for their race team and their road cars. I guess areo just loses out in the cost benefit world of production cars. How often do we go fast enough to justify it anyways?

 

would it be possible to perform aero testing via computer simulation?