Best armed fighter

[Juha]

Kurfürst
IMHO Your hand grenade metaphor isn't very good because we are talking on guns. IMHO nearest to a shell with zero kinetic energy is one which exploded in a gun chamber or in its ammo tray and its effect to enemy is nil. And how you value Japanese Ho-301 40 mm cannon with high rate of fire but with very low MV? MV has its role when we valued a/c armaments.

Juha

 

[Juha]

HoHun
IIRC the reduction of firing time with F4F-4 introduction to service was a major complain among USN pilots according to Lundstrom's excellent "The First Team". Pilots saw 4*.5 HMG as adequate armament against Japanese a/c and saw also that after you had run out ammo your chances to help the defence of your flat-top or your charges was minimal. And without flat-top... Simple as that.

Juha

 

[Burmese Bandit]

Summary of debate: .50 caliber very good, 20 mm world beater, mustang with 2 20 mm and 2 .50 caliber would have won the war by Christmas 1944...

(exaggerated - don't take me literally! - but you get my drift...)

 

[HoHun]

Hi Juha,

>IMHO Your hand grenade metaphor isn't very good because we are talking on guns.

It was a deliberately extreme example to highlight the shortcomings of Tony's approach.

With regard to guns, you'll see that in Tony's table the 30 mm shell of the MK 103 has almost twice the power of the same shell when fired from the MK 108. If it would be - for example on a firing range - be placed in a dummy target fuselage and detonated there, Tony's formula would give it zero power since the shell is at rest.

Here is the comparison:

Cartridge   V0   Weight  % HE    Power   Energy
30x184B    860      330    25       99      583
30x90RB    505      330    25       58      503
30 v=0       0      330    25        0      461

v0 [m/s], Weight [g], Power "Tony Index", Energy [kJ]

You can see that even at rest, the 30 mm shell has a very high energy content (82.5 g explosives going off ...), and that the energy gain the round has from being fired at a high muzzle velocity is nowhere near the twofold increase you'd assume from Tony's power figure.

Regards,

Henning (HoHun)

 

[Juha]

Hello HoHun
with all respects, Tony is comparing guns not shells. How you hit anything with with MV 0 m/s? What is the effect of a miss?

What is your opinion on Ho-301? How effective it was according to Your formula?

Juha

 

[HoHun]

Hi Juha,

>with all respects, Tony is comparing guns not shells.

Hm, check out his site:

WORLD WAR 2 FIGHTER GUN EFFECTIVENESS

See TABLE 1: CARTRIDGE DESTRUCTIVENESS ... Tony is comparing shells (and other projectiles) in preparation for the next step, comparison of guns in TABLE 2: GUN POWER AND EFFICIENCY.

Note that gun power is simply a multiplication of rate of fire and cartridge power in Tony's table - the power of the cartridge directly determines the power of the gun.

>How you hit anything with with MV 0 m/s?

The point about the "0 m/s" 30 mm mine shell is that it is still highly destructive, while Tony's formula gives it a power of zero. This proves that Tony's formula gives a nonsense answer when estimating the power of explosives as a charge of 82.5 g going off in a single or twin-engined aircraft will usually destroy it. (Luftfahrt International 7 shows pictures of the effect of 60 to 100 g charges gone off inside aircraft wings and fuselages ...)

>What is your opinion on Ho-301? How effective it was according to Your formula?

The fourth table on Tony's page shows that my calculation for the effectiveness of the Ho-301 yields an increase by a factor of 2.36 as his formula tends to underestimate the effect of slow explosive shells.

In absolute terms, the Ho-301 shell compares unfavourably to the MK 108 as it only contains 50.9 g explosives to the MK 108's 82.5 g, and the rate of fire is lower too.

MK 108 - 5,0 MW firepower
Ho-301 - 2,3 MW firepower

Additionally, the weight of the Ho-301 and its ammunition is much higher, though I don't have exact figures including belting. Accordingly, the MK 108 is a much better weapon than the Ho-301.

