 Optimization of Aerodynamic Aids for Autocross Racing |
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| chris914 |
 Jul 13 2006, 05:38 PM
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#1
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Member  Group: Members Posts: 489 Joined: 24-July 04 From: San Diego, CA Member No.: 2,393 Region Association: Southern California  |
I thought it would be fun to have the students were I work look at the Aerodynamics of my 914 and the 914 in general.
http://www.cassidy-online.com/porsche914/index.html Chris. (IMG:style_emoticons/default/popcorn[1].gif) |
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| J P Stein |
Jul 13 2006, 05:52 PM
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#2
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
Jeeze, what was that, a Corvette club AX?
You didn't bring enuff HP to that thing. I've never seen an AX course that open....but I'd like to (IMG:style_emoticons/default/biggrin.gif) |
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| nebreitling |
Jul 13 2006, 06:16 PM
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#3
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Member Emeritus Group: Members Posts: 3,314 Joined: 26-March 03 From: San Francisco Member No.: 478 |
THAT is interesting. those water-dye tests are remarkable! the water-dye test analagous to a 914 at what speed? do issues of scale change things? could you do some aero modelling with various spoilers and such available? so many questions...
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| chris914 |
Jul 13 2006, 06:30 PM
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#4
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Member Group: Members Posts: 489 Joined: 24-July 04 From: San Diego, CA Member No.: 2,393 Region Association: Southern California |
QUOTE(J P Stein @ Jul 13 2006, 03:52 PM)  Jeeze, what was that, a Corvette club AX? You didn't bring enuff HP to that thing. I've never seen an AX course that open....but I'd like to (IMG:style_emoticons/default/biggrin.gif) Yes the PCASDR (San Diego) AX's are a good size. Most lap times are 1:20 - 1:50 seconds Chris |
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| Brad Roberts |
Jul 13 2006, 06:33 PM
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#5
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914 Freak! Group: Members Posts: 19,148 Joined: 23-December 02 Member No.: 8 Region Association: None |
I knew several people who ran/run full composite belly pans front to rear under their 914's for AutoX. Specifically designed to work under low speed conditions. Absolutely amazing how much different the car handled. They won Parade one year with the setup in a SCCA GT2 914 (2.9 liter back then)
They now road race open wheeled cars in SCCA. He knew his aero shizznit also! Tell us how you can help us. B |
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| Jeroen |
Jul 13 2006, 06:35 PM
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#6
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914 Guru Group: Members Posts: 7,887 Joined: 24-December 02 From: The Netherlands Member No.: 3 Region Association: Europe |
excellent stuff!!!
the flow over the rear decklid looks even worse than I thought it would any chance you can do another test with some kind of gurney flap at the end of the top? |
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| chris914 |
Jul 13 2006, 06:38 PM
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#7
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Member Group: Members Posts: 489 Joined: 24-July 04 From: San Diego, CA Member No.: 2,393 Region Association: Southern California |
QUOTE(nebreitling @ Jul 13 2006, 04:16 PM) THAT is interesting. those water-dye tests are remarkable! the water-dye test analagous to a 914 at what speed? do issues of scale change things? could you do some aero modelling with various spoilers and such available? so many questions... Yes, scale is a big deal. That is why it was also done with computer molding using "Flow Works" as well. The Flow Works matched the Water Tunnel and Wind Tunnel at lower speeds. Flow Works was used for the higher speeds. Also the yarn tests showed the same results which was really nice. They also did several rear spoilers that I bought from Ebay. Chris. |
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| Dave_Darling |
Jul 13 2006, 07:15 PM
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#8
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914 Idiot Group: Members Posts: 14,981 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California 
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QUOTE(Brad Roberts @ Jul 13 2006, 05:33 PM) I knew several people who ran/run full composite belly pans front to rear under their 914's for AutoX. Specifically designed to work under low speed conditions. Absolutely amazing how much different the car handled. They won Parade one year with the setup in a SCCA GT2 914 (2.9 liter back then)... I was under the impression that the belly pans were intended for the Big Track, i.e. high speeds. Been a long time since I talked to him, though... I wonder whatever happened to his 914? --DD |
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| URY914 |
Jul 13 2006, 07:42 PM
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#9
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I built the lightest 914 in the history of mankind. Group: Members Posts: 120,319 Joined: 3-February 03 From: Jacksonville, FL Member No.: 222 Region Association: None |
QUOTE(Brad Roberts @ Jul 13 2006, 04:33 PM) I knew several people who ran/run full composite belly pans front to rear under their 914's for AutoX. Specifically designed to work under low speed conditions. Absolutely amazing how much different the car handled..... B Damnit Brad (IMG:style_emoticons/default/mad.gif) Now I gotta build a fuching belly pan. I'll NEVER be done with this car. Paul (IMG:style_emoticons/default/biggrin.gif) |
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| drew365 |
Jul 13 2006, 08:04 PM
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#10
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These are the good old days! Group: Members Posts: 2,004 Joined: 29-December 02 From: Sunny So. Cal. Member No.: 37 |
QUOTE(URY914 @ Jul 13 2006, 06:42 PM) QUOTE(Brad Roberts @ Jul 13 2006, 04:33 PM) I knew several people who ran/run full composite belly pans front to rear under their 914's for AutoX. Specifically designed to work under low speed conditions. Absolutely amazing how much different the car handled..... B Damnit Brad (IMG:style_emoticons/default/mad.gif) Now I gotta build a fuching belly pan. I'll NEVER be done with this car. Paul (IMG:style_emoticons/default/biggrin.gif) Your car will be like the Winchester House, you'll never die as long as you keep modifying it. (IMG:style_emoticons/default/biggrin.gif) |
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| URY914 |
Jul 13 2006, 08:06 PM
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#11
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I built the lightest 914 in the history of mankind. Group: Members Posts: 120,319 Joined: 3-February 03 From: Jacksonville, FL Member No.: 222 Region Association: None |
QUOTE(drew365 @ Jul 13 2006, 06:04 PM) QUOTE(URY914 @ Jul 13 2006, 06:42 PM) QUOTE(Brad Roberts @ Jul 13 2006, 04:33 PM) I knew several people who ran/run full composite belly pans front to rear under their 914's for AutoX. Specifically designed to work under low speed conditions. Absolutely amazing how much different the car handled..... B Damnit Brad (IMG:style_emoticons/default/mad.gif) Now I gotta build a fuching belly pan. I'll NEVER be done with this car. Paul (IMG:style_emoticons/default/biggrin.gif) Your car will be like the Winchester House, you'll never die as long as you keep modifying it. (IMG:style_emoticons/default/biggrin.gif) That's what I like about autocrossing.....so few rules to go by. (IMG:style_emoticons/default/biggrin.gif) |
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| Brett W |
Jul 13 2006, 08:38 PM
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#12
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Advanced Member Group: Members Posts: 2,856 Joined: 17-September 03 From: huntsville, al Member No.: 1,169 Region Association: None
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It would be interesting to see what happens to a 914 when you add GT flares.
You need to find the article published a couple of years ago in Racetech Magazine. They covered the FSAE car built by Missouri Rolla. They spent time in the Ford wind tunnel. According to the article they saw a 35% improvement in aero effectiveness below 45mph. |
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| Sammy |
Jul 13 2006, 08:38 PM
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#13
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. Group: Members Posts: 1,190 Joined: 21-January 03 From: Orange, Ca Member No.: 178 |
LOL, aero doan work iffn you don't get out of second gear. Kinda like putting a huge wing on the back of a front wheel drive honda civic that only goes 90 mph.
