Thrust required for a Car driven by a propeller

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    Car Propeller Thrust
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Discussion Overview

The discussion revolves around calculating the thrust required for a car propelled by a propeller, considering various speeds (30 MPH, 60 MPH, and 100 MPH) and the effect of an incline. Participants explore the forces opposing thrust and the relationship between thrust, speed, and power output.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants inquire about the thrust needed to initiate movement and maintain speeds of 30 MPH, 60 MPH, and 100 MPH for a 6000 lb car, including the effects of a 30-degree incline.
  • Questions arise regarding the opposing forces that must be balanced to maintain constant speed, including drag and friction.
  • One participant estimates drag forces at different speeds, suggesting that at 60 MPH, drag is approximately 500 N, and at 100 MPH, it could be around 1000 N.
  • Concerns are raised about the power output of electric motors, specifically questioning how a Tesla with a 362 hp motor can exceed 100 MPH despite torque figures of 440 N⋅m.
  • Several participants express a lack of mathematical understanding, seeking clarification on how to calculate thrust and force from power output.
  • There are suggestions to use the mechanical power equation to derive force and to consider the gearing of the vehicle as a factor in maximum thrust.
  • One participant mentions the possibility of calculating thrust based on fuel economy and engine efficiency, providing an example calculation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact calculations or methods for determining thrust. Multiple competing views and approaches are presented, with ongoing questions about the relationships between thrust, speed, and power.

Contextual Notes

Some participants highlight the need for assumptions regarding efficiency and the specifics of the vehicle's design, such as gearing and tire size, which may affect the calculations. There is also mention of the complexity of drag forces at higher speeds and the need for empirical testing methods like coastdown tests.

KuriousKid
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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.
 
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KuriousKid said:
... 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 forces are opposing the thrust and have to be balanced to move at constant speed?
 
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.
 
KuriousKid said:
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)...
Is that not enough?

KuriousKid said:
I'm missing something, which I don't know.
How can we know, if you don't post your math?
 
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The Maths is what I'm lacking... That's why I posted here.
 
KuriousKid said:
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.
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.
 
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?
 
KuriousKid said:
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?
Take the mechanical power equation from wiki, and solve for force.
 
  • #10
KuriousKid said:
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?
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
KuriousKid said:
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?
Previous posts have shown you how to calculate the force at any given velocity.

Force = power/velocity
 
  • #12
  • #13
KuriousKid said:
Out of curiosity,..., how much thrust would be required to get it rolling or moving, then drive at 30 MPH, at 60 MPH and at 100 MPH?

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
...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.
 

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