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ATST Snippet #6 (I think)

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Re: ATST Snippet #6 (I think)
Post by EdThomas   » Tue Sep 06, 2016 11:24 pm

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WeberFan wrote: Snip
CASE 1, the cannon is on a ship that is rolling. Snip

CASE 2: The ship is "heaving."

I think you missed another important factor - forward motion. Boats in a seaway move in three dimensions. The best way I've heard a boat's motion described is that of a corkscrew. Liners and large yachts have large fins that can be extended to limit the vessel's rolling motion. Trawlers extend large arms to the side to drag planes through the water to reduce rolling in order to improve control of the opening of the nets being dragged behind the boat.
The best way to reduce vertical movement is to place the vessel so that it's travelling with the waves (think synchronizing hull length with wave length - probably multiple waves :). Travelling across the waves may be the best way to reduce pitching (vertical and forward motion), but will put the vessel in the worst possible position for rolling. The worst possible course/path for a vessel to reduce roll and pitching is 45 degrees across the direction of the waves which creates the most extreme corkscrew (roll/vertical )motion.
If I'm driving a City or KHVII, I think I'm going to to turn downwind or upwind and try to match my speed with the waves to create the most stable platform I can. We've all seen too many war movies to not know carriers turn into the wind to launch aircraft. My question to any CV drivers out there is do you turn with the the wind to bring the kids home? And to any former gunnery officers out there, did your captain alter course to give you a more stable platform
BTW, Weberfan, thank you for your service.
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Re: ATST Snippet #6 (I think)
Post by n7axw   » Wed Sep 07, 2016 12:16 am

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WeberFan wrote:
n7axw wrote:I know that this idea would have its limitations. But I would think that a bigger, heavier ship would be a more stable, thus more accurate gunnery platform. And both the Cities and the Haarahlds are starting to be pretty good sized.

Don

-

Two kinds of errors that can cause a miss:
- Azimuth errors - shouldn't be too much of an issue given the relatively short ranges we're talking about here. To correct, just move the breech or muzzle a bit to the left or right. Of course you also need to adjust for the speed of the target and your own speed, but again the effects are relatively minor and easy to correct for.
- Ranging errors - a much more complicated issue, with two major factors:
If you know the ballistics of the projectile (either through a formula or through empirical testing), then you know how it will "fly through the air." This assumes (of course) that the launching platform isn't moving.
CASE 1, the cannon is on a ship that is rolling. A difference in the muzzle angle of as little as a single degree will cause a significant range error. The worse the roll (or the faster the roll) the less "easy" it will be to "time the shot" so that the projectile leaves the muzzle at exactly the right time. Further, with a ship that is rolling (let's assume the shot is fired "on the up roll"), the upward vector is imparted on the shell and will still be in effect AFTER the shell leaves the muzzle so you have to "lead the roll." The simple way to reduce this effect is to reduce the rolling of the shooting ship. Simplest way to do this is to increase its mass (reduce the rolling effect of wave action on the ship). A larger / more massive ship will inherently roll less than a smaller / less massive ship.
CASE 2: The ship is "heaving." In this case, the entire vessel is being displaced vertically. In this case, you have the same angle and projectile path of flight, but the entire path is displaced either up (top of the heave) or down (bottom of the heave). Mass is less of a factor in this case, because heaves are more often caused by larger ocean swells. And (as a former naval aviator who spent time landing on aircraft carriers massing up around 85,000 tons) I can tell you from personal experience that heaving is a non-trivial issue. Landed aboard ship one dark, dreary, stormy night in the Bering Sea where the entire 85,000 ton ship was heaving vertically in excess of 30 feet...

Range errors are far more difficult to correct for than azimuth errors. Improved fire control - to include a basic "automatic firing system" that takes into account roll angle, roll rate, firing system "lock time" (the time from when you pull the trigger to the time when the projectile actually leaves the barrel), and a couple of other factors, would be necessary if you want to improve the "first round" hit rate. And that (of course) also assumes a known, predictable ballistic flight path with known, predictable powder performance to give you that path.

Bismark's early hits on Hood were as much a feat of luck as they were of skill...


Thanks for the nice response. As I am interpreting what you are saying here is that while my earlier thought about bigger ships being more stable as weapons platforms is true but subject to some limitations and is only one of a variety of factors.

I don't have any problems with that. In fact, while aiming cannon from a completely stable ground installation you are still going to have variations that will prevent aiming accurately on a consistant basis from being completely automatic.

Don

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When any group seeks political power in God's name, both religion and politics are instantly corrupted.
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Re: ATST Snippet #6 (I think)
Post by JRM   » Wed Sep 07, 2016 7:05 am

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n7axw wrote:Thanks for the nice response. As I am interpreting what you are saying here is that while my earlier thought about bigger ships being more stable as weapons platforms is true but subject to some limitations and is only one of a variety of factors.

