If you were to jump in the air as high as you could and start firing a powerful gun (AK47 / M4A1 type of weapon) what would happen? Obviously your accuracy would be greatly reduced but what would the effects of the recoil be? Would you be forced backwards or be made to pivot so you landed on your back (if you fired the weapon from your shoulder)?
The precise direction of the force would depend on how you are holding the weapon and in what direction you fire, but yes, the recoil would push you back. Of course, even the recoil from a mighty AK-47 isn’t all that much compared to the weight of a human body, so it wouldn’t push you very far.
I’ve fired two fully automatic weapons that I can recall. The M-16 and the M-60. The M-16 from a prone or standing position and the M-60 from the prone using a bipod, weighted w/ sandbags. In mid air I’m sure there would be some reaction due to recoil, but it would be minimal from the M-16. The real problem is a rising action caused by recoil plus the rifling. The most effective use of automatic fire is short bursts of about 3-5 rounds. It’s very easy to burnout a barrel on full auto. Firing an M-60 from a handheld position is strictly for the movies.
Thanks for the replies, the reason I ask is that in a recent patch for a realism-based computer game they removed the ability to fire your weapon whilst in mid-air and someone was asking why this might be. It occured to me that in real-life the recoil would be sufficient to cause you to land flat on your backside if you fired such a weapon in mid-jump but I wasn’t entirely sure.
The recoil would tend to rotate your body unless you happen to have positioned yourself so that your centre of mass is in line with the axis on which the recoil forces are acting.
If you’re talking about Battlefield 2, death to bunnyhoppers!!!
And the weapons in question in that game include the PKM, SAW, M95 sniper rifle, and various other handheld high-powered long arms.
They jump in the air so they’re harder to hit, because they’re such bad shots that they can’t hit anything at range, or they can’t conceive of a first-person shooter where you don’t necessarily want to run every single second you’re in the game, so they run in to point blank and blaze away with an M-16 or heavier, hopping like a bunny and hoping that people trying to hit them from range can’t hit a moving target, and people up close can’t see where they are.
Putting on my amateur physicist’s hat (and I mean amateur, it’s pointy and has a ‘D’ on it) I came up with the following:
Bullet weight (5.56mm NATO): 3.95g
Muzzle velocity (M4A1): 905m/s
Individual bullet momentum = 0.00395*905 = 3.57475kgm/s
Assume you fire 10 bullets whilst in air, total momentum = 35.7475kgm/s
Assume soldier weighs 90kg.
momentum = mass * velocity
35.7175 = 90 * v
v = 35.7475/90 = 0.397 m/s
So, if the soldier is in the air for a second he will be pushed backwards about 40 cm.
Have I made any glaring mistakes or omissions here?
Nothing glaring, but a few things make that estimate high.
On the physics end, he’s not going to be instantly accelerated to 0.4 m/s. That’s the final velocity after all ten bullets. So for most of the time in the air he’s moving much slower that 0.4 m/s. As a reasonable estimate, halve the total movement. .
Also on the physics end, some of the momentum will go to turning the soldier, unless he’s got the rifle lined up perfectly with his center of mass.
And for the numbers in your estimate, being in the air for one second implies a vertical jump of about 4 feet (or 1. 22 m). That’s a little beyond human range. If you say a more reasonable 0.7 seconds, then that means only 7 bullets, and 70% of the acceleration time. Together, those two adjustments cut the distance in half.
So, even assuming a perfectly balanced aim, so the soldier isn’t tumbling at all, that leads to only about 0.1m of movement. Or four inches for us Yanks.
If instead of jumping up, you’re falling, say off of a 10 m high dive, and need to fire your M-16 to push yourself away from landing on the concrete and into the water, you’ll have 1.4 seconds of falling, which will move you (again assuming no tumbling), about 0.8 m. For the record, just walking off the edge at a normal speed would move you twice as far.
This question illustrates well a key point in the physics of jet (or rocket for that matter) propulsion:
At low to moderate speeds it is a whole lot more efficient (from a propuslsion standpoint) to use the available power to throw a lot of mass slowly rather than a little bit of mass quickly. Our jumping shooter cwould end up with substatially more velocity by throwing a large rock than by firing a FA gun, even though the gunpowder supplies much more energy than his arm.
I hate bunnyhopping bitches. They are even more annoying in their own way then people who tk for vehicles.
Or the ass munches that stand in front of the jet you just got, causing you to get the TK (which they punish for).
BF2 has issues. BF1942 (and especially it’s mods) was a much better game.
-Butler
Ah, Butler…join us here at the Battlefield 2 Players LIst Update Thread.
Oops…you already did…my bad. :smack:
I can’t wait to hear the whining when they realize they have to keep their feet (or even better, their bellies…) on the ground if they want to hit their target…
… but that just means they’ll all go back to using the n00b t00b… firing a M203 grenade launcher into the ground at your feet… 
unless the patch also introduces the concept of “arming range…” now that would be sweet…
If bunnyhopping pisses you of too much try Day of Defeat Source - you can’t even fire while running, much less jumping
No kidding. I also keep forgetting in DOD Source that you can’t shoot while going prone (lying down) or standing up. At least I can do that in BF2. I am pretty sure I can do that in real life also.
If I may just bring this thread back onto the original topic (yes the game was BF2)
A friend just pointed out that some amount of recoil would result due to the rocket like effect of the gas escaping the end of the muzzle, does anybody have any ideas on how to calculate the magnitude of this effect for the weapon in question?
Energy efficient, yes. Reaction-mass efficient, not so good. Turboprops beat turbofans beat turbojets for efficiency, but you have all the air in the world for reaction mass.
With rockets, you want to sling out as little as you can get away with, which means slinging it out as fast as you can get it to go. It also means you get to teach the Kzinti a Lesson!