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| [[Image:simpleionocraft.gif|thumb|right|A simple ionocraft, generating 15 [[gram-force|gF]] (0.147 [[newton (unit)|newtons]]) of thrust at 54 [[kilovolt|kV]]]]
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| An '''ionocraft''' or '''ion-propelled [[aircraft]]''', commonly known as a '''lifter''' or '''hexalifter''', is an [[electrohydrodynamic]] (EHD) device that uses an electrical phenomenon known as the [[Biefeld–Brown effect]] to produce [[thrust]] in the air, without requiring any [[combustion]] or [[moving parts]]. The term "Ionocraft" dates back to the 1960s, an era in which [[electrohydrodynamic|EHD]] experiments were at their peak. In its basic form, it simply consists of two [[Parallel (geometry)|parallel]] [[Electrical conduction|conductive]] [[electrodes]], one in the form of a fine wire and another which may be formed of either a wire grid, tubes or foil skirts with a smooth round surface. When such an arrangement is powered up by high [[voltage]] in the range of a few kilovolts, it produces [[thrust]]. The ionocraft forms part of the [[EHD thruster]]<!-- Just to aid comprehension for people thrown by this self-redirect: apparently that link originally pointed [http://en.wikipedia.org/w/index.php?title=Electrohydrodynamic_thruster&oldid=464338641 here]. That was before the Deletionista showed up.--> family, but is a special case in which the ionisation and accelerating stages are combined into a single stage.
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| The device is a popular [[science fair]] project for [[students]]. It is also popular among [[anti-gravity]] or so-called "[[electrogravitics]]" proponents, especially on the Internet.
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| The term "lifter" is an accurate description because it is not an anti-gravity device, but produces lift in the same sense as a rocket from the reaction force from driving the ionized air downward. Much like a rocket or a jet engine (it can actually be much more thrust efficient than a jet engine<ref>[http://www.sciencedaily.com/releases/2013/04/130403122013.htm Massachusetts Institute of Technology (2013, April 3). Ionic thrusters generate efficient propulsion in air. ScienceDaily] Quote: "...In their experiments, they found that ionic wind produces 110 newtons of thrust per kilowatt, compared with a jet engine's 2 newtons per kilowatt..."</ref>), the force that an ionocraft generates is oriented consistently along its own axis, regardless of the surrounding gravitational field. Claims of the device working in a vacuum also have been disproved.<ref name="Brian Dunbar">{{cite web|title=Ion Propulsion|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040171929_2004178266.pdf}}</ref>
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| Ionocraft require many safety precautions due to the high voltage required for their operation; nevertheless, a large subculture has grown up around this simple EHD thrusting device and its physics are now known to a much better extent.
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| == Description ==
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| The ionocraft is a propulsion device based on [[Ion (physics)|ionic]] [[air propulsion]] that works without moving parts, flies silently, uses only [[electrical energy]] and is able to lift its own weight plus additional payload, with the future prospect of its [[power supply]]. The principle of [[ionic wind]] propulsion with [[Corona discharge|corona]]-generated charged particles has been known from the earliest days of the discovery of electricity, with references dating back to 1709 in a book titled ''Physico-Mechanical Experiments on Various Subjects'' by [[Francis Hauksbee]]. However, its use for propulsion was first given serious thought by [[Thomas Townsend Brown]] in 1928 and later on by Major [[Alexander Prokofieff de Seversky]], who contributed much to its basic physics and construction variations in 1960. In fact, it was Major de Seversky himself who in 1964 coined the term Ionocraft in his ({{US patent|3130945}}). The basic external design of these devices can be found in older patents, dating back to 1960 filed by [[Thomas Townsend Brown]], titled "Elektrokinetic Apparatus". More recent research has cleared up many ambiguous issues relating to Brown's original work, and the somewhat elusive [[Biefeld–Brown effect]].
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| == Construction ==
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| [[Image:Typicalionocraft.gif|thumb|Typical ionocraft construction]]
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| A simple ionocraft derivative, also known as a lifter, can be easily constructed by anyone with a minimal amount of technical knowledge. The model in its simplest form has the shape of an [[equilateral triangle]] with sides generally between 10 and 30 cm. They consist of three parts, the ''corona wire'' (or emitting wire), the ''air gap'' (or dielectric fluid), and the ''foil skirt'' (collector). The electrical polarities of the emitting and collecting electrodes can be reversed. All of this is usually supported by a lightweight [[balsa]]wood or other electrically isolating frame so that the corona wire is supported at a fixed distance above the foil skirt, generally at 1 mm per kilovolt. The corona wire and foil should be as close as possible to achieve a saturated corona current condition which results in the highest production of thrust. However the corona wire should not be too close to the foil skirt as it will tend to [[Spark gap|arc]] in a spectacular show of tiny [[Lightning discharge|lightning bolts]] which has a twofold effect:
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| # It degrades the thrust as it is [[Short circuit|shorting]] the device and there is [[Current (electricity)|current]] flow through the arc instead of the [[Ion (physics)|ions]] that do the lifting
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| # It can destroy the [[power supply]] or burn the balsa structure of the Lifter.
