Need a Rocket Scientist!

the term "plasma" adds a different slant on the physics of the system. If the "bullet" with the decreasing diameter cavity can be propelled fast enough (regular bullet speeds would be a snails pace in comparison), and if a plasma can be created at the small end of the cavity, the resultant atomic bond energy now comes into play. That is the sought after chemical reaction we need to get something from nothing. In other words, the energy is inherent in the air atoms and molecules, but under normal conditions it cannot be released and therefore cannot be used for propulsion. Make it into a super hot plasma and you do get something from an apparent nothing.

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Would this require:
A) A more fierce explosion than primer setting off the usual powder?
B) A more compressed chamber for allowing such velocities to be possible?
C) The projectile to maintain a temperature for the majority of its flight?

I am completely uneducated here, but this is an intresting brain teaser

I call bullarky on this. Once again I know an object put into motion will not increase in motion. This ramjet theory about super heating a bullet to provide a propellant by intake and exhaust of air, as already mentioned here by some members requires an sustaining energy source.

Even if you were able to get the bullet hot enough if the ramjet without fuel, simple compression, burning of air theory is even plausible once the bullet leaves the barrel it starts to cool down and slow down. We already have that.

I've got an innovative idea. How about putting more energy behind it.

PB

Hmm

The bullet is its own fuel.

"Drag goes up with the square of speed,"

Only below the speed of sound.

The bullet can not accelerate unless there is an input of energy that provides more force than the drag force.

What is the source of that energy?

K

Physics said,

So if it's not a fuel source, where is this heat coming from? From drag, and the speeds you would need to heat that bullet up are pretty high (Honest question: How many guns do you know of that shoot a molten bullet?).

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Good heavens, Physics. At least five times I described a possible source for heating of the body of the missile. I also posited that the "bullet" might be made of a refractory material. The OP only said that it was a "hard substance."

Primary B,

as already mentioned here by some members requires an sustaining energy source.

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Once again: I'm not talking about sending it around the world. I'm talking about a possible short-term boost during perhaps 100 ms of its flight before the projectile cools down.

More:

Even if you were able to get the bullet hot enough if the ramjet without fuel, simple compression, burning of air theory is even plausible once the bullet leaves the barrel it starts to cool down and slow down. We already have that.

I've got an innovative idea. How about putting more energy behind it.

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This is not too clear, but once again, I'm not talking about "burning" the air. I don't know where that came from. And there are limits to how fast you can propel a bullet-type projectile from conventional propellants "behind it." (I recognise the sarcasm.)

Atblis:

The bullet is its own fuel.

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Now you're getting close. But instead of saying "fuel" (which once again implies compbustion), put it this way:

"The hot bullet is its own source of energy to heat the incoming air."

Sigh.

All I was trying to do is "reverse-engineer" what the boys at Redstone Arsenal might be trying to do, based on the meager information given in the OP:

1. A small R&D shop is assigned the task of fabricating an object which is given as some kind of missile or projectile.

2. It is open all the way from front to back and its internal structure is shaped like what one would expect for a ramjett tube.

3. It is made of some hard material.

4. Rumors have it that it is supposed to increase its velocity.

Now. What could the boys at Huntsville be thinking?

In doing this kind of reverse engineering I considered the following. (Now actively follow along here, without speed-reading it):

I presented the idea that it could be a simple ramjet which would accelerate this missile after being launched from some projector or another. We can reasonbly presume it was launched from a gun-like apparatus, presumably (again) by conventional powder propellants.

I discounted the idea that the incoming air was compressed and thereby heated, since this would violate the laws of thermodymanics. Many people pointed this out anyhow. Some came up with the idea that the air was heated by some kind of plasma-generating effect. OK, maybe.

Now since this projectile was open at the front, it was possibly not intended to be a "rocket" filled with fuel, like some of the tank rounds where the shell is rocket-boosted after leaving the gun.

What then could propel it?

