Best armed fighter

[Juha]

Hello Kurfürst
Thanks for the document. Yes, I also remembered as You indicated in Your earlier message, that the British test results said that .5 didn't have power to penetrate the back armour of the 109F/G if it had to travel through fuel. But on the other hand bullets which travel over aluminium armour usually penetrate the head armour. And probably those that travel through aluminium armour and over the fuel tank had over 50-50 chance to penetrate the back armour. I tried to balance those fact plus added the very small effect of overtaking speed and gave a bit shorter distance than 200y in my analyze.

And 20mm HEI was still effective and would probably ignitite the fuel tank.

I agree that 109F/G had reasonable pilot protection and one could not built an effective WWII era fighter by making it like a tank, one must try to best compromise between protection and weight.

And P-39 had only .25in armour plate to protect the oil tank behind the engine, so even if the pilot might have been well protected from behind, by the way at least in the later versions he also had armour glass head armour, I cannot say was that German or Soviet innovation, the plane wasn't very well protected against attack behind. I have not time to check the protection afforded by US fighters so I don't have opinion on 109's protection vs other fighters.

Juha

 

[Glider]

Wtf it's not like the average fighter had more or better pilot armor. Likewise Spitfire or Mustang pilot armor will have a hard time stopping a 20mm shell so what's your point. Oh right, make axis aircraft look bad by pointing out flaws that are non.

Lummy you are touchy. Can I ask if you would feel comfortable about being in a seat with a 30% chance of being drilled?
Did I say that a Spit or a P51 or any other aircraft was better protected, or would stand a better chance? I don't think so.

I certainly get the feeling that some people have the opinion that I am almost a rabid anti German poster but this is simply not true. Look at the postings I have made on the technology thread, or any thread about which is the best fighter in the early war period where I have always gone for the 109. Or any thread that the German Type XXI submarine has been mentioned.

In this thread there are some things that I don't understand and when I have asked questions have not been answered. Basically they are:-

1) I do not believe that the Mk108 was a good long ranged weapon. Soren has said it was and he has the pilot reports to prove it. I am happy to change my views; all I have asked is where I can read these reports. His posting showed a drop of 31meters at 1000 meters and in my book that isn't good. Henning's posting showed the effectiveness falling off a cliff after 500m which tends to support my view. Unfortunately Soren has not given me any clue as to where those reports are, he has just gone silent on that point.
2) I happen to believe that 4 x 20mm Mk V guns in the nose is a better set up than the Ta152. This is seen as sacrilege but you have 4 guns which are concentrated in the nose capable of long range fire with an excellent rate of fire. I concede (and always have) that the Ta152 may have more raw firepower and the guns are concentrated. However the sights on the Ta152 will be set up as a compromise meaning that you will not get the best out of each weapon as the ballistics are so different. On the Meteor the sight will be set up for the one gun and the fire more concentrated. I am not insisting that I am right or that everyone should agree with me, but it is a valid case.
3) The power ratings for each weapon I don't understand. I have asked how they were calculated and was put on an ignore list. It was a reasonable question. Tony Williams who is an expert in these matters has a different set of figures and the normal measure in the real world is K Joules or ft pounds. I have never seen the measure that Henning uses.
I do know something about ballistics have done target shooting for a number of years as well as taking coaching / instruction courses and until three years ago was an instructor which isn't that common in the UK outside the armed forces. The one thing I have learnt over the years is that i don't know everything and have concentrated on small arms, but I do know enough to feel that I can ask a question if i see something new.
Again I must emphasise that I am not saying that Henning is wrong, but I do get a little worried that when I ask for an explanation, I get put on an ignore list.

 

[Soren]

Don't feel bad about Hennings ignore list Glider, he is very quick to place you there, heck I'm on it too

As for the reports, I'll dig'em up for you. I remember reading about LW pilots lopping 30mm shells at the bombers from over 1,000m away, with good results. And when you think about it then it's really quite logical, you simply aim at what would be 31m above the target at 1,000m. And the 30mm shell, being as stable as it is, will hit very closely within the horizontal aimpoint at 1,000m.

 

[kool kitty89]

A comment on the armor issue. In the P-39's case, from what I've read the armored glass head armor was a Russian modification, with standard US aircraft either having armor plate, or no head armor.

