| Author | Message | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 665 Registered: 4-2002 |
Underbody venturies started out needing side skirts, then evolved to the current point where they work BETTER with air flowing in from the sides of the car and creating a vortex as they tumble into the venturi area. The vortex increases the low pressure in the venturi. "Race Car Aerodynamics: designing for speed" Joseph Katz | ||
| Ben Cannon (Artherd)
Member Username: Artherd Post Number: 322 Registered: 6-2002 |
Pretty much been sumed up here, Venturi has awesome potential (and has largely been baned in F1, hence wings, which are higher drag than venturi, though both induce drag...) Venturi on street cars is very limited by the high ride. Ideally, you actually have CONTACT with sacrafical side-scrapers made of a teflon-like polymer. One has to just look at the ride height of even a 360C to see why it's venturi is not race-car good (and it's a race car, so it should be!) Lastly, a rear wing produces a force vector located at that wing (in the BACK of a car, sometimes even aft of the rear axle!!!!!) Wheras a Venturi will locate the vector roughtly in the middle of the car (locations vary based on venturi design.) Ride height can mess this up too, it's possible the 360C's lower ride height means that the vector got moved FORWARD and is mostly sticking the front tyres down now, leaving the rear twitchy in the extreme. This may border down to: The 360C needs either a re-designed venturi, OR a rear wing!  Best! Ben. | ||
| Sunny Garofalo (Jaguarxj6)
Member Username: Jaguarxj6 Post Number: 480 Registered: 2-2003 |
Very interesting thread! More and more road cars are starting to come with auto-ride height reduction to generate more downforce and stability and these systems are getting smart (computer controlled and in some cases even variable height adjustments). Sunny | ||
| James Glickenhaus (Napolis)
Intermediate Member Username: Napolis Post Number: 1364 Registered: 10-2002 |
James The one in the Enzo seems to lower at 20mph. IMHO the overhang (distance from center of front wheel to tip of nose) and the low ride height make it impractical except for very smooth roads. Perhaps those with more Enzo/Merci seat time then me could comment... | ||
| James Selevan (Jselevan)
Member Username: Jselevan Post Number: 554 Registered: 6-2002 |
James - I believe the Murcielago and, perhaps, the Enzo have ride-height adjustments that automatically lower the car at speed. Jim S. | ||
| James Glickenhaus (Napolis)
Intermediate Member Username: Napolis Post Number: 1358 Registered: 10-2002 |
For street cars a wing may be a better idea. Lowering a car to the point that an undercar device works IMHO makes them undrivable on the street. I bet that's why P uses a wing. | ||
| Kristoffer Hansson (Maverick)
Junior Member Username: Maverick Post Number: 131 Registered: 3-2001 |
Jon - you make a good point about the 360:s. I spoke with a swedish gtr driver, kari m�kinen, last year. And he said that his 360 woudn�t do without a rear wing. I faced mr Luciano (head of ferraris F1 cfd) with this last week. He answered that "you cannot compare the venturi of the 360 with the enzo. The venturi of the Enzo is much much greater". Also, a venturi tunnel is suffering much on road cars since they are placed several inches from the ground. To get maximum effect the car must be lowered as much as possible and have sideskirts. It will be interesting to see what future Enzo gt:s (if there will be such cars) will incorporate. If they come with huge rear wings I guess I�ll have to talk to mr Luciano again | ||
| Greg (Teflon)
New member Username: Teflon Post Number: 2 Registered: 5-2003 |
Jon, There is one small point I'd like to make regarding your first post in this thread. The rear wing on the Carrerra GT is much larger than the enzo's and it extends higher also. You can see it in the extended positon by going to http://www.fastdetails.com and clicking on the pic in the upper left corner. Greg | ||
| Jon P. Kofod (95f355c)
Member Username: 95f355c Post Number: 661 Registered: 8-2001 |
Thanks everyone for taking the time to answer my questions. It appears that the downforce can be created without the use of a wing and that wings are used in most forms of racing to add more downforce to a car with unerbody effects or in some cases to keep costs down by limiting under body ground effects (thus the large rear wing). That being said, there was all sorts of "big" numbers thrown around hyping the superior ground effects of the 360 street cars without the use of any rear wing or electronic spoiler. Rob S. will remember all the Challenge guys complaining at the first race at Homestead that the 360 suffered from lack of downforce in high speed corners especially at corner entry. First race weekend 12 360 Challenge cars crashed and were badly wrecked. More than half the crashes were among former 355 Challenge guys who had rear wings on their previsou Challenge cars. Rumor has it (Rob might be able to shed some light on this) that the fast guys asked FNA for a wing of some sort but FNA declined worrying what this would say about the parent companies marketing of the 360 street car and it's underbody design. Matt Karson and I both agree that the 360 C seems very twitchy at the limit in fast corners. I drove one a year ago and while I wasn't going flat out, it did seem like the higher corner speeds provoked some twitching. Anyway, very interesting discussion! Jon | ||
| James Selevan (Jselevan)
Member Username: Jselevan Post Number: 553 Registered: 6-2002 |
