# External ballistics

Yes, I know this isn't strictly metalworking, but there are plenty of gun people here. A howitzer fires, with elevation 45 degs. So the shell exits, pointing
upward at 45 degs., spinning. When it hits the target, it is (to 1st approximation) falling at 45 degs., but the spin should have kept it pointing upward. This means it would be flying sideways-on. This sounds wrong to me, but where is the error?
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On Thursday, March 9, 2017 at 9:52:34 PM UTC-5, David R Brooks wrote:

I don't know if this is a really accurate description of the dynamics, but this is the way it was explained to me, and it makes sense. It starts with the idea that aerodynamic force overcomes the gyroscopic effect, and the pi tch of the shell is a response to greater aerodynamic force being applied * behind* the center of gravity:
http://www.4point2.org/ballistics.htm
Maybe someone will have a more precise explanation.
--
Ed Huntress

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On 10-Mar-17 10:52 AM, David R Brooks wrote:

Aerodynamics does the steering / turning?
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On Fri, 10 Mar 2017 10:52:30 +0800, David R Brooks

The short answer is that the entire shell is effected by gravity. The spin serves only to stabilize it just like a top. As the shell is symmetrical there is effectively no lift developed by the spinning shell, i.e., if one side is going up the other side with exactly the same shape, size and velocity is going down :-)
The spin serves to stabilize the shell and is a complex subject. See http://bisonballistics.com/articles/modern-exterior-ballistics-by-robert-mccoy for a review of a book giving a rather complete explanation of exterior ballistics.
It might also be noted that a cross wind does effect the bullet/shell's flight and a cross wind will generally move the bullet/shell. A wind from the right tends to move the bullet in the direction of 10 o'clock while from the left to toward the 4 o'clock. Note that this movement depends on the direction of spin of the bullet/shell as well as wind direction.
There has been rather extensive studies of exterior ballistics since at least the 1800's. Siacci's theorem in dynamics is the resolution of the acceleration vector of a particle into radial and tangential components, which are generally not perpendicular to one another. Siacci formulated this decomposition in two papers which were published in 1879.
--
Cheers,

John B.
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On Thursday, March 9, 2017 at 9:52:34 PM UTC-5, David R Brooks wrote:

The shell flies with its axis in line with the direction that the shell is moving. So the shell starts out pointed up by 45 degrees , it flight path changes a nd its orientation also changes. Since the shell is spinning , changing th e orientation causes it to precess. And the shell changes from not only th e angle up but also changes sideways. So a shell with a clockwise rotatio n fired due west, will turn so it is going south west.
And it gets worse. A shell fired due North in the Northern hemisphere wil l go somewhat East because of the Coriolis effect.
Dan
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On Thursday, March 9, 2017 at 9:52:34 PM UTC-5, David R Brooks wrote:

The shell flies with its axis in line with the direction that the shell is moving. So the shell starts out pointed up by 45 degrees , it flight path changes and its orientation also changes. Since the shell is spinning , changing the orientation causes it to precess. And the shell changes from not only the angle up but also changes sideways. So a shell with a clockwise rotation fired due west, will turn so it is going south west.
And it gets worse. A shell fired due North in the Northern hemisphere will go somewhat East because of the Coriolis effect.
Dan ============= At the WW1 Battle of the Falkland Islands the Northern Hemisphere Coriolis correction in the British firing tables didn't hurt their shooting. https://en.wikipedia.org/wiki/Battle_of_the_Falkland_Islands
The link to Felix von Luckner in 'Outcome' is interesting. English-language history omits a lot about our enemies, for instance in German history Rome never fell, they rightfully inherited control. https://en.wikipedia.org/wiki/Theoderic_the_Great "Seeking to restore the glory of Ancient Rome, he ruled Italy in its most peaceful and prosperous period since Valentinian.."
-jsw
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This is the British Dreyer Fire Control Table, literally a 4-leg table: http://dreadnoughtproject.org/tfs/index.php/Dreyer_Fire_Control_Table
The problem is to reconstruct the enemy's course relative to your own and then calculate the gun angles to place shells on where he will be after the shell's time of flight, assuming both ships hold straight courses, which they must when firing at each other this way. A fast ship too small to shoot back might confound the system by maneuvering.
By WW2 US radar fire control was automated enough to shoot back accurately while dodging enemy shells. https://en.wikipedia.org/wiki/USS_Johnston_ (DD-557) Large armor piercing naval shells tend to act like solid cannonballs and just punch a hole their size when they strike thin-skinned targets that don't slow the shells enough to detonate them.
Some of those torpedoes may have been the spread that chased the monstrous battleship Yamato away from the action. The Japanese mistook those incredibly bold little destroyers for larger cruisers.
-jsw
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snipped-for-privacy@krl.org wrote:

Well, it seems the people who designed the Rheinmetall Rh120 knew what they were doing.
--

"I'm a doctor, not a mechanic." Dr Leonard McCoy < snipped-for-privacy@ncc1701.starfleet.fed>
"I'm a mechanic, not a doctor." Volker Borchert <v snipped-for-privacy@despammed.com>
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wrote:

Joseph Whitworth knew what he was doing in 1860. http://civilwarwiki.net/wiki/12_pdr._Whitworth_Breechloading_Rifle "At 1600 yards the Whitworth gun fired 10 shots with a lateral deviation of only 5 inches."
But the Confederacy had only a few pieces of superior British artillery, and Lee's Chief of Artillery was incompetent. https://en.wikipedia.org/wiki/William_N._Pendleton At Gettysburg Lee chose a talented but inexperienced junior officer to command the artillery and Pendleton mainly interfered with him. The Union artillery commander tricked him by pulling guns out of action randomly as though they had been destroyed. Gunpowder smoke obscured what was really happening. Expecting a disaster he'd been unable to prevent, General Longstreet delegated the decision on when the infantry should charge to the junior artillery officer who didn't realize he hadn't really crushed the opposition that then massacred Picket's Charge.
-jsw
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On Sun, 12 Mar 2017 11:18:28 -0400, "Jim Wilkins"

I think I would take that figure with a grain of salt. After all, at 1,000 yards with a muzzle velocity of 1,300 fps ( probably similar to the Whitworth ) with a .45-90 rifle, wind drift is approximately 15" per mph of wind speed, at 90 degrees to the line of sight. Even air temperature and humidity has a measurable effect at these kind of ranges.

--
Cheers,

John B.
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wrote:

<snip>
I think he was referring to the Whitworth rifled cannon, 2.75" bore, hexagonal rifling with a matching twisted "long bolt" projectile. Don't know the velocity, but it probably had a very high ballistic coefficient due to mass as much as shape.
Pete
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On Mon, 13 Mar 2017 07:30:37 -0500, Pete Keillor

Yes, I was aware of that. But one of the determining factors in wind drift is the amount of time the projectile is exposed to the wind, i.e., distance and muzzle velocity. From all I could find on the net the Whitworth 12 pound had a muzzle velocity of 1,500 fps thus wind drift might have been in the neighborhood of 1300/1500 of the .45 cal rifle I mentioned. Perhaps 13"/mph.
My point was that the figure given (the Whitworth gun fired 10 shots with a lateral deviation of only 5 inches.), which seems to a quotation from one magazine article, is very highly unlikely.
--
Cheers,

John B.
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wrote:

I've read historical accounts on military matters that show reporters weren't any better educated in technology then than they are now. The report could be interpreted as a 5" radius of the pattern and doesn't tell how far it was from the point of aim. Presumably the team trying to sell the gun would choose a calm morning in Foggy Bottom. -jsw
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On Mon, 13 Mar 2017 21:20:14 -0400, "Jim Wilkins"

True, but even today's artillery, which one assumes are more accurate than a weapon built in the mid 1800's doesn't have the accuracy claimed for the Whitworth. In fact at the end of WW II the standard of accuracy for light artillery which approximates the 12 pound horse drawn artillery used the field in 1860 was "1 in 500" so for 1600 yards the standard, in 1945, would be 2.3 yards. (which is a bit different than 5 inches :-)
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Cheers,

John B.
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wrote:

You can't compare a new barrel to one worn to the relining standard.
A Whitworth in action:

http://www.accurateshooter.com/competition/1000-yard-benchrest-guide/ "When conditions are right, a good shooter can put ten shots into a pattern you can cover with the palm of your hand."
http://riflebarrels.com/winners-world-records/1000-yards/
https://en.wikipedia.org/wiki/Billy_Dixon
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wrote:

I've seen evidence that the allowance was 1 in 400 for battleship guns which had the added problems of the rolling of the ship and interfering with each other through their toilet-shattering vibration and the leading shell's shock wave. The middle barrel was delayed by 50 milliseconds to help.
They determined barrel life from the numbers of shots fired at various charge weights. It was a fairly small multiple of the number of shells they carried.
This shows how closely pairs of shells from new barrels hit: http://www.navweaps.com/index_lundgren/Kirishima_Damage_Analysis.pdf
The barrel of the WW1 Paris Gun wore so quickly that the shells had to be fired in numerical order of increasing diameter. http://www.firstworldwar.com/atoz/parisgun.htm
-jsw
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