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Low-pressure ramjet ion thruster

Ionic and thrusty.
  (+3, -1)
(+3, -1)
  [vote for,

So, there are various devices which are called "ion thrusters", including some very fancy expensive ones. This idea is for a non-fancy, inexpensive one.

If you look up "ion thruster" on Wikipedia, you'll get a page discussing ion thrusters for spaceflight. Basically, a propellant is ionized, and then high voltage is used to spit the ions out the back end at high speed.

This isn't that.

If you instead look for "ion thruster" on YoutUbe, you'll get a mixed bag, including some tombollockry about antigravity and free energy. But you'll also see some videos of little tin-foil kites which fly. These are what I'm talking about.

So, these tinfoil thrusters use a high voltage to ionize the air between a wire and the curved leading edge of a piece of tinfoil. Ions are accelerated rearward (toward the tinfoil), creating an ion wind. A small thruster uses a few watts of power (very high voltages, but also very low currents) and provides a thrust of at least a few grams (the lifter weighs a few grams, and has to be tethered to stop it flying off).

One nice thing about these ion thrusters is that the ions move very fast, thus packing a fair bit of kinetic energy. It's hard to get figures on the efficiency of these things (in terms of kinetic energy/second out versus electrical power in), but they are claimed to be quite efficient, as they should be since the power has few other places to go.

So, take a model glider with a wingspan of maybe a couple of metres, and plaster it with solar panels. Let's say you can get half a square metre of panels, with 5% efficiency - that's 25W of electrical power in full sunlight. Voltage up-steppers are needed, but I believe these can be made small and light. Obviously, you then strap four or five of these little tinfoil thrusters onto the glider, pointed backwards.

Sadly, though, this probably won't fly. The combined thrust of five little tinfoil gizmos is still only going to be maybe 50 grams, which isn't much.

The main problem is that only a tiny fraction of the kinetic energy of the ion thrusters is being used - the speed of the ions (the "exhaust", in effect) is far higher than the forward speed of the glider (at any reasonable airspeed), and thus most of the kinetic energy is being dissipated in the air.

So, ideally, we would want the forward speed of the glider to be comparable to the speed of the ions; if that were the case, then the ions are left "standing" behind the glider, and all of the available kinetic energy goes into the glider. Whoop and huzzah.

But, this means the glider has to fly at enormous speeds which, in seal-evil air, means huge drag - far far exceeding the available thrust.

So, obviously, we want our glider to be operating in a near-vacuum, say 40- 50km up. At this low pressure, the glider can travel at very, very high speed (and indeed will need to to generate lift in the almost- nonexistent air) whilst experiencing only modest drag. Thus, it might reach speeds comparable to the "exhaust" speed of the ion thrusters, thereby gaining full efficiency in terms of kinetic energy transfer.

But - ion thrusters (of this tinfoil variety, remember - not the ion thrusters which carry their own propellant) don't work at very low air pressures. Why? Because they rely on a high density of air molecules which can (a) get accelerated by the voltage and also (b) entrain additional air.

So (and we finally got here at last) what I propose is a sort of ion thruster ramjet. It would work broadly on the same principal as a conventional ramjet (use forward speed to compress air into the engine; then do something such as burn fuel to accelerate the air out the back end), except that the acceleration of the ram-grabbed air would happen via an ion thruster.

The graphs for this have all kinds of crossing lines on them (air pressure goes down; but then ion thrust decreases; but so does air resistance; and speed goes up, which increases the amount of kinetic energy which is used for propulsion, but then so does drag, except that pressure has gone down.... etc etc), but I don't know where they all intersect, which is quite important.

