Lift Force of a Rotating Sphere in the Air

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Discussion Overview

The discussion centers around the lift force experienced by a rotating sphere, specifically an airsoft BB, as it travels through the air. Participants explore the relevant equations, parameters, and effects of rotation on the BB's flight, including the implications of angular velocity and the Magnus effect.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant inquires about the equation for lift force given specific parameters such as mass, velocity, angular velocity, radius, air density, pressure, and temperature.
  • Another participant asks for clarification on the direction of the rotation of the sphere.
  • A participant references a Wikipedia article on the Magnus effect, suggesting its relevance to the discussion of lift force.
  • Concerns are raised about the potential loss of linear velocity due to the energy used for backspin, questioning whether CO2 discharge levels should be adjusted accordingly.
  • One participant states they focus on measuring the BB's velocity and angular velocity after it exits the barrel, indicating a method for assessing performance.
  • Another participant seeks to understand the decrease in muzzle velocity when the Hop-Up mechanism is employed.

Areas of Agreement / Disagreement

Participants express differing views on the effects of rotation and backspin on the BB's performance, particularly regarding the implications for linear velocity and lift force. The discussion remains unresolved with multiple competing perspectives on these aspects.

Contextual Notes

Participants have not reached consensus on the accuracy of the Reynolds number calculation or the specific effects of the Hop-Up mechanism on muzzle velocity. Assumptions regarding the relationship between backspin and linear velocity are also not fully explored.

Ruda975
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Hello,
I would like to ask one question. What is the equation for the lift force of a rotating sphere when flying through the air:
m = 0.25 g
v = 130 m/s
angular velocity = 105 rad/s
radius = 3 mm
air density = 1.2292 kg/m^3
air pressure = 101200 Pa
air temperature = 15 °C = 288.15 K
If anyone is interested, it is an airsoft bb. I have also calculated the Reynolds number to be around 49182. I don´t know if that´s correct or not.
I have not yet measured the angular velocity of my airsoft gun, but there is a wikipedia article about hop up (the mechanism that applies backspin to the bb), that says that the backspin can exceed 1000 rpm which is about 105 rad/s, so I am using that value.
 
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What is the direction of that rotation?
 

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Ruda975 said:
I have not yet measured the angular velocity of my airsoft gun, but there is a wikipedia article about hop up (the mechanism that applies backspin to the bb), that says that the backspin can exceed 1000 rpm
Do you also increase the CO2 discharge level to compensate for the lost velocity in the barrel? If energy is being put into the backspin of the BB, then linear velocity will be lost in the process, it would seem...

https://en.wikipedia.org/wiki/Hop-up_(airsoft)

1644251955182.png
 
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I only consider the behavior of the bb after it leaves the barrel. I do this through measuring the velocity and angular velocity of the bb once it leaves the barrel.
 
Ruda975 said:
I only consider the behavior of the bb after it leaves the barrel. I do this through measuring the velocity and angular velocity of the bb once it leaves the barrel.
Whate decrease in muzzle velocity do you measure with the Hop-Up mechanism in place?
 

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