Stevopia



The DREAD, and why it won’t work.

No heat, no recoil, no sound, no gunpowder, no flash — just 120,000 rounds per minute of pulverizing power. The next generation of weapons systems has arrived: the DREAD centrifuge-powered weapon system.”

Erm, no.

The DREAD is a weapon system that supposedly offers all sorts of benefits (outlined above). There are many gushing positive articles about it all over the web saying how it could revolutionise warfare ({1}, 2, 3). Unfortunately, they’re all wrong.

How it works

The DREAD consists, as far as I can tell, of a spinning frame that picks up little metal balls, spins them around at 3,000 ft/s (914 m/s), and in later versions, the inventors claim, at 8,000 ft/s (about 2.3 km/s). That’s very fast. Not only that, but it can fire 2,000 of these every second.

Here’s a picture of it.

Lets pick apart the claims shall we?

1. No Recoil

As every secondary (or ‘high’) school physics student knows, and as Mr. Newton so kindly demonstrated for us, there is no action without an equal and opposite reaction. Basically, if you throw something one way, you get pushed the other.

This manifests itself in the recoil of a gun — bullet flies off in one direction, the gun gets kicked back in the other. It’s how propeller, rocket and jet engines work (throwing air/fuel backwards in order to go forwards). Nothing is exempt from the rule. Not even the DREAD.

So how much recoil would a DREAD produce? By my calculations one of the 0.5 calibre balls would have a mass of about 60 g (assuming the density of iron). A simple calculation shows that at 8,000 f/s, 2,000 every second, the recoil would be like a force of 300,000 N. Thats equivalent to 31 tonnes of recoil. You’d have a hard time keeping that steady.

Note: For those of you who are picky, I know recoil is not a force but a series of impulses. What I’m quoting here is an ‘equivalent force’, if you like.

2. No Sound

True, there’s no explosion, which is most of the noise from a gunshot. But, there are metal balls travelling at 7 times the speed of sound, 120,000 a minute, and these will generate one hell of a sonic boom. However, I guess it’s fair to say it will be harder to tell where the shooter is.

3. No Heat

From what I can tell, the spinning bit on it can’t be more than about 30 inches wide. To have a rim speed of 2.3 km/s, it would need to spin at nearly a thousand times a second, or 60,000 rpm. That’s fast, but not outlandishly fast (some turbines can reach 150,000 rpm) so this claim I guess will not be too bad.

However, there is another problem, and that is:

4. No Gyroscopic Effect

Have you ever held a spinning bike wheel by its axle and tried to turn it? You’ll find it doesn’t move the way you want it to. This is called precession, or the gyroscopic effect. It’s what keeps a gyroscope or spinning top upright, and makes it difficult to turn spinning things. And the DREAD is spinning very, very, very fast, and so should experience a massive amount of gyroscopic effect. But it’s alright, because:

“According to Charles St. George, the DREAD’s inventor, the DREAD does NOT create/cause ANY gyroscopic forces or effects, whatsoever. To put it another way, the DREAD does NOT act like a gyroscope. So, the DREAD will NOT have ANY adverse effect on the mounting vehicle’s maneuverability, even while the DREAD is being fired on its highest rpm and velocity settings. NO adverse effect. None, whatsoever. I can’t make it any clearer than that.”

Well, that’s okay then.

4. Totally reliable

Defense Review claims that the weapon cannot stop or jam. No evidence has been produced to back up this claim, but it seems incredible that something with parts moving round at 60,000 rpm won’t experience at least a little wear and tear (especially in a combat environment, where its being knocked about and dust, sand etc. could get inside), and it seems reasonable to assume that this will eventually bring the whole thing to a stop.

Conclusion

I’m sure the concept could be made to work. However, not the way they’re saying it could. What’s worse, the inventors are promoting their device by making outrageous claims based on pseudo-physics and downright lies. The websites linked to above repeat these claims without knowing the first thing about basic physics (even New Scientist), and in doing so mislead the general public.

