Need a Rocket Scientist!

[tkendrick]

Here's one for all you hi tech guys to chew on for a while.

Have a buddy who works for a little R&D outfit near Redstone Arsenal. They primarily do testing and eval for some of the bigger firms and occasionally for the military.

They are currently working on a new projectile concept which may or may not be applicable to rifles. (I have my own opinion, but I'm not anywhere near smart enough or educated enough to make a guess)

Someone has come up with a cocept that goes like this:

The projectile (bullet) is hollow, made from a hard material, my guess is they're working with depleted uranium or solid copper or something in between, don't really know.

The bullet is milled, not cast, and looks like a standard bullet, except that it is hollow. The opening narrows down the farther back you go, until just before the base, where it opens up, constricts again, and finally forms a bell shape like a rocket nozzle.

The theory that they are working on, and are apparently having enough success that someone is willing to spend the money to test it, is that once the bullet hits a certain speed, the air entering the front of the bullet is compression heated to the point that it creates plasma and actually provides thrust which causes the bullet's velocity to increase as it moves down range.

This sounds like a scram jet to me, except there is no fuel.

From what I gathered from the three minute conversation I had with the guy, they are not having stability problems, the thing acts pretty much like a standard bullet, except that it does not drop or lose energy, in fact it gains energy the further it goes.

Seems they're mostly concentrating on anti-armor wepons, like those 37mm's mounted on the A-10, but have been looking at it for eventual use in small arms as well.

I am assuming (didn't get this from him) that the thing will continue to pick up speed until it reaches the point where friction or stress will cause it melt or disintegrate.

I see a lot of pro's and con's, but I'm interested in hearing what the folks in here think.

MODS: I had absolutely no idea where to stick this thread, so if it doesn't belong here, please move it.

 

[ArfinGreebly]

Metalurgy

I ain't no rocket surgeon, and I ain't no alchemist.

However, I'm wondering just how much compression would be required to cause the walls of a metallic chamber to go through a plasma conversion.

If you can actually get it going, its a nice exothermic process which should be self-perpetuating.

If you can actually get it going.

I don't have the math and physics, nor do I have enough data on the projectile.

Wish I could say more.

 

[GunTech]

Sounds like something for nothing - i.e. not plausible. It might work if equipped with Dean drive, however.

 

[Hoppy590]

ya. no chemist / physicist. but you dont get thrust from things that dont expell energy. and it just seems to me, anything short of atmosphere re-entry type speeds would not cause enough heat to start plasma type reactions

 

[armedandsafe]

Perpetual motion machine.

Pops

 

[JohnKSa]

Guy's yanking your chain.

If he's not you'll know it because he'll soon be in jail for talking about things he shouldn't.

 

[glockman19]

Concievably through quantum physics it sounds plausable on paper but you would require a projectile with a high melting point something along the lines of Titanium, Molebdeum, or a combination of the two. This would create a light weight projectile that was very hard and could penetrate at high temperatures.
Titanium:

The two most useful properties of the metal form are corrosion resistance, and the highest strength-to-weight ratio of any metal. In its unalloyed condition, titanium is as strong as steel, but 45% lighter.​

Molybdenum:

In alloy, steel molybdenum acts as a hardening agent and also improves the properties of the alloy at high temperatures; such alloys are used in making high-speed cutting tools, aircraft parts, and forged automobile parts. The pure metal in the form of thin sheets or wire is used in X-ray tubes, electronic tubes, and electric furnaces because it can withstand high temperatures. It was used in early incandescent light bulbs. Because it retains its strength and structure at very high temperatures, it has found use in certain critical rocket and missile parts.​

Scram Jet:

a scramjet essentially consists of a constricted tube through which inlet air is compressed by the high speed of the vehicle, a combustion chamber where fuel is combusted, and a nozzle through which the exhaust jet leaves at higher speed than the inlet air. A scramjet requires supersonic airflow through the engine. scramjets have a minimum functional speed. scramjets require acceleration to hypersonic speed.​

 

[pdowg881]

I think all you need is some Unobtanium.

 

[glockman19]

I think you mean:
Handwavium:

handwavium refers to a way of circumventing a problem by breaking the laws of physics, as if one might banish an insuperable objection by waving a hand at it. Bad science-fiction stories often employ handwavium to solve knotty problems. Star Trek is full of such devices, such as the replicator, the transporter or the phaser (which disintegrates a person neatly without a hint of energy release or even a puff of steam). Any writer who creates a faster-than-light space drive, for example, is employing handwavium, though this device is so consecrated by its widespread use and utility as to be acceptable within the SF genre.​

While Unobtanium refers to some useful material that suffers from the serious disadvantage that it either doesn’t (yet) exist,

 

[230RN]

Mmmm..... probably not, if you're looking at compression heating of the incoming air.

The heat of compression would have to be provided by the kinetic energy of the bullet. Thereby slowing it down.

