Down Force

[RLJ]

One of the changes I made to my car was the additon of a front splitter. This one addition has changed the ride of my car more than any singular thing. At 75MPH down the freeway the front end does not hop on every expansion joint. It seems to plow thru them smoothly. Like a sail boat driving thru the waves rather than a power boat blasting over them. I am running 22mm front torsion bars and 19mm front anti-sway bars on a light car. This front down force really makes a difference. Any one out there who understands calculating down force care to give me any idea how much force is being created at 75 MPH.

Randy Jones
1971 911

[campbellcj]

Looks sweet Randy! Do ya have a rear tail on this car too (I forget)? I've always heard that you should do front/rear spoilers in conjunction to avoid an imbalance at either end of the car.

Chris C.

[pbs911]

That is a GREAT color!!! What color is it?

All I know is that the air can no longer "lift" the front end. Do you have a rear spoiler? When you had a spoiler in front you must add one to the back. A ducktail would go well. Post more pics!!!


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Paul
78SC Targa

[Early_S_Man]

MEASUREMENTS ... not calculations, Randy!
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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 07-22-2001).]

[rstoll]

Yeah, that color is electric. show us some more.

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Robert Stoll
83 SC
83 944

[Jack Olsen]

Until Randy logs on with more, here's a (previously posted) picture of his gorgeous car:



Randy, I'm considering adding one of these, too. How far out from the spoiler does your lip extend? I've been told that the handling difference between adding 1 inch and 2 inches is substantial.

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Jack Olsen
My Rennlist home page • My Pelican Gallery page • My Porsche Owners Gallery page

[This message has been edited by JackOlsen (edited 07-22-2001).]

[lsolon]

Amazing looking car!

[Jack Olsen]

Randy's car might just be the most meticulously and intelligently put together early car on this board. A real work of art.

[pwd72s]

Jack must still be looking for a way to whup that oil temp heat devil, and still have a good looking front end. Right, Jack? I think Iris has a cute front.

[RLJ]

First off, thanks Jack!

The color is Iris Blue Metallic a Porsche color. The car has a ducktail.

The leading edge of the splitter is the same contoure as the bumper. I was told by Fred at GT Racing who mfg. the RS front bumper and rear deck lid I am using, that a front splitter that stuck out another 2" would work better and not over power the ducktail down force. That is the way I understood his comments. For street driving what I have is fine I think.

Randy Jones
1971 911

[island911]

Randy, If you want to calculate the downforce created by the splitter pick up Joseph Katz Book “Race Car Aerodynamics.” It’s a book I wish I had before I took my applied aerodynamics class, as it’s much more palatable than theoretical. Warren, of course, makes a good point in “Measuring” may be easier to get usable numbers.
In general the splitter should provide more downforce than a “wing” of the same size in free-stream. This is due to the stagnation pressure. . .hmmm, let me rephrase that. . .a bunch of air smacks into the front (windward side) body work of you car and produces high pressure. The splitter sees the high pressure (produced by the frontal area) on the top of the splitter, and free-stream (mostly) on the underside. Mmmmm, makes good downforce.
Jack, The handling difference between adding 1 inch and 2 inches should be substantial. Furthermore, you help the cooling air flow that much better by lowering the underbody pressure. Coool.


BTW, on the pict Jack posted, is that taken over at WSU? If so what was the event?

one more pic:

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'81 Platinum Metalic SC COUPE

[This message has been edited by island911 (edited 07-22-2001).]

[rvanderpyl]

Just as a matter of interest, none of the spoilers actually produce downforce, they just reduce the lift being produced at speed. I believe that the spoliers on the latest GT3 manages to produce 0 lift.

Robert

[pwd72s]

Pic that jack submitted was taken in May, at the R Gruppe meet in Cambria, California. Visit his site, if you have the time. Lots of "way cool" early 911's were there. Randy's "Iris the Slut", of course, was one of the leading characters in this cast of beautiful cars.

[island911]

Originally posted by rvanderpyl:
Just as a matter of interest, none of the spoilers actually produce downforce, they just reduce the lift being produced at speed. I believe that the spoliers on the latest GT3 manages to produce 0 lift.

Robert

none ? Not true. Many spoilers actually do produce downforce; that is they have a negative CL (lift coef.) The net effect of the whole car is indeed "less lift" but the spoiler/splitter here is producing downforce.

Randy, I'll give a shot at calculating the downforce. . . what are the dimensions of your splitter?

thanks pwd72s

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'81 Platinum Metalic SC COUPE

[This message has been edited by island911 (edited 07-23-2001).]

[Jack Olsen]

Yeah, pictures of the Cambria event are at:

http://members.rennlist.com/jackolsen/Cambria1.html
http://members.rennlist.com/jackolsen/Cambria2.html
and
http://members.rennlist.com/jackolsen/Cambria3.html

Prepare to start thinking about refinancing the house, robbing the local bank or entertaining other schemes to finance an early restoration...

Randy's color is one of those things that photographs never quite do justice to. In person, it's really a sight to behold.

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Jack Olsen
My Rennlist home page • My Pelican Gallery page • My Porsche Owners Gallery page

[RLJ]

As you can see from the pic's the splitter is about three inches wide and is bannana shaped tapering down to about 1/2" before dieing off at the wheel arch. If it makes any difference the splitter is about twice as wide as what you see. If it sticks out 3" then there is 3" under the bumper that is also flat. Thanks for the help.

Randy Jones
1971 911