DREAD weapon system, power requirements

[WellDuh]

Your examples are ill-conceived at best, and misinformation at worst. Several people have gone through intensive calculations analyzing the power requirements and physics involved. Unless you have some ACTUAL MATH to prove you point, your claims are no better than the mud-slinging inventor's.

Weapons almost never sustain peak fire rates. Most mechanical weapons systems must stop after a few hundred rounds at peak rates due to heating effects - anything from thermal expansion effects to incipient barrel damage (phase changes in metals). Think firing in bursts.

Here the limit is likely energy drawn from a storage bank and the recharge rate of the generating power source. Oh and you can probably "pre-charge" a number of bullets in the centrifuge itself at just below release speed. Plus if needed you might be able to plug in a second or third HUMVEEs generating system to your storage (capacitor?) bank -- especially useful as not all HUMVEEs would mount such weapons.

Also remember two things. Those bursts allow you to beat through armor or break an enemy charge. And if you need sustained fire on this weapon you can drop back to as low a rate as your power source can sustain.

 

[WellDuh]

1. Velocity 800 ms ~ approximation from literature
2. Diameter 762 mm – assumed from “32 inches wide” in literature
2. Rotational Speed ~ 20051 RPM (335 Hertz) - derived from diameter assumption.

While you're at it:

centripetal acceleration of disk:

(800 m/s)^2 / .4 m = 1,600,000 m/s^2

(I used 400 mm for the radius, that's rounded up, and closer to 16" than your figure).

For comparison, a typical high speed centrifuge generates "up to 30,000 gravities" (from the www - that's only 300,000 m/s^2), and it has only a static load, not the dynamic load generated by feeding it bullets.

I think if you look back in the thread you'll see calculations that the 800 m/s version will fragment a steel rotor even without any other loads.

And there is your problem -- you assume a mechanical rotor. Is there a rotor in a Cyclotron? Nope.

So what if you applied some room-temperature superconductors to levitate and spin only the bullets themselves?

 

[Danger]

So what if you applied some room-temperature superconductors to levitate and spin only the bullets themselves?

If you can find any, I want to buy one.

 

[WellDuh]

My approach would be to try to 1. not put the cart in front of the horse, and 2. not to reinvent the wheel.

There were some claims by the inventor and the supporters of the inventor that the weapon has "no recoil", emphasis on quotes. I will quote more loosely the other claims because I can't be bothered to look them up and that would be the 8,000 fps projectile velocity, with 120,000 rounds per minute, and a 150 W power supply.

All you need to do is to take the weight of the projectiles, the velocity, the firing rate, and to calculate the power requirement. Use physical constants like conservation of energy and momentum. Take the energy of each projectile divided by the rate of fire and come up with power. It's easy. You can also calculate the force on the weapon which will create recoil. And of course you, as physics students, know that this weapon cannot fire projectiles of ANY mass without recoil. That alone is enought to debunk the whole thing.

This thing is a hoax. Use your basic skills in physics.

Recoil is a tricky question in that they are obviously talking subjective recoil. Further for physics we are asking a question of momentum and not kinetic energy.

So given two counter-rotating centrifuge systems which release projectiles with opposite momentum essentially in synchronization --what is the net effect? Total system momentum is still in balance for each pair, is it not?
https://www.physicsforums.com/images/smilies/eek.gif


Duh 120k rounds per minute is a burst RATE. It does not say that burst rate can be sustained for a minute. In fact there are references that say a burst is like 10 rounds (or 1/200 of a second). Quoting fire rates to round per minute is merely for convenience in comparing different weapons systems.
https://www.physicsforums.com/images/smilies/grumpy.gif


I suspect the time between bursts varies with what is providing main power -- obvious quite different for man carried or HUMVEE or Jet engined vehicle. And sustained fire rate is going to be much lower for all but the largest powered vehicles. https://www.physicsforums.com/images/smilies/frown.gif


Hmmm...many devices have more than one power supply. I would suspect that the quoted 150W power supply primarily refers to powering the common control mechanisms. They did say the info given was incomplete.

 

[russ_watters]

If you can find any, I want to buy one.

You can buy it - what I want is the patent!

 

[WellDuh]

While we´re at it: During the development of guns ball shaped ammunition was abandoned more then a hundred years ago. With advertising it as accurate ammo Mr. St George is a bit late.

You probably need to readdress whether the old reasons for cylindrical ammo over ball ammo is still valid.

(1) Primary reason -- Cylindrical ammo gave a much better gas seal than spherical but irrelevant in this case

(2) The aerodynamic lift effects of spinning cylinder is more easily fixed than sphere spinning in random direction -- relevant for subsonic although spherical ammo doesn't bleed energy like tumbling cylindrical ammo; But I highly suspect this is not relevant for supersonic spherical ammo as the shockwave in front of the sphere will bury rotational effects.

Also dimpling addresses many of the subsonic issues.

