Post Battle of Britain: Luftwaffe/Axis options

tomo pauk

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Muzzle velocity is not a big deal, as you either have a non-manoevring target, which you can shoot at medium ranges with good chances of success regardless of muzzle velocity, or a manoeuvring target, which requires you to close to a very short range anyhow.

Muzzle velocity is/was enough of a thing, that made Luftwaffe asking for a 1000 m/s 20mm cannon, and for them to go with the modified MK 103 as a fighter gun on Ta 152C, Do 335 and Bf 109K-8.
 

Pioneer

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I would think that German war industry would be at its wits end, having to re equip to manufacture and facilitate another cannon round by this stage of the war. Logistically commonality of manufacturing was the name of the game as far as Albert Speer was concerned.

The mid-power 30mm needs to be in service at least by Spring of 1943. That probably means no MK 108 and no MK 103 - fine by me.
Please note tomo pauk, I'm no expert on the matter - just an observation

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Pioneer
 

T. A. Gardner

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If you are going to stick with a cannon, probably the best approach would have been for the Germans to invent something like the Mauser MG 213 earlier in the war. While that may or may not have been possible, the MG 213 has a ROF about double the MG 151 meaning a single MG 213 can deliver the firepower of two MG 151 at a fraction of the weight.
If you were to be able to cram, say 3 or 4 of these on an airplane, you get the equivalent of 6 to 8 MG 151 in terms of firepower. With the higher velocity of this gun over the MK 108 30mm, you can fire effectively from longer range and the sheer number of shells fired means more certain hits in higher number. That in turn would likely result in more shootdowns compared to using fewer Mk 108 with their low velocity and lower ROF.

One Mk 213 weighs about 10% less than 2 MG 151 and about 20% more than a single MK 108. When you add ammunition, the MG 213 comes out a clear winner all around.
 

HoHun

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Hi Tomo,

Muzzle velocity is not a big deal, as you either have a non-manoevring target, which you can shoot at medium ranges with good chances of success regardless of muzzle velocity, or a manoeuvring target, which requires you to close to a very short range anyhow.

Muzzle velocity is/was enough of a thing, that made Luftwaffe asking for a 1000 m/s 20mm cannon, and for them to go with the modified MK 103 as a fighter gun on Ta 152C, Do 335 and Bf 109K-8.

Good observation :) I'd argue that these were pre-1944 specification, not based on actual experience with the MK 108 in combat. In addition, the Do 335 was planned to be a heavy fighter/destroyer, so it's won't directly support the case for high muzzle velocity being descired for combat against fighters.

With regard to the 1000 m/s 20 mm cannon ... before the MG 213 in 20 mm even saw service, the Germans created the MG213C in 30 mm, firing the same ammunition as the MK108 at about the same (low) muzzle velocity.

The low-velocity MG 213C was in fact the highest ranked weapon in the Bad Eilsen comparison of 1945, defining the figure of merit of 100%, while the MG 213 in 20 mm was scored at 28.2%, hardly better than the MG 151/20 with 27.2%. (The MK 108 scored 72.4%, the MK 103 23.0%.)

Waffen Revue 25 - 3 - Comparison Table.jpg

Admittedly, that was in the anti-bomber role, but you could come up with a variable hit percentage modifer as a function of muzzle velocity to apply these results to a more dynamic environment. Still, the MK 108 was scored about 3 times as highly as the contemporary contenders, even the MK 213 in 20 mm, so you'd need a rather massive increase in hit percentage to come out better than the MK 108.

Regards,

Henning (HoHun)
 

HoHun

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Hi T. A.,

One Mk 213 weighs about 10% less than 2 MG 151 and about 20% more than a single MK 108. When you add ammunition, the MG 213 comes out a clear winner all around.

I think you've hit the nail right on the head with the approach of looking at the total battery weight!

However, you're probably underestimating the weight of the MG 213 cartridges - as the document I posted above shows, one MG 213/20 round weighs in at 390 g, compared to one MG 151/20 round's 197.2 g.

That means that in the total battery weight consideration, based on the requirement to achieve 20 hits at 5% hit ratio, the MG 151/20 actually comes out as the winner:

4 x MG 151/20 (630 rpm each) + 400 rounds: 247 kg
2 x MG 213/20 (1260 rpm each) + 400 rounds: 306 kg

For comparison, the MK 108 (which needs to score only 5 hits for the same effect):

1 x MK 108 (600 rpm) + 100 rounds: 113 kg

These three batteries all deliver about the same amount of destructive energy to the target in about the same total firing time (of 10 seconds).

Basically, the high-velocity weapons are less weight efficient than one would expect from only comparing the weapon weight as the cartridges themselves need to be heavier to achieve the higher muzzle velocities, even if the projectiles themselves are identical.

Regards,

Henning (HoHun)
 

T. A. Gardner

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Hi T. A.,

One Mk 213 weighs about 10% less than 2 MG 151 and about 20% more than a single MK 108. When you add ammunition, the MG 213 comes out a clear winner all around.

I think you've hit the nail right on the head with the approach of looking at the total battery weight!

However, you're probably underestimating the weight of the MG 213 cartridges - as the document I posted above shows, one MG 213/20 round weighs in at 390 g, compared to one MG 151/20 round's 197.2 g.

That means that in the total battery weight consideration, based on the requirement to achieve 20 hits at 5% hit ratio, the MG 151/20 actually comes out as the winner:

4 x MG 151/20 (630 rpm each) + 400 rounds: 247 kg
2 x MG 213/20 (1260 rpm each) + 400 rounds: 306 kg

For comparison, the MK 108 (which needs to score only 5 hits for the same effect):

1 x MK 108 (600 rpm) + 100 rounds: 113 kg

These three batteries all deliver about the same amount of destructive energy to the target in about the same total firing time (of 10 seconds).

Basically, the high-velocity weapons are less weight efficient than one would expect from only comparing the weapon weight as the cartridges themselves need to be heavier to achieve the higher muzzle velocities, even if the projectiles themselves are identical.

Regards,

Henning (HoHun)
The was no reason I can see that you couldn't have gotten the rounds down to about the same weight--yes, I understand the gas check systems for the breeches were different--as the MG 151 round. But even with the weights you give the two systems come out a wash on weight as the MG 213 weighs 20% less than 2 MG 151's while the ammo weighs 20% more at 400 rounds.
Ten seconds firing is forever in aerial combat. Given the closing speeds of mid- to late-war fighters versus a heavy bomber 3 to 5 seconds is more likely the norm for a MK 108 and about 4 to 8 seconds for a MK 213.

The higher velocity weapon is more effective because you can open fire further away accurately, and keep up fire longer than the low velocity slug thrower. This is really important if you have pilots who are short on practice, like most Luftwaffe ones would be. Opening up sooner and for longer gives them a chance to correct their fire and at least get hits rather than having to close and break off with a short burst of fire.

This was something that showed up most significantly with the Me 163 Komet. The plane was moving so fast and the MK 108's were so short ranged, that the pilot got little more than a snap shot off at a target and usually failed to kill it.
 

tomo pauk

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However, you're probably underestimating the weight of the MG 213 cartridges - as the document I posted above shows, one MG 213/20 round weighs in at 390 g, compared to one MG 151/20 round's 197.2 g.

That means that in the total battery weight consideration, based on the requirement to achieve 20 hits at 5% hit ratio, the MG 151/20 actually comes out as the winner:

4 x MG 151/20 (630 rpm each) + 400 rounds: 247 kg
2 x MG 213/20 (1260 rpm each) + 400 rounds: 306 kg

For comparison, the MK 108 (which needs to score only 5 hits for the same effect):

1 x MK 108 (600 rpm) + 100 rounds: 113 kg

These three batteries all deliver about the same amount of destructive energy to the target in about the same total firing time (of 10 seconds).

Basically, the high-velocity weapons are less weight efficient than one would expect from only comparing the weapon weight as the cartridges themselves need to be heavier to achieve the higher muzzle velocities, even if the projectiles themselves are identical.