On a real track it matters, on AX it don't. |
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| turboman808 |
Jul 13 2006, 08:45 PM
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#14
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Advanced Member Group: Members Posts: 2,718 Joined: 31-January 06 From: North Jersey Member No.: 5,505 Region Association: North East States |
QUOTE(Jeroen @ Jul 13 2006, 04:35 PM) any chance you can do another test with some kind of gurney flap at the end of the top? Yeah I was curious about the same thing. Lots of guys in the padock are playing with vortex generators on the roof. They are pretty darn ugly though. Very curious what a gurney flap would do. And for that matter the vortex generators. Gurney would be cool if it worked though. (IMG:style_emoticons/default/biggrin.gif) Wish I knew more about aerodynamics (IMG:style_emoticons/default/confused24.gif) |
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| MattR |
Jul 13 2006, 08:48 PM
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#15
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Advanced Member Group: Members Posts: 3,279 Joined: 23-January 04 From: SF Bay Area Member No.: 1,589 Region Association: Northern California |
QUOTE(nebreitling @ Jul 13 2006, 05:16 PM) THAT is interesting. those water-dye tests are remarkable! the water-dye test analagous to a 914 at what speed? do issues of scale change things? could you do some aero modelling with various spoilers and such available? so many questions... Yes you can scale aerodynamics. You're looking at the Reynolds number similarity. You must minimize compressibility effects when choosing a new medium too. Its a simple calculation, but obviously much more difficult to effectively analyze. Basically you assume the reynolds number (inertial over viscous forces) of the model equals the reynolds number of the actual. You'll also need to use ideal gas laws to include pressure. |
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| nebreitling |
Jul 13 2006, 10:22 PM
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#16
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Member Emeritus Group: Members Posts: 3,314 Joined: 26-March 03 From: San Francisco Member No.: 478 |
QUOTE(Sammy @ Jul 13 2006, 07:38 PM) LOL, aero doan work iffn you don't get out of second gear. mostly true -- but the FSAE, Amod, and other guys have proven that there is some benefit, as Brett pointed out. given a light weight/purpose built AX machine that would compete nationally, it's worth investigating. then again, i've driven 90mph AX courses.... |
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| MattR |
Jul 13 2006, 10:32 PM
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#17
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Advanced Member Group: Members Posts: 3,279 Joined: 23-January 04 From: SF Bay Area Member No.: 1,589 Region Association: Northern California |
I went to this year's FSAE West event at Cal Speedway. There were a few teams competing with full aero and it just looked like it slowed them down. Whatever aerodynamic grip they got was negated by the speed they lost trying to manouver around the cones with 2 feet of wing sticking out on each side. But FSAE is a totally different beast.
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| chris914 |
Jul 13 2006, 10:47 PM
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#18
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Member Group: Members Posts: 489 Joined: 24-July 04 From: San Diego, CA Member No.: 2,393 Region Association: Southern California |
QUOTE(MattR @ Jul 13 2006, 06:48 PM) QUOTE(nebreitling @ Jul 13 2006, 05:16 PM) THAT is interesting. those water-dye tests are remarkable! the water-dye test analagous to a 914 at what speed? do issues of scale change things? could you do some aero modelling with various spoilers and such available? so many questions... Yes you can scale aerodynamics. You're looking at the Reynolds number similarity. You must minimize compressibility effects when choosing a new medium too. Its a simple calculation, but obviously much more difficult to effectively analyze. Basically you assume the reynolds number (inertial over viscous forces) of the model equals the reynolds number of the actual. You'll also need to use ideal gas laws to include pressure. There are still limits based on the tunnel that the model is in. That is why the students used "Flow Works" for all the different speeds. The water tunnel with the laser doppler and the wind tunnel with the pressure rake was used to back up the results for the computer modeling. The dye and the yarn are more "old school" for the visual effects. Chris. |
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| Air_Cooled_Nut |
Jul 13 2006, 11:29 PM
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#19
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914 Ronin - 914 owner who lost his 914club.com Group: Members Posts: 1,748 Joined: 19-April 03 From: Beaverton, Oregon Member No.: 584 Region Association: None |
Very cool and, yes, so many questions!
What difference does the air intake for induction and cooling, as well as the exit of both said airflows, make towards the aerodynamics in testing (where those effects aren't being created) vs. real world? And shouldn't the side/underbody flows be tested with a "road surface" since underbody dynamics will affect airflow? Still, really neat stuff! (IMG:style_emoticons/default/smilie_pokal.gif) |
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| Chris Pincetich |
Jul 14 2006, 12:08 AM
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#20
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B-) Group: Members Posts: 2,082 Joined: 3-October 05 From: Point Reyes Station, CA Member No.: 4,907 Region Association: Northern California |
Nice poster, they get an A. I was a little disappointed to read the Conclusion, because I know that if it is a nice sunny day I will drive with the top off and the windows down even if it is a 5-6 hp loss (estimate). Although, some have said that having the top removed can help because it saves weight, then roll down the windows and it WILL lower the center of gravity. Good for autocross! (IMG:style_emoticons/default/beerchug.gif)
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