Ionocraft
Encyclopedia
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
, commonly known as a lifter or hexalifter, is an electrohydrodynamic (EHD) device (utilizing an electrical phenomenon known as the Biefeld–Brown effect
Biefeld–Brown effect
The Biefeld–Brown effect is an electrical effect that produces an ionic wind that transfers its momentum to surrounding neutral particles, first discovered by Paul Alfred Biefeld and Thomas Townsend Brown . The effect is more widely referred to as electrohydrodynamics or sometimes...
) to produce thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
in the air, without requiring any combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
or moving parts
Moving parts
The moving parts of a machine are those parts of it that move. Machines comprise both moving and fixed parts. The moving parts have controlled and constrained motions....
. The term "Ionocraft" dates back to the 1960s, an era in which EHD experiments were at their peak. In its basic form, it simply consists of two parallel
Parallel (geometry)
Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...
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
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
in the range of a few kilovolts, it produces thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
. The ionocraft forms part of the EHD thruster family, but is a special case in which the ionisation and accelerating stages are combined into a single stage.
The device is a popular science fair
Science fair
A science fair is generally a competition where contestants present their science project results in the form of a report, display board, and models that they have created. Science fairs allow students in grade schools and high schools to compete in science and/or technology activities...
project for students. It is also popular among anti-gravity
Anti-gravity
Anti-gravity is the idea of creating a place or object that is free from the force of gravity. It does not refer to the lack of weight under gravity experienced in free fall or orbit, or to balancing the force of gravity with some other force, such as electromagnetism or aerodynamic lift...
or so-called "electrogravitics" proponents, especially on the Internet, where it is commonly referred to as a lifter.
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, 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.
Ionocraft require many safety precautions due to the high voltage required for their operation, and also the risk of premature death from heart or lung disease due to the inhalation of their ionised air product, ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
. A large subculture has grown up around this simple EHD thrusting device and its physics are now known to a much better extent.
What it is
The ionocraft is a propulsion device based on ionic air propulsionAir propulsion
Air propulsion is the generation of thrust during flight by an aircraft or a creature such as a bird, bat or insect.-Aircraft:An aircraft propulsion system must serve two purposes. First, the thrust from the propulsion system must balance the drag of the airplane when the airplane is cruising...
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
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
. The principle of ionic wind propulsion with corona
Corona discharge
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...
-generated charged particles has been known as 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
Francis Hauksbee
Francis Hauksbee the elder , also known as Francis Hawksbee, was an 18th-century English scientist, and a Fellow of the Royal Society...
. However, its use for propulsion was first given serious thought by Thomas Townsend Brown
Thomas Townsend Brown
Thomas Townsend Brown was an American physicist.-Early and middle years:Brown was born in Zanesville, Ohio; his parents were Lewis K. and Mary Townsend Brown. In 1921, Brown discovered what was later called the Biefeld-Brown effect while experimenting with a Coolidge X-ray tube. This is a vacuum...
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 that in 1964 coined the term Ionocraft in his . The basic external design of these devices can be found in older patents, dating back to 1960 filed by Thomas Townsend Brown
Thomas Townsend Brown
Thomas Townsend Brown was an American physicist.-Early and middle years:Brown was born in Zanesville, Ohio; his parents were Lewis K. and Mary Townsend Brown. In 1921, Brown discovered what was later called the Biefeld-Brown effect while experimenting with a Coolidge X-ray tube. This is a vacuum...
, 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
Biefeld–Brown effect
The Biefeld–Brown effect is an electrical effect that produces an ionic wind that transfers its momentum to surrounding neutral particles, first discovered by Paul Alfred Biefeld and Thomas Townsend Brown . The effect is more widely referred to as electrohydrodynamics or sometimes...
.
Ionocraft construction
Balsa
Ochroma pyramidale, commonly known as the balsa tree , is a species of flowering plant in the mallow family, Malvaceae. It is a large, fast-growing tree that can grow up to tall. It is the source of balsa wood, a very lightweight material with many uses...
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 arc
Spark gap
A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the voltage difference between the conductors exceeds the gap's breakdown voltage, a spark forms,...
in a spectacular show of tiny lightning bolts which has a twofold effect.
- It degrades the thrust as it is shortingShort circuitA short circuit in an electrical circuit that allows a current to travel along an unintended path, often where essentially no electrical impedance is encountered....
the device and there is current flow through the arc instead of the ions that do the lifting - It can destroy the power supplyPower supplyA power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
or burn the balsa structure of the Lifter.
The corona wire
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 wireWire
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...
. While copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
wire can be used, it does not work quite as well as stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
. Similarly, thinner wire such as 50 gauge
American wire gauge
American wire gauge , also known as the Brown & Sharpe wire gauge, is a standardized wire gauge system used since 1857 predominantly in the United States and Canada for the diameters of round, solid, nonferrous, electrically conducting wire...
