By WW II, the data was fed directly into the computer by the various ship sensors and the computer even outputted "gun orders."
Other Sources of Error
Powder Conditions. Muzzle velocity increases with powder temperature. Figure a change of 2 fps per oF. (NAVORD 17B4 Col. 10). A damp powder burns more slowly, a dry one, more rapidly. Powder that has been in storage a long time may deteriorate, resulting in a lower initial velocity and also in increased pressure within the bore. (Alger 186).
Projectile Variation. Dahlgren, inspecting a heap of 32-pounder shot, found diameters of 6.22–6.28 inches, and weights of 32.43–33.00 pounds. With ten such rounds, at 3o elevation, the mean range was 1172 yards and the mean difference 18.4. If he used shot selected so the gauge range was 6.24–6.26 inches (weight 32.43–32.47), the mean range was 1195 yards and the mean difference only 10.3.
Variation in projectile weight has two opposing effects; a heavier projectile is accelerated less, in-bore, leaving with a lower muzzle velocity, and decelerated less in flight, giving it greater range for a given muzzle velocity.
Jump and Droop. If the gun, when fired, has a positive elevation, the force of discharge causes the gun to rotate, bringing the muzzle higher ("jump"). On the other hand, the length and weight of the gun may cause the muzzle to droop, so the "line" of bore is not truly a straight line. Jump and droop were not calculated directly, but the coefficient of form calculated by comparing computed ranges with experimental ranges is determined not merely by the projectile per se, but the jump and droop it experienced when fired. (Alger 167ff).
Air density. Early-twentieth-century range tables were calculated for a "standard atmosphere" of half saturated air, 15oC, 29.53" pressure. (Alger 189). Atmospheric pressure, temperature and humidity all affect air density and thus air resistance. For example, for Alger's standard problem 12" gun, range 10,000 yards, if the barometer were 29.00" and the thermometer 96oF, the air would be 9% below standard density, and the range achieved would be 194 yards higher. (189).
The effect of pressure and temperature can be determined by the ideal gas law, and that of humidity estimated by comparing the molecular weights of water vapor and dry air.
Pressure, temperature and humidity all vary from place to place and from time to time, and to take them into account, you need to be able to measure them. That measurement, of course, will be for where the gun is located and could be a bit different at the target (or in-between). The first mercury barometer was invented in the 1640s, whereas the aneroid barometer was introduced in 1843. The first sealed alcohol-type thermometer was made by Grand Duke Ferdinando II de Medici in the 1650s, and the mercury thermometer in 1714. You may measure relative humidity by comparing the readings of wet and dry bulb thermometers after the wet bulb is taken out of water so that evaporation can occur.
The variation of air density with altitude is usually significant only for a high trajectory fire. The US Standard Atmosphere is in CRC and relates density to altitude. So it's easy enough to modify a numerical integration spreadsheet to calculate the density for each altitude rather than treat it as a constant.
A further complication is that temperature and humidity also affect the velocity of sound, and thus the Mach number of the projectile for a given speed. (Ingalls vii).
Per my spreadsheet, if altitude effects are ignored, a 24-pound iron ball projected 1600 fps at 45o ascends to 4385 feet, and ranges to 3467 yards. Including the effects of decreased gravity (99.96% at apex), air density ( 87.98%) and speed of sound (98.45%) , it climbs to 4459 feet, and ranges to 3617 yards.
Drift. The spin of the projectile fired from a rifled gun causes it to be deflected to one side; this drift increases with distance flown and is the net result of several forces. (Denny 113ff).
Projectile Angle of Attack. 3DOF methods assume that either the projectile is spherical, or that if elongated, its long axis is always tangential to the trajectory (zero angle of attack). In practice, it isn't. If it's a spin-stabilized projectile, the longitudinal axis will precess (rotate around) an equilibrium line, which itself is at an angle (the yaw of repose) to the direction of motion. The line points right for a right-hand spin. The yaw of repose thus is the average angle of attack. Air resistance increases as the angle of attack increases. The yaw of repose at apogee is perhaps 2o for an elevation of 50o, but 10o or more for an elevation of 65–70o. (Pope). For a statically stable non-spinning projectile, the nose points slightly above the trajectory. (Carlucci 255).
