DREAD weapon system
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fletcher
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I'm downloading the video now - I'll mirror it once it finishes (looks like ~1 hour).
The concept seems quite impressive, I'll just have to see how it performs in the video to think anything else of it.
The concept seems quite impressive, I'll just have to see how it performs in the video to think anything else of it.
Justin
Moderator Emeritus
Zak (or anyone else who knows more about Physics than me)-
Regarding the ballistic coefficient of the projectiles, according to the pics on the Defense Review website there are dimples all over the surface similar to a golf ball.
I have a vague recollection that putting dimples on a spherical projectile helps it to fly straighter, or faster, or somesuch. How would that affect the BC, especially for something being flung that fast?
Regarding the ballistic coefficient of the projectiles, according to the pics on the Defense Review website there are dimples all over the surface similar to a golf ball.
I have a vague recollection that putting dimples on a spherical projectile helps it to fly straighter, or faster, or somesuch. How would that affect the BC, especially for something being flung that fast?
BryanP
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DelayedReaction
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I don't know what BC stands for, but dimples reduce the drag on a sphere. I think it improves the boundary layer (the stationary "zone" of air that is affected by the surface of the object) in such a way that it reduces drag. The end result is the ball flies farther (hence the use on golf balls).
fletcher
Member
Video is mirrored here. - I'll leave it up for a couple days.
Video has lots of animations, but nothing real. No real pictures/video of the DREAD. Looks interesting, but very sketchy.
Video has lots of animations, but nothing real. No real pictures/video of the DREAD. Looks interesting, but very sketchy.
Control Group
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Justin, DelayedReaction is right: the dimpling reduces drag. The dimples create turbulence around the surface of the ball, which keeps air "trapped" in the boundary layer. Air slides over air with much less friction than it slides over the cover of the ball, so the net effect is to significantly reduce drage. I've been led to believe this is the same reason NASCAR vehicles have that front plate (I'm not a NASCAR fan; I don't know the correct term) that extends down below the grill almost to the pavement. It draws a partial vacuum in its wake, creating turbulence and a pocket of air below the car for the passing air to slide over.
The dimples on a golf ball, however, also give it more of a response to spin in terms of flight path. It would be much harder to slice a drive with a perfectly smooth ball, since there would be nothing "grabbing" the air and collecting it on one side. Ditto curveballs, sliders, sinkers, etc. in baseball; without the seams, they wouldn't move.
The dimples on a golf ball, however, also give it more of a response to spin in terms of flight path. It would be much harder to slice a drive with a perfectly smooth ball, since there would be nothing "grabbing" the air and collecting it on one side. Ditto curveballs, sliders, sinkers, etc. in baseball; without the seams, they wouldn't move.
Dimples only work on subsonic air flow. Once the speed of sound is reached, the mach waves (a cone for a sphere) attach to the object and the aerodynamics change significantly. The simple Bernoulli equation of flow fails as soon as standing pressure waves occur.
The device will produce gyroscopic force, the question is how much.
There will be ‘recoil’ of one form or another since momentum must be conserved. The recoil should appear as a loss in angular momentum of the spinning disk that imparts energy to the projectile. If the loss of momentum is made up by the motor driving the spinning mass the recoil will appear here. You can move the force around, bt you cannot eliminate it.
The device will have a heat signature since it is using a motor and dissipating power, and it is going to need a lot of power.
Very high speed ball bearings typically have a relatively short life without a good supply of pressurized cooled lubricant. Magnetic bearings might be a possibility, but unless they are based on permanent magnets take a significant amount of power to operate.
There is going to be either a lot of noise generated when the projectiles are quickly accelerated or a huge gyroscopic mass if the entire supply is accelerated and then metered.
The energy from a 150 gr projectile at 8000 ft/sec is 21,313 ft-lbf (grains are not a unit if mass, slugs are the unit of mass).