MaxwellBuchanan, May 21 2013

Simple non-loopy video about tinfoil ion thrusters. http://www.youtube....watch?v=vzZy1Aqleno
The follow-on video shows airflow through the lifter. [MaxwellBuchanan, May 21 2013]

"Lifter" project http://jnaudin.free.fr/lifters/main.htm
This guy has been experimenting with this stuff (and other stuff) for quite a while. [Vernon, May 21 2013]

Patented. http://www.google.com/patents/US6145298
By somebody who hasn't actually built one, but if you get it to work, he'll gladly take your money. [lurch, May 21 2013]

Wikipedia: Ionocraft http://en.wikipedia.org/wiki/Ionocraft
I'd like to have a go at building one of these. [zen_tom, May 23 2013]

Roaming Goldfish Bowl. Roaming_20Goldfish_20Bowl
Stands as a warning. Unless the fish knocks it off the windowsill and breaks it. Is that possible? [lurch, May 23 2013]

Gold leaf http://aurumandarge..._04_01_archive.html
Good for lifter fins. And purty! [bungston, May 25 2013]


       I've taken the liberty of being the first to bone this for some obvious misunderhensions about thrust, lift and ion thrusters.
MaxwellBuchanan, May 21 2013

       post first, ask questions later.   

       AFAIK the ions aren't doing the propulsion since they're taken back at the far end of the craft; it's the wind generated by their passing.   

       However I might be mixing that up with those ionic air-fresheners.   

       I'm going to assume that there's no record of anybody trying this with a hydrogen balloon for humourous reasons.
FlyingToaster, May 21 2013

       //it's the wind generated by their passing.// (Pauses for wind-passing joke)   

       I think you're right (the other type of ion thruster, intended for space use, does get its thrust from ejected ions, but they somehow inject the counterions into the exhaust to keep things neutral).   

       That's one of the reasons why we need a ramjet- style thing, to create a locally high air density which the ion thruster can grab onto and entrain.
MaxwellBuchanan, May 21 2013

       OK, which damned fool bunned this? The physics here is complete pants.
MaxwellBuchanan, May 21 2013

       //completely pants// well, Bermudas maybe.
FlyingToaster, May 21 2013

       //which damn fool// you're welcome, dammit.   

       Mean free path at 50 km is still less than a tenth of a millimeter. So, before you claim you've got any pants, you'd ought to calculate the ratio of electrons injected into the field to ionizable air molecules in the field. (I can't do it for you; you didn't say how big your thruster's cross section is.)
lurch, May 21 2013

       I actually thought of using these things as a manner of holding up a space elevator... assuming you had an absolute ton of power.   

       //OK, which damned fool bunned this? The physics here is complete pants//   

       Now, THEY'RE pants science.
bs0u0155, May 21 2013

       //I can't do it for you; you didn't say how big your thruster's cross section is.// The thruster's cross section is going to be, ah, in metric units, ah, optimal.   

       But surely the rate at which electrons are injected depends on the rate at which air molecules are ionized? In other words, at lower pressure the current (hence power consumption) would drop, wouldn't it? And in any case I'm using a ramjettish scoop on the front end of this thing.   

       Moreovermore, if [lurch]'s linked patent is real...
MaxwellBuchanan, May 22 2013

       Ok, I'm reading up on Paschen's Law (q.G.) which I think you'll find interesting.   

       And as to the reality of the patent - if by "real" you mean that it's been issued, and is legally enforceable, then yes, it's real. If you mean that it describes an extant object or device, to the point which a Person Having Ordinary Skill In The Art could replicate it, thus meeting the social contract expectations and requirements for issuance of a patent, then the answer would be no.   

       (From the patent:
"As heretofore discussed the novel ion engine and applications of the novel ion engine in ambient atmospheric gas may be modified in various ways by those skilled in the art. The cathodes and anodes may be constructed of various conductive materials by those skilled in the art and those skilled in the art may utilize various means for adjusting the distance between the cathode and anode to implement the invention in a variety of applications and embodiments. It will be appreciated that these and other modifications can be made within the scope of the invention as defined in the following claims."

       Or in other words, any work-around you care to come up with is covered as well.)   

       I tried to tell you patents were too easily obtainable. No, you said, such was not the case. Well, here's the toll booth. The bridge building is left for you to do; then you can be liable for paying the toll.   

       See how that makes you want to spend all of your money on development?   

       <[lurch] gets bundled into straightjacket, hauled out of library, effectively ending rant />
lurch, May 22 2013

       Uh, [lurch], that reads like pretty standard patentese to me - it's a wording designed to claim as much as possible. For example, one of my patents specifies (somewhere) that a particular tube may be made of plastic, glass, metal, ceramic or any other material which is substantially impermeable to liquids; I happened to use polypropylene, but the patent shouldn't be open for anyone else to make something similar out of glass and claim it falls outside the patent.   

