gun synchronization to fire through propeller arc

[kolya1]

One thing worth noting is that, although an uncommon occurence, failures of the synchronisation system did sometimes happen. I think the first FW-190A captured by the Soviets in repairable condition was a plane that had cut its own propeller while straffing ground troops after the synchronisation system failed (wether because of mecanical failure or external damage, I don't know...). I can't look over all my books for that kind of incidents, but if I remember well, this wasn't a unique case, and it did also occasionnally occur in other air forces...

Anyway, as Graham said it, any fighter design is born out of a compromise between opposing factors, the goal being to have the best overall efficiency. Hubert Zemke and other US pilots remembered the P-38 for clearly having the best armament among US WWII fighters, while on the whole, they considered the Mustang or the Thunderbolt to be better fighters. Typical example of contradicting requirements was the Bf-109, which had to sacrifice part of its aerodynamics when it was needed to increase armament and MG-17s were replaced by MG-131s...

BTW, does anybody know how did the German pilots react to another of the firepower increases, namely the use of nose-mounted MK-108 30mm instead of MG-151 20mm cannon ? As far as I understand it, this change did not penalise the performance of planes as much as the MG-131 bulges, or the wing mounted gunpods, but I didn't read anything the usefulness of it in the fliers' eyes. By way of comparison, the Soviet experience with big guns (even bigger but with a slower rate of fire) is rather diversified : I've read praise about the higher hitting power in air combat of the Yak-9T's or P-39's 37mm guns, but also criticism regarding their slower rate of fire, or limited ammunition supply...

[kennethklee]

Originally Posted by kolya1

One thing worth noting is that, although an uncommon occurence, failures of the synchronisation system did sometimes happen. I think the first FW-190A captured by the Soviets in repairable condition was a plane that had cut its own propeller while straffing ground troops after the synchronisation system failed (wether because of mecanical failure or external damage, I don't know...). I can't look over all my books for that kind of incidents, but if I remember well, this wasn't a unique case, and it did also occasionnally occur in other air forces...

Anyway, as Graham said it, any fighter design is born out of a compromise between opposing factors, the goal being to have the best overall efficiency. Hubert Zemke and other US pilots remembered the P-38 for clearly having the best armament among US WWII fighters, while on the whole, they considered the Mustang or the Thunderbolt to be better fighters. Typical example of contradicting requirements was the Bf-109, which had to sacrifice part of its aerodynamics when it was needed to increase armament and MG-17s were replaced by MG-131s...

BTW, does anybody know how did the German pilots react to another of the firepower increases, namely the use of nose-mounted MK-108 30mm instead of MG-151 20mm cannon ? As far as I understand it, this change did not penalise the performance of planes as much as the MG-131 bulges, or the wing mounted gunpods, but I didn't read anything the usefulness of it in the fliers' eyes. By way of comparison, the Soviet experience with big guns (even bigger but with a slower rate of fire) is rather diversified : I've read praise about the higher hitting power in air combat of the Yak-9T's or P-39's 37mm guns, but also criticism regarding their slower rate of fire, or limited ammunition supply...

Kolya-

Thanks for your notes on gun synchronization system failure. I suspected there were incidents of failure, but I have not seen these reported except for one case in Helmut Lipfert's diary. I imagine such failures could occur if the engine suffered damage during combat or other means.

I can't answer your question directly about Luftwaffe fighter pilots' opinions on the MK 108 30mm cannon vs. MG 151 20 mm cannon, but you might find this article by Tony Williams and Emmanuel Gustin of interest:

http://www.quarry.nildram.co.uk/WW2guneffect.htm

It compares machine guns and cannon carried by fighters of the major air forces of WWII (Germany, Russia, UK, Japan, USA). Although methodology is not described, if you take the quantitations of "cartridge power" and "gun power" at face value, the MK 108 30mm cannon appears to be much more powerful than the MG 151 20mm cannon. I was somewhat surprised that the MK 108 rate of fire (rof) is only 17% less than the MG 151 20mm cannon; my former impression was that the MK 108 rof was about 50% that of the MG 151. Interestingly, the authors state that muzzle velocity is not critical in gun effectiveness and do not factor this in their comparisons of the major guns. The article's lack of references make some or many of the measurements, contentions, and pronouncements open to question, but the article is at least quite interesting reading.

With regards to your query about the pilots' opinions of the two cannon, the article states that the Luftwaffe considered the MK 108 30mm cannon their best fighter-carried gun. The article does not establish if this opinion of the Luftwaffe are those of the "upstairs brass" or the pilots actually using the weapons. I recall reading post-war interviews with several Luftwaffe fighter pilots who praised the MG 151/15 and MG 151/20 cannon. Finally Donald Caldwell in his JG 26: Top Guns of the Luftwaffe and/or JG 26 War Diary 1943-1945 Volume 2 describes a combat mission against the US heavy bombers in which one of the prominent flight leaders--I think it was Walter Matoni--flew a Bf 109G with a 30mm engine-mounted cannon (I presume it was MK 108) and "made good use of" the cannon, shooting down 2 bombers and damaging two others.

