This curious concept of a silent drone flies thanks to ionic propulsion

This curious concept of a silent drone flies thanks to ionic propulsion

While the majority of the industry is interested in electric or hydrogen engines, a Florida startup wants to make its funny fly thanks to ionic propulsion.

Undefined Technologies, a Florida startup, has just unveiled the Silent Ventus, a one-of-a-kind drone concept. On the menu: low noise and zero carbon emissions. “Silent Ventus is a telling example of our ambition to create a more sustainable, progressive, and less noisy urban environment,” explains Tomas Pribanic, CEO of the company in a press release spotted by Interesting Engineering.

And to give itself the means to achieve this ambition, Undefined Technologies has chosen to bet on an extremely surprising technology for a machine of this type: ion propulsion. Technically, it is an electric mode of propulsion; but it’s not about turning a rotor, as opposed to strictly electric motors. Here, current is used to accelerate ions (an atom or molecule that carries an electrical charge) to very high speeds to generate thrust.

An ion thruster test performed by NASA. The blue halo corresponds to the ionized air which becomes visible thanks to Cherenkov radiation. ©NASA/JPL

Atmospheric ion propulsion, a major engineering challenge

When we think of ion thrusters, we inevitably think of space probes. The latter are often equipped with engines based on this concept. Those built for this purpose produce a extremely low thrustbut with a exceptional performance; in the vacuum of space, where there is practically no force likely to oppose the advance of the vehicle, they allow these machines to travel immense distances while embarking very few resources.

On the other hand, on a planet like Earth, it suddenly becomes much more complicated to exploit. Because of the very low thrust delivered by these ion thrusters, it is traditionally difficult to overcome the resistance of the air and the pull of gravity which seeks to pin the craft to the ground; it is largely because of these forces that ion propulsion is not used on Earth.

However, this is what Undefined Technologies claims with its drone. “Silent Ventus uses proprietary technology to take advantage of the ion cloud that surrounds the vehicle to generate significant thrust into the atmosphere“, says the press release. On the other hand, even if it is a question of ionic propulsion stricto sensu, the basic concept is very different. (Thanks to Oygron for this important distinction!)

The thruster used by Undefined Technologies relies on the Biefield-Brown effect; without going into detail, it is essentially a corollary of the ion engines used by space probes. The problem is that this approach produces radically opposite results at some levels.

This can be seen in particular in terms of performance; even in the best of cases, the yield here is extremely low (see this study) while it constitutes the main argument of ionic propulsion applied to space vehicles. It is even much lower than that of traditional electric and propellant motors.

This did not prevent the firm from pushing the concept relatively far. In December 2021, the startup unveiled a tech demo that served as a proof of concept; it showed that its first prototype was indeed capable of staying at altitude using its ion thrusters alone for 2.5 minutes (see the video above). A small feat that the firm’s engineers have achieved in less than a year of work on this technology… but is it really worth it?

A more reasonable path than electric motorization?

Indeed, this segment is currently dominated by concepts of devices equipped with electric motors traditional. However, many observers are very critical of the relevance of this approach. It involves embarking batteries by definition very heavy; a paradox that does not go well with the traditional constraints of aeronautics, and which has significant consequences on the energy efficiency of these machines.

All-electric VTOLs like the one from Joby Aviation are marvels of engineering, but that doesn’t stop many observers from having doubts about the concept’s relevance. © Joby Aviation

Is it therefore very relevant to dig even further on this track, which is even worse off than standard electric propulsion in terms of performance? The startup thinks so, because this technology still has some advantages, especially in terms of integration into the urban environment.

Traditional eVTOLs, for example, tend to be very noisy, which is anything but ideal in a dense urban environment. The ionic propulsion, it is more discreet with about 70 dB at full speed, or about the noise of a washing machine in operation. For comparison, eVTOLs like Joby’s regularly emit more than 90 dB, a noise comparable to that of a lawn mower.

Will this be enough to encourage the emergence of other projects based on ion propulsion? It is still too early to say, especially since the startup has not even not yet proposed a more successful prototype as its initial proof of concept.

[Mise à jour 04/05 à 18h50 – Une partie de l’article a été réécrite afin de faire la distinction entre la propulsion ionique appliquée aux sondes spatiales et celle utilisée par Undefined Technologies. Merci à Oygron !]

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