Regards,

Henning (HoHun)

 

[Kurfürst]

IMHO Your hand grenade metaphor isn't very good because we are talking on guns. IMHO nearest to a shell with zero kinetic energy is one which exploded in a gun chamber or in its ammo tray and its effect to enemy is nil.

It is very hard to misunderstand why I brought up this example...
But here's the moral of it: kinetic energy does not factor into the chemical energy of the shell (the first is decreasing, and at typical combat distance its about 1/2 than what was it at the muzzle, the latter is constant regardless of range)

And how you value Japanese Ho-301 40 mm cannon with high rate of fire but with very low MV? MV has its role when we valued a/c armaments.

Juha

IMHO hit probability should be factored in into the total level of potential destruction done to the target, which you can break down to two components, time to target (better with high Mv) and dispersion/concentration of firepower (usually worse with high Mv and wing armaments).

Several models should be used, ie. a large bomber sized target travelling straight and level, and a fighter sized target doing maximum sustained/and maximum-g turn at a common firing distance of ca 200m. The calculated chance of hit for these different targets can be used as a multiplier for the total destructive potential of projectiles, and this can be expressed in various terms - no. of projectiles need to be expanded, time of steady fire solution required. This is pretty much that German reports approach the subject. But this is an increadibly complex and challanging simulation - it may be too tempting to HoHun as matter of fact, and he may actually go as far as doing it! 8)

I don't consider Tony's approach scientific, or accurate. Its however a good educated guess based on an unscientific rule of thumb method, and it gives results that match real world observations in most cases; however, the method quite clearly understates the effect of HE shells.

And like I said, there's also an immense number of factors with regarding well the shell may hit. AP hitting the wingtip will just pass harmlessly through, but AP or HE fragment hitting the pilot brings down the plane with a single round.

 

[Timppa]

.
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.
.

I agree. IMO the projectile power topic is one of those where it is is impossible to find the 'right' answer. While Tonys approach is simplistic (and incorrect when v=0) it gives results quite close to real world observations at realistic impact speeds.

HoHuns approach is also simple and logical, and stresses the explosive effect.

But even the Luftwaffe did not try to maximise the explosive effect in their ammunition belting, otherwise they would have used only, or mostly mine grenades. According the 'Schiessfibel' only one third of MG151 ammo was Mine, other were incendiary or AP rounds with no explosive effect whatsoever. This was against the hardest targets, 4 engined bombers (against other aircraft it was 3 mines out of 5). MK108 mix was half Mine and half incendiary (the latter also without explosives).

 

[renrich]

Ammo load can be a major factor in a battle. An example is in an article recently published, I think, by a Japanese studying the Midway Battle. The A6M carried only 60 rounds per gun for the 2-20mms in the wings. The two rifle caliber Mgs in the nose carried a lot of ammo but were not terribly effective against the US AC. During the period between the recovery of the Japanese first strike against Midway and the rearming of a strike to be launched against the US CVs, the attacks against the IJN CVs by land and carrier based air kept the IJN fight decks tied up in recovering, rearming and relaunching the A6Ms in the CAP that were running short of cannon rounds. Consequently, the strike force meant for the US CVs had to be kept below on the hangar deck until the flight deck was clear. It took about an hour to get a full strike up to the flight deck and launched, partly because the engines could not be started and warmed up on the hangar deck of IJN CVs. My guess is that the IJN pilots and admirals would have traded those two 20 mms in the wings for a pair of 50 BMGs with several hundred rds of ammo each during that battle.

 

[HoHun]

Hi Timppa,

>While Tonys approach is simplistic (and incorrect when v=0) it gives results quite close to real world observations at realistic impact speeds.

