h a l f b a k e r y"More like a cross between an onion, a golf ball, and a roman multi-tiered arched aquaduct."
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The problem with a ramjet is that you need to have air moving into it at around Mach 1 for it to even work properly, which means you need a booster propulsion system to kick it up to operational velocities. Adding boosters takes more time, more engineering, more components, and more maintenance. It's
a pain in the ass, especially when you're using it for a kill-vehicle (See: Bristol Bloodhound)
The problem with railguns is that they suck up eye-popping quantities of power, especially if you're using them correctly: as a Hyper-velocity Weapon. If you get a projectile up to 3.5km/s or so, it's impact energy is equal to it's own weight in TNT. Eventually, we hope to have portable powerplants that will fit on a helicopter or an APC, but for now it's impossible.
My answer is to use a rail-gun for the boost phase, accelerating the ramjet-rocket penetrator up to it's operating speed, at which point it will accelerate rapidly to speeds three to five times greater than it's muzzle velocity. Ideally, this will allow heavy weapon operators to carry a Mach 1 capable gun that hits the target at Mach 5. Also, there will be a ton of cheap ramjets lying around Air Force munitions plants, so there's a good chance that a bored Airman will earn a Darwin Award with one of them, and that's always good for laugh.
Iterative Space Railgun
Iterative_20space_20railgun
This idea, inverted. [bungston, May 21 2010]
MIM-104 Patriot
http://en.wikipedia...iki/Patriot_missile
"When is a 'kill' not a kill .... ?" [8th of 7, May 21 2010]
Aircraft catapult
http://en.wikipedia...i/Aircraft_catapult
Impressive to watch in action [8th of 7, May 26 2010]
X-51 'Waverider'.
http://www.theregis.../27/x51_first_shot/
Timely news from the exciting world of scramjets. [DrBob, May 27 2010]
prior art
Ramjet_20ammo
intended for small arms [notexactly, Nov 26 2015]
Save the effort, just use air augmented rockets
https://en.wikipedi...ir-augmented_rocket
The simplest explanation is to fill the ramjet cavity with rocket propellant, and burn that to accelerate it up to ramjet operating velocity, then switch over. In actuality, a bit more complicated... [Custardguts, Nov 27 2015]
Design and Testing of a Caseless Solid-Fuel Integral-Rocket Ramjet Engine For Use in Small Tactical Missiles
http://www.dtic.mil...text/u2/a246226.pdf
Kevin J. Fruge's thesis, 1991 [notexactly, Dec 04 2015]
Albert Fonó's ramjet artillery ammo proposal, 1915
https://en.wikipedi...et#Albert_Fon.C3.B3
As mentioned in my anno. [notexactly, Jan 11 2016]
[link]
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// ...and that's always good for laugh.// |
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Hopefully it will be [21quest]. He's been impeding my ascension to King Asshole for years. |
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My problem with this is that the railgun is asked to accelerate a bunch of rocket fuel. The railgun should be the thing accelerated with the rocket fuel; once up to speed the railgun discharges the projectile. A carbon fiber railgun powered by a charged capacitor will weigh only a few ounces, I here assert. See link for more edification. |
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I considered that too, Bungston, but instantly dismissed it because first, my system delivers a greater amount of mass to the target, which is the same as saying it's way WAY deadlier. Second; instead of having a moderately pricey ammunition for a gun you get to reuse as much as you like, you have to build an even more expensive gun for ever shot you fire. Third; the railgun itself, the fire control system needed to fire it, and the shock-management systems to keep it from turning to dust when you pull the trigger are all just more expensive, finicky on-board garbage that increase the cost while reducing effectiveness. Fourth; The thrust isn't provided by a rocket, it's provided by a Ramjet, and Jet Fuel is still cheaper than bottled water, so if anything it should be our flex-tech, not the railgun. |
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Alternatively, you could take an extremely heavy but unstoppable mass, and move it very, very slowly, very, very ominously. Warfare by creeping mountain of steel. |
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Why not launch it with an ordinary cannon? |
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[Idischler], I don't think a ram-jet could maintain structural integrity being launched by a cannon. A rail gun would Shirley be a bit softer on the initial impulse, yeah? |
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// If you get a projectile up to 3.5km/s or so, it's impact energy is equal to it's own weight in TNT. // |
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TNT yields 4.6 megajoules per kilogram. What you get is a bubble of very hot gas; most of the damage is done by things that the expanding gas propellls outward from the point of detonatation. |
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The kinetic energy of a one kilogram projectile travelling at 3500 m/s relative to its target is 6.125 megajoules - a respectable figure. But the downside is that the projectile needs to make direct physical contact with the target to yield up this energy; no "proximity fusing" for kinetic rounds. |