This is about 29 kJoule per projectile, and at full speed 120,000 RPM, 2000 shots/sec wil take 58 MW. And this is before any losses.
This will not be a very portable item. The power will scale with firing rate, but even 5000 RPM will require ~2.4 MW. A rather large power requirement. To place it in perspective, this is around 3,240 HP, so maybe a very large turbo-generator. And a very large vehicle.
Maybe the platform should be the world’s first nuclear powered tracked vehicle. We did it with ships, why not land vehicles?
The device will produce gyroscopic force, the question is how much.
There will be ‘recoil’ of one form or another since momentum must be conserved. The recoil should appear as a loss in angular momentum of the spinning disk that imparts energy to the projectile. If the loss of momentum is made up by the motor driving the spinning mass the recoil will appear here. You can move the force around, bt you cannot eliminate it.
The device will have a heat signature since it is using a motor and dissipating power, and it is going to need a lot of power.
Very high speed ball bearings typically have a relatively short life without a good supply of pressurized cooled lubricant. Magnetic bearings might be a possibility, but unless they are based on permanent magnets take a significant amount of power to operate.
There is going to be either a lot of noise generated when the projectiles are quickly accelerated or a huge gyroscopic mass if the entire supply is accelerated and then metered.
The energy from a 150 gr projectile at 8000 ft/sec is 21,313 ft-lbf (grains are not a unit if mass, slugs are the unit of mass).
This is about 29 kJoule per projectile, and at full speed 120,000 RPM, 2000 shots/sec wil take 58 MW. And this is before any losses.
This will not be a very portable item. The power will scale with firing rate, but even 5000 RPM will require ~2.4 MW. A rather large power requirement. To place it in perspective, this is around 3,240 HP, so maybe a very large turbo-generator. And a very large vehicle.
Maybe the platform should be the world’s first nuclear powered tracked vehicle. We did it with ships, why not land vehicles?
The Drew
Member
most likely for this weapon to work without major power requirements it has to work with spherical projectiles, With a turbine like disk that whips out projectiles like you do when you whip out a jai alai (sp) ball out of the basket. This doesn't require any more power from the person but rather works on centrifugal force... then directs the projectile outward instead of in a straight line it wants to travel... This would should lower the power requirements.
Definitely false. According to MacPhereson (quoted on firearmstactical.com somewhere, but I'm lazy), a sphere will crush a hole with an average diameter of 43% of the sphere's diameter. In other words, a 1" sphere will crush a cone-shaped hole which averages .43" wide. Regular FMJ pistol ammo averages 55%, and expanded hollowpoints are around 82%.
Being spheres, the projectiles this thing uses would be really light. A .30 cal lead sphere is around 40.55 grains, and a .50 cal sphere is 187.73 gr. If made of tungsten instead of lead, they'd still only be 69.01 gr and 319.51 gr. And tungsten is pretty much the heaviest stuff bullets can be made out of. Depleted uranium is slightly less dense. Gold is about equal. Platinum, iridium, osmium, and rhenium are denser, but are not suitable for bullets at all.
Oh, and at the end of that video, there are some pictures of the actual device followed by a picture of a bunch of holes appearing in a paper target. Coulda been faked with a shotgun or something, though, maybe.
DelayedReaction
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I'll get back to you on this. The book where I got my reference from is back in the library, but I'll snag it tommorrow. They may have been focusing on fragmentation devices and not actual projectiles, but I'll put my argument on hold until I get my source.
Did they discuss what material these tests were conducted in? Ballistic gelatin?
"This would should lower the power requirements."
You cannot lower the power requirements below the energy the projectile has.
Centripital force is already being exploited to impart the velocity from the spinning disk.
All the basket in jai alai does is increase speed. It takes more work to throw the ball at the faster speed.
You cannot lower the power requirements below the energy the projectile has.
Centripital force is already being exploited to impart the velocity from the spinning disk.
All the basket in jai alai does is increase speed. It takes more work to throw the ball at the faster speed.
