Ion Propulsion – A Plane with No Moving Parts [video] | Hacker News Reader

Ion Propulsion – A Plane with No Moving Parts [video]

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92 pointsrfreytag15 comments

If you want source material, it's a paper that was published in Nature in November (abstract at [0]) including video [1] and full system parameters [2].

It weighs 2.45 kg and has a wingspan of 5m. It flew multiple times and the distance flown / total time time in the air was limited by the size of the hangar that was used for the flight trials, not the ion drive.

[0] https://www.nature.com/articles/s41586-018-0707-9

[1] https://static-content.springer.com/esm/art%3A10.1038%2Fs415...

[2] https://www.nature.com/articles/s41586-018-0707-9/tables/1

At 6.25 N/kW it's not going to be flying for very long in terms of duration. It's a toy concept that's neat. The real accomplishment here is the design of the very low mass high voltage inverter. That's some serious engineering.

So there's nothing in the design that can be done at scale that's useful here? I'm not trying to nit-pick, but are you saying none of the design (except for the power supply) is novel or useful?

Exactly. Electrostatic lifters have been around forever. I even made one with a neon sign transformer back in the late 90s. But my power supply was literally heavy iron and with wall current connected to the balsa/foil craft with very light magnet wire. Making the electrical energy storage and high power HV generation light enough is no small feat. That's what should be celebrated here.

Could the energy be beamed from the surface, like a trolleybus powered by power lines?

> 6.25 N/kW

I wonder what the energy density of a NASA nuclear power plant is.

The radioisotope power plants? Very, very low. I think they output a few hundred watts of power. They're mostly used because they're very reliable and consistent over a long period of time.

Another flying engine without moving parts is the ramjet [1]. It's a compression engine that doesn't use turbine blades to compress the incoming air, but simply the speed of the flying object itself. Since it can't function at speed zero by definition it needs assistance to get to a minimum speed where it function (which is usually Mach 3). For this reason it's usually found in missiles; more recently it showed up in artillery shells [2].

An engine not having moving parts does not mean no noise though. I never heard a ramjet powered missile myself, but I doubt it's very quiet.

[1] https://en.wikipedia.org/wiki/Ramjet [2]http://www.thedrive.com/the-war-zone/21531/yes-this-is-a-ram...

Pulse jet is another simple jet engine design, was used by Germany in WW2 on their V1 flying bombs. Not particularly efficient, but cheap. And noisy.

Previous discussion with more details on how the ion wind is generated:

https://news.ycombinator.com/item?id=18503772

Turns out the madmen over at KSP we’re right, you can make a plan run by ion engines

The Real Engineering channel has deteriorated into drivel. He spent half the video discussing ion engines for spacecraft, presumably in a bid to drive up enthusiasm around efficiency and top speed, before embarrassing himself with his discussion of the ion plane experiment. This technology is stillborn for the reasons he himself gives, though he dances around that, hoping against hope that few enough users will understand that the video is a flimsy excuse for a SkillShare ad, so that he can continue wringing sponsorship dollars from his increasingly pathetic offerings.

I'm sure most people would rather see a critique of the science behind Ion Propulsion than a rant about the content of this youtube channel.

The critique of the propulsion scheme was laid out in the video. It was just framed in a way that tried to dodge the reality that this system cannot scale. For example, rather than presenting the thrust densities in a table for easy comparison, they were presented serially, so that the viewer might miss their relative scales. Quickly: What is the ratio of the thrust density of a jet engine to the thrust density of this ion propulsion scheme?[1]

Near the end, during the segue to the sponsorship at the end, he says, "This technology is in its infancy," alluding to his opening comparison to the Wright brothers. This is ridiculous. Not all weak or underpowered novel things are "in their infancy," awaiting further development into enabling technologies for our Glorious Future. This one, for example, has all the problems of battery energy density plus the problems of dragging, for example, tens of kilometers of wires through the atmosphere at passenger-jet speeds.

But, as I said at the beginning, that critique is contained in the video, just framed positively and obscured by weasel tactics. [2]

[1] Roughly 3300 to 1. An airliner using this scheme would need engines with a frontal area equal to 6600 high-bypass turbofan engines.

[2] Brought to you by Carl's Jr.

I just watched this, and it was abundantly clear that the presenter believes there is a scaling issue ("scaling these propulsion methods is not easy" at 6:37). They literally say this, and then present the 10,000N/m^2 vs 3N/m^2 numbers for the jet engine versus this engine. There is then a minute or so explaining why this is a problem.

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