Several times I brought up the notion that combustion of a "fuel" was not required to heat the air in order to generate a ramjet effect. I gave a fanciful example of an aircraft powered by a diesel generator set which fed power to resistance heaters in the ramjet tube, which is conceptually possible if not a practical way of going about things.

I then posed the notion that if the projectile itself was very hot, a "combustion" source of heat would not be required. The heat energy of the "hot body" ramjet could be transferred to the incoming gases, thereby giving them energy, accelerating them, and providing the thrust.

You will note that there is no violation of the conservation laws here! The energy to accelerate the gases comes from the hot body of the ramjet itself.

OK.

Now the question was, "how could this projectile be heated" in order to provide the energy to the gases "second-hand," so to speak.

(1) It could be heated up before launch.

(2) Other

(3) The hollow cavity could be filled with a substance which burns very hot, which could be ignited from the intitial propellant charge (like a tracer round) and when it burned out, would leave the front of the projectile open and the projectile very hot. Sych a "filler" substance might be a thermite or thermite-like composition.

Air would then enter, be heated from the now-hot body of the projectile, accelerated out the back (conversionof heat energy to kinetic energy) , and provide thrust, even for a short period of time, thereby enhancing the downrange performance of the projectile.

Just "reverse engineering," which is kind of a mind-reading game anyhow. That's all.

But obviously, based on what was said in all the above, it's all impossible, and the boys at Redstone are just wasting their time, and I am, too, by trying to reverse engineer the problem.

(Kentac, I have stated several times what the source of the energy might be. Re-read the above. Actively.)

I am afraid at this point I have bumped into the limits of my powers of explanation. I can't seem to penetrate the armor of conventional thinking on this one, even though what I am describing is all conceptually possible on a step by step basis.

Not blaming you guys. I'm blaming me.

"Air would then enter..."

Air will not flow through the hole if the object is moving faster than the speed of sound.

funny, i saw a special on one of the discovery-type channels a couple days ago, and this self-perpetuating-plasma-rocket thing was being theorized as a possible future method for space travel, only somehow magnets were involved,as well.
i'm thinking maybe the OP saw this too,and is pulling our leg.

:banghead:

Let me put it this way, you are not going to be able to heat up the air hot enough with just friction doing the heating. This is exactly why they put an energy source in a ramjet. There is no conceptual leap here, I'm sorry, I know what it's like and can relate.

I would also like to point out where in the ramjet the energy source is located.
http://www.grc.nasa.gov/WWW/K-12/airplane/ramth.html is a pretty simple explanation of a ramjet with a picture that I am basing this on. Notice the equation for thrust, you must have positive thrust to maintain any benefits here. You will not have a very good pressure difference without an energy source, which happens to be located where the higher pressure is necessary. The intake air in your system is the same temperature as the exhaust air, which is why I say, NO WAY, I am not convinced that you can obtain a positive pressure difference in this system. This means your whole pressure term is negative. Also notice that the only way to increase your thrust term, is to have a positive pressure term.

Can you explain another way to get a pressure term that is positive? I am asking that honestly, because I don't know a whole bunch about ramjets. If you can explain to me how you are getting a higher pressure at the back end than at the front end, and it obeys all physical laws, then yeah I'll believe you.

funny, i saw a special on one of the discovery-type channels a couple days ago, and this self-perpetuating-plasma-rocket thing was being theorized as a possible future method for space travel, only somehow magnets were involved,as well.
i'm thinking maybe the OP saw this too,and is pulling our leg.

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These have a fuel source powering an ion drive. Solar powered likely, but you are still adding energy.

Air will not flow through the hole if the object is moving faster than the speed of sound.

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I have never in my life heard of this. Why won't it enter?

How does air enter the intake of jets flying at supersonic speed?

Free Energy hasn't (at least that we are aware of ) been discovered yet. When it is, it will be the best thing since sliced bread.

The only source of free energy I'm aware of the glow from that shiny orb we orbit. Keep it qiuet, though. We don't want the politicos taxing it.

Woody

230RN, you do have a point - and in terms of the first law, it could work. However, practically, it can't work.

