Will the physics add up for near-silent, ion-propelled cargo drones?

Florida's Undefined Technologies claims it has managed to increase the thrust levels of ion propulsion systems to "unprecedented levels" with its "Air Tantrum" technology, enabling very quiet drones with no moving parts in the propulsion system, that look like flying pallets.

All aircraft propulsion systems provide thrust by moving air or another propellant, and for the vast majority of drones that means some kind of fan or propeller spinning angled blades to push air through and create thrust in the opposite direction. Ionic propulsion, on the other hand, is entirely electromagnetic.

The process uses a high-voltage electric field to ionize the nitrogen and oxygen molecules in the air, liberating electrons to create, primarily, a lot of positively-charged nitrogen molecules. These are drawn toward a negatively-charged electrode, usually in the form of a flat screen grid, and as they accelerate, they bang into other air molecules and bump them in the same direction to create an ionic wind.

Undefined's ion-propelled drone won't be the first machine to use this technology; for starters, NASA's been using something similar in space since the 1960s, bringing its own xenon propellant along as there's obviously no air in space to ionize.

Closer to Earth, ion propulsion has been more of a scientific curiosity – but in recent years, advances in energy storage have encouraged researchers to have a crack at ion-propulsion aircraft. Notably, one French project, Orville the mouse (we wonder what happened to Wilbur) took flight in a large, very lightweight "lifter" structure back in 2003. The resulting flights were filmed using one of the finest potatoes available at the time, and then encoded into the RealVideo format, which seemed certain to take off.

More recently, a team at MIT was able to achieve sustained flight by a solid-state aircraft in late 2018: a weirdly boxy lightweight aeroplane with a 5-meter (16.4-ft) wingspan. UC Berkeley followed up shortly afterward with an ion-propelled drone the size of a penny – the smallest flying robot ever made.

Now, Undefined Technologies, a startup based in Doral, about 15 miles out of Miami, says it has got ionic propulsion working on something considerably bigger: a large, square drone standing about 2 feet (0.6 m) high and about 4 feet (1.2 m) per side, at our estimates. It looks like a stack of pallets, but the company has released video of this thing undertaking a brief, wobbly flight.

Undefined Technologies is an excellent name for this business as it stands. Its entire website and presentation focuses on the benefits of an ionically propelled drone – namely, quiet flight that the company feels will be better for the urban soundscape (and noise pollution regulations) than the annoying buzz and whir of drone propellers. The target is 70 decibels, though, or about as loud as a vacuum cleaner. Or indeed a Mavic Pro Platinum, according to Silent Home Hub. The last Mavic I flew was loud enough to make my dog go nuts, but perhaps we're talking about a machine here with bigger lift capabilities.

How exactly this takes things to the next level is, well, undefined. Here's the entire text of the technology section on the company's website: "Since Thomas Townsend Brown discovered propulsion generated by asymmetrical electrodes in 1921 there had not been a significant break-thru which allow generation ion propulsion to levels which made it possible to develop VTOL crafts in atmospheric conditions. The Air Tantrum™ Technology (Patent Pending) uses innovative physics principles which increase thrust to unprecedented levels."

I've flown with a two-year-old, so I know a little about Air Tantrums, but we'll endeavor to get in touch with the team and learn more. Meanwhile, here are some of our remaining concerns: firstly, these aircraft will have to be quite large and extremely lightweight in order to carry the requisite battery resources, computers, cameras, instruments and cargo, meaning that they'll be a bit unwieldy, and even with strong, lightweight materials like carbon fiber, they might be fragile.

Secondly, their size will make them a bigger target for the wind, meaning they'll have to work harder to self-stabilize than a smaller drone with props. And it's unclear from the vision we've seen thus far just how responsive the ion propulsion units are and how quickly they can generate the kind of instant thrust you need for stability in changing winds. It sure looks wobbly in the video.

Thirdly, we don't know how efficient these thrusters are as compared to props; anything that burns through precious energy reserves faster than the props we're currently using may have a tough time establishing itself until the long-promised battery density revolution finally happens. Fourthly, without the torque reactions of multiple spinning props to draw on, it's unclear how an ionic drone will control its yaw precisely in the air.

Fifth, we don't know how well it'll scale. The Berkeley team responsible for the penny-sized drone seemed to feel that ionic propulsion made more sense the smaller the scale, and even its penny-sized drone was severely constrained by current battery technology.

The aircraft in the Undefined video appears to be quite large, but there's really nothing but the wall markings in Undefined's "test lab" to scale it by, and it only flies for a matter of seconds ... with the sound turned off so we can listen to a cello instead of the device's key benefit. Incidentally, Orville the mouse's flight didn't sound quiet enough to us in that 2003 video to cause a revolution, although noise levels can be tricky to convey accurately when you're filming with a potato.

So there are plenty of questions to be answered before this Air Tantrum tech can can "transform the field of transportation as we know it." We're interested enough to learn more, but Undefined will need to do a lot of defining around things like thrust, weight, physical size, energy consumption, carrying capacity, durability, responsiveness and yaw control – not to mention exactly which "innovative physics principles" it's using – before anyone gets too excited.

Check out the video here (the flight demo we refer to above is at about the 3-minute mark).

Editor's note (2020-11-24): This piece has been updated to correct two errors. The first is that the drone is projected to make around 70 decibels , not 7 – go to 0:16 seconds in the video linked above to see how we made that mistake. The second is that where we stated there are no moving parts on the aircraft, it's more accurate to say there will be no moving parts in the propulsion system. The drone will still run gyroscopic sensors and the like, which do have moving parts in them.

Source: Undefined Technologies