I also beleive the Bf 109's fitted with the "Galland Hood" used armored glass in leu of plate to better take advantage of the increased rear visibility.


Henning,

Hi Koolkitty,

>I agree that the US fighters' armaments were adequate for pretty much all they were used for [...]

"Adequate" - I have often seen this term used in discussions of US WW2 air-to-air weapons, usually to veil the fact that they were outdated and overweight. Sure, the US won the air war anyway, but that doesn't tell us much about the quality of their guns. The RAF won the Battle of Britain with 7.7 mm machine guns ... despite rifle calibre guns being obviously inadequate weaponry.

What I meant is that, for the most part, the armament they had were "good engough" for most of the missions they flew. Was it the bess posseble given the characteristics of the aircraft it was used in? No, it wasn't, but I wouldn't consider it "inadequate" either.
.303's aganst Medium bombers in the BoB, yeah, aganst fighters in the BoB possibly, but in the latter case I think they were "OK" for the job.

>I do feel that they would have been more successful with a heavier cannon armament.

If you had suggested to a 1944 Mustang pilot that you could increase his firepower by 50%, give him a centreline battery like the one that made the P-38 such a great firing platform, and get rid of more than 500 lbs of dead weight in his aircraft, it's hard to imagine he'd have declined because his armament was already "adequate". I think it's rather more likely that he'd have enthusiastically accepted your offer, and named his first-born son after you.

Certainly he'd take the greater firepower, that;s like saying a pilot would refuse to have his Mustang's engine replaced with a V-1650-9 had it been available.
Also there were other things about the P-38 that made it a good gun platform, the nose open for armament without prop or engine in the way, the large size and weight to better absorb recoil, the couterrotating props eliminating torq.
In this same vein, mounting a hispano on the centerline of the P-51 would have been impossible without modification to the gun to allow synchronization (ie electric priming or an independent firing pin) or modification to the engine design to allow an engine mounted gun.

Mounting 4x .50 in the nose should be possible -early models had 2x in the lower fuselage and 2x more should be possible above the engine, but as I've mentioned before the M2 BMG didn't synchronize very well, the RoF dropping by about 1/3, though given the advantages of a centerling installation this would still be greatly advantageous over wing mounting even 6x guns, not to mention the improvements in roll-rat that should be accompanied.
For some reason, even though the A-36 which had the lower fuselage .50's standard (along with 4x in the wings) the nose guns were often removed in the field. This seems strange, as I should think the extra firepower would be appreaciated.

The benefits I describe are just what designing the P-51D for a Focke-Wulf-style battery of two wing root cannon would have done for him:

6x ,50 Browning M2 - 400 rpg - 438 kg - 1,7 MW firepower
2x MG 151/20 - 250 rpg - 191 kg - 2,5 MW firepower

That is what technology can do for you ... of course you can win a war with inferior guns, but it will cost you.

Regards,

Henning (HoHun)

I pretty much agree, though given the continuing problems with US production of the Hispano and lack of a back-up they didn't realy have an alternative. (though at least they already had a decent aircraft HMG in wide used, unlike the RAF, had the Hispano been a failure for them they'd have been in bigger trouble)

 

[Juha]

Hello KK
at least some P-39s seemed to have armour glass head armour installed already at factory, but the idea might well have been orginated from Soviets.

Juha

 

[HoHun]

Hi Koolkitty,

>Henning,

Hm, could you use a different quotation style please? As the forum engine excludes quoted content from the answer's quote, I get almost none of your text into the editor field. I have to go back and copy it manually via the clipboard, and as you don't have used any signal characters such as ">" at the beginning of a line, this still leaves me confused about which bits were written by whom, so I have to go back and copy your text paragraph by paragaph. (And all-bold paragraphs are ugly to the eye, too.)

>What I meant is that, for the most part, the armament they had were "good engough" for most of the missions they flew.

Being 500 lbs overweight because the 12.7 mm Browning and its ammunition is twice as heavy as a contemporary 20 mm cannon has a negative impact on your aircraft's performance and thus on your operational success.

500 lbs is about the weight of the Gustav's gondola weapons, which in popular perception turned a nimble fighter into an iron dog. The same amount of weight doesn't suddenly become irrelevant if it's added to an aircraft marked with a star instead of a cross.