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So if you have a chain gu capable of flinging out 1200 rounds per minute of depleted Uranium, you have a chance; but the sort of "smart rocks" (self-guided kinetic projectiles) proposed during the glory days of SDI (sigh) are still on the drawing board. |
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Like the RAP and the Trommsdorf-Granaten of WWII, systems with post-launch boosters tend to be area weapons unless they have incredibly sohisticated guidance systems (waaay beyond your current technology, Earthling) if they rely purely on kinetic energy for their destructive effect, since the interception velocity is so high. |
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//I don't think a ram-jet could maintain structural integrity being launched by a cannon// |
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With no need for moving parts, it's hard to imagine a more robust engine than a ramjet. |
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[8th], My experiences over-seas ran somewhat counter to your position: Fragmentary weapons just made us change tires after RTB. EFPs sent the vehicle to the shop for a week or so... after being hosed out. |
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[Idleshire], how robust is the fuel tank? How forgiving is liquid when compressed? I and my fellow 21Bs tape .5 liter I.V. bags on either side of a couple feet of det cord and use it to blow steel doors in. |
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A ram-jet may very well hold up, but I would think the one is a helluva lot safer than the other. |
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What do those abbreviations mean, MikeD. I cannot guess, but can guess about the hose I am sad to say. |
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EFP = Explosive Formed Projectile |
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//How forgiving is liquid when compressed?// |
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Hey, [21Q], want an experience you'll never forget ? If you ever come to the UK, drop into Colchester, make your way to the Paratroop Regiment Mess, and announce in a loud voice that "I thought only faries had wings". |
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Oh, and don't forget to make the necessairy arrangements for the distrribution of your property and posessions. There will be no inquest or funeral, since no particle of your body will ever be found ... |
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//they don't likely remember any of it// |
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Marines *do* have a hard time remembering an unremarkable piece of ass. (That is why they sew name-tapes onto their fatigue trousers). |
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//drop into Colchester, make your way to the Paratroop Regiment Mess, and announce in a loud voice that "I thought only faries had wings".// |
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He need only come to Fort Bragg, [8th]. I could lead him to one of many Parachute Infantry Regiment's barracks where he could find the same. |
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Given modern Infantry Movement Tactics drastically reduce the incidences of casualties, I’d say you, [21Q] being un-trained in such techniques, would be more proficient at catching bullets. The numbers may indicate other-wise, but only because your pansy ass doesn't go "outside the wire"... or your aircraft, for that matter. |
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Joking aside, I realize your job is just as vital to success as mine or any other. I just wouldn't be able to sleep a night if I, as a combat arms soldier, didn't give you shit from time to time. |
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Now, shake hands, look at the camera, and smile. Try to look sincere. |
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I couldn't be more pleased with the way this turned out. |
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It's no end of fascinating to watch you guys go at it, knowing that you' probably both fling yourselves through the gates of hell for eachother on general principle. There's a word for that, you know. It's "Tsundere". Honestly, I'm suprised not more kissing. |
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Someday I'm going to get around to writing a book with the whole cooperation/competition dichotomy between military branches as a central theme, just so I can deconstruct the hell out of it. Also, add the kissing in where I see fin. |
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Meanwhile, pass the popcorn. |
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Most amused! However, back to the point of the thread... |
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Having had a bash at making a rail-gun at university (in the student house not the lab...), I've learnt a few things about them. Firstly, you're right, they're big and do use a lot of power. Secondly, the only point in using one is to reach speeds that are not practical with hot gas propelled projectiles (limited by the velocity of sound in the hot, compressed gas). |