Wind. If we can measure the wind force and direction, then we can take it into account. Wind direction is easy, that's shown by a wind vane. I am not sure of the practicality of the early mechanical anemometers; the cup anemometer was invented in 1846 and I think that it would be fairly easy to duplicate. It may even be possible to measure the speed of rotation by mechanical or electrical means, but one must cope with the way the wind fluctuates. It will be necessary to calibrate the anemometer, i.e., determine the relationship between the speed with which it is rotating and the force of the wind. (EB11/Anemometer notes that some scientific literature falsely assume that the cup speed was one-third the wind speed.) The relation of anemometer rotation to wind speed can be determined by mounting the anemometer on a car and driving the car at a set speed on a day the air is still. That still leaves the problem of relating wind speed to wind force; this may be in a civil engineering handbook since builders of tall buildings must worry about wind loads.
Of course, we will just know the wind felt by the firing ship, and this will be the apparent wind felt by the ship (which is moving), rather than the true wind. So we must be able to convert the apparent wind on the ship to the true wind, and then that to the apparent wind felt by the projectile. That requires knowing the speed and direction of the firing ship.
Wind is less consistent than the other atmospheric conditions; it can change in direction and strength while the projectile is in flight. And there's not much we can do about that other than look for telltales down-range of how the wind is behaving there. Also, in general, ballisticians only consider horizontal winds; updrafts and downdrafts are ignored.
Smoke. The smoke produced by a broadside can be such that it is no longer possible to tell by eye when the cannon is pointing horizontally. One nineteenth-century British captain used a spirit level while his ship was motionless, in harbor, to make sure that all his guns were pointing horizontally, and then added heel scales to them to indicate the correction for the angle of heel (which could be measured in battle with a ship's pendulum and called off to the gun crews). This became common practice. (EB11/Ordnance; Douglas 218). Fortunately, the enemy's masts would usually be visible above the smoke, even when the hull wasn't, so the horizontal direction of fire could still be determined by sight. (220).
Miscellaneous. At higher ranges, gunners consider the Coriolis force caused by the rotation of the Earth (six-inch deflection at 1000 yards), the decrease of gravitational force with altitude, and the curvature of the Earth.
Farnsworth Gun Error Computer. This was a mechanical device, constructed in 1915, for determining the errors in range and deflection attributable to wind, firing ship motion, target motion, powder temperature, and atmospheric density. It appears to have been a kind of circular slide rule with graphic representations of the values in the ballistics tables. (Alger App. B).
The following table provides a sample of how changing conditions could create range and lateral errors. Do not make the mistake of assuming that the stated errors will hold true for other guns or projectiles, or other ranges; the underlying equations are highly nonlinear.
****
This article continues in Part 4, "Implements of Destruction."
A Purist Grownup Nerd, Kinda
Written by Kristine Kathryn Rusch
I used to make faces at people like me. People who would say about a story and/or a TV show and/or a game, movie, comic book—we used to call that [x] and it was sooooo much better in those days.
Then I found myself at one of the Oregon Coast Writing Workshops in which everyone had turned in an (assigned) urban fantasy story, and I caught myself thinking—although I didn’t say, exactly—“back when we called that contemporary fantasy, and we didn’t just have to stick it in a city for genre reasons.” Okay, maybe I did say some of that, but not all of it.
Still. I annoyed myself. And probably a bunch of the listeners.
And I can’t help it.
Because I’ve developed some serious pet peeves in the last twenty years.
Here they are in no particular order:
1. Vampires as sexy love partners, particularly for teenagers. Let me ask you this: why in God’s name are we celebrating that non-human creatures who prey on human beings are falling in love with teenagers? Especially when these non-humans are at least 100 years old. Why isn’t that pedophilia? And why in the hell are these guys (and they’re usually guys) hanging around high schools? And why is that sexy?
