If you’ve been airsofting before, you’ve probably heard of a “hop-up”. The hop-up is a small, adjustable part of the airsoft gun which dramatically increases an airsoft gun’s range.
How does a hop-up improve range?
As the BB is fired from the airsoft gun using a burst of compressed air, a small and grippy rubber pad rubs against the top of the BB. This has the effect of adding backspin to the BB.
Imagine kicking a football that has someone’s foot placed firmly on-top, this would induce backspin and is the same principle.
The backspin of the ball whilst it’s flying through the air is what gives it its increased range by adding lift.
How does the spin add lift?
Now, this is where it becomes a little bit more technical. For us, it’s not enough to know that the “spin” makes the ball move, we need to know how that happens and why.
The cause is what’s known as the magnus affect. The magnus effect is what causes a spinning sphere to move seemingly defying physic. It may seem complicated, however, it’s actually a simple and understandable physics phenomenon.
Here’s how it works.
Fluids and gasses have a “friction”. This is exactly what causes water to cling to a vertical surface. The air that surrounds the BB shows a similar affect and wants to “cling” to the BB as it runs along its surface.
If the BB is fired without spin (i.e. the hop-up is off) the air will “cling” evenly across all the BBs surface. The BB is propelled forward by the gun and pulled downward by gravity. The air passing the BB simply slips behind it and fills in the void it leaves.
When you apply backspin, you induce a phenomenon known as the Magnus Affect. The spin, creates a difference in surface speed between the top and the bottom of the BB. The top of the BB is spinning with the air, so there’s less friction and more air-speed. The bottom of the BB is spinning against the air, so there’s more friction and less air-speed.
This means, the air from the top of the BB is moving faster, with more energy and so fills the area of low pressure behind the BB faster than the air below can.
Every reaction has an equal and opposite reaction.
Throwing air downward, throws the BB upwards.
Thus, producing lift.
How do you control it?
Since the spin is imparted onto the BB by a friction pad (called the hop-up rubber) you can control the amount of spin (and therefore the amount of lift) by increasing or reducing the amount of friction you impart. This is done by changing the amount that the hop-up rubber protrudes into the barrel.
This can also be improved by changing your hop-up rubber to one that’s made of a grippier material. Firing a BB at a very high fps or with a very heavy BB, could cause it to slip passed the hop-up rubber without receiving much spin, so this could be beneficial if you can’t lift those heavier BBs.