Kenneth

[Harri Pihl]

Originally Posted by kennethklee

Interestingly, the authors state that muzzle velocity is not critical in gun effectiveness and do not factor this in their comparisons of the major guns.

Well, even in the German wartime calculations the muzzle velocity appears to be noticeable factor. See the report claimed by George Hopp:

http://forum.12oclockhigh.net/showpo...3&postcount=62

It might also be one of the main reasons for poor results reported by Huhanantti on canon armed Fokker FR-76 (published in "Tarunhohtoiset Talvisodan Fokkerit" by Karhunen)

[Juha]

I recall 2 syncronization failures in FAF's Fiat G50s, one resulted a loss of plane, in the other case only result was a bullet hole in 2 blades.

Juha

[Juha]

Hello kennethklee
wing hmg failure produced yaw, like in Brewster B-239, cannon failure produced even more powerful yaw like in Bf 109G-6/R6, but for ex vääpeli/Master Sergeant Tani claimed that one could compensate the yaw with skillful and righttimed use of rudder.

Juha

[kennethklee]

Originally Posted by Harri Pihl

Well, even in the German wartime calculations the muzzle velocity appears to be noticeable factor. See the report claimed by George Hopp:

http://forum.12oclockhigh.net/showpo...3&postcount=62

It might also be one of the main reasons for poor results reported by Huhanantti on canon armed Fokker FR-76 (published in "Tarunhohtoiset Talvisodan Fokkerit" by Karhunen)

After reading the George Hoppe post you cited carefully, I conclude that Hoppe implies that muzzle velocity (mv) is a factor in a gun's power or effectiveness, but he does not state or opine its degree of influence, so a conclusion about mv cannot be made from his posting.

I'm not disagreeing with you that mv is important in a gun's effectiveness--in fact I was surprised also that Williams/Gustin seemed to dismiss mv as a factor in gun power--just that Hoppe doesn't make clear how much influence mv has. The thread that Hoppe posted to appears interesting and relevant to this subthread and I'll read it soon later when I have time (it comprises about 62 posts).

Thanks,
Kenneth

[Harri Pihl]

I have seen more detailed results (which contained hitting probabilities) posted by Mr. Hopp somewhere but can't find these right now.

[Jukka Juutinen]

Originally Posted by Harri Pihl

Well, even in the German wartime calculations the muzzle velocity appears to be noticeable factor. See the report claimed by George Hopp:

http://forum.12oclockhigh.net/showpo...3&postcount=62

It might also be one of the main reasons for poor results reported by Huhanantti on canon armed Fokker FR-76 (published in "Tarunhohtoiset Talvisodan Fokkerit" by Karhunen)

Is this perhaps one of Karhunen´s inventions like his claim of Magnusson praising the He 112?

[Jukka Juutinen]

Originally Posted by Graham Boak

The 4-cannon in fuselage Lavochkin was 1946, and used the much smaller lighter Russian cannon that did not appear until the very end of WW2. Nobody ever put 4 Hispanos into a single-engine fuselage. The Hispano was designed in the mid thirties: it is always possible to produce something better, ten years later.

As for quality standards, excessive quality in wartime production is a waste. This was normally very much the Russian approach, with high quality only applied where it was vitally necessary. After some development of the French original the Hispano worked: that's all that was needed. If the MG151 was "better" made, then it was worse made.

The Hispano´s DESIGN is utterly crude. So crude that it could not be synchronized. Perhaps the latter factor is the reason you never saw 4 fuselage mounted Hispanos in a single engines fighter...

The NR-23 had nothing that could not have been designed in the 1930s. Besides, Russians managed to put 3 ShVAK in the fuselage of a fighter with smaller wing than of the 109.

And finally, you prefer the Klimov VK-105 over the P&W R-2800? The former was certainly sufficiently badly made not to have "excessive quality" and surely is a fine example of "all that was needed".

[Don Caldwell]

The II./JG 26 pilots I interviewed on the topic were uniform in their praise of the Bf 109's nose-mounted MK 108 vs heavy bombers. The "gun tubs" could be dispensed with, and the Bf 109 thus lost none of its maneuverability, improving its survivability. I don't recall any comparisons of the MK 108 with the MG 151/20 vs fighters, but I don't think the difference would be significant; the increased destructive power of the 3cm shell per hit would be offset by the larger cannon's somewhat lower rate of fire.

Horrido!

Don