>Also there were other things about the P-38 that made it a good gun platform, the nose open for armament without prop or engine in the way, the large size and weight to better absorb recoil, the couterrotating props eliminating torq.

The reduction of firepower of a synchronized MG 151/20 was just around 5 % with electrical synchronization. As I have pointed out above, the benefit of centreline fire was worth a multiple of that due to the better hit ratio. The Focke-Wulf with its wing root cannon was a great firing platform without needing the size and weight of the P-38, and the counterrotating propellers were noted to induce yaw after each power change because the engines did not reach exactly the same power settings in practice, requiring re-trimming by the pilot every time. Not to say the P-38 wasn't a great firing platform ... but the primary reason was just that it offered centreline fire.

>In this same vein, mounting a hispano on the centerline of the P-51 would have been impossible without modification to the gun to allow synchronization (ie electric priming or an independent firing pin) or modification to the engine design to allow an engine mounted gun.

Certainly - I don't say that it was a realistic suggestion in 1944 to equip the P-51D with two wingroot 20 mm cannon. I have just highlighted the advantages to show that the 12.7 mm machine gun armament was overweight, far behind the state of the art, and detrimental to the flight performance of the USAAF fighters.

It's obvious that the USAAF won the air war over Germany, but it's similarly obvious that the USAAF did so with rather poor barrel weaponry. I'm sure you'll have no problem to get the former acknowledged by everyone here on this forum, but pointing out the latter is guaranteed to touch off a frenzy of spin-doctoring ...

Regards,

Henning (HoHun)

 

[drgondog]

Hello Kurfürst
Thanks for the document. Yes, I also remembered as You indicated in Your earlier message, that the British test results said that .5 didn't have power to penetrate the back armour of the 109F/G if it had to travel through fuel. But on the other hand bullets which travel over aluminium armour usually penetrate the head armour. And probably those that travel through aluminium armour and over the fuel tank had over 50-50 chance to penetrate the back armour. I tried to balance those fact plus added the very small effect of overtaking speed and gave a bit shorter distance than 200y in my analyze.

And 20mm HEI was still effective and would probably ignitite the fuel tank.

I agree that 109F/G had reasonable pilot protection and one could not built an effective WWII era fighter by making it like a tank, one must try to best compromise between protection and weight.

And P-39 had only .25in armour plate to protect the oil tank behind the engine, so even if the pilot might have been well protected from behind, by the way at least in the later versions he also had armour glass head armour, I cannot say was that German or Soviet innovation, the plane wasn't very well protected against attack behind. I have not time to check the protection afforded by US fighters so I don't have opinion on 109's protection vs other fighters.

Juha

Juha - I have to dig but the 109 definitely had better protection aft than either the 51, 47 or 38. IIRC each of the US Fighters had .25 to .40 inch thick armor on seat back. Mustang definitely had zero armor behind the fuselage fuel tank.

 

[drgondog]

Lummy you are touchy. Can I ask if you would feel comfortable about being in a seat with a 30% chance of being drilled?
Did I say that a Spit or a P51 or any other aircraft was better protected, or would stand a better chance? I don't think so.

I certainly get the feeling that some people have the opinion that I am almost a rabid anti German poster but this is simply not true. Look at the postings I have made on the technology thread, or any thread about which is the best fighter in the early war period where I have always gone for the 109. Or any thread that the German Type XXI submarine has been mentioned.

In this thread there are some things that I don't understand and when I have asked questions have not been answered. Basically they are:-