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| === Components ===
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| ==== Corona wire ====
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| The corona wire is usually, but not necessarily, connected to the positive terminal of the high voltage power supply. In general, it is made from a small gauge bare [[conductive]] [[wire]]. While [[copper]] wire can be used, it does not work quite as well as [[stainless steel]]. Similarly, thinner wire such as 50 [[American Wire Gauge|gauge]] tends to work well compared to more common, larger sizes such as 30 gauge, as the stronger electric field around the smaller diameter wire results in better ionisation and a larger corona current.
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| The corona wire is so called because of its tendency to emit a purple [[Corona discharge|corona]]-like glow while in use. This is simply a side effect of ionization. Excessive corona is to be avoided, as too much means the electrodes are dangerously close and may arc at any moment, not to mention the associated health hazards due to excess inhalation of [[ozone]] and [[NOx]] produced by the corona.
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| ==== Air gap ====
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| The air gap is simply that, a gap of free flowing [[air]] between the two electrodes that make up the structure of an ionocraft.
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| The air gap is a vital necessity to the functioning of this device as it is the [[dielectric]] used during operation. Best results have been observed with an air gap of 1 mm to every kV.{{Citation needed|date=September 2010}}
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| ==== Collector ====
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| The collector may take various shapes, as long as it results in a smooth equipotential surface underneath the corona wire. Variations of this include a wire mesh, parallel conductive tubes, or a foil skirt with a smooth round edge. The foil skirt collector is the most popular for small models, and is usually, but not necessarily, connected to the negative side of the power supply. It is usually conveniently made from cheap, lightweight [[aluminum foil]].
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| The foil skirt is named simply because it is shaped much like a [[skirt]], and is made from aluminum foil. It is by far the most fragile part, and must not be crumpled to work properly. Any sharp edges on the skirt will degrade the performance of the thruster, as this will generate ions of opposite polarity to those within the thrust mechanism.
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| Reversing the polarities of the corona wire with that of the foil does not alter the direction of motion. Thrust will be produced regardless of whether the ions are positive or negative. For positive corona polarity, nitrogen ions are the main [[charge carrier]]s, whilst for negative polarity, oxygen ions will be the main carriers and ozone production will be higher. The slight difference in their ion mobility, results in slightly higher thrust for the positive corona polarity case.{{Citation needed|date=July 2011}}
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| == Mechanism ==
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| The generated thrust can be explained in terms of [[Electrokinetic phenomena|electrokinetics]] or, in modern terms, [[electrohydrodynamics]] propulsion and can be derived through a modified use of the Child-Langmuir equation.<ref name="Leon Tribe">{{cite web|title=Electrokinetic devices in air|url=http://rimstar.org/sdprop/lifter/ltcalcs/Electrokinetic_devices_in_air.pdf|accessdate=2013-04-25}}</ref>
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| A generalized one-dimensional treatment gives the equation:
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| :<math>F = \frac{Id}{k} </math>
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| where
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| *''F'' is the resulting force, measured in [[dimensional analysis|dimension]] [[mass|M]] [[length|L]] [[time|T]]<sup>−2</sup>
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| *''I'' is the current flow of electric current, measured in dimension [[electric current|I]].
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| *''d'' is the air gap distance, measured in dimension L.
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| *''k'' is the ion mobility coefficient of air, measured in dimension M<sup>−1</sup> T<sup>2</sup> I (Nominal value 2·10<sup>−4</sup> m<sup>2</sup> V<sup>−1</sup> s<sup>−1</sup>).
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| In its basic form, the ionocraft is able to produce forces great enough to lift about a gram of payload per [[watt]], so its use is restricted to a tethered model. Ionocraft capable of payloads in the order of a few grams usually need to be powered by power sources and high voltage converters weighing a few kilograms, so although its simplistic design makes it an excellent way to experiment with this technology, it is unlikely that a fully autonomous ionocraft will be made with the present construction methods. Further study in electrohydrodynamics, however, show that different classes and construction methods of [[EHD thrusters]] and hybrid technology (mixture with [[Aerostat|lighter than air]] techniques), can achieve much higher payload or thrust-to-power ratios than those achieved with the simple lifter design. Practical limits can be worked out using well defined theory and calculations such as those given on the 'Ionocraft mathematical analysis and design solutions' paper (see external links). Thus, a fully autonomous EHD thruster is theoretically possible.
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| When the ionocraft is turned on, the corona wire becomes charged with [[high voltage]], usually between 20 and 50 [[kilovolt|kV]]. The user must be extremely careful not to touch the device at this point, as it can give a nasty shock. At extremely high current, well over the amount usually used for a small model, contact could be fatal. When the corona wire is at approximately 30 kV, it causes the air molecules nearby to become [[ion]]ised by stripping the [[electrons]] away from them. As this happens, the ions are strongly repelled away from the anode but are also strongly attracted towards the collector, causing the majority of the ions to begin accelerating in the direction of the collector. These ions travel at a constant average velocity termed the [[drift velocity]]. Such velocity depends on the [[mean free path]] between collisions, the external electric field, and on the mass of ions and neutral air molecules.
