MIT researchers study electro-hydrodynamic thrust

MIT researchers study electro-hydrodynamic thrust
An electrohydrodynamic lifter in action (Photo: Anonymous59.)
An electrohydrodynamic lifter in action (Photo: Anonymous59.)
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Elements of an electrohydrodynamic lifter (Photo: Blaze Labs Research)
Elements of an electrohydrodynamic lifter (Photo: Blaze Labs Research)
An electrohydrodynamic lifter in action (Photo: Anonymous59.)
An electrohydrodynamic lifter in action (Photo: Anonymous59.)

Imagine an aircraft that is silent, invisible to infrared detectors, has zero emissions and can hover in an eerie manner that helicopters can’t. Now imagine it coming from technology currently used to suck dust out of living room air. That’s what a team of researchers at MIT is doing. They've conducted a study that indicates that ionic thrusters, currently a science fair curiosity, might one day take to the skies.

Ionic thrusters sound like something you’d find on a spacecraft, and the principle is similar to that of the ion drives being developed by NASA and other space agencies. However, where an ion drive works like a rocket in the vacuum of space, an ionic thruster is more like a jet engine.

If you want to see an ionic thruster in action, just have a look at one of those electrostatic dust collectors found in many homes. These work on the very simple idea of using an electrostatic charge to pull dust motes out of the air and collect them on metal panels. What does this have to do with flying? Put your hand against the grille of the dust collector and you’ll feel a very slight breeze – despite the fact that the collector has no moving parts. What’s moving it? Ionic wind.

The proper name for “ionic wind” is ElectroHydroDynamic (EHD) thrust. It’s been known since the 18th century that electricity can kick up a tiny air movement, but it wasn't until the 1960s that EHD was identified and developed by scientists and engineers such as air pioneer Major Alexander Prokofieff de Seversky, who developed much of the physics and patented the basic technology.

Elements of an electrohydrodynamic lifter (Photo: Blaze Labs Research)
Elements of an electrohydrodynamic lifter (Photo: Blaze Labs Research)

Severskey used EHD to propel what he called an “ionocraft,” which are still built by students and hobbyists to this day. It works by using an negative anode to charge air particles. These charged particles or ions are drawn down to a positively charged cathode. As the ions move toward the cathode, they bump into other air molecules and push them down, creating the ionic wind.

In a working model, such as the one used by the MIT team, the anode is called the “emitter” and is made from a thin copper electrode. The cathode is of a thicker aluminum tube called a “collector.” These are mounted with a gap between them using a very light framework and powered by means of a wire connected to an outside electricity source.

Seeing an ionocraft in flight is slightly unnerving. Ionocraft aren't very large, being little more than bench top models, but when they take off, they don’t make a sound. Instead, they float up and hover on the wispy breeze forced down by the ion stream. The ionocraft can even be steered by varying the voltage, to turn and tip it like a helicopter.

In the ‘60s, the ionocraft seemed like a revolution in aviation. There was talk about them being used in all sorts of small aircraft, and the military were interested because ionocraft give off no heat, so there’s no infrared signature. Ionocraft were seen as replacing helicopters, as silent commuter ferries, as craft capable of operating at the edge of space, as traffic monitors or anti-missile platforms.

The problem was, the technology didn't scale very well. What worked for a small model that was built like a kite didn't do at all well as the ionocraft got bigger. It couldn't even carry its own power supply, so it wasn't long before ionic thrusters became the denizens of science fairs and the obsession of anti-gravity cultists.

Where MIT came in was at the point that the researchers realized that very few rigorous studies of ionic wind as a viable propulsion system had ever been carried out, and exactly what the ionic thruster is capable of hadn't been measured. So, they devised a test where an ionocraft was hung under a digital scale and tens of thousands of volts with enough amperage to run a light bulb were run through the craft.

The results were surprising. The team discovered that the ionic thruster turned out to be remarkably efficient compared to, for example, jet engines. Where a jet produces two newtons of thrust per kilowatt, the ionic thruster punched out 110 newtons per kilowatt. Furthermore, the thruster was most efficient at low thrust, which meant that power wasn't being wasted.

