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Howcome Yak 9 could fit machine guns over the nose

Moderators: hunter368, DerAdlerIstGelandet

Howcome Yak 9 could fit machine guns over the nose

Postby Invisible shadow » Wed Dec 21, 2016 6:52 pm

of 12.7 millimeter, but allies couldn't? Block size?


http://www.bing.com/images/search?q=yak ... ajaxhist=0
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Re: Howcome Yak 9 could fit machine guns over the nose

Postby lumino » Thu Dec 22, 2016 7:35 pm

https://en.wikipedia.org/wiki/Bell_P-39 ... ternal.jpg
P-39 had two synchronized 12.7mm ove the engine, no?
early P-40?


ussr was one of the allies, btw.
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Re: Howcome Yak 9 could fit machine guns over the nose

Postby Invisible shadow » Fri Dec 23, 2016 3:40 am

I thought P-40 had 30 cals.

How bout it, yer right.

http://www.p40warhawk.com/Models/Review ... /P-40B.htm

The P-40 was armed with two .50 machine guns in the nose and one .30 machine gun in each wing. Flush riveting was used to reduce drag. Since the P-40 lacked armor for the pilot, self sealing fuel tanks, and a bulletproof windshield, it was not considered suitable for combat and was pulled from combat duty on October 22, 1942


OK, Western Allies.
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Re: Howcome Yak 9 could fit machine guns over the nose

Postby Invisible shadow » Tue Dec 27, 2016 6:10 pm

P-39 doesn't count, not mounted over engine.
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Re: Howcome Yak 9 could fit machine guns over the nose

Postby Invisible shadow » Mon Jan 02, 2017 6:27 pm

The early P-51 had 30 cals under nose, but deleted these when Merlin adopted.

The Japanese switched to from 30 cal to 12.7 mm on I think it was the Hayabusa? but found the rate of fire dropped dramatically. Plus when one has 4 blades instead of 3, there is less romm for projectiles to pass through.
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Re: Howcome Yak 9 could fit machine guns over the nose

Postby Invisible shadow » Mon Jan 02, 2017 6:29 pm

The early P-51 had 30 cals under nose, but deleted these when Merlin adopted.

The Japanese switched to from 30 cal to 12.7 mm on I think it was the Hayabusa? KI 43 1c but found the rate of fire dropped dramatically. Plus when one has 4 blades instead of 3, there is less romm for projectiles to pass through.


Plus the germans had electric priming & Allies didn't, so there may be another clue.

http://www.militaryfactory.com/aircraft ... aft_id=617
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Re: Howcome Yak 9 could fit machine guns over the nose

Postby Denniss » Tue Jan 03, 2017 12:50 pm

US .50 lost a lot of RoF if synchronized, AFAIR japanese gun was based on/reverse engineered the US .50
Don't know how the russian 12.7 was but I assume they were better suited for sync firing.
With a good sync mechanism there should not be a huge RoF difference between 4 small blades or 3 wide blades on the prop.
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Re: Howcome Yak 9 could fit machine guns over the nose

Postby Invisible shadow » Tue Jan 03, 2017 7:58 pm

http://www.warbirdforum.com/jaafmgs.htm

By the time they went into combat, however, those planes had been relaced by the up-gunned Ki-43-I, whose usual armament was two large-caliber machineguns. In their postwar memoirs, Japanese pilots reported that the results were disappointing: the large-caliber gun fired so slowly that on many of their fighters, the armorers replaced the port weapon with the older, 7.7 mm gun, thus restoring the armament mix of the earlier plane.
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Re: Howcome Yak 9 could fit machine guns over the nose

Postby Invisible shadow » Sat Jan 07, 2017 7:00 pm

he says the chin guns were his idea, since guns mounted atop the fuselage somehow vibrated themselves out of synchronization and shot the propeller off!



My other grandfather, who’s still kicking at 78, is linked to two airplanes in my mind: the B-25 (he was bombardier on aircraft number 3!) and the A-36 Apache. He worked on the development of the Mustang at Wright-Patterson Army Air Base as a weapons expert, and he says the chin guns were his idea, since guns mounted atop the fuselage somehow vibrated themselves out of synchronization and shot the propeller off!

http://www.internetmodeler.com/1999/jan ... ustang.htm



Perhaps the Brownings vibrated too much compared to the MG 131? Electric priming make it smoother? One can only speculate.





















