Undefined's next-gen "silent" ion propulsion drone: still noisy

With two successful flight tests in the bag, and just under US$2 million in seed funding, Florida company Undefined Technologies has unveiled the next generation of its "silent" commercial drone, which uses ionic propulsion instead of propellers.

The new design is certainly a step up visually from previous efforts, but at the end of the day, an ionic propulsion system is going to look like an ionic propulsion system; by necessity it'll feature a large grid of electrodes with at least two layers, such that the top and bottom layers can be fed high and opposing voltages in order to accelerate ionized air downwards and produce thrust. So while the wraparound cover is a nice touch, it still looks like a flying dish rack underneath.

We had a lot of questions when we first saw this company's promises – ionic propulsion has proven very useful in space, but could it really be an efficient replacement for propellers closer to Earth? MIT has published research on its ion-drive fixed-wing plane, but you need a lot more thrust and a lot more onboard energy storage for vertical-lift aircraft.

Undefined Technologies has certainly chosen its name judiciously; a year and a half later, we still know very little about its "novel Air Tantrum™ technology," which the company says will be extremely quiet. But its December 2021 flight video and a presentation given by company CEO Tomas Pribanic at a logistics conference in January do turn up an interesting nugget or two.

The company's original proof of concept, as shown in the last video we published, flew for around 25 seconds, and made about 90 decibels, says Pibanic. The new prototype, he claims, has flown for around two and a half minutes, and was measured at 85 decibels. The ultimate target is around 70 decibels, or about the same as a DJI Mavic, but presumably in a larger airframe with some cargo carrying capability. It's unclear how the company expects to continue reducing noise on a device that already has no moving parts in its propulsion system. The company doesn't make any promises around range or endurance either at this stage.

In the video below you can see the new prototype airborne, but the company has chopped the footage up so we can't verify the full length of the flight. It looks a little more stable than the proof of concept, although it's flying indoors without any wind to contend with. Noise-wise, there's an interesting high-pitched whine involved, and the drone bends in a somewhat worrying way when it lands, just due to the size and light weight of its structure. It does not look heavy duty, and we imagine it'll be tough to scale these things up without making them fragile.

It certainly won't achieve high altitudes; as MIT's Steven Barrett and a number of astute commenters on our previous piece point out, the breakdown voltage of air rises with altitude. But most use cases for today's drones keep them close enough to the ground that this is unlikely to be the dealbreaker. We're not convinced the Silent Ventus will be silent or energy-efficient enough to compete with regular multicopters, but we're watching with interest.

Source: Undefined Technologies