DREAD weapon system

[Standing Wolf]

I'm keeping my Pythons, thanks all the same.

 

[Control Group]

no recoil because the projectile is already at speed when it's released.

Sorry, but svtruth is right: conservation of momentum doesn't play favorites. If it leaves the weapon in some direction at some speed, force was exerted in the opposite direction to do so. Consider a normal rifle. When the bullet leaves the barrel, it's already at speed, too (it certainly doesn't accelerate after leaving the muzzle), but you definitely feel recoil.

This weapon may do a great job at spreading recoil out across time and mass, but it can't get rid of it without completely and fundamentally changing our understanding of the universe.

 

[Zak Smith]

150gr 30 caliber projectile at 8000fps -> 29 KJ of energy at the "muzzle"
120,000 RPM -> 2000 per second

29KJ * 2000/second -> 58 MegaWatts "at the muzzle"

Because thermodynamic inefficiency, the input power will have to be much more than that.

Where are you going to get a 80 - 120 MW power source?

-z

 

[Owen]

time to do some Free Body Diagrams...

 

[middy]

I think it's a great idea. But it looks a little hard to conceal.

 

[Control Group]

Where are you getting the 150 grain figure? If they more than double the velocity (as compared to a rifle), they can more than halve the mass of the projectile to achieve the same total energy. That's what stopped me from going through the same calculations you did, I didn't feel comfortable assuming the mass of the .30 cal round.

In any event, if we do assume that mass to be correct, you're completely right. For comparison's sake, if your car goes through two gallons of gas an hour (30 mpg at 60 mph), it's generating roughly seventy kilowatts of power* (including all losses to inefficiency). Even given perfect energy conversion (!), coming up with 58 MW of power is equivalent to burning more than fifteen hundred gallons of gas an hour.

*These numbers are based on 125,000 BTU/gal. of gasoline, which is the number I remember, but I haven't confirmed.

 

[Zak Smith]

A typical 308 caliber projectile is 150 grains. They also mentioned 50 caliber projectile. If the projectiles have to be spherical, then 150 grains will be somewhere between 0.30" and 0.50". Even if the actual number is 75gr or 300gr, we're still talking a LOT of power.

Of course, if the burst rate is limited, we may be able to transform that power requirement to a capacitance requirement.

In this article about an electric warship, they mention it producing 78 MW, to get an idea what current systems can produce.

http://www.navyleague.org/sea_power/may_04_10.php

 

[Control Group]

Fair enough on the projectile mass. And you're right, cutting that even to 75 grains still leaves you with a huge energy requirement to meet. I was more trying to make excuses for not doing that calculation myself than trying to cast aspersions on yours.

Anyway, neat article. I particularly like the quote:

"Our bottom line is that if we can put millions of joules of energy onto a target, something will happen."

Which made me chuckle out loud.

In any event, that does give some idea what sort of energy production we're looking at, and really puts this proposed system in perspective. The new supercool ship puts out enough power to run one of these guns at speed.

*eyeroll*

The idea of capacitance occurred to me (though it'd be one huge murtherin' capacitor), but the article from the original post talks about firing the thing at full speed indefinitely, as long as the ammo held out. To live up to that billing, obviously, you need sustained power. And ~80 MW of sustained power is a "non-trivial exercise," as one of my physics professors would have said.

 

[Zak Smith]

The system proposes using spherical projectiles.

The ballistic coefficients for spheres SUCK. While a 30 caliber match bullet has a BC of 0.45 or so, and a 50BMG has one above 0.900, a 58 caliber 566 grain lead sphere has a BC of only 0.160. As the mass is decreased, the BC also decreases.

Even in the more favorable 0.58" case, here's how the velocity will drop off, compared to typical 308 and 50BMG rounds:

_Bullet_           _BC_ _MV_         0     300     600     900    1200 | YARDS
58 caliber        0.160 8000 >    8000    4637    2624    1318     866 | velocity (fps)
308 match         0.430 2700 >    2700    2131    1641    1257    1032 | velocity (fps)
50BMG             0.900 2700 >    2700    2419    2155    1908    1681 | velocity (fps)

For small arms which are employed within 300-500 yards max, there might be some benefit.

