Spirited Driving Question

[Racer Boy]

As mentioned, the rear spoiler doesn't create downforce, it cancels some of the lift. That is a big difference. That is where the spoiler gets it's name, it "spoils" the lift.

I track my 986, and it doesn't feel loose in any of the real corners, some of which are up to 75 - 80 mph (130 kph). However, there is a flat-out kink that I take at about 125 mph (200 kph) where the back end definitely does not feel as planted.

The spoiler is up at that speed, so I bet it if I lowered the spoiler it would be exciting, in an unpleasant way. Could I handle it? Yes, because I would expect it to behave that way every lap, and I'm an experienced racing driver. For an average driver on the street, it would be alarming, and a high percentage of drivers would probably not be able to handle it. That's why Porsche put the spoiler on, just as they set up the car to understeer. Customers crashing their cars because they spin easily would be bad for business!

To answer the OP's question, the spoiler won't make any difference at under speeds under 200 kph!

[TeamOxford]

Originally Posted by Racer Boy

To answer the OP's question, the spoiler won't make any difference at under speeds under 200 kph!

This.

I sometimes feel that one of the reasons Porsche put a retractable spoiler on the Boxster was to avert possible high speed problems, like the ones that haunted Audi in the early TT models.

Just sayin'.............

TO

[Starter986]

Originally Posted by Racer Boy

As mentioned, the rear spoiler doesn't create downforce, it cancels some of the lift. That is a big difference. That is where the spoiler gets it's name, it "spoils" the lift.

I track my 986, and it doesn't feel loose in any of the real corners, some of which are up to 75 - 80 mph (130 kph). However, there is a flat-out kink that I take at about 125 mph (200 kph) where the back end definitely does not feel as planted.

The spoiler is up at that speed, so I bet it if I lowered the spoiler it would be exciting, in an unpleasant way. Could I handle it? Yes, because I would expect it to behave that way every lap, and I'm an experienced racing driver. For an average driver on the street, it would be alarming, and a high percentage of drivers would probably not be able to handle it. That's why Porsche put the spoiler on, just as they set up the car to understeer. Customers crashing their cars because they spin easily would be bad for business!

To answer the OP's question, the spoiler won't make any difference at under speeds under 200 kph!

Isn't the downforce necessary to cancel the lift? That's the ying and yang of it. No? Can't have one without the other. The spoiler is solid, so when the air hits it... it pushes down. No? Isn't that downforce? Absent that downforce you couldn't cancel the lift. No? Tell me I'm wrong. I'd like to know. Thank you.

[edc]

Originally Posted by Starter986

Isn't the downforce necessary to cancel the lift? That's the ying and yang of it. No? Can't have one without the other. The spoiler is solid, so when the air hits it... it pushes down. No? Isn't that downforce? Absent that downforce you couldn't cancel the lift. No? Tell me I'm wrong. I'd like to know. Thank you.

You are wrkng unfortunately. The answers to your questions are in the main already above.

[Burg Boxster]

Originally Posted by Starter986

Isn't the downforce necessary to cancel the lift? That's the ying and yang of it. No? Can't have one without the other. The spoiler is solid, so when the air hits it... it pushes down. No? Isn't that downforce? Absent that downforce you couldn't cancel the lift. No? Tell me I'm wrong. I'd like to know. Thank you.

Would you believe us if we told you downforce is lift?

[thstone]

Originally Posted by Burg Boxster

Would you believe us if we told you downforce is lift?

^^^ This. Is. Awesome. ^^^

[The Radium King]

see where the airflow departs from the roofline - that is where the air over the car transitions from smooth laminar flow into turbulent flow. at the rear, between the smoke and the car, picture air just swirling around with no cohesion.

note how the smoke has the shape of the upper half of an airplane wing. imagine the air under the car forming the lower half of the wing. the closer that transition point is to the front of the car, the less airfoil shape you have. conversely, the closer to the back it is, the more it looks like a wing.

ever notice how a big ship pushes a bow wave ahead of it? how does the water know the ship is coming? ditto spoilers. they create a larger pocket of turbulent air, which pushes the transition point forward and decreases lift.

the turbulent air has no cohesion, so does not provide any downforce by hitting the spoiler and shooting upwards. in fact, the air directly in front of the spoiler isn't even moving backwards at that point - it is just confused air.

this is why, if a car has a real, effective wing, that wing is high enough to grab the laminar airflow above the car. and realise that it is an upside-down wing, designed to use that clean air to produce negative lift that pushes down on the car.

this is also why the porsche gt3, etc., have both a spoiler (tailbase) and a wing - they serve two different purposes.

[Cunningr]

I was looking for a picture similar to this demonstrating the 986 air flows, but no luck. The website i did find had a 911 with similiar picture as this one. But the site gphad some diagrams of nascar setup, which explains the concept well. Nice pic. Rk!

[78F350]

I really miss Fred and hope he's doing okay. Check out this thread around post #67 for some interesting pics with the spoiler up.
http://986forum.com/forums/boxster-general-discussions/65306-boxster-986-aerodynamics-%40180km-hr-4.html

..and his Flickr:
https://www.flickr.com/photos/gtcollection/with/32407835180/

[MWS]

Originally Posted by 78F350

I really miss Fred and hope he's doing okay. Check out this thread around post #67 for some interesting pics with the spoiler up.
http://986forum.com/forums/boxster-general-discussions/65306-boxster-986-aerodynamics-%40180km-hr-4.html

..and his Flickr:
https://www.flickr.com/photos/gtcollection/with/32407835180/

Thanks for linking to this thread...I read through it some time ago, but forgot about it; this should close all discussions regarding airflow...

Regarding Fred...doesn't anyone have another social connection with him? He was a prolific poster, then just disappeared. I do hope it's nothing health related.

[10/10ths]

...in "Excellence Was Expected", the original designers and engineers for the 986 explained the spoiler in interviews with the author.

The designer wanted the rear end of the Boxster to drop like the rear end of the 550 Spyder, RS60, et al.

The aerodynamicist wanted the rear or the car higher for better aero--less drag, less lift at high speed.

The spoiler that pops up on the 986 was a solution that solved BOTH issues.

The pop up spoiler allowed the designer to design a rear end that sloped DOWN like the original racing Spyders, and still have the ability to raise up at speed and "spoil" the rear end lift, like a Gurney Flap.

Like others have posted above, it does not push down on the rear end, but it keeps the rear end from LIFTING at high speed.

For an autocross, no advantage.