DREAD homepage (now defunct, 8/05/2008)

Edit: Why the DREAD produces recoil

There has been some doubt expressed as to whether allowing a projectile to leave (rather than forcing it) can generate recoil. I argue that it can, and here’s my why.

Note: secondary (high) school physics required.

In a normal rifle, there is an explosion that exerts a force forwards on the bullet, pushing it forward. There is an equal force on the rifle, pushing it backwards. This means the rifle has a momentum backwards, towards your shoulder.

In order to bring the rifle to a halt, your shoulder has to exert a force on the rifle butt, forwards. This, by Newton’s third law, means that rifle exerts a force on you, into your shoulder (backwards). This is the force that is felt as recoil.

In the DREAD, we have the scenario of a spinning disk with masses arranged equally around the edge. For simplicity, we will assume there are just two. This disk is spinning, but because the centre of mass is not moving and so has no overall momentum. With the disk spinning clockwise:

DREAD with two balls

COM is the centre of mass of the entire system, p denotes the momentum of each ball. Notice how, because the balls are travelling in opposite directions, the momenta cancel out to zero.

However, imagine that the left projectile is now released. It is no longer attatched to the gun, and so can be discounted as not part of the system. We now have this situation:

DREAD with 1 ball

The ball on the left is detatched from the disk, and now rapidly flying towards the top of the picture, but we can ignore it.

Now, the total momentum of the system is p, backwards into your shoulder. This, like the situaton described above, means that your shoulder pushes against the gun, the gun pushes against your shoulder, and hence: we have recoil.

If your shoulder wasn’t there, the DREAD would continue to fly backwards forever (or until it hit something). Notice that it has momentum p, thus momentum is conserved. I know I’ve only demonstrated it with two balls, but this argument can be generalised to more.

If you’ve managed to follow this, congratulations, hopefully you too can decry the DREAD as pseudoscientific blather.

If you haven’t, please don’t make angry posts.

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Trackbacks & Pingbacks

  1. FUTURE WARS: RESHAPING THE ETHICS AND NORMS OF WAR | featuresgalleried pingbacked on 2 years, 2 months ago

Comments

  1. * Edd says:

    Woo Steve is back! And with a suitably controversial and combat-oriented article. And only one typo for me to correct too :p

    Edd

    | Reply Posted 10 years, 6 months ago
  2. * Cj Claus says:

    Regarding your comment on the lack of recoil, you are working under the wrong assumption. The weapon is NOT propelling the projectile forward. The weapon is spinning a disc full of them, all at the same speed and the equal and opposite reaction is outward from the axis of the spin. When the portal is opened, a projectile is ALLOWED to exit, not forced to. No energy is expended to push the projectile forward other than it’s already created inertia, ergo, no perceived (or felt) recoil. If you take a stone in a sling and wirl it around your head, when you release it you will feel no recoil. That is because you have already imparted it’s inertia with the spinning effort.

    As for your comment on the gyroscopic effect, of course there is, but as long as it’s in the same relative plane as the vehicle, it’s going to be negligible.

    | Reply Posted 10 years, 5 months ago
  3. * steve says:

    This is a very complicated issue. I think I might have to update the page with a section on why the DREAD would produce recoil. However, what you are implying, Cj Claus, is that it is possible to build a little black box that spits mass out in one direction and but not another. This violates the principle of conservation of momentum.

    As for my comment of the gyroscopic effect: true, but I would prefer it if they said that, rather than deny it existed.

    | Reply Posted 10 years, 5 months ago
  4. * Cj Claus says:

    Steve,
    I agree that it’s a complicated issue, but you apparently didn’t read my remark completely. I never said that there was no reaction to the movement of the projectile. As I believe I explained thoroughly, the mass is accelerated within the disc, generating inertia (and gyroscopic effect) around the axis of the device. Remember that it is inerita that produces the equal and opposite reaction, and that forcing a stationary object to accelerate in a given direction produces recoil in the opposite direction. Since you are accelerating the projectiles in a circle within a confined space, your equal and oposite reaction would be making the other projectile (assuming for a second that there are only two) move to the opposite side of the circle, accross from the first, and at exactly the same speed, and with the same force. The faster that you spin the disc, the more force (again inertia, or momentum) is applied to the disc. If you could continue to accelerate the disc beyond it’s ability to withstand the forces being generated by the projectiles inside of it, it would burst. Would you not agree that the projectiles would fling out at whatever velocity they had gained by the rotation of the disc? Now, if only one of them escaped (key word there… escaped) the only “felt” recoil would be the unbalanced load inside the disc. There is a reaction, however it isn’t anything that could be considered “recoil” in the sense of a bullet leaving a rifle. As any good shooter would tell you, recoil is in the perception. Ergo the use of compensators, heavy stocks/barrels, and rubber or other soft compound pads on the butt. The less you feel, the better you’ll like it, but it does not change what is actually happening, just the perception of it. Conservation of energy is observed. There is nothing magic here.

    Also, I would assume that as one projectile leaves, another is dropped in to the spinning disc at the same time, and as it would then begin to accelerate to the speed of the disc, the energy consumed to accelerate it should equal your reaction. One out, one in. Ought to shake like hell when it’s running out of ammo, though, I’d think.

    The last thing is that I didn’t intend to insult you or even to imply that in any way. If that’s the way my writing comes off, I am sorry. Oh, you really don’t need to use my full name. Cj would be fine.

    | Reply Posted 10 years, 5 months ago
  5. * steve says:

    You’re right CJ, recoil is perception. In a normal rifle, the explosive charge gives an impulse (by this I mean a change in momentum) to the bullet and an equal impulse to the rifle in the opposite direction. This means the rifle is travelling towards your shoulder. In order to slow it down, your shoulder imparts a force on the butt of the rifle. It is the reaction force to this — that of the rifle pressing into your shoulder — that is percieved, and that is uncomfortable. The use of compensators/rubber/pads etc. is only used to reduce this force and spread it out over a longer period of time, to make things more comfortable.

    I agree with almost all of what you have written. To try and settle the matter, I’m writing a new paragraph that’ll try and explain things the way I see them. Remember: ‘recoil’ that is felt is your shoulder trying to slow the weapon down after it has been given an impulse (given momentum, or given velocity, or speed, however you want to put it).

    Oh, and I didn’t feel insulted. I’m sorry if it came across that way.

    | Reply Posted 10 years, 5 months ago
  6. * Wz says:

    Good article steve. However I think the company developing this weapon will be able to over come these problems. Im not an expert in any of these areas so Im not going to start saying who’s right or wrong out of yourself and CJ, however from what I know it seems what CJ is saying could be correct.

    | Reply Posted 10 years, 1 month ago
  7. * KL says:

    First of all, sorry about resurrecting an article that’s been dead 7 months – but I’ve only recently heard about DREAD, and this is the first place I’ve seen anything but advertising drivel…

    @CJ:
    I agree with your analysis of the cause of recoil; indeed, it would come from the sudden force imbalance caused by the ‘escaping’ ball. However, just ‘adding another ball the chamber’ immediately will not right the balance – the new ball starts at zero velocity, so it contributes no force in the direction of firing. In order for it to immediately step in place of the vacating ball, it must be pre-accelerated to the same velocity, which could only really be done by exerting an opposing force on the mounting. Suffice to say that regardless of whether this is actually attempted or not (I assume we need some way of injecting the new ball at an already comparable velocity, otherwise it’ll get nailed by the others coming around), we still get the recoil from a single ball leaving the chamber, equivalent to that of a rifle in terms of momentum transfer. With this established, it seems that Steve’s initial calculation is still correct.

    | Reply Posted 9 years, 9 months ago
  8. * leob says:

    One other problem with this device. Has anyone computed the power required to accelerate this mass of metal? Assuming that you are accelerating 60 g from 0 to 2000 metres per second – that’s 120,000 Joules. You are apparently able to do this 2,000 times per second – that gives 240 million Joules per second, or a power supply of 240 MW. Probably a little more than the average car alternator can handle.

    | Reply Posted 9 years ago
  9. * rich says:

    1. You don’t take into account rotation forces. There is no recoil you should look at the definition of the word before using it. The weapon douse become out of balance by the weight of the lost round. This is easy to compensate for using many existing technologies. You should research auto-balancing turbines. It’s a simple search I’m sure you have the time. Also releasing a whole track of balls which from the video looks to be the action that is taking place. The whole gun would re-balance in one rotation; 1/60,000 of a second by your calculations.
    2. Gyroscopic force. A gyroscope of course has two planes of force. You just totally ignored the fact my guess is lack of education. The weapon since it can engage multiple targets at one time means that it has multiple release points. This means the weapon does not need to be rotated to aim. The one thing I can’t account for is what would happen on x orientation of fire. It would quite significantly resist movement along that axis. The vehicle would have very little problem negotiating until it tried to climb a steep hill quickly producing resistance along x axis again.
    3. The only thing about the weapon I don’t understand is how u would aim up and down. Some sort of mechanical assist I would assume.

    | Reply Posted 3 years, 9 months ago
  10. * superjuice says:

    One word for your recoil argument – inertia.

    | Reply Posted 2 years, 4 months ago
  11. * Jed says:

    “However, imagine that the left projectile is now released. It is no longer attatched to the gun, and so can be discounted as not part of the system.”

    Easy. Re-introduce a ball for every one that is released. (You know, reloading? )

    Presumably the gun would stop firing once the magazine was expended, leaving the device full of un-fireable projectiles until the magazine was replenished.

    | Reply Posted 2 years, 3 months ago
  12. * J Rizzo says:

    you deflate your message in the very beginning by stating “as far as I can tell” and you are right because you CAN’T tell because you have nothing to do with the project.
    However I can see a possible counter to a couple things you say simply by assuming that DREAD has 2 independent firing systems counter rotating, one above the other. I am not a physicist but I have flown helicopters with counter rotating blades.
    I guess we will see in the end if it ever comes out into action though. And that is assuming that your estimation of what drives DREAD is as you think it is.

    | Reply Posted 1 year, 5 months ago
  13. * Shish says:

    I think that the recoil is smaller than you say because there are other balls that are shoted every second and the recoil lasts a fraction of second from one direction and the recoil causated by only one ball is diminished by the presence of other balls that have a centrifugal force

    | Reply Posted 1 year, 5 months ago
  14. * David says:

    from what I figure after reading everyone’s comments, I agree with Steve that in a closed system with only 2 masses rotating around the center there would be recoil. He did a very good of presenting it and made it easy to understand. However, as Shish put it, the “recoil” from a single ball would be diminished given that there would be a full track of metal balls each with there own inertia at almost every other point around the circle.
    But, going back to Steve’s point each ball leaving the DREAD track would produce its own recoil leaving one less ball to diminish the recoil of the next. By the time the last ball leaves the track there would be no balls left to counter the recoil in addition to the recoil built up by the rest of the balls before hand.
    And for those saying you can just add a ball for every one that leaves the track, the track is spinning so fast that, as KL pointed out, you couldn’t just add a ball to a rotating disc going that fast, unless there was a device pre-accelerating the balls before inserting them. If that was done, then there would be the recoil of that machine making the no recoil of the DREAD pointless.

    Then there is the whole power issue. As leob put it, it would take “a power supply of 240 MW” to power this device (I’m making this point assuming his math is good, if its wrong then either my point still stand but to lesser effect, or the researchers have found a way to power it). Given that this number is 1/8 the amount (approx.) of the Hoover Dam’s current production capacity (2,000 MW), I doubt that this is even plausible for a vehicle mounted weapon system.