       In other cases, patents obfuscate to make it harder for others to copy the device - not in the spirit, perhaps, but not surprising.   

       Also, if you download the PDF, there are photos of two embodiments of the invention. Not saying they work as advertised, but it's not as if the guy's just built the whole thing in Word.
MaxwellBuchanan, May 22 2013

       But coming back to the idea, the limiting factor seems to be ensuring that the ions (as they whip from the foremost electrode to the rearmost, completing the circuit) collide with enough air molecules to give up a substantial part of the their kinetic energy.   

       The patent describes ways to encourage this, at reduced atmospheric pressure, by controlling the distance the ions travel (ie, distance between electrodes), and by preventing 'streaming' whereby all the ions flow in a single narrow stream. Whether it works, and to what extent his data are real, I have no idea.   

       Paschen's law describes the breakdown voltage of gases as a function of temperature. This is important, because (as I understand it), an ion thruster is at its highest efficiency at voltages just below the breakdown voltage. But the distance between the electrodes can be varied (this is one of the things described in the patent).   

       So, in an ideal world you would have a huge voltage available; you would then space the electrodes far enough apart that you just avoid breakdown (arcing). Then the ions are given the greatest possible acceleration between the electrodes. As they move, they collide with uncharged air molecules and impart some of their kinetic energy to them, which is where the thrust comes from.   

       In thinner air, there are presumably (1) fewer ions (since they can only be formed as fast as air molecules hit the front electrode); and (2) those ions have less opportunity to collide with uncharged molecules as they travel to the rearmost electrode.   

       Item (1) isn't an efficiency issue: current consumption (hence power consumption) will drop off in proportion to the rate of ion formation, so power will decrease but efficiency stays the same. (2) _is_ an efficiency issue, because any of the ions' kinetic energy which _isn't_ transferred to uncharged air molecules by collision will be dumped into the rear electrode.   

       But (2) can be overcome by increasing the distance between the electrodes, until any ion has multiple opportunities for collision before it reaches the rear electrode. I think this is why the patent describes an electrode which can be moved axially.
MaxwellBuchanan, May 22 2013

       I wonder... the patent describes a multi-stage arrangement of linear aligned serial accelerations.   

       You want a "scoop" for a ramjet-style compression/accumulation of extra air to give more working fluid to the engine.   

       How about ... place your engine behind and below your leading edge, so that the ambient air is confined and compressed (perhaps better said "slightly de-rarified") under the airfoil; then a semi-circular ring of thruster elements (acting as "first stage" ion accelerators) forms the outside edge of the scoop intake. This ring would accelerate air, Bussard-ishly, transverse to the direction of travel that it might be ingested into the maw of your main stage thruster. (*That* is not contemplated in the claims of the given patent. There's probably another one...)   

       The transverse scoop-thrusters aren't constrained by the necessity to develop thrust by momentum transfer, so they can work in any conditions below breakdown. If the field is in series with that of the main stage, any ions they develop don't have to be re-ionized when they join the main flow.
lurch, May 22 2013

       // This ring would accelerate air, Bussard-ishly, transverse to the direction of travel that it might be ingested into the maw of your main stage thruster.// That's the point where you lost me.   

       Hang on. Maybe I get it. You're saying (1) Put the air intakes in the slightly-higher-pressure region behind and below the wings. And then (2) Use a first-stage ion thruster to push air from these intakes into the main thruster. And then (3) Put these intakes at right angles to the direction of travel, so their pulling air in sideways before the main thruster pushes it backwards?   

       I get (1) and (2), but not (3). If I understand the geometry you propose, the air is going to make a dog-leg: relative to the aircraft it comes backward past and under the wings, then has to turn sideways, then gets spat out backwards again by the main thruster.   

       Why not just have it go straight from front to back through two consecutive thrusters, each being run at conditions just below breakdown? With the dog leg, you effectively stop and then have to restart the air (apart from its transverse movement).
MaxwellBuchanan, May 22 2013

       Ramjet is essentially the least aerodynamic possible configuration, with a wide open area to accumulate atoms in the forward direction, trailing with likely a tapered jet for propulsion.
rcarty, May 22 2013

       //essentially the least aerodynamic possible configuration//   

       Yes, and yet also no. Which is why conventional (fuel-burning) ramjets are generally very very fast and also very efficient.   

