6 ms·

What would it take to power an airliner? Wireless power transmission would be ideal for a lot of applications, transportation (electric cars, planes, maybe tra

What would it take to power an airliner? Wireless power transmission would be ideal for a lot of applications, transportation (electric cars, planes, maybe trains, UAVs, boats) chief among them. You could shave a lot of weight out of an electric plane by reducing its battery capacity to an emergency supply. This would also greatly reduce the carbon impact of flight transportation, while making a case for bootstraping a beamed power constellation and ecosystem. I guess that's something Nikola Tesla first envisioned :) Unfortunately, from what I know, microwaves are not really harmless, unless diffused over a large area, and you then need a large collector. An airliner could do, if big enough. I don't know either if a beam can be steered fast enough, and what would the economics behind be.

Someone 6y ago
http://large.stanford.edu/courses/2013/ph240/eller1/ http://large.stanford.edu/courses/2013/ph240/eller1/: “The power required to keep a Boeing 737-300 flying at a constant altitude and speed is 7.2 × 10⁶ watts.” So, ballpark 7 MegaWatts, more during ascent, and add a bit if passengers want to watch movies, eat hot meals, drink soft drinks, etc. On the plus side, if the airplane doesn’t have to carry fuel, carrying capacity could go up (with some redesign to make the plane strong enough to land fully loaded), so that 737 might be equivalent to a 747. That 737-300 has about 125m² of wing area, and, guessing, about the same are for the body, so that would be 7MW/250m² = 28kW/m². The sun delivers about 1,400W/m², so that’s 20 times what the suns delivers on a cloudless day. Now, most of the time, the ground station (or solar space array) beaming the energy wouldn’t be directly below/above the plane, so the required power/m² could go up a lot ⇒ I would make sure that any windows in the plane wouldn’t let the microwaves through. Doable? Possibly, but on ground level, I guess it would be wise to use a lot more area for sending that amount of power up, to prevent killing birds.
- deleted 6y ago
  [deleted]
- johndough 6y ago
  I don't know if you could kill birds with this, considering that the beam would move at something like 250 m/s during regular flight. Is microwave radiation more deadly than solar radiation? Might be a problem at the base station, but there should be multiple of those for greater fault tolerance anyway.
  - dghughes 6y ago
    I'm pretty sure the beam would be traveling at 299,704,644.54 m/s. It is electromagnetic energy.
    - deleted 6y ago
      [deleted]
    - krisoft 6y ago
      The point where the beam is aimed would be moving with 250m/s. (or about so) Therefore the hypothetical bird which crosses the beam would only get the energy for a fraction of a second. I don't know if this reasoning is correct or not, but definitely has nothing to do with the speed of light in air. I'm not even sure why you are bringing it up.
    - CrazyStat 6y ago
      I think he's referring to the motion of the beam to track the target.
  - jws 6y ago
    Sun light is about 1kW/square meter. A 737 has a wing area of 125 square meters. To deliver 7.5MW to those wings will need 60kW/square meter. That's a far greater energy density. As for "time in beam" of a moving beam. Presumably one end of the beam is fixed, and depending on the target's velocity the beam might not be moving much at all (oncoming plane).
  - Someone 6y ago
    The beam’s horizontal motion speed goes down linearly with height if the beam is sent from a fixed location. So, picking 30,000 feet for flight height and 250m/s for the plane’s speed, at 900 feet the beam’s speed would be 7½ m/s. That’s quite doable for birds. More importantly, if the beam isn’t sent from directly below the plane, and the plane flies more or less directly towards or away from the beam’s source, the speed at which it moves horizontally goes down considerably (1/cos(α), where α is the deviation from the vertical, I think), and its width when flying through it in the direction of the beam’s source at constant height will go up considerably. The beam’s width, and, with it, intensity, will likely be larger on the ground, but my gut feeling is this won’t be enough to correct for both these factors in all cases (corrections welcome)
- MayeulC 6y ago
  Thanks for the figures. I'd guess that most of that power is used to combat drag, which can be lowered by going slower. The rest is probably used to combat gravity, especially during ascent, which should be improved by lowering the amount of fuel. A small battery, and/or a ground station at the airport could provide a bit of extra power during ascent, and the battery recharged during flight. I guess the extra power shouldn't amount to a lot more than 10kW... Depending on the wavelength, it should be fairly easy to have the plane act as a Faraday cage to shield its passengers. I guess the geometry could be slightly tweaked as well to make a larger surface area, possibly using trailing metallic wires to improve the energy collection area at a minimal cost (I get that cylindrical wires are the worst aerodynamic shape, but it should be less of a problem behind the wing). If the wavelength is low enough, a coarse mesh could collect power quite efficiently, but you'd have to worry a lot more about radio interference.