When you start to talk about vehicle or airborne platforms, where the engagement distances are increased, the ballistic problem becomes obvious.

50BMG SLAP rounds (very high BC .40" penetrator in a 50 caliber sabot at over 4000fps) have made vehicle kills well beyond 2000 yards, from a HMMV platform.

-z

 

[Rebar]

Finally finished the download - verdict, don't bother. Pretty much just goes through the existing text with cheesy graphics.

 

[rwc]

Wouldn't a "rail gun" be a more efficient design?

 

[Taurus 66]

It looks like the Star Ship Enterprise with pistol grips. It may offer hyper rapid rate of fire, but how practical is this idea? A shooter could zip through more rounds than originally intended (after one quick burst where 1 normal shot becomes 100 spent rounds) and suddenly be left with an empty useless Star Ship Enterprise. Now the owner/user is left to flee a bad scene at warp 6.

Even if it actually worked according to the presented theory, it's impractical!

 

[DelayedReaction]

Rail guns are totally unrelated to this concept, and are horribly inefficient to boot. I think the best they ever got was around 15% efficiency (15% of the energy input was imparted into sending the projectile forward), and the rest of the energy was dumped out as heat and light. Enough heat was generated to vaporize the rails after a few shots, assuming the bullet wasn't welded to the rail.

(I'm a railgun nut)

There is no recoil on this device; in essence it's a technologically advanced version of a sling. Same principal: rotational motion is converted into linear motion by releasing the restraints and allowing the object to move in its natural direction (which is tangential to the travel of the circle). When you release a rock from a sling, is there recoil?

They didn't say the device could fire in every direction, they said the mounted version had a 360 degree field of fire. It's probably mounted like a regular machine gun.

Although spheres suck aerodynamically, they have the best wound characteristics. That's why claymores contain hundreds of tiny steel balls acting as fragmentation; studies performed while designing it showed that lots of tiny spheres traveling at high velocity provided the best probability of lethality. This thing would shred people.

I'm interested in knowing how the gyroscopic forces are accomodated. A large disk rotating at extremely high RPM is not going to want to move.

 

[Zak Smith]

Although spheres suck aerodynamically, they have the best wound characteristics.

If this is the case, then why isn't anyone designing spherical handgun and CQB carbine bullets?

A sphere isn't going to fragment causing a deep but "wide" wound profile, like the best performing carbine rounds do today.

 

[DelayedReaction]

If this is the case, then why isn't anyone designing spherical handgun and CQB carbine bullets?

Beats me. I'm just basing my information off of what I've studied, and they concluded that when it comes to fragments, nothing beats a ball. Bullets probably catch the rifling (and trap the gas behind them) better than a ball would, but I don't know.

I think the DREAD system (I already hate that name) loads and projects bullets irrespective of orientation, which is why they need something like a ball. I suspect they follow the "accuracy through volume" school of marksmenship.

 

[Cool Hand Luke 22:36]

Must be hell to elevate that thing with all that rotational inertia, conservation of angular momentum would seem to dictate that a disc spinning a 5000 rpm is going to be difficult to translate about its axis.

 

[Darkmind]

Another pipe dream that our tax money will be wasted on!

 

[thorn726]

Sorry, but svtruth is right: conservation of momentum doesn't play favorites. If it leaves the weapon in some direction at some speed, force was exerted in the opposite direction to do so. Consider a normal rifle. When the bullet leaves the barrel, it's already at speed, too (it certainly doesn't accelerate after leaving the muzzle), but you definitely feel recoil.

someone pretty much said it already , but yer missing someithng here=

the "recoil" ebnds up being received by the centrifuge, already turning, it sends that energy with the spin. so there is a recoil, but it wont be felt

 

[Catuela]

Although spheres suck aerodynamically, they have the best wound characteristics.

If this is the case, then why isn't anyone designing spherical handgun and CQB carbine bullets?