Anyone know the barrel life of a 50 cal browning?

barrel wore out much less quicky in MG 131, (barrel life of the MG 131 was 17 000 rounds), which meant that ballistic properties detoriated more slowly. Compared to Browning.
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Re: Howcome Yak 9 could fit machine guns over the nose

Postby HoHun » Fri Mar 17, 2017 5:00 pm

Hi Invisible,

>In their postwar memoirs, Japanese pilots reported that the results were disappointing: the large-caliber gun fired so slowly that on many of their fighters, the armorers replaced the port weapon with the older, 7.7 mm gun, thus restoring the armament mix of the earlier plane.

If someone would come up with an explanation for this, I'd really like to know.

Not that I doubt that the Japanese memoirs reported correctly, it's just that I have no clear idea on why a synchronizer would on one hand work well enough to synchronize effectively, but on the other hand work badly enough to slow down the rate of fire.

Regards,

Henning (HoHun)
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Re: Howcome Yak 9 could fit machine guns over the nose

Postby HoHun » Fri Mar 17, 2017 5:05 pm

Hi Invisible,

>Perhaps the Brownings vibrated too much compared to the MG 131? Electric priming make it smoother?

Since the Browning fired a significantly more powerful cartridge, it's quite reasonable that it might produce more powerful vibrations. I don't think electric priming made much of a difference in that regard.

Regards,

Henning (HoHun)
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Re: Howcome Yak 9 could fit machine guns over the nose

Postby Denniss » Sat Mar 18, 2017 8:44 pm

The firing mechanism of the .50s was not well suited for synchronized firing and lost a lot of RoF while doing so.
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Re: Howcome Yak 9 could fit machine guns over the nose

Postby HoHun » Sun Mar 19, 2017 11:08 am

Hi Denniss,

>The firing mechanism of the .50s was not well suited for synchronized firing and lost a lot of RoF while doing so.

You're probably right, but what I'd like to know is the root cause :-)

The time for cyclic operation was obviously low enough for a high rate of fire ... for example, 600 rounds per minute would give a cycle period of 100 ms.

At full engine speed of 3000 rpm (50 Hz), the V-1710 would turn the propeller at half the speed (25 Hz), and with three blades on the propeller, we'd have propeller blades going past the muzzle at 75 Hz. One thing I haven't been able to figure out is whether propeller synchronizers utilized every gap between the blades, or only one per revolution. If it's just one firing opportunity per revolution, as I tend to believe, we'd be stuck at 25 Hz, or every 40 ms.

So this would lead to the sequence ...

0 ms = gun fires
40 ms = gun is cycling
80 ms = gun is cycling
100 ms = gun has cycled and could fire again
120 ms = gun is triggered

Instead of 100 ms per cycle, we'd be up to 120 ms per cycle, but that's a loss of just below 20%, and it would be independend of the type of gun.

Maybe the root cause would be a very slow trigger action? In the above example, there are 20 ms "idle" time before the gun is triggered the second time, and if the trigger action needs 20 ms or less, the synchronizer would actually have been adjusted to trigger a bit early. However, if the free firing gun requires 100 ms for a cycle, but the trigger mechanism needs 100 ms between actuation and firing, then the rate of fire for individually triggered shots would be only have the free-firing rate.

I have no idea if this thought is correct though, and how I could confirm it - I have never seen data on this aspect of gunnery.

I would think that it is desirable to have a fast-acting trigger mechanism in air combat, and I believe the British pressurized air system was designed to provide faster acutation of wing guns then possible with Bowden cables. I have also seen slow initial spin-up listed as a disadvantage of Gatling guns, which is a related issue.

(By the way, years ago there was a neat animation of the synchronization on Emmanual Gustin's site, but I can't seem to find it anymore. If someone had a link to that, it would be highly appreciated!)

Regards,

Henning (HoHun)
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