Lift Force of a Rotating Sphere in the Air

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SUMMARY

The lift force of a rotating sphere, such as an airsoft BB, can be calculated using the parameters provided: mass of 0.25 g, velocity of 130 m/s, angular velocity of 105 rad/s, radius of 3 mm, air density of 1.2292 kg/m³, air pressure of 101200 Pa, and air temperature of 15 °C. The Reynolds number calculated is approximately 49182, indicating turbulent flow. The discussion also highlights the impact of backspin on linear velocity and the need to adjust CO2 discharge levels to maintain muzzle velocity when using a Hop-Up mechanism.

PREREQUISITES
  • Understanding of lift force equations in fluid dynamics
  • Familiarity with the Magnus effect and its application to rotating objects
  • Knowledge of airsoft mechanics, specifically the Hop-Up system
  • Basic principles of aerodynamics and Reynolds number calculations
NEXT STEPS
  • Research the lift force equation for rotating spheres in fluid dynamics
  • Explore the Magnus effect and its implications on projectile motion
  • Investigate the effects of varying CO2 discharge levels on airsoft BB velocity
  • Learn about advanced measurement techniques for velocity and angular velocity of projectiles
USEFUL FOR

Airsoft enthusiasts, engineers in fluid dynamics, and anyone interested in optimizing the performance of airsoft guns through understanding lift forces and projectile behavior.

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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