       The difference here is that I want to use an ion thruster to provide the oomph, rather than combustion, and to do it in thinner air. Of course, the difference may also be that my idea is completely unworkable. But it will be unworkable for more subtle and more interesting reasons.   

       Remember, if you can't succeed, at least fail interestingly.
MaxwellBuchanan, May 22 2013

       No, I wasn't proposing "intakes", per se. Let's see if I can create a better word picture.   

       The first half is just the fact of having the intake area be below the wing/body, as in an XB-70. The reasoning there was for "compressibility lift"; basically surfing the wing's leading edge on top of its own shock wave. Well, we're not looking for lift, just gathering extra air into the eligible-for- ingestion area. (Perhaps I should reference Pat McManus' "The Grasshopper Trap", except it's mostly irrelevant.)   

       So, in our now somewhat updensified air, the "first stage" thrusters. This will be nothing more than a fancy electric fence - a wire ring with corona-points pointing toward a conductor extending in front of the center electrode of the main stage(s). The air won't be "stopped", therefore this ring will have to be some distance - perhaps a substantial distance - ahead of the main intake, so that air can be deflected at an angle of (uncalculated) and thus enter the main intake. The electrically-deflected air won't necessarily get a direct path into the intake, as it is still subject to momentum-sapping collisions with ambient air as it's trying to dogleg across, but that's just more grasshoppers in the haul if the net's set up to collect 'em.   

       "Bussard" I mentioned - I'm sure you've run eye across the "Bussard Ramjet", which was supposedly going to collect fusion fuel out of interstellar space using an electromagnetic funnel for the ram scoop. Just a huge electrical field, and all the ions in the area leap at the chance to get scooped up. I'm suggesting - in a huge surge of practicality - that there's more probability of ions if you reach out and ionize something. However, since I'm still expecting those ions to leap across emptiness to get to the other electrical pole, the greater part of the intake surface is made out of Nothing, which has a fairly decent ratio of Area to Weight.
lurch, May 22 2013

       OK, I think I now get it. I'm fine with the "put the intakes in the higher pressure region". Then, basically, the first stage is just creating ions, and the second stage is just accelerating them?   

       [NOTE: I am somewhat Merloted, so my comprehension skills are impeded].   

       But why is this better than using both stages to accelerate the ions?   

       [FURTHER NOTE: I am feeling obtuse, so please feel free to defer further explanation until I am feeling more acute.]   

       Ah, hang on - you edited while I writ. Will wait for my brain to reboot tomorrow.
MaxwellBuchanan, May 22 2013

       <looks down over reading glasses, tears off printout over shoulder> A whale, Beaumont. </ldorg,topos>   

       Larger swept intake area yields more reaction mass.   

       First stage input may be ions, may be neutral. Doesn't matter. It's just More Stuff than would be available without the first stage.   

       Your question://But why is this better than using both stages to accelerate the ions? // I refer back to your idea: //But - ion thrusters [...] don't work at very low air pressures. Why? Because they rely on a high density of air molecules[...]   

       So, do you want more air molecules for accelerating, or not?
lurch, May 22 2013

       //New Ownership... Hull contingent... Slough crew...//   

       Don't worry. By the time the people from Hull have got over the novelty of using a telephone the meeting will be almost over.
MaxwellBuchanan, May 23 2013

       Since that has been clarified, what does my Indian friend Ramjet have to do with anything?
rcarty, May 23 2013

       Say you built a ring of ion thrusters all angled such that their ion streams all funnelled onto a point central and slightly behind, where an appropriately placed secondary thruster imparted a second degree of oompf into the enriched stream, how would that go?   

       Building on from that, you could construct a series of concentrator/collector nacelles, and increase the thrust that way.
zen_tom, May 23 2013

       If I am on a fanboat, I am propelled forward by the mass of air thrown backwards. What that air entrains or otherwise gets involved with after being thrown is in the swamp behind me and so irrelevant to the propulsion generated by the fan.   