    Most of the points stated here are not from me, just clarification from me for me of most of the points stated by others before me, stating my take on the various arguments posted above. that last sentence was redundant. lol.

    | Reply Posted 1 year, 4 months ago
  15. I don’t think there will be any recoil. As we know F=ma in this case once the ball is up to speed, a=v^2/r towards the axis of rotation. The reactionary force is a normal force between the outside surface of the ball and the inside surface of the case. If you take away the case the ball will fly unimpeded in a straight line. It’s acceleration that causes the force of recoil (acceleration causes all forces). Bringing the ball up to speed uses angular acceleration and will generate a reactionary force. Once the ball is spinning at a constant velocity you have the acceleration towards the axis of rotation. Take away the case holding the ball and you remove all acceleration wrt to the gun so there will be no force applied on it.

    | Reply Posted 1 year, 4 months ago
  16. * Physics Guy says:

    There will clearly be recoil, though it may be in a direction normal to three path of the projectile. As the original article essentially states, there are so many basic physics problems/lies here that it’s a joke.

    | Reply Posted 1 year, 1 month ago
  17. * Physics Guy says:

    “The path” not “three path” — sorry for typo

    | Reply Posted 1 year, 1 month ago
  18. * James says:

    I clicked this link hoping for any information about this system, because I know there’s a lot unexplained. I was hoping for a good argument against the system (because I like to hear both sides, as everyone should). But this article is probably the worst thing I’ve read in a while. I feel like it ought to be a Buzz Feed List-icle or a Tweet. The informality and absolute lack of any real information, examples, or supporting stories, show that the writer obviously has no Idea what they are talking about, and obviously just got assigned this topic to do a shitty article on to get the page views. I painfully read it to the end hoping for intelligence, but none was found..

    Though I do appreciate the Edit, as you are trying to support your argument with math/physics, but please, leave the hard thinking to the professionals.

    | Reply Posted 1 year, 1 month ago
    • * Jane says:

      Gucca, quanto ao setlist, cara, não há como, sempre vai faltar a sua pr#3&ridaee82f0;e não é má idéia uma semana inteira de show, se for naquele patamar de qualidade, hein? hehehe

      | Reply Posted 4 months ago
  19. * me says:

    Because of the way the disc is spinning when a ball is “released” would it put spin on the ball as well? If so that would not be good as they would be subject to the magnus effect and would curve much like slider in baseball. That would make the weapon terribly hard to aim with the ammo going all wonky.

    | Reply Posted 12 months ago
  20. * 1amb0b says:

    ummm… i don’t do maths and stuff but when i throw a baseball i don’t experience any forces pushing back at my hand when I release the ball… is that not a fair analogy?

    | Reply Posted 11 months ago
  21. * noahspurrier says:

    When a bullet leaves the muzzle of an ordinary gun it ceases to be a source of recoil. Recoil is not a single event, but it a continuous build up of force as the explosive gas expands and pushes the shell down the barrel. People tend to think of the recoil as a single event — an instant pulse pulse of force felt as the bullet leaves the muzzle. In fact, that’s the moment the force of recoil ends… OK, so get to the point. Imagine you have a weapon that consists of 8 pistols arranged in a circle pointing away from each other. You can can fire each pistol one at a time sequentially. If you fire the pistols in sequence fast enough then the recoil would be balanced, more or less. There would be little to no recoil. The guns don’t have to fire at the same time. It’s like a boxer engine in a Subaru, a Volkswagen Beetle, a Porsche, or a Chevrolet Corvair. The pistons don’t have to fire at exactly the same time (in fact, that would be impossible), but the engine is still extremely smooth and well balanced…. The Dread gun would be analogous. Multiple projectiles would be accelerated down the shaft. Since the thing is spinning then some projectiles will be on the opposite side of the axis of rotation from some other projectile. The projectiles do not have to be perfectly lined up with another on the opposite side of the axis. The forces would all get smoothed out and more or less cancel the recoil of any one projectile. By the time a projectile has reached the edge of the ring accelerated to the edge of the ring and it is ready to be released you have already paid the price to get it there in terms of the forces of recoil.

    | Reply Posted 10 months, 3 weeks ago
  22. * Blacktail says:

    Looks like an awful lot of people who can make a comment appear to be technically-minded have flunked high school-level science. Who remembers that “Every action has an equal and opposite reaction”?