Jon - there is no free lunch. -------------------------------------------------- "If you could generate the appropriuate downforce without the use of such wing using under body aerodynamics you could have the best of both worlds (more downforce, less drag). However the two are a trade off and a non winged car is never going to produce as much downforce even with extensive underbody aero than a winged car. " -------------------------------------------------- Whether generated by a wing or underbody, force normal to the direction of airflow (downward force) will result in drag. Simplest way of visualizing this is to imagine the cross-sectional shape of various airplane wings. More lift (force normal to airflow) requires more drag (Boeing 747). Less lift, less drag, greater speed (F18). The "...best of both worlds..." is a style issue; generate downforce (underbody) without an ugly wing. Jim S. | ||
| Rob Schermerhorn (Rexrcr)
Member Username: Rexrcr Post Number: 587 Registered: 11-2002 |
Jon, I think you have your answer: underbody venturi effect has awesome potential. Also, just like many other aspects of such a complex machine operating in such a complex environment, it is difficult to compare numbers generated by different methods with different conditions. BTW, even with a crude by F1 standards Trans Am car, I can generate over 1000 lbf at 140 mph with nose undertray design and rear spoiler (not wing)! | ||
| Kristoffer Hansson (Maverick)
Junior Member Username: Maverick Post Number: 128 Registered: 3-2001 |
Jon - The "tiny gizmo" is not what generates the downforce on the enzo. Its the venturi. Look a the link below for my recent thread about F1 and enzo aerodynamic. Jens - "rear wings as only downforce factor". Take a look at the link below for my latest thread. http://www.ferrarichat.com/discus/messages/21/250621.html?1053336666 | ||
| Jens Haller (Jh280774)
Member Username: Jh280774 Post Number: 657 Registered: 9-2001 |
Topdaytrader, Most probably a different transmission with different gear ratios (Tuned for more speed and little less acceleration) also perhaps the GT3 is lighter than a stock 360. Could be a mix of different reasons that cause these figures. Note: Porsche has always had less hp than comparable F models and still got very good performance figures. In Germany you say the Porsche has less hp but these are "Porsche hp" which means that cars put much more performance out of it than comparable sport cars with higher hp figures. (Hope you understood what I meant! Sorry for the bad english.) Con saluti cordialissimi, Jens Haller | ||
| Topdaytrader (Topdaytrader)
New member Username: Topdaytrader Post Number: 26 Registered: 9-2002 |
How come Porsche GT3 (380hp, 190 mph) has higher top speed than F360 (400hp, 183 mph)? | ||
| Jens Haller (Jh280774)
Member Username: Jh280774 Post Number: 656 Registered: 9-2001 |
F1 uses these wings simply because of regulations. Aerodynamic underbodies are forbidden in F1. These former ground effect cars produced much more downforce thus allowed high corner speeds. In fact if you produce a normal street legal car you can produce enough downforce with an aerodynamical underbody (Venturi channels etc.). Even more interesting is that rear wing spoilers mostly disturb the air flow produced by the aerodynamical underbodies thus destroying the ground downforce of these. This is one of the reasons why no Ferraris have rear spoilers anymore. You simply don�t need them anymore. They destroy downforce of the underbodies and look bad. Race car engineers in F1 don�t have a choice anymore: They have to use rear wings as only downforce factor. Con saluti cordialissimi, Jens Haller | ||
| Faisal Khan (Tvrfreak)
Junior Member Username: Tvrfreak Post Number: 133 Registered: 3-2003 |
From various articles in Racecar Engineering and also from another recent thread on the Enzo guy doing the computational fluid dynamics, it seems like you can get the same amount of airflow management without using the monster wings. I don't know why wings are utilized so extensively in some series. Maybe they're required? Maybe this requirement will change over time? Rgds, Faisal. | ||
| Jon P. Kofod (95f355c)
Member Username: 95f355c Post Number: 658 Registered: 8-2001 |
Yeah, but if you start hyping F1 type downforce figures without a large rear wing your kidding folks. Look at any F1, CART, Prototype, GT car and you will see a monster rear wing. If you could generate the appropriuate downforce without the use of such wing using under body aerodynamics you could have the best of both worlds (more downforce, less drag). However the two are a trade off and a non winged car is never going to produce as much downforce even with extensive underbody aero than a winged car. Jon | ||
| Faisal Khan (Tvrfreak)
Junior Member Username: Tvrfreak Post Number: 132 Registered: 3-2003 |
I am sure there's marketing fluff in the manufacturer's stated claims, but downforce is not generated from the "tiny gizmo" alone. | ||
| Jon P. Kofod (95f355c)
Member Username: 95f355c Post Number: 656 Registered: 8-2001 |
The issue of the Enzo's claimed downforce in the last issue fo Rosso was a thread for discussion a month or so back. I argued than that Ferrari was using more marketing fluff with their figures as they did when touting the downforce figures for the 360 street car when it came out. In this months issue of Road and Track Porsche's engineers claim that their Porsche Carerra GT produces a maximum downforce of 640 pounds is generated at 204 mph. Rosso claims the Enzo produces 758 pounds of downforce at ONLY 124 mph. Looks like a lot of baloney to me! How can two cars, albiet different and from different car companies, differ so greatly. Both cars use a tiny electronic spoiler that looks to be about the same size and both cars weight in pretty close and have extensive underbody downforce. Who's right? Well I am putting my money on Porsche. No way the Enzo makes that kind of downforce at 124 mph. If that were tru it would be making F1 levels of downforce at over 200 with that tiny gizmo. What's everyone else's take on this. Would be interested to hear from our engineers on this board. Regards, Jon P. Kofod 1995 F355 Challenge #23 124 758 |