The point he was trying to convey is that you need to set a MPH that you will travel at and design for benefit at that rate, you also need to set a top for your maximum speed so you can insure that you don't get too much downforce for your spring rate.

Ryan

 

That won't be a problem. Really. The only way you're going to get actual downforce is with a big ugly wing. The best you can hope for is reducing lift somewhat.

The Ferrari 360 was optimized for max downforce without a wing. A team of engineers used up a massive amount of funding writing fluid simulations and spending 3000 hours in a wind tunnel. The end result: 400 lb downforce at the 180 mph top speed. That corresponds to 80 lb at 80 mph.

Essentially, they eliminated lift. That amount of downforce is only slightly relevent at the car's top speed, and does nothing below that.

Again, this completely underwhelming result was acheived by a team of people with real training, experience from F1, time, money, equipment, and the option to design everything from scratch. You can't hope to compete with that. I'm not saying that improvements can't be made on our cars, but don't get too carried away with how effective they'll be.

 

With that in mind, it would be best to choose a speed you actually plan on going at some point. Sometimes what's best for 215 may be bad for 100. You probably know this, but a car that can get to 215 could very well be extremely slow to 60. Without modern supercar technology, it definitely would! That being said, I love the idea of a low first gear 6-speed with 2 ODs and a high (low numerically) diff. ratio, best of both worlds.

I've also been wanting to do this with that area, both to hold some things (aux. tranny cooler, tiny spare, possibly nitrous bottle) but also for aero reasons. Clutchdust and I IMed a bit about it a while ago, and there are a few threads if your search function is working. Anyhow, I have much higher priorities on the car now, but I'm always up for some theorizing!

-Chris

EDIT: In response to the above post. No production/stock car can hope for downforce from underbody things. To get downforce you need ground effects, venturi-effect and gravel-shovelling front airdams, that doesn't jive with a car needing ground clearance and cabin space. That doesn't mean it can't be done though. I think the best option is something removeable. Clip on the ultra-low airdam when you're going for a run on the highways, or preferably the local racetrack. An easily removeable airdam, underbody panels, and maybe even a rear wing could be created fairly easily, excepting the issues already mentioned here (ventillation).

About the rear wing... What is the weight capacity of our luggage racks? For those of us (un)lucky enough to have one, it would be a convenient temporary wing mounting point.

If you're just wanting an all-the-time show-worthy highspeed cruiser, in a word, a supercar, you'd have to go permanent, and a little more elegant than this. I don't know if 215 is a reasonable expectation, but hidden underbody panels would definitely be a good step.


[Modified by RUXperienced, 6:44 PM 1/27/2004]

 

first thing to think about is to stop LIFT, a few extra lbs at???????? i think someone brought up 180 MPH is possible to stop the front lift is as important
if you open a couple of books, sit in a chair, get on a creeper and roll under
and use the graymatter , you'll find improvements, i started this kind of silly
crap at 17 in a 67Mtang fastback, i was able to increase my top speed 30
mph with 90% aero imprivements, 2 good books(old school) THE UNFAIR
ADVANTAGE , Mark Donohoe & SMOKEY'S Best Damn Garage, all the
basic things are in there, :thumbs: :thumbs:

 

And NO i didn't do a tunnel/ venturi under it .. id design a floating, slipper
side skirts, big change :thumbs: :thumbs: they worked a little like the old
Can-Am cars but mine didn't drag all the time :thumbs:

 

Ok ... I was thinking in broader terms of Aerodynamics with the statement about setting an upper limit.

I've toyed with the idea of a wing, definitely going with some type of front spoiler and I've toyed with the Venturi concept.

Ryan

 

a true Venturi $$$$$$$ this is poor boy engineering :lolg: :lolg: front air dam(ajustable) basicly as low and wide as possible(think Boonneville)
side skirts to not allow air under on sides and direct it to rear, smooth under-
neth , and a rollpan from rear -end to back bumper, :cheers:
no wings, yet :thumbs: :cool:

 

Could you describe this in more detail. What I'm imagining wouldn't be reasonable on a street car.

 

What that means, is you have a set height where the suspension can go no lower and you have nothing dragging...

You have a front air dam that may not be form fit off the front bumper changing the look of the car, but it does extend a couple inches off of the front in close to the stock mounting location.

Make it smooth, make it low... make it look fast :jester

 

your kinda getting it (I"M bad at this part) "picture" sit on the ground and look under the front of your car, find a ball that will (just) roll all the way
out the back... now, lay there and think of a way to (just)allow a ball 1/2
the first ***** size to roll under...... does this make any sence???i'm a
shiity teacher, it's taken 5 yrs for my girlfriend to figure some of this out
:withstupid: you need the dam & side skirts a close to the ground as possible
if you don't like the look, change it (mental image)

 

Ya... Your taking something that takes up x amount of space... and forcing it to take up more or less space.

Either creating a vacuum under the car, or trying to limit the amount of air going under.

For me, I'd like to try for a vacuum, because it lets the top of the car do its own thing... and doesnt increase drag! For me, less drag and more downforce is ideal... but the idea is less drag with a side benefit of more downforce!