Trick is to achieve the 5% hit ratio in the 1st place. A high MV gun will have easier job to achieve that percentage than a low MV gun.
German problem was (yes, I'm boring you to death by now) was that there was no mid-power 30 mm gun in their inventory.
 

Tony Williams

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I wouldn't bother with the MG 213C in either calibre: revolver cannon turned out to be very difficult to get right, it took years of development before the Aden and DEFA guns saw service. And even with the perfected revolver cannon like the BK 27, they do not shine as far as power-to-weight ratio is concerned by comparison with the Soviet twin-barrel or even conventional recoil-operated guns.

I would go with the twin-barrel guns (which were based on the German WW1 Gast anyway); the little GSh-23 hits 3,000+ rpm for only 50 kg weight.
 

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Hi Tomo,

Trick is to achieve the 5% hit ratio in the 1st place. A high MV gun will have easier job to achieve that percentage than a low MV gun.

Hehe, you're right of course, but how much of an advantage do you think a certain increase in hit probability would convey in a dogfight?

Even if it doubles the hit probability, the MK 108 gives three times the firepower-to-weight ratio of the MK 103, so the MK 108 still is the superior choice.

And I doubt you'll get anywhere close to doubling the hit probability ... increasing the muzzle velocity from 500 m/s to 700 m/s (about halfway to the MK 103's muzzle velocity), or 40%, basically results in extending effective range against a manoeuvring target to sqrt(1.4), or by 28% only.

Regards,

Henning (HoHun)
 

HoHun

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Hi Tony,

I would go with the twin-barrel guns (which were based on the German WW1 Gast anyway); the little GSh-23 hits 3,000+ rpm for only 50 kg weight.

What was the typical development time of German WW2 era cannon, from project start to service introduction?

That would give us an indication of the required point of departure from the original timeline to make the decision to go for a Gast-type cannon.

(I imagine it wouldn't be ideal for use as an engine cannon, though! ;-)

Regards,

Henning (HoHun)
 

Tony Williams

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Hi Tony,

I would go with the twin-barrel guns (which were based on the German WW1 Gast anyway); the little GSh-23 hits 3,000+ rpm for only 50 kg weight.

(I imagine it wouldn't be ideal for use as an engine cannon, though! ;-)

Regards,

Henning (HoHun)
That'a true! A better option for the RAF and USAAF, perhaps.
 

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Hi T. A.,

The was no reason I can see that you couldn't have gotten the rounds down to about the same weight--yes, I understand the gas check systems for the breeches were different--as the MG 151 round. But even with the weights you give the two systems come out a wash on weight as the MG 213 weighs 20% less than 2 MG 151's while the ammo weighs 20% more at 400 rounds.

Well, taking the 30 mm guns as an example, the MK 103's shell had about 3 times the kinetic energy of the MK 108, so it would have to have at least 3 times the propellant. And I'd expect the barrel pressures to be higher as well, so the casing of the projectile would need to be stronger as well. That seems pretty unavoidable to me, not sure how engineers would be able to work around that - unless you're thinking about reducing projectile mass, which in turn would reduce the destructiveness of the individual mounts.

Ten seconds firing is forever in aerial combat. Given the closing speeds of mid- to late-war fighters versus a heavy bomber 3 to 5 seconds is more likely the norm for a MK 108 and about 4 to 8 seconds for a MK 213.

You're right, and in fact the Bad Eilsen comparison used twice the number of barrels in the battery for these two guns.

However, your earlier email was suggesting that one MG 213/20 would replace two MG 151/20, and as the Bad Eilsen comparison was starting with a 4 MG 151/20 battery, I used a 2 MG 213/20 battery to go along with that, and the single MK 108 as it gave the same firing time too.

This is really important if you have pilots who are short on practice, like most Luftwaffe ones would be. Opening up sooner and for longer gives them a chance to correct their fire and at least get hits rather than having to close and break off with a short burst of fire.

The problem with that is that the hit probability drops inversely with the square of range, as the angular target size decreases with range. (This is outlined in the Luftwaffe's training manual "Des Jägers Schießfiebel", p. 6: http://rafiger.de/Homepage/Literatur/Schiessfibel.pdf ). If you shoot from 141% the range, the target is only 50% the size, so with the typical aim deviations to be expected from inexperienced pilots, you could expect them to need to fire twice as many rounds from that range for the same number of hits.

Regards,

Henning (HoHun)
 

tomo pauk

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Hehe, you're right of course, but how much of an advantage do you think a certain increase in hit probability would convey in a dogfight?

Even if it doubles the hit probability, the MK 108 gives three times the firepower-to-weight ratio of the MK 103, so the MK 108 still is the superior choice.

MK 103 warranted a heavier Mine shell. Talk the 450 g ballpark.

And I doubt you'll get anywhere close to doubling the hit probability ... increasing the muzzle velocity from 500 m/s to 700 m/s (about halfway to the MK 103's muzzle velocity), or 40%, basically results in extending effective range against a manoeuvring target to sqrt(1.4), or by 28% only.

28% improvement of hit probability is very good. Makes one hit the target with 9 shells instead of hitting with just 7 shells.
 

T. A. Gardner

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However, you're probably underestimating the weight of the MG 213 cartridges - as the document I posted above shows, one MG 213/20 round weighs in at 390 g, compared to one MG 151/20 round's 197.2 g.

That means that in the total battery weight consideration, based on the requirement to achieve 20 hits at 5% hit ratio, the MG 151/20 actually comes out as the winner:

4 x MG 151/20 (630 rpm each) + 400 rounds: 247 kg
2 x MG 213/20 (1260 rpm each) + 400 rounds: 306 kg

For comparison, the MK 108 (which needs to score only 5 hits for the same effect):

1 x MK 108 (600 rpm) + 100 rounds: 113 kg

These three batteries all deliver about the same amount of destructive energy to the target in about the same total firing time (of 10 seconds).

Basically, the high-velocity weapons are less weight efficient than one would expect from only comparing the weapon weight as the cartridges themselves need to be heavier to achieve the higher muzzle velocities, even if the projectiles themselves are identical.

Trick is to achieve the 5% hit ratio in the 1st place. A high MV gun will have easier job to achieve that percentage than a low MV gun.
German problem was (yes, I'm boring you to death by now) was that there was no mid-power 30 mm gun in their inventory.
Some time back I did this in an on-line exchange with Tony Williams on another board. I did a rough analysis of a German fighter closing on a bomber at X speed while the bomber flew at Y speed, assuming a tail chase. Using a range of 1 and 2 seconds of flight for the shells and the closing speed with a pre-determined break off point--to avoid crashing into the bomber--what you find is the higher velocity gun is far more effective particularly when the fighter is going fast. You need to open fire accurately at longer ranges with higher closing speeds or you have no time to fire.
So, what happens with the 30mm MK 108 is that it can't throw enough shells in the very short time the pilot has to fire accurately (assuming an average pilot not an experten) to ensure that hits will be scored. This is most clearly demonstrated by the Me 163 which could easily reach a firing position but rarely shot down bombers because it closed too fast to get off more than a few accurately aimed rounds.
 

T. A. Gardner

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Hi T. A.,



The problem with that is that the hit probability drops inversely with the square of range, as the angular target size decreases with range. (This is outlined in the Luftwaffe's training manual "Des Jägers Schießfiebel", p. 6: http://rafiger.de/Homepage/Literatur/Schiessfibel.pdf ). If you shoot from 141% the range, the target is only 50% the size, so with the typical aim deviations to be expected from inexperienced pilots, you could expect them to need to fire twice as many rounds from that range for the same number of hits.

