Let's talk aerodynamics
06-15-2003, 01:43 PM
#16
Burning Brakes
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Ok if you prefer let's call it a valance under the rear bumper - that's what I was referring to. Just take it off and try your car at 140+. I have - whilst it was repainted - trust me night and day!!
06-15-2003, 02:41 PM
#17
Nordschleife Master
Regarding tire noise and tread design, this I have some first hand knowledge about. GoodYear was the first to develop and patent that technology. Then everyone copied them. Unfortunately for GoodYear, they sort of screwed up their patent application by filing it over a year after starting to commercially sell them. So everyone can copy for free.
The technology was developed in conjunction with the "all season" tire tread to reduce the noise when running on dry pavement so the consumer would actually consider the tires as all season.
The technology was developed in conjunction with the "all season" tire tread to reduce the noise when running on dry pavement so the consumer would actually consider the tires as all season.
06-15-2003, 04:40 PM
#18
Burning Brakes
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Rich, just wanted to ask a question about the undertray. I think that if you have the undertray on , as you state the airflow is smoother under the car. This should make for slightly higher velocity under the car and thus a lower pressure than without the undertray. The lower pressure does mean reduced lift compared to without the undertray. Also the nose of the 951 adds a good amount of negative lift by its shape as compared to the 944 nose. The combination of the nose, the undertrays and the rear valence do make the 951 very stable at high speeds with an exceptional amount of grip when compared to the 944. I would guess Porsche designed in a slight amount of downforce but not a lot. There objective was probably trying to minimize lift.
Don't we all wish we had a windtunnel to use!
Don't we all wish we had a windtunnel to use!
06-15-2003, 05:23 PM
#19
Nordschleife Master
Well, my car is missing the metal "undertray" behind the plastic "batwing."
There has been some PO induced damage to the car, and he bent the rad frame back about 1 inch. this means I can't install the OEM tray. Sooo, I was thinking of simply making my own from a sheet of aluminium, and using whatever bolt on holes I can find on the crossmember and such.
But what I'm really interested in are the little vents on the metal undertray. Apparently they divert air upwards to cool? the engine bay. I'm wondering if I can reproduce this effectively..
I think doing this should help a smidgeon with top speed on the highway, and perhaps give the rear valence a little more clean air to give me more stability too. Also, my car is lowered a bit, so that reduces the Lifting affect a bit too, but also give the rear valence less air. trade off I guess.
There has been some PO induced damage to the car, and he bent the rad frame back about 1 inch. this means I can't install the OEM tray. Sooo, I was thinking of simply making my own from a sheet of aluminium, and using whatever bolt on holes I can find on the crossmember and such.
But what I'm really interested in are the little vents on the metal undertray. Apparently they divert air upwards to cool? the engine bay. I'm wondering if I can reproduce this effectively..
I think doing this should help a smidgeon with top speed on the highway, and perhaps give the rear valence a little more clean air to give me more stability too. Also, my car is lowered a bit, so that reduces the Lifting affect a bit too, but also give the rear valence less air. trade off I guess.
06-15-2003, 06:07 PM
#20
Nordschleife Master
Thom, it would be interesting to see the airlfow pattern if the shape of the 944 nose was actually correct. The model he used is horribly under-detailed.
06-16-2003, 06:47 AM
#21
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Rich Sandor:
<strong>The model he used is horribly under-detailed.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">No need to use a more detailed geometry here, the main curvatures are fine.
Anyway a finer meshing would not deliver dramatically different results (IMHO).
<strong>The model he used is horribly under-detailed.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">No need to use a more detailed geometry here, the main curvatures are fine.
Anyway a finer meshing would not deliver dramatically different results (IMHO).
06-16-2003, 11:54 AM
#22
Former Sponsor
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Thom:
<strong>One of our members works in this field and has done a little <a href="http://www.club944.net/nuke/html/modules.php?name=News&file=article&sid=34&mode=&order=0&thold=0" target="_blank">report</a>.
(You may find interesting to notice that <a href="http://www.club944.net/images/articles/aero08.png" target="_blank">the front pressure distribution</a> proves that an aditionnal opening on the front panel between the pop-ups (for the intercooler) is useless)</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Is this in english somewhere??
<strong>One of our members works in this field and has done a little <a href="http://www.club944.net/nuke/html/modules.php?name=News&file=article&sid=34&mode=&order=0&thold=0" target="_blank">report</a>.
(You may find interesting to notice that <a href="http://www.club944.net/images/articles/aero08.png" target="_blank">the front pressure distribution</a> proves that an aditionnal opening on the front panel between the pop-ups (for the intercooler) is useless)</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Is this in english somewhere??
06-16-2003, 01:04 PM
#23
Racer
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Go To:
<a href="http://babelfish.altavista.digital.com/cgi-bin/translate?" target="_blank">Alta Vista (Babelfish) Translation...</a>
Choose French to English, copy & paste URL in the URL field.
