wings below the roof line can be as effective for many reasons, than ones above it. as was mentioned by Jack, there is a 8-10+ degree deflection in the air flow, and if that is now the new angle of attack of the air flow, 0 angle of attack of the wing can be very effective.

keep in mind, wings that are below the roof line can be assisted with vortex generators, like seen on the Evos, by alowing more air flow, although somewhat turbulent, to come in contact with the wing, increasing its effectiveness, especially at slower speeds.

The more rearward the wing is mounted the more leverage on the rear of the car it willl have. so, it would need a lot less lift dowforce to equal the downforce of the #1 pictured wing. PLus, the second picture would tend to effect overall vehicle drag as well as being somewhat effective in creating downforce. Lots of trade offs.

Drag is not as important as most give it. most efficient air foils are near 10:1 lift/drag in ratio. this means, if you get near 250lbs of downforce at 100mph, generally, this would be at less than 5hp cost. Obviously, if we are talking a miata, it would be a concern, but remember, this is at 250lbs of wing downforce.

The nice thing about wings, as you can get as much downforce as your stock wing that has been modified, kicked up, etc, with a lot less drag.

Still, my fastest times at Sears Point is with my old kick tail stock wing on my 928. (not my new efficient porsche cup car wing) Tuning is probably the most important factor. balance of downforce front to rear will be more important than just downforce alone at the rear of the car.

mk

 

The flow coming off the brick has a lot to do with things, but - keep in mind when a wing is working, it has a relatively low pressure underside and a higher pressure on top. With the first setup, the low pressure is above the rear portion of the body, tending to "lift" it. So, even if the wing itself produces additional downforce in that position, the wing + body net total might actually be less. Would have to measure to know.

Ideal for max downforce would be more like the higher position of the first one, with the rearward positioning of the second.

 

It's true that bodies in a flow tend to interfere with each other, but there is a big difference between "less than perfect" and "ineffective".

All else being the same, and keeping in mind these are just notional sketches, the first sketch would generally be more effective.

It's likely true that both wings would be more effective if they were higher, but you have to get really high (like that Porsche picture) before the car and the wing stop interfering with each other. It's usually not a practical option.

 

new question..

SAY THAT THE MAKER OF THE WING CLAIMS THAT @ 100MPH, IT WILL PRODUCE 120LBS OF DOWNFORCE. DOES THIS MEAN THAT I CAN HAVE A 120LBS FEMALE GIRL SIT ON THE WING AND NOT BREAK IT?

cuz it's obvious that the wing works on the differences of pressure above and below.. i wonder if that's different from directly adding weight to the upper deck.. it seems like the wing of a vehicle works by "pulling down" by vacuum instead of getting pushed down by the air. But adding weight would PUSH down on it...

 

As opposed to a non-female girl?

 

There is a difference between point loads and distributed loads, but leaving aside those details, the wing does have to be strong enough to support all the loads it is generating.

 

When I built my backyard wing, I tested it with 350 pounds of static load. I used sandbags, since they were readily available and would distribute the weight more evenly (and with fewer complaints) than a female girl.

 

I'd hope its a female girl, I'd be afraid and confused by a female guy.

 

I just noticed I typed female girl

 

To make it clear: Yes, the whole of the wing will support that weight. On the other hand, a point on the wing only as wide as a person's ass may not support that weight.