Aces High Bulletin Board
General Forums => The O' Club => Topic started by: Halo on May 02, 2007, 05:31:29 PM
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Friend of mine forwarded a 1955 magazine blurb that says ... well, I can't paraphrase it accurately, so here it is in its entirety:
Q. Suppose a plane were traveling at 2000 fps and fired a projectile rearward at 2000 fps. My friend believes that the slug would fall harmlessly to the ground, but I believe that it would perform the same as if it had been fired from a stationary gun. Who is correct?
A. I am sorry to have to tell you that you are wrong and your friend is quite correct. A bullet fired under those conditions would have zero velocity in relation to the earth, although it would have 2000 fps velocity in relation to the plane that fired it.
-- General Hatcher (January 1955, American Rifleman)
Huh? If the first part of that answer means the bullet would fall straight down (subject to atmospheric influences), what does the last part mean ("it would have 2000 fps velocity in relation to the plane that fired it")?
Is it really as basic as, if you're going x velocity forward and a bullet would be going the same velocity backward, there is in effect no motion by the bullet? Would the bullet even go out of the gun barrel only presumably from the higher initial blast since the 2000 fps would be a subsequent average?
You can see I am severely challenged by physics. And I think I have plenty of company.
Seems we've had similar discussions in relation to tailgunners modeled in Aces High. I always thought a tailgunner with two .50s had an advantage over a P-51 firing six .50s at him.
Please enlighten my friend and me. Make it real, real simple. :confused:
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It's all relative, and american rifleman is trying to confuse you.
All of our basic ideas of velocity is based off of being stationary on the ground. But if you are in a different situation, with a different point of view, the relative velocity will *Seem* different.
From the point of view of the earth, it will stay stationary in the air (and technically, the plane will speed up a little) and have a 0 horizontal velocity, and just drop down.
In relation to the plane, it will have 2000 FPS rearward velocity (because the plane is moving at 2000 FPS forward).
Now to really throw in a mind-****, if you were to have 4 different things and they were all to fire at the same time (assuming the earth is really flat), the bullets will hit the ground at the same time.
Let's say you have those 4 things at the same height. One is stationary, and fires to the left. Another is stationary and fires to the right. One is moving at 2000 FPS and fires a bullet aft at 2000 FPS. One is moving at 2000 FPS and fires a bullet forward at 2000 FPS.
All 4 bullets will hit the ground at the same time.
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Sounds like a neat mythbuster episode. It would be nice to see how they would run with it.
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This is a brainteaser... It would seem that a fighter would certainly have the upper hand attacking from a bombers 6
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Originally posted by Mr No Name
This is a brainteaser... It would seem that a fighter would certainly have the upper hand attacking from a bombers 6
It's not that much of a brain teaser. Remember, EVERYTHING IS RELATIVE.
If you were to just analyze the fighter and the bomber's universe, then there's really nothing special about it. If both are moving at 2000 FPS, a 2000 FPS bullet fired rearward would still have just as much damage on the fighter as if the fighter was stationary on the ground.
The trick comes when the fighter is moving away from the bomber, then it becomes complicated. For example, let's say the fighter B&Z's the bomber. He swoops down from the rear, and extends out in front.
Let's say that the fighter has 1000 FPS extra velocity. The bomber would be going 2000, the fighter 3000. If the bullet were to reach the fighter, it would be similar to a 1000 fps bullet striking it when it was stationary on the ground.
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(quote) In relation to the plane, it will have 2000 FPS rearward velocity (because the plane is moving at 2000 FPS forward). (quote)
Along that line, my friend reasoned it would have 4000 fps velocity (plane 2000 fps forward + bullet 2000 fps backward).
Realizing the 2000 fps is an average, and I think obtainable only at some point outside the barrel, paradoxically, isn't the bullet's 2000 fps independent of external vehicle speed until it leaves the barrel?
Aren't you glad I'm not a student in your class?
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Originally posted by lasersailor184
It's not that much of a brain teaser. Remember, EVERYTHING IS RELATIVE.
So you're saying that muzzle velocity of a bullet is it's velocity relative to the muzzle? That just does not make any sense. Now it would make sense if it were relative to 1000 meters below MSL along the prime meridian.
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It would fall straight down as seen from a static point of view (e.g. standing a few paces perpendicular from the point in the airplane's path where the bullet is shot), and fly out the barrel normally (ignoring air friction) as seen from the shooter/plane's point of view.
