Downforce Theory

[Antony Snook]

I found this app for my mobile phone called Wind Tunnel from the google play store. This app shows a simple wing and a airo image that explains how air runs over it. This explains downforce. Vital to a open wheel race car to grip through turns.

It starts with a ellipse or a stretched egg shape. with a downward slope. So the air travels further underneath and faster on top. This is a airfoil and the basics for a airplane wing. The air underneath is slowed down. And on top sped up creating lift. Panels called ailerons exaggerate this going down to increase sharp lift for take off. And up to raise top pressure on top making plane drop to land. You can build a simple paper airplane and put slots in wings for ailerons to test this for yourself.

On a race car the wings are upside down so tires are pushed into track. If the car got airborne the ability of the brakes and steering would be compromised. So you want to minimize time the tire is not on the track surface. The tire will bounce in cornering and if if a curb is choped to hard.

In the video the red represents high pressure and blue represents low pressure. So the energy of the air is pushing down, making it Downforce.

 

[dud]

Well, the airfoil part of the wings is important, but a lot of race car aerodynamics are achieved not by airfoil like force but by elements simply acting as air deflectors, or spoilers.

Effects under the car are endlessly debated, just to open up the mess - in aircraft dynamics "ground effect" is an upforce, in car dynamics "ground effect" is a downforce. So you mess up nomenclature right there.

It is a fascinating topic. I always wanted to start messing around with a proper fluid dynamics software package and the actual 3D models we use in our games. But alas the tutorials are barely digestible for a dummy like me.

 

[Antony Snook]

Efectivley the car is a airfoil on wheels. Just like the JPS Lotus that discovered ground affect. The air underneath is sped up. And slowed down on top.
Below is a paper airplane with ailerons sicking up of rear wings.

 

[maelstrom]

Effects under the car are endlessly debated, just to open up the mess - in aircraft dynamics "ground effect" is an upforce, in car dynamics "ground effect" is a downforce. So you mess up nomenclature right there

It depends on the shape of the bottom surface. If it's convex, the airflow sucks you down. If it's concave (or flat, with an angle of attack) it makes you float.

 

[BillGuy]

FWIW below is a video from the physics-oriented Sixty Symbols YouTube channel about how a wing functions.

The thing that has had me scractching my head for the past several years in F1 is the high rake design. I just look at the seemingly giant gaps under the rear of the cars and think "How can that possibly be beneficial?"

 

[Antony Snook]

I did not know it was so complicated and miss understood.

 

[Leonardo Chaves]

FWIW below is a video from the physics-oriented Sixty Symbols YouTube channel about how a wing functions.

The thing that has had me scractching my head for the past several years in F1 is the high rake design. I just look at the seemingly giant gaps under the rear of the cars and think "How can that possibly be beneficial?"

The idea is that angling the car you create a giant diffuser.
Controlling spill becames the problem which is why you all these cuts and holes on floor edges, it's an attempt at creating an air skirt.
Of course since 95 regulations introduced stepped floors spill is problem for everyone, even teams running the cars as close to the ground as possible will have some.

There are other benefits like bringing the front wing closer to the ground, you can make a less aggressive FW, one that disturbs less air, generate the same amount of downforce