A researcher who was involved in the development of the silent plane explains the physics behind it
Author: Steve Barrett, Professor of Aeronautics and Astronautics, Massachusetts Institute of Technology
Since they were invented more than a century ago, airplanes move through the air by turning the surfaces of propellers or turbines. But from watching sci-fi movies like the Star Wars, Star Trek, and Back to the Future series, I imagined that the propulsion systems of the future would be quiet and still—perhaps with some kind of blue glow and a whoosh noise, but no moving parts. , and without a stream of pollution coming out from behind.
It doesn't exist yet, but there is at least one physical principle that could be promising. About nine years ago I started researching the use of ionic winds—flows of charged particles through the air—as a means of propelling flight. Based on decades of research and experiments by academics and hobbyists, professionals and high school students studying science, my research group recently flew a near-silent airplane without any moving parts.
The plane weighed about 2.5 kg with a wingspan of 5 meters, and flew about 60 meters, so it is a long way to effectively carry cargo or people over long distances. But we have proven that it is possible to fly a heavy craft from the air using ion winds. And it even has a glow that you can see in the dark.
Return to neglected studies
The process used by our airplane, formally called electro-aerodynamic propulsion, was already studied in the XNUMXs by an eccentric scientist who thought he had discovered anti-gravity - which of course was not the case. In the XNUMXs, aerospace engineers explored using it for flight propulsion, but concluded that it would be impossible with the understanding of ion winds and the technology available at the time.
But in the more recent past, a large number of hobbyists – and high school students doing projects for science classes – have built small electro-aerodynamic propulsion devices that suggest it might still work. Their work was very important to my team's early work period. We wanted to improve their work, mainly by conducting large series of experiments to learn how to optimize the design of electro-aerodynamic propellers.
move the air, not the parts of the plane
It is relatively simple to explain and apply the physics underlying electro-aerodynamic propulsion, although some of this physics is not simple.
We use a thin wire that is charged to a voltage of +20,000 using a lightweight power converter that gets its power from a lithium polymer battery. The thin wires are called emitters, and are closer to the front of the plane. Around these emitters the electric field is so strong that the air is ionized - neutral nitrogen molecules lose an electron and become nitrogen ions with a positive charge.
Further down the plane we put an airfoil - like a small wing - whose leading edge is electrically conductive and charged to a voltage of -20,000 by the same electrical converter. This is called the receiver. The collector attracts the positive ions. As the ions flow from the emitter to the collector, they collide with uncharged air molecules, causing what is called an ionic wind that flows between the emitters and collectors, propelling the aircraft forward. This ionic wind replaces the airflow that a jet engine or propeller would create.
I headed a study that investigated how this type of propulsion actually works, and developed a detailed knowledge of how efficient and powerful it can be.
My team and I also worked with electrical engineers to develop the electronics needed to convert battery output into the tens of thousands of volts needed to create ionic wind. The team was able to create a much lighter power converter than any converter that existed before. This device was small enough to be practical in the design of an airplane, which we were eventually able to build and fly.
A demonstration of the way the MIT plane works
Our first flight, of course, is a long way from flying people. We are already working on making this type of propulsion more efficient and with the ability to carry larger loads. The first commercial applications, assuming we get that far, could be in the production of quiet fixed-wing drones, including for environmental monitoring and communications platforms.
Looking to the more distant future, we hope it can be used in larger aircraft to reduce noise and even allow the outer shell of the aircraft to help create thrust, instead of engines or to add to their power. It may also be possible to miniaturize electro-aerodynamic equipment, enabling a new variety of nano drones. Many may believe that these possibilities are unlikely or even impossible. But this is what the engineers in the sixties thought about what we are already doing today.