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Old 02-14-2013, 10:45 AM   #1
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Understanding The Physics Behind Airsoft

I'm making this write-up because the only way to achieve greater accuracy is by understanding why different things make our bbs more accurate, or inaccurate as the case may be. We should also understand how our sport of airsoft works because not knowing why our hobby works just isn't right.


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Why The Hopup Works:
We all know the bucking gives the bb a backspin, which keeps the bb from falling to the ground. Too many people though don't even know why this happens. The whole idea behind the hopup is the Magnus Effect. As the bb is flying through the air, the backspin creates a low pressure zone (going into aerodynamics here) on the top of the bb, and a high pressure zone on the bottom. What this does is suck the bb up into the air. We can't just give it backspin and expect it to work perfectly though, we need to get just the right amount of backspin to counter gravity. This is how we get that flat trajectory.


One way you can see an exaggerated version of the Magnus effect is with a ping-pong ball (table tennis ball) because of the high surface area and low mass. Try throwing the ping-pong straight through the air while giving it a backspin. Then try throwing it with the same strength and speed, but giving it a forward spin. You'll see the ball flies much straighter with the backspin than with the front spin.


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BB Vibration:
The bucking makes the bb have a backspin, but if that backspin is applied too fast the bb will vibrate in the air as a result of the center of rotation being off the center of mass (like drilling a hole for an axle on a wheel off center and trying to spin it). This vibration makes the bb unstable and causes inconsistencies in the flight patterns. It also makes the backspin slow down faster than it should. The slower the backspin is applied (like with an r-hop), the more stable the bb is, the more consistent it will be, and the longer it will maintain its flat trajectory.



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Momentum By FPS:
Giving the bb more momentum by increasing fps will only help if gravity is somehow turned off and the bb maintains a straight trajectory forever. Unless that happens the bb will run out of backspin and fall to the ground long before you run out of momentum. Of course you may lose enough momentum that the person may not feel the bb hitting them, but that doesn't happen very often.


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LRB (Long Range Barrel):
What the LRB does is stabilize the backspin by forcing the bb to the top of the barrel as it exits, so the bb basically rides along the top. This stabilized backspin then allows the bb to maintain it's straight trajectory for a longer period of time. You want to get as straight a trajectory as possible.

Quote:
Originally Posted by Cheese Man View Post
One thing to note is that an LRB doesn't give a perfectly flat trajectory - it's a very wide parabola that opens up. The bb is actually climbing for most of its flight until the last little flick at the end, when it starts to fall. That's why the LRB is so desirable - its path is even more predictable than a flat trajectory because an arc is more physically stable than a line.

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Why The Size Of The Bore Matters (Barrel ID):

Less contact with the bb means you have fewer external forces interrupting the flight and rotation. Therefore, wider bore is better. Too wide gets you turbulence, hence my dislike for the ORGA barrels. The sweet spot seems to be 6.03-6.05, but the quality of the bore is always top priority, and Prommy 6.03 has the nicest bore, in my experience.

(Credit goes to Cheese Man for writing this)

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I'm sure I'm missing something, or I got something wrong, so please if something can be corrected or made better, as always just tell me. It will make this write up better and help me and anyone who reads it.
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Last edited by Masterjuggler98; 04-28-2013 at 10:30 PM.
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Old 02-14-2013, 11:33 AM   #2
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Thank you for making one post for all to see, great information, clear and concise!
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Old 02-14-2013, 11:38 AM   #3
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Great information Juggler, a lot of physics I didn't know in there. +1
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Old 02-14-2013, 11:50 AM   #4
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Could it be argued that an LRB with a 6.01 barrel could have a greater stability than a larger bore, as the tighter bore would conform to the BB better? Or would that only work in a perfect system, where no vibration is present? Because couldn't that throw the BB around even more if it's tighter?
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Old 02-14-2013, 03:08 PM   #5
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This post was very helpful, Thank you. I had a general concept on how the hop up worked, but nothing exact. I see why it's so important to get your hopup just right, now.

Very informative.
Very helpful.
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Old 02-16-2013, 06:33 PM   #6
 
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Any outside forces on the bb will impact the spin. That is why you want a wider bore. The bb's spin acts like a gyroscope and it keeps the bb from wobbling in midair *if the spin is applied gradually and properly*

Just remember, slow is smooth, smooth is fast. That applies to just about everything with an airsoft rifle. Hell, i just finished a piston mod that doesn't release the nozzle until it hits a certain pressure (I read about it on another forum and thought I'd try it) and now I can have my piston moving at less than .02 m/s.



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Old 02-16-2013, 07:11 PM   #7
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Cheese, can you elaborate on why a wider bore is better? If you do I can add it to the original post. And can you link to the mod you're talking out? That sounds really interesting.
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Old 02-17-2013, 03:51 AM   #8
 
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Less contact with the bb means you have fewer external forces interrupting the flight and rotation. Therefore, wider bore is better. Too wide gets you turbulence, hence my dislike for the ORGA barrels. The sweet spot seems to be 6.03-6.05, but the quality of the bore is always top priority, and Prommy 6.03 has the nicest bore.

The mod I'm talking about never had a formal guide as far as I know, I just saw that somebody did that (never knew how) and I just tried it. It's not difficult, I'll write something up when I get it perfected.



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Old 02-17-2013, 09:20 AM   #9
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Thanks Cheese, I just added your explanation.
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Old 02-17-2013, 02:27 PM   #10
 
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Add "in my experience" to the end, there are people who will disagree. Thanks. :)

One thing to note is that an LRB doesn't give a perfectly flat trajectory - it's a very wide parabola that opens up. The bb is actually climbing for most of its flight until the last little flick at the end, when it starts to fall. That's why the LRB is so desirable - its path is even more predictable than a flat trajectory because an arc is more physically stable than a line.



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Old 02-17-2013, 03:33 PM   #11
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I added the "in my experience" part. Can I quote you on what you just said about the LRB?
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Old 02-17-2013, 03:38 PM   #12
 
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Thanks man.

Go for it. As long as it's a quote, anything I say is fair game.



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Old 02-17-2013, 03:42 PM   #13
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I'll do it a little bit later, thanks. For some reasson I can't make new paragraphs with a boxee box (google it).
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Old 02-18-2013, 12:15 AM   #14
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I wonder the diameter size of bb is important or not ? I see common BB Brand ~ 5.95 +/- 0.01mm, some other 5.98 +/- 0.01mm. :D
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Old 02-18-2013, 08:40 AM   #15
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I just added the quote about the LRB not having a perfectly flat trajectory.
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