Author Topic: Differences between the "Type 99" and MG-FF? (Read 1357 times)

niklas · « **Reply #45 on:** April 30, 2002, 09:00:21 AM »

What were the fusing times for the Hisp. shell then?

Why should a quick mechanism be always bad? Imagine you have a delay that is equal to a travel way of 50cm, ~0.5yard. If you fire at an aircraft from behind the shell may enter the fuselage and penetrate deeper, though not much deeper.
But what happens when you fire at a fighter from above (imagine he is banked 90° in a turn) ? When you hit a wing, the shell will leave the wing on the other side before exploding right? Even bomber wings aren´t 0.5y thick, right? The width of a fighter fuselage isn´t much larger. So if you don´t have the luck to hit the main spar you get only a nice little hole.

niklas

niklas · « **Reply #46 on:** April 30, 2002, 09:26:16 AM »

Nice picture illo! Can you show us also "chart1", the left part? Thx!

Did you notice that the "Sprenggr. ÜB" is listed in the row GB/USA and seems to be a Hispano Shell? The same designition can be found in the trajectory pictures for the FW190. That´s really strange

niklas

HoHun · « **Reply #47 on:** April 30, 2002, 01:09:04 PM »

Hi Niklas,

>Did you notice that the "Sprenggr. ÜB" is listed in the row GB/USA and seems to be a Hispano Shell? The same designition can be found in the trajectory pictures for the FW190. That´s really strange

Good observation! Looking at it more closely, I seem to read it as actually "Sprengr. Üb." like "Übungsmunition" ('practice ammunition'). I've seen the same abbreviation for German 20 mm before.

The drawing doesn't indicate any fuze, and though the shell looks like the flat-nosed explosive shell, there's no indication of any filling either on the drawing or in the table.

I'd say this is an inert projectile for practice (and testing) purposes.

That you found the same designation on the trajectory diagram for the Fw 190 seems logical since inert shells were more useful for test-firing as they merely punched neat holes :-) That's much better for checking the weapons' alignment than having your targets torn to pieces by explosive rounds.

Regards,

Henning (HoHun)

HoHun · « **Reply #48 on:** April 30, 2002, 01:20:53 PM »

Hi Tony,

>Yes they did, but according to British tests of the German ammo I have seen, the German 20mm HE had exactly the same problem until about 1941.

That's interesting, I hadn't read about that before. Are we talking about mine shells or regular HE shells now?

I guess if we're talking about mine shells, the problem must have been less common since they remained in service while the Hispano HE shells apparently were withdrawn for a while.

Regards,

Henning (HoHun)

Tony Williams · « **Reply #49 on:** April 30, 2002, 03:50:53 PM »

Quote

Originally posted by HoHun
That's interesting, I hadn't read about that before. Are we talking about mine shells or regular HE shells now?

This is from report AVIA 6/13387 in the PRO: "Firing Trials of German 20mm HE/HEI from Bf 109F-2".

Among other things, the report noted "no evidence of a delay action to the fuze". I presume that this applied to both HE-T and M-Geschoss.

Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://www.quarry.nildram.co.uk
Military gun and ammunition discussion forum:
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Tony Williams · « **Reply #50 on:** April 30, 2002, 03:57:01 PM »

Quote

Originally posted by niklas
Why should a quick mechanism be always bad?

Any fuze setting has to be a compromise, taking into account the most likely attack angle. In most cases against fighters, this would have been very close to directly behind, with the fuselage being the target. Some delay would therefore have been an advantage.

Slightly OT, but I understand that the Israeli Air Force was disappointed with the performance of the DEFA cannon in their planes in the 1960s-70s conflicts. It turned out that the French ammo had been designed for hitting Soviet bombers, so the fuzes had such a long delay that they didn't detonate until they were clean through the fighters they were shooting at.

Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://www.quarry.nildram.co.uk
Military gun and ammunition discussion forum:
http://forums.delphiforums.com/autogun/messages/

niklas · « **Reply #51 on:** April 30, 2002, 05:37:41 PM »

The fuselage must be the target when your goal is to set the target to fire, what was at the beginning the most successful method to destroy it. But this changed with the M-shell. Now the structure became directly the target.

Do you know the fuzing time for a Hispano HE-shell? If it was equal to a travel way of 1-2 yard, it should be pretty useless when hitting a wing from above or a fuselage from the side.

