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general_kalle
07-17-2008, 03:00 PM
if a machinegun into the air the projektiles are gonna fly with a certain distance between each other depending on the machine guns rate of fire and also how steady it operates.

if the gun is moving in say an airplane (what a coincidence http://forums.ubi.com/images/smilies/16x16_smiley-very-happy.gif) are the bullets then gonna be closer than if the gun is stationary?

will the projektile have shorter range between each other if the gun is moving fast than if its moving slow, or is completly stationary?

would there be any difference in weather the projektiles are fighting gravity or they are going downwards with the gravity?


wheres Raaaid? http://forums.ubi.com/images/smilies/metal.gif

FoolTrottel
07-17-2008, 03:11 PM
are the bullets then gonna be closer than if the gun is stationary?
Don't think so.... they will be if the aircraft is accelerating fast during firing ... but, as firing them bullets will slow the aircraft down, they'll probably be further apart...


would there be any difference in weather the projektiles are fighting gravity or they are going downwards with the gravity?
Differences in weather will probably have other causes... http://forums.ubi.com/images/smilies/blink.gif

TinyTim
07-17-2008, 03:25 PM
Let's have two systems: a ground mounted, fixed MG, firing horisontally, and a similar plane mounted fixed MG, firing forward.

The only difference between the two systems is higher drag that will slow plane-fired bullets down faster. Let's take 800m/s as a typical muzzle velocity, and 120m/s as a typical airspeed of a plane during firing (that's about 430km/h). Plane fired bullets are now of course moving thru air with 800m/s+120m/s=920m/s.

Drag force goes with the square of velocity, that's why aeiral fired bullets will experience (920/800)^2= ~30% more drag than the ones fired from the ground MG.

Distance between bullets will be the same for both MGs initially, but aerial fired bullets will slow down a bit quicker, so consequently the distance between them will be reducing faster than with ground fired bullets.

Gravity has no effect on the difference in flight paths whatsoever given both MGs are fired in the same direction relative to earth surface.

Mr_Zooly
07-17-2008, 03:33 PM
My head hurts http://forums.ubi.com/images/smilies/53.gif

TinyTim
07-17-2008, 03:55 PM
Originally posted by jayhall0315:
Yes the bullets will be closer when the plane is flying (at least if you are shooting from the front of the aircraft in a forward direction). This is exactly analogous to the doppler effect and how light is perceived from someone afar (or the state troopers radar detector, http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif) as being blue shifted in the direction of motion. As the flying plane fires one bullet, it then moves in the same direction of the bullet, in effect closing the gap, so that when it fires the next bullet, its proximity to the first bullet is now much closer than what it would have been if the bullets were only being fired from a stationary plane on the ground.

As true as this phenomena is, it does not apply to light itself; if you travel at almost light speed (3 x 10^8 m/sec) and then fire a bullet from your gun, the bullet is not traveling at 3 x 10^8 m/sec plus 700 m/sec, it is still traveling at only 3 x 10^8 m/sec. This is the basis for the Special Theory of Relativity (1905 Einstein paper).

Jay

Wrong.

Bullets fired from an airplane forward will

1. will travel thru a surrounding air with muzzle velocity + velocity of an airplane

2. will move away from the plane with muzzle velocity only, which is just like when bullet is fired on the ground.

Conclusion: Initially the gap will be exactly the same.

With the doppler effect situation is different: speed of sound is constant relative to air, not to the emmiter! If an emitter is stationary, then sound waves will move away from it with the speed of sound. If an emiter moves, then the sound waves will move away from it with speed of sound MINUS speed of emitter (in forward direction that is).

Speed of light is the same in all inertial systems.

If you fire a bullet, while you are travelling relative to the Earth with the speed of light - 1 m/s and fire a bullet forward, bullet will still be traveling away from you with 800m/s.

TheFamilyMan
07-17-2008, 04:05 PM
+1

The only time the distance will be different is if the aircraft is accelerating/decelerating, or turning (which BTW happens to be an acceleration).

jayhall0315
07-17-2008, 04:13 PM
Uhh yes, in a shocking display of the very thing I criticize so many Americans for, I have done myself, LOL. You are correct Tiny Tim, I just posted without checking my brain first.

Good and correct answer.

Thanks for the correction,
Jay

TinyTim
07-17-2008, 04:46 PM
Hey np Jayhall, it was a tricky question anyway, a kind that many of us slip on from time to time I guess.