If you were in outer space, where the only difference is gravity and vacuum, riding a (flat and straight tracked) roller-coaster going forward and dropped a marble from your hand extended out to the side of the wagon, it would follow you along, the same way a cigarette would only fall straight to the floor if you dropped it as you sat in a train cabin itself moving forward on its rails, or the same way an astronaut really moving at a few thousand miles per hour inside a space station can let go of his razor without it moving at all, relatively.
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then it stands to reason that the bomber could theoretically hit the fighter 4K away whereas the fighter, traveling the same speed would shoot itself down provided they were using the same ammo/guns and the rounds actually left the barrel.
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Originally posted by Mr No Name
then it stands to reason that the bomber could theoretically hit the fighter 4K away whereas the fighter, traveling the same speed would shoot itself down provided they were using the same ammo/guns and the rounds actually left the barrel.
There is more energy in the round being shot from the nozes of the airplane than out the back.
Muzzle velocity of a 50 cal from a b-17 = 2900 fps Velocity of b-17 = 350 fps
2900 + 350 vs 2900 - 350
3250 vs 2550 fps....
get hit with a 2550 50 cal you can't just shake it off...
>edit... of course a fighter approches the bomber at at least 350 fps or it would not be approaching.... so the relative velocity of a 50 cal to a 109's canopy would be back up near 3000 fps once again.
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Please see this very old post where not only do I make an idiotic statement, I do the math that proves it.
http://forums.hitechcreations.com/forums/showthread.php?s=&threadid=172137&highlight=buff+guns
It explains why / how a .50cal fired from the tail gun of a bomber is more powerful at impact than the .50cal fired back at it from the trailing plane. Just make sure you get past my first (very poor) WAG at initial deceleration of a .50cal bullet to where HiTech gives the true deceleration. .
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Time to pull out this old thing:
The 50 cal. Buff Gun Laser Myth, Part 2: Ballistics andEnergy
In a parked M-16:
How easily could you kill a parked P-51 at 760 yards?
How easily could you kill a parked B-17 at 1320 yards?
What does this have to do with buff gun performance?
The 2 examples above illustrate the real-world energy difference between a B-17 exchanging fire with a P-51 at 1000 yards (6:00 chasing at 250 mph).
Why the difference? Get a A6M up to 300 mph, auto-pilot on and kill the engine. Watch the airspeed indicator needle drop like mad the instant you kill the engine. Now do the same thing at 200 mph. The needle still drops sharply, but not as fast (300 - 250 = 5 sec., 200 - 150 - 7 sec.). Faster moving objects have more air drag than slower moving ones, a lot more (drag is a function of the square of the speed, if I recall).
Imagine: A P-51 chasing a B-17 at 1000 yards, both planes are exchanging fire and are traveling at 250 mph.
The B-17 tail gun round:
When a 50 cal. bullet leaves the muzzle of the tail gun in a B-17, it actually has a slower airspeed than a 50 cal. bullet fired from a fixed ground fired gun (about 367 fps slower if the buff is flying at 250 mph). This means that it will lose speed and energy at a slower rate than the ground fired gun (even though it has less speed and energy as soon as it leaves the muzzle). It's target (the P-51), is actually moving toward the point in space from which the 50 cal. bullet was fired, so this round has less than 1000 yards to travel before colliding with the P-51. When it collides with the P-51, it instantly gains 367 fps to its speed and energy state (the speed of the P-51).
The Mustang round:
When a 50 cal. bullet leaves the muzzle of one of the P-51's guns, it is actually going faster than a 50 cal. bullet fired from a fixed ground fired gun (about 367 fps faster when the stang is flying at 250 mph). This means that it will lose speed and energy at a faster rate than the ground fired gun (because is has more speed and energy as soon as it leaves the muzzle). It's target (the B-17), is actually moving away from the point in space from which the 50 cal. bullet was fired, so this round has more than 1000 yards to travel before colliding with the B-17. When it collides with the B-17, it instantly loses 367 fps from its speed and energy state (the speed of the B-17).
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The actual math:
250 mph is equal to 367 fps (the speed of the planes).
A 50 cal. round weighs 708 gr. and is moving 2845 fps, right out of the muzzle.
Ballistic Coefficient: 0.700
Drag Function: G1
The B-17 tail gun round:
Leaves the tail gun at 2478 fps (airspeed). 2845 fps (50 cal. muzzle velocity) - 367 fps (aircraft speed) = 2478 fps (true airspeed of the 50 cal. round)
The round travels 840 yards (before colliding with the P-51) in 1.284 sec and has a final velocity of 1558 fps.
1558 fps (the speed of the round just before impact) + 367 fps (the speed of the P-51) = 1925 fps (the true impact speed of the round). A 708 gr. round traveling at 1925 fps has 5800 foot pounds of energy.