Regards,

Henning (HoHun)
This is the precise reason you need high velocity cannon. The average pilot needs more time and space to accurately aim and hit the target. That makes the MK 213 the weapon of choice, and even in 20mm with mine shells it should score enough hits using 3 or 4 to take a bomber down or at least cripple it which is really just as effective.
The longer-range opening fire allows the pilot to correct his aim as he closes, as compared to what is more of a snap fire with low velocity cannon. So, if the pilot is off a bit correcting aim is easier as there is less drop in the shells from the higher velocity weapon.
 
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HoHun

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Hi Tomo,

MK 103 warranted a heavier Mine shell. Talk the 450 g ballpark.

Hm, I'm not sure what you mean - I thought the MK 103 used the same mine shell as the MK 108?

28% improvement of hit probability is very good. Makes one hit the target with 9 shells instead of hitting with just 7 shells.

It's actually a 28% increase in effective range, not in hit probability (because that's easier to figure out on an "everything else being the same principle" basis).

For the sake of the discussion, let's assume that it's possible to build a 30 mm cannon that fires the same shells as the MK 103 and the MK 108, but that in all other aspects is a half-way design, i. e. with regard to muzzle velocity, rate of fire, weight, etc.

Let's also assume that hit probability against a manoeuvring target is proportional to muzzle velocity.

This midway gun would only need to fire 126 rounds against a "standard" manoeuvring target to score 5 hits, compared to 172 rounds for the MK 108. (The "standard" target is, for purposes of comparison, a target that the MK 103 achieves a 5% hit ratio against.)

However, ammunition weight would be 93 kg for the intermediate gun vs. 95 kg for the MK 108, and total battery weight would be 296 kg for a 2-gun battery of the intermediate gun, and 269 kg for a 3-gun battery of MK 108s.

The score for the intermediate gun would be 28%, and that for the MK 108 would be 40%. The MK 108 battery, in spite of being lighter, would score 5 hits in 5.7 seconds, while the intermediate gun battery for the same count of 5 hits would require 7.4 seconds.

So the MK 108 battery would offer about 25% higher firepower at about 10% less weight against manoeuvring targets, and against a non-manoeuvring target, its lower muzzle velocity would not be an issue at all, so there it would enjoy a 75% firepower advantage at a 15% weight advantage.

Here a comparison table including the MK 103:

Code:
Gun              MK 103    Tomo Gun     MK 108
Barrels               1           2          3

Against Manoeuvring Targets ...
Battery Weight   219 kg      296 kg     269 kg
Firing time       14.1s       7.4 s      5.7 s
Score               20%         28%        40%

Against Non-Manoeuvring Targets ...
Battery Weight   219 kg   277 kg   229 kg
Firing time       14.1s    5.9 s    3.3 s
Score               20%      38%      81%

Regards,

Henning (HoHun)
 

HoHun

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Hi T. A.,

Some time back I did this in an on-line exchange with Tony Williams on another board.

If you have a link to that, I'm sure I would enjoy reading through that! :)

It also would help me to prepare a more intelligent response ;-)

Regards,

Henning (HoHun)
 

tomo pauk

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Hm, I'm not sure what you mean - I thought the MK 103 used the same mine shell as the MK 108?

It used the same shell.
It should've been using a much heavier one, my suggestion is around 450g.

For the sake of the discussion, let's assume that it's possible to build a 30 mm cannon that fires the same shells as the MK 103 and the MK 108, but that in all other aspects is a half-way design, i. e. with regard to muzzle velocity, rate of fire, weight, etc.

Let's also assume that hit probability against a manoeuvring target is proportional to muzzle velocity.

Agree so far.
The mid-way 30mm gun was made in ww2 days, the Japanese Navy's Type 5 was 30mm, 345g shell @ 710 m/s.

This midway gun would only need to fire 126 rounds against a "standard" manoeuvring target to score 5 hits, compared to 172 rounds for the MK 108. (The "standard" target is, for purposes of comparison, a target that the MK 103 achieves a 5% hit ratio against.)

However, ammunition weight would be 93 kg for the intermediate gun vs. 95 kg for the MK 108, and total battery weight would be 296 kg for a 2-gun battery of the intermediate gun, and 269 kg for a 3-gun battery of MK 108s.

93 kg of ammo / 126 rounds = 0.74 kg for each round; that is almost as heavy as the MK 103 M-shell round, that weighted 0.86 kg each.
My math: 330 g (shell) + 60g (propellant; vs. 30g for Mk 108 ammo) + 200 g casing (vs. 125 g for the MK 108 ammo) = 0.59 kg each, call it 0.60 kg. 0.60 x 126 rds =74.34 kg. This ammo also offers a better ballistic similarity with the MG 151/20 than the MK 108, the 151/20s still remaining in the wing roots of the Fw 190. 2 guns x 100 kg + ~75 kg of ammo = 275 kg. For the MK 108 3-gun battery: 3 x 60 + 96 = 276 kg.
The Fw 190A will be carrying only 2 x 30mm cannon set-up? What weapon set-up for Bf 109, so it can also tackle the 'fighter type' targets?

So the MK 108 battery would offer about 25% higher firepower at about 10% less weight against manoeuvring targets, and against a non-manoeuvring target, its lower muzzle velocity would not be an issue at all, so there it would enjoy a 75% firepower advantage at a 15% weight advantage.

If the non-maneuvering target fires back, the low MV is certainly an issue.
We know that air forces 10 years after the ww2 have had a choice of low MV guns armament, and actual gun if someone wanted it. There was no takers, the lowest they went was 690 m/s for the Soviet guns. Luftwaffe was eager to have the high MV guns, too. Japanese Navy went from low MV 20mm cannon type to medium MV 20mm type by 1943.
 

T. A. Gardner

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Hi T. A.,

Some time back I did this in an on-line exchange with Tony Williams on another board.

If you have a link to that, I'm sure I would enjoy reading through that! :)

It also would help me to prepare a more intelligent response ;-)

Regards,

Henning (HoHun)
I think the site died some time ago. I'll see if I can find my notes. I know I used his figures from his site on WW 2 fighter guns for data on that part of it.
 

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Hi Tomo,

It should've been using a much heavier one, my suggestion is around 450g.

Well, then you'd either reduce muzzle velocity, or increase weapon and cartridge mass even further, and you'd also decrease rate of fire.

Additionally, with the 30 mm mine shell being a single-shot killer against fighter planes already anyway, using even larger shell would make it an unproductively overkilling round against this aircraft category. I would also suggest that even against larger aircraft, when the historical 30 mm shell didn't kill with a hit, that was predominantly a question of hit placement and not one of explosive content. If you blow off a wingtip with a mine shell, the plane will not become unflyable either if you blow off same wingtip with an even greater charge ;-)

93 kg of ammo / 126 rounds = 0.74 kg for each round; that is almost as heavy as the MK 103 M-shell round, that weighted 0.86 kg each.

I used the data straight from the WW2 document in https://www.secretprojects.co.uk/th...ftwaffe-axis-options.38375/page-4#post-505129 ... I presume they used the total weight including belting, not just the naked cartridge, so I guess that coiuld a reason it differs from your data point.

The Fw 190A will be carrying only 2 x 30mm cannon set-up? What weapon set-up for Bf 109, so it can also tackle the 'fighter type' targets?

My point is, a central 30 mm cannon is a great choice for tackling fighter-type targets. I haven't considered actual armament installations yet, but since the MK 108 is not suitable for synchronized firing, on the Focke-Wulf the MK 108 will have to go into the wings in Fw 190A-8/R2 style.

If you are looking to improve the Luftwaffe's 30 mm cannon, creating a synchronizable MK 108 might be the best way to achieve that.

(In a fighter-versus-fighter context, convergence/divergence caused by wing mounts is much worse for the hit probability against manoeuvring targets than a low muzzle velocity, in my opinion.)

If the non-maneuvering target fires back, the low MV is certainly an issue.
We know that air forces 10 years after the ww2 have had a choice of low MV guns armament, and actual gun if someone wanted it. There was no takers, the lowest they went was 690 m/s for the Soviet guns. Luftwaffe was eager to have the high MV guns, too. Japanese Navy went from low MV 20mm cannon type to medium MV 20mm type by 1943.

