Overview Of Fluid Dynamics Applied To The Ballistic Characteristics
Of Paintballs and Paintball Markers
Background – Since my introduction to paintball, I have heard the same thing as everyone else, namely that a paintball fired at 300fps has the same range as any other paintball fired at 300fps. Like many others, I realized that this did not hold true in an actual paintball environment. Many times I have been in a position where I could hit my opponent and no matter what he did, his paint would drop off long before it got to me.
This paper is meant to bring to light some of the hidden factors of paintball and explain why certain markers do have more range and accuracy than others.
Topics – In this paper I will cover several aspects of fluid dynamics and dynamic phenomena associated with paintball. Among these are:
- Types of airflow
- Bernoulli effect
- The effects of drag
- Reynolds Number
1. Airflow - There are 2 basic types of airflow. Laminar flow and Turbulent flow.
Laminar flow can best be seen when you turn on a garden hose. At a certain pressure and volume, the water flows smoothly from the hose in a solid glossy column. This type of flow allows for the maximum volume of gas/liquid to pass at the fastest rate possible. Laminar flows columns are less likely to mix with the surrounding environment.
Turbulent flow can also be seen with a garden hose when you turn the pressure up. The nice Laminar flow column will gradually become distorted and disappear completely as the pressure is increased. The flow of water will become turbulent and erratic. As you can see from the resulting spray, a turbulent flow is more likely to mix with the surrounding environment.
2. The Bernoulli effect - This is a phenomenon that can best be described by that silly thing we have all seen at supermarkets. A horizontal fan is placed so that it blows through a traffic cone. When a ball is placed on the column of air that blows up through the cone, it hovers in place and even if it is moved, it re-centers itself in the air column.
3. Drag in aero/fluid dynamics is a bizarre and very nebulous concept dealing with friction and the actual dynamic properties of an object.
4. Reynolds Number – This is a theory that describes the close order effects of turbulence on an object and can best be described by looking at a golf ball. Golf balls are dimpled to take advantage of the fact that small pockets of turbulence along the surface of a wing can actually cause air to flow over it faster than a completely smooth surface.
Assumptions – In this paper, I am assuming several things for consistency. I am aware that most of these factors are not the same in a real world scenario.
- All paintballs are exactly the same size and perfectly round and do not distort when fired.
- Barrels for each marker are the same length (breech to end).
- Temperature, barometric pressure, humidity, and elevation are constant.
- I may be assuming other things but nothing that comes to mind.
Main – For simplicity sake, I will use 2 markers that I am familiar with and we will examine a scenario for each. I will be using the Bushmaster/Defiant and the Shocker as my case studies because I am familiar with both of them.
The Bushmaster is a high-pressure blowback style marker with an operating pressure or about 350psi. When a paintball is fired, this marker produces a sharp high-pressure blast of air that propels the paintball out of the marker at 300 fps. While this is occurring, the bolt travels back so that the next ball can drop into the breech to be fired. This sharp blast of air combined with a sudden backpressure in the breech causes a turbulent airflow behind the paintball.
The Shocker is a low-pressure, closed bolt style marker that runs at an operating pressure of about 180psi. When fired, this marker produces a relatively high volume of low-pressure air that propels the paintball out of the marker at 300 fps. After this occurs, the bolt travels back so that the next paintball can drop into the breech. This method of propelling a paintball produces a much less turbulent, or Laminar flow.
After the paintball has left the marker, it is natural to assume that nothing else is acting upon the flight of the paintball, but this is not entirely true. Upon exiting the barrel, we must look at the method the paintball was propelled by.
The paintball fired from the first marker is followed out of the barrel by a turbulent volume of air that begins to immediately mix with the surrounding environment and quickly dissipates. This does little to aid the flight of the paintball, and since this turbulent air acts in a highly unstable and unpredictable manner, can actually slightly skew the flight of the paintball by causing high and low pressure zones behind the paintball.
The paintball fired from the second marker is also followed by a larger volume of air that is much more orderly. This air will resist rapid mixture with the environment outside of the barrel and continue to follow the paintball until it dissipates. In effect, this produces an aerodynamic shape rather like a comet or a teardrop instead of a sphere until this effect dissipates. Additionally, due to the phenomenon of Bernoulli’s effect, slight deviations in the flight path of the paintball will actually be corrected as this ordered column of air exerts equal pressure to the spherical shape of the paintball.
Drag will have an effect on each paintball based on its aerodynamic properties. The first paintball will succumb to the effects of drag before the second one due to the temporarily elongated wing effect that the Laminar column lends to the second paintball. This should be a relatively small difference but it is worth mentioning because we are discussing a projectile that is traveling just over 200mph and at that speed, even little differences count.
Last but not least, we need to discuss the theory behind the Reynolds Number. As I stated before, the reason that golf balls are dimpled instead of smooth is to change the way that the air flows across the surface of the ball. A golf ball is in actuality a spherical wing and the dimples create small pockets of turbulence as air travels across it. This evenly created turbulence changes the properties of the wing and actually allows more air to flow across the slightly expanded surface. The surface is actually expanded by the turbulence. This allows a dimpled golf ball to travel further than a smooth golf ball given equal or nearly equal swings from an experienced golfer (which is why they haven’t been used in ages). This also has applications in paintball. If a manufacturer could make a paintball that had the same type of consistent dimpling as a golf ball, we would see a significant increase in range for paintballs as well.
Conclusion – There are many factors that come into play in the ballistic flight of a paintball. Due to the different operating methods employed by different markers, it is safe to say that not every paintball traveling at 300fps has the same aerodynamic properties. Since this is the case, it is also safe to say that some markers will have better or worse range and accuracy depending on what properties they impart to their projectiles.
I hope this helps to clear up what seems to be a longstanding myth in the sport of paintball, and helps to explain why that guy at the end of the field with a Shocker can hit an opponent while paint from the opponent’s Angel falls short of its target.