Angelus

I'm sure it does, it's not there for good looks. We carried out experiments with the 928 S4 rear spoiler, all very technical by putting snow on it in the winter and driving it. Changing the shape made for very interesting results. While the car in this case is the 996, my point is, I'm sure Porsche don't fit complicated pieces of kit just because they want to.

Was there not a conversation recently about removing the front spoiler if you have the factory aero kit? Not recommended by Porsche, as the front counter acts the rear downforce. I'm sure they calculate what's needed.

Dock

The rear spoiler reduces lift in the back by creating downforce; it is not there as a conversation piece.

I can probably get the aero data for the 996 Turbo, but I can tell you that on the 996 the rear spoiler being up reduces lift at both the back and the front. See the data in this article:

http://www.autozine.org/technical_sc..._aero.htm#Drag

kezcapt

I just want to relate to you how I fixed my spoiler as it may be a help for you. The spoiler was giving me the red message so I actuated the spoiler manually in the garage and listened to it. It sounded like the operation was intermittent. When I took the system apart it was clear that everything was in order. I tapped the end of the hydraulic pump and it started to work! I used a CRC lube especially made for electrical devices and lubed the end bearing (there are actually small holes at the end of the pump housing). I ran it some more and there was a dramatic improvement. I gave it a few more "shots" using the supplied straw in the holes on the pump and have never had a problem since.

Just as an aside, I noticed someone recommended WD-40 for the ram. WD-40 is petroleum based and will attack certain rubber compounds. It also attracts dust. I lubricate the rams with either a silicone lube which evaporates or a sprayable "dry" lubricant that is teflon based.

Lastly, as a person who has had the car to 150mph (closed track, professional driver, yadda, yadda) I can tell you that the aerodynamics don't really kick in until about 100-110 mph. One must remember that in Germany the car is expected to be driven off the show room floor and do maximum speed. In the states we don't even touch the true potential of the car (except on a track). As the spoiler produces very low amounts of down force to begin with, I seriously doubt you will have control problems at US highway speeds without the spoiler. I say this as someone who handles aircraft at 120-150 mph on the ground every day. I hope my experience with the spoiler proves helpful.

Dock

Which is why I asked him if he drives faster than 75 MPH.

I don't think there would be any adverse aero issues driving without the spoiler at speeds below 75 MPH.

Dock

Do you have hard data to back that up with?

cannon1000

I am sure I read somewhere that both the front and rear spoilers do provide aerodynamic benefit and are designed to work together. Adding more front or rear force independently will change the balance of the car at high speeds.

Does this mean you need them at 75 mph. Probably not. But at the speeds these cars are capable of - yes.

kezcapt

Yes.

First, let me say that my intention was to HELP the owner with the spoiler problem to fix their car without spending thousands. But as you are compelled to focus on the secondary element of my post, yes, I can support my contention that our spoilers contribute low amounts of downforce at low speeds. Most pilots are familiar with the formula:

L = 1/2 p V^2 S Cl, we can make a rough calculation;

where L = Lift, what we want to find

p = density of air 1.225 Kg/M^2
V = velocity say 33 m/s (around 119kmph or 74mph)
S = Plan surface area say .15m^2 (around 1m by .15m)
Cl = lift coefficient say 1.5 which is a good high value for this size and speed

the equation looks like

.5*1.225*33^2*(1*.15) which yields 61 newtons or 6.2 kg's (13.2 lbs) of downforce at 75mph.

This comports well with Paul Frere's statement in the 911 story (excellent book by the way) where he states about the GT2:

“Porsche claims that a front down force of 2.2 kg and a rear down force of 7.5 kg at 200 kph (124 mph) are produced. Corresponding forces at 300 kph (186 mph) would be 5 and 17 kg respectively”.

Since our spoiler is smaller than a GT2 then the numbers are pretty close. Most pilots also know that you cannot have lift without drag so a better way to make downforce is to create suction with a smooth underbody and thus take advantage of Bertonian and Newtonian effects.