10 years after WW2, we're talking about jet fighters intercepting jet bombers - if you'd express the muzzle velocities as percentage of the target speed, they probably didn't change all that much compared to the 1945 values.

The Japanese Navy was not using mine shells, so the kinetic component of their cannon ammunition was more important than it was to the Luftwaffe for the overall effectiveness of their gun. The RAF on the other hand switched from the Hispano II to the Hispano V with reduced muzzle velocity and increased rate of fire, so there certainly was no universal trend towards higher muzzle velocities.

The Luftwaffe fielded the EZ42 LCOS which compensated for bullet drop, and the Bad Eilsen report noted that bomber kills had been achieved at 800 m combat range with it, and other Luftwaffe reports show that they had full confidence in the sight to allow hits from long ranges even with the MK 108. And I don't see why not, considering that even with a fixed reticle sight, the MK 108's trajectory would be within 200 cm of the aiming point out to 600 m or maybe a bit more.

Regards,

Henning (HoHun)
 

tomo pauk

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Well, then you'd either reduce muzzle velocity, or increase weapon and cartridge mass even further, and you'd also decrease rate of fire.

Additionally, with the 30 mm mine shell being a single-shot killer against fighter planes already anyway, using even larger shell would make it an unproductively overkilling round against this aircraft category. I would also suggest that even against larger aircraft, when the historical 30 mm shell didn't kill with a hit, that was predominantly a question of hit placement and not one of explosive content. If you blow off a wingtip with a mine shell, the plane will not become unflyable either if you blow off same wingtip with an even greater charge ;-)

The MV will go down with the 450g shell on the MK 103 - a trade-off that I'm willingly accepting. Only one such a weapon is still viable for killing of bombers. Yes, the gun will need to be redesigned in a timely matter so it can fit through the tube between the Vee of the V12 engines 1st, don't wait until late 1944/early 1945.
Hit was a requirement for kill. Explosive content mattered a lot, as seen by desire to go with ever bigger guns firing the M-shell that was filled with a big %-tage of explosive itself.

I used the data straight from the WW2 document in https://www.secretprojects.co.uk/th...ftwaffe-axis-options.38375/page-4#post-505129 ... I presume they used the total weight including belting, not just the naked cartridge, so I guess that coiuld a reason it differs from your data point.

Okay, roger that.

My point is, a central 30 mm cannon is a great choice for tackling fighter-type targets. I haven't considered actual armament installations yet, but since the MK 108 is not suitable for synchronized firing, on the Focke-Wulf the MK 108 will have to go into the wings in Fw 190A-8/R2 style.

If you are looking to improve the Luftwaffe's 30 mm cannon, creating a synchronizable MK 108 might be the best way to achieve that.

(In a fighter-versus-fighter context, convergence/divergence caused by wing mounts is much worse for the hit probability against manoeuvring targets than a low muzzle velocity, in my opinion.)

What needs to be done 1st IMO is to take the limitations of a platform 1st, then make guns. That way we don't arrive to the point of potentially excellent MK 103 that does not fit on Bf 109, and it is a lousy fit on a Fw 190. Germans were not the only ones with that mistake, the M4 37mm comes to mind, and we can recall the problems British had in order to fit the excellent guns on contemporary tanks. Japanese Army never fitted the powerful (even if with low RoF) Ho-1/-3 within the wings of their 1-engine fighters, they used the LMGs and HMGs until the Ho-5 was available (and a small quantity of the MG 151/20s).

An 'MK 151/30' would've indeed be interesting.
The Japanese Navy was not using mine shells, so the kinetic component of their cannon ammunition was more important than it was to the Luftwaffe for the overall effectiveness of their gun.

I'd still safely assume that a mid-power 30mm cannon was a feasible thing to do in all 'major' gun-making countries of the day :)

The RAF on the other hand switched from the Hispano II to the Hispano V with reduced muzzle velocity and increased rate of fire, so there certainly was no universal trend towards higher muzzle velocities.

820 m/s for the Hispano V. That is even higher than for what I suggest.

And I don't see why not, considering that even with a fixed reticle sight, the MK 108's trajectory would be within 200 cm of the aiming point out to 600 m or maybe a bit more.

At 300 m and at sea level, the drop was about 200 cm; at 600m, the drop was 877cm; all for the MK 108 firing the 330 g shell.
The MK 103 had the drop of 319 cm at 600 m, for the 440 g HE shell fired at 800 m/s.
 
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Hi Tomo,

The MV will go down with the 450g shell on the MK 103 - a trade-off that I'm willingly accepting. Only one such a weapon is still viable for killing of bombers. Yes, the gun will need to be redesigned in a timely matter so it can fit through the tube between the Vee of the V12 engines 1st, don't wait until late 1944/early 1945.
Hit was a requirement for kill. Explosive content mattered a lot, as seen by desire to go with ever bigger guns firing the M-shell that was filled with a big %-tage of explosive itself.

Well, the Bad Eilsen report argued against big guns even against bombers for various reasons, not the least were that the fewer rounds you fired overall, the less predictable the results of an attack would become, and that a partial success with smaller rounds would still leave a damaged target.

As the total explosive amount of 360 g was seen as being necessarily to destroy a bomber with a high probability, they concluded that the maximum sensible calibre was 45 mm to 50 mm, as that would allow a single shell to carry the required amount of explosive. However, that was not an option they favoured, for the reasons pointed out above.

What needs to be done 1st IMO is to take the limitations of a platform 1st, then make guns. That way we don't arrive to the point of potentially excellent MK 103 that does not fit on Bf 109, and it is a lousy fit on a Fw 190.

It was a tight squeeze on the Me 109, but it fit with a re-designed muzzle brake, so the problem was not really that the gun was oversized, but that the muzzle brake wasn't designed with engine installation in mind from the outset. (However, I consider the gun oversized in the sense of being inefficient, wether you can fit it or not.)

An 'MK 151/30' would've indeed be interesting.

An MK 151/25 maybe even more, if I may come back to your earlier calibre suggestion!

I'd still safely assume that a mid-power 30mm cannon was a feasible thing to do in all 'major' gun-making countries of the day :)

Feasible probably, but sensible?

820 m/s for the Hispano V. That is even higher than for what I suggest.

Right, I just meant to point out that there by no means was an unbroken trend towards higher muzzle velocities.

At 300 m and at sea level, the drop was about 200 cm; at 600m, the drop was 877cm; all for the MK 108 firing the 330 g shell.

Sure, but that's not important to the pilot as long as the impact point is close to the aim point.

As the sight line was depressed to follow the initial drop, from the pilot's point of view the MK 108's trajectory first rose a bit, and then dropped off a little. For the Me 109G-6/U4, the top of the arc was reached at 64 cm at 250 m out, and the drop at 400 m was zero, as the descending arc of the trajectory intersected the sight line there.

As the sight line was depressed 104 cm/100 m, out at 600 m, the sight line was at -624 cm, so if the trajectory dropped at the same range to -877 cm, the center of the impacts was just 253 cm below the aim point. And that's all sea level data ... in actual combat, the Me 109 would be more likely to fire at bombers at altitudes closer to at 18000 ft, where the air density is only half that at sea level. That means that the shells it fires encounter much less air resistance, leading to a flatter trajectory, and a smaller deviation from the aim point.

Which in turn translates to an even longer effective range for the MK 108 at the normal operational altitudes of the bomber formations.

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Henning (HoHun)
 

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Well, the Bad Eilsen report argued against big guns even against bombers for various reasons, not the least were that the fewer rounds you fired overall, the less predictable the results of an attack would become, and that a partial success with smaller rounds would still leave a damaged target.

As the total explosive amount of 360 g was seen as being necessarily to destroy a bomber with a high probability, they concluded that the maximum sensible calibre was 45 mm to 50 mm, as that would allow a single shell to carry the required amount of explosive. However, that was not an option they favoured, for the reasons pointed out above.

