| Jonnyfilmboy | 04-29-2006 08:26 PM |
Aerodynamics Explained: Downforce without Wings
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Installed a new 06 STi diffuser? Want to know how your vortex generators will effect you car's performance? Wondering why your mileage is so bad? Want to know the difference between a spoiler, a splitter and a dam?
Since there is no technical board on aerodynamics, and since there is a lot of mis-information out there regarding aerodynamics, I have decided to post this article I found a few years ago. It's the best article I have ever read on aero and I think it will help a lot of people understand this complicated subject more. It helped me.
This article is extensively detailed with lots of illustrations and photos but written with clarity and intelligence; the way a great teacher would explain it to a class.
[SIZE=3][url]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_without_wings_protec.doc[/url][/SIZE]
It's a protected Word .doc file about 1.62 MB in size.
The title is:
[b][u]Downforce Without Wings[/u][/b]
Fordonsaerodynamik
Institutionen f�r Termo-och Fluiddynamik
Chalmers Tekniska H�gskola
2000-12-05
[b][i]Authors:[/i][/b]
Yuping Li
Maria del Carmen Fernandez Visiedo
Hector Vallejo Paz
Luciano Rafael Bello de Aranaga
[b]Abstract:[/b]
[i]"Motor sports are all about maximum performance, to be the fastest is the absolute. There is nothing else. To be faster you need power, but there is a limit to how much power you can put on the ground. To increase this limit force must be applied on the wheels, increasing weight can do this, but weight makes handling worse. So we need some virtual weight, we call it downforce and get it from airflow around the car.
"A wing can make a plane fly, but if we put it upside down, it can make a car NOT fly. However, we can also achieve this without using wings. In this report we will explore how.
"Basically we will not use wings, but try and make the whole car be a wing, and take advantage of what is called �ground effect� which makes wings much more effective on the ground. There are also plates, which if placed in the right place, will push the car down; we will talk about these near the end.
Downforce has to be balanced between front and rear, left and right. We can easily achieve the balance between left and right by simple symmetry, so it will not be discussed. Front and rear is a different thing. Flow in the front greatly affects flow in the back of the car, and vice versa. But to simplify the explanations, we will divide the car in three parts, front, middle and rear, talk about what can be done in each part, and finally explain how each part affects the other."[/i]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/NEW_RIMS/WRX_Rims_Shoot_0009.jpg[/img]
Enjoy! And let me know if anyone has any problems with the download. And remember...
[SIZE=6][i]Ipsa Scientia Potestas Est[/i][/SIZE]
[size=1](Knowledge is power)[/size]
Sir Francis Bacon
Since there is no technical board on aerodynamics, and since there is a lot of mis-information out there regarding aerodynamics, I have decided to post this article I found a few years ago. It's the best article I have ever read on aero and I think it will help a lot of people understand this complicated subject more. It helped me.
This article is extensively detailed with lots of illustrations and photos but written with clarity and intelligence; the way a great teacher would explain it to a class.
[SIZE=3][url]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_without_wings_protec.doc[/url][/SIZE]
It's a protected Word .doc file about 1.62 MB in size.
The title is:
[b][u]Downforce Without Wings[/u][/b]
Fordonsaerodynamik
Institutionen f�r Termo-och Fluiddynamik
Chalmers Tekniska H�gskola
2000-12-05
[b][i]Authors:[/i][/b]
Yuping Li
Maria del Carmen Fernandez Visiedo
Hector Vallejo Paz
Luciano Rafael Bello de Aranaga
[b]Abstract:[/b]
[i]"Motor sports are all about maximum performance, to be the fastest is the absolute. There is nothing else. To be faster you need power, but there is a limit to how much power you can put on the ground. To increase this limit force must be applied on the wheels, increasing weight can do this, but weight makes handling worse. So we need some virtual weight, we call it downforce and get it from airflow around the car.
"A wing can make a plane fly, but if we put it upside down, it can make a car NOT fly. However, we can also achieve this without using wings. In this report we will explore how.