Hm, I don't think he has validated his rule of thumb. If we consider it realistic in the middle of the velocity band, which I think is a reasonable assumption, his table 4 shows that in fact the most serious differences between rule of thumb and energy approach are for guns that fall out of the middle of the speed band, such as the Ho-301 and the MK 108. For other guns, the high-explosive rounds get under-valued by Tony's formula while the armour-piercing rounds get overrated, so that in the mix the differences more or less even out - which maybe helps to justify the rule of thumb.

>HoHuns approach is also simple and logical, and stresses the explosive effect.

In fact, my approach treats all kinds of energy equal and does not particularly stress the explosive effect. If you meant to stress to contrast to Tony's formula which neglects the explosive effect a bit, then I'd of course agree

>According the 'Schiessfibel' only one third of MG151 ammo was Mine, other were incendiary or AP rounds with no explosive effect whatsoever. This was against the hardest targets, 4 engined bombers (against other aircraft it was 3 mines out of 5). MK108 mix was half Mine and half incendiary (the latter also without explosives).

That's right. I did in fact base my analysis on Tony's data because he's an accepted source, knowing well that there are detail differences to other sources I have - partially because the ammunition often came in different variants. If I'd use my source data, some German weapons would look better, others would look worse than with Tony's data. (It's not limited to German guns - as Tony only gave data on the API for the 12.7 mm M2 Browning, which historically was the most effective ammunition, I have based my estimate on a pure API belting. The Hispano II was historically used with a share of ball ammunition untill 1942, but I'm basing my calculation on the more effective HE and AP projectiles Tony provided the data for.)

The 1:3 mine shell mix against bombers against the 3:5 mine shell mix against all other aircraft is consistent with the trials published in Luftfahrt International 7 - in fact, I've been long trying to dispel the myth that mine shells were designed as anti-bomber ammunition only.

If you have data on the Brandgranate for the MK 108, I could re-estimate the firepower for that gun. I have one data sheet suggesting 140 g chemical content and 500 m/s muzzle velocity, but unfortunately it does not give the projectile weight which would be necessary to establish the kinetic energy.

Regards,

Henning (HoHun)

 

[Juha]

Hello Kurfürst
thanks for your comments, it seems that we agree in the subject matter even if we might sometimes disagree on methods of how to present some points.
Yes the question is very complex one and I also see Tony's method more as a rule of thumb which correlates reality best in the middle ground as rules of thumb tended to do.

Hello HoHun
my point is that you need first to hit. And that explained why after arming Ki-44-II Otsu with two 40mm Ho-301s changed the wing armament of the next model (Ki-44-II Hei) to two .5 HMGs and even modified in field some Otsus to Hei armament configuration. Ho-301 simply had too low MV for an effective fighter armament even if its ROV of 450rpm was very high for 40mm weapon and it was an interesting try. Of course only hitting isn't enough, the hit must also be effective.

Juha

 

[HoHun]

Hi Juha,

>my point is that you need first to hit.

In actual combat no doubt, but a formula for shell effectivess should be expected to work for tests on the proving ground too where the hit is assured by other means

>Ho-301 simply had too low MV for an effective fighter armament even if its ROV of 450rpm was very high for 40mm weapon and it was an interesting try.

I haven't seen any trajectory data, but the extremely low muzzle velocity suggests that the shells travelled on a rather steeply dropping curve.

To use such a gun successfully (which to make matters worse had only a small ammunition supply), it would probably have been necessary to close to the very short ranges of the Luftwaffe "Rammjäger". However, I don't think the Ki-44 was adequately armoured for that, as short-range defensive fire is rather deadly, especially if the fighter has not much of a speed margin over the bomber - which probably applies to the Ki-44 vs. B-29 situation.

Regards,

Henning (HoHun)

 

[drgondog]

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?

K- while I tend to generally agree this point relative to the velocities we are discussing, Tony is absolutely correct as the velocities increase. The fundamental question is how does the energy of the system translate to force when the system is brought to rest?

