PorKen

I was wondering the same thing; how to test for improvement with aerodynamic additions.

The only thing I could come up with was better 0-100 times.

Jim bailey - 928 International

Porken this is an informative sight and indicates that it is NOT intuitive.... www.insideracingtechnology.com/tech102drag.htm

slate blue

Hi Realist your are incorrect about the downforce of the current formula one cars. I saw a program about the 2002 Williams grand prix car and I believe the speed to drive it upside down is only about 130kph. The aerodynamics have been adapted to the rule changes such as no skirts and ramped underbodies and this is why I corrected you on the need to block out all the air at the front with a air dam.

The reason the wings are high mounted is that they are letting more air underneath so that it can do some work for them. This application is more similar to road cars than thatof the early F1 cars, as a road car needs a certain amount of ride height for practicality.

Current F1 cars generate more downforce than the early ground effect cars due to advancing technology and millions spent in the wind tunnels.

Jim bailey - 928 International

Just to beat this poor horse a bit more . The above article states ..."you quadruple the drag or lift when you double the speed " If that is factual and the 120 lbs LIFT at 140 + MPH is true ............... then at 70 mph you have LESS THAN 35 lbs of LIFT !! Slow it down to 35 MPH and your looking at less than 6 lbs of lift . Perhaps that is part of why aerodynamics at legal road speeds are not that important for all but the underpowered electric cars .

2V4V

Realist,

My information comes from the engineers who design race cars. The very basic "recipe" I enumerated has been tested in the real world, by a real race car driver, on a real tracks, in a real race. Not my recipe, theirs.

It was concocted over 30 years ago. And was really promptly banned.

Long ago, engineers figured out how to generate literally tons of downforce - yes, tons. The reason that it has not evolved even farther, is that the cars were getting too fast, and like all things racing, new rules attempted to slow this progress.

Without restrictors, F1, NASCAR, and just about every other series would see a doubling/tripling/quadrupling of HP, almost overnight. But the rules exist to limit speed, and to force efficiency.

Downforce is the same way. Without annual rules changes, F1 cars would quickly evolve into "switch-on-200MPH-suction-cups" with computer controlled active aero-aids on every car. Just enough to keep you stable down the 220MPH straight, and huge directable downforce for cornering.

Think of it as a hovercraft with the blower reversed. Same principle, and I promise you, very tight moveable side skirts, very low front air dam, and a 'kinda' sealed (you have to exhaust the fans somewhere) is exactly the recipe that has been cooked and worked. It's really not hard to do at all, however, there are rules against it.

Current F1 etc., offerings are the way they are because of the rule book, not because it's the best way to generate downforce.

This stuff is not my opininon, just what I've been told by engineers who test racecars in windtunnels.

Greg

ViribusUnits

That right, however, rember back in the days when they could get away with such stuff, they noticed an annoying fault. If there was an inperfection in the road way, the down force could change drasticly. This drastic change could easily throw the car out of control.

Thus it was banded for safty reasons as well. Haveing cars lose control sucks.

Nicole

Hmmm... Why do the good Formula 1 teams work in the wind tunnel 24 x 7, and the top teams even in multiple wind tunnels? Would they do that, if it was a simple type of science?

The reason why we don't see "ground effects" on street cars is because if the airflow is ever interrupted (e.g. by a bump or pothole, or whatever) and air gets below the car, you suddenly and instantaneously lose downforce and possibly also your car and your life. Way too dangerous for the real world...

Keep in mind that aerodynamics are so much more than just drag. There is cross wind stability, wind noise, how dirty certain parts of the car get under bad weather condition, and much more. Putting together a balanced package that's pracctical to use has been a challenge for the longest time. I was amazed to find out that the current Lexus is one of the sedans with the lowest drag coefficient these days. I have no idea how it does in the other areas. I know my 928 does not have the lowest possible Cd, but it is darn stable in cross wind and at high speed. I'm happy the way it is.

heinrich

S4 Cd is 32. Or, latest number quoted is 34.

PorKen

"I was amazed to find out that the current Lexus is one of the sedans with the lowest drag coefficient these days"

Have y'all seen the Lexus TV commercial touting the golf ball 'dents' on the underside of the car for less drag?

