What Is the Correct Calculation of Lift Force for an Ascending Helicopter?

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Homework Help Overview

The discussion revolves around calculating the lift force exerted by a helicopter that is accelerating upwards. The original poster presents a scenario involving a helicopter with a specified mass and upward acceleration, seeking to determine the correct lift force in this context.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore the relationship between mass, acceleration, and lift force, with some attempting calculations based on Newton's second law. Questions arise regarding the correct interpretation of forces acting on the helicopter, particularly in different scenarios such as hovering versus ascending.

Discussion Status

There is an ongoing exploration of the calculations involved in determining lift force, with participants providing various interpretations and calculations. Some guidance has been offered regarding the relationship between total force, lift force, and gravitational force, but no consensus has been reached on the correct approach to the original problem.

Contextual Notes

Participants are grappling with the implications of gravitational force and how it interacts with the lift force during different phases of flight. There is also confusion regarding the signs of forces and the overall setup of the problem.

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Homework Statement



A helicopter with a mass of 2090 kilograms accelerates up at 3.13 meters per second per second. What lift force is exerted by the air on the propellers?

m = 2090 kg
a = 3.13 m/s/s

Homework Equations



F = ma ?


The Attempt at a Solution


Force = 2090 kg * 3.13 m/s/s = 6541.7 N

Which is apparently incorrect, then I thought I might have read it wrong and I tried -6541.7, which is also wrong. Can anyone tell me what I am doing wrong? Did I forget to factor something in?
 
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What would be the lift force if the helicopter were just hovering?
 
2090 kg * 9.8 ( 9.8 N in 1 kg)
= 20482 N?
 
Or would it just be 0? I'm very confused.
 
20482 N is correct.

Ftotal = Flift + mg

The lifting force pushing up on the propellers must be of equal to the weight of the helicopter in the opposite direction as gravity when it hovers (when Ftotal = 0).

So what would the lifting force be if it accelerated upwards as your original question stated?
 
Ftotal = Flift + mg
Ftotal = 6541.7 N + 2090 * 9.8?
Ftotal = 27023.7 ?

I'm just so confused.
 
jrbillbrian said:
Ftotal = Flift + mg
Ftotal = 6541.7 N + 2090 * 9.8?
Ftotal = 27023.7 ?

I'm just so confused.

Two points here:

1.) Acceleration due to gravity (g) is -9.8 m/s2, you forgot that it's negative since it acts downwards.

2.) The acceleration of the helicopter is cause by the total force acting on it, not just the lifting force.

So what force would the lift have to be so that the total force accelerates the helicopter upward at 3.13 m/s2?
 
so 6541.7 N + (2090 kg * -9.8)
= -13940.3 N

So you would need 13940.3 N?
 

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