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What makes it go so far?

  1. Oct 5, 2014 #1
    I'm wondering about the huge 16 inch guns from world war 2 battleships. The muzzle velocity was About 2700 fps. This is similar to a rifle bullet.

    A battleship shell could travel about 33 miles! A riffle bullet with similar muzzle velocity not nearly so far (as far as I know). I don't know of any tests confirming this.

    What determines distance. Isn't it velocity. Once the shell leaves the muzzle it's travel depends on it's speed doesn't it? And If two objects have a muzzle velocity of 2700 fps wih the same elevation angle won't they travel the same distance?

    In other words won't a rifle bullet with the same muzzle velocity and elevation travel 33 miles?
     
  2. jcsd
  3. Oct 5, 2014 #2
    Bigger projectiles generally will have higher Reynolds number. The ratio of the mass to the air drag felt by a larger projectile is much lower than a small projectile.
     
  4. Oct 6, 2014 #3
    Plus I understand that a rifle bullet is generally fired horizontally, while a 16" ship gun is fired at a steep angle, artillery style. This will obviously increase the distance traveled. Then there's the question of what do you consider range: how far it can travel, or how far it can travel AND hit something AND do some damage.

    In a perfect world though with no air resistance, indeed both projectiles could travel the same distance.
     
  5. Oct 6, 2014 #4

    SteamKing

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    Besides angle of elevation, or Reynold's number, or whatever, the key factor in determining the range is going to be how much energy is imparted to the projectile when it is fired. A rifle bullet has a weight of less than an ounce (1/16 pound), while a 16" projectile weighs more than a ton (2000 lbs). The kinetic energy of a moving body is directly proportional to its mass and to the square of its velocity, thus, if two projectiles are fired at the same velocity, the heavier projectile has more kinetic energy leaving the gun. The 16" projectile will, however, not travel >2000 times farther than the rifle bullet fired at the same velocity and angle of elevation because the range of each projectile will be limited by the amount of energy lost overcoming friction as each travels thru the air.
     
  6. Oct 6, 2014 #5

    russ_watters

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    I'd describe it as a matter of geometry. Most of the drag comes from the cross sectional area and while doubling the dimensions yield four times the cross sectional area, it has eight times the volume and mass. So since mass scales more than area and drag, drag has much less of an impact on a larger shell.

    This is also why large vehicles (trucks, trains, ships) are more efficient than smaller ones(cars) and large planes more efficient than small ones per mass moved.
     
  7. Oct 6, 2014 #6

    I dont think energy is relevant since muzzle velocity takes that into account. If each projectile leaves the muzzle at the same speed then from that point on gravity is the only factor (if you dont take into account air resistence).

    The reason I ask is precisely because we always think of a rifle being shot most horizontally, not at elevation. And, even if a bullet went 33 miles there would be no way to know because we'd never find it. As opposed to a 16 inch shell that will explode on contact, giving us that information.

    We always hear that we shouldn't shoot a rifle or pistol into the air because we don't know where it will hit. It never occurred to me that it might hit tens of miles downrange rather than just one or two miles.

    I guess the Reynolds number would come into play in penetration power thru the air making the smaller bullet more susceptible to air resistence.

    Here's another interesting thought. If you got directly behind one of those 16 inch guns when it fired do you think you could see that big of a projectile as it traveled away from you even at 2700 fps. I think so because after one second it would only be a mile from you and I think I could see a 72 inch x 16 inch projectile at one mile, maybe two.

    tex
     
  8. Oct 6, 2014 #7

    russ_watters

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    I'm not sure if you were agreeing or disagreeing with me, but I didn't mention energy in my post...

    It may be instructive at this point to do a theoretical projectile motion problem and calculate the theoretical maximum (no air resistance) range. Do you know how to do that?
     
  9. Oct 6, 2014 #8

    SteamKing

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    That's the problem. You must account for air resistance, and it is a problem which occupies quite a bit of time for designers of projectiles large and small.

    People warn against such behavior with firearms because if you shoot straight up, the guy firing the gun might become his own target.

    As also would having less mass. All the Reynolds number does is ensure that the flow conditions in different situations, for example testing a scale model against a full-sized object, are roughly equivalent.

    Several photographs of battleships firing main battery salvoes also captured the projectiles in flight quite clearly. However, it is not recommended that a person stand exposed near the blast of a large naval gun, as the overpressure can cause injury.

    Anywho, here is a shot of the USS Missouri firing her guns in WWII:
    http://www.history.navy.mil/photos/images/g40000/g47015.jpg [Broken]
    If you look at the upper right corner of the image, you'll see the shadows of the six shells which have just been fired from the forward turrets.
     
