How powerful would an engine have to be to lift 150lbs?

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Discussion Overview

The discussion revolves around the question of how powerful an engine would need to be to lift a payload of 150 lbs against Earth's gravitational pull. Participants explore various factors affecting thrust requirements, including engine weight, drag forces, and the type of propulsion system used, such as jet engines or rockets.

Discussion Character

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

Main Points Raised

  • Some participants suggest that the thrust produced by the engine must exceed the total weight of the payload, engine, and fuel to achieve vertical lift.
  • Others argue that thrust is the primary measure needed, rather than power, as thrust must be slightly above 150 lbs for lift.
  • A few participants note that the specifics of the propulsion system, such as whether it is a jet engine or rocket, influence the efficiency and power requirements.
  • One participant highlights the importance of considering drag forces, which depend on velocity and can affect the thrust needed for lift.
  • Another point raised is that different propulsion methods, like ion thrusters, have varying thrust-to-power ratios and efficiencies, particularly in different environments.

Areas of Agreement / Disagreement

Participants generally agree that thrust must exceed the weight of the payload and engine for lift, but there are multiple competing views on the role of power versus thrust and the implications of different propulsion systems. The discussion remains unresolved regarding the optimal approach and specific calculations needed.

Contextual Notes

Participants mention various assumptions, such as the need to account for the mass of the engine and fuel, as well as the effects of drag, which are not fully resolved. The discussion also touches on the efficiency of different propulsion systems without reaching a consensus on the best method for lifting the specified weight.

Who May Find This Useful

This discussion may be useful for individuals interested in aerospace engineering, propulsion systems, or those exploring the physics of lift and thrust in practical applications.

BigFly
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just out of curiosity if i wanted to lift something about 150lbs out of the air with a jet engine or rocket, to hold it against the Earth's gravitational pull 9.8m/s how much energy/power would i need? would it also depend on how heavy the engine is? and what other factors are there in this problem?
 
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Really just comes down to how many lbs of thrust the engine can put out. You need slightly more thrust than the weight of the engine and payload in order to go up. All just basic physics.

Want to build a jetpack? Just assuming since you said 150 lbs.
 
chayced said:
Really just comes down to how many lbs of thrust the engine can put out. You need slightly more thrust than the weight of the engine and payload in order to go up. All just basic physics.

Want to build a jetpack? Just assuming since you said 150 lbs.

Might be handy to bring fuel as well.

You only need more thrust than the weight of your contraption if you need to go straight up. You could also use wings and you would only need 1/5 or so.
 
Yea, I wouldn't use power. Power is really just work per unit time. So, an infinitely small engine could be geared to lift the weight infinitely "fast". But rockets and jet engines are typically measured in thrust force, so you would really just need slightly more than the weight of the vehicle + fuel + weight. Excess force can be used to calculate a possible acceleration.

It all really depends on how high you want to go and how long burn time you have.
 
If you want to lift a total load of a 150lbs, you would need to engine to produce slightly above 150lbs of thrust in a focused direction.
 
One would have to consider all masses involved, i.e. not only the 150 lb payload (or person), but also the mass of the engine and propellent (fuel - and oxidizer if the engine is not airbreathing). If one want's to accelerate vertically, the thrust must exceed the total weight, or thrust/weight ratio must > 1.
 
Don't forget drag forces too.
 
FredGarvin said:
Don't forget drag forces too.
which are roughly dependent on the magnitude of velocity squared, so if the thrust is barely above the total weight, then drag will not be significant.

Is the original question related to a jetpack?

http://www.popularmechanics.com/technology/transportation/4217989.html
 
Last edited by a moderator:
BigFly said:
just out of curiosity if i wanted to lift something about 150lbs out of the air with a jet engine or rocket, to hold it against the Earth's gravitational pull 9.8m/s how much energy/power would i need? would it also depend on how heavy the engine is? and what other factors are there in this problem?

Like other people said, the thrust has to be greater than 150 lbs.

To generate 150 lbs of thrust, the output power required depends on how fast you have to move the propellant to generate the force needed. A propellant that is moved faster to generate the same force will result in a higher specific impulse, which means it willl reduce amount of that propellant mass need to deliver the same momentum (e.g. ion propulsion rocket). However, to take advantage of that lower propellant mass, it will require more output power to generate the same force.

[PLAIN]http://en.wikipedia.org/wiki/Ion_thruster said:
The[/PLAIN] thrust created in ion thrusters is very small compared to conventional chemical rockets, but a very high specific impulse, or propellant efficiency, is obtained.

Due to their relatively high power needs, given the specific power of power supplies, and the requirement of an environment void of other ionized particles, ion thrust propulsion currently is only practicable in outer space.

In this sense, for your purposes, a jet engine would be far more efficient than a rocket. A fan of larger diameter would be even better in terms of efficiency, since it distributes the power over a larger swath of air, reducing the power needed to generate the same force. That's why helicopters don't use jet engines and why airliners don't use rocket engines.
 
Last edited by a moderator:
  • #10
That's why helicopters don't use jet engines

But helicopters do use jet engines (gas turbines). Well said either way ;)
 

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