I certainly would not endeavor to go with such the big weapons. The MK 103 is probably the biggest & heaviest weapon that is still practical from the platform, recoil and RoF stanpoints.

It was a tight squeeze on the Me 109, but it fit with a re-designed muzzle brake, so the problem was not really that the gun was oversized, but that the muzzle brake wasn't designed with engine installation in mind from the outset. (However, I consider the gun oversized in the sense of being inefficient, wether you can fit it or not.)

Muzzle brake was indeed removed. Also the barrel shroud (next to the receiver) was also made with smaller diameter, while the under-barrel tube and it's attachment point were removed from the previous big shroud. Please compare the "MK 103" and "MK 103 mot" at the 'Junkersflugzeuge 1933-45' book, pg. 116 and 117 respectively.
What puzzles me is the date for the 'MK 103' mot drawing - July of 1943.

Feasible probably, but sensible?

For the Soviets and Germans, that manufactured fighters with a single cannon in the motor-cannon fashion: certainly. It makes sense to have that single cannon as powerful as it can be (but not too powerful, like the Soviet 37mm was, as installed on LaGG-3-37 and Yak-9T).
For Americans and Brtish - makes sense for P-39, P-63, P-38, and the fighters with R-2800 and their big and thick wings; less sensible for Hurricane, Spitfire, P-40, P-51; sensible also for night fighters.
For Japanese: very much needed, but where is the engine power before 1943 (for the IJA; the IJN was in an even worse position wrt. power installed on their 1-engined fighters), since at least 2 will be carried by fighters? Their 30mm guns firing the ~270g shells will be less a burden to performance, late as they were.
 

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However, you're probably underestimating the weight of the MG 213 cartridges - as the document I posted above shows, one MG 213/20 round weighs in at 390 g, compared to one MG 151/20 round's 197.2 g.

That means that in the total battery weight consideration, based on the requirement to achieve 20 hits at 5% hit ratio, the MG 151/20 actually comes out as the winner:

4 x MG 151/20 (630 rpm each) + 400 rounds: 247 kg
2 x MG 213/20 (1260 rpm each) + 400 rounds: 306 kg

For comparison, the MK 108 (which needs to score only 5 hits for the same effect):

1 x MK 108 (600 rpm) + 100 rounds: 113 kg

These three batteries all deliver about the same amount of destructive energy to the target in about the same total firing time (of 10 seconds).

Basically, the high-velocity weapons are less weight efficient than one would expect from only comparing the weapon weight as the cartridges themselves need to be heavier to achieve the higher muzzle velocities, even if the projectiles themselves are identical.

Trick is to achieve the 5% hit ratio in the 1st place. A high MV gun will have easier job to achieve that percentage than a low MV gun.
German problem was (yes, I'm boring you to death by now) was that there was no mid-power 30 mm gun in their inventory.
Some time back I did this in an on-line exchange with Tony Williams on another board. I did a rough analysis of a German fighter closing on a bomber at X speed while the bomber flew at Y speed, assuming a tail chase.
T.A Gardner , would be interesting to know this from head-on attack aspect of bomber's, as I think was deemed the most effective attack method by the Luftwaffe analysis, if I remember correctly...

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However, you're probably underestimating the weight of the MG 213 cartridges - as the document I posted above shows, one MG 213/20 round weighs in at 390 g, compared to one MG 151/20 round's 197.2 g.

That means that in the total battery weight consideration, based on the requirement to achieve 20 hits at 5% hit ratio, the MG 151/20 actually comes out as the winner:

4 x MG 151/20 (630 rpm each) + 400 rounds: 247 kg
2 x MG 213/20 (1260 rpm each) + 400 rounds: 306 kg

For comparison, the MK 108 (which needs to score only 5 hits for the same effect):

1 x MK 108 (600 rpm) + 100 rounds: 113 kg

These three batteries all deliver about the same amount of destructive energy to the target in about the same total firing time (of 10 seconds).

Basically, the high-velocity weapons are less weight efficient than one would expect from only comparing the weapon weight as the cartridges themselves need to be heavier to achieve the higher muzzle velocities, even if the projectiles themselves are identical.

Trick is to achieve the 5% hit ratio in the 1st place. A high MV gun will have easier job to achieve that percentage than a low MV gun.
German problem was (yes, I'm boring you to death by now) was that there was no mid-power 30 mm gun in their inventory.
Some time back I did this in an on-line exchange with Tony Williams on another board. I did a rough analysis of a German fighter closing on a bomber at X speed while the bomber flew at Y speed, assuming a tail chase.
T.A Gardner , would be interesting to know this from head-on attack aspect of bomber's, as I think was deemed the most effective attack method by the Luftwaffe analysis, if I remember correctly...

Regards
Pioneer
I did it as a stern chase from behind. Head on attacks might be more effective but they require far higher piloting skills. As I've pointed out before, the best attack strategy is the high-side pass from ahead where the attacking fighter rolls into a diving turn to present the most target area on the bomber. This does require some skill at deflection shooting though. It also minimizes effective defensive fire as the gunners have to use deflection shooting too against a high-speed target.
 

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American bombers B-17 and B-24 were much better armed than their British counterparts and their crews had been trained to fly in self-defence formations only a few meters apart from each other. The rules of air combat determined that an attacker fighter would not risk flying through such a compact formation, having to choose between shooting from far away and deviating at the last moment exposing their ventral surfaces to the powerful defensive crossfire of American gunners, who were considered statistically lethal from a distance of one thousand yards.

A lonely fighter attacking a 'box' got in the gunsight of as many as 40 Browning M2 heavy machine guns. The Germans tried many different Pulkzerstörer (formation destroyer) tactics to break the boxes without having to get too close. The four engine bombers, which they called Viermots or Dicke Autos, were attacked from a distance of 1,800 m by Me 410 A-2/U4 heavy fighters, fitted with Rheinmetall-Borsig BK.5 cannons of 50 mm that capable of dismantling a B-17 with a single hit. But they were so heavy that prevented the Me 410 could escape the Mustangs escort.

The Viermots were attacked from 1,300 m with W.Gr.21 rockets of 210 mm, launched from specially modified aircraft Bf 110 G-2/R3, Fw 190 A-7/R6 and Bf 109 G-6/R2. However, this type of spin-stabilised rocket was very inaccurate and, after the attack, the launcher plane could not release the launch tubes on flight, which considerably diminished its speed. From a distance of 900 m, some Ju 88 P-2 and Bf 110 G-2/R1 fired their Rheinmetall-Borsig 'Flak 38' of 37 mm, an anti-tank canon with a low rate of fire that was too heavy to be installed on a single seat fighter and which use in air-to-air mode was a failure.

The Luftwaffe also tested various air-to-air bombing techniques in the summer of 1943, using fighters Bf 109 G-4 that flew at 1,000 m over the stream bombers, throwing AB 50 containers, each one loaded with 34 standard infantry fragmentation grenades. The Fw 190 A-4/U3 of the I./JG1 launched SC 250 bombs and AB 500 containers, loaded with 370 kg of HE and provided with time and proximity fuses, over the 'boxes' without achieving success.

At the beginning of 1944 there were already designs and prototypes of air-to-air missiles created to solve the '1000 yards problem', but until they reached service status, the Luftwaffe was forced to fight the Viermots using Sturm (assault) fighter units specialized in schnauze auf schnauze (frontal attacks) combat. The advantage of a head-on pass was that the fighter remained only 5 seconds in the 1,000 yards area and took it another 9 seconds to cross the 'box', if it was lucky enough to not collide against any bomber. The downside was that the aircraft crossed so quickly that the fighter barely had time to fire. And to shoot down a Viermot were needed many shots!