The early Mercury and Gemini Programs devoted a lot of study time on meteorite survivability (small particles) and came to realize that at the speeds one was dealing with, that the energy inherent in a 40-50000 fps BB sized particle of inert plutonium driven by shaped charge in a vacuum chamber is simply awesome.



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..!

OTOH a BB sized solid particle hitting your head at 20000fps will vaporize your head.

Back to the debate at hand. The ammunition, delivered in sufficient quantity to the vital target area, in a small enough time delta for which the ammunition package is expended and the target remains in position, to ensure the destruction of the target - is 'adequate'

The target, if a B-17, requires a lot more 'killing' than an Me 109 or Mustang and therefore either the quantity of a lesser ammunition, or the quality of the greater ammunition is more of a factor. With lesser ammunition, the survivability of the attacking a/c on a B-17 should be less but I doubt this to be true against a P-51.

IMHO, the survivability of the Fw 190 and Me 109 in combat with a P-51 was not enhanced by virtue of superior firepower.

One may debate forever the greater vulnerability of the 109 or 190 to an Mg 151/20 equipped Mustang over 4x 50.'s or 6x .50's. Intuitively? yes.

 

[Juha]

Thanks Drgondog for the info on US fighter armour.
In Spitfire pilot's back armour was 4+7mm and head armour 6+6mm. at least in Mk XIV according to Alfred Price. Its purpose was to keep out MG 131 and MG 151/20 API from medium range, what ever it was, fired from inside 20 deg cone behind. So appr same than in Bf 109F/G but without the protection of fuel tank and the 22mm aluminium sheets armour. And I don't know the quality and type of armour.

Juha

 

[Kurfürst]

I have some doubts about the XIV, I have never seen it described it as such, or having changed so radically from the Mk IX.

On the Mk IX the back plate was 4,5mm thick, the head plate was 6,2mm thick. There was no plate under the pilot, but there was a very small (88mm tall) plate behind his legs, at the level of the knee, again 6,2mm thick. There was no other pilot armor.

The upper fuel tank was protected by a plate in front of it, between the upper tank and the engine, 4,25mm thick; there was a inverted-U shaped cowling above the top tank, a deflector plate made out of aluminium of 3.5mm thickness, aimed to deflect rounds coming in from shallow angle.

This was supplemented by 38mm thick armor glass in the front of the canopy.

There was another iverted U shaped piece of armor in front of the horshoe shaped glycol tank between the engine and the propeller, of 6.2mm thickness.

There were 6.2 to 6.5mm thickness armor plates in front of the cannon ammunition boxes.

The whole armor package weighted 71 kg. Information from a rather detailed German technical report from 1943.

 

[Juha]

Hello Kurfürst
Yes I also think that Mk IXs and XIVs should have some kind protection at least late IX and all XIVs. According to Price's Spitfire book the back armour was 2 part system, 4 mm plate shaped like a L or a seat and a bit more backward a 7 mm thick straight plate. But of course it is possible that with heavier engine in nose it was possible to increase pilot's back armour. I have not seen any documents on the matter. If I would have time I would check from the Spitfire Bible but Shacklady's book is a bit haphazardy organized so finding something specific from it is somewhat difficult.

Juha

ADDITION: Out of curiosity made a quick look on Morgan's Shacklady's book. Didn't find drawings on armour layout but Spitfire Mk VIII had armour weight of 202lb, IX had 200 lb and XIV had 180 lb, so Germans seems to have missed something that weighted 20 kg, 200 lb is appr 90,7 kg.

 

[slaterat]

Juha is correct. The extension of the nose some 18 inches in converting a mkV to a IX would necessitate ballast aft of the pilot hence the additional armour plate. The armour layout Kurfurst posted is that for a Spit V except there was also a 10 swg[3.5mm] aluminum deflector plate above and below the ammo boxes. It appears that the back plate was missed in the German report as well as the deflector plates on the ammo boxes.