"Basically we will not use wings, but try and make the whole car be a wing, and take advantage of what is called �ground effect� which makes wings much more effective on the ground. There are also plates, which if placed in the right place, will push the car down; we will talk about these near the end.
Downforce has to be balanced between front and rear, left and right. We can easily achieve the balance between left and right by simple symmetry, so it will not be discussed. Front and rear is a different thing. Flow in the front greatly affects flow in the back of the car, and vice versa. But to simplify the explanations, we will divide the car in three parts, front, middle and rear, talk about what can be done in each part, and finally explain how each part affects the other."[/i]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/NEW_RIMS/WRX_Rims_Shoot_0009.jpg[/img]
Enjoy! And let me know if anyone has any problems with the download. And remember...
[SIZE=6][i]Ipsa Scientia Potestas Est[/i][/SIZE]
[size=1](Knowledge is power)[/size]
Sir Francis Bacon
| Jonnyfilmboy | 04-29-2006 08:26 PM |
Some images from the article. (note: they look better in the Word doc.)
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_01.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_02.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_03.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_04.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_05.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_06.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_07.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_01.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_02.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_03.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_04.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_05.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_06.jpg[/img]
[img]http://www.lightstormimages.com/gallery/cars/nasioc/downforce_07.jpg[/img]
| Jonnyfilmboy | 04-29-2006 09:12 PM |
Here's the Index:
1.....Abstract.....2
2.....Why is downforce needed?.....3
3.....History.....4
3.1.....Spoil the flow.....4
3.2.....The Inverted Wing.....4
3.3.....Sealing skirts.....5
3.4.....The "Ground effect" era.....5
3.5.....Diffusing air.....6
4.....The Physics of Lift and Drag.....7
4.1.....Bernoulli.....7
5.....Vehicle Body Concepts.....8
6.....Downforce on the rear axle.....10
6.1.....Rear Spoilers.....10
6.2.....Diffusers.....10
6.3.....Downforce Generation Mechanisms in the Diffuser.....12
7.....Downforce on the front axle......14
7.2.....Air dams.....15
7.3.....Splitters.....15
7.4.....Dive plates.....17
7.5.....Wheel well gurneys.....18
7.6.....Louvers over front wheel.....18
7.7.....Front underbody contouring: undertrays.....18
8.....Downforce in the middle.....21
8.1.....Reducing inflow from the sides.....21
8.2.....The vacuum cleaner concept.....21
8.3.....Other uses of vortex lift.....22
9.....Relationships.....23
10.....References.....24
1.....Abstract.....2
2.....Why is downforce needed?.....3
3.....History.....4
3.1.....Spoil the flow.....4
3.2.....The Inverted Wing.....4
3.3.....Sealing skirts.....5
3.4.....The "Ground effect" era.....5
3.5.....Diffusing air.....6
4.....The Physics of Lift and Drag.....7
4.1.....Bernoulli.....7
5.....Vehicle Body Concepts.....8
6.....Downforce on the rear axle.....10
6.1.....Rear Spoilers.....10
6.2.....Diffusers.....10
6.3.....Downforce Generation Mechanisms in the Diffuser.....12
7.....Downforce on the front axle......14
7.2.....Air dams.....15
7.3.....Splitters.....15
7.4.....Dive plates.....17
7.5.....Wheel well gurneys.....18
7.6.....Louvers over front wheel.....18
7.7.....Front underbody contouring: undertrays.....18
8.....Downforce in the middle.....21
8.1.....Reducing inflow from the sides.....21
8.2.....The vacuum cleaner concept.....21
8.3.....Other uses of vortex lift.....22
9.....Relationships.....23
10.....References.....24
| Jonnyfilmboy | 04-29-2006 09:13 PM |
Reserved for future posts
| djerickd | 04-29-2006 09:16 PM |
wow, sticky?
| Uncle Scotty | 04-30-2006 11:29 AM |
......MOST interesting......indeed.
| steve | 04-30-2006 12:27 PM |
That explains why cars like late model Ferraris and Lambos are able to achieve such high speeds without the use of huge GT wings and aggressive front ends.
neat thread.
neat thread.
| hanzo918 | 04-30-2006 01:19 PM |
*SiGh*
Hopefully this read can convert some of the idiots on the board that bash aerodynamics and how "they do not work until 150mph".....