       But Max says the lifters entrain air and that is important. I wonder - are the fins of these lifters working as wings? Is it pressure differences on different sides of the wing/fin that make them work such that they are flying upwards like a plane?   

       Those ionic propulsion space vehicles worked, I thought, like a fan boat except with a heavy caliber machine gun mounted on the back instead of a fan. But if emission of ions by an ionic lifter does not push the ion emitter maybe I have that wrong.
bungston, May 23 2013

       // lifters entrain air and that is important. I wonder - are the fins of these lifters working as wings? // Yes to the first, no to the second.   

       The triangular lifter creates a downdraught which can be seen easily with smoke, so in that sense it's working a bit like a hovercraft. The foil is there to attract and recapture the ions coming off the top wire. Beyond that, it's job is just not to interfere much with the flow of entrained air.
MaxwellBuchanan, May 23 2013

       If they are not wings, then once the ion has left the wire, what does it matter what it entrains? On leaving the wire it ceases interacting with the lifter.Is emitting an ion like shooting a machine gun, with the recoil propelling the lifter?   

       I need to see some vectors. I need a diagram to understand how the emitted ions cause lift.
bungston, May 23 2013

       Well, [bungston] has a point. The lifter's lift is normally explained as coming from the downdraught of entrained air.   

       However, it would be more accurate to say that the lift comes from the reaction on the leading- edge wire, as ions are fired backward. But the air entrainment is important: without it, the ions would have the same momentum when they reach (and are captured by) the trailing (foil) electrode, and thus would cancel out their initial thrust.   

       What the entrained air does is to capture and dissipate some (much) of the momentum of the ions as they are driven electrostatically from the front electrode to the rear electrode.   

       However, if you view the lifter as a 'black box', then its thrust can be considered as coming from (and being equal and opposite to) that of the entrained air which is pushed backwards.   

       You can make the same argument about rockets. Technically, their thrust comes from the impact of gas molecules on the front of the combustion chamber and on the inside of the rocket bell; but it's easier to consider the thrust as being equal and opposite to that of the hot gases expelled from the back.
MaxwellBuchanan, May 23 2013

       If the lifter were enclosed in a tight fitting airtight box would it still fly?
bungston, May 23 2013

       No, of course not.
MaxwellBuchanan, May 23 2013

       Have the solar panels power an electromagnetic field that causes ions to slam into the craft pushing it like a photon sail.
rcarty, May 23 2013

       If ions being fired produces the momentum (lifter recoils as ion fires), and air captures and dissipates the energy (as heat) then it should lift the airtight box. Which will get hot.
bungston, May 23 2013

       You mean, like if I sat here in this box - er, room - and threw a tennis ball repeatedly at that <points> spot on the wall, but somehow the impact points will be uniformly distributed over all the walls, therefore the room will move because that's the required reaction to my action?   

       Won't quite work that way, because the tennis ball can't go off in some other direction until its target-spot-ward momentum has been transferred to something else (air, cat, model airplane, whatever) and eventually dissipated into the room structure - perhaps not at the spot, but still a vector (or sum of vectors) with the same direction as me to spot, aligned parallel to the vector from me to spot, and the same magnitude as I gave the initial throw.   

       Same goes for the ions - you shoot 'em, they may hit something other than the target, but that momentum vector doesn't perish, reorient or escape unless your sealed box isn't sealed.   

       ([bigsleep], mentioning goldfish in this thread is a greater danger than you can possibly imagine. If we start discussing momentum, sealed containers, balanced/unbalanced forces, and goldfish... well, check out the linked "Roaming Goldfish Bowl" to see how bad that can get)
lurch, May 23 2013

       //If ions being fired produces the momentum (lifter recoils as ion fires), and air captures and dissipates the energy (as heat) then it should lift the airtight box. Which will get hot.//   

       Heat is generally assumed to mean random motion of molecules with zero overall motion. In this case, the impacted air molecules will be accelerated not in random directions, but backwards. Thus, the motion of the air molecules is more like wind (concerted motion in one direction) than heat (random motion in all directions). Were this not the case, you'd be violating all kinds of laws, including conservation of momentum.
MaxwellBuchanan, May 24 2013

       //then it should lift the airtight box// and so it should... for the brief moment between being shot out one end and being captured by the other.   