Let me just preface this by saying that I actually do have experience with supersonic combustion and scramjets - I have worked on a design team for the X-43 (although, they took a different direction and none of my work made it onto the project) when I was at Marshall.

Using the thermal energy of the bullet to heat the air is just not practical. The thermal mass of even a Uranium bullet would be just too small - even if the bullet was near melting, the thermal energy converted 100% into kinetic energy wouldn't be much of an energy boost at all. Let's say you've got an 800 grain .50 BMG bullet, at 1400K (near melting temp of 1405K) with C=28 J/molK. That's a thermal energy of (28J/molK*51.8g*(1/238g/mol)*(1400-300K)) 6703 Joules. Assuming the muzzle energy is 16000 J, the entire thermal energy would be enough to speed up the bullet by... an impressive 175 m/s or 574 fps.

That won't work, however, because the heat transfer between the bullet and the air passing through the bullet would be very, very small. The heat transferred to the air would be so little that it wouldn't add any velocity to the bullet.

However, if using thermite (III) as a solid rocket fuel to heat the incoming air which would then be exhausted through a small nozzle (as in a solid-fuel scramjet), assuming 1/4 of the bullet mass was thermite (thermite is not particularly dense, and you'd need a fairly heavy nozzle), you could have 200 grains of thermite (or 12.95 g = 0.0605 mol) to generate (0.0605 mol * -851.5 kJ/mol) 51515.75 Joules of thermal energy. At mach 2, a ramjet is pretty efficient - let's say maybe up to 20% efficiency. You could gain 10,000 Joules of kinetic energy, or about 215 m/s or 705 fps.

Of course, that thrust would be spread out over the trajectory, and could probably be tweaked to keep the velocity constant for around 400 yards - imagine adding 400 yards worth of velocity!

I think that could be plausible, assuming you had some method of igniting the thermite.

Thank you, thank you, the naked prophet. I had decided not to answer any more posts which did not address the conceptual possiblities as I presented them --and would wander off into "free energy" and "plasmas" and would insist on asking where the fuel was and confusing kinetic energy with pressure.

Ahhhhh.... thanks......

You are probably correct here:

That won't work, however, because the heat transfer between the bullet and the air passing through the bullet would be very, very small. The heat transferred to the air would be so little that it wouldn't add any velocity to the bullet.

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.. but I was also thinking that since heat transfer basically depends on the square of the inter-medium velocity, and the projectile would be moving pretty fast, and that there was the possibility that internal shock waves (which are of high density) might also aid the heat transfer rate. And of course much of the heat would be lost to the ambient gases on the surface of the projectile, radiation, etc.

However, I was looking at the conceptual possibilities inherent in the original post.

Thank you for seeing them.

I still think it's worth losing a little money on, even if it is not as I tried to reverse engineer it. After all, the research itself might lead to other advances.

Actually I have been thinking on this one and it might work, MORE OR LESS as it is described. Remember the Gyrojet and how it's projectiles contained fuel that caused it to start off slow and have a better higher velocity than a standard bullet down range. If you took something like a Gyrojet round and then put a casing behind it so as to fire it like a regular bullet and have the jet add to that it would work. It would be very expensive and you would gain nothing but extended range and better terminal ballistics at the cost of reliability.

...if a plasma can be created at the small end of the cavity, the resultant atomic bond energy now comes into play. That is the sought after chemical reaction we need to get something from nothing.

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If the bullet is not made of metal! You do not have chemical bonds that produce energy on forming in most common metals, you have metalic bonds which are the result of the loosely held electrons in the metals being shared to some extent. If it have an organic fuel source (something with a lot of double and triple bonds), or you have a extreme of oxidation potentials (as in the termite discussed above), but common metals in the a bullet would not be a source of chemical bond energy.

Several times I brought up the notion that combustion of a "fuel" was not required to heat the air in order to generate a ramjet effect. I gave a fanciful example of an aircraft powered by a diesel generator set which fed power to resistance heaters in the ramjet tube, which is conceptually possible if not a practical way of going about things.

