6 ms·

Ion Engines Could Work on Earth Too, to Make Silent, Solid-State Aircraft

18 points by sohkamyung 5y ago

UltraViolence 5y ago
These are essentially winged versions of "lifters" which were first produced in the 1960's. Their power per watt ratio is very low, so they may not be very useful. Also, they need the surrounding air to generate ions and therefore cannot reach high altitudes where the atmosphere is very thin.
kragen 5y ago
It's a little confusing that the headline describes electroaerodynamic thrusters as "ion engines". I was going to protest that it's wrong, but in a sense the principle is pretty much the same: you have a source of ions and a large potential difference that accelerates the ions, producing thrust. But the differences between EAD and ion-engine rockets are as important as the similarities. In an EAD thruster, or "lifter", the ions are produced from the surrounding atmosphere by a corona discharge around a wire, while in an ion-engine rocket they're sourced from an onboard propellant reservoir. In an EAD thruster, the ions are constantly colliding with air molecules as they fall down the electric potential gradient, so when they reach the cathode they're not going very fast, and a lot of them get deionized at that point. The kinetic energy the ions gained in the process has been almost entirely transferred to the much larger mass of neutral air molecules, which are what produces the jet out the back of the aircraft and gives you thrust. On the other hand, in an ion-engine rocket, the ions are your only reaction mass and you want as few of them as possible to actually hit the cathode. They are ejected with essentially all of the kinetic energy they gained in falling down that potential gradient. An interesting thing is that in both cases the conversion of electrical energy into the kinetic energy of the reaction mass is nearly 100% efficient, so the kinetic energy comes out the same in both cases. But the ratio of reaction mass to energy is vastly different, and consequently so is the reaction mass velocity.
jimmyreilly 5y ago
Brings back memories of building 'lifters' powered with old CRT monitors as a kid.
- muttled 5y ago
  With aluminum foil, toothpicks, and a total disregard for safety!
  - kragen 5y ago
    Normally yes, but a normal-sized lifter doesn't require dangerous amounts of current. Normally they lift about a gram per watt, weigh about 5 grams, and run at about 20kV, so they only require about 250 microamps. So at least in theory you could put, say, 20 megohms of resistance in series with your power supply, to limit the current to below a milliamp. You can buy that off the shelf; Digi-Key has a 10-megohm 10kV resistor in stock for 67¢ in quantity 10, (https://www.digikey.com/en/products/detail/vishay-beyschlag-draloric-bc-components/VR68000001005JAC00/1995209 https://www.digikey.com/en/products/detail/vishay-beyschlag-...) but it's kind of a specialty product, so if you're getting your HV power supply parts from broken TVs you may not have one. Worse, while measuring the resistance of such a resistor is pretty straightforward in the modern digital multimeter age, measuring its safe breakdown voltage requires destructively testing dozens of them with some kind of characterization of the manufacturing process (so you know that the one your life depends on isn't from a different factory from the ones you've tested). And enough capacitance in parallel with a high-voltage load will make all this moot anyway.
ericbarrett 5y ago
Would they really be silent? Ion thrusters are very efficient because they accelerate particles to high velocities (typically 30 km/s exhaust velocity, up to 80). They're low-thrust because they do this to a very tiny quantity of them—nanograms per second. This is fine once you're already in orbit and you can plan your maneuvers and a 3-hour burn isn't a big deal. Compare this to a typical kerosene rocket exhaust, ~3 km/s velocity but much more of it, over 2,500 kg/sec of fuel flow in the extreme cases (e.g. Apollo F-1), and maybe between 0.5 and 10 kg/sec for a passenger jet engine in atmosphere (very efficient because it doesn't have to carry its own oxygen). So it seems to me if you've got enough thrust to fly a plane, even with a very gentle impulse, something that's almost a glider, it's still going to make some noise. Probably very high frequency, maybe high enough that it won't be audible. If you're hauling people or cargo, then I think it would be as loud as any jet.
- foxyv 5y ago
  Especially considering that nowadays, most of the noise from aircraft is the air running over the body, wings and landing gear. Engines are stupid quiet compared to a building moving through the air.
  - kragen 5y ago
    I don't think that's true, but at any rate it's conditional on the aircraft moving fast, which is not an option with electroaerodynamic engines.
- Schroedingersat 5y ago
  Also consider that they're mass efficient, not energy efficient. You want low exhaust velocity for energy efficiency. The opposite of an ion drive.
Khelavaster 5y ago
Check out US Navy patents by Salvatore Pais. Such engines work, powered by bleeding-edge power sources.
Schroedingersat 5y ago
So directly producing ozone and NOx instead at vastly lower efficiency than a propellor?

