Plasma actuators use ionized gas to create aircraft control surfaces without moving parts or hydraulic systems. They offer greater reliability and maneuverability, but altitude and speed affect performance. The technology is practical and has been tested in wind tunnels at supersonic speeds.
A plasma actuator is a form of advanced servo mechanism developed primarily for aircraft control surfaces as of 2011. The actuation system uses the flow of plasma, which is a highly ionized gas, to create an easily shaped surface that can operate like typical ailerons or flaps do on aircraft, creating drag and lift at key points in flight maneuvers such as takeoffs and landings. The effect is created by high voltage alternating electric current and uses normal atmospheric air to create the plasma gas itself.
The specifications for a plasma actuator follow a multi-layered rectangular pancake-like design in the general shape of an airplane wing. Two sheets of conductive electrodes are separated by a dielectric insulating material. One sheet of electrodes is exposed above the dielectric medium and one is embedded within it and off-center with respect to the other electrode. The air first flows over the exposed electrode, and as the high voltage current passes through the system, a region of gas plasma is formed in the air directly behind the top electrode and above the embedded one, which can then be controlled and molded to affect airflow over the entire actuator region during flight. This mimics the effect of a mechanical aileron without requiring any moving parts or hydraulic systems, while also creating a more versatile shape with potentially greater control over the aircraft’s aerodynamics.
The Air Force Research Laboratory (AFRL) in the United States has been researching the plasma actuator since at least 2006 for use in supersonic aircraft designs. Such devices are believed to offer greater reliability than traditional mechanical flaps with the likelihood of reduced weight to the vehicle body, which would give it greater maneuverability and long-range capability. In research at AFRL, the plasma actuator was tested in a wind tunnel at speeds up to five times the speed of sound.
The technology for a plasma actuator system is considered relatively practical as of 2011. This is, in part, because plasma technology is commonly employed in consumer devices such as fluorescent lighting and plasma television screens and it does not require high temperatures to generate it where it is naturally produced by stars. The ability to turn a plasma field on and off at extremely high speeds also gives the technology a unique advantage in aircraft maneuvering that cannot be accomplished with conventional hydraulic means.
Some of the technology’s limitations still exist as of 2011. Flow control for the actuator required the addition of fluidic oscillators, where two plasma actuator systems work in tandem to create pulsed or modulated flow patterns. The function of the actuator parts is also inherently based on the density of the surrounding gas being converted to plasma, so altitude for aircraft, as well as their speed, can have direct effects on performance which must be fine-tuned before they are can be counted on to perform reliably when needed.
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