Dispersion Angle for rapid fire WW2 aircraft guns

[Tony Williams]

Originally posted by gripen
Generally it seems that in long range deflection shooting, the amount of bullets (more hits) and velocity of the bullets (less lead needed) are the most important factors.

I would agree that you will get more hits in those circumstances. However, when comparing with RL, you should bear in mind the following:

1. In RL, scoring hits at long range was uncommon. Scoring hits at any significant deflection angle was also uncommon. Scoring hits at long range and in deflection was virtually impossible. So your point is rather theoretical.

2. Also in RL, if you pulled off the remarkable trick of landing a few .50 hits in those circumstances it is unlikely that a B-24 would take any significant damage, let alone get shot down.

Tony Williams: Military gun and ammunition website and discussion forum

[Kurfürst]

Originally posted by gripen
I have compared the new AH K-4 to the AH P-47D-11. At long range between 600-800, I can definately kill the drone B-24 easier with with the P-47 than with the K-4. It's just much easier to get correct lead with the 8 mgs and the needed lead seem to be less ie there is less room for error. Generally it seems that in long range deflection shooting, the amount of bullets (more hits) and velocity of the bullets (less lead needed) are the most important factors.

gripen

edit: Convergence was default.

True for AH2, where the hit model is a joke, and I can score hits even when completely aiming stupidly in the 'general direction' of the airplane. That's becasue AH uses hit boxes, which are much larger than the actual aircraft.l

Try it in Il2FB, where the bullets only hit if the actually hit the 3d model of the enemy... your POV will change drastically. Someone getting regular 50% hit perctange in AH will be happy to get 5% in Il2FB's realistic gunnery model.

[gripen]

Originally posted by Tony Williams
I would agree that you will get more hits in those circumstances. However, when comparing with RL, you should bear in mind the following:

1. In RL, scoring hits at long range was uncommon. Scoring hits at any significant deflection angle was also uncommon. Scoring hits at long range and in deflection was virtually impossible. So your point is rather theoretical.

2. Also in RL, if you pulled off the remarkable trick of landing a few .50 hits in those circumstances it is unlikely that a B-24 would take any significant damage, let alone get shot down.

Ýep, overall I was just wasting ammo at ranges above 400. When I tried to shoot smaller targets (AH drones P-51D and Fw 190D-9), the results were even worse.

But the purpose of the test was just to show that in practice there is some "shotgun effect" which helps to find the correct lead and also the high velocity of the bullets helps to find the correct lead.

Originally posted by  Kurfürst

True for AH2, where the hit model is a joke, and I can score hits even when completely aiming stupidly in the 'general direction' of the airplane. That's becasue AH uses hit boxes, which are much larger than the actual aircraft.

So in real life deflection shooting at long range was actually even more waste of ammo, right?

gripen

[hitech]

Originally posted by Kurfürst
True for AH2, where the hit model is a joke, and I can score hits even when completely aiming stupidly in the 'general direction' of the airplane. That's becasue AH uses hit boxes, which are much larger than the actual aircraft.l
.

You are totaly miss informed and full of dog dodo.

HiTech

[Waffle]

lol! made my morning!

[HoHun]

Hi Tony,

>2. Also in RL, if you pulled off the remarkable trick of landing a few .50 hits in those circumstances it is unlikely that a B-24 would take any significant damage, let alone get shot down.

Based on total projectile energy, I'd say a figure of about 170 12.7 mm hits would be in line with the German expectations for a 95% kill chance.

With about 150 rounds per barrel being possible for a Browning M2 in a single attack run without overheating issues, and a battery of 6 - 8 barrels, this would require a hit probability of 14 - 19% for a 95% kill chance per attack run.

Evaluating the 8 x 12.7 mm Browning M2 battery according to the Luftwaffe scoring criteria (total battery weight multiplied by required firing duration) for anti-bomber weapons, I get a suitability factor of 0.055. That's about the same as 6 x 15 mm MG151 with 0.056. 2 x MK108 score 0.724, 2 x MG 213/30 1.00.

Regards,

Henning (HoHun)

[gripen]

Originally posted by HoHun

With about 150 rounds per barrel being possible for a Browning M2 in a single attack run without overheating issues, and a battery of 6 - 8 barrels, this would require a hit probability of 14 - 19% for a 95% kill chance per attack run.

Actually I did my testing flying at about same speed as target (at various deflection angles) and shooting short bursts until all ammo was used. With the K-4 it was almost impossible to find the correct lead in deflection shooting, while with D-11 that was quite easy (less lead needed and more bullets in air). Notable thing here is that the AH D-11 can take 425rpg (8x12,7mm) while the K-4 can take only 68rpg (1x30mm). In practice most shooting runs (until the end of the ammo) at long range ended without single hit with the K-4, while with the D-11 I allways scored large number of hits and sometimes got a kill.

