So far their best result is 0.886 kW/kg (0.539 hp/lb), comparable to a helicopter, by using a pulsed DC power supply at 70 Hz:
So a helicopter with that could lift 1.13 kg/kW (1.86 lb/hp).
A plane with a 10:1 lift to drag ratio would fly with 0.0886 kW/Kg (0.0539 hp/lb). It could lift 11.3 kg/kW (18.6 lb/hp).
A 200 kg (440 lb) helicopter, including human passenger, would take 177 kW (237 hp).
The same mass airplane would take 17.7 kW (23.7 hp).
Of course the pulsing would add a buzz which may not be desirable. It looks like the pulsed DC uses 17.72 RMS W vs 69.58 DC W, so is about 3.927 times more efficient than DC. Maybe a plane could have both silent and high efficiency modes for takeoff and cruising.
I have no idea how these numbers compare to the ones in the article, but they should be within the same magnitude. Please someone double check my math :-)
I hate the fact that phenomena worthy of proper scientific examination are often also massive nut-job magnets.
Seems to be possible in theory, but appears to require pretty extreme energies
Problem was, that was all the power you could get, and even then it wasn't enough to keep the cell afloat. Back then, we were using 10%-ish efficiency cells. Where I work now, we just toss 21+% monocrystalline cells which are 1/8th the mass of the originals around and don't care if they break, because as long as you can still put a bus ribbon on them all the way, they will produce full rated power, even if it looks like they were nailed with a sawed-off shotgun on the EL image.
“You want to play with 40,000 volts on an aircraft? That technology didn’t exist. Steve [Barrett] found a clever way to get that efficient conversion.”
So, the technology existed (when you do PWM with DC it mostly acts like AC so you can run it through a basic transformer) but they figured out the circuitry to make it efficient (nevermind solar efficiency now is enough to do what we want today without the basic transformer tech from almost 20 years ago.)
Still neat, but this really hints of amateurs that never checked some basic math which hinted at this possibility, and existed back in the 70s, which was before I was even born.
EDIT: added the second half after re-reading, edited again to make the PWM DC statement more clear.
(Edited for tone)
In general, the lift to drag ratio (L/D) of an airfoil is proportional to the square root of the aspect ratio (AR). For airplane wings, this hits a limit of about 60 simply due to the difficulty of reinforcing a long wing while keeping weight down.
A helicopter rotor spins, so has different requirements (like greater strength near the hub) so can have a higher aspect ratio. Unfortunately the inner third of the rotor turns too slowly to contribute much lift, and the tips shed large toroidal vortices that diminish efficiency. The tips also encounter turbulence near the speed of sound which diminishes efficiency. So rotors (even on wind turbines) can't really get higher than 60% efficiency:
There has probably been more research in helicopter rotors over the years than increasing the L/D ratio of light aircraft, which explains how they reduced some of the discrepancy between the two.
When I was doing research for the Sikorsky human powered helicopter competition (unfortunately someone already won it haha), I did a lot of napkin calculations for this sort of thing:
Success came down to having the fewest, longest, thinnest, lightest rotor blades possible:
There are many ways of increasing lift using winglets, vortex generators, EHD devices, etc (a few other keywords to look for are boundary layer and Reynolds number):
Personally I don't think we've even scratched the surface of what's possible in L/D ratios. With modern materials science and computer simulation at our disposal, I'd like to see someone break 100. Probably by using an array of airfoils and some EHD effects. I don't think anyone is seriously looking at it though other than maybe Bigelow Aerospace (JP Aerospace) and their defunct airships-to-orbit project:
I think this idea has merit and is one of the only ones that can compete on price with a space elevator. But it's not sexy enough, and people are still stuck on the idea of using helium instead of hydrogen, which sabotages it from ever succeeding (due to the limited supply of helium).
I would love to work on revolutionary ideas like this, but like most of you, I'm building SPA CRUD apps on the web to pay the mortgage. Sorry there's a lot of info here, but hey it's black friday on HN. What else are we gonna do.
Looks like they developed advancements with lightweight high-voltage converters and performance of the thrusters.
Airships (dirigibles/blimps), and to a lesser extent, sea and land vehicles.
Surprisingly, not by much!
To the first approximation an optimized plane will use 50% of its power during cruise generating lift ("not crashing into the ground"), and 50% of its power overcoming drag. The tie is broken because planes expend extra more energy climbing than they save descending, and that's also part of "not crashing into the ground." :)
Not disputing you, but do you have a quick argument for this? My understanding is that passenger planes fly at high altitudes because at lower altitudes (higher pressures) they would expend most of their energy pushing air out of the way.
