# I Thrust required for a Car driven by a propeller

1. Mar 12, 2018

### KuriousKid

Out of curiosity, If suppose a car is driven/propelled by Propeller, how much thrust would be required to get it rolling or moving, then drive at 30 MPH, at 60 MPH and at 100 MPH? Consider the car weighs 6000 lb including passengers. If same car is inclined at 30 degrees, how much thrust is required to move it forward.
What could be the formula to formulate this relationship of thrust and speed etc? Assume all standard road conditions.

2. Mar 12, 2018

### A.T.

What forces are opposing the thrust and have to be balanced to move at constant speed?

3. Mar 12, 2018

### KuriousKid

On plane level road, friction force [negligible], at higher speed drag and turbulence. At about 60 mph, drag force is about 500 N. If at 100 mph it goes about 1000 N or so. But what I see is Tesla having Motor of a 362 hp (270 kW) and 325 ft⋅lb (440 N⋅m) motor. How does it go beyond 100 mph, if output is 440 N.m? I'm missing something, which I don't know. Something basic.

4. Mar 12, 2018

### A.T.

Is that not enough?

How can we know, if you don't post your math?

5. Mar 12, 2018

### KuriousKid

The Maths is what I'm lacking... That's why I posted here.

6. Mar 12, 2018

### Staff: Mentor

That 440 Nm number is the motor's torque, which has very little to do with the question you're asking. You want to focus on the power output - 270 kW, meaning that the motor will produce 270000 joules of energy per second (one watt is one joule per second).

This may not be helpful to you, though, unless you understand the relationship between force in Newtons, energy in joules, and the distance the car moves in a given amount of time. For that, you'll need the equation $W=Fd$ (W is the energy, F is the force, d is the distance). Google for "W=Fd examples" to get started.

7. Mar 12, 2018

### A.T.

8. Mar 13, 2018

### KuriousKid

Hello, Thank you for explanation. Is there a way to calculate the maximum thrust produced by 270 Kw machine? What I mean is, the force being applied in between tires and ground to move the car?

9. Mar 14, 2018

### A.T.

Take the mechanical power equation from wiki, and solve for force.

10. Mar 14, 2018

### Staff: Mentor

It depends on the gearing. In principle there's no upper limit - halve the diameter of the wheel and you double the maximum possible force at the tire-wheel interface (and halve the speed the car is moving at, for a given power output).

Have you tried googling for $W=Fd$ yet? What did you find?

11. Mar 14, 2018

### CWatters

Previous posts have shown you how to calculate the force at any given velocity.

Force = power/velocity

12. Apr 2, 2018

### KuriousKid

13. Apr 2, 2018

### jrmichler

You can measure the thrust required to hold a constant speed by a coastdown test. Here's an example of one: http://ecomodder.com/forum/showthread.php/coastdown-test-06-gmc-canyon-20405.html. It works for any road vehicle.

The thrust required to accelerate is simply the thrust required at a speed added to the force of acceleration: F = ma.

14. Apr 2, 2018

### Staff: Mentor

....these are late, but...

You can also calculate the thrust required from the fuel economy at any speed, and an assumption about engine efficiency. For example, if I remember a previous calculation I did (I think 25% efficiency), 60mph and 30mpg = about 17hp, or 12.7kW or 5,600N.