At short range the K-4 did well, I quess less than five hits is enough to destroy the drone B-24 but also the D-11 seem to be quite lethal at short range.

Originally posted by HoHun

Evaluating the 8 x 12.7 mm Browning M2 battery according to the Luftwaffe scoring criteria (total battery weight multiplied by required firing duration) for anti-bomber weapons, I get a suitability factor of 0.055. That's about the same as 6 x 15 mm MG151 with 0.056. 2 x MK108 score 0.724, 2 x MG 213/30 1.00.

Hm... I wonder if this criteria include aiming errors and differences between the guns caused by velocity of the bullets? It's quite obivious that at long range deflection shooting  it's much easier to get hits with the gun which can shoot high velocity projectiles.

gripen

[Charge]

"Hm... I wonder if this criteria include aiming errors and differences between the guns caused by velocity of the bullets? It's quite obivious that at long range deflection shooting it's much easier to get hits with the gun which can shoot high velocity projectiles."

I think the question is more about the projectile destructiviness and how well does a light projectile retain its energy and thus how much it can cause damage after flying, say, 600 yards plus the result of the forward movement component of two a/c which is detrimental to the energy of the projectile. Then again the forward velocity component might have a very small effect as the drag builds up rather slowly after the projectile has been launched well above the speed of sound.

The German standard belting for 151/20 has 3 MG of the 5 (1AP+1HE+3MG?) and at least the AP and MGs have the same flight time to 400m which, consequently, is the standard convergence range for German a/c, IIRC that is. I'm not sure what is their drop to that range although I'll have that checked when I get back home.

HoHun, what is that score for 151/20? What is the required limit? Is it some certain amout of Joules after which the bomber is considered destroyed or what?

BTW i'm sure any modern gatling type aircraft cannon benefits of disperison as a single projectile can cripple the enemy a/c sufficiently and the RPM is what, 6000rpm? So the less RPM the gun has the more accurately it has to hit the center of the sight. (what is the dispersion caused by the sight? Which is better in this sense, fixed pipper of LCOS?)

Also with a gun with heavy drop to get a hit on enemy its not only to get a hit in long range in vertical plane but as the projectile starts to plummet downwards you have to hit it in horizontal plane, too.

Err, I mean that if you use a "friggin lazer beam" you aim only in vertical plane, where as firing a mortar you need to get a hit in both vertical, AND horizontal planes. So if you are lined just behind a bomber at long range and try to hit him with a large bore cannon you are actually trying to "drop" a huge grenade ON him. But of course your hit probabilty might as well stay the same as the probable hit area increases, too.
Am I making sense here?

More questions than answers...

-C+

[gripen]

Originally posted by Charge

I think the question is more about the projectile destructiviness and how well does a light projectile retain its energy and thus how much it can cause damage after flying, say, 600 yards plus the result of the forward movement component of two a/c which is detrimental to the energy of the projectile. Then again the forward velocity component might have a very small effect as the drag builds up rather slowly after the projectile has been launched well above the speed of sound.

The original question of this thread was about the optimal dispersion angle of the gun. It can be theoretically proved that due to aiming error some amount dispersion is an advantage but how much, is a good question.

What I can say based on my not so scientific testing is that a large gun with a low velocity projectile, low rate of fire and low dispersion is quite uneffective at long range because aiming is extremely difficult, while battery of the smaller guns with high velocity projectiles, high rate of fire and rather high dispersion (due to installation and/or dispersion of the gun itself) appear to far easier to aim and seem to give much better results at least in the realm of AH.

gripen

[Crumpp]

It can be theoretically proved that due to aiming error some amount dispersion is an advantage but how much, is a good question.

I understodd your contention Gripen was that guns have purpose engineered dispersion as a feature.

Mass production automatic weapons have plenty of dispersion inherently especially when combined with mass production ammunition.  

Engineers work to eliminate dispersion not add it.

All the best,

Crumpp

[gripen]

Originally posted by Crumpp
I understodd your contention Gripen was that guns have purpose engineered dispersion as a feature.

Well, it has been pointed out that in this thread that there is gun installations with purpose built dispersion as well guns which have different barrels for different dispersion patterns.

gripen

[HoHun]

Hi Charge,

>"Hm... I wonder if this criteria include aiming errors and differences between the guns caused by velocity of the bullets?

The Luftwaffe used an average hit figure of 5% as basis for that comparison.