The way I think about it is that commercial flights spend the vast majority of the time at "cruising speed", where the engines are most efficient on a power/fuel basis. The flight already dissipates 100% of engine power output into pushing air out of the way, so what altitude does is determine what airspeed that happens at. At lower altitudes, there's more air molecules displaced per foot of travel, so the airspeed is lower.
So airplanes fly up at 30k feet because it's faster at the same power output, which also happens to be more fuel efficient, but it's not like the plane runs the engines any harder if they cruise at a lower altitude.
These ion thrusters have worse thrust/watt than an electric propellor drive, and far worse than the jet engines they use.
So there's not really any reason to use ion thrusters at cruising altitude, unless the relative silence is worth paying a lot more per-ticket.
From the Ars article (for others who were curious about this):
> Measurements showed the thrusters collectively generated five newtons for each kilowatt of power, which is actually similar to the output of jet engines. But because of many inefficiencies in the system, the overall efficiency was only about 2.5 percent—well below that of conventional aircraft.
Even then, I'd imagine that a significant portion of the noise in an airliner is wind noise rather than engine noise. Your plane is only going to get "less noisy", not "silent". Good noise canceling earphones are a far better solution (I have some specifically for plane flights, they're awesome!)
Because you would need to restart the engines to land, and that is when they are at a higher risk of failure. You could maybe throttle them right back but keep them ticking over.
Personally, I'm a little surprised we don't have them in the Bay Area. With our traffic and (mostly) year round nice weather, and great solar energy potential it seems like it could be a win.
But then again I don't know much about the technology or it's limitations.
Missiles jumped to mind. That's their whole purpose.
The point was that this current design won’t be enough energy to keep a heavy vehicle aloft, but it could be enough to propel something that can passively stay airborne.
"Excellent... when do they hit?"
"According to our calculations... ohhh about 6 weeks from now"
I was thinking how Musk could do that. Launch some tungstan rods into a highly eliptical orbit, small thruster + control pack on them to adjust their orbit when required. When it's out at say 300,000k+ fire the engine for a few seconds, adjusting the orbit so it will crash into the chosen target a few days from now. The high apogee means not a lot of power to change orbit to collision, and almost impossible to detect. It would likely appear to be an asteroid hit.
"Air ionisation can cause the following: forming of ozone molecules
Ozone is produced naturally in the stratosphere when highly energetic solar radiation strikes molecules of oxygen (O2), and cause the two oxygen atoms to split apart in a process called photolysis. If a freed atom collides with another O2, it joins up, forming ozone(O3). Most of the ozone in the stratosphere is formed over the equatorial belt, where the level of solar radiation is greatest. The circulation in the atmosphere then transports it towards the pole . So, the amount of stratospheric ozone above a location on the Earth varies naturally with latitude, season, and from day-to-day."
Per https://en.wikipedia.org/wiki/Tropospheric_ozone you see that ozone in the lower atmosphere is a pollutant.
We want lots of ozone up in the stratosphere. Blocking UV, well away from us.
Maybe combine the whole thing with project loon like internet relays. With a source of thrust like this it would be much easier to keep them where you want them.
 https://en.wikipedia.org/wiki/Ozone_layer , in particular: https://upload.wikimedia.org/wikipedia/commons/thumb/c/cb/Oz...
I suppose it would make more sense to pair the battery and voltage conversion tech with a high altitude balloon covered in thin film PV, so there's less competition between 'ozone generation' and the 'lift generation'.
The market dried up because they were borderline bullshit, and produced ozone, sometimes far in excess of their claims. They did make air move quietly tho.
Ah on second thought
My lifter, probably like most, eventually caught fire.
Efficiency seems fairly poor , and from my experience, ozone is absolutely a problem.
I found this company in the ad section of Boy's Life in the mid 90's, this power supply is adjustable 30kV-75kV
They have lots of hard to find high voltage stuff.
Hobbyist machinists, makers etc will spend several times that on a single machine.
The flyback transformers from a TV (or neon sign) are fairly low power because they don't need all that much. The goal is high voltage for both. A microwave transformer is meant to pump a thousand of Watts into your high specific heat food and will very easily kill you. They should not be used for any sort of hobby work.