    This is the main reason guns have recoil — the mass emitted from the weapon. The gas produced in the chamber of a rifle is not the source of the recoil, but rather the back-pressure inside the barrel. Anyone who has ever seen the puny puff of smoke that comes out of a rifle without a bullet in the cartridge (not even a blank) has seen this firsthand. And what causes that back-pressure against the gas expansion? The projectile.

    Hurl a given projectile at a given muzzle velocity, and the force that projectile exerts on anything unfortunate enough to be in front of the muzzle is equal to the force it exerts back against the weapon that fires it.

    In short, the blog post’s recoil estimation is dead-on.

    And to put 31 tons of instantaneous recoil into perspective, think of the 105mm gun used on an M60 Patton tank. Firing a live round from that weapon produces 30 tons of instant recoil.

    And the DREAD’s inventors seriously proposed using their weapon on satellites!

    | Reply Posted 9 months, 2 weeks ago
    • * Working Box says:

      Somehow I doubt they spent millions of dollars on research and development, only to lie about something like recoil. In the weapons world, “no recoil” could just as easily be translated into “very manageable recoil”, or in some cases “unnoticeable to the point of being negligible recoil”. There are a lot of brains here pumping out theories, but apparently very few people with experience firing various weapons systems. Maybe there is a little recoil, but it’s not likely something significant enough to alter aiming, target acquisition, repetitive fire, or transport. This isn’t to say that the concept doesn’t have some logistical flaws from a military application standpoint, but I think we can “believe” the researchers and creators of this weapon system, without necessarily worrying about what some random guy “feels” is the reality of the situation based on his assessment applying high-school physics.

      | Reply Posted 8 months, 2 weeks ago
      • * noahspurrier says:

        Well said.

        Posted 8 months, 2 weeks ago
      • * Brandon says:

        Imagine a glass of water, imagine the water being spun into a high-speed vortex. The water in the center of the glass starts to lower an centripetal force pulls water towards the glass edges.
        What spot in the glass would have the pressure? center access or between the water and glass rim? Everyone is talking about equal reaction, if the force is applied on the glass rim the reaction would take place between the glass rim and the water edge. glass reflecting from its torsional deflection furthermore this would be a local to a specific area
        For instance if you were submerged yourself in water at a density equal to your body mass giving you neutral buoyancy and that water was put into a vessel mounted to rocket fired at at a extreme acceleration (8 + G) you would not even notice the ship was moving if you were not touching the walls.
        Just my two cents from a guy who’s not an engineer.

        Posted 7 months ago
  23. * Patrick says:

    Wow. You have absolutely NO understanding of basic physical laws! Don’t, please don’t state bad opinions as fact! The equal and opposite forcell you claim would create “recoil” is at the motor mount! Just like when your tire turns on your car the opposite force is against the mounts on the differential. So no there is no recoil from a slung projectile! The bit about the gyro effect is funny, considering that we use gyros to steady all sorts of ballistic weapons in use today! The effect would stabilize the weapon for better accuracy during releases! Lean, research, test, examine, compile, adjust, test, compile, confirm, then write! Never speak from authority when you are not one!

    | Reply Posted 5 months, 4 weeks ago
  24. * Patrick says:

    As for the satellite mount “debunked”, how does a satellite change objective trajectory and given focus areas with out affecting orbit speed, angle, distance, and orientation? Oh yeah gyroscopes counter any force large enough to destabilize orbit functions! Same as launching ICBMs!

    | Reply Posted 5 months, 4 weeks ago
  25. * Dikdik says:

    Working prototype seem has no recoil problem, terrible accuracy did.

    | Reply Posted 3 weeks ago


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