Originally posted by TheFamilyMan:
+1

The only time the distance will be different is if the aircraft is accelerating/decelerating, or turning (which BTW happens to be an acceleration).

Exacly. Even in this later case (when plane is turning), the distance between bullets fired from ground machinegun and plane will be matched assuming that ground machinegun undergoes the same angular movement as a plane.

However, accelerating/decelerating in the direction of firing would have to be beyond any rational value in order to considerably change the gap.

Taking a ShKAS as an example:

mv=~810m/s
rof=~1800rpm
gap=~27m

To shorten this 27m gap a single meter to 26m, a plane would have to accelerate with an acceleration:

a=2s/t^2=1800m/s^2 =~ 180g

julian265
07-17-2008, 04:49 PM
Projectiles fired at a stationary target from a given gun, from a position moving closer to the target, will arrive at the target with higher frequency (ie more per second) than if the same gun was also stationary.

Also, the range of any projectile, (measured from directly under the point where it was fired, to the point on the ground that it hits) fired whilst the gun is moving forward, is greater than that from a stationary gun fired from the same altitude, due to the increased energy of the projectile.

Also, at any given time and distance after firing, the projectiles from a forward moving gun are ALWAYS faster than those shot from a stationary gun. (it's only the INITIAL deceleration that is higher for the projectiles fired from a moving base)

TinyTim
07-17-2008, 04:56 PM
Originally posted by julian265:
Projectiles fired at a stationary target from a given gun, from a position moving closer to the target, will arrive at the target with higher frequency (ie more per second) than if the same gun was also stationary.

Also, the range of any projectile, (measured from directly under the point where it was fired, to the point on the ground that it hits) fired whilst the gun is moving forward, is greater than that from a stationary gun fired from the same altitude, due to the increased energy of the projectile.

Also, at any given time and distance after firing, the projectiles from a forward moving gun are ALWAYS faster than those shot from a stationary gun. (it's only the INITIAL deceleration that is higher for the projectiles fired from a moving base)

Agreed 100%.

Still, the two systems look much more alike if you observe both from their respective inertial systems: first one from the ground, and second one from the plane that is firing. Range meassured this way (ie the distance between where bullet landed and the plane, not where the plane was when it fired the bullet) is quite similar, with ground gun being slightly better.

general_kalle
07-17-2008, 05:14 PM
from this i can conclude that the distance between bullets only change if platform is accelerating/deaccelerating

but why is it that the bullets will impakt with an increasing frequency if the distance to the target is decreasing?

assuming the gun platform is maintaining a constant speed.?

TinyTim
07-17-2008, 05:16 PM
Because each next bullet that hit, traveled shorter overall distance than the one before it.

M_Gunz
07-17-2008, 07:35 PM
Originally posted by jayhall0315:
Uhh yes, in a shocking display of the very thing I criticize so many Americans for, I have done myself, LOL. You are correct Tiny Tim, I just posted without checking my brain first.

Good and correct answer.

Thanks for the correction,
Jay

You must watch too much Ami TV and movies and been made less than perfect.
Now you must emigrate to the US in order to keep wherever you are from pure.

WTE_Galway
07-17-2008, 07:54 PM
Originally posted by general_kalle:
from this i can conclude that the distance between bullets only change if platform is accelerating/deaccelerating

but why is it that the bullets will impact with an increasing frequency if the distance to the target is decreasing?

assuming the gun platform is maintaining a constant speed.?

Not an increasing frequency. The hits occur at a higher frequency if the gun is moving towards you but it is still a constant frequency regardless of the distance from gun to target.

The frequency is higher because the stream of bullets fired by the moving gun have a faster overall velocity. The frequency of hits does NOT change when the distance between gun and target reduces.

PanzerAce
07-17-2008, 09:26 PM
Actually, Galway, if I understand your comment, it does. if delta V != 0, then the rate of bullet impacts (assuming each one hits it's target) is going to change. If the firing plane (presumably behind the target), is closing the target, then the frequency of hits will increase, since, as mentioned earlier, each bullet has to travel less distance than the other, and so for a given V initial, takes less time to reach it's target.


Tiny, the ONLY point I disagree with you on is the slowing affect. While the concept is correct, remember that as the air fired projectile slows, the drag it experiences will converge to the drag that the ground fired one experiences. Given no gravity (or no ground to hit), the air fired projectile will always be faster than the ground fired. It might be an imperceptible amount, but it will be faster still.