Might get sorta close to looking like it might work if the bullet itself were hot enough to heat the incoming air... like with a combustion-operated ramjet.

In that case, heating the incoming air would be provided by the heat of the bullet material --if you could transfer that heat from the bullet material to the air fast enough. The bullet would have to around white heat for this to come close to working. However, heat tranfer rate is related to the square of the relative velocity between the two materials, and even conventional bullets move along at at least Mach 2.

Perhaps that is why they are talking about refractory metals like moly. Maybe they heat it up with thermit in the hollow space of the bullet --when the thermit burns out, leaving the bullet hot, the supposed ramjet effect starts up.

If, if.

All in all, it sounds like one of those concepts which is worth testing, but not investing in right away.

(Hatcher's Notebook has a table on p 399 which gives the heat distribution from the powder in a cal .30 cartridge but does not mention heat energy given to raising the temperature of the bullet --so it can't be much. Although conventional bullets do get hot, they don't get white hot.)

"Cannot the common man add and subtract neutrons in his head?" (Philip Wylie, in Opus 21)

 

[TexKettering]

except that it does not drop or lose energy, in fact it gains energy the further it goes.

That doesn't seem to follow basic laws....

 

[Czar]

Rocket Scientist checking in-


Sounds fishy to me. But to qualify my remarks I don't work with aerodynamics, I'm just a Mechanical Engineer working as a Systems Engineer.

If such a system would work as advertised you'd see supersized versions of your bullet matching your description loaded in an spoke array turning a generator and we wouldn't need nuke or coal power plants anymore, just the free-jets. Unfortunatly we have the laws of Thermodynamics which basically state - you never get something for nothing. If you get energy out, then you have to put that energy in. So if you're creating a state change from gas to plasma, then mechanical/thermal engergy needs to be put in to do it. Also, that means you have a plasma jet upon leaving the barrel... I can only imagine the damage a small plasma jet would cause to the crown if not the entire barrel.

Not to mention, just try shooting a hollow bullet... granted you could use a wadding or sabot, but how to get it to reliably separate...

Now, if it had some sort of fuel encased in the lining, that could give extra umph.

The hole itself may have some aerodynamic efficiencies, but I'd have to see some math behind it... like I said above, while a skeptic, I'm no aero guy...

 

[Lucky]

Glockman technically warp drives moved space (warp) rather than the ship, to give the effect of 'traveling' FTL.

And the replicator is cleansed for TV. IRL they create a copy of you and the original one must be thrown in a wood chipper (that's why they stand on those circles, they're trap doors). Ugly business.

TKendrick, Besides the obvious problems, one must ask why such an AT weapon would be competitive at all? A rocket can also increase velocity as it goes down-range, and unlike the fictional bullet it really can counter 'drop'. Furthermore a rocket can mount a stronger penetrator, one that's not milled out and compromised. And on top of that you don't need a heavy and complicated gun to fire the rocket.

The big problem is that Oxygen generally isn't fuel, it's an oxidizer. And Nitrogen alone isn't fuel. And if somehow they did create plasma, it's just the same matter minus some electrons. It's strength is conductivity, responsiveness to magnetic fields, etc. The described idea doesn't use those properties at all. So let's say it's the same amount of matter, propelled backwards at a velocity. That propulsion is coming from the bullet, which is obviously slowed down a like amount. And of course there's inefficiency, like every machine has, normally friction, and heat, you know. This means that the bullet will slow down even more than if it were plain, and at best without any inefficiency it would simply act normally (if it worked as described). Ironically the theory takes this deficiency and puts it forward as a desired effect!

 

[tkendrick]

[/Guy's yanking your chain.[HTML]

Chain?   You get a chain?   How come you got a chain and I'm stuck with this scratchy old rope around my neck?:scrutiny:

Actually, that was my first reaction.....however (see the following)

[HTML]If he's not you'll know it because he'll soon be in jail for talking about things he shouldn't.

I wasn't going to post this, didn't figure it was worth the time or energy, until;

This conversation took place about 6 months ago. We were at a mutual vet-friends funeral. (Seems like that's the only time we ever get together any more...and it's happening with depressing regularity.)

Anyhow, flash forward to about 2 weeks ago:

I'm reading one of John Ringo's new novels (and before you guys jump on me, Yes, I know he writes science fiction....the key word being "fiction") and by an odd coincidence, there is a blurb in there about this very thing. In almost exact detail. So it can't be too much of a secret.

Since most of these guys get a lot of their ideas from hanging around with real rocket scientists, I figure that maybe there is something to it.

Given what little I know about scramjets, metalurgy and physics, and what I do know comes mostly from the discovery channel, I am kind of the same opinion as most of you here...I just don't see how it could work.

But I'm a slow learner, and a slow thinker. This idea started rattling around in my brain, where it didn't meet much resistance, but did raise some other questions for me.

If you could get the thrust thing to work, and I heartily agree that's a BIG if, there were 2 problems that came to me almost immediately.