I honestly just wanted to save a fellow rennlister some time and money. I am not interested in arguing. I will leave that to discussions about oil viscosity !

rage2

Go dig it up, and you'll find 9kg of downforce at 300km/h (188mph). At 75mph, you'll get more downforce putting a laptop in the back seat than the rear wing in the up position would generate. At top speed, you can get the same amount of downforce by installing the factory subwoofer.

To me, that's a conversation piece.

Edit - kezcapt, you forgot that the area where the wing is, even in up mode, is a low pressure area. If you look at the rear wing of 911 race cars, you'll notice it's much higher, a few inches under the roofline, to get the most air energy as possible.

"02996ttx50

outstanding.

kezcapt

Damn auto correct feature! Obviously it is Bernoullian effect not Bertonian effect that works with the under body panels. (We can save the wing vs. spoiler discussion for the next oil viscosity thread).

I do hope however that the gent that had the original problem is able to fix his spoiler inexpensively. After I discovered my end bearings having lube issues I wondered how many people spent 2 thousand or more to replace the hydraulics etc. I know that for some this my be a temporary fix on an inevitable failure but if even if a few make it work then our little forum was worth it.

Happy driving and share your fixes/problems with the rest of us

"02996ttx50

bernoullian/bertonian, lets call the whole thing off. thats sh*t you posted was great! even if i didn't understand it. i'm just glad our cars aren't rubenesque all kidding aside though, i am in fact one who has paid the price for the factory recommended fix, which is to replace the entire set of components once they fail at $1500.00+.

but the second time around, the spoiler re-bleed DIY was a wing saver for me and the step by step was found posted here.

i concur, a great little room.

Kevinmacd

According to the owners manual, if the spoiler is not deployed at 75mph, the car will not handle properly and can become unsafe due to lack of downforce and should not be driven!

Macster

The small amount of downforce may seem insignificant but we can't know how much lift is also eliminated. There could be significant amount of lift that is negated by the spoiler in the act of creating just a few kg of downforce.

IOWs, if the aero hardware was removed the car may not just lack a few kg of downforce at speed, but may experience considerable lift.

I can recall when the failure to anticipate lift and deal with it properly caused some early Audi TTs to leave the road surface as speeds well below the Turbo's top speed.

Also, while the spoiler comes up at 75mph, although with my car the actual speed is 73mph (the speedo reads 2mph optimistic) in some areas I drive the top speed is 80mph.

Lastly, even at 75mph I have sometimes driven in high wind in which the speed of the wind passing over/under/around the car is the vehicle's speed plug the speed of the wind. I have driven in 30mph+ winds maybe more if one takes into account gusts of wind. On some roads I drive on in certain areas known for wind problems, there are windsocks at the road shoulder to show the direction of the wind and give one a chance to estimate its speed.

In one place I can recall the 75mph speed limit is posted to 65mph due to the frequent presence of high winds in this section of the road.

Then there are even at highway speeds the blasts of wind from vehicles going in the opposite direction.

I can sympathize with the OP's reoccurring spoiler problem but doing away with spoiler is wrong-headed unless I guess if the OP would be willing to fit the car with a speed limiter to prevent the car from ever obtaining a speed at which Porsche deemed the spoiler should be deployed.

Sincerely,

Macster.

Kerrage

Anyway back to spoiler problems haha..I have 47k kms and mine works great however I am noticing a bit of leackage on the driver side ram. Does anyone have advice if it is not to far gone yet?

I wish ours sounded like the GT with the loud noise when the wing comes up.

I usually force mine up before I drive so that it doesnt operate so much

Tytus

11 years old, 70,000 miles, driven daily and through the winter, tracked for the last 3 years, no additional maintenance performed other than general washing...spoiler working as good as new.

Now I just jinxed myself to add this bit of info to the forum...

Tytus