Aircraft guns and bullet behavior

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Felix C
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Re: Aircraft guns and bullet behavior

Post by Felix C » 30 Aug 2014 18:40

I imagine the guns on that particular aircraft are harmonized to concentrate somewhere from 1000 to 400 yards.

Have all seen footage in color of a P51 strafing an IJN minor warship, DE, and causing a boiler explosion due to the .50s penetrating the hull/deck plating. One can see how the tracers close in towards an apex. It is in one of the Time-Life volumes dealing with the late war years against Japan.

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Re: Aircraft guns and bullet behavior

Post by Carl Schwamberger » 30 Aug 2014 20:31

Felix C wrote:I imagine the guns on that particular aircraft are harmonized to concentrate somewhere from 1000 to 400 yards.
....
IIRC it was 250 yards for USAAF wing mounted MG on single engine aircraft. However the optimal concentration zone was far longer.

islandee
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Re: Aircraft guns and bullet behavior

Post by islandee » 31 Aug 2014 03:45

Carl Schwamberger wrote ". . . 250 yards for USAAF wing mounted MG on single engine aircraft. However the optimal concentration zone was far longer."

I would guess I have a problem with jargon: for example, "optimal concentration zone", and more. If we can discuss, for starters, this from Manual for Fighter Gun Harmonization, p 1:

Image

I must be looking at this wrongly, for it seems to contradict itself.

I look at the various patterns for, say, a P-51D, in the manual (p 37):

Image

And in the second chart above I see the focus or point of convergence at 1100 feet with a dispersion width of 6 feet (3 feet either side of the centerline). At 1200 feet, a trajectory width of 8 feet (4 feet either side); and at 2000 feet, a trajectory width of 22 feet (11 feet either side). The dispersion pattern for 1200 feet shows closely overlapping MG patterns while that for 2000 feet shows two groupings with larger diameter component circles separated by 2 and 4 feet. The situations at 1200 and 2000 feet appear quite different.

I can't reconcile that with ". . .a harmonization based on 1200 feet would result in the same bullet patterns as for 2000-foot harmonization . . . ."

What am I missing?

And then (finally) I come to "optimal concentration zone". Does that term fit in with the data in these diagrams?

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Re: Aircraft guns and bullet behavior

Post by Carl Schwamberger » 01 Sep 2014 05:12

Hmmm... my expertise is in field artillery, with a minor in ground machine gun technique. But lets look at the diagram, the top view. Convergence there starts at about 700 to 800 feet, which is close enough to 250 yards. This 'converged' zone extends out to about 1300 feet or 400 to 430 yards in the graphic.

islandee
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Re: Aircraft guns and bullet behavior

Post by islandee » 01 Sep 2014 09:07

Okay: I see how you're defining "concentration zone". It fits. Thank you.

Any thoughts on how/why the book equates bullet patterns at 1200 and 2000 feet?

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Re: Aircraft guns and bullet behavior

Post by Carl Schwamberger » 02 Sep 2014 02:10

No. Looking at the diagrams I cant see a correlation between those two ranges. Either in cross section or the horizontal plane. In the vertical plane the difference is not very great. Maybe I am missing the point in the math?

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LWD
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Re: Aircraft guns and bullet behavior

Post by LWD » 02 Sep 2014 13:41

Just a guess. It looks to me like that setting the guns to converge at 1,200 ft would mean that the bullets at 2,000 ft are close to the same seperation as the guns (all be it mirror imaged). After that hitting would become quite problematic.

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Re: Aircraft guns and bullet behavior

Post by Carl Schwamberger » 03 Sep 2014 01:10

Yeah, looking at the cross sectional diagrams the number of rounds per sq meter or foot is dropping off and does so rapidly beyond 1000 or 1200 feet.

islandee
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Re: Aircraft guns and bullet behavior

Post by islandee » 04 Sep 2014 08:17

Thanks: I'll live with that.

islandee
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Re: Aircraft guns and bullet behavior

Post by islandee » 23 Sep 2014 16:29

I'm in the process of writing up what all I have to date on the two 20mm shell holes in the San Khayom bridge. I still have to deal with the 57mm shell hole (Point G).