Major Hans Georg von Kornatzki proposed the OKL to use saturation tactics by which a group of at least thirty fighters simultaneously attacked a 'box' to avoid the concentration of defensive fire against a single fighter. Kornatzki did not get the thirty fighters but he obtained approval from the general Adolf Galland to test new tactics with a section of fifteen aircraft that was named I./JG1 Sturmstaffel 1. The tests began in Achmer-Osnabrück in late 1943 using Fw 190 A-6 fighters in mock combat against an Fw 200 bomber.

Further analysis of the films made with the EK16 gun cameras served to determine that the optimal firing distance was of 200 m, approximately when the four engines of the bomber appeared to be in the target circle of the Revi 16B gunsight. The 'Sturmstaffel 1' became operational in February 1944 under command of major Kornatzki with eighteen Fw 190 A-6 aircraft based in Dortmund.

His combat method consisted in carrying out a head-on pass with twelve aircraft flying wing-tip to wing-tip in a broad arrow formation that was called Breitkeil by the Germans and 'Company Front' by the Americans. Upon receiving an order from the staffelführer all airplanes simultaneously fired their MG 151/20 cannons. In a typical head-on pass, the four guns of an Fw 190 - with a rate of fire of 780 rpm - could make 160 shots launching between 960 and 1760 grams of HE against the target, depending on the type of ammunition used. According to statistics from the Luftwaffe, at least 400 grams of HE were required to destroy a B-17 with a 95% certainty, therefore the attacker fighter should hit the target with 36 shots of M-Geschoss or 67 shots of MX-Geschoss ammunition.

In a frontal attack, the punch of the MG 151 was increased thanks to the combined speed of both aircraft on collision course. In those combat conditions, the radial engines, the Plexiglas nose and the cockpit windshield of the bomber were very vulnerable and the Sturm tactics were so effective that in early May the Sturmstaffel 1 became a Sturmgruppe within the JG3. After the head-on pass all Breitkeil aircraft broke left and right and organized to repeat the attack until breaking the cohesion of the 'box'. When this was achieved as a result of panic, the bombers were individually attacked by fighters of other units that had kept at a distance during the Pulkzerstörer combat.

In December 1943, the Focke-Wulf company began manufacturing a series of eighty Fw 190 A-7/R2 aircraft specially modified for the Sturm combat, replacing the two MG 151 located outboard of the wings by other more powerful type MK 108/30 cannon, called Kurzgerät by the pilots. In February 1944, the 2./JG11 started operational testing with these aircraft, testing head-on pass tactics as they flew into a shallow dive of fifteen degrees to increase attack speed. In April, the 5./JG1 made operational tests with the new MK 108 cannons, attacking from the rear of the 'box'. They noted that the low range and high dispersion fire factor of the Kurzgerät required shooting from less than 100 m from the target to obtain results. From this distance, the attacker fighter should make at least 52 shots to achieve the three impacts that, statistically, would cause the destruction of the Viermot.

The Fw 190 A-7/R2 could only carry 110 shells of the Minengeschoss 30 x 90 RB type, so in a classic attack from the rear, the pilot should start shooting from 90 m reaching up to 30 m from the target before breaking contact. The casualties of the 'Sturm' units were terrible, The Sturmstaffel 1 pilots boasted of ‘not shooting until you see the whites of the eyes of the tail gunner’. This phrase became the slogan of the unit and was materialized in a couple of eyes painted on the flying jackets.

Losses increased even more when the bombers began to be escorted by large groups of Mustangs, Thunderbolts and Lightnings. Some Staffeln lost a third of its members in each combat and in August 1944 the Sturmgruppen were losing one fighter by every bomber that was shot down. During its existence, the I./JG1 withstood a 350% loss of pilots, the IV./JG3 a 200% and the II./JG4 lost 72 pilots in six months.
Some fascinating insight and information thanks Justo Miranda!

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Pioneer
 

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Hi Pioneer,

Some fascinating insight and information thanks Justo Miranda!

Well, I would certainly like to know what the sources are ... some stuff sounds rather Caidin-esque:

The rules of air combat determined that an attacker fighter would not risk flying through such a compact formation, having to choose between shooting from far away and deviating at the last moment exposing their ventral surfaces to the powerful defensive crossfire of American gunners, who were considered statistically lethal from a distance of one thousand yards.

The Herbert K. Weiss report (BLR 727) paints a quite different picture of Luftwaffe fighter operations against bombers than Justo's post.

Here's a graph showing observed number of hits over closing range (the distance at which the fighter stopped attacking):

BLR 727 Hits over Closing Distance P40.jpg

Note that not all hits were visible on film (armour piercing shells for example would tend to impact without visual signature), and from a comparison of the number of observed fires to the number observed hits, it's clear that beyond 600 m range, hits rarely show up on film (while fires are visible at longer ranges). Thus, the qualification "observed hits" in the graph.

Regards,

Henning (HoHun)
 

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Hi Tomo,

For the Soviets and Germans, that manufactured fighters with a single cannon in the motor-cannon fashion: certainly. It makes sense to have that single cannon as powerful as it can be (but not too powerful, like the Soviet 37mm was, as installed on LaGG-3-37 and Yak-9T).
For Americans and Brtish - makes sense for P-39, P-63, P-38, and the fighters with R-2800 and their big and thick wings; less sensible for Hurricane, Spitfire, P-40, P-51; sensible also for night fighters.
For Japanese: very much needed, but where is the engine power before 1943 (for the IJA; the IJN was in an even worse position wrt. power installed on their 1-engined fighters), since at least 2 will be carried by fighters? Their 30mm guns firing the ~270g shells will be less a burden to performance, late as they were.

I certainly agree that a 30 mm cannon of any kind would be a sensible addition to the arsenal of any air force that failed to develop one! However, that an intermediate 30 cannon would be superior to a MK 108 is something I really doubt. The MK 108 had a very competitive set of parameters, and any attempt to improve on one of them would inevitably harm one or more of the others.

Regards,

Henning (HoHun)
 

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If you are looking to improve the Luftwaffe's 30 mm cannon, creating a synchronizable MK 108 might be the best way to achieve that.

Henning (HoHun)

Some rear-seared (open-bolt firing) cannon could be adapted for synchronisation, either by adding a front sear or (the easiest way) to convert to electric priming - the 20mm Hispano is an example of that, in its post-WW2 M24 form. However, this was inherently impossible with API blowbacks like the MK 108.

As a quick and dirty upgrade, the Germans did experiment with necking up the 20 x 138B case to 23mm, although I don't have details. The 20 x 138B was of course used in Flak guns and various others, including the MG C/30L aircraft gun (aka the MG 102) tested in an He 112 during the Spanish Civil War. This only fired at 300-350 rpm but that was a slightly souped-up version of the Rheinmetall action; switching to the 20mm Mauser Flak 38 action would have increased this to 450 rpm and possibly more, through tuning it up as an aircraft gun.
 

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The MK 108 had a very competitive set of parameters, and any attempt to improve on one of them would inevitably harm one or more of the others.

I'm readily willing to harm one thing that it was the MK 108's forte (light weight) in order to improve where it was weak (low MV).

To move a bit from all of this gunnery pr0n, some fiddly bits that engine companies might either steal from others already by 1941-42, or introduce earlier:
- don't wait until 1944 (Jumo) or even until 1945 (DB) to copy the swirl throttle device from the captured Mikulin engines. That was an easy way to circumvent the lack of high-octane fuel, since it allowed greater power under the rated altitude.
- copy the supercharger from Merlin 60 series once some of these engines is captured (again, don't wait until late 1944)
- until that is done: DB 601/605 and Jumo 211 engines with a big S/C from late 1942 or thereabout (yes, the DB engines will also need to have the chrome-plated valves as it was done on BMW 801D, as well as introduce the oil/air separator from the Jumo engines)
- BMW 801 will really need a much better S/C for 1943, no point in waiting until late 1944 to introduce it
- MW 50 is a feasible way to have a lot of power, don't wait until 1944/45 to do it
 

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Hi Tony,

However, this was inherently impossible with API blowbacks like the MK 108.