2V4V

[QUOTE]Originally posted by Nicole
[B]Hmmm... Why do the good Tormula 1 teams work in the wind tunnel 24 x 7, and teh top teams even in multiple wind tunnels? Woul they do that, if it was a simple type of science?


True Nicole but.....

I think what the good Dr. Nick was trying to get to was that as one of my buddies who used to work at JPL always used to say, "even rocket science ain't rocket science".

There's not a whole lot (a little, but very little) mystery left in the actual mechanics of airflow. It is almost completely 'modeled out' in the fluid dynamics sense, its now just a matter of very accurate algorithms and such to make the windtunnel trip just a validation exercise.

Just like doing an engine in cyberspace - which the "big 3" US automakers can now do - through the magic of finite element analysis, the computer can test run and optimize the virtual motor for NVH, heat, HP, TQ, emissions, etc.

The virtual wind tunnel is coming soon, and it will be sooooo useful.

Formula one guys spend a ton of time in wind tunnels trying to get back what this year's rules have taken away, and trying to optimize a car whose shape is dictated by lots of rules designed to take away (or at least keep stagnant) last year's advances in aerodynamics.

There's been very little new under the sun for the last 20+ years regarding automotive aerodynamics, the R&D time is all about making an aerodynamic package out of this years safety and styling directives, not about learning something new.


Greg

Nicole

Where did you find the 0.32 number? All publications I have seen, including official ones from Porsche, listed 0.34.

Nicole

No, but did you notice that certain BMW models have these "bumps" on the rearview mirrors, towards the side windows? They are for smoothening the air flow and reducing wind noise.

Generally, "detached" rearview mirrors make a lot less noise than the ones that are completely attached to the A Pillar.

2V4V

Nicole,

I think .32cd is what we all wish it were, as opposed to the .34cd that Porsche admits to.

That way we could almost brag about it, rather than saying that "It's still better than _some_ pickup-trucks..."

Greg

Hammerhead

For clarification on the downforce data listed on http://www.mulsannescorner.com/data.htm

The following is the reply from Mike Fuller, whom I believe is a former engineer for the Jim Downing Mazda Kudzu LMP program.

My email:
If downforce is listed as 3000 lbs. @ 100mph, then a 2000 lbs. vehicle would weigh 5000 lbs. @ 100mph. Is this a correct statement? I ask because a colleague of mine believes that the downforce listed has to counteract the lift produced by the vehicle. So, he believes that the actual downforce is much less than listed. He also backs up his argument with the statement that the cars would collapse with that much downforce applied to them.

Mike's Reply:
John,
Your first statement is correct. Downforce, as listed, does not include vehicle weight.

But downforce as listed is total force, not simply total downforce from which you would subtract lift generated. Your colleague is missing one important concept. The numbers are extrapolated to a theoretical 200 mph. Most of the cars are pulling far too much drag to even reach that speed, so a more representative speed regime for usable downforce (not theoretical) would be the either the 180 mph or 150 mph bracket.

As testament to the aero. loads being applied by late generation GTP cars, a story is told about the first test of the Intrepid GTP. Goodyear forced the testing to be stopped when the Intrepid experience tire blow outs caused by exceeding the load limits of the tires. These blow outs where not caused by foreign objects breaching the tire's carcass, but by the loads squashing the cords right out of the tires.

Regards,

Mike Fuller

In summary, the downforce listed is net downforce. So, the Carrera GT would weigh 343 lbs. more at 150mph, than at rest. The Lister Storm LMP would weigh 2600 lbs. more at 150mph, than at rest. How do they keep the cars from collapsing? They do it through super strong and stiff body, chassis, and suspension components (carbon fiber, aluminum honeycomb, etc.) It is interesting to note that the tires ended up being the weak link in the end.

For our cars, I think that just decreasing the drag through a flat bottom sheet with or without a rear diffuser would be great. It would improve top speed and it would improve highway fuel mileage. I realize many folks believe that this is a waste of time, but I think that any performance enhancement, whether for acceleration, cornering, fuel mileage, or top speed, is worth looking into.

Vlocity

I have always been very curious about the rear diffuser that was on the Devek White Car. I doubt that I will ever have a chance to spend several days running over 200MPH as they have, but I think looking at what has worked for them may be a good indication as to what will work.

Does anyone have any underside DEVEK car photos they can post?

Just curious.


Regards

Ken