Fast cars and downforce!

The other day my girlfriend and I were watching one of those educational channels on satellite. The program was about super road cars. She was very interested in all that very expensive hardware that I could never afford so; though she could understand most of the English commentary I would explain the rest to her. Came to the point where the guy on TV said that this particular car weighed “X” and the ground force it generated was “X+” so you could drive it upside-down. She thought about this for a moment then national pride kicked in and she said “In Bangkok there they do this, in a big round thing they drive upside-down, before have only motor bike but now have car”. Erm! Yes and I tried to explain to her the difference between centrifugal force and ground force. But this got me thinking has it ever actually been done? Has some one actually driven a car upside down, on a roof of some sort solely dependant on down force generated by the cars own aerodynamics? :slight_smile:

But downforce is dependant on velocity and maintaining that velocity requires a certain amount of friction between the tires and the road. For it to drive upside down, it would need the excess downforce to be sufficient to maintain the velocity without wheel slippage.

In a sense, it becomes a giant aerofoil right?

Good point.

On a real race car, the aspect ratio of an airfoil would necessarily be limited by considerations of maximum width. I think we can thus assume that the ratio of lift to drag would not be better than 4:1. So if we have a 1000-lb racecar running upside down, at least 250lbs of traction force would be needed to generate the down- (or perhaps I should say up-) force necessary to offset the weight of the car.

To this must be added the normal drag of the vehicle and the downforce necessary to allow traction for that, and the induced drag that results from that additional downforce.

If we assume our hypothetical car (rightside up, in a straight line) can do 180mph while its engine produces 700hp then (based on the equation power = force * speed) we can calculate that the traction force needed for this is 1458 lbs. A further assumption is that a realistic maximum coefficient of friction for tires is 0.8.

If all this is valid and my calcs are correct, the car will run upside down under the following conditions:
Speed: 180 mph
Traction force: 2575 lbs
Downforce: 4469 lbs
Power required: 1236hp

This looks as if it would be quite difficult, but not necessarily impossible.

Right I get the math’s, well in principal anyway and given enough down / up force the tires would have enough traction. I have often heard the aerofoils on racing cars described as upside-down wings like on an airplane. So my guess is that given enough speed a car could fly “upside-down” on the roof of something. It would have to be a tunnel of some sort where the car could get up speed on the ground and then gradually sort of corkscrew up the walls till it was on the roof. But the question remains has it ever been done ??? Could be a stunt for the next James Bond movie. :slight_smile:

Search on this topic and you will find that it has been discussed to death in this forum. I don’t think anyone found any examples of it being done.

Seeing as how you’re a guest, I’ve done the search for you.

Princhester: Thanks for the pointer. Don’t know where that thread came from cos it was not there when I posted my original question, but as you say that just about covers it all. :slight_smile: