do they actually produce downforce at speeds?

 

yes actually the oem spoiler provides a zero lift rear end (the front end stock is zero lift)

 

would you know offhand the amount of downforce, in pounds, at speed.....say 60mph.? just curious..

 

Don't forget the 4 difusers that make it zero lift.
Which mostly boils down to the ones in front of the wheels that push the air down to keep it out of the bumper/rearend.

I don't think the spoiler actually provides and measured downforce. The combination of the diffusers and the spoiler prevent lift. Essentially keeping the weight of the rear static at "any" speed.

 

correct me if I am wrong... coming with aerospace background

I can tell you that it is the job of the spoiler to create downforce; NOT the diffusiors, which mostly act to decrease the amount of turbulent flows generated..

 

60 mph doesn't matter - the spoiler does little if anything back there at that speed. The spoiler and underbody diffusers create zero lift intended for high speed.

I read yesterday at 186 mph, the 911 GT-3 creates only 55 #'s of downforce with an adjustable Gurney flap. The spoilered G creates no downforce but would have lift without it, creating some instability at the drive wheels. The amount of air that ever gets to the spoiler is apparently quite small for most cars but they work with what they have, those pesky engineers.

The diffusers, I believe, act to move air flow in a way that keeps lift from resulting under the car. Air moving slower under the car creates a wing-like effect, so I guess they route the air more efficeintly around the wheels. No downforce is at play, but the results are the same if lift is avoided.

 

I guess it really depends on your definition of what a spoiler is. If you believe that a huge rear wing is considered a spoiler, then yes a spoiler will provide downforce.

I've always thought of a spoiler as something that disrupts (modifies) the flow of air.

I don't think our aerodynamics are advanced enough to provide actual downforce. Downforce meaning an actual force pushing down on the vehicle that is independent of gravity. However, I do believe that it is advanced enough to prevent any high pressure zones underneath the car to cause an upward force.

 

That's a very good explanation, however, please do also note that the downforce generated from a constant angle spoiler..flap or whatever is dependent on the speed of an object.

Thus, you may say that at 60mph, the spoiler is not advanced enough to provide actual downforce but a 0 lift situation; however, at 120mph, the situation might be a bit different

We will never know w/o a wind tunnel =)

 

On the G sedan, the rear spoiler causes the drag coefficient to drop from .028 down to .026. Either way, the car is still zero lift.

 

They are advanced enough to push the butt of the car down, ala downforce, and pressure zones are avoided via the diffusers. Two different things - same goal. Like I said - little air gets over to the spoiler, but it's not a big deal to make it work and actually defy the flying intentions of the car.

 

i recall the zero lift from the spoiler from the brochure days, so basically it's there to create a zero lift rather than to "push" the rear wheels to the ground to give it more bite at triple digit speeds? what would happen if the spoiler is angled up 15degrees? no more zero lift?

 

+1 coming with mechanical background, haha

 

actually i thought stock 05 sedans had a CoD of .27 and the spoiler brought it down to 0.26 9thats what the infiniti site said

 

I stand corrected... The advertising for the 03 indicated 0.28 and 0.26. I guess they refined their figures sometime after 03.

 

I don't think the rear spoiler on the G is intended to create any downforce. It barely has any angle to it. I believe it is only present to shape the air off the back of the car. This is why it protrudes rearward and not upwards.

You'd really need something like the Evo spoiler to get real measurable downforce. something that is low is not going to do a whole lot. The Porsche is case in point. Move it up in the airstream and you would get a lot more downforce. IIRC the Evo has more than that 55# at that speed.