I'm guessing it was in the context of fragmentation. Spheres have pretty rotten terminal ballistics compared to bullets (assuming they don't flatten on impact, in which case they're probably roughly equal to light JSPs), but they're head and shoulders above randomly shaped bits of metal.
I'm not sure what they used for the tests from which those specific numbers were taken, but a large number of tests did use live (anesthatized) pigs, so that coudl have been where they were from. I really doubt the figures are from gelatin testing, since gelatin has a much lower tensile strength (and will have much larger holes in it) than living tissue.
DelayedReaction
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The advantage that ballistic gelatin offers is that it's more reproducable, and actually mimics the properties of innards pretty well. Cadaevers and pigs are less so.
Yeah, now that I think about it they were focusing on fragmentation. They were examining lethality of grenades, and discovered that large quantities of small fragments traveling at high velocities produced a greater probability of letahlity inside specified ranges (when compared to larger chunks in smaller numbers). At the sizes we're talking about, a hollow point is going to cause much more damage due to deformation.
Good call.
Yeah, now that I think about it they were focusing on fragmentation. They were examining lethality of grenades, and discovered that large quantities of small fragments traveling at high velocities produced a greater probability of letahlity inside specified ranges (when compared to larger chunks in smaller numbers). At the sizes we're talking about, a hollow point is going to cause much more damage due to deformation.
Good call.
cidirkona
Member
That video's 80's game show midi music track had me completely convinced until I saw the part about the DREAD making a horrible pattern on a peice of cardboard...
-Colin
-Colin
Control Group
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D'oh (with appropriate forehead-slap)! You're right, of course. I was focused so much on dimples' effect on airflow, I completely ignored the actual velocity involved. My bad.
Exactly what I've been trying to say, but not as well.
And kg aren't units of weight (force), they're units of mass. But good luck trying to get people referring to English-measure mass in slugs and metric weight in Newtons at 1g.
Oh, Lordy. I'm all for it, but if people kvetch about the environmental impact of depleted uranium rounds, can you even imagine the hue and cry once nuclear reactors started getting blown up on a battlefield? Greenpeace would set a new record for sudden apoplectic embolisms.
Nope. Conservation of energy means there's no such thing as a free lunch: if you want to deposit energy on-target, you have to expend the energy to do it. If you're sending ~29kJ per round downrange (as other people have calculated), you have to be generating ~29kJ per round at the source. Moreover, this is just the theoretical minimum energy required. In actuality, you'd better be coming up with more than that to make up for inefficiency.
As a side note, there's no such animal as centrifugal force. The force you feel when you're twirling a ball on a string is just the inertial vector of the ball. You're exerting centripetal force to accelerate the ball in a circle. When you let go of the ball, it isn't directed outward, it flies away on exactly the straight line it wants to travel (tangential to the curve of the circle it made when spinning). Try it sometime: spin something on a string such that it's going forward past you at the top of its arc. Then let go of it when it's at the top of its arc: it will fly forward (and down, because of gravity, of course), not up.
I only made the remark about slugs since many folks try to use lbf in the KE equation and canot understand why they do not get the correct answer.
At least metric has a unit besides good old 'slugs' (NOT a vote for metrication in everyday life).
At least metric has a unit besides good old 'slugs' (NOT a vote for metrication in everyday life).
cidirkona
Member
Maybe the dimples are there for cuteness?
-Colin
-Colin
Control Group
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Ah - I see. It never occurred to me that someone might try to use English measure when calculating kinetic energy, so I mistakenly thought you were just being a bit didactic. My apologies. I'm a die hard fan of English measure, right up until I start doing science. Then everything gets converted to metric, because it's easier to just know what the units are going to be, rather than actually doing dimensional analysis.
Slug-feet squared per second squared? Yuck.
GunnyBob
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Interesting. Wouldn't want to limpwrist that sucker though.
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