  - loeg 6y ago
    Drag and lift are related. Wings work by literally displacing lots of air towards the ground. If you go slower, you need bigger wings (also no one really wants longer, slower flights in cramped airplane cabins).
    - krasin 6y ago
      Unless it's cargo. Cheaper than "normal air" / faster than sea shipping is a reasonable niche.
      - loeg 6y ago
        I don't know if it's a big enough niche. There are quite a lot of costs to air cargo aside from marginal fuel efficiency and somehow developing novel cargo-specific aircraft has to translate into both increased profits for Boeing/Airbus and decreased costs to shippers. Keeping in mind that these slower craft would be unsuitable for some of the most profitable uses of air freight today. I'm not sure it makes sense.
        6y ago
- inamberclad 6y ago
  7MW in cruise, but keep in mind the power margins that are required for a transport category aircraft.
taf2 6y ago
I’d imagine a safety feature on the airplane to be a battery or even capacitors to help smooth out any drops in transmission. At least the batteries could be small
pjc50 6y ago
Beam steering can be done at pretty high speed, essentially limited by the weight of the mirror. And the further the mirror is the faster the effective linear speed of the 'spot'. But the safety question is more serious. The beam is dangerous to birds, unshielded aircraft, and persons on the ground. I don't think it's great giving the US military even more power to start a fire anywhere on earth with zero warning.
- Analemma_ 6y ago
  Couldn't phased arrays ensure that everywhere (within region) but the target gets only a small amount of power?
  - madengr 6y ago
    In theory, yes, but practice no. The antenna required to collimate the beam from LEO, down to a person sized spot on earth, would be massive. Single antenna apertures are limited to about 90 dB of gain, and I doubt that is near enough, but I’d have to run some calculations.
- oblio 6y ago
  > I don't think it's great giving the US military even more power to start a fire anywhere on earth with zero warning. They already have hydrogen bombs :-)))
  - iso947 6y ago
    Fairly hard to deploy that quietly.
    - oblio 6y ago
      True, but they also have drones and a million other ways they can kill people relatively unnoticed. And if the US Gov. really wants to, there are always Black Ops. This is a bit like complaining about a knife in a gun shop :-)
- 6y ago
joshvm 6y ago
It's not that microwaves are intrinsically harmful, it's the intensity of the beam. For example microwave ovens operate around 2.4Ghz, same as Bluetooth/WiFi. I'm not sure what power delivery operates at. If you get hit by a megawatt beam, you're going to get burned regardless of the wavelength (unless either it's short enough to pass through you, or somehow you reflect 100% of it). As another comment points out, you can beam steer quite fast. You only care about angular rate, and an airliner at cruise altitude moves fairly slowly (eg you can follow it with your eyes easily).
sandworm101 6y ago
This has nothing to do with aircraft. This is about beaming power to low-orbit satellites. The problem with low-orbit radar satellites (the spy satellites tracking ships) is that they need lots of power. In the past this was done with small nuclear reactors but today that is unacceptable and virtually all satellites use solar panels. But sarge solar panels means higher drag and shorter lifetimes in low orbit. Being able to 'beam' power from a higher orbit means one could power more aerodynamic low orbit satellites.
- MayeulC 6y ago
  Ah, my bad. That said, beamed power could be applied to anything, and the post I wrote above is one of the better use cases, in my opinion.
- goodcanadian 6y ago
  This has nothing to do with aircraft. Actually, yes, the article explicitly mentions the possibility of powering unmanned aerial vehicles.
  - sandworm101 6y ago
    >> the article explicitly mentions Ya. The public report on the super-secret space plane touts that it is studying far-off green energy solutions when those same technologies have much more immediate military effects. It's like the USAF saying that it is studying lasers in order to build better CD players. Everyone takes such statements with a grain of salt. Nobody thinks that we are getting the full story behind these experiments and we chuckle a bit at the poor junior officer instructed to "be creative" with descriptions in public statements.
    - goodcanadian 6y ago
      I didn't say anything about green energy, and while the grandparent comment did, I don't think it was implied that it was the motivation of the experiment. Powering military drones for indefinite dwell time is a very plausible use case among many listed in the article.