The second was answered in the first one when it was stated that spheres suck aerodynamically. There is almost no way to get a high velocity sphere to travel in a consistant straight path. Just think about a baseball pitcher. The smallest amount of spin in one direction or the other in a small projectile travelling and 1000fps or so would quickly veer off it intended course and become wildly innacurate.
To make it easy think of a pithcher throwing a curveball or slider. With a certain amount of spin in a certain direction he can make the ball travel a significant amount to the left or right. However a quarterback throwing a football places a great deal of spin on his projectile yet it flies straight as an arrow. I don't pretend to know the math but that's how it works.

 

[feedthehogs]

While debating the physics of the operation, its practicality in actual combat is useless.

Other than maybe an initial use in an open field combat situation against a known and identified enemy, insurgent or close quarters makes this thing useless.

As has been proven in Korea, Vietnam, Afganistan, Serbia and Iraq, regular army and more important, insurgent gorilla attacks using the natural terrain and civilian towns, will tie a superior force in knots despite having the best technology in the world.
Unless you do what the US did to Japan and just nuke a few towns and kill everyone, mostly civilians. Why need these goofy weapons at all?

More star trek watching geeks salivating over pictures of Pam Anderson trying to come up with 23'rd century crap.

 

[Control Group]

the "recoil" ebnds up being received by the centrifuge, already turning, it sends that energy with the spin. so there is a recoil, but it wont be felt

That's just spreading the recoil over mass (through the centrifuge and the carrying body) and time; given the velocities they're talking about, I don't buy into the "you won't feel it" argument.

Consider throwing a baseball: you're essentially doing exactly what this is doing, and you definitely feel the recoil (try throwing a pitch while standing on warm ice sometime). Granted, you feel the recoil prior to releasing the ball, but you haven't gotten rid of it. For the rate of fire this thing is supposed to have, the ball is going to be picked up, accelerated (generating the recoil), and thrown so fast that the recoil might as well be upon firing.

Now, if you pre-load the disk with all the rounds you're going to fire, then spin it up to speed, you'll be generating recoil along all vectors at once, with a net force of zero, which is what I'm assuming you're saying. In that case, you're right, there'd be no effective recoil. But if they're talking about thousands of consecutive rounds, there's no way you can achieve that. There has to be a feed system putting balls on the disk, at which point they're transitioning from stationary (relative to the weapon) to high velocity (again, relative to the weapon) in a short time frame, generating effective recoil.

Although, as I think about it, I suppose you could solve this problem by loading balls in pairs at diametrically opposed points on the disk. Hrm. Of course, you'd have to also fire them in pairs, or you're going to end up with recoil (albeit on a weird vector compared to conventional arms) when the centripetal force of one round goes away and the centripetal force of the other doesn't, which should lead to a net acceleration of the whole.

In any event, the system is generating net acceleration along a given vector when it fires, you simply cannot avoid the fact that there's a matching compensatory net acceleration. This doesn't change just because it's spinning, or you've invented a jetless drive.

 

[Bemidjiblade]

Death By Frisbee!!!!

I'm going to take a long, somber moment to consider the depth of thought that all y'all have put into considering the feasability of this weapon. (I for one, would never have thought of the gyroscope deal).

That moment being over, I'm going to spend the rest of my day walking around with a grin similar to this:

And the thought, "Death by Frisbee!" stuck in my head.

Peace (through superior firepower)

 

[walking arsenal]

wouldnt the spheres come out of the thing spinning and therefore curve in flight?

 

[Control Group]

wouldnt the spheres come out of the thing spinning and therefore curve in flight?

Not necessarily. A good knuckleballer can throw a pitch with almost no spin on it, I'd think one could design a throwing mechanism to do something similar.

Now that you mention spin, though, another problem does occur to me. The ball wouldn't be spinning, which would include not spinning around the axis of its flight path, which might well prove to be a real detriment to accuracy. On the other hand, at 8K fps, perhaps it doesn't matter.

 

[2nd Amendment]

I'm not reading this whole thing again so I may have missed it but, did anyone mention the gyroscopic effects? What kind of mount would it require to hang on to this thing? What would be the effects in a moving vehicle as weight and balance change?

Two pistol grips. Yeah, that'll let a guy hold this thing down. Riiiight...