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Punski 30 mm

The subjective side of the coin.

Moderators: hunter368, DerAdlerIstGelandet

Re: Punski 30 mm

Postby HoHun » Sat Feb 04, 2017 6:23 pm

Hi again,

A clip from the British firing trials ... first time I've seen this, though the pictures of the torn-apart Spitfire and Blenheim fuselages from these trials are fairly well-known.

Nice to see the result of firing at a wing, too:

https://www.youtube.com/watch?v=ZoLLDi-M3fk

Regards,

Henning
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Re: Punski 30 mm

Postby Invisible shadow » Sat Feb 04, 2017 8:07 pm

As a general rule, long-barreled high-velocity weapons had a higher dispersion due to the greater effect of barrel oscillations (and the greater recoil).


In simple terms, this means the Spit cannon with 7 foot length has greater dispersion than 4 foot german 20 mm. This dispersion then increases even more when installed mid wing.
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Re: Punski 30 mm

Postby HoHun » Sun Feb 05, 2017 11:05 am

Hi Invisible,

>In simple terms, this means the Spit cannon with 7 foot length has greater dispersion than 4 foot german 20 mm. This dispersion then increases even more when installed mid wing.

Yes, that's my impression too. There was also the problem of systematic bore-line displacement when Gs where pulled, as the wing guns where slightly out of their original position due to wing flex. I think to compensate for this, the RAF at least for some time used a harmonization pattern that had the dispersion cones not converging as usual, but more or less stacked on each other. Larger beaten zone at the cost of effectiveness ...

I'm not sure if other aircraft with wing guns were affected by wing flex under Gs as much as the Spitfire, but as the Spitfire was famous for its thin wing, I could speculate it might have been worse off than other fighters of the era.

Regards,

Henning
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Re: Punski 30 mm

Postby Invisible shadow » Sun Feb 05, 2017 11:42 pm

There was also the problem of systematic bore-line displacement when Gs where pulled, as the wing guns where slightly out of their original position due to wing flex.


Like bending a water hose, water angle changes, hence cannon shells would angle up slightly in a turn? depending on which way the bend was.
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Re: Punski 30 mm

Postby HoHun » Mon Feb 06, 2017 12:05 am

Hi Invisible,

>Like bending a water hose, water angle changes, hence cannon shells would angle up slightly in a turn?

Hm, more like twisting the wing between cannon and fuselage a tiny bit so that the cannon are no longer perfectcly aligned with the sight.

Wings bend when you pull Gs, and while you try to keep it to a minimum, it's almost inevitable that they also twist a little.

(According to David Lednicer's analysis, this even happens with the Fw 190, which is famous for its stiff wing, and this does impact the aerodynamic properties of the type enough to give it a sharp accelerated stall.)

Regards,

Henning
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Re: Punski 30 mm

Postby Bren » Mon Feb 06, 2017 6:38 pm

HoHun wrote:From an older post I made on Aces High forum:


Hohun - great information on dispersion.

I myself have been collecting everything I can on data like this as it pertains to British (and American to some extent) aircraft.

If at any point in the future you are able to point me towards German documentation like this - or similar writeups you have done on the subject I would be most grateful.
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Re: Punski 30 mm

Postby Bren » Mon Feb 06, 2017 6:46 pm

The British system for determining group sizes made by machine guns/cannon was to indicate 'Percent Zones'.

ie:
1.000 degree for a 100% zone
0.500 degree for a 75% zone
0.333 degree for a 50% zone

"So that the size of the group is not largely increased by odd bullets round the edge, it is customary to specify a group by the diameter of the circular zone at the centre, containing 75 percent of the total number of bullets fired. This is also convenient because the bullet density can be assumed to be almost constant throughout this zone"

Do you know what standards the Germans used?
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Re: Punski 30 mm

Postby Invisible shadow » Mon Feb 06, 2017 7:32 pm

Macci 205 wasn't bad for "best gun setup for a piston fighter"

one engine-mounted 20 mm cannon, two wing-mounted 20 mm cannon, and two fuselage-mounted 12.7 mm (.5 in) machine guns

A K-4 with a 30 mm, 2 MG 131 & 2 15 mm in wing root with widened wing & landing gear would be close to perfect. Or 1 20 mm, 2 15 mm & 2 machine guns all grouped around centerline.
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Re: Punski 30 mm

Postby lumino » Tue Feb 07, 2017 5:23 pm

Invisible shadow wrote:Macci 205 wasn't bad for "best gun setup for a piston fighter"

one engine-mounted 20 mm cannon, two wing-mounted 20 mm cannon, and two fuselage-mounted 12.7 mm (.5 in) machine guns


this was the armanent of the other series 5 fighters : Fiat G.55 and Re 2005. the Veltro did not have an engine cannon.
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Re: Punski 30 mm

Postby Invisible shadow » Wed Feb 08, 2017 7:56 pm

The maiden flight of the second prototype, the C.205N2, took place on 19 May 1943, reaching 628 km/h (390 mph) during testing, which was marginally slower than the C.205N1 with a correspondingly longer time to reach its operational altitude. It was equipped with one engine-mounted 20 mm cannon, two wing-mounted 20 mm cannon, and two fuselage-mounted 12.7 mm (.5 in) machine guns. The ammunition load comprised 600 or more 12.7 mm (.5 in) rounds, and a maximum of around 900 20 mm rounds which was much heavier than that carried by the C.205N1, and more than that of the Reggiane and the Fiat which carried 490-550 and 650 20 mm rounds respectively. Although 1,200 aircraft were initially ordered, the design was abandoned due to the Armistice between Italy and Allied armed forces.

The N-series aircraft should have performed better than the C.205V, but Macchi test pilot Guido Carestiato noted that their flying characteristics were inferior to the lighter and more agile C.205 Veltro. The later series also experienced overheating while climbing.[7]
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Re: Punski 30 mm

Postby Denniss » Thu Feb 09, 2017 12:27 am

If you just type C.205 it's the C.205V "Veltro", the only mass-produced version. This had no engine cannon.
The C.205N "Orione" were prototypes
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Re: Punski 30 mm

Postby Invisible shadow » Thu Feb 09, 2017 3:14 am

Regardless, still a near best gun setup for a piston fighter.
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Re: Punski 30 mm

Postby HoHun » Sun Mar 19, 2017 11:50 pm

Hi Bren,

>If at any point in the future you are able to point me towards German documentation like this - or similar writeups you have done on the subject I would be most grateful.

Apologies that this is taking me so long ... I just managed to fix the old computer with my "unsorted documents" folders, but so far I haven't been able to locate the document I'm looking for. Please stay tuned, I'll find it eventually!

Regards,

Henning (HoHun)
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