>It's quite obivious that at long range deflection shooting it's much easier to get hits with the gun which can shoot high velocity projectiles."

As reported by the USAAF bombers, the vast majority of Luftwaffe fighter attacks came from straight 12 or 6 o'clock positions and involved little to no deflection.

As Tony pointed out, "long range deflection shooting" was not a sensible tactic in WW2.

>I think the question is more about the projectile destructiviness and how well does a light projectile retain its energy and thus how much it can cause damage after flying, say, 600 yards plus the result of the forward movement component of two a/c which is detrimental to the energy of the projectile.

The total energy of mine shells is preserved pretty well downrange because it's primarily a function of its explosive content. 12.7 mm projectiles lose energy much more quickly. If the 12.7 mm API projectile starts with a muzzle velocity of 890 m/s and is down to 650 m/s 500 m downrange, it is down to 64% of its total energy. The 30 mm mine shell stores more than 90% of its energy in its explosive, so it hardly loses destructive power going downrange.

>HoHun, what is that score for 151/20? What is the required limit? Is it some certain amout of Joules after which the bomber is considered destroyed or what?

The 4 x MG151/20 battery scores 0.262. The main criterium seems to have been mass of explosive delivered, but apparently with some modification to account for the more uniform results delivered by a higher number of smaller projectiles. (Less overkilling with smaller projectiles.)

>Also with a gun with heavy drop to get a hit on enemy its not only to get a hit in long range in vertical plane but as the projectile starts to plummet downwards you have to hit it in horizontal plane, too.

That's accounted for in my initial example on lang range shooting that assumes that the pilot does not compensate for bullet drop at all. The MK108 is a "friggin lazer beam" out to 500 m, but beyond that - no way :-)

(As far as I know, the EZ42 was the only WW2 sight to compensate for bullet drop, and it saw only very limited use.)

>But of course your hit probabilty might as well stay the same as the probable hit area increases, too.
>Am I making sense here?

Yes, you are! Interesting consideration, I hadn't thought of that before :-)

Regards,

Henning (HoHun)

[HoHun]

Hi Crumpp,

>Engineers work to eliminate dispersion not add it.

Tony has pointed out one example of the RAF intentionally enlarging the bullet pattern for air-to-air combat, but this is an isolated recommendation which seems to coincede with the time at which the RAF was desperately trying to come up with a way to deal with the Fw 190.

The other examples probably are intended for air-to-ground or ground-to-air fire.

As all contemporary documentation on air-to-air firing technique stresses accuracy and none of it recommends "walking the rudders" to increase dispersion (as suggested in WW2 manuals for ground attacks), I'm highly sceptical of the claim that dispersion is helpful.

The Luftwaffe explicitely warned against that assumption.

Regards,

Henning (HoHun)

[gripen]

Originally posted by HoHun

The Luftwaffe used an average hit figure of 5% as basis for that comparison.

That's for unspecified range. According to LW instructions posted by you and others, the max practical range was 400m so the average might be around 200 m (about convergence range). Dispersion is actually not issue at so close range particularly in the case of the bomber size target.

Originally posted by HoHun

As reported by the USAAF bombers, the vast majority of Luftwaffe fighter attacks came from straight 12 or 6 o'clock positions and involved little to no deflection.

So even assuming convergence range and no deflection, an average pilot could hit 5%.

Originally posted by HoHun

As Tony pointed out, "long range deflection shooting" was not a sensible tactic in WW2.

Yep, but as Tony also pointed out, adding dispersion to the 20mm installations, improved results in the deflection shooting.

Originally posted by HoHun

The total energy of mine shells is preserved pretty well downrange because it's primarily a function of its explosive content.

Yep, but explosive content does not help if you can't hit, an it's obivious that aiming is much easier with high velocity gun than with low velocity gun if the target is moving.


 

Originally posted by HoHun

The MK108 is a "friggin lazer beam" out to 500 m, but beyond that - no way :-)

The idea of the "lazer beam" term is to be able to shoot with minimum deflection to the moving targets using extremely high velocity of the projectile. The MK 108 is not such weapon.
 
gripen

[Crumpp]

As all contemporary documentation on air-to-air firing technique stresses accuracy and none of it recommends "walking the rudders" to increase dispersion (as suggested in WW2 manuals for ground attacks), I'm highly sceptical of the claim that dispersion is helpful.

I agree, Hohun.

I have some ballistic diagrams for the Mk 108 I could dig out and send if you would like.

In the Ta-152C motor cannon installation, it crosses the vision line at 85m and 400m with a max ord of 66cm.

A surprisingly flat shooting weapon in comparision.

All the best,

Crumpp