1) I do not believe that the Mk108 was a good long ranged weapon. Soren has said it was and he has the pilot reports to prove it. I am happy to change my views; all I have asked is where I can read these reports. His posting showed a drop of 31meters at 1000 meters and in my book that isn't good. Henning's posting showed the effectiveness falling off a cliff after 500m which tends to support my view. Unfortunately Soren has not given me any clue as to where those reports are, he has just gone silent on that point.
2) I happen to believe that 4 x 20mm Mk V guns in the nose is a better set up than the Ta152. This is seen as sacrilege but you have 4 guns which are concentrated in the nose capable of long range fire with an excellent rate of fire. I concede (and always have) that the Ta152 may have more raw firepower and the guns are concentrated. However the sights on the Ta152 will be set up as a compromise meaning that you will not get the best out of each weapon as the ballistics are so different. On the Meteor the sight will be set up for the one gun and the fire more concentrated. I am not insisting that I am right or that everyone should agree with me, but it is a valid case.
3) The power ratings for each weapon I don't understand. I have asked how they were calculated and was put on an ignore list. It was a reasonable question. Tony Williams who is an expert in these matters has a different set of figures and the normal measure in the real world is K Joules or ft pounds. I have never seen the measure that Henning uses.
I do know something about ballistics have done target shooting for a number of years as well as taking coaching / instruction courses and until three years ago was an instructor which isn't that common in the UK outside the armed forces. The one thing I have learnt over the years is that i don't know everything and have concentrated on small arms, but I do know enough to feel that I can ask a question if i see something new.
Again I must emphasise that I am not saying that Henning is wrong, but I do get a little worried that when I ask for an explanation, I get put on an ignore list.

Very articulate summary Glider. Great post.

 

[renrich]

Hmmmmmm, Re. " the 12.7 Browning and it's ammunition is twice as heavy as a contemporary 20 mm cannon," my source on US AC guns for WW2 has the 50 cal gun weighing 70 pounds and 54 inches long. Weight of belted ammo is .30-.311 pounds per round depending on AP or tracer. The 20 mm weighs 129 pounds and is 78 inches long. The belted ammo ranges from .54-.616-.766 pounds depending on explosive or tracer. Consequently, six fifties would weigh 420 pounds and four 20mms would weigh 516 pounds plus the additional weight for ammo. Perhaps some 20 mms were available outside the US which were lighter. The 20 mm in the A6M weighed 82.83 pounds(still more than the 50cal) but had a lower rate of fire and much lower MV than the US 20mm. The F4F3 mounted four 50 cals with around 400 rds per gun which was plenty as far as Navy pilots were concerned. The F4F4 only went to six guns with reduced rds per gun because the British insisted on it. Late F4F4s , as well as the FM2s went back to 4- 50s which was plenty adequate against Japanese AC and the occasional FW Kondor or JU88. Of course the above info which seems to contradict some other posts probably won't count as I am on the ignore list.

 

[drgondog]

>What I meant is that, for the most part, the armament they had were "good engough" for most of the missions they flew.

Being 500 lbs overweight because the 12.7 mm Browning and its ammunition is twice as heavy as a contemporary 20 mm cannon has a negative impact on your aircraft's performance and thus on your operational success.

20mm (US) = 3lbs/5 rounds with links, 75 pounds per 125 rounds per gun, 100 pounds per 20mm gun on Mustang. Basic armament including ammo for a 4x20mm installation in P-51A was 700 total pounds.

50 cal = 1lbs/3 rounds with links, 1260 rounds for 4x .50 cal = 420 pounds for ammo, 280 pounds for 4 guns = 700 total pounds for P-51B/C.

1880 rounds plus 6x 50 for the D/K = 627 lbs for ammo plus 420 pounds for the guns = 1047 total pounds for the 51D/K and just a little less for the H.

For this comparison the P-51D weighed 347 pounds more than the P-51A



500 lbs is about the weight of the Gustav's gondola weapons, which in popular perception turned a nimble fighter into an iron dog. The same amount of weight doesn't suddenly become irrelevant if it's added to an aircraft marked with a star instead of a cross.

Nobody is arguing that 50 caliber is better than 20mm, but your thesis that the .50 weighed more than 20mm seems silly. The question posed should be "given the multi role mission of the Mustang (for example), is 6x 50's plus 1880 rounds of API a better choice than 4 x20mm plus 500 rounds for the mission (destroying fighters and strafing) and reduce climb performance and range as a consequence? The gentlemen behind those design decisions in the US made the choice and stuck with it. They also did not have the 151/20 and ammunition as a choice.

Certainly - I don't say that it was a realistic suggestion in 1944 to equip the P-51D with two wingroot 20 mm cannon. I have just highlighted the advantages to show that the 12.7 mm machine gun armament was overweight, far behind the state of the art, and detrimental to the flight performance of the USAAF fighters.

The four gun P-51B/C did very well with the extra 700 rounds of 50 caliber ammo in comparison to the P-51A with four 20's - of couse the engine and the extra range made it possible to engage in a superior flight envelope.