"St George says the projectiles travel at around 300 metres per second upon release from the weapon, about the same speed as a handgun round."...

Does anyone have the formula for velocity drop of subsonic spherical projectiles in air?

Maybe the prototype does only fire at 300 m/s. Whatever makes you feel good about your old blackpowder guns. https://www.physicsforums.com/images/smilies/biggrin.gif


However, if DREAD really does use superconductors to speed bullets similar to how a Cyclotron speeds atomic sized particles...then supersonics is easily in range given enough impulse power (as in capacitor high rate flash discharge).

I don't believe the unmodified Stokes Law applies to supersonic objects. But the rate of velocity loss is probably similar for any two simple objects presenting the same frontal surface area and without any designed supersonic aerodynamics such as wasp waisting. That would be an advantage for conventional projectiles - they can be designed to have supersonic aerodynamics for a price and at risk of complicating and jamming ammo feeds. However I've vaguely recall that once you breach the hypersonic range most of those supersonic aerodynamics once more go out of play. So unless someone can enlighten us with some links to equations --

I suspect that spherical and cylindrical ammo are just about equal in performance near and above the speed of sound. Further for anti-tank/anti-missile uses you are really at the limit of your range once your ammo drops below sonic. https://www.physicsforums.com/images/smilies/rolleyes.gif


So cylindrical ammo has a measurable range advantage for anti-personal work and unarmored vehicles once at subsonic speeds. On the other hand if the ammo starts as supersonic you are likely talking miles of range...which might mean extra range is a disadvantage because you can't see exactly who you are hitting (civilians or allies trying to flank the enemy). https://www.physicsforums.com/images/smilies/eek.gif

 

[WellDuh]

Room Temperature - maybe maybe not

If you can find any, I want to buy one.

Can you afford military prices?

Well actually technically high temperature superconductors are what is known proven state of the art. And they would be usable with a good liquid nitrogen supply.

On the other hand you did notice this might be a Bell labs guy didn't you?

 

[WellDuh]

Practical Superconductors 101

You can buy it - what I want is the patent!

Well do you think it is practical with Type IIs?

Feed me some detailed knowledge on something I am not that familiar with.

 

[WellDuh]

Practical Superconductors 101

You can buy it - what I want is the patent!

Well do you think it is practical with Type IIs?

Feed me some detailed knowledge on something I am not that familiar with.

Really I would think price would be what would make this a weapon of the distant future (20+ years).

 

[Danger]

Will somebody please lock this thread before my head explodes?
Or, at least, teach Duh how to either use smileys properly or not at all.

 

[Battleaxe12]

I agree, there has to be a recoil, if something shoots out the front, and nothing shoots out the back, conservation of momentum demands that there be a recoil.

I am studying physics in school, and I think that you are forgetting centripetal force, the reaction force happens before the projectile leaves the weapon. That force is the projectile pulling out away from the center of the centrifuge and when the projectile leaves the weapon the force goes with it. Have you ever spun around with a heavy object? the object pulls on your arms and if you release it it goes flying without pushing you back. But that doesn't mean that I believe that the weapon works as they say or even works at all there are many things that make me say it wouldn't work.

 

[Battleaxe12]

I never even thought about a superconductor but that is about the only way the claims of the manufacturer can be true, but then you would not be able to use tungsten ammo and air resistance might melt the bullets.

 

[Battleaxe12]

In WWII the air force (I can't remember whether British or American) needed bombs to destroy dams, so they decided on giant ball bombs spun to give backspin to keep them up next to the dam. Anyway they did tests and found that a dimpled ball flew further with more accuracy than a smooth ball.

 

[bassplayer142]

It is sad that the beauty of physics is clouded by advanced weaponry and destruction.

 

[farfallen]

I know i may be poking a dead post here, but i just saw the dread weapons system video on military.com, googled it, and found your forum. After reading some of the posts, I had some thoughts; firts, the 'no-recoil' thing, best guess? industry standard double speak. It is true, Newtonian physics and all that, but it is also true that given an electric propulsion coupled with proper mounting that this 'gun' would have a negligable amount of recoil; frictionless? doubtful given the rate of fire, but since the F117 can mask its thermal signature, i don't see why a gun can't; soundless? again highly doubtful, the rate of fire alone would produce *some* sort of sound, and unless theyre usingsubsonic munitions, there would be the breaking of the sound barrier, yet if they really are using subsonic munitions, then they have already defeated the purpose of the weapon. given that the spead of sound is 1125 ft/s and given that a projectile has a good chance to break skin (though not puncture) at around 200 ft/s, i suppose it's possible, but if the target were waering clothes, then the velocity of the projectile would need to be doubled; and forget about anything considered a 'soft' target ie-car door, house wall, person in body armor. This coupled with the shape of the projectiles tells me that all they have right now is a rapid fire BB gun; oh that and in the video they demonstrated their prototype against drywall