Slaterat

 

[Kurfürst]

The armour layout Kurfurst posted is that for a Spit V

No, it is for the Spit IX. The Spit V is also covered the report, but only differring marginally

except there was also a 10 swg[3.5mm] aluminum deflector plate above and below the ammo boxes. It appears that the back plate was missed in the German report as well as the deflector plates on the ammo boxes.

Slaterat

The German report mentions all of these, as do my post.. The report contains everything that was there on the Spit IX.

The 200+lbs figure is extremely dubious, unless it counts items as 'armor' which are not that in the traditional sense, ie. weight of self sealing tanks. This is quite likely as these were quite heavy, the one in the Bf 109G weighting 121 lbs.

I have certainly not seen anything that would suggest a 'second' back plate on any Spitfire models.

 

[Juha]

Hello Kurfürst
if you don't have seen anything that would suggest a 'second' back plate on any Spitfire models, why not take a look on page 101 in Price's Spitfire. A Complete Fighting History (1997)
And in Morgan and Shacklady p. 289 Modification 1193 for Mk VIII: Split armour for rear protection, it may well indicate to the armour layout that is in Price's book. BTW Morgan and Shacklady gives armour weight for Mk V as 73 lb. And for PR Mk XI no armour weight but same fuel capacity in fuselage tanks as in Mk IX which indicates that self-sealing isn't counted in armour weight.

It might well be that rear armour protection in Spitfire was reinforced in stages.

Juha

 

[HoHun]

Hi Juha,

>Pilots saw 4*.5 HMG as adequate armament against Japanese a/c and saw also that after you had run out ammo your chances to help the defence of your flat-top or your charges was minimal.

If you check the actual ammunition supply, the 4x 12.7 mm battery had 1720 rounds of ammunition while the 6x 12.7 mm battery had only 1440 rounds. What the pilot bemoaned was that the new aircraft had less ammunition, not that the extra guns fired off the same the number of rounds more quickly.

4x ,50 Browning M2 - 430 rpg, 33 s duration - 305 kg - 1,1 MW firepower - 37.5 MJ total supply
6x ,50 Browning M2 - 240 rpg, 18 s duration - 332 kg - 1,7 MW firepower - 31.4 MJ total supply

In fact, the F4F-4 example is great for showing what was wrong with the 12.7 mm Browning guns ... they were extremely heavy.

Here is an alternative battery that would have done a much superior job:

2x Hispano II - 417 rpg, 42 s duration - 305 kg - 2,1 MW firepower - 88.5 MJ total supply

What would these cannon have done for the US navy?

- They would have increased firepower by a factor of almost 2 over the F4F-3 battery (at the same weight).
- They would have increased the total firing duration by a factor of 1.3 over the F4F-3 battery (at the same weight).
- They would have increased the total ammunition supply by a factor of 2.4 over the F4F-3 (at the same weight).
- It would have increased firepower by more than 20% over the six-gun battery of the F4F-4 (at lower weight).

So whatever way you look at it, the 12.7 mm Browning armament was inferior to contemporary cannon, and replacing it with a different type of gun would have had considerable performance and tactical benefits for the US forces.

>Pilots saw 4*.5 HMG as adequate armament against Japanese a/c and saw also that after you had run out ammo your chances to help the defence of your flat-top or your charges was minimal. And without flat-top... Simple as that.

Taking a second look at this statement, I find it to be a very good illustration for the danger of using the term "adequate" ... I know that you meant to describe the firepower of the four-gun battery which against unarmoured Japanese aircraft with unprotected fuel tanks, against which it obviously was lethal, but what you wrote - inadvertently, I guess - actually was "adequate armament".

As the weight and the available ammunition supply have to be judged along with firepower, and weight and ammunition supply were basically "much more than adequate" and "much less than adequate" respectively, the battery as a whole was "far from adequate". As the survival of an entire aircraft carrier depended on the quality of the guns of its fighters, your example is a great illustration that having obsolete and overweight aircraft guns is a problem even for the side that is winning the war.

Regards,

Henning (HoHun)