Ion-wind-powered aircraft makes its first flight

Modern aircraft fly with propellers and turbines fueled by the burning of fossil fuels emitting greenhouse gases. A new article published on November 21 in Nature reported the first flight of an ionic wind aircraft (1). The small lightweight device called "elevator" uses a solid state propulsion, also called electro-dynamic propulsion, and requires no combustion process or moving parts.

The mechanism behind this type of propulsion has been known for years. In short, charged molecules in the air are accelerated by an electric field and, when they collide with neutral air molecules, momentum transfer creates a phenomenon called ionic wind. . However, the authors claim that no other type of aircraft with a solid state propulsion system has ever been flown.

During the validation study, researchers at the Massachusetts Institute of Technology (MIT) were able to use ionic wind propulsion to support the flight of a small aircraft. The aircraft was designed using a method called geometric programming in order to find the optimal design that could minimize the span and therefore the weight, the power requirements and the costs. This ended up being a 5 meter span, with a mass of 2.5 kg, a flight speed of 4.8 meters per second and a power of 600 watts.

The entire power system and batteries were on board the plane. This included a specially designed high voltage (40 kilovolts) ultra-light power converter. The aircraft has been flown ten times, demonstrating that widely accepted limitations "were until then impossible to make electroerodynamics unachievable as a method of aircraft propulsion".

To obtain a constant level flight, an electric field has been applied to the area surrounding the emitter – a thin wire that produces the free electrons that collide with the air molecules to ionize them – thus creating a region of molecules charged air, phenomenon called a corona discharge. When the charged molecules move away from the transmitter, they generate a propulsive ionic wind and are eventually accelerated to the collector, thus generating enough propulsion to fly the elevator.

It is still unclear whether researchers will be able to upgrade the propulsion system. The authors hope that further improvements in overall efficiency and thrust density will "open up new design spaces and unexplored applications for near-silent electric aircraft based on solid-state propulsion." One of the main challenges will be to get enough thrust – the mechanical force needed to accelerate the plane. Although the researchers were able to generate enough thrust to fly the unmanned aerial vehicle, current technology would not be capable of high-speed commercial flights. The ionic wind may not be able to withstand the flight of several-ton aircraft, but much lighter solar-powered aircraft could be more practical.

Be that as it may, this latest concept validation will contribute to a better understanding of ion wind physics and has opened the way for increased optimization of transmitters and collectors. In addition, the solid state propulsion could be applied to urban UAVs to limit associated noise impacts and could lead to further technological advances in favor of aircraft 'quieter, mechanically simpler and nondescript'. emitting no combustion emissions ".

(1) Xu, H. et al. Flight of a propelled airplane in the solid state. Nature (2018). DOI: 10.1038 / s41586-018-0707-9

Image credit: Hu, H. et al. Nature (2018)

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