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Lurch1962
12-27-2007, 06:09 PM
More navel gazing?? http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

The Doppler shifting of sounds in the game has got me to thinking. Given the speeds of planes and bullets, there should be a very significant variation in hitting power (and, to a lesser extent, weight of fire per unit time) when relative aspects/speeds change.

To take a not atypical case; a 300kt fighter vs a 200kt bomber, with the former firing in a head-on run, and the latter's rear gunner firing back while said fighter retreats.

Let's take the muzzle velocity of most aerial ordnance to be about 800m/s. A plane's speed in m/s = knots/2. So our 300kt fighter's velocity is 150m/s, and the bomber's is 100m/s; the combined velocities are 250m/s.

So a bullet's relative velocity in a head-on attack is 800 + 250 = 1050m/s, and when separating is 800 - 250 = 550m/s. The difference between the two cases is 1050 - 550 = 500m/s. A better way to look at is 800 +/- 250m/s (800m/s +/- 31%).

For the fighter pilot, you can see that for a given duration of fire, the rounds hit 31% more rapidly in the head-on run as opposed to a co-speed, tail-on attack.

While the effective rate of fire does differ a fair bit, the hitting power really differs. The kinetic energy of a projectile varies as the square of the velocity, and hence a 31% change in velocity results in a change in hitting power by more than a factor of two!.

The relative hitting power as velocity changes:
550m/s (let's use 5.5 squared): 27.5
800m/s (let's use 8 squared): 64
1050m/s (let's use 10.5 squared): 110.25

I wonder if this is modeled?

Lurch1962
12-27-2007, 06:09 PM
More navel gazing?? http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

The Doppler shifting of sounds in the game has got me to thinking. Given the speeds of planes and bullets, there should be a very significant variation in hitting power (and, to a lesser extent, weight of fire per unit time) when relative aspects/speeds change.

To take a not atypical case; a 300kt fighter vs a 200kt bomber, with the former firing in a head-on run, and the latter's rear gunner firing back while said fighter retreats.

Let's take the muzzle velocity of most aerial ordnance to be about 800m/s. A plane's speed in m/s = knots/2. So our 300kt fighter's velocity is 150m/s, and the bomber's is 100m/s; the combined velocities are 250m/s.

So a bullet's relative velocity in a head-on attack is 800 + 250 = 1050m/s, and when separating is 800 - 250 = 550m/s. The difference between the two cases is 1050 - 550 = 500m/s. A better way to look at is 800 +/- 250m/s (800m/s +/- 31%).

For the fighter pilot, you can see that for a given duration of fire, the rounds hit 31% more rapidly in the head-on run as opposed to a co-speed, tail-on attack.

While the effective rate of fire does differ a fair bit, the hitting power really differs. The kinetic energy of a projectile varies as the square of the velocity, and hence a 31% change in velocity results in a change in hitting power by more than a factor of two!.

The relative hitting power as velocity changes:
550m/s (let's use 5.5 squared): 27.5
800m/s (let's use 8 squared): 64
1050m/s (let's use 10.5 squared): 110.25

I wonder if this is modeled?

Waldo.Pepper
12-27-2007, 06:36 PM
Yes it is even mentioned in the manual. I also made a modest movie about this several months ago.

Lurch1962
12-27-2007, 08:43 PM
Yep, I saw mention of hitting power in the manual, too. But AFAIK what's stated relates to decreasing velocity over distance/time as the bullet slows down due to friction. This could be accounted for in a simple fashion, such as decreasing power as flight time increases--no complicated calculations required.

What I was wondering about was if the more complicated situation was handled, i.e., relative velocity of the round at impact, whatever the flight time happened to be, based on the velocity vectors of the round and its target.

Of course, this applies to kinetic ordnance, and to only a small, if any, extent for explosive shells.

M_Gunz
12-27-2007, 09:22 PM
Once you start playing with squares the errors square also.

From Wiki:
1 international knot = 1 nautical mile per hour = 1.852 kilometres per hour exactly = 1.1507794 miles per hour.

So don't divide knots by 2, divide by 1.852.

Here's a big rush, bullets slow down with range so muzzle velocity is not how to determine
speed for kinetic impact. The size, shape and density of the round all make big differences.

More important is what the relative speeds do to bullet travel time and where above or below
the sight line that puts the shot at any range. How that plays out differs between nose and
wing guns as well. The higher the closure rate and the longer the range, the closer the shot
is effectively --- shots that miss have zero impact.

M_Gunz
12-27-2007, 09:34 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Lurch1962:
Yep, I saw mention of hitting power in the manual, too. But AFAIK what's stated relates to decreasing velocity over distance/time as the bullet slows down due to friction. This could be accounted for in a simple fashion, such as decreasing power as flight time increases--no complicated calculations required. </div></BLOCKQUOTE>

If you don't much care for accuracy then sure. Otherwise there's a handful of factors that
differ per bullet and there's the altitude you are shooting at just for starts. Yah, simple,
right.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">What I was wondering about was if the more complicated situation was handled, i.e., relative velocity of the round at impact, whatever the flight time happened to be, based on the velocity vectors of the round and its target.

Of course, this applies to kinetic ordnance, and to only a small, if any, extent for explosive shells. </div></BLOCKQUOTE>

Mike Williams shows relative kinetic to explosive power of many shells at his site. Some are
like 40%-60% at muzzle. With 30% the velocity scrubbed off those shots still have considerable
kinetic energy. The ones with delayed fuse (milliseconds delay) need that to penetrate enough
to cause the most damage.

Good luck with your career but I hope it's nothing to do with determining ballistics.

Lurch1962
01-02-2008, 05:03 PM
As is quite obvious, my "career" has nothing to do with computing ballistics. http://forums.ubi.com/images/smilies/35.gif

I was only working out the problem to first order, not conducting a rigorous analysis. That's why I didn't feel it necessary to get bogged down in the finer points such as frictional drag, ballistic coefficients, trajectory droop, pattern dispersal, convergence setting, ambient density and temperature, G-load, the pilot's mood, etc., etc., etc.

But I do appreciate your contribution, M_Gunz!

S!