It's obvious that the USAAF won the air war over Germany, but it's similarly obvious that the USAAF did so with rather poor barrel weaponry. I'm sure you'll have no problem to get the former acknowledged by everyone here on this forum, but pointing out the latter is guaranteed to touch off a frenzy of spin-doctoring ...

Seems like everyone agrees 20mm is better than .50 caliber on a per hit basis - so no detectable spin doctoring or frenzy seems to arise?

Regards,

Henning (HoHun)

I have talked to quite a few German pilots who absolutely agree that things probably would have been worse had the Mustang and Thunderbolt been equipped with 20mm versus .50 cal. None of them expressed joy that they were 'only' confronted with .50 caliber.

A lot of ammo of .50 caliber seems to have worked in the context of taking out many multiple scores of 3 and above per sortie versus the LW so it wasn't the detrimental condition you suggest...

 

[claidemore]

One important factor being overlooked is firing time.
For example:
P51A, with 4x20mm has firing time of 12.5 seconds.
P51B/C- 4x.50 has firing time of 23/24 seconds.

Given the low hit probability of -10 % in WWII, on a long range mission over enemy territory, double the firing time is a good thing.

The Spitfire Mk XVI and Mk XIVE with 2x20mm and 2x.50 were highly rated by the pilots who used them, particularly against ground targets. Firing times of 20 seconds for the .50s and 13 seconds for the 20mm. An excellent compromise of extended firing time and long range capability (.50s) with destructive power (20mm Hispano).

 

[HoHun]

Hi Claidemore,

>One important factor being overlooked is firing time.

I don't think it has been overlooked - remember the "muzzle loader effect"?

Firing time is meaningless by itself - the question is how much damage you can do with the ammunition supply you carry.

Though I have already addressed it once, it seems I have to repeat it here: Cannon armament does not translate into a smaller ammunition supply.

This erroneous conclusion is based on the comparison of firing times, which of course is inaccurate - 20 shot are 20 shot, and if you're firing them from a muzzle loader, you don't have any advantage over a guy who's firing them from an assault rifle just because it takes you longer to do so.

Everything else the same, long firing time (or "ammo duration", as it's sometimes put) simply equates to "poor firepower", as illustrated by the muzzle loader example.

Here is a comparison of the mass efficiency of various rounds, showing mass of the complete cartridge (including belting) in relation to the total muzzle energy (kinetic plus chemical, typical mix):

MK 108 (30x90RB): 860 kJ/kg
MK 103 (30x184B): 634 kJ/kg
MG 151/20 (MX) (20x82): 547 kJ/kg
MG 151/20 (20x82): 494 kJ/kg
Hispano II (20x110): 432 kJ/kg
MG-FF (20x80RB): 288 kJ/kg
MG 151 (15x96): 201 kJ/kg
,50 Browning M2 (12,7x99): 198 kJ/kg
MG 131 (13x64B): 180 kJ/kg
MG 17 (7,92x57): 147 kJ/kg
Browning ,303 (7,7x56R): 146 kJ/kg

So the Hispano ammunition is more than twice as effective per unit of weight than the 12.7 mm Browning ammunition, and the MG 151/20 ammunition about 2.5 times as effective.

The MG FF looks a bit inefficient in this comparison due to the inclusion of the weight of the drums, which means that it is not entirely comparable since belt-fed guns required ammunition boxes that were not considered in this comparison. However, leaving out the weight of the drums would make the MG FF look artificially good, so that's no solution either.

30 mm cannon further increase their weight efficiency, with the high-velocity MK 103 projectiles being three times as effective per unit of weight than the 12.7 mm Browning, and the MK 108 projectiles even four times as effective.

Regards,

Henning (HoHun)

 

[lesofprimus]

Good stuff here fellas...

 

[Glider]

Hi Claidemore,

>One important factor being overlooked is firing time.

I don't think it has been overlooked - remember the "muzzle loader effect"?

Firing time is meaningless by itself - the question is how much damage you can do with the ammunition supply you carry.

Though I have already addressed it once, it seems I have to repeat it here: Cannon armament does not translate into a smaller ammunition supply.