I then posed the notion that if the projectile itself was very hot, a "combustion" source of heat would not be required. The heat energy of the "hot body" ramjet could be transferred to the incoming gases, thereby giving them energy, accelerating them, and providing the thrust.

You will note that there is no violation of the conservation laws here! The energy to accelerate the gases comes from the hot body of the ramjet itself.

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I think I have to disagree here. You are assuming that the energy "in" that is needed to heat to the gases and the projectile is less than the energy "out" that is the energy produced by the hot gases escaping. This assumes a better than perfect transfer of energy.

Quote:
Air will not flow through the hole if the object is moving faster than the speed of sound.
I have never in my life heard of this. Why won't it enter?

How does air enter the intake of jets flying at supersonic speed?

The Mach wave stalls the air flow.
Supersonic aircraft have to be designed to prevent the Mach wave from entering the intake or the air flow stalls and the engine flames out.
The SR-71 did this with the moving cones in front of the intake (wide speed range required them to be adjustable).
Bernoulli's law does not apply at supersonic speed since standing pressure waves form.

Drag also peaks right around transonic flow and then starts to decrease above about Mach 1.1 as the angle of the shock waves (the Mach angle) decreases.
Supersonic wings are often not even very airfoil shaped. Lift is created by 'flat plate' effect. An inclined surface to the oncoming air stream deflects the air down and creates an upward force on the wing.
Even now, planes can operate below Mach 1 or above Mach 1, but not AT Mach 1. The instability produced by shock wave formation and attachment is to disruptive to control surfaces and introduces large buffeting.
Other issues with supersonic flight include things like a Mach wave from one portion of the aircraft intersecting other portions of the plane.

Dr Dickie makes an interesting point. If the projectile is metallic and ionically bonded, how could it maintain those structural bonds in the higher energy reaction required to break apart a covalently bonded fuel source?
I wonder what say ceramic would do in a similar situation.

Nothing, since you'd have to input an enormous amount of energy to break those bonds - at which point the energy you have available for thrust is the energy you just converted FROM kinetic energy (ie, by slowing down the bullet).

In skimming the posts above I didn't see anything about using the effect to push the projectile faster.

What if...

The projectile contained (was lined with?) some type of fuel that was shock and thermally stable in an everyday environment. The only way it would ignite is from the intense heat and pressure created at transonic speeds in excess of, say, Mach 4 (appx 4100 fps), a speed that is reasonably obtainable in a standard military field gun. Heck, maybe it just ignites from the heat and pressure of the propellant gasses. The ram-jet effect begins once it reaches a pre-determined air speed. Being that max velocity for a gun is at the muzzle, the projectile would already be experience the ram effect as soon as it exits the bore.

What you have is, in reality, a two-stage rocket where the first stage is detached. The projectile is launched to speed from the gun, only needing to reach a velocity to ignite the propellant charge. Once ignited, the charge burns until consumed. Since the flight time is relatively short, only slight variations in charge burn rates would have two very distinctly different and effective results.

The first possibility would be to maintain velocity and increase range. Imagine a 105mm field piece, a self-propelled 155mm, or a main battel tank with a 100-200 Km effective range. You've suddenly accomplished one of two things: A) Using the same number of guns and gun placement you have exponentially increased the density of firepower over a given geographic area, or; B) You drastically reduce the number of guns needed to effectively support a given geographic area presuming fields of fire consistent with current military strategy.

The second would be to maintain range and increase velocity. A field gun with an impact velocity of, say, Mach 10 or 12 now has a kinetic energy far beyond what can be achieved with a chemically propelled projectile in current field guns, even combined with an explosive charge in the projectile. The current total projectile+charge energy available on target pales in comparison to the same projectile at four or five times the velocity. Imagine the main gun on the agile and battle-tested M1A1/2 Abrams, but with the same terminal effects as a 16-inch shell from a destroyer's main guns. Each platform can carry a couple dozen shells, you can station forty or fifty of them to any point on the battle field, and you can rearrange them at a moments notice.

