An ion-propelled aircraft or ionocraft is an aircraft that uses electrohydrodynamics (EHD) to provide lift or thrust in the air without requiring combustion or moving parts. Current designs do not produce sufficient thrust for crewed flight or useful loads.

History

Origins

The principle of ionic wind propulsion with corona-generated charged particles was discovered soon after the discovery of electricity with references dating to 1709 in a book titled Physico-Mechanical Experiments on Various Subjects by Francis Hauksbee.

VTOL "lifter" experiments

American experimenter Thomas Townsend Brown spent much of his life working on the principle, under the mistaken impression that it was an anti-gravity effect, which he named the Biefeld–Brown effect. Since his devices produced thrust in the direction of the field gradient, regardless of the direction of gravity, and did not work in a vacuum, other workers realized that the effect was due to electrohydrodynamics.

Vertical take-off and landing (VTOL) ion-propelled aircraft are sometimes called "lifters". Early examples were able to lift about a gram of weight per watt. This was insufficient to lift the heavy high-voltage power supply necessary, which remained on the ground and supplied the craft via long, thin and flexible wires.

The use of electrohydrodynamics propulsion for lift was studied by American aircraft designer Major Alexander Prokofieff de Seversky in the 1950s and 1960s. He filed a patent for an "ionocraft" in 1959. He built and flew a model VTOL ionocraft capable of sideways manoeuvring by varying the voltages applied in different areas, although the heavy power supply remained external.

The 2008 Wingless Electromagnetic Air Vehicle (WEAV), a saucer-shaped EHD lifter with electrodes embedded throughout its surface, was studied by a team of researchers led by Subrata Roy at the University of Florida in the early part of the twenty-first century. The propulsion system employed many innovations, including the use of magnetic fields to enhance the ionisation efficiency. A model with an external supply achieved minimal lift-off and hover.

Onboard power

Twenty-first century power supplies are lighter and more efficient. The first ion-propelled aircraft to take off and fly using its own onboard power supply was a VTOL craft developed by Ethan Krauss of Electron Air in 2006. The company currently owns US patent 10119527B2 and 11161631B2 in relation to this field. The craft developed enough thrust to rise rapidly or to fly horizontally for several minutes.

In November 2018 the first self-contained ion-propelled fixed-wing airplane, the MIT EAD Airframe Version 2 flew 60 meters. It was developed by a team of students led by Steven Barrett from the Massachusetts Institute of Technology. It had a 5-meter wingspan and weighed 2.45 kg. The craft was catapult-launched using an elastic band, with the EAD system sustaining the aircraft in flight at low level.

Principles of operation

Ionic air propulsion is a technique for creating a flow of air through electrical energy, without any moving parts. Because of this it is sometimes described as a "solid-state" drive. It is based on the principle of electrohydrodynamics.

In its basic form, it consists of two parallel conductive electrodes, a leading emitter wire and a downstream collector. When such an arrangement is powered by high voltage (in the range of kilovolts per mm), the emitter ionizes molecules in the air that accelerate backwards to the collector, producing thrust in reaction. Along the way, these ions collide with electrically neutral air molecules and accelerate them in turn.

The effect is not directly dependent on electrical polarity, as the ions may be positively or negatively charged. Reversing the polarity of the electrodes does not alter the direction of motion, as it also reverses the polarity of the ions carrying charge. Thrust is produced in the same direction, either way. For positive corona, nitrogen ions are created initially, while for negative polarity, oxygen ions are the major primary ions. Both these types of ion immediately attract a variety of air molecules to create molecular cluster-ions of either sign, which act as charge carriers.

Current EHD thrusters are far less efficient than conventional engines. An MIT researcher noted that ion thrusters have the potential to be far more efficient than conventional jet engines.

Unlike pure ion thruster rockets, the electrohydrodynamic principle does not apply in the vacuum of space.

Electrohydrodynamics

The thrust generated by an EHD device is an example of the Biefeld–Brown effect and can be derived through a modified use of the Child–Langmuir equation.

A generalized one-dimensional treatment gives the equation:

<math display="block">F = \frac{Id}{k} </math>

where

  • F is the resulting force.
  • I is the electric current.
  • d is the air gap.
  • k is the ion mobility of the working fluid, expressed in A⋅s<sup>2</sup>⋅kg<sup>−1</sup> in SI units, but more commonly expressed with the unit m<sup>2</sup>⋅V<sup>−1</sup>⋅s<sup>−1</sup>. A typical value for air at surface pressure and temperature is ).

The emitter is sometimes referred to as the "corona wire" because of its tendency to emit a purple corona discharge glow while in use. This is simply a side effect of ionization.

Air gap

The air gap insulates the two electrodes and allows the ions generated at the emitter to accelerate and transfer momentum to neutral air molecules, before losing their charge at the collector. The width of the air gap is typically 1&nbsp;mm / kV.

Collector

The collector is shaped to provide 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. Sharp edges on the skirt degrade performance, as it generates ions of opposite polarity to those within the thrust mechanism.

See also

  • Atmosphere-breathing electric propulsion
  • Biefeld–Brown effect
  • Hall-effect thruster
  • Ion thruster
  • Ion wind
  • Magnetoplasmadynamic thruster
  • Plasma actuator

References

Further reading

  • DR Buehler, Exploratory Research on the Phenomenon of the Movement of High Voltage Capacitors. Journal of Space Mixing, 2004
  • FX Canning, C Melcher, E Winet, Asymmetrical Capacitors for Propulsion. 2004.
  • GVi Stephenson The Biefeld Brown Effect and the Global Electric Circuit. AIP Conference Proceedings, 2005.
  • Electrostatic Antigravity on NASA's "Common Errors in propulsion" page
  • NASA: Asymmetrical Capacitors for Propulsion
  • "Full analysis & design solutions for EHD Thrusters at saturated corona current conditions", NASA, 2004, https://www.gsjournal.net/h/papers_download.php?id=1830

fr:Propulsion électrocinétique