Ugly rear wing on WRX

Are you insinuating that the 350Z is Nissan's equivalent of my "Daddy's Buick!?" There's a pretty wide range betwen STi and LaSabre...

They don't. Or rather they do, but like a truck. Or maybe a Buick. I'm guessing here, not having driven a Buick since we sold the 1978 Century my father-in-law gave my wife and I. That was about 15 years ago.

I've subscribed to C&D since I was 13. Their articles are very useful in helping me decide which cars to consider, but one's own personal taste inevitably wins out over somebody else's personal taste, and can sometimes outweigh every *objective* measure the testers can conceive. C&D does a fantastic job of doing what they do -- and that thing isn't telling me what car to buy, it's telling me their impressions of the various cars that are out there. Don't misunderstand me: I like fast cars. But it's not the

*only* thing that I like. Your preference obviously places more emphasis on power and handling and less on the aforementioned coddling than my own. That's fine. There's nothing wrong with that. But neither is *my* preference to opt for a little more coddling at the expense of performance.

And I've never denigrated the performance of the STi, or its value when measured strictly as performance / $. But as I suggested before, there are other considerations than just performance. There are cars that turn down the performance and turn up the comfort for the same price. (Nissan 350Z.) There are cars that keep the performance and turn up the comfort, but also turn up the price (Audi S4). I've never suggested that any of these cars -- or any other -- are objectively "better" or "worse" overall than any other. It all depends on your tastes (and your budget).

And I most definitely never intended to imply that anybody had made a bad choice by going for the STi. Unless they did it just for the ugly wing, of course. ;-)

- Greg

Poser.

- Greg

I had that coming.

With regard to the "functionality" of any spoiler or wing: It MUST be mounted in such a position as to encounter an undisturbed air flow to be effective in any aerodynamic sense. With regard to the "8-inch high wing spoiler": In order for the wing to have an effect, it would have to be mounted at least 4 or 5 inches above the roofline of the vehicle. Its position causes it to contact air that is mostly part of the boundary layer flowing off the roof of the vehicle, thereby negating any aerodynamic effect. The ends of the spoiler do become involved with some of the small Karmann vortices that are generated by the vehicle's passage through the air, but these forces are negligible and fail to generate enough down force to have any significant effect on handling.

I see. So you're saying the Subaru WRC Team, rather than spending hundreds of thousands of dollars on professional mechanical and aerodynamics engineers to design the spoiler for the WRC Impreza (which is not unlike the spoiler on the road WRX STi), could have just read Usenet instead.

"Patrick Fisher" wrote in news: snipped-for-privacy@speakeasy.net:

I have to question the logic as well. It may be true at lower speeds but apparently Porsche and many other sports car makers think differently.

Look at the tiny wing on the Audi TT which was added when too many of them became uncontrollable at high speeds. In all cases these spoilers are well below the roof line.

Every American stock car has an adjustable spoiler that runs along the rearmost edge of the trunk.

But as someone else pointed out, they all could have skipped the wind tunnels and gone straight to Google.

Barry

See attached file on the scanned page from Subaru regarding aerodynamics of the rear wing. BlueSTi "Scary-Fast"

Got a link?

Please don't put words in my mouth. What I wrote, paraphrased in the simplest of terms, is that the amount of down force generated by a wing, such as that mentioned in this thread, is roughly equivalent to a flea fart in a hurricane.

instead of generating downforce, how about cancelling lift?

Subaru specs states that the spoiler "increases down force up to 38 Kg at higher speeds". I don't know if that is considered a significant amount of down force or not. I do know that a lot of research was put into the aerodynamics of the body design. I can't imagine they did all that wind tunnel work than just "threw" an big wing on the back for the heck of it.

BlueSTi "Scary-Fast"

Regardless of the terminology involved, the vector addition is the same. In this case it is a negative number because the wing is mounted upside down.

