Aerodynamics ? Front splitter...

[masraum]

Hey, I've noticed in several front splitters in lots of cars, not just Porsches, that in the center of the front spoiler there is often a notch. The front lip spoilers didn't have it, but the early S spoiler did, and the new 996 tt front end have them. What is that for?? To balance the front to rear aero advantage?

[Don Plumley]

I believe the splitter helps to separate or move the air more smoothly over and under the car. Instead of having the air pile up in front of the car, the splitter helps to direct it either over or under the vehicle. In particular, having smooth air under the car is important - remember the Bernoulli principle; fast air = low pressure, slow air = high pressure. Get that air under the car as smoothly as possible to balance the fast moving air over the top of the car. Or something like that.

Hopefully one of the engineers will chime in here - as long as its not like the jack plate thread

[Randy Webb]

The jack plate has splitters to prevent separation of the flow of brken metal from rusted out cars.

I'm a scientist, not a mere engineer, so can I reply?
The splitters can help the air flow to the sides (splitting the flow) and/or maintaining laminar flow and/or reducing air from going under the car. You would have to have the wind tunnel data in front of you to know for sure.

[Bill Verburg]

This is purely an educated guess on my part - Esthetics

You will never see a notch on a race car.

On a street car function is usually secondary to form.

There is a large very high pressure area in front of the lower valance, the pressure decreases toward the sides of the car so max increase in lift reduction will be at the sides(anything that can be done to keep the air in front instead of under the car will reduce lift)

The best exit for air through a central scoop is out the top rather than out the bottom.

[Tyson Schmidt]

The early S had the gap in the middle of the spoiler for a very simple reason. So the tow hook would be usable without tearing the front bumper off.

[Chuck Moreland]

Interesting thought, but the tow hook eye on early cars is on the passenger side, outside the control arm. Not front and center.

[Randy Webb]

Yes. But Ludvigsen has a stmt. similar to the one by TS in his book. I'm not sure what it means -- maybe the original 901 had a different tow eye location?

[john70t]

Air moving through a venturi (underside and ground?) creates a vaccum on the surfaces. The 911 profile is kind of like a wing though, so the effect might be to push most air to the sides, create a vaccum under the sides of the skirts and channel a high speed strean through the center? Only a guess.

Check of this one for areodynamics:
http://www.ashcom.homestead.com/Elford2J.html

[GeorgeK]

Chuck,
The tow hook is on the crossmember, in the middle of the car, at least on my '73
GeorgeK

[Chuck Moreland]

Not on my '73. There must be different configurations.

[Mike M]

The tow hook on my 69S is right in the middle of the car,that must be the reason there is a notch in the S spoiler...

[Chuck Moreland]

Errr, ummm,,, yes. My '73 pan was replaced.

[TRE Cup]

Rumour i heard: The notch was there for assembly line reasons- the car was towed thru the line with the center hook and it would not clear the spoiler if it was solid.
But then again, what about those 1500+ RS's?
From peronal experience
I can say that the convolution of all those curves don't work too well when you try to "connect" the two sides of the 73 S spoiler in the middle

[Randy Webb]

Well, this is one for the wind tunnel isn't it? Anyone have a wind tunnel they want to donate? Maybe the factory's "Early Car Uber Alles" worker group(*) will do it at Weissach? Or we could build a small tunnel and play with some models by adjusting the Reynolds No. and putting some clay in the gap middle of the ridge.


* OK, I made that up, but it is something that _should_ exist.