Spirited Driving Question

[particlewave]

Originally Posted by MWS

And thanks for adding one of the classic engineering brain experiments to the mix. LOL. I've always contended that a model plane on a treadmill won't take off (it's not moving through the air, hince no pressure change and no lift) BUT you said jet. A jet engine moves air, so even if the wing isn't moving through a medium, the jet is moving air over the wing producing *some* lift. Would it be enough to take off? Doubtful, but reason would say that if it DID move enough volume of air to sufficiently reduce pressure, then lift would occur. Think of a model plane in a wind tunnel...the planes forward motion (same as with the treadmill) would be zero, but relative speed through the air would still create lift...theoretically if the fan in the wind tunnel was mounted on a sufficiently sized wing, it would lift itself. With that, back to our regularly scheduled programming...

Well...

An aircraft engine (model or full size) moves air, not the wheels. Once inertia on the treadmill is overcome, the amount of forward thrust to balance the forces of the tread on the wheels is minuscule.

If one is arguing that forward thrust is applied only to overcome that tread to wheel friction and hold the plane stationary, then it won't lift off. However, the amount of power needed to hold it stationary is tiny.

For example, if the plane needs to be moving forward at 60mph to take off, and treadmill is moving at 60mph in the opposite direction, the amount of power needed to take off would be almost exactly the same as it would without the treadmill.

The Mythbusters did it.
https://m.youtube.com/watch?v=YORCk1BN7QY

What were we talking about?

[edc]

Originally Posted by husker boxster

Be aware that Cup2s are not very good in the rain. They are track tires that "can" be used on the street. But their forte is dry track tire, not necessarily a street tire. If you're buying Cup2s, you should be running it primarily on a track, not the street.

You may have had PS2s, which is an old design and not a great tire IMHO - rides rough and takes significantly longer to warm up on the track than SuperSports or Conti DW.

In your opinion of course. I have used my Cup2s only on the road and even in winter and rain. Cup2 are fine in the rain a long as it isn't torrential or with big standing water. In the UK it can rain any time any day of the year. Also here and Europe there are a fair few standard cars released as standard on Cup2 or other manufacturer equivalent tyres. We get a bunch of hot hatches that you don't get on these and of course in the same stable the GT4.

[Rich XTR]

Originally Posted by Cunningr

Ah now we are getting to the heart of my question. I am Sure no stability issue with slower, but is there a traction benefit?

I suppose the 70 or 75 point was some type of tested safety zone.

Anyway, can you dicern more traction when taking the lower speed corners with the spoiler up, or not?

In theory should have some, but what does buttometer say?

I ask here as I have no oputunities for a driver course! Thanks

My GUESS is the real benefits are at an even much higher speed than 70 or 75. Look at all the cars on the road with no spoilers and no issues at speed in that range and much higher. things get drastically different in higher speeds these cars are capable of. I understand that the shape of the car has everything to do with it. Porsche needed the spoiler to make the car safe at a much higher speed but didn't want to put a spoiler on that no one would see work until ultra illegal speeds(in the usa) so they made it come on at speeds that are legal. As far as the low on speed, once you determine you up speed you need a big gap for the down speed to prevent frequent up and down of the spoiler.

[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

[Cunningr]

Originally Posted by edc

In your opinion of course. I have used my Cup2s only on the road and even in winter and rain. Cup2 are fine in the rain a long as it isn't torrential or with big standing water. In the UK it can rain any time any day of the year. Also here and Europe there are a fair few standard cars released as standard on Cup2 or other manufacturer equivalent tyres. We get a bunch of hot hatches that you don't get on these and of course in the same stable the GT4.

For me We get so few rainy days where I live, unless my daily is in the shop I don’t drive my boxster in the rain. Actually get so hot I worry about tar road patches getting slippery. We are already in the 40s here.

[Frodo]

Originally Posted by particlewave

The Mythbusters did it.
https://m.youtube.com/watch?v=YORCk1BN7QY

Of course it'll fly. What I can't believe is that the guy at the yoke and throttle believed that it would not! This guy's a pilot??

[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.
Boxster 986 Aerodynamics @180km/hr

..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.
Boxster 986 Aerodynamics @180km/hr

..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.