Puffy Ack

[SEseph]

10 miles is 52800 feet.  Half of that is 26,400 feet.

Someone who is a physics pro do the calculations that prove kinetic energy decreases by half.

~
wrongway

Kinetic energy does not increase/decrease linearly with respect to changes in velocity.  When velocity has decreased in half, kinetic energy has decreased by 1/4th.

I could figure out exactly how high it would take for it to lose half/.75/etc of its energy except I don't have my big boy calculatard with me right now.

Anyone bored though, have at it:

E_k=1/2mv²
V_f²=v_i²+2ad

While I was wrong on half, using what Grizz said, by the time the shell makes it to it's maximum alt, it's going slower than Lushe in salt, there by giving it virtually no kinetic energy (0*n=0). Remember, everything that goes up, must come down and if something goes straight up, it will normally stop at some point (if it maintains the 90 degree climb the entire time) and possibly flop over depending on were the weight of the projectile is. Since the round is also unguided, we must also assume that, like a rocket launch (which is faster than said AA shell) the shell will deviate off course the higher it goes, not only from gravity but also because of basic human inaccuracy. Someone also put it quite well when they said (can't find the quote and too lazy to look) the gunners would need a chart to know the speed and alt of the enemy aircraft, the trajectory of the bomber as opposed the ship, take into account the movement of said ship, be able to lob the shell up 30,000 feet while praying the plane doesn't move slightly off the course and accurately hit the plane (or general area for the puffy). Now if they could accurately and regularly hit these planes at 30,000k or even their max 37k as you said WW, then how could they possibly ever miss at 10k? 15k? 20k?

So, why did we lose ships to enemy Aircraft in WWII? 

[grizz441]

What is a round's initial velocity seseph?

[Lusche]

What is a round's initial velocity seseph?

A AAC Mark 49 projectile has a mass of 25kg and a muzzle velocity of 762 m/s

Just for comparison: the 8,8cm FlaK 41  fired a 9.4 kg HE shell at 1000 m/s. Maximum altitude was given as 14,700m and maximum range was 19,800m

[Spikes]

This thread just got really nerdy...LOL

[grizz441]

A AAC Mark 49 projectile has a mass of 25kg and a muzzle velocity of 762 m/s

Just for comparison: the 8,8cm FlaK 41  fired a 9.4 kg HE shell at 1000 m/s. Maximum altitude was given as 14,700m and maximum range was 19,800m

I'll figure this out during lunch.   

[JunkyII]

buffs roll through the ack too fast to be hit by it

That statement just came off wrong to me for some reason....

Temp and B24 at same alt...the B24 is too fast to be hit?

[SEseph]

Don't forget this:

Generally people calculate muzzle velocity neglecting friction (v=1/2gt), as if there was no big deal - when there really is huge difference.

A man fires a rifle of muzzle velocity 500ms at a fixed target 100m away. If the gun is pointing directly at the target, the bullet misses by 1.96m
(muzzle velocity)^2 / 2(gravity)

[Lusche]

Don't forget this:

Could you give a better link? I'm sure not gonna search that forum for that quote.

[SEseph]

Could you give a better link? I'm sure not gonna search that forum for that quote.

I edited the statements so they weren't questions which was why I didn't give the exact post, but here they are:

http://www.physicsforums.com/library.php?do=view_item&itemid=39  (friction formulas)

http://www.physicsforums.com/showthread.php?t=97423 (this is a long one with alot of formulas)

I'm also going to pull out my old physics books later to see if I missed some other formula on some of the movement factors I mentioned earlier.

[Lusche]

I edited the statements so they weren't questions which was why I didn't give the exact post, but here they are:

That's what I thought and made me curious, because both statements in that single quote aren't really related to another


On the first one "Generally people calculate muzzle velocity neglecting friction (v=1/2gt), as if there was no big deal - when there really is huge difference."
It doesn't really apply here, because it's referring to theoretical calculation of muzzle velocity. The number I gave are actually velocities at the muzzle.

[grizz441]

Assumptions:

-I don't know the cross section dimensions of a Mark 49 round so exact drag is difficult to calculate, so I just assumed a 20% drag reduction in calculations, which seemed reasonable. (Although it could be higher which would lower the ceiling)
-Projectile is fired 90 degrees upward

Findings(With lusches data):

-Projectile launched with 7.26kJ energy @ 762m/s, Sea Level.
-Projectile with half impact energy (3.63kJ) @ 539m/s, 38,900 Ft.

