Calculating helicopter lift

In summary, the conversation discusses different equations for calculating the lift or thrust of a RC helicopter. The equations involve circular area swept by rotor blades, density of air, velocity of air exiting disk, and induced velocity. However, there is some confusion over the first equation due to the presence of velocity appearing twice. Induced velocity is defined as the downdraught or the velocity of the air below the disk. The correct units for the thrust are also discussed.
  • #1
hbooth93
2
0

Homework Statement



I've been trying to find a simple equation for calculating the lift (or thrust) of a RC helicopter and I've found a few that are different.

Homework Equations


1) Lift = circular area swept by rotor blades [itex]\times[/itex] density of air [itex]\times[/itex] velocity of air exiting disk [itex]\times[/itex] velocity of air exiting disk

2) Thrust = 2 [itex]\times[/itex] air density [itex]\times[/itex] length of rotor blades 2 [itex]\times[/itex] induced velocity

The Attempt at a Solution


I am unsure which is the correct equation. Also, can someone explain what 'induced velocity' is please?

thanks!
 
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  • #2
hbooth93 said:

Homework Statement



I've been trying to find a simple equation for calculating the lift (or thrust) of a RC helicopter and I've found a few that are different.

Homework Equations


1) Lift = circular area swept by rotor blades [itex]\times[/itex] density of air [itex]\times[/itex] velocity of air exiting disk [itex]\times[/itex] velocity of air exiting disk

2) Thrust = 2 [itex]\times[/itex] air density [itex]\times[/itex] length of rotor blades 2 [itex]\times[/itex] induced velocity

The Attempt at a Solution


I am unsure which is the correct equation. Also, can someone explain what 'induced velocity' is please?

thanks!

The equations seem very similar. Each contains a term having units of length2 (we call that area), and density of air and velocity of air column. So I'd say you are in error in having velocity appearing twice in the first equation. This leaves us with two equations almost identical, except for a Pi and I'd surmise that you may have accidently left that out, too. :frown:

So I'd conclude that induced velocity is the downdraught, the velocity of the air below the disk.

Have you decided what units you would expect this 'thrust' to have? Do the units of the terms on the right hand side of the equations seems to amount to that?
 
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1. How do you calculate the lift of a helicopter?

The lift of a helicopter can be calculated using the following formula: lift = 1/2 x air density x rotor disk area x coefficient of lift x velocity squared. This formula takes into account the air density, size of the rotor blades, and the speed at which the blades are rotating.

2. What is the coefficient of lift for a helicopter?

The coefficient of lift for a helicopter is a measure of the efficiency of the rotor blades in generating lift. It is affected by factors such as the shape and angle of the blades, and can vary depending on the design of the helicopter.

3. How does air density affect helicopter lift?

Air density plays a significant role in helicopter lift as it affects the amount of air that can be displaced by the rotor blades. Higher air density means more air can be displaced, resulting in higher lift. Air density is influenced by factors such as altitude and temperature.

4. What is the relationship between helicopter speed and lift?

The lift of a helicopter is directly proportional to the square of its speed. This means that as the speed of the helicopter increases, the lift also increases, and vice versa. However, there is a maximum speed at which the helicopter can generate lift, known as the critical speed.

5. How does the weight of the helicopter affect its lift?

The weight of a helicopter has a direct impact on its lift. As the weight of the helicopter increases, more lift is required to keep it airborne. This can be achieved by increasing the speed of the rotor blades or increasing the angle of attack of the blades, both of which require more energy from the engine.

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