Thanks for chiming in! If I understand it correctly, API guns fire while the bolt is still moving forward, so even a switch to electric priming will not make them synchronizable, as that would require firing with the bolt at rest?

Regards,

Henning (HoHun)
 

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Hi Tony,

However, this was inherently impossible with API blowbacks like the MK 108.

Thanks for chiming in! If I understand it correctly, API guns fire while the bolt is still moving forward, so even a switch to electric priming will not make them synchronizable, as that would require firing with the bolt at rest?

Regards,

Henning (HoHun)
Correct. The MK 108 was of course electric primed anyway (as was the MK 103).
 

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Hi Tomo,

I'm readily willing to harm one thing that it was the MK 108's forte (light weight) in order to improve where it was weak (low MV).

So what would be the minimum muzzle velocity you'd accept would be? Using the linear interpolation approach, the 680 m/s cannon sitting halfway between the MK 103 and the MK 108 wasn't really an improvement.

(See https://www.secretprojects.co.uk/th...tain-luftwaffe-axis-options.38375/post-505261 )

- don't wait until 1944 (Jumo) or even until 1945 (DB) to copy the swirl throttle device from the captured Mikulin engines. That was an easy way to circumvent the lack of high-octane fuel, since it allowed greater power under the rated altitude.

I'm not even sure it wasn't actually a German invention, or maybe even a French one, considering the Sverdlovski-Planiol supercharger. In any case, I agree there might have been a chance to apply it to operational engines earlier.

- copy the supercharger from Merlin 60 series once some of these engines is captured (again, don't wait until late 1944)

I don't think the Germans needed the Merlin 60 supercharger to develop a two-stage supercharging system with intercooling of their own. I think they originally considered such a system economically ineffcient, and then were stumped by the lead times necessary to develop it. That leads to the question, what do you consider the decisive point out departure from the original timeline for the purpose of this thread?

- MW 50 is a feasible way to have a lot of power, don't wait until 1944/45 to do it

It would in fact be interesting to know why this wasn't introduced earlier, as it seems to have been a relatively simple and well-established method.

Regards,

Henning (HoHun)
 

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So what would be the minimum muzzle velocity you'd accept would be? Using the linear interpolation approach, the 680 m/s cannon sitting halfway between the MK 103 and the MK 108 wasn't really an improvement.

(See https://www.secretprojects.co.uk/th...tain-luftwaffe-axis-options.38375/post-505261 )

700 m/s, give or take.

I'm not even sure it wasn't actually a German invention, or maybe even a French one, considering the Sverdlovski-Planiol supercharger. In any case, I agree there might have been a chance to apply it to operational engines earlier.

DB was mooting the swirl throttle before 1940. Polikovsky's device (= Russian term for the swirl throttle as used on their engines) was the 1st that was put in actual service and mass produced.
The French gentlemen used the radial layout of vanes, set around the 1st row of impeller vanes (there was several rows of the impeller blades, that looked a bit like a combination of radial and axial compressor without stator); Germans and Soviets did the axial layout, where the throttle was in front of the impeller.
FWIW, the thread where I've dabbled about it: link

I don't think the Germans needed the Merlin 60 supercharger to develop a two-stage supercharging system with intercooling of their own. I think they originally considered such a system economically ineffcient, and then were stumped by the lead times necessary to develop it. That leads to the question, what do you consider the decisive point out departure from the original timeline for the purpose of this thread?

Point of departure is 'post BoB', ie Autumn of 1940.
If indeed they considered the Merlin 60s S/C 'economically inefficient', that is either arrogance or ignorance on the side of RLM/LW. The 2-stage S/C on Merlin was a stroke of genius, that allowed the major boost in power (especially at high all altitudes) vs. 1-stage S/Ced previous engine versions.
The German engine program, where companies were trying to make spanking new engines like every 6 months, was a paragon of both economical and military inefficiency. Calum's book is a gold mine for this and a lot more.

It would in fact be interesting to know why this wasn't introduced earlier, as it seems to have been a relatively simple and well-established method.

The water-alcohol injection was a known thing back in the days of the DB 601R engine, ie. before 1940. Americans were experimenting with it in the 1920s.
 

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Hi Tomo,

So what would be the minimum muzzle velocity you'd accept would be? Using the linear interpolation approach, the 680 m/s cannon sitting halfway between the MK 103 and the MK 108 wasn't really an improvement.

(See https://www.secretprojects.co.uk/th...tain-luftwaffe-axis-options.38375/post-505261 )

700 m/s, give or take.

This results in the following comparison:

Code:
Gun            MK 103    Tomo Gun   MK 108
v0             860 m/s   700 m/s   500 m/s
Rate of Fire   425 rpm   503 rpm   600 rpm
Barrels          3         3         4

Against Manoevuring Targets
Battery Weight 527 kg    412 kg    327 kg
Firing Time    4.7 s     4.9 s     4.3 s
Score           25%       31%       44%

Against Non-Manoevuring Targets
Battery Weight 527 kg    395 kg    287 kg
Firing Time    4.7s      4.0 s     2.5 s
Score           25%       40%       87%

DB was mooting the swirl throttle before 1940. Polikovsky's device (= Russian term for the swirl throttle as used on their engines) was the 1st that was put in actual service and mass produced.

Thanks for the additional background! Seems that the swirl throttle would be a valid improvement for our "what if" scenario then.

If indeed they considered the Merlin 60s S/C 'economically inefficient', that is either arrogance or ignorance on the side of RLM/LW. The 2-stage S/C on Merlin was a stroke of genius, that allowed the major boost in power (especially at high all altitudes) vs. 1-stage S/Ced previous engine versions.

Well, it wasn't so much a stroke of genius as the basic concept had been around for quite a time, and openly discussed in interwar NACA reports, for example. It wasn't even all that bold to build one, as Germany had the DB 628 laid out before they ever saw a Merlin 61 (if I understand the timeline correctly). Rolls-Royce started a bit earlier I guess, and they didn't have the problems with bearing reliablity that Daimler-Benz had (outlined in Calum's book).

I'd consider the avoidance of using silver in the bearings' plating an economical decision, and Calum also points out that the DB 628 installation had additional weight and drag (as the Merlin 61 had in the Spitfire), while a calculated performance comparison showed that the Me 109G with GM-1 system had superior high-altitude performance over its DB 628-engined counterpart, so there was a more economical alternative to the DB 628. (And in 1944, it would have competed against the DB 605D, which gave quite good altitude power too despite being a single-stage supercharged engine only.)

I'm not sure when the Merlin 61 would have been available for copying, but considering that Daimler-Benz had prototypes of the DB 628 ready by May 1942 (if I get that right from the "Secret Horsepower Race"), it seems difficult to imagine the same engine would have been ready earlier.

So, yes, the Merlin 61 was a great engine, but within the restrictions of this what-if, I'm not sure the Luftwaffe could have gained anything from an attempt to copy its supercharger, especially when the DB 605 really required more air at a lower pressure than the Merlin, so a direct copy wouldn't have been possible anyway.

Regards,

Henning (HoHun)
 

Tony Williams

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If you are looking to improve the Luftwaffe's 30 mm cannon, creating a synchronizable MK 108 might be the best way to achieve that.

Henning (HoHun)

As a quick and dirty upgrade, the Germans did experiment with necking up the 20 x 138B case to 23mm, although I don't have details. The 20 x 138B was of course used in Flak guns and various others, including the MG C/30L aircraft gun (aka the MG 102) tested in an He 112 during the Spanish Civil War. This only fired at 300-350 rpm but that was a slightly souped-up version of the Rheinmetall action; switching to the 20mm Mauser Flak 38 action would have increased this to 450 rpm and possibly more, through tuning it up as an aircraft gun.