Not a good translation... but you'll get the idea....
<a href="http://babelfish.altavista.digital.com/cgi-bin/translate?" target="_blank">Alta Vista (Babelfish) Translation...</a>
Choose French to English, copy & paste URL in the URL field.
Not a good translation... but you'll get the idea....
06-16-2003, 01:39 PM
#24
Three Wheelin'
His conclusions are incorrect, He did not take several factors into account.
ALso If the vented nose panels were useless, than 1: howcome the factory used it on the 931 and 937?
2: why did the factory use it on race cars?
3: There has been a significant MEASURED, difference in intercooler temps with the vent.
After all results count, theory is just guys talking about stuff they have no experience with because no one will hire them because all they can do is BS.
ALSO, porsche has show air flow pressure distribution in one of their Ads already, so this is old news <img src="http://club924.tripod.com/924ad5.JPG" alt=" - " />
ALso If the vented nose panels were useless, than 1: howcome the factory used it on the 931 and 937?
2: why did the factory use it on race cars?
3: There has been a significant MEASURED, difference in intercooler temps with the vent.
After all results count, theory is just guys talking about stuff they have no experience with because no one will hire them because all they can do is BS.
ALSO, porsche has show air flow pressure distribution in one of their Ads already, so this is old news <img src="http://club924.tripod.com/924ad5.JPG" alt=" - " />
06-16-2003, 04:21 PM
#25
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by M Danger:
<strong>3: There has been a significant MEASURED, difference in intercooler temps with the vent.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Okay, then show me these results please before insulting people.
PS : it is not because the factory does something that it is inherently good. I do not think the vent panel did work on the 931 and 937.
<strong>3: There has been a significant MEASURED, difference in intercooler temps with the vent.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Okay, then show me these results please before insulting people.
PS : it is not because the factory does something that it is inherently good. I do not think the vent panel did work on the 931 and 937.
06-16-2003, 06:17 PM
#26
Race Director
You guys are talking about two different things. Vented nose panels do not affect the aerodynamics that much compared effects created by the overall shape of the body or wings. The most important area for aerodynamics is the tail-end of the car. This is where the boundary layer starts to separate and there's less energy to enforce laminar-flow.
" I think that if you have the undertray on , as you state the airflow is smoother under the car. This should make for slightly higher velocity under the car and thus a lower pressure than without the undertray. The lower pressure does mean reduced lift compared to without the undertray."
I have noticed less understeer around Willow Springs in turns 9, 1 and 2 (100mph+) with the full underbody trays installed. It really does help reduce the turbulence and helps the air flow under the car faster, thus reducing the pressure-differential between the upper and lower surfaces.
Also the shape of the underbody cavity is a classic 'rake' form. The front-most nose section (batwing) is the part closest to the ground. As you move towards the back, the gap between the body and the ground gets larger and larger. This has the effect of increasing velocity and reducing pressure. I doubt it does it significantly enough to combat the lift forces.
I think the only cars that have sufficient development and attention to underbody trays and aerodynamics to actually negate lift is the Ferrari 360 Modena and 550 Maranello. They have less lift than any previous Ferrari without the antagonistic use of downforce from wings. And the Ferrari Enzo actually has some downforce from its venturi tunnels as well.
Even cars with agressive wings for downforce can have a net lift effect. Check out the two Mercedes that flew at LeMans a couple of years ago or the Porsche-GT1 at Road Atlanta. Although these cases were more of an angle-of-attack issue than lift I think.
" I think that if you have the undertray on , as you state the airflow is smoother under the car. This should make for slightly higher velocity under the car and thus a lower pressure than without the undertray. The lower pressure does mean reduced lift compared to without the undertray."
I have noticed less understeer around Willow Springs in turns 9, 1 and 2 (100mph+) with the full underbody trays installed. It really does help reduce the turbulence and helps the air flow under the car faster, thus reducing the pressure-differential between the upper and lower surfaces.
Also the shape of the underbody cavity is a classic 'rake' form. The front-most nose section (batwing) is the part closest to the ground. As you move towards the back, the gap between the body and the ground gets larger and larger. This has the effect of increasing velocity and reducing pressure. I doubt it does it significantly enough to combat the lift forces.
I think the only cars that have sufficient development and attention to underbody trays and aerodynamics to actually negate lift is the Ferrari 360 Modena and 550 Maranello. They have less lift than any previous Ferrari without the antagonistic use of downforce from wings. And the Ferrari Enzo actually has some downforce from its venturi tunnels as well.
Even cars with agressive wings for downforce can have a net lift effect. Check out the two Mercedes that flew at LeMans a couple of years ago or the Porsche-GT1 at Road Atlanta. Although these cases were more of an angle-of-attack issue than lift I think.