Ideally the front of the car has enough surface area to at speed force the suspension down a fraction of an inch to put some preload on it... with the rear you have to have the suction of the underside working with you! Every "race car" I have seen that is a C3 has a rather large spoiler tacked on to the rear, and I would like to optomize what we have already before adding to it.

Its the old deal of designing a better mouse trap... some people start from scratch, others try to rebuild the trap when it breaks! I like to try and build from the strong points of the old, and remove the weak points... while "robbing" other locations for ideas. No need to reinvent the wheel in my opinion, just a need to keep it greased!

On that note, I'm starting to wonder about running an encapsulated engine compartment, somehow its possible, Pantera's nearly acomplish it with a wall to the front of the engine, a wall to the back and the wheel wells. Aircraft acomplish it with the cover they put over em... outboard engines do it quite well... But in this case what I (we?) are asking is for the body to do some of the work for us!

No longer can the body just be the pretty face, we have so many tools at our hands when it comes to the design and feeding of radical mills, late model transmissions and race trim suspensions... but how much time do we spend tuning the body? I know Gkull has redone the front facia of his car and added a rear spoiler... but I wonder what would happen if you built a copy of his wild ride and looked at the weak points of the actual design of the body!

A car:
The body
The frame
The running gear

So far, as hot rodders we look at the frame and the running gear... and the body as just a pretty face! :cheers:

 

:rolleyes:

 

Thanks red...

I know I've got your stamp of aproval if it works... and if it does I'll be sure to send ya the blue prints :p:

Nah, On a serious note the topic is just something I've been mulling over for awhile... its not a huge problem, but its one of those many little big problems our cars have. Kinda like the bump steer that is norvals obsession ( :jester ) this is one of mine... :cheers:

 

http://www.m3forum.com/ubb/Forum3/HTML/000557.html
http://www.tech.volvo.se/ivs/courses...ro_rapp_sp.pdf
http://wings.avkids.com/Book/Sports/...acecar-01.html
http://aerodyn.org/aero.html

Wing specific: http://aerodyn.org/Annexes/Racing/hlifts.html

A ferrari that does it... http://www.myautoworld.com/autos/aut...rrari-f50.html
http://www.motorsportsengineering.sa...gy/ferrari.htm

:cheers:

 

NASCAR, CART and IRL teams spend MILLION$ in the wind tunnel (not to mention the professional classes in NHRA) to improve the aerodynamics of their cars. If it was as easy as rivets and aluminum they would all do it.
...redvetracr

 

Redvet, I know you know your stuff, why don't you do some pros and cons instead of just saying it's hopeless? Do you really think it's hopeless?? Obviously there are improvements to be made...

I don't pretend to be an aerodynamicist, but some simple things like air dams are well established facts. Might not be a Formula 1 front wing but it's a step.

 

:thumbs: i'm going to kill a tree printing info from these site's :party:
on my old Tang the only thing i had to jugde by was top speed(calibrated
speedo from boss' Pantara) the handling(was stuck & controlable) and 35mm
pic's taken at speed, at 120 the car droped (about) 2 1/2" in front and 2 in
the rear, i was rolling on 1976 tech bias plys ( :eek: ) g60 front L60 rear
and yes god must like me, i ran it to it's max 148 a few time's a week

 

The reason they spend millions on wind tunnel testing is cause they have no choice. The limits are set on the engine, the susp, and the general design of the body. The only way for them to get that edge is to make what they got more efficent.

I would much rather just make the flow more efficent under the car. I like the idea of building a tunnel from the rear suspension to the end getting rid of any pockets of air going ALL THE WAY to the top of the fenders. I can't see any negative effects of that at least.
I would focus on this. What can be done to help get that air our from under the car as fast as possible???? make is flow smooth!!! thats about all I think you should expect. The best way to aid in this is either a lip on the rear end "on top" or a spoiler. They both do the same thing, but still nothing like a fully functional wing spanning twice as high as the deck of the car.
With a decent spoiler you get the air traveling over the back of the car to make a final leap, "think of the lip like a motorcycle jump and the motorcycle being the air. You want the air to jump and land far behind the rear of the car. This creates a lower pressure area right behind the car, thus allowing the air under the car to escape much easier. So think smooth, turbulance free, I would panel from the side skirts "rocker panels" to the transmission, still allowing air to flow all over the trans, then fill in that rear end leaving the center section open. I wouldn't play with the engine bay much, but lower the front as much as is acceptable so you limit the inital amount of air going under the car. Then in effect the most air you will see is the 4 or so inches of clearance and what travels through to the radiator.
I think many of you are on this side of the topic, but this subject always seems to become focused on the idea of stopping the air from getting there in the first place. That can't be done (easily). It's much easier to escort the air our rather than trying to block it out.


ugh.. I'm talking out my @ss again.

 

:thumbs: your azz seams to know something :lolg: went threw those site's
no real numbers to help work with , i pick up home-built and kit-plane if they
look interesting on areo articals.

 

Washington,
Your approach seems feasible. My 71 model was tested by Road and Track or Car and Driver decades back and posted a drag coeficient of around .43!
The Volvo article indicates that cleaning up the underside can reduce total Cd by .17. I think that's optimistic for my 71 but if I could get half that I'm now at .35 which is a huge improvement.
If you try this, please post pics.