Crown

fritz:

If you are really interested, downforce is in fact negative lift.
When aerodynamic lift is reduced (by using such sensible measures as spoilers) to a value below zero, then it starts to distance itself from its nasty reputation for destabilizing cars at high speed by calling itself downforce.

 

Thanks fritz.  

Definitely interested! although my bad habit of adding humor at all times might not indicate that.

I have always amateurishly equated downforce with “spoiled” lift.  I wonder about it this way:

If you could weigh the rear axel when the car is at top speed would it show an additional (approx) 136 kg.? Or would it show the same weight as when the car is at rest because the airfoil (lift) has been merely neutralized?

Seems like the scale would indicate a gain of 136 kg.

Oops..., if it read +136kg that would be a "subzero" lift right?

Now I'm betting the scale at top speed would show the same value as when the car's at rest.

--
2007 997 Turbo

fritz:

In fact, a handful of road cars like, for instance, the Porsche 996 and 997 GT2 models, have aerodynamic downforce (= negative lift) in spite of not having wings as large or pronounced as an F1 car.

--

fritz

Wow, that surprises me.

On the other hand, that means that the total negative lift generated by the wings, front lip, etc is bigger than the total lift generated by the "normal" shape of the car.

Sounds logical, especially when you keep in mind that the shape of the car is designed not to generate too much lift, and the wings are especially designed to generate as much negative lift as possible.

Concluding: ignore my earlier remark about F1 cars :)

At MMD:

Look at it like this: if you don't apply wings, the weight put on the wheels of a car will be less at top speed than at v=0. If you do apply spoilers and aerodynamic aids to that car, the effect of the lift is reduced by the negative lift of those aids. If this negative lift generated by these aids is bigger than the normal lift generated by that car, the net result will be downforce. So, then the weight on the wheels at top speed is higher than at v=0.

Does this answer your question?

PS: I love this thread!!!

MMD:

fritz:

If you are really interested, downforce is in fact negative lift.
When aerodynamic lift is reduced (by using such sensible measures as spoilers) to a value below zero, then it starts to distance itself from its nasty reputation for destabilizing cars at high speed by calling itself downforce.

 Definitely interested! although my bad habit of adding humor at all times might not indicate that.

I have always amateurishly equated downforce with “spoiled” lift.  I wonder about it this way:

If you could weigh the rear axel when the car is at top speed would it show an additional (approx) 136 kg.? Or would it show the same weight as when the car is at rest because the airfoil (lift) has been merely neutralized?

Seems like the scale would indicate a gain of 136 kg.

Oops..., if it read +136kg that would be a "subzero" lift right?

Now I'm betting the scale at top speed would show the same value as when the car's at rest.

 

Actually, I am not adverse to humor myself.  

It might be better to think of lift as being "spoiled downforce", since downforce is the  desirable quantity in a car whereas lift is more useful in a plane.
Using that logic though, I should have written above that lift is negative downforce.

To use figures to illustrate it:

If the static weight acting on your car's rear axle is 800 kg at standstill and the car has efficient aerodynamics which generate a downforce of 100 kg on the rear axle at 200 km/h  and you were to drive over your notional scales at 200 km/h, then the scales reading when just the rear axle is bearing on them would be 900 kg.

If, OTOH, you have sawed off the rear wing and the resultant configuration results in rear-end lift of 100 kg at 200 km/h in the wind tunnel, then the scales reading would be 700 kg under the conditions described above.

The additional 200 kg acting on your rear axle, aided by an appropriate force acting on your front axle to give balanced handling, would make the car that much more stable at speed. So lock that saw away in case you go sleep-walking some night. 

A wind tunnel just has load cells under all the wheels of the car measuring its net weight (static weight minus lift or plus downforce, as the case may be), as well as measuring the horizontal force imposed on the car due to aerodynamic drag.

fritz

ing the MMD:

Whoopsy:

 

 

What you really want is something like the 996 C4S, which looks exactly like the 996 Turbo sans wings and side inlets. Too bad the 997 C4S doesn't look like the 997 Turbo.

With such a body, have someone souped up the engine to at least Turbo spec and you will be in heaven.

HAHA! Good idea; but how will other Turbo owners know I'm "cool?"  (kidding)

You make a good observation though. Perhaps the 997T wing is needed even more because the intercooler vents add additional upward aerodynamic forces?!

Hummmm..., I feel better now if that's true. 

The intercooler vetnts take in air horizontally and exits them rearward and downwards, it does not generate downforce, it may even generate lifts because of the downward path of the air.

At best the air exits sideways out of the vents and it does not generate lift nor downforce.

