Determining Drag Coefficient

  • Thread starter finlejb
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  • #1
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A fire helicopter carries a 560-kg bucket at the end of a cable 20.6 m long as in the figure below. As the helicopter flies to a fire at a constant speed of 39.2 m/s ,the cable makes an angle of 39.6 with respect to the vertical. The bucket presents a cross-sectional area of [tex]3.96m^2[/tex] in a plane perpendicular to the air moving past it. Determine the drag coefficient, assuming that the resistive force is proportional to the square of the bucket's speed.

I've got that [tex]C_d = 2mg / (V_T)^2A\rho[/tex], but I don't know how to find the terminal velocity of the bucket to find the coefficient of drag. Can anyone help?
 

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Answers and Replies

  • #2
NateTG
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You don't need to use the terminal verlocity at all, but a more general expression for the force of friction. You have enough information to determine the force of friction, and you know the airspeed.
 
  • #3
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But the equation for the force of friction is [tex]f_f = \mu N[/tex]. I don't know the coefficent of friction.... unless it's 1 since it's flying through the air?
 
  • #4
Pyrrhus
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Remember Newton's 1st Law!

[tex] \sum F_{x} = 0 [/tex]

[tex] \sum F_{y} =0 [/tex]
 
  • #5
NateTG
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Sorry, what I meant is that you need a more general expression for drag (rather than friction). You should be able to calculate the force that the drag exerts and work from there.
 
  • #6
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What do you mean a more general equation for drag? That's all my book gives me....
 
  • #7
Pyrrhus
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Try

[tex] F_{drag} = \frac{C_{D}}{A} \frac{\rho v^2}{2} [/tex]
 

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