Best of all, in either possibility the projectile is usable in currently fielded equipment with little, or no, modifications other than battle tactics.

Brad

Where to start.......

Wow, there is alot to be said here, I will hit some main points but not all. In short I'd say this is NBL (Not Bloody Likely) Being a senior aerospace engineering student, specializing in aeronautics, I was going to chime in......then I read all the posts with right/wrong/right in idealized situation responses and decided rather than try and correct some of these I will say a few things. First, I foresee many stability issues with what is basically a freestanding engine. In contrast to what other said, it sounds like this isn't trying to get free energy; it is using the thermal energy created by the shock wave of a supersonic bullet and converts it into mechanical energy. My first thought:

The cost outweighs the benefit; I doubt we will see this put into effect.
Different alloys have been mentioned using exotic materials, which are expensive, but if it travels as fast as a regular bullet, these wouldn’t be needed. I believe they make shells out of depleted uranium due to its strength so it can penetrate armor, not for its thermal properties. If the bullet does reach speeds (which it most likely would) that need different thermal properties, then as I said, the cost outweighs the benefits. Ok now for some boring aerodynamics, without doing the math to see if this is possible, I will theorize some of the necessary situations:

The projectile would have to have a blunt tip in order to get a larger amount of heat transfer (providing this is where the energy is coming from. The majority of heat transfer in supersonic flight isn't from friction on the body; it is from heating of the air from the shock wave. This heats the boundary layer (the thin layer of air that is touching the surface of an object in flight and does not move) which in turn heats the body.

So if the nose of the bullet is very blunt, then the air behind the shock wave would be at its hottest, this would also drastically decrease aerodynamic efficiency. The air would also be hot all around the bullet, not just inside the hollow cavity. The speed needed to create plasma is dependant on the angle of the Shock wave, which is dependant on the shape of the body. Also, if there is a hole in the front of the bullet, then it would no longer act like a rocket engine (because there is an area for the gas to escape forward of the bullet.) Too much math to do here without any specific numbers. This hole causes LOTS of changes in the real world (And more math then I would like to do in spare time ) We could use entropy to figure out how hot the air would be behind the shock wave.

In my opinion, the aerodynamic drag, which would have to be overcome by this makeshift "Engine”, would outweigh the benefits. It would also require more energy to reach supersonic speeds. But like I said before, there is way to many variables here to just speculate without doing the number crunching. It seems like a good "idea" but when you add in the numbers, it just doesnt work

In the words of the Mythbusters, I’d say this is "busted"


oh and the ion engines they use for space travel, they increase speed exponentially, but take a loooooooooooong time to get there. remember these are geting their momentum from ejecting an ion (extremely low mass)

Unfortunately I'm an aerospace engineering dropout, but I've heard that if you fire a bullet greater than the speed of light, you'll kill the guy before you press the trigger.

In my opinion, the aerodynamic drag, which would have to be overcome by this makeshift "Engine”, would outweigh the benefits. It would also require more energy to reach supersonic speeds.

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Not nessecarily. The tube could easily be configured as a circular wing, or at least an aerodynamically efficient shape. Using some self-contained fuel source to reach supersonic speeds is no issue as the projectile is already at supersonic speeds when it exits the gun bore. Controlling a hyper-sonic shock wave for the ram effect has been possible for half a century or more. Configure it with a self-contained fuel source shouldn't be a problem. It should be simple to bond a solid propellant to the interior of the tube (probably in a recessed cavity just aft of the interior constriction or shock wave location).

I don't see it as trying to reinvent something. I see it as dramatically extending the capability of equipment already in place.

I find the whole idea quite intriguing.

Brad

The tube could easily be configured as a circular wing

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That is not what was described in the original post, it was a cavity similar to that of an engine bell that runs off of air, that is what I was responding to. There are too many "what if" posts for me to try and respond to some of the varients suggested.