Someone 6y ago

http://large.stanford.edu/courses/2013/ph240/eller1/ http://large.stanford.edu/courses/2013/ph240/eller1/: “The power required to keep a Boeing 737-300 flying at a constant altitude and speed is 7.2 × 10⁶ watts.” So, ballpark 7 MegaWatts, more during ascent, and add a bit if passengers want to watch movies, eat hot meals, drink soft drinks, etc. On the plus side, if the airplane doesn’t have to carry fuel, carrying capacity could go up (with some redesign to make the plane strong enough to land fully loaded), so that 737 might be equivalent to a 747. That 737-300 has about 125m² of wing area, and, guessing, about the same are for the body, so that would be 7MW/250m² = 28kW/m². The sun delivers about 1,400W/m², so that’s 20 times what the suns delivers on a cloudless day. Now, most of the time, the ground station (or solar space array) beaming the energy wouldn’t be directly below/above the plane, so the required power/m² could go up a lot ⇒ I would make sure that any windows in the plane wouldn’t let the microwaves through. Doable? Possibly, but on ground level, I guess it would be wise to use a lot more area for sending that amount of power up, to prevent killing birds.

deleted 6y ago
[deleted]
johndough 6y ago
I don't know if you could kill birds with this, considering that the beam would move at something like 250 m/s during regular flight. Is microwave radiation more deadly than solar radiation? Might be a problem at the base station, but there should be multiple of those for greater fault tolerance anyway.
- dghughes 6y ago
  I'm pretty sure the beam would be traveling at 299,704,644.54 m/s. It is electromagnetic energy.
  - deleted 6y ago
    [deleted]
  - krisoft 6y ago
    The point where the beam is aimed would be moving with 250m/s. (or about so) Therefore the hypothetical bird which crosses the beam would only get the energy for a fraction of a second. I don't know if this reasoning is correct or not, but definitely has nothing to do with the speed of light in air. I'm not even sure why you are bringing it up.
  - CrazyStat 6y ago
    I think he's referring to the motion of the beam to track the target.
- jws 6y ago
  Sun light is about 1kW/square meter. A 737 has a wing area of 125 square meters. To deliver 7.5MW to those wings will need 60kW/square meter. That's a far greater energy density. As for "time in beam" of a moving beam. Presumably one end of the beam is fixed, and depending on the target's velocity the beam might not be moving much at all (oncoming plane).
- Someone 6y ago
  The beam’s horizontal motion speed goes down linearly with height if the beam is sent from a fixed location. So, picking 30,000 feet for flight height and 250m/s for the plane’s speed, at 900 feet the beam’s speed would be 7½ m/s. That’s quite doable for birds. More importantly, if the beam isn’t sent from directly below the plane, and the plane flies more or less directly towards or away from the beam’s source, the speed at which it moves horizontally goes down considerably (1/cos(α), where α is the deviation from the vertical, I think), and its width when flying through it in the direction of the beam’s source at constant height will go up considerably. The beam’s width, and, with it, intensity, will likely be larger on the ground, but my gut feeling is this won’t be enough to correct for both these factors in all cases (corrections welcome)
MayeulC 6y ago
Thanks for the figures. I'd guess that most of that power is used to combat drag, which can be lowered by going slower. The rest is probably used to combat gravity, especially during ascent, which should be improved by lowering the amount of fuel. A small battery, and/or a ground station at the airport could provide a bit of extra power during ascent, and the battery recharged during flight. I guess the extra power shouldn't amount to a lot more than 10kW... Depending on the wavelength, it should be fairly easy to have the plane act as a Faraday cage to shield its passengers. I guess the geometry could be slightly tweaked as well to make a larger surface area, possibly using trailing metallic wires to improve the energy collection area at a minimal cost (I get that cylindrical wires are the worst aerodynamic shape, but it should be less of a problem behind the wing). If the wavelength is low enough, a coarse mesh could collect power quite efficiently, but you'd have to worry a lot more about radio interference.
- loeg 6y ago
  Drag and lift are related. Wings work by literally displacing lots of air towards the ground. If you go slower, you need bigger wings (also no one really wants longer, slower flights in cramped airplane cabins).
  - krasin 6y ago
    Unless it's cargo. Cheaper than "normal air" / faster than sea shipping is a reasonable niche.
    - loeg 6y ago
      I don't know if it's a big enough niche. There are quite a lot of costs to air cargo aside from marginal fuel efficiency and somehow developing novel cargo-specific aircraft has to translate into both increased profits for Boeing/Airbus and decreased costs to shippers. Keeping in mind that these slower craft would be unsuitable for some of the most profitable uses of air freight today. I'm not sure it makes sense.
      - 6y ago
inamberclad 6y ago
7MW in cruise, but keep in mind the power margins that are required for a transport category aircraft.