Please don't misunderstand me, I do respect the engineering that went into the wing. Analysis of a typical wing of 6 foot span, optimally mounted, yields a force of approx. 58 lbs. The well designed and mounted STi wing generates significantly more force as stated in your post. The key to the mystery is the differential between the force generated by the wing and the mass of the vehicle. With a 1499.01 Kg (3,298 lbs) vehicle, and 38 Kg (83.6 lbs) of negative lift, there is a 2.5% differential. IMO this would be significant on the track , but for street use it plays a more aesthetic role. BTW 38 Kg. is roughly equivalent to 65% of the fuel tank capacity, and the effect of the mass of the fuel in the vector equation is present at any speed. Therefore, keeping the tank topped up as much as is practical should do more to improve handling at all speeds, than the wing adds at the higher speeds.

Homer

That amounts to the same.

By design, a car moving at speed is generating lift quite efficiently at two points: The air passing underneath is compressed between body and road creates lift at the front axle; airflow above and around the body, especially the downdraft in the rear creates upward lift at the rear axle.

Two things can be done about this:

1. minimize the amount of air entering under the car using a front spoiler/skirt and
2. attaching a wing that generates downforce proportional to the speed and the lift generated by the rest of the body.

Creating foils that counteract the upward forces with downward oriented lift will also increase overall drag the effects of which is a reduction of top speed and fuel economy.

That said, the sedan design with the step between trunk lid and roof line is generally not ideal for fast moving vehicles and the application of spoilers. Hence the need for such a big wing on the WRX.

florian /FFF/

Not Really. Adding 38kg of downforce from a wing does not add 38kg worth of inertia to accelarate both longditudionally and centripetally when cornering. 38kg of downforce is almost (The wing weighs summat) inertia free and adds to the grip in the tyres without increasing the lateral load when cornering. The 38kg of fuel will increase the lateral conering load and cancel out the additional grip because the tyre has to work harder under more load to hold the same G in a turn.

R

The one thing you haven't looked at is the design of the rear wing. It is not an inverted airfoil like an upside-down wing. It has slightly less curvature on the top than on the bottom. The spoiler is a box spoiler and the actual downforce is produced by the lower plane; which is a conventional ducktail-type spoiler. The wing's job is to bisect the airflow comming off of the roofline at lower speeds, and compress the air onto the lower plane. It smooths the air over the rear deck. At higher speeds, the wing will produce a bit of downforce, and it reduces lift because it is swept back and the vortex is somewhat behind the car. Its actually a pretty ingenious design. Though I have never calculated the downforce at speed, it appears to be pretty balanced and roughly consistent at all speeds. The lower element of the spoiler would have little on no effect at very high speeds, while the wing forces air onto the lower element at lower speeds. Subaru says this effect will become noticeable at about 85KM.

In addition, the gas tank is roughly in the middle of the car and applies roughly equal pressure to all wheels. It holds approx 50KG of fuel, which equates to roughly 12.5 KG of force on each tire. The spoiler produces a little over 30KG of downforce, which is about 15KG of downforce on each back tire if the spoiler was located over the back axle; which it is not. It is actually located nearly a meter behind the rear axle, and so will produce a small amount of leverage, still further increasing the downforce on the rear wheels.

The job of the spoiler is not to counteract lift forces, it is to balance them between the front and rear of the car; although because it does produce some negative lift, it does counteract some of the lift forces.

Interesting thread - the 30kg of downforce on the rears, does that mean 30k (approximately because of the "leverage") less on the front tire?

FNO wrote: snip

There would obviously be some effect, but it would be negligible. The spoiler is nearly a meter behind the rear axle. But the front and rear axles are nearly two meters apart. Therefore, also because of leverage, the amount of force reduction on the front wheels would be something less than half; around 15KG over both wheels. But, that would be more than offset by the downforce on the front end because of its shape. Remember, the spoiler's job is to balance the lift forces between the front and rear of the car.