This erroneous conclusion is based on the comparison of firing times, which of course is inaccurate - 20 shot are 20 shot, and if you're firing them from a muzzle loader, you don't have any advantage over a guy who's firing them from an assault rifle just because it takes you longer to do so.

Everything else the same, long firing time (or "ammo duration", as it's sometimes put) simply equates to "poor firepower", as illustrated by the muzzle loader example.

I must disagree with this assumption. What matters in particular in air combat where you are only likely to have about two seconds to fire, is how much damage you can do in those two seconds. This of course relates to firpower.
What also matters is how long you can keep firing which relates to the amount of ammunition that you carry.
The Whirlwind is a classic example, in its time with 4 x 20mm in the nose it had almost unmatched firepower. However it only had 6 seconds of ammunition.
The Muzzle loader example has very poor firepower but a long duration.

Here is a comparison of the mass efficiency of various rounds, showing mass of the complete cartridge (including belting) in relation to the total muzzle energy (kinetic plus chemical, typical mix):

This is the bit that I feel needs explanation as Muzzle Energy has nothing to do with Chemical Energy. Unless we know how you get from the real Muzzle Energy Figures to these figures you quote which are NOT Muzzle Energy, there must be a question mark.

I invite anyone to do a search and find out the definition of Muzzle Energy.

 

[lesofprimus]

Muzzle energy is the kinetic energy of a bullet as it is expelled from the muzzle of a firearm. It is often used as a rough indication of the destructive potential of a given firearm or load. The heavier the bullet and the faster it moves, the higher its muzzle energy and the more damage it will do.

The general formula for the kinetic energy is:

E = 0.5 • m • v2
In SI units, mass m is in kilograms and velocity v is in metres per second, giving kinetic energy E in joules.

When using a system of units that is not self-consistent, or if the weight of the bullet is used rather than the mass, a conversion factor must be added. For example, to get muzzle energy E in foot-pound force, where

v is the velocity of bullet (in feet per second)
m is the mass of bullet (in grains)
the formula is

E = m • v2 / (2 • 32.1739 • 7000).
Most sporting arms publications within the United States report muzzle energies in foot-pound force, and, when publishing kinetic energy tables for small arms ammunition, use a dimensional constant of 32.163 lbm • ft / lbf • s² rather than the standard acceleration of gravity of 32.1739 ft / s².

The bullet energy, remaining energy, down range energy and impact energy of a projectile may also be calculated using the above equations.

 

[HoHun]

Hi Les,

>Muzzle energy is the kinetic energy of a bullet as it is expelled from the muzzle of a firearm.

Note: as pointed out above, I considered the total muzzle energy (kinetic plus chemical, typical mix). As the point in firing shells is to increase destructive power far beyond what would be possible on kinetic energy alone, it doesn't make sense to limit the consideration to kinetic energy alone.

To compare total muzzle energy is indeed flattering for projectiles that rely mostly on kinetical energy ... here is a comparison of downrange speeds:

Weapon                      v0  v400   v_av   T400
12.7 mm AP M2 (36" Barrel) 867   680  773,5   0,52 <- 12.7 mm Browning M2
20 mm API (from AP M75)    750   555  652,5   0,61 <- 20 mm Hispano II
20 mm mine shell           805   424  614,5   0,65 <- MG 151/20

Speeds in m/s, Time to 400 m in s

In terms of total muzzle energy, this yields (figures are approximates as I don't have full details on each ammunition type):

Weapon                        E0   E400 E400 %
12.7 mm AP M2 (36" Barrel)  21.0   14.7   70 % <- 12.7 mm Browning M2
20 mm API (from AP M75)     94.7   78.1   83 % <- 20 mm Hispano II
20 mm mine shell           142.9  121.3   85 % <- MG 151/20

Energies in kJ, percentage downrange in relation to full energy at the muzzle.

Regards,

Henning (HoHun)

 

[claidemore]

Hi Claidemore,

>One important factor being overlooked is firing time.

I don't think it has been overlooked - remember the "muzzle loader effect"?

Firing time is meaningless by itself - the question is how much damage you can do with the ammunition supply you carry.

Though I have already addressed it once, it seems I have to repeat it here: Cannon armament does not translate into a smaller ammunition supply.

