Jeff Vader - boscoj

<ul><li><a href="http://www.nasg.com/afdb/list-airfoil-e.phtml">http://www.nasg.com/afdb/list-airfoil-e.phtml</a</li></ul>

Mark Dalen

Most wing designs are made for the high speeds of jet aircraft and will not produce enough negative lift (downforce) to work at auto racing speeds.

One of the most effective designs for auto use is the Liebeck airfoil. The biggest problem with a sedan is that you have a hard time getting any clean air for a wing to work. Many times you will end up slowing the car down - having added drag and almost no downforce.

Jeff Vader - boscoj

and compare it to the foils commonly used on cars. I'm primarily trying to determine what wing were using now. And I was looking for a low speed medium lift low drag foil. Thanks for the airfoil name though, can you tell me what cars use this airfoil?

I finally found it, root is NACA 64A418

ryoung

Even with the flap at 15 deg, the upper rear wing of our Formula Continental provides a whopping 69 lb of downforce at 100 mph (and
only 135 lb of downforce at 140 mph).

The front and rear wings combined do provide ~360 lb of downforce at 140 mph. In addition, this car has a diffuser which provides
additional downforce, especially when it's aided by the rear wing's lower elements. The total downforce is significant on an 1190 lb car,
but a single element on the rear of an S4 doesn't won't much of anything.

<img src="http://www.pccchicago.com/images/paul/midohio/MidOhio_wallpaper2.jpg">

NASA racer

some are more or less efficient SCALED and at low speeds. Unfortunately the database doesn't differentiate. Eppler airfoils are a favorite among model plane designers as are the "RG" airfoils and they work in a low-speed regime. If I was going to just pull an airfoil out of thin air, I'd probably use the E374 and "squash" it to 7%. At 80-90mph it would add a few lbs of downforce. It's a realatively "lifty" airfoil but not too draggy...at least in a model aircraft.

Mark Dalen

I am setting up my new car (Stohr) and am curious what others are doing.

I am doing a Motec w/ shock package. Then Dave &amp; Ellen Ferguson (Veracity Racing Data) will set up math channels to 'measure' ride height and downforce.

NASA racer

I finally finished the body work on the Radical...four months later the car is still a month from being ready.

D'oh!

<img src="http://pictureposter.allbrand.nu/pictures/nasa+racer/radical/smurfe.jpg">

Mark Dalen

Should be done 3rd week of December. I plan on going up to Portland to pick it up between XMas and New Years. Stohr is installing the Motec during assembly.

ryoung

Not having access to a wind tunnel, or even data acquisition, I had to calculate downforce the old fashioned way ... on paper.

Three handy references,

1. "The Theory of Wing Sections", Abbott and Doenhoff -- This book contains lift/drag charts for many NACA wing forms, including charts for wings with high lift devices; i.e., flaps at various angles.

2. "The Illustrated Guide to Aerodynamics" by Smith -- Contains the equations to convert the data into lbs of downforce and HP of drag.

3. "Competition Car Downforce" by McBeath. This is by far the best reference for all aspects of racecar aerodynamics.

A few watch-outs: You must use lift/drag plots at the lowest Reynolds numbers. These are airplane wing sections, and only the plots at low Reynolds numbers are relative to the "low" speeds of race cars. Also, the end-plate correction can be significant. The relatively short span of a racecar wing results in significant amounts of high pressure air creating a vortex as it spills over the end of the wing (you may have seen these on humid days). The endplates, especially like those on our car, tend to emulate a wing with a very long span, which improves efficiency.

Since you'll be using data acquisition to get downforce data, I won't dig out the rather lengthy formula I'm using (unless you need it), but a few key points,

1. Downforce increases in proportion to speed squared; drag, speed cubed. Needless to say, you quickly reach the point of diminishing returns when you add wing to a low HP car.

2. Don't add a wickerbill to the wing unless you absolutely need it to keep flow attached to the underside; wickers add more drag than downforce. You can do a simple test by putting a few drops of dirty oil under the leading edge of the wing. If the oil streaks straight back to the trailing edge, you're OK. We don't have a problem with our rear wing, but we did have flow seperation under the front wing. Rather than a wickerbill, though, we glued thin plastic diamond-shaped <A HREF="http://www.microaero.com/">micro vortex generators</a> under the wing.

3. It's easy to get carried away with all the wing combinations and permeations. In the end, since we don't have a fraction of the test days that we'd need, we use just three wing set-ups. A low drag/downforce set-up for Road America, a high downforce set-up for rain and Gingerman, and a moderate downforce set-up for everywhere else. The last has the 135 lb of downforce I quoted in my earlier post.

Also, the advantage of downforce when cornering is obvious, but don't estimate the benefits when braking. Gingerman is a very low speed track, and you don't pay much of a drag penalty there with a lot of wing. The upper element of our rain wing has two flaps, gobs (relatively) of downforce. With this set-up, we can out brake and pass every other FC at the end of the back straight into T11. I've never seen another FC with a 3-element upper rear wing :-)

Mark Dalen

Thee is an awful lot of creativity in club racing where we can't just throw millions of $ at everything. I do actually understand the stuff you are doing and have many of the same books you mention (plus there is a ME degree in my deep dark past). One thing that particularly caught my attention was your comment about wickerbills. Most of the books suggest using one as they claim that is close to free downforce. However, Lee Stohr does not use one - I suspect he feels the same as you. I will have to ask him about that.

I agree with your comments about braking. When I have the Radical in high downforce, the braking is amazing.

I will have two dive planes that can be on or off, and a single element rear wing. That along with ride height is the aero adjustment for now. CSR/DSR is probably only a year or two away from full tunnels and that should crank it up another notch.

For those interested, the data acquisition plan is this...
Shock data will be filtered (smoothed) and turned into ride height. This will be looked at on various straights.
Knowing the wheel rate, the ride height is used to calculate channels that provide the force on each wheel, and then the downforce and center of pressure.
These would be data channels available just like directly measured data, after the download into the computer.