As I understood what I was told, the bullet is still being stabilized the old fashioned way, ie from rifling in the barrel. I've always thought that bullet stabilization was a function of rate of twist and velocity. So, if a bullet is constantly accelerating, would it not quickly destabilize?

Secondly, the thrust would have to be exactly centered (there's probably a term for that) when it left the "nozzle?" at the base of the bullet. It would seem to me that no matter what material you made the thing out of, it's going to start to erode from the gas, and as soon as it does, it's going to create unequal thrust which, as there is no other stabilizing system, would cause it to veer one way or another.

Either way, there goes your accuracy, riki-tik....No?

I think I'm getting a headache, just from thinking about it

 

[Bazooka Joe71]

I'm reading one of John Ringo's new novels (and before you guys jump on me, Yes, I know he writes science fiction....the key word being "fiction") and by an odd coincidence, there is a blurb in there about this very thing. In almost exact detail

It seems like you answered your own question.

 

[Ithaca37]

This is impossible. It is a perpetual motion machine and is thermodynamically impossible. It can not gain energy without work being done on it.

 

[ctdonath]

the air entering the front of the bullet is compression heated to the point that it creates plasma and actually provides thrust which causes the bullet's velocity to increase as it moves down range.

Air is not fuel. The plasma is the result of more energy being dumped into heating the air than the hot air will release - net energy loss.

Add some fuel to the mix, however, and you have a scramjet. NASA is working on one, and it's actually not very big (a few feet long).

 

[358minus1]

"Titanium:
The two most useful properties of the metal form are corrosion resistance, and the highest strength-to-weight ratio of any metal. In its unalloyed condition, titanium is as strong as steel, but 45% lighter."
-Glockman19

First sentence is very true. Second sentence should read "In its alloyed condition, titanium is as strong as steel, but 45% lighter." Unalloyed titanium (or what is sometimes called 'commercially pure titanium') is not very strong at all.

 

[alex_trebek]

In my fluid mechanics course, we only breifly covered supersonic air flow. However I do know that in order to have air flow velocity greater than mach 1, you have to have a nozzle of some sort. I cant remember exactly why this is, it probably has something to do with air compression at supersonic speeds, and the expansion aspect. For this reason i tend to believe that this would only work on a projectile moving faster than mach 1.

As for the plasma issue, I dont think that a bullet is moving fast enough. Yes it is possible to turn air into plasma simply by moving fast enough, this is what happens to space vehicles upon rentry I believe. I dont think a bullet is moving anywhere near fast enough.

I think this concept would eliminate the vapor trail that you will sometimes see. The vapor trail is caused by the sudden expansion of gas directly behind the bullet. It forms because of the bullet's speed. I believe this design would reduce the drag this effect would cause on a bullet.

 

[usp9]

I'm left wondering what propelled a hollow projectile to hyper-sonic speed in the first place? I'll wait for the Phasers of Star Trek, heck most all the other gadgets on the show are actually used today.

 

[robert garner]

O-kay

Tanstaafl
However there IS a venturi effect, so while such a bullet wouldn't gain any
energy or speed, perhaps its flight could be prolonged a few %?
In the early days of our experience with vents (trying to stay away from using a cuffed trach) a venturi was used to increase air intake , theory was the compressing air increased velocity which drew further air from atmosphere thru
a series of holes arranged around the central core.
Perhaps our rocket scientist could make better sense outa this for us?
Often people tend to either oversimplify,or exagerate when dragging the un-enlightened outa the mud,maybe there is some thing here?
robert

 

[lee n. field]

except there is no fuel.

So where would the energy come from? Gotta come from somewhere.

If it's not burning fuel it's carrying, and not burning fuel scooped up from the intake, it's not burning anything.

 

[230RN]

Re-read Post #10:

Might get sorta close to looking like it might work if the bullet itself were hot enough to heat the incoming air... like with a combustion-operated ramjet.

In that case, heating of the incoming air would be provided by the heat of the bullet material --if you could transfer that heat from the bullet material to the air fast enough. The bullet would have to around white heat for this to come close to working. However, heat tranfer rate is related to the square of the relative velocity between the two materials, and even conventional bullets move along at at least Mach 2.

Just noodling in the above, but you should get off the idea that the air is heated by compression:

The heat of compression would have to be provided by the kinetic energy of the bullet. Thereby slowing it down.

 

[BigSoundRacing]

Not rocket scientist, but.....

Sounds interesting enough.... Push the bullet fast enough down range, so it can compress air to a high enough temperature to start to burn the interior of the bullet, thus energy to propel it forward further through the nozzle. You only need a one or two second burn to help carry the bullet down range further.

Or, line the nozzle with a material that will burn from the compressed air, providing propellant, yet would not actually burn the bullet and would not ignite as it traveled down the barrel.

Or, a bullet that separates as it leaves the end of the barrel, so that a heat shield drops off the back of the bullet.

This could be fun!

 

[WayneConrad]

Ask him if he's an ex navy seal.