The Mustang round:
Leaves the Mustang's gun at 3112 fps (airspeed). 2845 fps (50 cal. muzzle velocity) + 367 fps (aircraft speed) = 3212 fps (true airspeed of the 50 cal. round)
The round travels 1180 yards (before colliding with the B-17) in 1.497 sec and has a final velocity of 1750 fps.
1750 fps (the speed of the round just before impact) - 367 fps (the speed of the B-17) = 1383 fps (the true impact speed of the round). A 708 gr. round traveling at 1383 fps has 3010 foot pounds of energy.
So there you have it.
In the B-17 / P-51 chase example, the rounds hitting the B-17 have 3010 ft.# of E. and the rounds hitting the P-51 have 5800 ft.# of E.
By the way, a 50 cal. round fired from a fixed point (like a parked M-16) has 5800 ft# of E. at 760 yards. It drops down to 3010 ft.# of E. at 1320 yards.
That's why bombers' guns seem so powerful at longer ranges.
Back to my original statement:
In a parked M-16:
How easily could you kill a parked P-51 at 760 yards?
How easily could you kill a parked B-17 at 1320 yards?
The greater the distance between the buff and the fighter, the more exaggerated this effect becomes. At close ranges, however, the difference between the two practically go away.
To kill buffs with a fighter, you must get in close, WITHOUT GIVING THE BUFF GUNNER A GOOD SHOT AT YOU, before you have the firepower advantage.
There are many effective ways of doing this, but that is a whole new topic.
eskimo
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Originally posted by eskimo2
To kill buffs with a fighter, you must get in close, WITHOUT GIVING THE BUFF GUNNER A GOOD SHOT AT YOU, before you have the firepower advantage.
There are many effective ways of doing this, but that is a whole new topic.
eskimo
The math is good, but it aso shows why attacking a buff head on is so affective. At that point you are only adding velocity to the energy equation.
(aircraft velocity) + (buff veocity) + (bullet veocity) = BIG energy
Would also be interesting to caculate the difference in bullet energy between a plane at top speed firing head on and a plane in a high speed dive since the veliocity of the round reative to the buff would be lower.....
cos(theta)((bullet velocity)+(aircraft velocity))+(buff velocity)...... maybe i need to break out the old 49G+....
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Thanks, guys, for resurrecting the older threads about rearward vs. forward firing gun efficiency. They are challenging to plough through for non technical types like me, but I'm getting a better idea of what's going on.
A crucial part I had not realized was a faster starting bullet slowing faster because of more drag (e.g., when fired from a pursuing fighter) and a slower starting bullet retaining velocity longer because of less drag (e.g., from the bomber tail gun firing to the rear).
On a cruder example, consider standing in the bed of a pickup truck and throwing pebbles at a bad guy car behind you, and then facing forward and throwing pebbles at a bad guy car coming at you. The physics become quite apparent.
In one case the motion works for you; in the other the motion works against you. We don't have to know the math to appreciate the effects. It's the difference between peeing upwind or downwind.
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The bullet is already going 2000 fps before it is even fired. It would take all of its 2000 fps velocity when fired in the opposite direction to break even. Thats the way I see it.
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Originally posted by eskimo2
To kill buffs with a fighter, you must get in close, WITHOUT GIVING THE BUFF GUNNER A GOOD SHOT AT YOU, before you have the firepower advantage.
There are many effective ways of doing this, but that is a whole new topic.
eskimo
The math is good, but it aso shows why attacking a buff head on is so affective. At that point you are only adding velocity to the energy equation.
(aircraft velocity) + (buff veocity) + (bullet veocity) = BIG energy
Would also be interesting to caculate the difference in bullet energy between a plane at top speed firing head on and a plane in a high speed dive since the veliocity of the round reative to the buff would be lower.....
cos(theta)((bullet velocity)+(aircraft velocity))+(buff velocity)...... maybe i need to break out the old 49G+....
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Q:In AH does the thinner air up high(say 30k) give a MG round better ballistics?
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I'm pretty sure Hitech said so a long while back on the blue Q&A channel.
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Is the plane in question on a treadmill?
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Originally posted by SirLoin
Q:In AH does the thinner air up high(say 30k) give a MG round better ballistics?
I'm pretty sure its modeled for bullets the same as it is for planes.
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What I get for posting without reading the entire thread. :D
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Originally posted by Curval
Is the plane in question on a treadmill?
That was one of the funniest threads I had ever seen in my life. It really did make me question if there actually is a god.
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Originally posted by lasersailor184
That was one of the funniest threads I had ever seen in my life. It really did make me question if there actually is a god.
Questions are harmless, it's the answers that get ya.