Tuner1

I don't have a copy of the original 996TT Porsche technical docs or press release for the 996TT. Is the up/down hydraulic rear wing blade claimed to offer an actual aero or downforce benefit or is it just an unreliable gimmick?

rabbit1445

I believe the owners manual states it reduces air resistance at lower speeds and reduces rear axle lift at higher speeds. There was an article in issue 113 of Total 911 that took a look at Porsche's Active Aerodynamics and specifically talks about and shows the 996 Turbo in wind tunnel testing. It gives coefficient of drag and other numbers but does not give an exact amount downforce it provides.

Macster

Yes, but I do not recall the source or the amounts involved.

Also, I vaguely recall German regulations are pretty strict and any claims for aerodynamic benefits have to be backed by real numbers/facts from testing. I've seen these for the Turbo but I do not recall where.

The front aerodynamic body component mainly the air dam reduces the amount of air under the car which improves air flow through the radiator ducts and works to help create a low pressure area behind/under the car to improve air flow through the engine compartment and through the intercooler ducts. These as you know do not have any fans to aid air flow but rely solely upon air flow from speed and the aerodynamic characteristics of the car.

At low speed air flow through the engine compartment is aided by the shape of the rear spoiler while retracted and at higher speed when the spoiler is deployed. When deployed the spoiler also works to cancel any lift and in fact some downforce is generated but I do not recall how much, but I believe it is under 100 lbs of downforce. It doesn't have to be much if the lift is canceled and too much down force restricts top speed.

Based on my unscientific observation (no instrumentation) and experience from driving my Turbo over 120K miles in all kinds of weather and on all kinds of roads at sometimes high speeds, I have to add that aerodynamically (as well in other ways) the 996 Turbo is an impressive piece of kit. The air flow is so good that the radiator fans seldom have to come on even in hot weather. At high speed (approx. 165mph) the car is quite stable and confidence inspiring and appears to be able to handle the considerable heat load produced by the engine with aplomb. At the same time wind noise is not severe. The car is really in its element at high speed and a contributor to this is the car's aerodynamics.

Scott.

Old thread here: http://www.6speedonline.com/forums/9...downforce.html

"Porsche claims the rear spoiler generate 9 kg down force at top speed 190 mph"

With the OEM aero wing (see avatar), the increase is 20% greater than stock from what I remember.. I'll have to dig up a source on that one.

jpflip

In fact, in the book "Porsche turbo" by Peter Vann, it is mention a downforce of 9 kg at 300 km/hr…. Source from Michael Preiss head of Porsche aerodynamics department in Weissach. The problem was to get downforce without affecting drag!

Scott.

Thanks for the confirmation! Does it also mention the aerokit or just stock?

jpflip

After reading your post I did some more research and sorry nothing mention about the aerokit ;-(

Carlo_Carrera

9kg is not much considering the problems some have had with the hydraulics.

Tuner1

Exactly the info I was looking for! Since my car will rarely see over 150mph the raised wing likely provides little to no benefit.

This comment is interesting "At low speed air flow through the engine compartment is aided by the shape of the rear spoiler while retracted..." and if it is accurate would mean that permanently fixing the wing in the raised position would be a bad idea unless it was a dedicated track car.

TeCKis300

9 kg doesn't tell the whole story. It's really about how much gross downforce is generated. That is how much lift is cancelled + the 9 kg. I wouldn't be surprised if without the raised wing, there'd be something like 100 kg of lift at the rear @ 150mph.

It would sure be nice to have some real numbers though to understand better.

On another note, I passed a 997 turbo on the fwy today and noticed his rear spoiler was down. And that they had some luggage in the rear shelf. Wonder if he manually lowered it to reduce drag. Anyone doing long road trips ever notice any measurable effect at the pump?

DaveCarrera4

1. Interesting fact.

2. The 997 TT has the same faulty hydraulic system as the 996 TT. Could have been broken.

Macster

Exactly right. I recall the intro of the new Audi TT with a few early examples experiencing crashes that were traced to high speed lift. The solution was that tiny kick up spoiler lip. Not much downforce generated but it sure canceled out the lift. And the cars stayed on the autobahn.

While I have taken many a long trip in my Turbo and Boxster I never bothered to manually raise the spoiler and drive say at 70mph -- frankly this is expecting too much as the speed limit is on long stretches of highway -- hundreds of miles in cases -- 75mph (or higher) -- and do a mileage check then repeat with the same conditions except the spoiler was deployed.

My WAG is while there is probably some drag associated with the spoiler at 70mph or even higher speeds, the drag is nil, probably in some proportion to the downforce generated. IOW's, when the car is moving at a high enough speed to that lift reduction becomes real, when down force is generated, then there is some drag also being generated.

You could do a test like was done some years ago by a car mag to test the function and "efficiency" of a factory spoiler fitted to a late model Mustang.

Lap times, corner speeds, were measured with the spoiler present and removed. (The spoiler was fixed and not retractable so it had to be removed with the mounting holes taped over.) Then coast down times were measured with the spoiler present and removed. In the case of the Mustang testing found lap times were unaffected by the presence or absence the spoiler which indicated there was no downforce being generated and no lift being eliminated. Furthermore, testing found the presence of the spoiler affected to a measurable degree how slow or fast the car lost speed when coasting from a high speed.

It was determined from the test results the spoiler had no positive benefit and in fact represented a bit of negative benefit in the form of increased drag when present. (Which made the fact I had lucked upon a similar model sans the factory spoiler a nice bit of knowledge.)

Kevinmacd

The owners manual actually states do not run the car over 75mph if the rear spoiler does not deploy!

DaveCarrera4

Wow, hope that's not logged in the onboard computer - I bought my car with broken hydraulics and I'm pretty sure I went faster than 75 once or twice before fixing it...

"02996ttx50

i'd say that there has to be some measurable ( as noted ) downforce appreciation when the wing is deployed as there is no way weisach all just wanted us to have plumage during matting season..

balanced by the notion that at 75mph whether the wing is deployed or not would not be felt by anyone other than the MOST discerning test driver that has a/b'd all manner of this car, spoilers up/down fixed gt3 etc. at track speeds.

but over 150mph? i'm going to ask for a spoiler thanks very much. i fondly remember my c2 and then my 993 that all had these incredibly novel ( for their time ) deployable ( well, something moved ) appendages and it simply made me feel inadequate. though i loved to watch it rise and fall and would see folks marvel with envy

maybe that's why they put them there initially, to counter the notion that all porsche 911 owners were trying to ( ahem ) "compensate" for "something" HAH. just my thoughts..yours truly, dirk diggler