I have a minimum height of 2.5R. So, if the roundabout is 4 meters high (with a radius of 2 meters), the car will have to start 5 meters above the ground to only create loops. Of course, this assumes no energy loss due to friction; you may want to start a little higher to account for that.
But Not Too High…
In fact, why cut it at all? Why not start much higher and remove all doubts? The reason is because the faster the car goes, the higher the g-force the driver experiences during the loop.
Think about this: If you let a car go around at minimum speed, it will Are not force from the rail (FT). You will feel weightless—zero g—for a moment. If the car is dropped from a height greater than 2.5R, its velocity will be greater than the minimum at the top of the loop. To still move in a circle, gravity will not be enough. The track will also have to overlap the car. This will create g-forces greater than zero.
Let’s go back real stunt videos. By comparing the loop with bystanders, I guess it has a radius of 2 meters. Apparently the vehicle was dropped from a height above a minimum of 5 meters—say 8 meters. The force at the end of the loop (divided by the weight, in g) will be 3 g. Its Humans can withstand forces of up to 20 gso this should be fine.
But what if you go to extremes? If you start too high and make the loop too small, bad things can happen. What about a height of 20 meters with a radius of 1.5 meters for the loop? This will create a force of 21 g. It may look cool but it can also kill you. That’s not fun anymore.