“It’s kind of surprising, but if you have a high-velocity jet, you leave in your wake a load of wasted kinetic energy,” said Steven Barrett, an assistant professor of aeronautics and astronautics at MIT. “So you want as low-velocity a jet as you can, while still producing enough thrust.”

Despite these promising findings, don’t expect to see any ionocraft in the skies soon. One problem with ionic propulsion is that even with its remarkable efficiency, it requires incredible amounts of voltage. Even a small craft would need megavolts to lift it, so a lot of work needs to be done to build up thrust while bringing down powerplant weight.

However, the characteristics of the ionic thruster means that increasing its thrust means increasing the gap between the anode and cathode. For an ionocraft to get off the ground with its own power supply and payload, the engine would need to be so large that the craft would be inside the engine. What that means is that an ionocraft would probably be large, round, carry its workings and payload in a bulgy middle section, and take off in vertical silence.

In other words, we might one day see flying saucers.

The team’s results were published in the Proceedings of the Royal Society.

Source: MIT

Concerning powering the craft and the electrical concepts involved, I feel there small clarification is justified. First, voltage value, while necessary for proper corona discharge, isn't the key attribute that determines the thrust estimation. Instead, it's power (aka rate of work). It makes sense when you think that to lift the craft and any payload is the classic example of doing work. In an electrical system, power is defined as voltage times current. Thus, high voltage with little current isn't going to do much work (think static shock). Any EE graduate can design a relatively cheap and lightweight high voltage power supply, but with existing technology, it's unlikely anyone can design one that not only can deliver the kinds of power needed to lift a craft but also carries it's own energy source. What we're talking about is a generator with massive coils and cooling support, powered by (combustion, chemical, nuclear) fuel all being carried by the craft. Secondly, on the issue of radar detection, even if you could completely mask the metallic electrode system (corona wire and anode surface), would be hard to hide the fact that the craft is essentially a wide band RF generator. In other words, the craft is a beacon in the EM wavelengths. You won't even need a radar to spot it. That said, it would be pretty cool to have silent aircraft.
Paul van Dinther
come on. Do us a favor and link to a youtube of a device like that.
Gee whiz
Is the author aware of the current state of small fusion power sources i.e. at skunkworks and the University of Washington+NASA?
If the setup creates an electric arc, wouldn't that make ozone? That's considered a detectable emission.
Noel Frothingham
The eddy currents would be fairly easy to detect as well.
re; kayanlau
When operating properly it does not arc.
Dave B13
I had never heard of this before. But I recall seeing an article about similar system of propulsion for submarines involving ions (charged particles) in the mid 1960's, it involved hacking a isolation transformer and then running salwater in a plastic tube through a gap where the transformer laminiations are removed, and watching movement of particles suspended in the water. IMO the maglev trains are a completely different animal, those are more like electric motors.
Stephen N Russell
Isnt this the basis for those V wing UFOs seen in AZ in 1997? Use this power source??
Actually this is old news. In fact there have been very detailed studies done on Lifter's, payed for by NASA and published as internal reports. The problem is this kind of research goes through cycles and everyone except for a few of us remember the prior cycle.
The main issue of the Lifter is that, it does not scale well and you loose all your efficiency. Any engineer will tell you that this is a common problem with a lot technologies. They look good in the small scale or in a purely controlled laboratory setting, but try making bigger or take them out of the laboratory and other new factors start taking away all the benefits.
Also a Lifter's ion wind thrust is completely dependant on pressure. As pressure drops (as you gain altitude) efficiency and thrust drop dramatically. It's been a dead end road since day one.
It's funny the way they describe the end result sounds remarkably like the Tesla flying ship. It never flew but Tesla's concept describes a vehicle shaped like an elongated ellipsoid, vaguely like a US football, with corrugated skin. I think he wound up with the same issue the article attributes to blocking Electro-Hydro-Dynamic thrust, lack of a sufficiently dense power supply to make it possible. It will be interesting to see what it looks like if anyone ever builds it.
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