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To reach Mach 1 and thus be fast enough to get a ram jet working, the cannon suggestion does seem like the simpler solution. Cannons can be quite gentle and linear in terms of acceleration. It all depends on the burn characteristics of the gas generating system. |
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On the other hand I would like a rail-gun that fired stuff as fun as ramjets. My one only managed very small bent bits of welding wire. Wasn't really a weapon of doom as the welding wire bits would only just go through a piece of paper at point blank range. |
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...and on that note; I've also considered replacing the Railgun with a down-scaled and weaponized Ram Accelerator. They're similar to cannons, but using something like a Thermobaric (read: Fuel/Air Bomb) accelerant rather than a powder. It's a stable technology (NASA and Aerospace Contractors use them to simulate micro-meteor strikes) so they'd be easy to modify, and they're chemically fueled so they're relatively portable. |
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They're even more attractive when one takes into account that they're currently used to accelerate projectiles to hypervelocities, meaning they can be freely re-scaled in relation to our ramjet penetrator for whatever size or impact profile is required. A battleship could mount a huge turreted RA, while it's little sister could be pintle-mounted on a light vehicle. The only difference would be that in the later case, you have to dedicate more of the projectile's fuel and effective range to ramjet-acceleration to make up for the shortfall in RA performance. |
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It's just that... cool as Ram Accelerators are, they just aren't Railguns, are they? Railguns are made of SCIENCE! and The Future. Ram Accelerators are just made of Gun and Bomb. Oh, also; a railgun can fire as rapidly as you can recharge the capacitors, so you could potentially get cyclic rates of >100 RPS (Lead
Laser!) with small payloads. RA's need long cooldown to limit barrel stresses just as normal firearms do (possibly more or less, I couldn't find any information of Ram Accelerator cyclic rates) |
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So, yeah. Just thinkin'... |
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This might seem like a dopey question, but why is a capacitor a superior power supply for a rail gun, in comparison with, say, a flywheel? |
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Besides the obvious lack of moving parts, that is. |
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//Now, shake hands, look at the camera, and smile. Try to look sincere.// |
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And during the fleeting moments of visual disorientation after the camera flash, I will introduce [21Q] to the "Sack Tap"; a time honored tradition of combat arms. |
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Will you two just fuck already? |
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WOOT! somebody had to say it. now go back to talking about fantasy guns. |
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Quest, you're assuming that I use soap, and you know what happens when you assume, right? |
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//to launch unguided ramjet missiles// Herein lies the rub me-hearties. |
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Mostly weapons systems are concentrating on accuracy nowadays. This coupled with weapons systems being deployed in all manner of load bearing vehicles in all manner of geographic locations, means you don't have to launch a projectile from another continent, more like a from a continental f**k. |
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You do seem to be correct in two facets though. Projectiles are being launched by EMF, and also projectiles are being made to be "smart" i.e. follow non-ballistic trajectories. |
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Neither of these mechanisms are presumed to be soon on the battlefield. Purely a matter of energy density. It is cheaper (both in labour and cost) to transport a chemical round (gunpowder and slug) than a battery and rail. |
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Folly super-weapons and a rant in one! |
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Someone mentioned capacitors and the comparison with a flywheel. If anyone wants to implode their brain, read about a compulsator. They're interesting, but very complicated. They're also the only flywheel solution that could work with a rail-gun - for which they were conceived. |
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Capacitors on the other hand are nice little things that sit still and don't require converting energy from kinetic to electric in the 10 to 100GW power region. They also have a really good power to weight ratio these days. About 3J/cc for commercial and slightly better for cutting edge. So for a 10MJ cap bank (who would want less for their rail gun??) that would be a 3.3m3 volume for energy storage. All quite simple and reasonably inexpensive ~£1M. Icar, GAEP and AVX all sell such capacitors and I've been looking into purchasing some for a different purpose (big lightning machine - should put order in next week!). |