I know from 2 german fuses for mineshells, one had a delay of only 36us, the other 275us.

niklas

Tony Williams · « **Reply #52 on:** April 30, 2002, 11:08:55 PM »

I'm sorry, I don't have any specific information about the delay time on the Hispano fuze.

It's worth pointing out that 80% of RAF Bomber Coomand losses were attributed to fire rather than structural damage. The "I" part of HEI was very important; in fact the last type of M-Geschoss 20mm ammo tried was nearly all I with just a small bursting charge of HE.

Tony Williams
Author: "Rapid Fire: The development of automatic cannon, heavy machine guns and their ammunition for armies, navies and air forces"
Details on my military gun and ammunition website:
http://www.quarry.nildram.co.uk
Military gun and ammunition discussion forum:
http://forums.delphiforums.com/autogun/messages/

Hooligan · « **Reply #53 on:** April 30, 2002, 11:14:23 PM »

Henning wrote:

Quote

A typical WW2 fighter might present as little as 10% critically vulnerable surface..

I believe this is wrong. I did a rough measurement of the presented target area of a spitfire from a cross-sectional drawing presented from the front quarter (“The Great Book of World War II Airplanes”, various Authors, 1984 Zokeisha Publications, Ltd. pg. 284). The major structural components take up approximately this much of the presented area:

Forward fuselage: 19%
Cockpit: 9%
Read fuselage: 21%
Wings: 44%
Tail: 7%
----
Total: 100%

The “critical targets” take up approximately this much of the presented area:
Engine/glycol/coolant jacket: 9%
Oil Tank: 1%
Pilot: 4%
Fuel: 7%
Oxygen tanks: 1%
Ammo boxes: 4%
Fuel pipes, cables etc.. : 1%
----
Total: 27%

From a more typical attack angle of the dead 6 of a fighter, a larger cross sectional percentage of the target (as much as 50% or 60%) contains a critical target. From the dead 6 approximately 1 in 2 hits on a fighter would be heading towards something potentially catastrophic (given sufficient penetration power), such as an ammo box or the engine or pilot.

Hooligan

HoHun · « **Reply #54 on:** May 01, 2002, 04:25:18 AM »

Hi Tony,

>It's worth pointing out that 80% of RAF Bomber Coomand losses were attributed to fire rather than structural damage.

I think that figure may be the best possible estimate, but the difficulties of arriving at accurate figures for the resons for bomber losses over enemy territory at night must be considerable. (Just think of how long it took the RAF to recognize the "Schräge Musik" attacks as what they were.)

And catastrophical damage to a bomber would typically involve fire, too - no matter if it was the cause of the catastrophical damage or the result.

Regards,

Henning (HoHun)

HoHun · « **Reply #55 on:** May 01, 2002, 04:32:42 AM »

Hi Tony,

>Among other things, the report noted "no evidence of a delay action to the fuze". I presume that this applied to both HE-T and M-Geschoss.

Niklas' figure of 36 micro seconds is a very short fuzing delay that will only allow the shell to travel a few centimeters before detonating (which suited the damgage mechanism of the mine shell). I could imagine the RAF verdict is based on the mine shell's failure to match the RAF's expectation of a substantially longer delay.

Regards,

Henning (HoHun)

HoHun · « **Reply #56 on:** May 01, 2002, 04:46:19 AM »

Hi Hooligan,

>I did a rough measurement of the presented target area of a spitfire from a cross-sectional drawing presented from the front quarter (“The Great Book of World War II Airplanes”, various Authors, 1984 Zokeisha Publications, Ltd. pg. 284).

Good approach!

Note that my lower figure for critically vulnerable area (10% versus 27%) comes from the requirement for an immediate kill raised earlier in this thread, while you've included targets that lead to the aforementioned "slow" kills.

To arrive at a complete analysis with your approach, we'd need to assign kill probabilities for each of the critical targets you mentioned to get the overall kill probability. For example, the engine is a pretty hard target and has a good chance of surviving even a direct hit, and the pilot armour is going to stop a certain proportion of the attacking projectiles (even if they're 20 mm armour piercing).

For comparison, the Luftwaffe considered 6 x 20 mm enough to kill a fighter. That's an average probability of kill of 17%. You're starting with 27% now, presuming a 100% probability of kill per component. By adjusting the Pk for each component to a realistic value, you can check how well your model compares to the Luftwaffe's analysis.

Regards,

Henning (HoHun)