Aircraft gun article

[Charge]

"the latter calculated from mass of the chemically active content at the energy density of TNT"

Ok, but I think you need to use PETN figures to get correct energy for Minengeschoss if you use historical belting.

Exlosive velocities are 8,400 m/s for PETN (pure at dens. 1,7) and 6,900 m/s for TNT. (PETN was not used as such in ammo.)

-C+

[Tony Williams]

Originally posted by gripen
Actually the FN version of the M2 with 1100 rpm  was a production and combat ready gun allready 1939. Check your mail box.

gripen

I have FN's booklet on the 13.2mm Browning (no date, but obviously pre-1940) in which they claim 1,050 rpm.

Tony Williams: Military gun and ammunition website and discussion forum

[Knegel]

Hi,

Nice article Tony,

the .50 cal was the better weapon for the US need, cause, while the gun was good enough to destroy all japanese planes rather fast and to keep the german fighters away from the Bombers, it did provide a much better hitprobability than the relative slow firing Hispano.
Better 6 x 12,5 rps than 4 x 10 rps, so around 35 rps more flying toward the target.  Who need cannons, if the enemy dont have big tough bombers?
The much higher gunpower isnt a advantage, if the smaler weapon already is able to bring the enemy fast down, specialy if the smaler gun provide a much higher hitprobability.

The hitprobability is what i miss a bit in your articles, at least imho you should point more to this very important aspect of armament.

For example the MK108 was a nice powerfull weapon, maybe similar powerfull like 2 x MG151/20,  but this only count vs very big strait flying targets(bombers). VS fighters, where some 20mm rounds already was enough, the MK108 was not nearly as effective as the 2 x MG151/20.

Without to point to the hitprobability in a realy drastical way, people run around and compare the armament performence by comparing the gunpower with 100% hitquote for all guns.

Anyway, here i wanna say a special thank you! Your work is the base to my damage model work in EAW.

Greetings, Knegel

[Karnak]

Knegel,

To paraphrase an ace "If a man can't hit with two guns, he isn't going to hit with eight."

Basically the RoF of four Hispano's or six Browning .50s is more than enough to get you hits if your aim is right and the Hispano is much more likely to kill.

[HoHun]

Hi Tony,

>I have FN's booklet on the 13.2mm Browning (no date, but obviously pre-1940) in which they claim 1,050 rpm.

Actually, rate of fire is strictly secondary in the machine gun vs. cannon issue.

The amount of energy released by cannon ammunition is much greater than that of machine gun bullets. This means the cannon win by the weight of the ammunition, not (primarily) by the lower weight of the guns themselves.

Here is a comparison of the ammunition mass alone required for the same total energy:

2x Hispano II - 193 rpg - 95 kg
4x 0.60" MG 151 copy - 281 rpg - 205 kg
6x ,50 Browning M2 - 313 rpg - 207 kg
12x Browning ,303 - 782 rpg - 282 kg

The total Hispano II reference battery  - cannon and ammunition - had a mass of just 195 kg, about the same as the bare ammunition weight of the 0.50" Browning battery. Even if you had a Browning machine gun capable of 5850 rounds per minute to equal the firepower of the dual Hispanos, it would still be heavier than the cannon battery:

2x Hispano II - 193 rpg - 195 kg - 125% firepower - firepower per weight: 244%
1x Wonder Browning - 1880 rpg - 236 kg - 125% firepower - firepower per weight: 202%

Regards,

Henning (HoHun)

[HoHun]

Hi Charge,

>Ok, but I think you need to use PETN figures to get correct energy for Minengeschoss if you use historical belting.

>Exlosive velocities are 8,400 m/s for PETN (pure at dens. 1,7) and 6,900 m/s for TNT. (PETN was not used as such in ammo.)

The problem is, destructiveness and energy are not directly tied in different explosives. The higher blast wave velocity you pointed out will increase damage beyond what you'd expect from the energy comparison alone.

The TNT assumption just serves as a rational and verifyable approximation, it's not perfect of course!

"The guide is always correct, reality is frequently inaccurate" ;-)

Regards,

Henning (HoHun)

[HoHun]

Hi Knegel,

>Better 6 x 12,5 rps than 4 x 10 rps, so around 35 rps more flying toward the target.  

Well, that's a common misconception. You don't just want to hit the enemy, you want to knock him down. To achieve that, you need heavy hits - it probability terms, you want to maximize the product of the rate of fire, the probility of achieving a hit and the probability that the hit kills.

Cannon are considerably superior in Pk, so ROF and Ph can be allowed to drop a bit without sacrificing overall superiority.

>Without to point to the hitprobability in a realy drastical way, people run around and compare the armament performence by comparing the gunpower with 100% hitquote for all guns.

You are confusing rate of fire and hit probability, by the way. I know what you mean, but hit probability is really just the ratio of hits to total shots fired and has nothing to do with rate of fire. For example, a modern air-to-air missile has a great hit probability, but a rather lousy rate of fire :-)

Regards,

Henning (HoHun)

[gripen]

Originally posted by HoHun

Actually, rate of fire is strictly secondary in the machine gun vs. cannon issue.

Hm... the point here is that there was 50% firepower increase available with existing technology and minor modifications to airframes.

gripen

[Knegel]

Originally posted by Karnak
Knegel,

To paraphrase an ace "If a man can't hit with two guns, he isn't going to hit with eight."

Basically the RoF of four Hispano's or six Browning .50s is more than enough to get you hits if your aim is right and the Hispano is much more likely to kill.

