Aerodynamics Question.

DWNSHFT wrote: Finally, add a bunch of downforce and you add a ton of stress on the suspension and chassis.

FWIW (and since someone already mentioned Chaparral), notice that in the Chaparral 2E, Hall put the downforce from the big moveable rear wing directly to the rear uprights. That bypassed the chassis and most of the suspension. When that was banned, Chaparral looked more at ground effects. That’s where the sucker car came in.

I’m not sure how moveable wings, rear uprights, and suckers apply to a Pontiac Lemans, but , then, this IS GRM.

DaewooOfDeath wrote:

GameboyRMH wrote: +1 for the Daewoo (never thought I'd recommend a Daewoo for anything but destruction)

If I get the LeMans, it will be my second Daewoo track car. What the hell has gone wrong with my life?

It's not terribly strange by GRM standards, we have people on here who buy Maserati Biturbos on purpose

@GameboyRMH

I shudder at the thought.

slantvaliant wrote:

DWNSHFT wrote: Finally, add a bunch of downforce and you add a ton of stress on the suspension and chassis.

FWIW (and since someone already mentioned Chaparral), notice that in the Chaparral 2E, Hall put the downforce from the big moveable rear wing directly to the rear uprights. That bypassed the chassis and most of the suspension. When that was banned, Chaparral looked more at ground effects. That’s where the sucker car came in. I’m not sure how moveable wings, rear uprights, and suckers apply to a Pontiac Lemans, but , then, this IS GRM.

I appreciate you posting this. I was unfamiliar with the 2E.

Can someone give me a run down of this car, particularly it's aero features? I am seeing a lot of interesting things, but I'd like a little clarification.

Pics of the 2E

So, I see that the movable wing transfers directly to the rear uprights. It is operated by a foot pedal. Was this outlawed because of it's effectiveness, or because of the potential for driver error?

It looks like the front wheels have vents at the rear side of the fender to eliminate the negative pressure space behind the front tires.

There is almost no frontal area or chin spoiler, but it appears that the car pulls air from under the front and ducts it through the hood to the negative pressure space a the cowl. What's the undercarriage design like?

I am also noticing the radiators are moved to the rear. Is the air pulled down from the vents above, or ducted through the boxed chassis? Does it dump into the rear wheel wells and out through the rear deck? What is the net contribution of this element? What do the intakes in front of the rear wheel do?

I see very little similar to modern aero- no chin, no front splitter, no rear splitter, no side skirts, nothing deflecting the air directly at the rear of the car.

Can anyone describe the basic flows and concepts?

Thanks!

Figured out the radiators... they are essentially outside the car, or at least the aero.

Still trying to figure out the rear wheel wells, and the vents above above the engine.

If you are near Midland you can see the car and talk directly to Jim (sometimes)

Don't make me cry!

OR, you could pay my gas & I'll go and take loads of pics and ask questions for you. They have these new things called cell phones so I could even call you and you could ask the questions.

I'm only a few hours away. (which is close by Texas standards)

The chin spoiler came later when they discovered the front was lifting. "RaceCar Vehicle Dynamics" by Bill andDoug Milliken has a whole lot of the Chaparal development plus more ,

So then Jim Hall says to me ...

Here's what a lot of competitors missed in looking at the 2E:

The front ducts were also controlled.

Undercar, from the front:

The cars (and sometimes Jim Hall, too!) are on on display in Midland, in their own wing at the Permian Basin Petroleum Museum on Interstate 20. It's just a couple of miles from the Chaparral offices and Rattlesnake Raceway, both south of I-20 on 349.

I saw the front flaps. Missed that they were operable.

Still not really seeing it in your pic. Are you saying it drops lower than the position it is in, or that it opens a duct through the chassis? Where is the increase in aero resistance?

Here's how I understand it:

There is a flap controlling how much air passes through the front ducts, linked to the wing. Both are controlled with a pedal where the clutch would normally be. The 2E had a torque converter semi-automatic transmission.