This erroneous conclusion is based on the comparison of firing times, which of course is inaccurate - 20 shot are 20 shot, and if you're firing them from a muzzle loader, you don't have any advantage over a guy who's firing them from an assault rifle just because it takes you longer to do so.

I don't think the comparison of a muzzle loader ( 3 rpm) to an assault rifle (600 rpm?) has any relevance to a comparison of a 600 rpm cannon to a 800 rpm heavy machine gun. Firing time is important for similar rates of fire and the muzzleloader example is misleading.

Remember the 9-5% hit ratio? Double the firing time and you double the number of hits. Plus the shooter has twice as much time to learn from his mistakes and increase his accuracy.

The question is not which round produced more damage, but whether or not a certain round produced 'enough' damage. As drgondog pointed out, the 4x.50s and 6x.50s in the varous Mustang models certainly produced 'enough' damage.

USN pilots bemoaned the change from 4x.50s to 6x.50s because of the reduced firing time. While the 'brass' wanted more destructive capability, the pilots wanted more firing time. Every soldier wants more firing time (no matter what the rate of fire).

Canon armament vs HMG or LMG, given a limited amount of space on a given airframe for storage of ammunition will definately translate into a smaller ammunition supply, (fewer rounds). The E wing Spitfire for example carried 135 x 20mm rounds and 356 x .50 rounds, compared to 120 rds per gun in a twin 20mm 'C' wing. Those 2 x20mm cannons may be more effective or efficient, but there are definately fewer rounds and reduced firing time.

That being said, and at the risk of ambivalence, I believe that the 4 x 20mm armament is a better choice than the 6 or 8 x.50s.

 

[Glider]

The definition suppplied by Les is of course correct and its normal in millitary applications to multiply this by the rate of fire for a second and arrive at a figure per second.

This is a rough and ready figure as Henning would agree, as the explosive content should be catered for in some way but there is no agreed standard for this. I do not pretend to have the best solution.
Tony Williams on his site explains how he caters for such additional energy and if you wish to disagree with him then he has explained how his figures work on which you can base a case. Full marks to him
Re Hennings figures the $24000 question is how does he calculate the Chemical Energy and build it into his figures?

Tony is an expert who has devoted a lot of time and effort on this topic and unless there is an explanation as to how Henning calculates his numbers then people may want to consider both solutions as the differences in some cases are quite significant.

To use the often quoted
1 x 20mm Mk151 and 2 x 13mm HMG Tony gives a factor of 288
6 x 0.5 HMG Tony gives a factor of 360

 

[Kurfürst]

Energy content of different kind of explosives can be relatively easily found in specific books.

As for Tony's calculation of projectile 'power', it is a simple approach and Tony readily admits it may not be perfect one but rather an educated guess if I recall his explanation in his article correctly. It needs to be understood that it is a very complex subject with an insane amount of variables, especially with regards what structure the projectile hits.

The most severe flaw of Tony's calculation of KE and CE total of the projectile is that it derieves CE from existing KE - but there's simply no corellation between the two! To use a simple example, how much greater is the explosion from a hand granade if I throw it away than if I hold it in my hand?

In Tony's way calculation, the hand granade would be more destructive the faster I throw it (but we all know that if I throw at and hit someone with a hand granade, 99% of the damage he will get will be not from being hit with a relatively heavy object, fast moving object - KE -, but the fact it blows up, tearing his head off!). OTOH, in Tony's calculation I can safely hold a hand granade in my hand until it blows up, it will do zero damage (at least in this theory) because, well, its KE is also zero..!

 

[HoHun]

Hi Claidemore,

>Remember the 9-5% hit ratio? Double the firing time and you double the number of hits.

Hm, you implicitely assume that when you double the firing time, the number of firing opportunities obligingly doubles itself, too. This is not a given, and actually the reason why firepower is important at all.

Ask yourself why the USAAF fighters carried six to eight guns instead of just one or two ... here are two batteries of equal weight:

8x ,50 Browning M2 - 390 rpg, 30 s duration - 575 kg - 2,3 MW firepower
1x ,50 Browning M2 - 4965 rpg, 382 s duration - 575 kg - 0,3 MW firepower

So why is the first battery better suited for air-to-air combat then the second battery, which has more than 12 times the firing duration?