2. Were-creatures as sexy love partners, for frickin’ anyone. I’m going to be clear here: What follows is not metaphorical. If my lover turns into some big hairy beast in the middle of lovemaking, I am going to run screaming out of the room. I might call the police, if I think they’ll believe that I’m not totally insane, and then I will never ever ever see this guy again, even if when he’s a non-hairy non-beast he’s the nicest guy in the world. Prejudiced? Okay. I’m not into bestiality. Sorry. (Although my cats are probably relieved.)
3. The urban fantasy glut. Some urban fantasy writers are fan-tastic. I love what they do. The rest seem to follow a very stupid formula. Fight scene with the emotional depth of a game scenario, some character interaction, sex, fight scene, character interaction, Revelation!!!, fight scene . . . and I just don’t care any more. Theme? Nah. Voice? Not unless you count snark that sounds the same from character to character. Ethics? Not really. Morality? Not really.
And, I’m sorry, I’m probably being insulting to game scenarios. Some have tremendous emotional depth. Which means I’d rather be exploring some mythic world in a MMPRPG than reading one of these novels. . . .
4. Unintelligible science fiction. Okay, this one has always been a pet peeve of mine, from the time I started reading sf. I got my start with sf through Andre Norton, Star Trek, and Flowers For Algernon, so I’m biased toward human-centered sf adventure stories or at least to stories that have some rigorous science that makes me cry. The stuff that is all about the latest scientific discovery extrapolated to the year 2233 and written in “future language”? I find that stuff pretentious as hell.
And the idea that you can’t write an sf story without being original should be tossed out along with a lot of the other assumptions of the 1960s. Seriously. If you don’t want genre tropes to invade your fiction, then read nonfiction. Because every other genre allows repetition and expansion of basic ideas.
You know, like murder in a mystery or happily ever after in a romance. Sometimes spaceships go “whoosh!” in space opera. Get over it.
5. Post Human stories. These things are about what happens when humans are no longer human. You know, when technology gets so advanced that we no longer seem like people.
Um, humans are hard-wired to be human. Sorry. If you could figure out a way past the language barrier and some of the customs, you could have a great conversation with someone from Ancient Greece. You could talk democracy or slavery or heck, human sexuality in all of its forms. You could talk theater or whether or not your last marriage was happy. You could even discuss food.
Humans are humans are humans. If you want to write/read about something that’s not human, either pick an existing creature (Robert Crais just wrote a great dog point of view in his latest mystery novel, Suspect) or make up an alien. A true alien, not a Star Trek alien, which is often so American-normal that there are people in other countries who are weirder.
I admit, some of my crankiness does come from more than forty years of reading sf and fantasy. I do crave something—well, new isn’t exactly accurate. Well done is probably better.
Sure, I’ll read a story about a vampire in high school if the voice is good and the creep isn’t hitting on 16 year old girls (or if he is, make him the villain of the piece, for heaven’s sake). I’ll read about were-creatures if they can control their shifting (or nearly control it—I’m thinking of you, Mr. Banner. Yes, I know you’re not a werecreature, per se, but you do shift form) or if the out-of-control shifting is an issue, and not something that is (ahem) sexy. Unless, of course, the creature that finds it sexy is another werecreature of the same vintage. And even then, you’ll have to write me past some of the more graphic parts.
Eventually urban fantasy won’t be glutted and there will be room for a good contemporary fantasy set in Small Town USA with a little bit of magic or a hint of the supernatural. And there won’t be tons of senseless fight scenes.
When the glut goes away, only the best urban fantasy authors will remain. The copycats who can’t write good characters will leave, and we’ll move on to some other trend. But the best authors will remain, and urban fantasy or contemporary fantasy or whatever the hell you want to call it will be the better for it.
Honestly, I’ve read a few post-human stories that I like. Those stories have managed to convince me that some kind of technology will change part of the human condition, but not all of it. Those stories are rare.