Concerning the 'cool' part, no one's stopping you into putting a big ass turbo sign on the rear or the side :)

Whoopsy:

ing the MMD:

Whoopsy:

 

 

What you really want is something like the 996 C4S, which looks exactly like the 996 Turbo sans wings and side inlets. Too bad the 997 C4S doesn't look like the 997 Turbo.

With such a body, have someone souped up the engine to at least Turbo spec and you will be in heaven.

HAHA! Good idea; but how will other Turbo owners know I'm "cool?"  (kidding)

You make a good observation though. Perhaps the 997T wing is needed even more because the intercooler vents add additional upward aerodynamic forces?!

Hummmm..., I feel better now if that's true. 

The intercooler vetnts take in air horizontally and exits them rearward and downwards, it does not generate downforce, it may even generate lifts because of the downward path of the air.

At best the air exits sideways out of the vents and it does not generate lift nor downforce.

 

Concerning the 'cool' part, no one's stopping you into putting a big ass turbo sign on the rear or the side :)

The intercooler cores are in fact inclined downwards at the rear, so that the air flow through them would result in some lift. The main air resistance should be in the cores, not the inlet / outlet vents.
 

fritz

Whoopsy:

Concerning the 'cool' part, no one's stopping you into putting a big ass turbo sign on the rear or the side :)

HAHA!   

 I forgot what was actually going on in the photo below, but here's a "Turbo" without intercoolers.  

Joost:

fritz:

In fact, a handful of road cars like, for instance, the Porsche 996 and 997 GT2 models, have aerodynamic downforce (= negative lift) in spite of not having wings as large or pronounced as an F1 car.

--

fritz

Wow, that surprises me.

On the other hand, that means that the total negative lift generated by the wings, front lip, etc is bigger than the total lift generated by the "normal" shape of the car.

Sounds logical, especially when you keep in mind that the shape of the car is designed not to generate too much lift, and the wings are especially designed to generate as much negative lift as possible.

Joost, you may be interested in these extracts from Sport Auto Supertests of the 997 GT2 and, for comparison purposes, the now "obsolete" Opel Speedster Turbo and BMW M4. 
VA or Vorderachse is front axle and HR/HR is naturally rear axle.

You'll note that the Speedster (a Lotus Elise in a party dress) also has downforce on the front axle, presumably mainly due to Lotus exhausting the air from the front radiator over the top of the car instead of under the car. The lift of the Z4 is more typical of cars in general.

Sport Auto is one of the few magazines to routinely put test cars into a wind tunnel and publish the results in this way in its Supertest reports.

--

fritz

So someone asked a simple question about the lift cylinders in the rear wings, we completely, utterly hijacked the thread and turned it into a 3-page discussion about areodynamics :)

The intercooler vents'  main path is angled downwards but the vent slates kind of redirect them sideways to reduced the lift generated. I recall seeing a airflow diagram of the 997 Turbo and it shows the air path exiting the vents is coming out sideways.

Whoopsy:

So someone asked a simple question about the lift cylinders in the rear wings, we completely, utterly hijacked the thread and turned it into a 3-page discussion about areodynamics :)

The intercooler vents'  main path is angled downwards but the vent slates kind of redirect them sideways to reduced the lift generated. I recall seeing a airflow diagram of the 997 Turbo and it shows the air path exiting the vents is coming out sideways.

 

Blame the guy who didn't start a thread on aerodynamics, making us have to hijack this one instead!

I have to take back what I wrote earlier because the intercooler cores slope upwards to the rear, not downwards. The intercooler cores will cause downforce, not lift as I think I wrote above.

fritz

Yes, that guy has long lost interest in the technical discussion on aerodynamics , even though it sounds interesting.  In fact, it even seems my cousin has lost interest in getting the lift cylinders changed!!  (so carry on guys - you're on your own!!)

fritz:

Whoopsy:

So someone asked a simple question about the lift cylinders in the rear wings, we completely, utterly hijacked the thread and turned it into a 3-page discussion about areodynamics :)

The intercooler vents'  main path is angled downwards but the vent slates kind of redirect them sideways to reduced the lift generated. I recall seeing a airflow diagram of the 997 Turbo and it shows the air path exiting the vents is coming out sideways.

 

Blame the guy who didn't start a thread on aerodynamics, making us have to hijack this one instead!

I have to take back what I wrote earlier because the intercooler cores slope upwards to the rear, not downwards. The intercooler cores will cause downforce, not lift as I think I wrote above.

Getting close to page 4 now :)

I am no fluid dynamic engineer, but looking at the path, the air comes in horizontal, hits a slope curving upway above the rear wheel, I suspect there will be a tiny bit of downforce generated there, the air then shoots downwards hitting the intercooler, probably generate a little bit of downforce there, it then exits down but directed sideways by the vent slots, the sideway motion probably cancel out any lift it might cost.