I don't have any problems with that. In fact, while aiming cannon from a completely stable ground installation you are still going to have variations that will prevent aiming accurately on a consistant basis from being completely automatic.

Don

-


Hi Don,

You are entirely right. Accuracy in naval gunnery is not an either/or, it is a continuum. ICN gunners are the best on Safehold because they aim the gun with sights, and because the gun captain fires the gun when he senses the ship has achieved a desired point in its' constant motion. Larger ships decrease the rolling motion.

PeterZ's gyroscope can move accuracy along the continuum, if it can decrease the degree of error caused by a ship rolling. I would add that PeterZ's gyroscope may be powered and triggered by pnuematic energy, but the transfer of the signal from the gyroscope to the gun, should be hydraulic. Air compresses, and the longer the line, the more compression and resulting signal lag you will get.

Observation balloons move accuracy further along the continuum. Strictly observation alone helps to reduce the degree of both azimuth, and range errors. Using range finders in combination with firing charts will reduce the number of shots required to zero in on the target.

We have not even talked about firing control computers (analog of course). To get the most value out of a firing control computer, the gun turret rotation, and the barrel elevation has to be controlled by the computer.

Could the ICN do all of this. Probably, but not this year. In ATST we will be lucky if we get gyroscopes and range finders.

Regardless of what is not there, what is there will make ICN and ICA guns significantly more accurate than any of their enemies.

James
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Re: ATST Snippet #6 (I think)
Post by Joat42   » Wed Sep 07, 2016 8:08 am

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Anyone considered what happens to a balloon thats tethered to a steaming ship?

Unless the balloon has a somewhat efficient aerodynamic shape it will bob madly which will put undue strain on the tether (and probably make any observer in the balloon spill his lunch).

---
Jack of all trades and destructive tinkerer.


Anyone who have simple solutions for complex problems is a fool.
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Re: ATST Snippet #6 (I think)
Post by WeberFan   » Wed Sep 07, 2016 11:03 am

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EdThomas wrote:
WeberFan wrote: Snip
CASE 1, the cannon is on a ship that is rolling. Snip

CASE 2: The ship is "heaving."

I think you missed another important factor - forward motion. Boats in a seaway move in three dimensions. The best way I've heard a boat's motion described is that of a corkscrew. Liners and large yachts have large fins that can be extended to limit the vessel's rolling motion. Trawlers extend large arms to the side to drag planes through the water to reduce rolling in order to improve control of the opening of the nets being dragged behind the boat.
The best way to reduce vertical movement is to place the vessel so that it's travelling with the waves (think synchronizing hull length with wave length - probably multiple waves :). Travelling across the waves may be the best way to reduce pitching (vertical and forward motion), but will put the vessel in the worst possible position for rolling. The worst possible course/path for a vessel to reduce roll and pitching is 45 degrees across the direction of the waves which creates the most extreme corkscrew (roll/vertical )motion.
If I'm driving a City or KHVII, I think I'm going to to turn downwind or upwind and try to match my speed with the waves to create the most stable platform I can. We've all seen too many war movies to not know carriers turn into the wind to launch aircraft. My question to any CV drivers out there is do you turn with the the wind to bring the kids home? And to any former gunnery officers out there, did your captain alter course to give you a more stable platform
BTW, Weberfan, thank you for your service.

Thanks, Ed.

As to the "forward motion" issue, I addressed it partially in the "azimuth error" section of my response. Of course that's not completely correct either. It's only truly valid if the vectors of the two vessels are parallel. If the target is moving generally parallel to the shooting ship, but there's SOME movement toward or away from the shooter, then you need to take that into account as well...

Get the sense that it's not an easy problem to solve "on the fly?" I recall from RFC's snippet the description of the gunner on Hektor's ship being in almost a zen-like state as he was preparing to fire...

Hardest thing I ever did was teach student pilots (last tour) how to drop bombs accurately... Maneuver a high performance aircraft to exactly the right altitude, exactly the right dive angle, exactly the right airspeed, exactly the right G-loading (1.000), in three-dimensional space, just as the pipper on the gunsight crossed the bullseye (or the correct aimpoint if there was any wind), then release your 28-pound blue practice bomb. Any errors would result in some pretty horrendous hits... Oh the stories I could tell you about students doing bone-headed things... :shock:
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Re: ATST Snippet #6 (I think)
Post by Dilandu   » Wed Sep 07, 2016 11:27 am

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Joat42 wrote:Anyone considered what happens to a balloon thats tethered to a steaming ship?

Unless the balloon has a somewhat efficient aerodynamic shape it will bob madly which will put undue strain on the tether (and probably make any observer in the balloon spill his lunch).


Please. just use kite baloon:

Image
------------------------------

Oh well, if shortening the front is what the Germans crave,
Let's shorten it to very end - the length of Fuhrer's grave.