But I’ll be frank: I’ll never get past my prejudice against unintelligible science fiction. I really don’t care about the latest idea, in fiction form. I love reading that stuff in non-fiction—by writers who make such topics interesting. Most of this “original” science fiction doesn’t have anything I read for, from characters, to heart, to a cool setting, to adventure. So I have to chalk this one up to disliking that particular genre is as hard-wired in my brain as . . . well, being human is.
Maybe I’m becoming a cranky old fart. Or maybe I’ve just read so much it’s hard to surprise me any more. But I do find that I’m a lot more tolerant of fiction that would have driven me bonkers in my politically correct twenties. So maybe I’m just a different person.
Or maybe it’s time you get off my lawn.
****
Contraflow!
Written by Paula Goodlett
One of my favorite cities is New Orleans, LA, so I was pretty happy when Eric told the Edboard that was where we're doing our annual mini-con.
Doubletree Hotel, New Orleans Airport, 2150 Veterans Memorial Boulevard, Kenner, LA, October 18 - 20, 2013.
Come see us, y'all.
Panels this year are going to be Weird Tech, two hours with Rick Boatright, Walt Boyes, Gorg Huff, Kevin Evans and no telling who else, in which we'll have an AK4 among other things—like working steam engines! Also, two hours of Music of the Ring, with David Carrico as our presenter and all that wonderful, wonderful music. There's going to be a whole panel on airships, hosted by Iver P. Cooper and Charles E. Gannon. Virginia is going to tell us how she built the grid; we'll do "how to get published in the Gazette," and the ever-popular "Snerking the Plots" with Eric. For details go here: http://www.contraflowscifi.org/
And then there's the food . . .
Poor boys. Boudin. Sauces galore. Gumbo. Shrimp Etouffe. Heck, red beans and rice. . . . The bread. Oh, my word, the bread. Chicory coffee and beignets at the Cafe du Monde. Oh, and jazz. Lots and lots of jazz.
Drool, drool, drool. Gotta stop this, girl.
I gain pounds I don't need just thinking about it. Not to mention all those happy feet over the jazz.
Y'all just gotta come on down, really you do.
Paula
Time Spike: Evening in Cahokia
Written by Garrett W. Vance
Part One of Two: Pyramids in the Corn
If Nate closed his eyes, he could almost imagine he was back home in Texas, sitting under the shady willows at his family's ranch on a summer evening, the smoke from the barbecue heralding the pleasures of the meal to come. Unfortunately, he co
uldn't close his eyes. He needed them to watch for approaching danger. For approaching monsters. He wasn't home anymore, nowhere near, and was pretty sure he would never set foot there again. At least he was sitting in the shade, although it was provided by a plant that looked like it couldn't make its mind up whether it was a tree or a cactus. He was careful not to lean against its thorny trunk.
The smoke actually did smell pretty good, but that was no trusty Texas beef they were roasting. It was a slab of genuine dragon leg. Nate watched as Gonzalo used a long, mean-looking dagger to carve it up as pretty as a Christmas goose. Nate took a careful bite. The dark, stringy meat reminded him of bird, but more hawk than chicken. This was the lean flesh of a predator. To call it 'gamey' didn't quite suffice, but it was made palatable by the salt and herbs the tribesmen had rubbed it with. As he ate the pungent fare, he decided he was just plain glad to be alive, considering the ordeal of the previous days.
Instead of reviewing his long list of complaints, hurts, and mistakes, Nate made himself focus on the situation at hand. He looked over at his new traveling companion, the ex-conquistador Gonzalo, who was gobbling down dragon meat like it was a slab of first-prize barbecue ribs at the county fair. Who knew what awful food this man from some three hundred years before Nate's own time had endured? Compared to the rations of a conquistador in the New World of the 1540s, monster meat might just taste like heaven. Their three new acquaintances obviously agreed. They were tucking in with relish. Well, at least no one was starving in this hellish place they had all ended up in, not yet anyway. He would count that as a good thing, in a time and place where good things were rare.
When breakfast was finished, they broke camp quickly. Nate and Gonzalo tended to their horses, while their ever-efficient guides put out the fire and packed up their supplies. Within minutes they were on the march, the too-bright sun still fairly low in the sky.