HN Theater @HNTheaterMonth

Works for fixed wing planes!

https://youtu.be/IorDYGI1uqc

⬐ dr_dshiv

But not pushed with electromagnets, yeah?

⬐ TaylorAlexander

oh right! that plane is electrostatic rather than magneto fluid dynamic. good point I totally spaced on that one. MHD stuff is super cool tho!

I hope air-breathing ionic propulsion takes off because even if it turns out to not be great for satellites it'd be wonderful for (small) aircraft. Aircraft are very loud thanks to their engine and propellers/jets. Recent experiments showed its possible to fly with no moving parts using ionic flow: https://www.youtube.com/watch?v=IorDYGI1uqc (9min) I for one would love to fly (on) such a quiet plane, like a glider. Compare muscle car rev to electric car silence.

It also reminds me of the Bussard ramjet, which I thought is considered ineffective due to creating more drag than thrust. Maybe the environment makes a difference?

I wonder if it'd be more effective to use antipodal ground transmitters to beam power up to the satellite, rather than the satellite using solar panels? Less concern about sCaRy high-power microwaves when aiming them from rather than at Earth, though it could still interfere with aircraft and unintended satellites in the cone of effect.

⬐ mlindner

The noise from engines isn't from their combustion or their moving parts. It's from the massive air flow they cause. Ionic engines aren't going to be much quieter for aircraft, assuming they're even possible to move that much air.

Also air breathing ionic propulsion kind of depends on the external presence of ions, which requires space conditions, not normal atmospheric conditions.

⬐ None

None

⬐ lazide

Eh, kinda. While most noise from a jet engine at the ground comes from the shear forces from the fast moving compressed exhaust stream interacting with slow moving surrounding air, the engine itself isn’t quiet.

Even in situations where you don’t get that exhaust stream, (such as helicopter turbines spinning up with the clutch out), they’re very loud. Hearing protection required loud.

And very little of a rotary planes noise is coming from airflow or from the prop directly, most of it is coming from the engine itself. At best at least half.

Presumably an ionic drive couldn’t create the pressure differential levels of a jet engine, or probably even a prop, so they’d have relative large, relatively slow moving masses of air to work. So noise should be a lot lower from that, and also from lack of a internal combustion or turbine engine screaming it’s hardest.

This same principle has been incorporated in full blown air planes. Admittedly very short operational range at the moment https://www.youtube.com/watch?v=IorDYGI1uqc

⬐ dharmab

From reading their research, it seems the range was artificially limited to the size of the gym because the team didn't have access to a larger test area.

⬐ credit_guy

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...

⬐ ams6110

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.

⬐ zackmorris

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

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

⬐ mmirate3

tl;dw: the presence of air, solves the propellant-related issues (i.e. this is an electroaerodynamic drive, not a reaction-thruster), allowing this engine to provide, novelly, several whole Newtons of thrust; but scaling it to a practical size increases the thrust requirements by (overall) a high-degree polynomial, and will therefore likely require further scientific effort.

⬐ majui

Ion propulsion: a future way for tiny drones to spy on us silently.

⬐ village-idiot

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

⬐ theothermkn

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.

⬐ imustbeevil

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.

⬐ theothermkn

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.

⬐ frankmcsherry

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.

⬐ KineticLensman

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

⬐ superkuh

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.

⬐ WrtCdEvrydy

> 6.25 N/kW

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

⬐ Boxxed

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.

⬐ rhacker

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?

⬐ superkuh

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.

⬐ DavidSJ

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