       //heat// interesting... so if done right the airtight box will not only float upwards but glow while doing so.
FlyingToaster, May 24 2013

       My confusion stems from picturing ions as tennis balls / bullets but realizing that they are not. A putative ion-propelled spacecraft shoots the ions out its rear at near the speed of light, so even if one considers only ion mass, tiny m * huge V still equals something meaningful.   

       But with these ionic lifters I have to think most of the interaction between ion and anything else has to do with charge. The concept of "entrained" here is slippery - with stuff we can see entrained air is from frictional interactions, as I understand it but that cannot be the case for tiny ions.   

       I am going to read the idea again and muse on it.
bungston, May 24 2013

       Lurch I must say it is fun to read your annos on a physics idea.   

       /Same goes for the ions - you shoot 'em, they may hit something other than the target, but that momentum vector doesn't perish, reorient or escape /   

       Ions are not tennis balls, because they have so much charge compared to mass. Suppose the flying ion is turned electrostatically in flight such that it impacts the side of the enclosed box at a right angle to its initial vector. Does turning an ion electrostatically alter its momentum vector?   

       Also, I wonder if the lifter were separate from the fins, with the fins attached to the table, whether the lifter would bob up and down atop the fins. It seems to me that it should.
bungston, May 24 2013

       //Does turning an ion electrostatically alter its momentum vector?// Yes - but can only do so in strict obedience to conservation of momentum. In other words, the forward component of momentum got transferred to something; something had to provide the sideways component. Trade & share.
lurch, May 24 2013

       Oh, and visualizations. Perhaps the electrons could be visualized as dung-beetles, molecules as shit-balls, and an ion as a ball with an attached dung beetle. Mean free path is how far the beetle can roll a ball before hitting another ball, atmospheric pressure is how many balls, current density is how many beetles... Ok, never mind. Most of my analogies turn to shit, but usually not that thoroughly.
lurch, May 24 2013

       //with stuff we can see entrained air is from frictional interactions, as I understand it but that cannot be the case for tiny ions.//   

       Au contraire. "Friction" in all cases is just atoms (or ions) getting in each others' way (or, in some cases, attracting one another). When two big airstreams meet and deflect eachother, they are only doing so because molecules in one airstream hit molecules in the other airstream. Likewise with the ions hitting ambient air.   

       If you want to go into more detail, each molecular collision comes down to electrostatic repulsion between the electrons on the outside of each molecule. This is not qualitatively altered just because one of the molecules is, in this case, ionized (it still has an outer cloud of electrons - just one more or less than it should have).   

       If it helps (and I am fairly sure it won't), the lifter can be thought of a sort of paddle steamer but turned inside out, upended, made of tinfoil and without the paddles or the steam.
MaxwellBuchanan, May 24 2013

       I am understanding more and more These lifters are cool. There is a good mythbusters on yourube where the build one and test it in a vacuum.   

       I wonder if the lifter could serve double duty as the glider wing. Maybe one could even step several one after the other. They could sequentially accelerate the same wind. A question I have is whether an ion source set up as one of a series on a wing would still send its ions to top of the leeward fine behind it or the bottom of the windward fin in front of it. It looks like the shape of the fin is important - the leading edge catching the ions should be rounded and the trailing edge sharp. Maybe this will help attract ions in the right direction.   

       Wondering more - maybe gold foil would be good lifter material. I think this is available much thinner than aluminum foil. One could use the stuff they wrap Kobe beef filets in (linked).   

       Wondering more and more - high voltage and low current sounds familiar. Could one of these lifters be powered by a teslacoil? I have one handy?
bungston, May 25 2013

       //mythbusters on yourube where the build one and test it in a vacuum.// Yep - won't work in a vacuum, as there are no gas molecules to ionize and accelerate, and moreovermore no gas molecules with which ions could collide.   

       But at low pressures, it could/should still work. You need enough air to provide the ions, and you need to make sure that those ions undergo several collisions with other air molecules before they reach the rearmost (collecting) electrode. But whether the parameters (voltage, distance between electrodes, geometry of the electrodes) can be adjusted to give useful thrust at very low (non-zero) air pressures, I'm not sure.   