I turned out to have more details than I had thought. An extract from my new book, Autocannon:

"In 1940 Rheinmetall examined a pro- posal to improve the destructive effect of the 20 × 138B round in the MG C/30 by necking the case up to take a 22mm projectile. It is not known whether this was actually made, but factory drawings of three different nose-fuzed HEI-T loadings survive; one with a 170g shell containing 21g HE and a large tracer (MV unspecified); one with a 146g shell containing 24g HE and a small tracer, fired at 905m/s; and a slight variation on this weighing 150g, containing 26g HE and fired at 880m/s. Overall cartridge length is 228mm, significantly more than the 20 × 138B suggesting that the action and magazines would have required lengthening. The cartridge shown here is a replica.

An almost identical 23mm version of the above also exists, as does a different 23mm version (possibly by Polte?) in which the visible length of the projectile is considerably less to keep the overall round length to 202mm, the same as the 20 × 138B, thereby making the conversion of existing 20mm guns much easier. The cartridge shown here is a modern mock-up of this round using a replica projectile."
 

tomo pauk

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This results in the following comparison:

Code:
Gun MK 103 Tomo Gun MK 108
v0 860 m/s 700 m/s 500 m/s
Rate of Fire 425 rpm 503 rpm 600 rpm
Barrels 3 3 4

Against Manoevuring Targets
Battery Weight 527 kg 412 kg 327 kg
Firing Time 4.7 s 4.9 s 4.3 s
Score 25% 31% 44%

Against Non-Manoevuring Targets
Battery Weight 527 kg 395 kg 287 kg
Firing Time 4.7s 4.0 s 2.5 s
Score 25% 40% 87%

Thanks for the math.
Think that we can agree that a Soviet fighter, Bf 109 or P-39 will be hard pressed to carry aloft more than one 30mm cannon until/unless the major power increase happens. IMO that cannon better be as powerful as it is practically possible.

Well, it wasn't so much a stroke of genius as the basic concept had been around for quite a time, and openly discussed in interwar NACA reports, for example. It wasn't even all that bold to build one, as Germany had the DB 628 laid out before they ever saw a Merlin 61 (if I understand the timeline correctly). Rolls-Royce started a bit earlier I guess, and they didn't have the problems with bearing reliablity that Daimler-Benz had (outlined in Calum's book).

Yes, the concept of 2-stage superchaging was around by almost a decade before RR made the Merlin 60 for the Wellington; Junkers before the Jumo happened made 2- and IIRC 3-stage supercharged engine for altitude records, so did Farman, and so did Bristol. What was important from military point of view was that Hooker (and his team) managed to make the idea practical enough for installation on engines that are in mass-production, while the power increase above 20000 ft was great, and above 25000 was dramatical when compared with Merlins with 1-stage S/C.
For better or worse, the DB 628 idea didn't get any traction. Same for different DB engines with two separate superchargers (= 2-stage supercharging in effect), each on it's side of engine. We can note that both Jumo and DB eventually decided for two impellers driven by a single-shaft (the same idea that was on Merlin 60s) for Jumo 213E and J, and for DB 603L and 605L. Some of these engines were without intercoolers (605L, 213F), requiring the use of MW 50 for more aggressive power settings.
I've suggested before that DB copies the oil de-aerator from Jumo 211s (presence of air in oil was killing the bearings), and chrome-plated valves from BMW 801D - things they actually did by late 1943.

I'd consider the avoidance of using silver in the bearings' plating an economical decision, and Calum also points out that the DB 628 installation had additional weight and drag (as the Merlin 61 had in the Spitfire), while a calculated performance comparison showed that the Me 109G with GM-1 system had superior high-altitude performance over its DB 628-engined counterpart, so there was a more economical alternative to the DB 628. (And in 1944, it would have competed against the DB 605D, which gave quite good altitude power too despite being a single-stage supercharged engine only.)

Usage of silver is in the crankshaft bearings, S/C was away from it. Someone still needs to make the GM-1 system and the mixture it uses. If used, it can also be added to a 2-stage engine for even better performance at altitude.
Late 1944 is too late for a DB 605 with a big S/C, like the DB 605AS and 605D were in effect (S/C taken from DB 603A and installed on the DB 605A to produce the 605AS and ASM). That needs to be done by winter of 1942/43, followed up by a 2-stage S/C by late 1943, ie. an early DB 605L, that can power both Bf 109 and Fw 190 (so can the early '601AS' or 605AS).
So, yes, the Merlin 61 was a great engine, but within the restrictions of this what-if, I'm not sure the Luftwaffe could have gained anything from an attempt to copy its supercharger, especially when the DB 605 really required more air at a lower pressure than the Merlin, so a direct copy wouldn't have been possible anyway.

Direct copy is certainly out of question. The idea of a compact, simple and compact unit is important.
 

HoHun

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Hi Tomo,

Think that we can agree that a Soviet fighter, Bf 109 or P-39 will be hard pressed to carry aloft more than one 30mm cannon until/unless the major power increase happens. IMO that cannon better be as powerful as it is practically possible.

For comparison, the Fw 190A-8's armament weight could be broken down as follows:

168 kg - 4 x MG 151/20
167 kg - 880 rounds 20 mm ammunition
34 kg - 2 x MG 131
74 kg - 950 rounds 13 mm ammunition
-------
443 kg

The Me 109G-6/R6:

42 kg - 1 x MG 151/20 nose gun
43 kg - 200 rounds 20 mm ammunition for nose gun
84 kg - 2 x MG 151/20 wing guns
58 kg - 270 rounds 20 mm ammunition
34 kg - 2 x MG 131
47 kg - 600 rounds 13 mm ammunition
-------
308 kg

The Me 109G-6/U4:

60 kg - 1 x MK 108
48 kg - 65 rounds 30 mm ammunition
34 kg - 2 x MG 131
47 kg - 600 rounds 13 mm ammunition
-------
189 kg

The Me 109G-6:

42 kg - 1 x MG 151/20
43 kg - 200 rounds 20 mm ammunition
34 kg - 2 x MG 131
47 kg - 600 rounds 13 mm ammunition
-------
166 kg

Considering that the Me 109G-6/R6 was perceived as too heavy for air-to-air combat, while the /U4 modification doesn't seem to have raised any objections, we can probably say that for the Me 109, 308 kg of armament weight is too mich, but 189 kg is OK. I'll set the limit at a nice round 200 kg.

This gives us the following options:

1 x MK 103 with 60 rounds: 200 kg, 425 rpm
1 x Tomo Gun with 124 rounds: 200 kg, 503 rpm
2 x MK 108 with 76 rounds per gun: 200 kg, 1200 rpm

So the MK 108 battery has the highest rate of fire by far, and the biggest round count. Admittedly, it again requires wing guns.

In this case, I'd be tempted to take the Tomo Gun because having centreline armament is a significant advantage, even if the slow rate of fire is a bit inconvenient. Considering that historically, the Me 109 seems to have been used more often to cover the bomber-killing Fw 190s against escort fighters than as a bomber killer, maybe I would prefer a MK 108 with a smaller mine shell so that a higher rate of fire is possible at the increased muzzle velocity that seems inevitable if this thread is ever to go anywhere! ;-)

Usage of silver is in the crankshaft bearings, S/C was away from it. Someone still needs to make the GM-1 system and the mixture it uses. If used, it can also be added to a 2-stage engine for even better performance at altitude.

Usage of silver is from Calum's book, I didn't actually know that before looking it up :)

Calum's book also has a description of the production and logistics of GM-1, so that was pretty much covered. I'm not quite sure why it wasn't used at a larger scale to fight the USAAF though - maybe it's in the book, I only read it once so far, and there are a lot of details that I couldn't commit to memory on the first go.

You can use it with a two-stage supercharger, but you'll be alone at the altitudes where it's useful, and you'd probably need a spacesuit as well! :-D Even the bog-standard Gustav could get up to around 13 km with GM-1 only, and GM-1 could only be used above full throttle height. Accordingly, with a two-stage supercharger that would not have yielded much of a useful operational envelope.

Regards,

Henning (HoHun)
 

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