Arshad:

Yes, that guy has long lost interest in the technical discussion on aerodynamics , even though it sounds interesting.  In fact, it even seems my cousin has lost interest in getting the lift cylinders changed!!  (so carry on guys - you're on your own!!)

By the way, tell you cousin if he had a chance to drive the Turbo in a rainstorm on the highway, (I know you don't get much rain but there is always hope) check out the rain drops coming off the rear of the car with the wing up and down.

I did that the 2nd day I owned mine, I did a 5hr round trip on highway from Vancouver to Seattle in a downpour, I kept pushing the button to raise and lower the spoiler to check out the change in air flow pattern, it was facinating, I thought it was a fun thing to do on a boring drive and I'd probably spent more time looking at my mirrors than looking forward.

O and a short answer to the original question is yes, changing the cylinders will have the desire effect, the cylinder is a dump part, there is only 2 settings, up or down, so a higher cylinder gives a higher lift.

fritz:

Whoopsy:

So someone asked a simple question about the lift cylinders in the rear wings, we completely, utterly hijacked the thread and turned it into a 3-page discussion about areodynamics :)

... 

Blame the guy who didn't start a thread on aerodynamics, making us have to hijack this one instead!

I have to take back what I wrote earlier because the intercooler cores slope upwards to the rear, not downwards. The intercooler cores will cause downforce, not lift as I think I wrote above.

I'd say forum's admin should give the original poster a warning for starting a thread with the wrong title.
 

--
 

Regards,
Can
997 Turbo + Bilstein Damptronic (Review) + ECU Tune (???) + Cargraphic Exhaust (Heavenly Race Car Noise Review)

we should all vote him 5 stars for bearing with us....

cannga:

I'd say forum's admin should give the original poster a warning for starting a thread with the wrong title.
 

 

Doesn't matter, we routinely hijack thread for no apparent reasons, not his fault that we have decided to hijack his.

Whoopsy:

cannga:

I'd say forum's admin should give the original poster a warning for starting a thread with the wrong title.
 

 

 

Doesn't matter, we routinely hijack thread for no apparent reasons, not his fault that we have decided to hijack his.

Hijacking threads is a big problem. Good thing in our case there're no hostages and no damage or loss to property.

Ah, so that's what you guys look like!!! 

Arshad:

Ah, so that's what you guys look like!!! 

BTW, was just kidding about banning you for posting the wrong title for the thread. It has turned out to be an excellent one & in addition took car of MMD's wing fetish for good (I hope). The funniest thing is your cousin is not even interested in doing the lift anymore. Cheers.

--
 

Regards,
Can
997 Turbo + Bilstein Damptronic (Review) + ECU Tune (???) + Cargraphic Exhaust (Heavenly Race Car Noise Review)

cannga:

 The funniest thing is your cousin is not even interested in doing the lift anymore. Cheers.

 

Ahhhhh..., We succeeded!  Wheeeew. THAT was close!  

(joking)
--
2007 997 Turbo

Of course, guys, I get all the humour!   I''ve also enjoyed myself thoroughly!  This is the best part of being on such a friendly forum as is Rennteam, and besides is possibly the best way anyone could be hijacked!!! 

It was your invaluable inputs that made my cousin decide against going ahead with his idea, so thanks again!  (And besides, we are MUCH better informed about the mechanics of the rear wing!) 

Now that we got the rear wing taken care of, can we start on the front bumpoer? :)

Whoopsy:

Now that we got the rear wing taken care of, can we start on the front bumpoer? :)

LOL. Yeah! WTF is with that grille? I'm thinking of hack-sawing mine. 

Hmm, interesting look, might even say it looks better.

Shall we start another 3 pages discussing the areodynamic effect of those grilles?

I think I am going to get inline and discuss the raised Porsche badge on the hood, would the car look better and perform better with a flushed fitting one?

Of course it would! You can buy them from Porsche exclusive department (as a GT3 RS part) for the special prize of €299,- excl. vat. :-)

This one is the BOMB!!

Ron (Houston):

This one is the BOMB!!

Somebody call the bomb disposal squad!

fritz

fritz:

Ron (Houston):

This one is the BOMB!!

 

Somebody call the bomb disposal squad!

LOL! I just spit out my coffee thru my nose. 

--
2007 997 Turbo

that's to dry the laundry i guess.......

fritz:

Ron (Houston):

This one is the BOMB!!

Somebody call the bomb disposal squad!

What is this "wing?!?" for?

wheelie?