I've not found as yet any aircraft, either Allied or IJAAF, operating over Thailand that used a 57mm cannon. On the ground, the Japanese had a Type 97 57mm Tank Gun, used in a Type 97 Medium Tank "Chi-Ha". The gun would have been firing at the RAF Beaufighter or USAAF P-38 which was putting the 20mm holes in Points A and F of the bridge. The scenario in itself is not farfetched: 170 km SE at the Kaeng Luang Bridge, an enterprising Thai gunner using an anti-tank gun shot down a B-25. But at the San Khayom bridge, no Allied plane was downed though it might have been targeted.

I've found no record of tanks with 57mm guns or independently-mounted (jury-rigged) 57mm tank guns having been assigned or used at Lamphun; however, I see two possibilities by which such a tank or tank gun might have been present to defend the Lamphun bridge (plus a longer bridge just 6 km north):

1. One of the main IJA supply routes for Burma followed the railroad from Bangkok to Lampang, 80 km south of San Khayom, where goods were transferred to road vehicles for transport to Kengtung, on to Mandalay, and then in 1944 to Imphal/Kohima, etc. There is also a story that an alternate supply route continued north by rail to Chiang Mai where goods were transferred for transport north into Burma. In both cases, rail transport came under heavy attack by Allied aircraft starting in early 1944 (there doesn't seem to have been much recorded of attacks on road convoys). I'm guessing that those Allied air attacks might have damaged one or more tanks or their carriers sufficiently that they were abandoned along the way. Afterwards, enterprising Thais or Japanese might have salvaged a tank, or a tank gun, for anti-aircraft defense at Lamphun.
2. In preparation for defending Thailand very near the end of the war, various IJA units were assigned to the general Chiang Mai area to meet any Allied ground attack from the north. IJA units included elements of the 4th and the 56th Divisions as part of the 15th Army which was itself headquartered in Lampang. All were essentially in position by June 1945. These units might somehow have acquired some Type 97 Medium Tanks, or at the least a Type 97 57mm Tank Gun, which found its way to the Lamphun area.

While this is wholly speculative, I do have the hole in the bridge which records the diameter of the projectile, its angle of impact, and its bearing. If I could get a set of ballistics curves for the tank gun, I might be able to estimate the location of the gun, if it had been fired from the ground, and check that ground for any possible evidence (that's where the metal detector will be a necessity).

So I ask, does anyone have or know how to get ballistics curves for this Type 97, 57mm tank gun?

I thank you.

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Re: Aircraft guns and bullet behavior

Post by Carl Schwamberger » 24 Sep 2014 12:12

My first thought is to ask here: http://forum.axishistory.com/viewforum.php?f=65

islandee
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Re: Aircraft guns and bullet behavior

Post by islandee » 25 Sep 2014 16:04

Done. Thank you.

islandee
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Re: Aircraft guns and bullet behavior

Post by islandee » 03 Nov 2014 02:05

I've attempted to finalize my webpages on this subject, but am of course still interested in feedback. There are some topics which I leave open: some seem more effort than is warranted; others can have no answers; a metal detector is on order as a long shot.

I greatly appreciate the direction I've received from various contributors on this forum: I think I've learned a good bit about ballistics and have hopefully corrected all of my naive statements in my first draft aired here in early March. I especially appreciate LWD's guidance.

My treatment of this subject has grown to 11 webpages (which start here), and offers more detail than the average reader probably cares to wade through. As a result, I've started the subject off with a single page condensation --- it's a long page, but just one.

I thank you again.

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colt45
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Re: Aircraft guns and bullet behavior

Post by colt45 » 05 Dec 2014 14:20

a 20 MM ...noen 375 on bottom with 1943 date , 7" long . was it used in a P - 38 plane?

islandee
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Re: Aircraft guns and bullet behavior

Post by islandee » 05 Dec 2014 16:14

You've got the advantage of me. I don't understand "neon 375".

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