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| The fact that the current is carried by a [[corona discharge]] (and not a tightly-confined [[Electric arc|arc]]) means that the moving particles are diffusely spread out into an expanding ion cloud, and collide frequently with neutral air molecules. It is these collisions that create a net movement. The momentum of the ion cloud is partially imparted onto the neutral air molecules that it collides with, which, being neutral, do not eventually migrate back to the second electrode. Instead they continue to travel in the same direction, creating a neutral wind. As these neutral molecules are ejected from the ionocraft, there are, in agreement with [[Newton's laws of motion#Newton's third law|Newton's Third Law of Motion]], equal and opposite forces, so the ionocraft moves in the opposite direction with an equal force. There are hundreds of thousands of molecules per second ejected from the device, so the force exerted is comparable to a gentle breeze. Still, this is enough to make a light balsa model lift its own weight. The resulting thrust also depends on other external factors including air pressure and temperature, gas composition, voltage, humidity, and air gap distance.
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| The air gap is very important for the function of this device. Between the [[electrodes]] there is a mass of air, consisting of neutral air molecules, which gets in the way of the moving ions. This air mass is impacted repeatedly by excited particles moving at high [[drift velocity]]. This creates resistance, which must be overcome. The barrage of ions will eventually either push the whole mass of air out of the way, or break through to the collector where electrons will be reattached, making it neutral again. The end result of the neutral air caught in the process is to effectively cause an exchange in momentum and thus generate thrust. The heavier and denser the gas, the higher the resulting thrust.
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| Recent research suggests electrohydrodynamic propulsion is more energy efficient than any other means of propulsion, generating up to 100N of thrust per kilowatt of power.<ref>{{cite journal|last=Barrett|first=Stephen R.H.|coauthors=Masuyama, Kento|title=On the performance of electrohydrodynamic propulsion|journal=Proceedings of the Royal Society|date=5 March 2013|url=http://rspa.royalsocietypublishing.org/content/469/2154/20120623.abstract?sid=9494059d-0ba7-4d99-b219-73ca7fe837be|accessdate=3 April 2013}}</ref> Such high thrust to power ratio comes at a price of low power density, however.
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| == See also ==
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| * [[Alexander Prokofieff de Seversky]]
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| * [[Electrohydrodynamics]]
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| * [[Ion thruster]]
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| * [[Hall effect thruster]]
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| * [[Magnetoplasmadynamic thruster]]
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| *[[Wingless Electromagnetic Air Vehicle]]
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| == References ==
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| * Talley, R .L., "''Twenty First Century Propulsion Concept''". PLTR-91-3009, Final Report for the period Feb 89 to July 90, on Contract FO4611-89-C-0023, Phillips Laboratory, Air Force Systems Command, Edwards AFB, CA 93523-5000, 1991.
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| * Tajmar, M., "''Experimental Investigation of 5-D Divergent Currents as a Gravity-Electromagnetism Coupling Concept''". Proceedings of the Space Technology and Applications International Forum (STAIF-2000), El-Genk editor, AIP Conference Proceedings 504, American Institute of Physics, New York, pp. 998–1003, 2000.
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| * Tajmar, M., "''The Biefeld-Brown Effect: Misinterpretation of Corona Wind Phenomena''". AIAA Journal, Vol 42, pp 315–318 2004.
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| * DR Buehler, ''[http://www.neophysicslabs.com/data/Documents/article2.pdf Exploratory Research on the Phenomenon of the Movement of High Voltage Capacitors]''. Journal of Space Mixing, 2004
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| * FX Canning, C Melcher, E Winet, ''[http://www.intalek.com/Papers/Lifters.pdf Asymmetrical Capacitors for Propulsion]''. 2004.
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| * GV Stephenson ''[http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=APCPCS000746000001001249000001&idtype=cvips&gifs=yes The Biefeld Brown Effect and the Global Electric Circuit]''. AIP Conference Proceedings, 2005.
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| == External links ==
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| {{Commons category|Ion driven air thrusters}}
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| * [http://web.archive.org/web/20050305114743/www.grc.nasa.gov/WWW/bpp/ComnErr.html#ELECTROSTATIC%20ANTIGRAVITY Electrostatic Antigravity] on [[NASA]]'s "Common Errors in propulsion" page
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| * [http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040171929_2004178266.pdf NASA: Asymmetrical Capacitors for Propulsion]
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| <references>http://www.nasa.gov/centers/glenn/technology/Ion_Propulsion1.html</references>
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| {{Spacecraft propulsion}}
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| [[Category:Propulsion]]
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| [[Category:Levitation]]
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| [[Category:Physics experiments]]
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| [[Category:American inventions]]
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| [[Category:Russian inventions]]
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| [[fr:Propulsion électrocinétique]]
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