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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.
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 24 2013]
Gold leaf
http://aurumandarge..._04_01_archive.html
Good for lifter fins. And purty! [bungston, May 25 2013]
aeroplane using the power of ionic wind
https://www.abc.net...ionic-wind/10516032
[xaviergisz, Nov 21 2018]
Different article on MIT plane
https://techcrunch....l6CuOC0GPbLrd0z_fnI
Reports 2.6% efficiency [scad mientist, Nov 26 2018]
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Annotation:
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I've taken the liberty of being the first to bone this
for some obvious misunderhensions about thrust,
lift and ion thrusters. |
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post first, ask questions later. |
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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. |
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However I might be mixing that up with those ionic air-fresheners. |
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I'm going to assume that there's no record of anybody trying this with a hydrogen balloon for humourous reasons. |
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//it's the wind generated by their passing.//
(Pauses for wind-passing joke) |
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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). |
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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. |
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OK, which damned fool bunned this? The physics
here is complete pants. |
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//completely pants// well, Bermudas maybe. |
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//which damn fool// you're welcome, dammit. |
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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.) |
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I actually thought of using these things as a manner
of holding up a space elevator... assuming you had an
absolute ton of power. |
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//OK, which damned fool bunned this? The physics
here is complete pants// |
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Now, THEY'RE pants science. |
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//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. |
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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. |
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Moreovermore, if [lurch]'s linked patent is real... |
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Ok, I'm reading up on Paschen's Law (q.G.) which I
think you'll find interesting. |
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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. |
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(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." |
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Or in other words, any work-around you care to
come up with is covered as well.) |
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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. |
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See how that makes you want to spend all of your
money on development? |
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<[lurch] gets bundled into
straightjacket, hauled out of library, effectively
ending rant /> |
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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. |
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In other cases, patents obfuscate to make it
harder for others to copy the device - not in the
spirit, perhaps, but not surprising. |
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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. |
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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. |
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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. |
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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). |
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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. |
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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. |
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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. |
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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. |
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I wonder... the patent describes a multi-stage
arrangement of linear aligned serial accelerations. |
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You want a "scoop" for a ramjet-style
compression/accumulation of extra air to give
more working fluid to the engine. |
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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...) |
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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. |
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// 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. |
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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? |
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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. |
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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). |
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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. |
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//essentially the least aerodynamic possible
configuration// |
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Yes, and yet also no. Which is why conventional
(fuel-burning) ramjets are generally very very fast
and also very efficient. |
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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. |
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Remember, if you can't succeed, at least fail
interestingly. |
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No, I wasn't proposing "intakes", per se. Let's see
if I can create a better word picture. |
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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.) |
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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. |
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"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. |
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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? |
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[NOTE: I am somewhat Merloted, so my
comprehension skills are impeded]. |
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But why is this better than using both stages to
accelerate the ions? |
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[FURTHER NOTE: I am feeling obtuse, so please
feel free to defer further explanation until I am
feeling more acute.] |
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Ah, hang on - you edited while I writ. Will wait for
my brain to reboot tomorrow. |
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<looks down over reading glasses, tears off
printout over shoulder> A whale, Beaumont.
</ldorg,topos> |
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Larger swept intake area yields more
reaction mass. |
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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. |
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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[...] |
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So, do you want more air molecules for
accelerating, or not? |
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//New Ownership... Hull contingent... Slough
crew...// |
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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. |
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Since that has been clarified, what does my Indian friend Ramjet have to do with anything? |
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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? |
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Building on from that, you could construct a series of
concentrator/collector nacelles, and increase the thrust
that way. |
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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. |
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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? |
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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. |
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// 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. |
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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. |
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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? |
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I need to see some vectors. I need a diagram to understand how the emitted ions cause lift. |
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Well, [bungston] has a point. The lifter's lift is
normally explained as coming from the
downdraught of entrained air. |
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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. |
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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. |
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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. |
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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. |
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If the lifter were enclosed in a tight fitting airtight box would it still fly? |
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Have the solar panels power an electromagnetic field that causes ions to slam into the craft pushing it like a photon sail. |
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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. |
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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? |
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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. |
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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. |
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([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) |
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//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.// |
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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. |
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//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. |
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//heat// interesting... so if done right the airtight box will not only float upwards but glow while doing so. |
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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. |
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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. |
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I am going to read the idea again and muse on it. |
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Lurch I must say it is fun to read your annos on a physics idea. |
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/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 / |
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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? |
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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. |
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//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. |
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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. |
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//with stuff we can see entrained air is from
frictional interactions, as I understand it but that
cannot be the case for tiny ions.// |
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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. |
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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). |
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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. |
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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. |
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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. |
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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). |
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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? |
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//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. |
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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. |
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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. |
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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. |
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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. |
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Sequential acceleration also gets maximal work
out of the painstakingly collected high altitude air
molecules. |
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Do you think this idea deserves to go into a category yet? |
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Coolest discussion in a while. Brain, hurting a little... the dung-beetle analogy really put things in perpective. |
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//Do you think this idea deserves to go into a
category yet?// Fixed. |
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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? |
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I am thinking of fin as glider wing - it would be best
to accelerate over the top of the wing and not the
bottom |
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/we would want the forward speed of the glider to
be comparable to the speed of the ions |
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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. |
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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. |
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//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. |
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//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. |
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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? |
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Of course, that only applies if the ion doesn't hit
any other molecules en route. |
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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. |
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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. |
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//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. |
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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. |
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But, is there a way to use sunlight directly ? bypass the convert-to-electricity stage, go straight to ionization. |
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The hazy blue radioactive go-fast paint at the intake will look really cool. |
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Well, you seem to have quite a few ions in the fire here. |
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Re the link - well, blimey and I'll be goldfish's aunt. It
actually bleedin' works. |
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One thing to note is that this ion powered plane made by
MIT is only 2.6% efficient at converting electricity to thrust.
See link. They seem to think that is an improvement over
previous attempts. Considering that standard propellers are
70% to 90% efficient, it may be a while before this has a
large market. |
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^ All these ikon-o-planes programs are still in short trousers,
like they haven't even bothered to see what happens when
it rains. 40,000 v + H2O = unhappiness I suspect. |
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In my theory, if drizzle get zapped, it'll be more forward
motion, possibly. Or not. Volunteers to hold this wire... |
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...weird, where did everyone go? |
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