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.
The corona wire is so called because of its tendency to emit a purple corona
Corona discharge
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...
-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
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
and NOx
NOx
NOx is a generic term for the mono-nitrogen oxides NO and NO2 . They are produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures...
produced by the corona.
The air gap
The air gap is simply that, a gap of free flowing air between the two electrodes that make up the structure of an ionocraft.The air gap is a vital necessity to the functioning of this device as it is the dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
used during operation. Best results have been observed with an air gap of 1 mm to every kV.
The collector
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.The foil skirt is named simply because it is shaped much like a skirt
Skirt
A skirt is a tube- or cone-shaped garment that hangs from the waist and covers all or part of the legs.In the western world, skirts are usually considered women's clothing. However, there are exceptions...
, 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.
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
Charge carrier
In physics, a charge carrier is a free particle carrying an electric charge, especially the particles that carry electric currents in electrical conductors. Examples are electrons and ions...
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.
How it works
The generated thrust can be explained in terms of electrokinetics or, in modern terms, electrohydrodynamicsElectrohydrodynamics
Electrohydrodynamics , also known as electro-fluid-dynamics or electrokinetics, is the study of the dynamics of electrically charged fluids. It is the study of the motions of ionised particles or molecules and their interactions with electric fields and the surrounding fluid...
propulsion and is given by the equation:
where
- F is the resulting force, measured in dimensionDimensional analysisIn physics and all science, dimensional analysis is a tool to find or check relations among physical quantities by using their dimensions. The dimension of a physical quantity is the combination of the basic physical dimensions which describe it; for example, speed has the dimension length per...
MMassMass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
LLengthIn geometric measurements, length most commonly refers to the longest dimension of an object.In certain contexts, the term "length" is reserved for a certain dimension of an object along which the length is measured. For example it is possible to cut a length of a wire which is shorter than wire...
TTimeTime is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....
−2 - I is the current flow of electric current, measured in dimension IElectric currentElectric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
. - d is the air gap distance, measured in dimension L.
- k is the ion mobility coefficient of air, measured in dimension M−1 T2 I (Nominal value 2·10−4 m2 V−1 s−1).
In its basic form, the ionocraft is able to produce forces great enough to lift about a gram of payload per watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
, 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 lighter than air
Aerostat
An aerostat is a craft that remains aloft primarily through the use of buoyant lighter than air gases, which impart lift to a vehicle with nearly the same overall density as air. Aerostats include free balloons, airships, and moored balloons...
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.
When the ionocraft is turned on, the corona wire becomes charged with high voltage
High voltage
The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements...
, usually between 20 and 50 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
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
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
Drift velocity
The drift velocity is the average velocity that a particle, such as an electron, attains due to an electric field. It can also be referred to as Axial Drift Velocity since particles defined are assumed to be moving along a plane. In general, an electron will 'rattle around' in a conductor at the...
. Such velocity depends on the mean free path
Mean free path
In physics, the mean free path is the average distance covered by a moving particle between successive impacts which modify its direction or energy or other particle properties.-Derivation:...
between collisions, the external electric field, and on the mass of ions and neutral air molecules.
The fact that the current is carried by a corona discharge
Corona discharge
In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized...
(and not a tightly-confined arc
Electric arc
An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...
) 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 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.
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
Drift velocity
The drift velocity is the average velocity that a particle, such as an electron, attains due to an electric field. It can also be referred to as Axial Drift Velocity since particles defined are assumed to be moving along a plane. In general, an electron will 'rattle around' in a conductor at the...
. 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.
See also
- Alexander Prokofieff de Seversky
- ElectrohydrodynamicsElectrohydrodynamicsElectrohydrodynamics , also known as electro-fluid-dynamics or electrokinetics, is the study of the dynamics of electrically charged fluids. It is the study of the motions of ionised particles or molecules and their interactions with electric fields and the surrounding fluid...
- Ion thrusterIon thrusterAn ion thruster is a form of electric propulsion used for spacecraft propulsion that creates thrust by accelerating ions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic ion thrusters use the Coulomb force and...
- Hall effect thrusterHall effect thrusterIn spacecraft propulsion, a Hall thruster is a type of ion thruster in which the propellant is accelerated by an electric field. Hall thrusters trap electrons in a magnetic field and then use the electrons to ionize propellant, efficiently accelerate the ions to produce thrust, and neutralize the...
- Magnetoplasmadynamic thrusterMagnetoplasmadynamic thrusterThe Magnetoplasmadynamic thruster is a form of electrically powered spacecraft propulsion which uses the Lorentz force to generate thrust...
External links
- Electrostatic Antigravity on NASANASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's "Common Errors in propulsion" page - NASA: Asymmetrical Capacitors for Propulsion