       I very much like the idea of using the rear (collecting) electrode as a wing. You might even be able to adjust the flow of ions (plus entrained air) over the top and bottom surfaces to increase lift, though I'm sure some law of physics would try to bite you in the arse.   

       And yes, I would imagine a Tesla coil would do the trick. But for a self-contained vehicle, you'd want lightweight solar panels and a lightweight voltage stepper-upperer. Stepper-upperers can be very simple and light (just diodes and capacitors - and small since the currents are low), although you need to feed them with AC rather than DC.
MaxwellBuchanan, May 25 2013

       Thinking about sequential acceleration - I bet the ions are way faster than the wind they make. I wonder if the % acceleration conferred to air moving thru the field is the same regardless of how fast the air is initially moving. Given that the gap can only be so wide before this trick will not work, a ladder of accelerators under a wing makes sense.   

       Sequential acceleration also gets maximal work out of the painstakingly collected high altitude air molecules.
bungston, May 25 2013

       Do you think this idea deserves to go into a category yet?
lurch, May 26 2013

       Coolest discussion in a while. Brain, hurting a little... the dung-beetle analogy really put things in perpective.   

       //Do you think this idea deserves to go into a category yet?// Fixed.
MaxwellBuchanan, May 26 2013

       Suppose the fin receiving the ion were half coated. Maybe more than half - the top fold is coated and then one side. Would the ions and thus the airflow go down only one side of the fin?   

       I am thinking of fin as glider wing - it would be best to accelerate over the top of the wing and not the bottom
bungston, May 26 2013

       /we would want the forward speed of the glider to be comparable to the speed of the ions   

       How fast are these ions?
bungston, May 26 2013

       One more and then I will hush. There have been bandied about schemes to power vehicles by tapping the charge differential between up high and down low. The little scientific american electrostatic motor taped such to make a little thing spin.   

       I wonder if a ionic thrust powered glider trailing a long very fine wire could power itself by tapping the charge differentials between different regions of air. Like lighting (this is fetal lightning we are talking about) these are high voltages but low current - perfect.
bungston, May 26 2013

       //Would the ions and thus the airflow go down only one side of the fin?// Good question. But the ions would still be attracted to the insulated side, I would guess, only to suffer disappointment when they actually got there and couldn't reach the conductor. I'm not sure how the momentum of disappointment can be calculated.   

       //How fast are these ions?// Someone who is less bewined than I could probably calculate the velocity of a dinitrogen ion after traversing, say, 1 metre in a field just below breakdown voltage.   

       Actually hang on. Let me try. The breakdown voltage of a metre of air (at stp) is something like 3MV, so a singly-charged ion will acquire 3MeV of energy, or 5 x 10^-13 Joules. The mass of a molecule of nitrogen is about 10^-26 kilograms. So, e=(m*v^2)/2, so the velocity would be 10^7m/s. Wait - is that right?   

       Of course, that only applies if the ion doesn't hit any other molecules en route.
MaxwellBuchanan, May 26 2013

       Accelerating an ion through //a metre of air (at stp)// and expecting that //the ion doesn't hit any other molecules en route// sounds PFU* to me.   

       But, yes, 3 megavolts, one meter, one nitrogen molecule, getting up to 1 part in 3000 of c - sounds about right. If you go any higher than that, though - like looking at a loose electron, or higher voltage - you'll probably want to start taking relativistic effects into account. Preferably, there will be a goodly number of collisions and the max velocity will remain much lower.   

       *"Pretty Unlikely"   

       //less bewined// You may want to sober up a bit and find out *why* the butler keeps you in a state of unclarity. He may be Up To Something.
lurch, May 26 2013

       Apart from the question of whether it would work, it could only fly at or near the solar equator for obvious reasons unless it's a dirigible or other roundy thing, and during daylight.   

       But, is there a way to use sunlight directly ? bypass the convert-to-electricity stage, go straight to ionization.
FlyingToaster, May 29 2013

       The hazy blue radioactive go-fast paint at the intake will look really cool.
wjt, Jun 02 2013

       Well, you seem to have quite a few ions in the fire here.   

       (slinks away in shame)
not_morrison_rm, Jun 02 2013


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