Cars and Drafting

Factual Questions
1

After reading the Wiki article on Drafting I still have a couple questions which i’m sure somebody can clear up.

  1. How exactly does the car being drafted benefit from it? The Wiki article states that the lead cars fuel expenditure decreases slightly as a result of drafting. But why is this?

  2. Does the benefit of drafting increase as more cars are involved? Could a trucking corporation save tons of gas by having all of their trucks follow in a line down the freeway?

2

Because the drag is reduced. Two cars together produce less drag then each car operating alone. They get to split that savings, essentially. The lead car ends up with less drag to overcome so it saves gas. It would be like adding an aerodynamic fairing to extend the tail of the lead car; which would reduce drag and save gas. But instead of a fairing you use another car.

Yes, they are called trains. :slight_smile:

Sure, if you could safely do it and schedule all the trucks to be going to the same place, yes. But that is what trains are for.

3
  1. The article mentions how. Both cars can go faster and you can do a slingshot maneuver to take the trailing car and leap frog it ahead of the front car. Also saves gas.

It works because you are splitting the drag across two (or more) cars. Air resistance at those speeds is significant. Remember the air is not only pushing against the front of the car but also pulling from the back of the car (like a suction). When two cars draft only one is being “pushed” on by the air from the front and only one is being “pulled” on from the back. In this way both have reduced drag on each individual car and can thus go faster.

  1. Yes, gas is saved at the least by all vehicles in the drafting chain. They can all go faster too. Of course drafting is extremely dangerous which is why you do not see it on normal roads. Race car drivers practice this a lot and use teammates who work with them to make it all work.
4

The area immediately behind a moving car is an area of low pressure, which represents drag. A drafting vehicle in this area makes the pressure not quite as low, which represents slightly lower drag.

5

One thing I noted from my days in tutoring Physics is that a lot of people don’t see the “balance” of things in Physics. Newton’s 3rd Law is a famous example.

People easily see that there is an area of increased pressure in front of the car but that means that there has to be low pressure somewhere else. In this case, at the rear of the car. And this low pressure (aforementioned drag) is as harmful to efficiency as the high pressure.

Always look for such balancing of forces.