Hopefully this read can convert some of the idiots on the board that bash aerodynamics and how "they do not work until 150mph".....
| Jonnyfilmboy | 04-30-2006 05:15 PM |
Yes, that's my intention for posting this. It's a great article and I'm hoping there will be more intelligent discussions as a result of it.
Now all we have to do is get someone to set up a wind tunnel in their garage. :)
Now all we have to do is get someone to set up a wind tunnel in their garage. :)
| Bishop | 04-30-2006 05:19 PM |
great read. thx
| chudlo | 04-30-2006 06:00 PM |
Great Stuff!
Sticky Bump!!!!!
Sticky Bump!!!!!
| Uncle Scotty | 04-30-2006 11:04 PM |
[QUOTE=hanzo918]*SiGh*
Hopefully this read can convert some of the idiots on the board that bash aerodynamics and how "they do not work until 150mph".....[/QUOTE]
:lol: ....yeah....really....
Hopefully this read can convert some of the idiots on the board that bash aerodynamics and how "they do not work until 150mph".....[/QUOTE]
:lol: ....yeah....really....
| LA | 04-30-2006 11:19 PM |
very interesting
| Handsdown | 04-30-2006 11:40 PM |
freaking awesome read. i'm going to put wheel gurneys on now:lol:
| buzz367 | 05-01-2006 12:01 AM |
sweet find. actually answered many questions i had about aerodynamics. thanks. maybe this should be a sticky.
| digitalboy40 | 05-01-2006 12:13 AM |
nice find! i'd really like to read more in depth articles like this pretaining to various issues (like the trail braking post from last week)
| Black-Falcon | 05-01-2006 12:45 AM |
Definately a good read.
| that1dude | 05-01-2006 01:10 AM |
A little long, but very informational. So decreasing lift is just as important as increasing downforce!! That gives me an idea... :devil:
| Jonnyfilmboy | 05-01-2006 03:20 AM |
Well, I think since lift and downforce are inversely related, decreasing lift is the same as increasing downforce. In fact, the article refers to downforce as "negative lift". For example, a rear wing element will reduce the lift on the back of the car caused by the body shape. Another way of saying this is that the wing will increase downforce onto the rear section of the car.
| supermarkus | 05-01-2006 03:31 AM |
[QUOTE=Handsdown]freaking awesome read. i'm going to put wheel gurneys on now:lol:[/QUOTE]
I think STis come with them. They should be easy to get.
I think STis come with them. They should be easy to get.
| drees | 05-01-2006 11:01 AM |
No, according to the article wheel gurneys are metal strips on the fender, not the air flaps underneath in front of the wheels (though those help, too). The 04+ WRX/STI comes with front/rear air flaps and fit onto the 02-03 perfectly.
| RooRunner | 05-02-2006 01:00 AM |
^^^^^ Got pictures of those?
| Uncle Scotty | 05-02-2006 01:11 AM |
[QUOTE=Jonnyfilmboy]Well, I think since lift and downforce are inversely related, [B]decreasing lift is the same as increasing downforce.[/B] In fact, the article refers to downforce as "negative lift". For example, a rear wing element will reduce the lift on the back of the car caused by the body shape. Another way of saying this is that the wing will increase downforce onto the rear section of the car.[/QUOTE]
....not quite......in most cases, increasing downforce by the use of wings--which increase drag......and decreasing lift by whatever means that do not increase drag,.....make the difference.
Wings = drag...always....and that drag can be quite substantial, hence the tremendous efforts at reducing lift without the use of external wings and their associated drag penalty....
Proper management of the airflow is quite interesting....and thus the GREAT humor at all the kiddie wings running around :lol: :lol: :lol: :rolleyes:
....not quite......in most cases, increasing downforce by the use of wings--which increase drag......and decreasing lift by whatever means that do not increase drag,.....make the difference.