    Last edited by a moderator: May 7, 2017
  10. Oct 6, 2014 #9

    A.T.

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    Without air resistance, the entire premise of your question is gone, because rifle bullets fly just as far as bigger rounds of same muzzle speed.
     
  11. Oct 6, 2014 #10

    A.T.

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    Might still be healthier than trying to spot them coming in.
     
  12. Oct 6, 2014 #11

    SteamKing

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    When the Iowa class was being reactivated and modernized in the 1980s, blast overpressure was a serious concern, because it was not known how modern electronics, weapons, and missiles would respond to the continuous firing of the main battery. A series of instrumented trials was conducted at the Naval Proving Grounds and aboard ship to collect data on how blast overpressure was affected by a number of different variables.

    I read one of the reports of these trials which was later published in the Naval Engineers' Journal. he article showed a photo of a regular basketball backstop which had been built by the after 16" turret on the USS New Jersey, I believe. After firing the guns of the after turret, the entire backboard had been shredded by the blast overpressure, so a new, specially reinforced backboard had to be constructed for crew recreation.

    I also believe the glass in the bridge windows forward was also made heavier to resist shattering when the forward guns fired. (The glassed in bridge was not part of the original design of these ships, but was added soon after they were commissioned in WWII.)
     
  13. Oct 6, 2014 #12

    OldEngr63

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    I think that there is no question but that these large guns were fired at relatively high elevation angles. If you look at the elevation of the guns on the MIghty MO as posted above by Steamking, it is pretty clear that they are firing at 25 deg above the horizontal, give or take a few degrees.

    There is also a question about just what the elevation angle is when the ship is rolling while firing. One of the "advances" in gunnery was to be able to time moment of firing with the roll of the ship.

    Accuracy was not great with these big guns. The British conducted some tests and discovered that they could rarely hit a target even at point blank range. I think intimidation was a major purpose, as well as actual destructive power.
     
  14. Oct 6, 2014 #13

    SteamKing

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    With all due respect to the Royal Navy, most of their heavy naval guns were leftovers built in World War I, and the ships which mounted them probably did not have the most advanced fire control equipment. The British introduced only one large naval gun between the wars, the 14"/45 caliber rifles which were carried by the King George V class of battleships. One of those vessels, the HMS Duke of York, engaged and sank the German battlecruiser Scharnhorst off the North Cape of Norway in a night action, where the British vessel did use radar to locate the enemy vessel.

    During WWII, the introduction of radar and its use as an aid to spotting the fall of shells and locating and tracking enemy vessels was a great advance in naval gunnery. Engaging a moving target at sea is one thing, but using naval gunfire to attack fixed, land-based targets is inherently more accurate, since a variety of means can be used to improve the aiming of the guns. In the Gulf War, the battleships Wisconsin and Missouri used UAVs launched from their decks to carry TV cameras, which allowed the fire-control personnel to observe the fall of the shots and to correct the aiming of the guns. It is said that when Iraqi soldiers saw UAVs flying overhead, they emerged from their positions and surrendered, lest they be blasted by the 16" gunfire which would soon follow.

    According to this article:

    http://arstechnica.com/information-...-mechanical-analog-computers-ruled-the-waves/

    the analog fire control systems on the battleships permitted an accuracy (CEP) of about 80 m when engaging targets ashore.

    More modern projectiles have been planned which would incorporate GPS and active guidance, but the cost per unit has prevented widespread adoption. In contrast, most aerial bombs use some sort of precision guidance system to increase accuracy.

    Edit: The Royal Navy actually introduced two classes of heavy guns between the wars. The first was the 16"/45 cal. weapon mounted on HMS Nelson and HMS Rodney, commissioned in 1927. The later 14" weapon was did not enter service until 1940, after WWII had started, although the this weapon was designed before 1939.

    OTOH, the USN in the 1930s designed and developed the 16"/45 Mk. 6 and the 16"/50 Mk. 7 guns for new construction, the 16"/45 Mks. 5 and 8 to replace weapons in older battleships; the 14"/50 Mks. 7 and 11 and the 14"/45 Mks. 8, 9, 10, and 12 were re-manufactured weapons designed to improve accuracy and firing life for older battleships equipped with these calibers; and an entirely new 12"/50 Mk 8 weapon carried by the large cruisers USS Alaska and USS Guam.
     
    Last edited: Oct 11, 2014
  15. Oct 7, 2014 #14
    A few comments and a question -
    I recall reading somewhere that a .22 LongRifle bullet fired at 45 degrees will travel ~1 mile.
    I am curious about the risk of firing straight up since the bullet cannot exceed terminal velocity at ground (or head) impact. It seems it would hurt rather a lot and if it hit point first, probably break the skin, but almost certainly not cause any significant bone damage.