18 points by sohkamyung 5y ago

These are essentially winged versions of "lifters" which were first produced in the 1960's. Their power per watt ratio is very low, so they may not be very useful. Also, they need the surrounding air to generate ions and therefore cannot reach high altitudes where the atmosphere is very thin.

kragen 5y ago

It's a little confusing that the headline describes electroaerodynamic thrusters as "ion engines". I was going to protest that it's wrong, but in a sense the principle is pretty much the same: you have a source of ions and a large potential difference that accelerates the ions, producing thrust. But the differences between EAD and ion-engine rockets are as important as the similarities. In an EAD thruster, or "lifter", the ions are produced from the surrounding atmosphere by a corona discharge around a wire, while in an ion-engine rocket they're sourced from an onboard propellant reservoir. In an EAD thruster, the ions are constantly colliding with air molecules as they fall down the electric potential gradient, so when they reach the cathode they're not going very fast, and a lot of them get deionized at that point. The kinetic energy the ions gained in the process has been almost entirely transferred to the much larger mass of neutral air molecules, which are what produces the jet out the back of the aircraft and gives you thrust. On the other hand, in an ion-engine rocket, the ions are your only reaction mass and you want as few of them as possible to actually hit the cathode. They are ejected with essentially all of the kinetic energy they gained in falling down that potential gradient. An interesting thing is that in both cases the conversion of electrical energy into the kinetic energy of the reaction mass is nearly 100% efficient, so the kinetic energy comes out the same in both cases. But the ratio of reaction mass to energy is vastly different, and consequently so is the reaction mass velocity.

jimmyreilly 5y ago

Brings back memories of building 'lifters' powered with old CRT monitors as a kid.

muttled 5y ago
With aluminum foil, toothpicks, and a total disregard for safety!
- kragen 5y ago
  Normally yes, but a normal-sized lifter doesn't require dangerous amounts of current. Normally they lift about a gram per watt, weigh about 5 grams, and run at about 20kV, so they only require about 250 microamps. So at least in theory you could put, say, 20 megohms of resistance in series with your power supply, to limit the current to below a milliamp. You can buy that off the shelf; Digi-Key has a 10-megohm 10kV resistor in stock for 67¢ in quantity 10, (https://www.digikey.com/en/products/detail/vishay-beyschlag-draloric-bc-components/VR68000001005JAC00/1995209 https://www.digikey.com/en/products/detail/vishay-beyschlag-...) but it's kind of a specialty product, so if you're getting your HV power supply parts from broken TVs you may not have one. Worse, while measuring the resistance of such a resistor is pretty straightforward in the modern digital multimeter age, measuring its safe breakdown voltage requires destructively testing dozens of them with some kind of characterization of the manufacturing process (so you know that the one your life depends on isn't from a different factory from the ones you've tested). And enough capacitance in parallel with a high-voltage load will make all this moot anyway.

ericbarrett 5y ago

Would they really be silent? Ion thrusters are very efficient because they accelerate particles to high velocities (typically 30 km/s exhaust velocity, up to 80). They're low-thrust because they do this to a very tiny quantity of them—nanograms per second. This is fine once you're already in orbit and you can plan your maneuvers and a 3-hour burn isn't a big deal. Compare this to a typical kerosene rocket exhaust, ~3 km/s velocity but much more of it, over 2,500 kg/sec of fuel flow in the extreme cases (e.g. Apollo F-1), and maybe between 0.5 and 10 kg/sec for a passenger jet engine in atmosphere (very efficient because it doesn't have to carry its own oxygen). So it seems to me if you've got enough thrust to fly a plane, even with a very gentle impulse, something that's almost a glider, it's still going to make some noise. Probably very high frequency, maybe high enough that it won't be audible. If you're hauling people or cargo, then I think it would be as loud as any jet.

foxyv 5y ago
Especially considering that nowadays, most of the noise from aircraft is the air running over the body, wings and landing gear. Engines are stupid quiet compared to a building moving through the air.
- kragen 5y ago
  I don't think that's true, but at any rate it's conditional on the aircraft moving fast, which is not an option with electroaerodynamic engines.
Schroedingersat 5y ago
Also consider that they're mass efficient, not energy efficient. You want low exhaust velocity for energy efficiency. The opposite of an ion drive.

Khelavaster 5y ago

Check out US Navy patents by Salvatore Pais. Such engines work, powered by bleeding-edge power sources.

Schroedingersat 5y ago

So directly producing ozone and NOx instead at vastly lower efficiency than a propellor?