Wings = drag...always....and that drag can be quite substantial, hence the tremendous efforts at reducing lift without the use of external wings and their associated drag penalty....
Proper management of the airflow is quite interesting....and thus the GREAT humor at all the kiddie wings running around :lol: :lol: :lol: :rolleyes:
| drees | 05-02-2006 02:15 AM |
[QUOTE=RooRunner]^^^^^ Got pictures of those?[/QUOTE]Here's pics and part numbers in this post. Pics are off of BIGSKYWRX's 04 wagon, but they fit exactly the same on my 03. I've been too lazy to take pics of them mounted on my car. :p
[url]http://forums.nasioc.com/forums/showpost.php?p=13538772&postcount=82[/url]
[url]http://forums.nasioc.com/forums/showpost.php?p=13538772&postcount=82[/url]
| Jonnyfilmboy | 05-13-2006 01:52 PM |
Interesting. I always wondered what those were.
| chimchimm5 | 05-15-2006 02:18 AM |
Great article. Although it's purely a racing application article aimed at reducing lift or increasing downforce. Although it mentions reduction of drag, this is usually a side benifit to whatever method they are using to reduce lift.
They touch on another concept not focused on in the article: the speed record shape. In this case, they said that reduction of drag is foremost, and turning is not involved so downforce is less important. Reduction of drag is useful on the street where we actually care about eaking fuel efficiency out. Racing application generally don't care about fuel efficiency, especially not to the degree that a street/consumer application does. I wonder if there's an article focused on fuel efficiency, like analyzing the Honda Insight to death.
Great article none the less and definitely one I'm saving.
They touch on another concept not focused on in the article: the speed record shape. In this case, they said that reduction of drag is foremost, and turning is not involved so downforce is less important. Reduction of drag is useful on the street where we actually care about eaking fuel efficiency out. Racing application generally don't care about fuel efficiency, especially not to the degree that a street/consumer application does. I wonder if there's an article focused on fuel efficiency, like analyzing the Honda Insight to death.
Great article none the less and definitely one I'm saving.
| hanzo918 | 05-15-2006 04:07 AM |
[QUOTE=chimchimm5]Great article. Although it's purely a racing application article [/QUOTE]
Wrong.
[QUOTE=chimchimm5]Racing application generally don't care about fuel efficiency, especially not to the degree that a street/consumer application does. [/QUOTE]
Can't be wronger.
Wrong.
[QUOTE=chimchimm5]Racing application generally don't care about fuel efficiency, especially not to the degree that a street/consumer application does. [/QUOTE]
Can't be wronger.
| NA impreza~J | 05-15-2006 11:54 AM |
I agree with Hanzo918, same amount of fuel in race car and get an extra lap in...sounds like that's a winner right there to me.
| Jonnyfilmboy | 04-07-2007 01:43 PM |
[quote=Uncle Scotty;13631507]....not quite......in most cases, increasing downforce by the use of wings--which increase drag......and decreasing lift by whatever means that do not increase drag,.....make the difference.
Wings = drag...always....and that drag can be quite substantial, hence the tremendous efforts at reducing lift without the use of external wings and their associated drag penalty....
Proper management of the airflow is quite interesting....and thus the GREAT humor at all the kiddie wings running around :lol: :lol: :lol: :rolleyes:[/quote]
(insert year long pause before response)
I think actually, the point of the article is that you can increase downforce by decreasing lift. They are saying that they are the same thing. For example, the Ferrari 360 and F430 greatly increase downforce at the rear without the use of wings. They employ diffusers and the F430 uses an upward sweep at the rear of the trunklid to help improve the effect of the diffuser (Tiff on Top Gear's review of the F430 spyder shows this well - see YouTube).
So in essence, you can increase downforce without use of drag-enducing wings. But alternatively, you don't need to have wings to have drag. Just the shape of the body has its own drag, obviously.
