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XyZspineZyX
08-12-2003, 10:07 AM
I've done a few calculations to determine how much the speed of the aircraft affected the velocity of rearward firing guns.

take a MG34 machine gun, the type used in many Axis aircraft.

muzzle velocity is 755 metres / s

that equates to .755 kilometres / s

which equals 45.3 kilometers / min

which equals 2718 kilometers / hour.

so we have a bullet leaving the barrel of the gun at 2718 kilometers p/h. A plane with rearward firing guns generally cruises at 300-350 km/h

that means that a planes speed causes roughly a 10 percent reduction in initial bullet velocity.

enough to have an effect on power?

I wonder if this speed loss is modelled in IL2.

-Hareball

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We should have all the generalizing extremists taken out and shot.
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XyZspineZyX
08-12-2003, 10:07 AM
I've done a few calculations to determine how much the speed of the aircraft affected the velocity of rearward firing guns.

take a MG34 machine gun, the type used in many Axis aircraft.

muzzle velocity is 755 metres / s

that equates to .755 kilometres / s

which equals 45.3 kilometers / min

which equals 2718 kilometers / hour.

so we have a bullet leaving the barrel of the gun at 2718 kilometers p/h. A plane with rearward firing guns generally cruises at 300-350 km/h

that means that a planes speed causes roughly a 10 percent reduction in initial bullet velocity.

enough to have an effect on power?

I wonder if this speed loss is modelled in IL2.

-Hareball

--------------------------------------
We should have all the generalizing extremists taken out and shot.
--------------------------------------

XyZspineZyX
08-12-2003, 10:12 AM
Hareball wrote:

- that means that a planes speed causes roughly a 10
- percent reduction in initial bullet velocity.
-
- enough to have an effect on power?
-
- I wonder if this speed loss is modelled in IL2.

Like Einstein said, everything is relative. If you fire at another aircraft with the same airspeed and vector as you, (like when your rear gunner is firing at the Bf109 on your six) then it doesn't matter.

--
Joques
Ok, so you've got a Yak
That don't impress me much

XyZspineZyX
08-12-2003, 10:16 AM
Yes I guess that is true... so if you fire at an aircraft in front of you you still have to make up the speed. Good point.

I'm not whining or anything, just interested I guess.

An interesting fact is that if you can get an aircraft travelling 2718 km/h, and fire backwards with an MG34, the bullet drops straight to the ground.

-Hareball


joques wrote:
-
- Hareball wrote:
-
-- that means that a planes speed causes roughly a 10
-- percent reduction in initial bullet velocity.
--
-- enough to have an effect on power?
--
-- I wonder if this speed loss is modelled in IL2.
-
- Like Einstein said, everything is relative. If you
- fire at another aircraft with the same airspeed and
- vector as you, (like when your rear gunner is
- firing at the Bf109 on your six) then it doesn't
- matter.
-
---
- Joques
- Ok, so you've got a Yak
- That don't impress me much
-
-



--------------------------------------
We should have all the generalizing extremists taken out and shot.
--------------------------------------

Tully__
08-12-2003, 10:26 AM
If you're shooting at another aircraft that's at the same heading and speed as your gun platform, the direction of fire only affects one thing - how quickly the bullet slows down due to drag.

As an example, lets take a muzzle velocity of 2000mph and an airspeed of 200mph. Also note that drag is proportional to the square of the airspeed/bullet velocity.

If you're firing forward, you add your airspeed to the muzzle velocity for a 10% increase. This will give a 21% increase in intial drag over a stationary gun platform (1.1^2 = 1.21)

If you're firing rearward from the same gun platform, you get a 10% decrease in bullet speed through the air, resulting in a 19% drop in intitial drag relative to a stationary gun platform (0.9^2 = 0.81) and a 33% reduction in initial drag compared to a forward firing gun ( (1.21-0.81)/1.21 = 0.33). Clearly the rear firing bullets have a distinct advantage over forward firing at the same range, muzzle velocity and ammunition type. As speed increases, so does the difference between forward and rear firing guns.

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Salut
Tully

XyZspineZyX
08-12-2003, 10:34 AM
Hareball wrote:
- An interesting fact is that if you can get an
- aircraft travelling 2718 km/h, and fire backwards
- with an MG34, the bullet drops straight to the
- ground.


Ah yes but no, although the bullet would seem to be hanging in the air (or falling downward) to an observer standing still on the ground, the persuing aircraft, which is also travelling at 2718 km/h, will feel the impact as.... and so on =)

XyZspineZyX
08-12-2003, 12:46 PM
Nice... i've been thinking the same thing.../i/smilies/16x16_smiley-happy.gif but when you dive for a tank and shoot your guns and you cruise about 400km/h and shoot a bullet what cruises at 2718km/h + the speed of your aircraft... 2718+450=3168kmh. the bullet hits pretty hard to the tank... /i/smilies/16x16_smiley-happy.gif

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XyZspineZyX
08-12-2003, 02:36 PM
Hey all!



I know this may sound anal but MG 34's weren't used on any Luftwaffe aircraft for defense. They used MG 15's. It had the same caliber (7.92mm), but I'm not sure if there were any differences in muzzle velocity and rate of fire. The Luftwaffe may have tweaked with the guns because (as I'm sure you know) guns used in aerial combat must have different standards for those used just for ground work. Just tryin' to put my 2 cents in. /i/smilies/16x16_smiley-happy.gif


Capt. Arnold

XyZspineZyX
08-12-2003, 02:53 PM
When a gun is fired backwards from a plane though, the bullet would travel a bit faster due to less wind resistence. instead of 350 mph headwind, it has 350 mph tailwind. Also, usually the attacking planes is incoming at a faster speed then the plane with a gunner so all this adds up to higher impact velocity.


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