    Which brings up the question - Does anyone know if large naval rifle's bullets began to tumble at some point in their trajectory? I've heard rifle afficionados say that tumbling is rather commonplace is some hand held rifles
     
  16. Oct 7, 2014 #15

    SteamKing

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    Recent incidents of bystanders getting hit by 'celebratory gunfire' during New Years Eve, etc., would belie this estimation. IMO, you don't want to beonthe wrong side of a bullet, spent or otherwise.

    Shells are designed to be spun to sufficient speed during their travel thru the rifling of the gun to stabilize them in flight. However, when firing simultaneously two or three guns located close together, the flight of the shells can disturb one another sufficiently to cause loss of accuracy at the target. To prevent this interaction, special timing circuits are installed in the firing controls, so that the guns fire with momentary delays from one another, to give each shell separation from the others to minimize any adverse interaction during flight.
     
  17. Oct 7, 2014 #16

    A.T.

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    Is this only for subsonic shells, or because all go subsonic at some point? Or can even supersonic shells flying side by side affect each other?
     
  18. Oct 7, 2014 #17

    SteamKing

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    Shells traveling at supersonic speeds generate shock waves which emanate from the body. How these shock waves interact between shells traveling in close proximity to one another is difficult to study, so the most practical solution is to allow the shells to proceed downrange at slightly staggered intervals to minimize the interaction. The intervals we are talking about are less than 0.10 sec, so a shell fired with a muzzle velocity of 2500 fps would be traveling about 200 feet or so (say 60 meters) from the next shell.

    The earlier in the flight of a projectile any problems occur will only magnify the inaccuracy of the shell when it reaches its target, especially at longer ranges.

    Most shells fired at supersonic speed remain so during their entire trajectory, as a spent shell (one traveling at very low speed) reaching the target loses almost all of its ability to penetrate any armor or other protection. Armor-piercing naval shells, like those fired from a 16" gun, weigh 2700 pounds (1225 kg), are designed to penetrate the armor on the target vessel and explode inside the ship. The shell carries a small bursting charge, which is the explosive which detonates inside the target once the shell has penetrated the armor, which is only about 40 lbs (less than 20 kg). Most of the weight of the shell is devoted to providing the steel which defeats the armor, and the shell can only defeat the armor if it strikes it while still traveling at high speed.

    Only certain types of weapons, AFAIK, are designed to fire subsonic rounds, and these are intended for use in short range situations.
     
  19. Oct 7, 2014 #18

    SteamKing

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    When the Iowas were reactivated in the 1980s and fitted with modern fire control technology, the USN conducted a series of gunnery tests in the Mediterranean. As result of these tests, the Navy found:

    When the USS New Jersey was operating off Vietnam in 1968-69, her gunfire was sometimes used for unconventional, though eminently practical purposes:

    Source: http://www.navweaps.com/Weapons/WNUS_16-50_mk7.htm
     
  20. Oct 7, 2014 #19

    A.T.

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    I was thinking about two supersonic shells traveling side by side, but outside of each others shock cones. In such a case they should not affect each other. But while they get slower, the cones open up and reach the other projectile.

    It is obviously simpler to just delay them, so they are inside the cone of the previous shell, and never cross the shock wave.
     
  21. Oct 7, 2014 #20

    SteamKing

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    When arranging land-based artillery, one can certainly place individual guns to lessen interference with one another. Also, a firing schedule is usually developed and followed in which a battery of guns may fire at different times.

    On a ship, however, the guns are usually mounted in a turret, close together. When firing salvoes, that is several or all guns firing at once, about the only factor which can be controlled is inserting a slight delay in the firing circuit. For example, in a USN 16" turret, you have three guns located 10 feet apart, so the interaction between shells is a distinct possibility.

    I read a story one time about a problem which occurred during gunnery practice which a particular US battleship experienced. The practices were held before WWII, so spotting of the shot had to be done visually. The ship in question was firing all three guns from one turret during the practice, but the accuracy in hitting the practice target was less than expected. Many practice shots were made, and various fixes were tried. Finally, someone looked at the data collected and realized that due to various interactions while the shells were in flight, the shells from the right gun and the left gun 'flipped over' one another while aloft, and this motion was affecting the accuracy of the shells downrange. By inserting a slight delay in the firing mechanism, the effects of the flips were reduced, and accuracy improved.

    The Royal Navy experience similar problems with some of their cruiser guns in some ships constructed just before the war. The solution chosen by the British was to mount the center gun in the turret in a location slightly offset from the outer two guns, rather than using timing delays. This arrangement can still be seen in the cruiser HMS Belfast, which is moored at London:

    HMS+Belfast+a+%2526+B+turrets.JPG
     
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