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A flywheel would be cool, but they're better at longer pulses and lower peak powers. The JET experiment near Oxford, UK has a pair of rather large flywheels underground. They produce a 10 or more second pulse of many MW. There's no way they could produce rail gun type power outputs as the pulse would be too short. |
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On another matter, I don't use soap either. Shower-gel works just fine and has a convenient hook for hanging it on the shower bracket rather than dropping - and so avoiding whatever you chaps (fine as you may be) get up to. |
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// whatever you chaps (fine as you may be) get up to // |
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"The Truth ? You can't handle the Truth !" |
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//Will you two just fuck already?// |
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Well *that* is skipping a few steps, isn't it? We still haven't gotten into a fist-fight, made-up, went out for a few drinks at a local sports-bar and made uncomfortable eye-contact during half-time while the Pretender's "I'll Stand By You" plays over the radio, yet. |
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Sheesh. Not everyone is a big a slut as you, [Victory]. |
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You forgot the bit about falling out, then saving one another's lives (sometimes more than once), then one asking the other, "Are we even now ?" and the other saying (after a suitable pause), "Yeah, guess we're even." |
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It's in all those buddy movies (except, perhaps, Brokeback Mountain). |
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why not just use a traditional chemical rocket to hit Mach 1? |
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maybe I'm biased as I work for a rocket manufacturer, but they are more than capable of hitting mach 1. Linear accelerators are fine and dandy but not neccessary to hit mach 1. |
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It's the external power source thing. Why do you thing carriers use steam catapults instead of JATO units ? Sure, you can fling aircraft off the deck using rockets, but it's considerably more cost-effective to use a largely-reuseable steam catapult. Whereas you'd have to stock lots of JATO packs in your stores, with high unit cost; and you have to fond somewhere to hang them off the airframe. |
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This, of course, begs the question "would a steam catapult be as good as a linear accelerator ?" |
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V-1's (with their Argus pulse-jet engines) used catapult launch. |
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//V-1's (with their Argus pulse-jet engines) used catapult launch//
Unlike a scramjet, the V1's pulse-jet would work at zero airspeed - there is footage of static engine tests. |
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The catapult was used because the stall speed of the airframe was so high, and the thrust was low, so a self-powered take-off in a short distance was impossible. |
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Two reasons - low stall speed for the wing, and the low specific impulse of the pulse jet at zero forward speed. |
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Wait a sec - isn't a railgun even more destructive of the projectile than a cannon, what with the bollocking huge amount of current passing through it, and the massive acceleration? Any ramjet that could survive that, structurally intact and operational, would surely survive being fired out of a cannon, no? I mean you can forget any onboard electronics for a start. |
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//railgun more destructive of the projectile than a cannon ?// per unit of velocity I imagine a railgun would be less destructive... would depend on what the projectile was made out of. |
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//I mean you can forget any onboard electronics for a start.//
Why? Copperhead rounds survived 25k g launch acceleration back in the 1980s, and modern GPS-guided artillery rounds are available. |
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I was referring to the effect on the electronics of the massive current, not the acceleration. |
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See link. Use an air augented rocket - which operates as a rocket during the boost phase, then a ramjet once up to operating speed. Simple, and cheap compared to carrying linear accelerators and cubic metres of capacitor around. |
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All up, gives 3-6 times the kinetic performance of a pure rocket. |
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Wow. Another place where the terrorists deleted all of [21Q] annotations, and I have prime opportunity to make up something to fill those spots. |
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The problem is, I could not begin to approach what the actual remnants of the exchanges have presented. Oh well... |
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I happened to be reading up on ramjets today, and it turns
out that ramjet-powered artillery projectiles were first
proposed in 1915 (!!): [link]. |
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