Blindman-
07-17-2008, 10:23 PM
I am truly impressed with the answers found on this thread. I would point out that the drag effect at higher velocities would be nullified since the kinetic energy is also directly proportional to the square of the velocity.

WTE_Galway
07-17-2008, 10:27 PM
I follow what you are saying.

However my claim is the effect you are talking about is constant for every bullet and hence the gap (and frequency of hits) does not change as the aircraft approaches the target. Basically the movement of the aircraft forward reduces the gap between bullets but if the aircraft is moving at a constant velocity that reduction is the same for any random adjacent pair of bullets.

Lets put it another way.

Assuming a constant bullet velocity, the frequency of hits is linearly related to the gap beween bullets. If the gap stays the same the frequency of hits stays the same.

The target is of course an arbitrary point somewhere forward of the aircraft. For the frequency of hits to increase as you approach such an arbitrary point the gap between bullets must be reducing in some mathematical relationship to the distance from the point.

There is no mechanism for this to occur.

PanzerAce
07-17-2008, 11:40 PM
Ah, I'm seeing it now. I'm arguing that the frequency changes with delta V, you're arguing a ddV of zero = constant freq. We're arguing the same thing basically. I agree that if both speeds are constant, frequency will stay constant as well.


Actually though, what you say is only true if you ignore friction http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif, since as planes close, the bullets are also going to be going FASTER when they hit....which would do interesting stuff to the freq I'm betting.

TinyTim
07-18-2008, 05:03 AM
Originally posted by PanzerAce:
Tiny, the ONLY point I disagree with you on is the slowing affect. While the concept is correct, remember that as the air fired projectile slows, the drag it experiences will converge to the drag that the ground fired one experiences. Given no gravity (or no ground to hit), the air fired projectile will always be faster than the ground fired. It might be an imperceptible amount, but it will be faster still.

Agree with you completely. But I was correct in my post as well, maybe just not clear enough. You are looking at the bullet, which is fired from an airplane, from stationary observarion point on the ground. I am looking at the same bullet from an aircraft that fired it. If you are looking from an aircraft, then it will be slowing down faster (compared to where it was fired from - the plane) than the ground fired bullet (compared to where it was fired from - the ground).

It's just like looking at two ground fired bullets: one is fired without wind, second one with 150m/s frontal wind. Naturally second one will slow down faster.

BUT if you look at both bullets from a fixed point on the ground, then, of course aerial bullet will always be faster. Llike you said, it will start to behave exactly like ground fired bullet after it's velocity will decrease to the level of muzzle velocity of ground bullet.


Originally posted by Blindman-:
I am truly impressed with the answers found on this thread. I would point out that the drag effect at higher velocities would be nullified since the kinetic energy is also directly proportional to the square of the velocity.

Same problem as above: The two of us are looking at the bullet from the different intertial systems. If you look at both systems from the ground, then aerial bullet will certainly be faster initially, and it's velocity will at one point in its flight path decrease to the level of muzzle velocity of ground fired bullet, and after this point both bullets will behave identically. But if you fire the bullets at the same time, then aerial fired bullet will be decreasing faster, simply because it has not yet reached (velocity decreased to) the velocity of ground bullet (and it never will!).

Or, physically: Yes, kinetic energy goes with v^2 but this does not change the fact that the faster bullet will decelerate quicker. It's drag force that increases with square of velocity, which means that drag power (= rate at which bullet is loosing kinetic energy) goes with the cube of velocity, not with its square:

P=F*v= C*v^2*v= C*v^3 (where C is some constant).

Hope that clears it up.

KrashanTopolova
07-20-2008, 07:47 PM
One could look at from the pilot's view as well.

1. when wing-mounted guns fire they receive a vector not straight ahead to the aircraft's track because when fired the aircraft shakes from side to side. Each bullet has a different vector than the one preceding or going before it. This results in a spray of bullets and though effective it was one of the reasons why wing-mounted guns were often dropped in favour of fusealage-mounted guns. Because of having different vectors each bullet is actually moving away from or toward the next or next after etc..

2, Due to air temp differences a bullet fired at higher altitude loses its friction heat more quickly than one fired a lower altitude. At higher altitude it is also passing through thinner air mass. This has the effect of changing the projectile motion.

3. a bullet is accelerating much faster than the object which propelled it (if indeed the object is accelerating - it could be more likely slowing down as it propels the bullet ie, every reaction produces an equal...etc.)