>The question is not which round produced more damage, but whether or not a certain round produced 'enough' damage. As drgondog pointed out, the 4x.50s and 6x.50s in the varous Mustang models certainly produced 'enough' damage.

Firepower is a continuous value, and more is better. I have not seen any historical report on WW2 firepower that uses the term "enough", and to be honest, it sounds just like the kind of "peacock term" that one would use to gloss over inconvenient facts. See also: Wikipedia:Avoid peacock terms - Wikipedia, the free encyclopedia

>USN pilots bemoaned the change from 4x.50s to 6x.50s because of the reduced firing time.

Hm, you must be thinking of the armament upgrade from the F4F-3 to the F4F-4 which was discussed in detail in another thread on this forum. I'm sure that if it hadn't resulted in an considerable weight increase of the F4F-4, only part of which was owed to the increased armament, it would have been received much better. In fact, this example highlights the importance of weight as a factor - and the problem with the 12.7 mm machine gun batteries, regardless of the number of barrels that were actually used, was that they were much heavier than the contemporary state-of-the-art.

>Canon armament vs HMG or LMG, given a limited amount of space on a given airframe for storage of ammunition will definately translate into a smaller ammunition supply, (fewer rounds).

Do you have actual figures on the volume per round for cannon versus heavy machine-gun rounds? I might be able to provide some figures for German ammunition ...

With regard to weight, there is no question that cannon ammunition is a great deal more efficient than machine gun ammunition. Here is a comparison of the mass efficiency of various rounds, showing mass of the complete cartridge (including belting) in relation to the total muzzle energy (kinetic plus chemical, typical mix):

MK 108 (30x90RB): 860 kJ/kg
MK 103 (30x184B): 634 kJ/kg
MG 151/20 (MX) (20x82): 547 kJ/kg
MG 151/20 (20x82): 494 kJ/kg
Hispano II (20x110): 432 kJ/kg
MG-FF (20x80RB): 288 kJ/kg
MG 151 (15x96): 201 kJ/kg
,50 Browning M2 (12,7x99): 198 kJ/kg
MG 131 (13x64B): 180 kJ/kg
MG 17 (7,92x57): 147 kJ/kg
Browning ,303 (7,7x56R): 146 kJ/kg

This energy efficiency has direct bearing on your above statement on the 9-5 % hit ratio: You can calculate the energy of the ammunition supply of a certain fighter, then multiply it by your assumed hit ratio - and you have the amount of destructive energy applied to the target if all ammunition is used up.

Note that firing duration, rate of fire, firepower etc. do not even enter this equation.

Here some examples:

8x ,50 Browning M2 - 390 rpg, 30 s duration - 343 kg ammunition, 67,9 MJ total
1x ,50 Browning M2 - 4965 rpg, 382 s duration - 546 kg ammunition, 108 MJ total
2x MG 151/20 - 250 rpg, 21 s duration - 107 kg ammunition, 52,9 MJ total
2x MG 131 - 475 rpg, 32 s duration - 74 kg ammunition, 13,3 MJ total

You can see that the ammunition supply for the P-47D is good for 67,9 MJ total energy, with 9-5 % of that being brought to bear upon the target if all of it is fired off during a mission.

The Fw 190D-9 has a total ammunition supply of 66,2 MJ total energy, with the same 9-5 % being brought to bear if all is fired off.

(Note that the Thunderbolt's ammunition weighs 343 kg while the equivalent Focke-Wulf ammunition weighs only 181 kg.)

The firepower comparison is telling:

Fw 190D-9: 3,0 MW
P-47D: 2,3 MW

Same amount of ammunition, the P-47 has lower firepower and thus the longer firing duration. The "muzzle loader effect" is in fact evident here, but of course with realistic rates of fire it is not as dramatic as in my musket-vs.-assault-gun example, which was just meant to demonstrate the principle.

>That being said, and at the risk of ambivalence, I believe that the 4 x 20mm armament is a better choice than the 6 or 8 x.50s.

Quite clearly, and by a considerable factor:

Tempest: 4,9 MW
Typhoon: 4,2 MW
P-47D: 2,3 MW
P-51D: 1,7 MW
P-51C: 1,1 MW

I don't expect anyone will contradict that part of your assessment

Regards,

Henning (HoHun)