Aircraft armament....

Hi again,

>Unfortunately I'm unable to make a proper comparison to the MG 151/20 battery vs. battery as I don't have the ammunition weight data for the B-20 (cartridge weight plus weight of belting).

I found a cartridge weight (no belting) listed here:

ShVAK cannon - Wikivisual

Ignoring the weight of the belting, this gives the following rough comparison:

2x MG 151/20 (MX) - 187 rpg - 164 kg - 124% firepower - firepower per weight: 342%
2x MG 151/20 - 207 rpg - 172 kg - 112% firepower - firepower per weight: 294%
4x Berezin B-20 - 221 rpg - 264 kg - 113% firepower - firepower per weight: 193%
4x 20mm ShVAK - 221 rpg - 332 kg - 113% firepower - firepower per weight: 154%

So despite underestimating the weight of the Soviet ammunition a bit, neither the B-20 nor the older ShVAK (which fired the same ammunition as the B-20) compare too well to the MG 151/20.

The B-20 was an efficient gun, but it didn't have the powerful ammunition that was available for the MG 151/20, and this shortcoming affected the total efficiency of the battery negatively.

Regards,

Henning (HoHun)

vanir said:

Apparently the Oerlikon liked to tear large sections of airframe skinning away, but it had what pilots described as "sledgehammer recoil" (due to its origins not really being designed for aerial use), it felt like it was trying to tear the wings off when being fired, this seriously concerned many pilots. Mounted to fire through the engine vee, more recoil was absorbed by engine weight but it overheated and jammed frequently in this configuration.

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That contradicts many things I've read. Firstly the Oerlikon FFF is derived from the WWI 20 mm Becker gun, designed for aircraft use. (the entire FF family was specificaly designed for aircraft use, with emphesis on wing mounting) The Oerlikon S and improved SS were used as AA guns and were more robust (heavier) versions of the FFS. Additionally the API blowback operating principal of the Oerlikon means that recoil is spread out throught the operating cycle, resulting in a smoother recoil pulse. The MG FF also used a less powerful amunition than the MG 151/20, so recoil should be even less by comparison.

(due to its origins not really being designed for aerial use)

Click to expand...

Indeed this was a piece of speculation on my part. I've read Becker didn't originally design the gun for aerial use, but the aerial versions like the FF were descended variants. I put that together with the musings of an ex-Messerschmitt employee on pilot feedback about MG FF mountings.

Upon closer examination of technical details the API blowback system does appear a "softer" system than the short-recoil of the MG151. As you've outlined. Quite right.

Perhaps the concern was related to the light structure of early 109 wings, these were not originally intended to mount weapons and were modified for machine guns at RLM request (ref. Alfred Price).

My apolegies.

You'd have to compare it to the characteristics of the underwing pod mounted MG 151/20's. (though this would only be an apromation as the mountings were different and the internal wing structure had been altered on later models as well)

Hi Vanir,

>it felt like it was trying to tear the wings off when being fired, this seriously concerned many pilots.

I've never heard about that before. Where did you find it?

Regards,

Henning (HoHun)