06-17-2003, 12:37 AM
#27
Drifting
The funny thing is, as you smooth the airflow under the car, you help create more "Lift"
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This is not true. Adding panels under the car will create a (mostly) flat surface. The flat surface of the underside of a car running at speed, slightly above a flat surface (the road) will create what is know as "ground effect". Ground effect produces downforce with no or minimal drag. If you have a clean flat surface you can create ground effect and actually use a smaller splitter or less camber/small Gurney in your wing and acheive the same results.
Mind you that this takes some trial and error unless you have access to a windtunnel or a scale model and scale tunnel.
------------------------------------------------
This is not true. Adding panels under the car will create a (mostly) flat surface. The flat surface of the underside of a car running at speed, slightly above a flat surface (the road) will create what is know as "ground effect". Ground effect produces downforce with no or minimal drag. If you have a clean flat surface you can create ground effect and actually use a smaller splitter or less camber/small Gurney in your wing and acheive the same results.
Mind you that this takes some trial and error unless you have access to a windtunnel or a scale model and scale tunnel.
06-17-2003, 03:41 AM
#28
Burning Brakes
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Thom, would agree with mdanger. Factory car development programe is a a multi million big $$$$$$ project for each car they develop. I really think at Porsche their experts with the available resources (wind tunnels) would know a bit about cars and their aero's?
06-17-2003, 05:45 AM
#29
Nordschleife Master
Okay, we can agree that having the undertrays smooth out the underbody airflow, right?
We all agree that running WITH the undertrays reduces oversteer. Therefor, it gives you UNDERSTEER, therefore, there is less weight on the front end of the car, or suspension. There fore, it is LIFTING the car. Therefore, having the undertray present, induces more lift.
HOWEVER, the smooth airflow it creates, reduces Form Drag at lower speeds, but increases Induced Drag at higher speeds. So it's a trade off.
Ground effect as you described it is a misnomer. In aerodynamics, ground effect reduces drag by eliminating downwash from the wing at low levels. It does not affect lift at all, it reduces drag only, and therefore increases speed and acceleration. A car is already on the ground, and therfore always benefits from ground effect. Having air flow smoothly under the car is not ground effect. That is a term that was stolen from the aviation world and bastardised for Formula One, and then again stolen and used by the ricer body kit crowd.
Ground effects in formula one, as it was originally used, constituted of a plastic skirt around the rocker panels of the car, which actually made full contact with the ground, preventing air from exiting out the sides, and funneled it all to the back, where a rear diffuser shot it upwards, giving more downforce. It was so effective, that cornering speeds increased to such a point that the FIA banned them right away.
Anyways, my point is that you keep the undertray in order to reduce DRAG and therfore increase top speed. If you want downforce, you need to add front and rear wings to create it. (Also the rear valence does this too by shooting air up!) But again as you add downforce, you add drag, and decrease top speed. So it's a trade off and you have to find the right balance for any given track.
We all agree that running WITH the undertrays reduces oversteer. Therefor, it gives you UNDERSTEER, therefore, there is less weight on the front end of the car, or suspension. There fore, it is LIFTING the car. Therefore, having the undertray present, induces more lift.
HOWEVER, the smooth airflow it creates, reduces Form Drag at lower speeds, but increases Induced Drag at higher speeds. So it's a trade off.
Ground effect as you described it is a misnomer. In aerodynamics, ground effect reduces drag by eliminating downwash from the wing at low levels. It does not affect lift at all, it reduces drag only, and therefore increases speed and acceleration. A car is already on the ground, and therfore always benefits from ground effect. Having air flow smoothly under the car is not ground effect. That is a term that was stolen from the aviation world and bastardised for Formula One, and then again stolen and used by the ricer body kit crowd.
Ground effects in formula one, as it was originally used, constituted of a plastic skirt around the rocker panels of the car, which actually made full contact with the ground, preventing air from exiting out the sides, and funneled it all to the back, where a rear diffuser shot it upwards, giving more downforce. It was so effective, that cornering speeds increased to such a point that the FIA banned them right away.
Anyways, my point is that you keep the undertray in order to reduce DRAG and therfore increase top speed. If you want downforce, you need to add front and rear wings to create it. (Also the rear valence does this too by shooting air up!) But again as you add downforce, you add drag, and decrease top speed. So it's a trade off and you have to find the right balance for any given track.
06-17-2003, 06:01 AM
#30
Nordschleife Master
Also, I hate to keep nitpicking, but the model that Thom's friend used IS horribly innaccurate, and doesn't convey the pressure correctly because it is not shaped correctly. The way the hood/nosepanel/bumper slopes down in steps is not modeled correctly. If you noticed the factory vents are on the stepped area that has a steep slope, right below the nose badge. Thom's friend did not model this section at all correctly, and thus the airflow diagram doesn't show it properly either.
If he needs a more accurate model, I can supply one myself. Just tell me what format to put it in.
If he needs a more accurate model, I can supply one myself. Just tell me what format to put it in.