(Red Army lyrics from 1945)
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Re: ATST Snippet #6 (I think)
Post by Louis R   » Wed Sep 07, 2016 11:28 am

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Ed, I think you accidentally cut an end quote too many. I stuck one in where it looks like it should be, but if i missed, apologies to both of you.

Neither an airplane driver nor a cannon-cocker, but I do know that aircraft _always_ land into the wind, or as close as they can get to it. The idea is to reduce speed over the ground compared to airspeed. Makes it a lot easier to stay up and in control until the wheels are down, and cuts the braking needed once they are. IIRC, carriers not only turn into the wind but go to flank speed for recovery. Gives the airdales as much as 50-60 knots of free lift at just the time they need it most.

Be interesting to see if there's anyone around who can answer the second question - actual gunnery isn't something most navies indulge in nowadays, and truly long-range gunnery hasn't been done for almost 1 career-length now even in the USN.


EdThomas wrote:
WeberFan wrote: Snip
CASE 1, the cannon is on a ship that is rolling. Snip

CASE 2: The ship is "heaving."


I think you missed another important factor - forward motion. Boats in a seaway move in three dimensions. The best way I've heard a boat's motion described is that of a corkscrew. Liners and large yachts have large fins that can be extended to limit the vessel's rolling motion. Trawlers extend large arms to the side to drag planes through the water to reduce rolling in order to improve control of the opening of the nets being dragged behind the boat.
The best way to reduce vertical movement is to place the vessel so that it's travelling with the waves (think synchronizing hull length with wave length - probably multiple waves :). Travelling across the waves may be the best way to reduce pitching (vertical and forward motion), but will put the vessel in the worst possible position for rolling. The worst possible course/path for a vessel to reduce roll and pitching is 45 degrees across the direction of the waves which creates the most extreme corkscrew (roll/vertical )motion.
If I'm driving a City or KHVII, I think I'm going to to turn downwind or upwind and try to match my speed with the waves to create the most stable platform I can. We've all seen too many war movies to not know carriers turn into the wind to launch aircraft. My question to any CV drivers out there is do you turn with the the wind to bring the kids home? And to any former gunnery officers out there, did your captain alter course to give you a more stable platform
BTW, Weberfan, thank you for your service.
[/quote]
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Re: ATST Snippet #6 (I think)
Post by jgnfld   » Wed Sep 07, 2016 12:00 pm

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WeberFan wrote: ...

Hardest thing I ever did was teach student pilots (last tour) how to drop bombs accurately... Maneuver a high performance aircraft to exactly the right altitude, exactly the right dive angle, exactly the right airspeed, exactly the right G-loading (1.000), in three-dimensional space, just as the pipper on the gunsight crossed the bullseye (or the correct aimpoint if there was any wind), then release your 28-pound blue practice bomb. Any errors would result in some pretty horrendous hits... Oh the stories I could tell you about students doing bone-headed things... :shock:


I would have thought that modern avionics computers would show where the (dumb) bomb was hitting in real time so that the pilot could maneuver to any one of a number of possible launch points. Not true???
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Re: ATST Snippet #6 (I think)
Post by WeberFan   » Wed Sep 07, 2016 1:23 pm

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jgnfld wrote:
WeberFan wrote: ...

Hardest thing I ever did was teach student pilots (last tour) how to drop bombs accurately... Maneuver a high performance aircraft to exactly the right altitude, exactly the right dive angle, exactly the right airspeed, exactly the right G-loading (1.000), in three-dimensional space, just as the pipper on the gunsight crossed the bullseye (or the correct aimpoint if there was any wind), then release your 28-pound blue practice bomb. Any errors would result in some pretty horrendous hits... Oh the stories I could tell you about students doing bone-headed things... :shock:


I would have thought that modern avionics computers would show where the (dumb) bomb was hitting in real time so that the pilot could maneuver to any one of a number of possible launch points. Not true???

What you say is very true. Called Constantly-Computed-Impact-Point (CCIP), the reticle or HUD continuously shows where the weapon will impact if you release it right....... NOW :P

What I was referring to in my post was "old-school" bombing instruction without any of those new-fangled computer thingies....
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Re: ATST Snippet #6 (I think)
Post by Weird Harold   » Wed Sep 07, 2016 1:40 pm

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WeberFan wrote:What you say is very true. Called Constantly-Computed-Impact-Point (CCIP), the reticle or HUD continuously shows where the weapon will impact if you release it right....... NOW :P

What I was referring to in my post was "old-school" bombing instruction without any of those new-fangled computer thingies....


Even with CCIP a pilot needs to fly a fairly smooth bombing run to have any reasonable sort of accuracy. The more you jimk, the harder it is to get the reticle to settle down so you can aim with it.
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Answers! I got lots of answers!

(Now if I could just find the right questions.)
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