Conclusions:

If you cross paths with the projectile up to 40k, you are going to get hit hard still
For comparison sake, an NS37 spud shooter launches with 0.298kJ energy.

[AWwrgwy]

That statement just came off wrong to me for some reason....

Temp and B24 at same alt...the B24 is too fast to be hit?

I believe it was meant as "irony".   

So, why did we lose ships to enemy Aircraft in WWII? 

Because they weren't being bombed from 20,000 feet. 

Virtually no moving, turning ships were successfully hit by heavy bombers from altitude.

From: 

Although Gen. Kenney's high-altitude bombers had been able to claim a few enemy ships, he was convinced that it was too hard to hit a moving vessel from high altitude.  it was estimated that only one percent of the bombs dropped from high altitude on moving ships actually hit their mark.

Of course they didn't have as much experience as we do nor did they know to lead the ships by one carrier length per 10,000 feet.

Neither did the defenders, for the most part, have proximity fused AAA shells.  Imagine having to set an altitude for the shells to explode as well as aim them.


wrongway

[SEseph]

Assumptions:

-I don't know the cross section dimensions of a Mark 49 round so exact drag is difficult to calculate, so I just assumed a 20% drag reduction in calculations, which seemed reasonable. (Although it could be higher which would lower the ceiling)
-Projectile is fired 90 degrees upward

Findings(With lusches data):

-Projectile launched with 7.26kJ energy @ 762m/s, Sea Level.
-Projectile with half impact energy (3.63kJ) @ 539m/s, 38,900 Ft.

Conclusions:

If you cross paths with the projectile up to 40k, you are going to get hit hard still
For comparison sake, an NS37 spud shooter launches with 0.298kJ energy.

Okay, I concede that they can get up that high, but still, the accuracy is a bit off.

German Flak

Unit                         1939 1940 1941 1942 1943 1944
Heavy Guns               2600 3164 3888 4772 8520 10,600
Light Guns                 6700 8290 9020 10,700 17,500 19,360
Searchlights               2988 3450 3905 4650 5200 7500
% Under The Luftwaffe 50% 61% 54% 64% 74% 70%

Aircraft Sorties In World War 2

Campaign           Allied       Axis    Allied Kills Per 1000 Axis Kills Per 1000 Allied Lost Per 1000 Axis Lost Per 1000
France 1940       4480      21,000       28.6                    12.5                   58.5                      6.1
Britain 1940        31,000   42,000        21.8                   29.5                   29.5                      9.6
Pre D-Day 1944   98,400   34,500       12.7                    29.3                   10.3                      36.1
Post D-Day 1944  203,357 31,833       17.3                    16.2                   2.5                       110.6

http://www.world-war-2.info/statistics/

Germany and more specifically, Berlin, had massive antiaircraft abilities, even holding troops there when needed on both fronts, then acting as shelter for up to 30,000 civilians as Berlin fell. They were massive concrete towers that held their heaviest AAA guns and did only paltry damage to bomber formations. "Prior to the battle of Berlin, Berlin had been subject to a large raid on 23/24 August of 700+ aircraft. A raid half that size, losing 7% of the aircraft, had taken place in September." This number included losses to fighter aircraft. So here we have city sized AAA platforms, that are stationary barely killing bombers... why does this ship based puffy fluff kill us faster.. and we can maneuver. Once Air Command learned it was better to do a staggered box formation, the bombers couldn't maneuver independently.

[Lusche]

I'm not saying our puffy is "right"...


... but keep in mind that German ack had no proximity fuses, and (almost toe the end of war) didn't even use contact fuses. It was purely based on timers.

[SEseph]

Because they weren't being bombed from 20,000 feet. 

Virtually no moving, turning ships were successfully hit by heavy bombers from altitude.

The point I was making about that was if you can hit me at 30k+, then you best hit me at 15k or less 90% of the time or someone should fire/shoot you. If a SBD is coming in or a TBM and they are with in 5k and they don't die immediately, then again, the person who did it should be fired/shot because remember, the same dude can hit me at 30k. That is my argument. If you say: "well 30k is unrealistic cause they didn't do that alot" then make it not hit me but one in a 1000 bursts or more because of the inaccuracy at even 5k from many many gunners. I'm not disagreeing with your points of fact, more the point of fact of there is no "fall off accuracy"

I'm not saying our puffy is "right"...


... but keep in mind that German ack had no proximity fuses, and (almost toe the end of war) didn't even use contact fuses. It was purely based on timers.

lol same page, different paragraph it seems. Never realized they used soley timers at the end!