This is only true if you have time and the distance to aim well!! While a fightercombat  (not a suprise attack) you barely have this time. While a attack to a bomber you wanna stay as far away as possible.

Specialy while shooting with big deflection more bullets to the target = better hitprobability.
Better bring 3 emenys damaged downward, than 1 exploded, specialy if you 'only' wanna cover your bombers.

Greetings,  Knegel

[Knegel]

Originally posted by HoHun
Hi Knegel,

>Better 6 x 12,5 rps than 4 x 10 rps, so around 35 rps more flying toward the target.  

Well, that's a common misconception. You don't just want to hit the enemy, you want to knock him down. To achieve that, you need heavy hits - it probability terms, you want to maximize the product of the rate of fire, the probility of achieving a hit and the probability that the hit kills.

Cannon are considerably superior in Pk, so ROF and Ph can be allowed to drop a bit without sacrificing overall superiority.

>Without to point to the hitprobability in a realy drastical way, people run around and compare the armament performence by comparing the gunpower with 100% hitquote for all guns.

You are confusing rate of fire and hit probability, by the way. I know what you mean, but hit probability is really just the ratio of hits to total shots fired and has nothing to do with rate of fire. For example, a modern air-to-air missile has a great hit probability, but a rather lousy rate of fire :-)

Regards,

Henning (HoHun)

Hi,

the hitprobability have much to do with rate of fire(of course its not the only aspect)! Not that much while shooting to a strait flying target on close distance or on big targets. But as longer the range to target and as more the target move, as more aiming is a weak point.
Not many pilots was able to aim like marsaille, not many had the skill to get always that close into a perfect attacking position.

Rate of fire = many bullets to target = more possible hits.

How whas the hitquote of a average WWII pilot, around 2% of the amoload??
If we consider this, i would say if almost twice as many bulltes fly to target the hitprobability will get increase a 'bit'.

Of course if we use Marsaille as representative WWII pilots, this dont count that much anymore.


As i wrote before: Cannons make sence on big tough targets.

Shooting with cannons to japanese planes simply wasnt needed, the .50 cal was more than enough.
Same count for german fighters.

Greetings, Knegel

[Karnak]

Knegel,

You are very greatly exagerating the effecvt of rate of fire on landing rounds on the target.

If you are off target with eight .50s you will just miss with a lot of bullets.  If you are on target with eight .50s or two 20mm cannon you will hit in either case.  There is no significant difference in hitting with them.

All of the other combatant nations had no exceptional difficulty hitting fighters with 20mm cannon.

You are creating an issue where there is none.


Long range shooting is just dumb regardless of your armament.  I am not going to say that because George Buerling shot down a Bf109 at 800+ yards with the Hispanos on his Spit that long rang fire was practical.  In all cases you should get as close as you can.

Saburo Sakai certainly didn't feel threatened by USN pilots using their "long range fire" to try to hit him.  He mentally urged them to continue throwing their ammo away.

[HoHun]

Hi Knegel,

>the hitprobability have much to do with rate of fire(of course its not the only aspect)!

Nothing at all. You are confusing terms.

Nf = number of rounds fired
Nh = number of hits
Ph = hit probability

Ph = Nf / Nh

You are talking about Nh, not about Ph.

ROF = rate of fire

Nh = ROF * Ph

Ph only depends on the ballistic capabilities of the gun and the skill of the shooter, not on the rate of fire.

>As i wrote before: Cannons make sence on big tough targets.

You have been wrong before. Cannon are superior against every kind of target.

>Better bring 3 emenys damaged downward, than 1 exploded, specialy if you 'only' wanna cover your bombers.

Scaring doesn't win battles. You need to kill people to win.

If you look at the way the war was actually fought, the USAAF didn't achieve air superiority by merely scaring the Germans. They only managed to reduce the bomber losses when they unleashed the escort fighters to seek out and shoot down the Luftwaffe fighter pilots. With the production rate of the German aircraft industry, aircraft or spare parts hardly mattered.

Regards,

Henning (HoHun)

[gripen]

While Knegel is confusing the terms a bit, there is still point in the rate of fire. With 50% increase in rate of fire you get 50% more hits at same amount of time assuming that all other parameters remain the same.

And there is even point in the probability of the hit, as these are burst type weapons which means that in the case of the uncertainty (range, aiming error, dispersion etc.) there is better probability to get hits with faster rate of fire with one burst (ie larger concentration of the projectiles in the target area).

Besides, that comparison (FN M2 vs American M2) does not rely on questionable rating system of the HEI content of the projectile; in some targets might be easier to destroy with large HEI content while others might be easier with pure hitting power.

gripen

[Tony Williams]

The hit probability question really depends on gun harmonisation.

If the guns are mounted in the nose, or are otherwise harmonised to group tightly at a particular distance, then it doesn't matter what the rate of fire is, if you're off-target all of your shots will miss.

You can only use RoF to increase the hit probability if you spread the aim of your guns to cover a wide area. You then stand a better chance of scoring hits if your aim is bad.

The problem with spreading the aim of the guns is, of course, that you will only achieve a few hits even if your aim is very good; so although you may score hits, you are less likely to shoot down your opponent.

If you're only going to score a few hits, then you're better off with cannon than HMGs, because a cannon hit is more likely to inflict serious damage.

Tony Williams: Military gun and ammunition website and discussion forum

[MANDO]

Looking at the big dispersion of six wing-mounted 50"s, ROF will, certainly, increase the hit %.