Also, you make an interesting statement that all wings always cause drag. I'm not so sure. Of course, we have to define what a "wing" is. One look at the recent 2007 Ferrari F1 car will greatly confuse the issue. There are dozens of little flaps and winglets which are hard to singularly define as a "wing". I'm sure many of these are used to improve the airflow around the wheels and engine cover which actually improve fuel economy (by decreasing OVERALL drag).
Wings = drag...always....and that drag can be quite substantial, hence the tremendous efforts at reducing lift without the use of external wings and their associated drag penalty....
Proper management of the airflow is quite interesting....and thus the GREAT humor at all the kiddie wings running around :lol: :lol: :lol: :rolleyes:[/quote]
(insert year long pause before response)
I think actually, the point of the article is that you can increase downforce by decreasing lift. They are saying that they are the same thing. For example, the Ferrari 360 and F430 greatly increase downforce at the rear without the use of wings. They employ diffusers and the F430 uses an upward sweep at the rear of the trunklid to help improve the effect of the diffuser (Tiff on Top Gear's review of the F430 spyder shows this well - see YouTube).
So in essence, you can increase downforce without use of drag-enducing wings. But alternatively, you don't need to have wings to have drag. Just the shape of the body has its own drag, obviously.
Also, you make an interesting statement that all wings always cause drag. I'm not so sure. Of course, we have to define what a "wing" is. One look at the recent 2007 Ferrari F1 car will greatly confuse the issue. There are dozens of little flaps and winglets which are hard to singularly define as a "wing". I'm sure many of these are used to improve the airflow around the wheels and engine cover which actually improve fuel economy (by decreasing OVERALL drag).
| louis110 | 04-09-2007 12:05 PM |
Very good report.
| STiShawn | 04-09-2007 01:28 PM |
great post..but
reducing lift is NOT the same as creating downforce
reducing lift is NOT the same as creating downforce
| Jonnyfilmboy | 04-09-2007 11:00 PM |
Yes it is, if you reduce lift to the point where you create downforce.
| Uncle Scotty | 04-10-2007 12:41 AM |
[QUOTE=Jonnyfilmboy;17665316]Yes it is, if you reduce lift to the point where you create downforce.[/QUOTE]
...d0000d...YOU are smoking crack....LOTS and LOTS of industrial strength crack.
...d0000d...YOU are smoking crack....LOTS and LOTS of industrial strength crack.
| Jakes02 | 04-26-2007 09:06 AM |
Hmm... very good article.
Jonny--- I think I know what you're saying....If you put a wing on the back you will get downforce BUT if the downforce provided by the wing is less than the lift of the car than you still have lift..just less of it giving you the feeling of downforce.
If the car weighs 3,000lbs sitting still and it weighs 2,700lbs while travelling at 100mph then it has 300lbs of lift. If you do some fancy aerodynamic mods that give you 200lbs of "downforce" you are still creating more lift than downforce. Or if you get 400lbs of "downforce" from aero mods then you have true downforce
You can only reduce lift to the point where the car is neutral. After that point you are creating downforce. Is that what you are saying???
"A vertical force directed downward, produced by airflow around an object. Downforce is generated from the front and rear wings and the venturi tunnels on a ground effect car."
[url]www.nas.nasa.gov/About/Education/Racecar/glossary.html[/url]
Jonny--- I think I know what you're saying....If you put a wing on the back you will get downforce BUT if the downforce provided by the wing is less than the lift of the car than you still have lift..just less of it giving you the feeling of downforce.
If the car weighs 3,000lbs sitting still and it weighs 2,700lbs while travelling at 100mph then it has 300lbs of lift. If you do some fancy aerodynamic mods that give you 200lbs of "downforce" you are still creating more lift than downforce. Or if you get 400lbs of "downforce" from aero mods then you have true downforce
You can only reduce lift to the point where the car is neutral. After that point you are creating downforce. Is that what you are saying???
"A vertical force directed downward, produced by airflow around an object. Downforce is generated from the front and rear wings and the venturi tunnels on a ground effect car."
[url]www.nas.nasa.gov/About/Education/Racecar/glossary.html[/url]
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