Back in high school I spent a lot of time on sites like scitoys.com, rimstar.org, Bill Beaty's site, etc. I really miss those days. Now similar content is all on YouTube with clickbaity thumbnails that start with "WHATS UP YOU GUYS".
Does that mean it produces nitrogen oxide as exhaust? If yes, how long does that live?
If such planes were to be scaled up, that could be a potential hazard to be aware of.
With a modified design, is it possible to accelerate the ionized air so fast that all of it vents out the exhaust (e.g. using magnets)? Would that result in higher efficiency / higher thrust? Are there already atmosphere-breathing engines that do this and what are they called?
Generally this kind of engine is called Magnetohydrodynamic drive. I'm not sure about atmospheric engines, but according to wiki there are prototypes that uses water as working fluid.
The idea of a totally silent tiny drone that can get real close is scary to think of.
Reading this reminded me of the two Wright brothers, who had similar issues, and similar people around them, not believing it would work.
Kudos. It sounds pretty amazing to me.
Different approach to flying but it’s interesting how some of the described reactions are similar about the silence and no moving parts.
I remember reading this article when I was a kid in a stack of PMs in the early 70s.
Yet all the pictures are renderings, artist's impressions.
So, do they have a working model or not? There are no links to any supporting documents; Scientific American used to be better than this, very disappointing.
This from 2011 Does anyone know if something like this exists at large scales today?
So is there any other advantage to ion propulsion besides quiet operation?
(Also, the fact that it can be outperformed by a sparrow is only relevant if we can build a reliable, efficient artificial sparrow, which AFAIK we absolutely can't.)
mv/mv^2 ~ 1/v
You could lower ion energy by lowering the voltage, but then the thrust-to-weight is going to be prohibitively low (and at one point you won't be able to ionize air anymore?).
High efficiency flight means either wings or slow moving propellers (and aircraft itself preferably). You'd need to look no further than a glider to fullfil the potential claimed here. Overall flapping wings are probably superior though, since they allow vertical takeoff and high manueverability; but they're much harder to develop and maintain.
Since ions already exist in water maybe you can skip the ionizing step.
> “In Star Trek you have shuttlecraft gliding silently past,” he says. “I thought, ‘We should have aircraft like that.’”
It's a good sign when inspiration comes from Star Trek.
Edit: Also, reminds me of this: https://xkcd.com/2072/
Not every movie and TV show.
You are right though that that it wouldn't be the same.
If you don't have that, you're a little more limited to relying on visual information for everything
Only works for well-trodden paths where everyone is doing basically the same thing. Does this apply to self driving cars?
Mind this is all in reference to DC current. AC is another beast.
They were really popular with the UFO/Free energy crackpot crowds back in the late 90s and early 2000s.
It does carry it's own power supply and battery:
"Finally Barrett used a computer model to get the most out of every design element in the aircraft, from the thruster and electrical system designs to the wires that ran through the plane. “The power converter, the battery, the caps and fuselage—everything was optimized,” Barrett says. “The simulations failed all the time. We had to make hundreds of changes.” In the end, they had the triumphant Version 2."
Here's the researchers earlier publication (2015) on the physics behind it:
Edit: found some more material. No video of the actual plane yet. But the professor has a website here.
That said, ionization does have it's place in aircraft in terms of controlling attachment or detachment of turbulent airflow over wings. It can significantly improve fuel consumption by reducing drag.
But it is not a viable propulsion source. At least not on Earth for things larger than a meter or so.
Why would you say something like this? You sound arrogant and stupid.
You are talking about an article which says "he built the thing and flew it". And you deny that based on your balsa wood experiments?
Someone else has done you the favor of posting a video of it flying. Perhaps you'll believe that?
>But it is not a viable propulsion source. At least not on Earth for things larger than a meter or so.
It's 5m wide
see the top of page 534, figure b. You are correct that the initial forward momentum is from the launch rail, but the graph clearly shows that the ion engine provides thrust.
Is the title of the HN submission misleading? Yes.
Did the plane achieve flight with the ion engine alone? No.
Was the plane able to maintain and gain altitude because of the ion engine? Yes.
A step forward in the right direction but not as much of a breakthrough as the submission title would have you think.
>As far as I can tell it doesn't exist outside of the person's mind.
Based brah. I'm being serious when I say that I think HN needs more of this type of comment. They seem to love rigidity in comments, but not any bluntness or banter thrown in there.
Sucking almost 3A out of the battery, it's not going to fly very long, but that's also a fairly inefficient power converter design. There is lots of room for improvement.