Geo

Actually Rich, we are in agreement. Go back and check what I wrote.

Geo

Be careful with such assertions. A splitter (a true splitter) increases downforce and also reduces drag.

What you state is generally true, but you should not make such general statements as absolutes.

streckfu's

There are different types of drag. You would be more correct in stating an increase in downforce increases rolling resistance (friction) which can be independent of aerodynamic drag (a whole other set of factors).

Geo

Thanks you. Again, a matter of semantics, but I think critical to understanding the various interactions.

Actually, I think almost all cars generate lift.

By reducing the air under the car it also creates a pressure differential.

Not necessarily. The diffusers in modern F1 cars use such a thing. Colin Chapman, when building the first ground effects F1 cars built the underside like an inverted wing. It worked, but was VERY sensitive to pitch and some other things which I cannot remember off the top of my head. In later testing his engineers developed the ground effect tunnels - they are a set of venturies which are far more efficient and far less sensitive to pitch. They work by making a given amount of air occupy a larger space, reducing the pressure (and creating/increasing a/the pressue differential). They worked so well, they were outlawed and the only place you'll find them today in any major series is Champ Cars and Formula Atlantics.

This is an interesting thread. I'm certainly learning some new things. I'm reading some of the links and some of the links they provide. This is a real learning opportunity.

Sam I am

Geo and steckfu are mostly correct. Spoilers are used to simply to incease downforce or negative lift on the top of the car. However, they significantly increase drag because they cause a large seperation in the boundary layer. (you want the smallest possible boundary layer thickness. Within the boundary layer the fluid is more viscous than outside which equates to larger shear stresses and drag forces).

Now, air dams or splitters can be used in two ways. One is used to create a venturi effect where flow under the car essentially sucks the car to the road and increases with speed. The second method has to do with the underbody design. When done correcty the drag is decreased and with a velocity increase, it can also reduce lift

GlenL

So much (dis-)information.

Airfoils don't just use a planing effect to create lift. If that were true then the engines of the aircraft would need to produce the same force as the lift. The trick is that the airfoil produces force but as the plane is moving (mainly) forwards and not up, there's no work done and no power consumed. Pretty cool, actually.

Compare a spltter system to a ground effects system. What's been learned is that you can create downforce by using aerodynamics under the car and reduce drag by letting the air flow both over and under. Again, pretty cool.

A splitter increases the drag on the car by forcing all of the air up-and-over the car. This moves the air from ground-level a long way and that requires more power. It creates down-force by inducing a slight vacuum underneath. Nice, but not ground-effects cool.

A typical car (e.g., 944) will have downforce on the front due to air impacting the sloping hood and windshield. The there'll be lift as the fast moving air over the roof and tail created by airfoil-style lift along with lift from lower pressure air over the rear.

Ahhh, Fun!

(No resonance effects. Still waiting for that white paper.)

Rich Sandor

Geo: thanks for correcting me. you are right. Since I have an aviation background, I apply a lot of that here. Thing is, the ground doesn't usually play a role (other than takeoff/landing) when talking about lift and drag on an airplance. Hence my sweeping generalisation.

Rich Sandor

Glen, I'm surprised that someone who can write so much about aero would have that "parachute" for a rear valence installed on thier car.

Geo

A splitter does in fact increase drag, but the effect is so little as to be considered virtually zero.

Here is a clip from a Racecar Engineering article on splitters than I scanned for a friend of mine last year.

Geo

Splitters and airdams do not create a venturi effect in any way. They simply reduce the amount of air underneath the car and this creates a pressure differential.

What spoilers actually try to do is keep the airflow attached. This includes rear spoilers (not wings) and even the so-called "dive-planes" you see on many sports cars.

Front spoilers reduce the air flow under the car (if they are any good at all).

Rich Sandor

No. A spoiler is a device that SPOILS airflow. Hence the name.

The duck tail on a 911RS is a perfect example of a spoiler.. it SPOILS the downward flowing air and prevents lift on the car. It doesn't actually create downforce though.

A "spoiler" on the front of a car is actually incorrect terminolgly. It should be called a splitter or an airdam, or a wing, but not a spoiler.

Rich Sandor

here is a drawing for reference:

GlenL

Looking faster counts for something, doesn't it? And how about those bad boy rocker boxes. I'm getting another 5mph for those and the car is parked!

inactiveuser92616

You are correct in that no actual (gravitational) work is done holding the plane aloft, but power is indeed consumed; and frictional work is done. Your engines have to produce enough power to overcome the drag created by the wings, sufficient to allow the wings to create the force required to counter act gravity.

shiners780

Good thread.

However, I'm beginning to get flashbacks to that damn "interesting question" thread regarding the airplane being able to take off....AAAAGGGGGHHHHHH!!!!!