More flow through the front duct would cause more air drag - and more downforce. Just what you need in the turns. Level the wing and close the vent for less drag on the straights.

Cool.

Does the big boxed chassis duct air, or just sit there like a big boxed chassis?

You have to remember that the Chaparrals were designed and built in the 1960s, when no one (at all!) was doing anything nearly as creative with aero. The Midland museum is amazing for real car nuts, because the cars are protected with proximity alarms - so as long as you don't touch them, you can get as close as you like. They even have a 2E replica that you can sit in. The 2C, 2D, 2E, 2F, 2H (the whale) and 2J sucker are all there, as well as the 2K "Yellow Submarine" Indy car, which is mounted about 6 feet off the ground wo you can see the tunnels!

The moveable wings were banned by the FIA not because of any Chaparral problems, but because when F1 adopted them, they built their wings too flimsy, and after several catastrophic failures, the FIA banned all moveable aero devices (until recently, that is).

For a small sedan-based project, I'd build a sucker if you can run it legally. Lots of unrealized potential there, and you get serious downforce at low speeds, which you don't get with passive aero. If you're really into aero, try to get copies of the magazine Racecar Engineering - the math gets pretty heavy, but the concepts are well explained.

Something you need to consider is the effects of serious downforce on ride height. Let's say you succeed in generating 1600 lb. of downforce at a given speed, and let's say (for this thought experiment) that it's evenly distributed front and rear. That's 400 lbs per corner. If you're running, say, 200lb/inch springs, you have just lost 2 inches of ride height. Two problems here: If you're generating your downforce by airflow undeneath the car (ground effects in one form or another) it's very dependent on ride height. To maintain consistent downforce, you'll need to run stratospheric spring rates to maintain a constant ride height, like they did in the GE era in F1. This is also why the Chaparrals mounted the wings directly to the suspension uprights - direct loading of the tires by the aero without going through the springs, which allowed conventional rate springs and handling adjustments. The other problem is bottoming out the suspension. You can very easily get into the bump stops, at which point the spring rate effectively becomes infinite, and your handling goes out the window - unless you plan on using compliant bump stops with a calibrated spring rate (this is done in some types of racing - I think NASCAR does a lot of this).

Plus, to generate significant downforce at relatively slow speeds encountered in tight corners will require some BIG wings.

Like I said, I'd investigate a sucker. Look for the sucker Vette article from the GRM challenge a few years ago - it worked!

Good luck, sounds like a challenging project!!

@ Jim Pettengil

Thanks for the information. It's obvious you know way more than I do about this!

Reading between the lines, it seems like you assume my car would make a whole lot of downforce. How much could I realistically expect with a 3 inch ride height and no external wings?

Wow, I hope that question doesn't sound as ridiculously vague to you as it does to me ...

I was thinking about doing the sucker car. I have that issue of GRM in my apartment, actually. I'm just not sure if they would let me on track.

Why wouldn't they let you on track?,your doing tham a favour by vacuuming all the dust and debris off to make it safer for everyone else.At least thats the angle I'd work on.

Throwing all that crap on the track at high speed into whoever is following me seems like a problem.

That said, if I do decide I need a trillionty pounds of downforce, I would like to copy the castered rubber skirt the sucker Vette guys used.

I worked the track as the sucker vette ran.

There WAS a rain drizzle of crap vacuumed off the track.

But it wouldn't really effect the cars behind you. First off, it was really high- like 25' in the air. If it showered on competitors, it would be from above, not in front of them.

Secondly, it really wasn't THAT much. Tracks start reasonably clean.

Third, it's crap they would have encountered anyway (kicking from tires in front of them, etc.)

DaewooOfDeath wrote: That said, if I do decide I need a trillionty pounds of downforce, I would like to copy the castered rubber skirt the sucker Vette guys used.

Anchor it well. Skirts flapping around are not always Marilyn moments.