taf2 6y ago

I’d imagine a safety feature on the airplane to be a battery or even capacitors to help smooth out any drops in transmission. At least the batteries could be small

pjc50 6y ago

Beam steering can be done at pretty high speed, essentially limited by the weight of the mirror. And the further the mirror is the faster the effective linear speed of the 'spot'. But the safety question is more serious. The beam is dangerous to birds, unshielded aircraft, and persons on the ground. I don't think it's great giving the US military even more power to start a fire anywhere on earth with zero warning.

Analemma_ 6y ago
Couldn't phased arrays ensure that everywhere (within region) but the target gets only a small amount of power?
- madengr 6y ago
  In theory, yes, but practice no. The antenna required to collimate the beam from LEO, down to a person sized spot on earth, would be massive. Single antenna apertures are limited to about 90 dB of gain, and I doubt that is near enough, but I’d have to run some calculations.
oblio 6y ago
> I don't think it's great giving the US military even more power to start a fire anywhere on earth with zero warning. They already have hydrogen bombs :-)))
- iso947 6y ago
  Fairly hard to deploy that quietly.
  - oblio 6y ago
    True, but they also have drones and a million other ways they can kill people relatively unnoticed. And if the US Gov. really wants to, there are always Black Ops. This is a bit like complaining about a knife in a gun shop :-)
6y ago

joshvm 6y ago

It's not that microwaves are intrinsically harmful, it's the intensity of the beam. For example microwave ovens operate around 2.4Ghz, same as Bluetooth/WiFi. I'm not sure what power delivery operates at. If you get hit by a megawatt beam, you're going to get burned regardless of the wavelength (unless either it's short enough to pass through you, or somehow you reflect 100% of it). As another comment points out, you can beam steer quite fast. You only care about angular rate, and an airliner at cruise altitude moves fairly slowly (eg you can follow it with your eyes easily).

sandworm101 6y ago

This has nothing to do with aircraft. This is about beaming power to low-orbit satellites. The problem with low-orbit radar satellites (the spy satellites tracking ships) is that they need lots of power. In the past this was done with small nuclear reactors but today that is unacceptable and virtually all satellites use solar panels. But sarge solar panels means higher drag and shorter lifetimes in low orbit. Being able to 'beam' power from a higher orbit means one could power more aerodynamic low orbit satellites.

MayeulC 6y ago
Ah, my bad. That said, beamed power could be applied to anything, and the post I wrote above is one of the better use cases, in my opinion.
goodcanadian 6y ago
This has nothing to do with aircraft. Actually, yes, the article explicitly mentions the possibility of powering unmanned aerial vehicles.
- sandworm101 6y ago
  >> the article explicitly mentions Ya. The public report on the super-secret space plane touts that it is studying far-off green energy solutions when those same technologies have much more immediate military effects. It's like the USAF saying that it is studying lasers in order to build better CD players. Everyone takes such statements with a grain of salt. Nobody thinks that we are getting the full story behind these experiments and we chuckle a bit at the poor junior officer instructed to "be creative" with descriptions in public statements.
  - goodcanadian 6y ago
    I didn't say anything about green energy, and while the grandparent comment did, I don't think it was implied that it was the motivation of the experiment. Powering military drones for indefinite dwell time is a very plausible use case among many listed in the article.