6 ms·

It's surprising that even with the energy it takes to generate a plasma strong enough and in enough quantity to achieve the desired effects, it can still result

by Feneric 10y ago

It's surprising that even with the energy it takes to generate a plasma strong enough and in enough quantity to achieve the desired effects, it can still result in an estimated 25% energy savings. It goes to show how much energy just deals with drag in the current system.

phkahler 10y ago
>> It's surprising that even with the energy it takes to generate a plasma strong enough and in enough quantity to achieve the desired effects, it can still result in an estimated 25% energy savings. It goes to show how much energy just deals with drag in the current system. You've made an assumption that they are taking the energy required to create the plasma into account in their aerodynamic efficiency calculations. I didn't see any indication of the power required to produce the plasma, much less that number of power already required to fly. I did see the suggestion of using it on electric planes or wind turbines where larger amounts of electric power are readily available - one can interpret that availability as a convenience (high voltages and power are already there meaning less complexity) or an oversight (we're just neglecting the energy required). Nowhere in the article is this directly addressed. It would not surprise me if the truth were somewhere in between - it takes a lot of power, but saves even more. I've seen a similar situation in the hybrid car world when making certain comparisons.
- Justsignedup 10y ago
  Do we know if there's a lot or a little lost electricity that is generated as a result of the main engines running? I know cars waste a bunch of electricity (which is how hybrid batteries charge themselves when driving).
  - hx87 10y ago
    Cars and planes don't "lose" electricity when their engines are running; otherwise their batteries would be constantly overcharged. Hybrid cars just have more powerful alternators.
    - JonathonW 10y ago
      Hybrid cars don't necessarily have an alternator in the sense that an all gasoline car does-- for example, Toyota's hybrid system uses a pair of motor/generators (electric motors which can be configured to generate power too) connected to each other and to the gasoline engine through a planetary gearset.
      - jacquesm 10y ago
        Electric motors and alternators are mostly equivalent, the difference is that the diode assembly on a car alternator would stop you from using one as a motor. Otherwise, they are roughly identical. That you don't find a 'traditional' alternator in an electric or hybrid car is simply because the electric motor doubles in that role when required. Almost all electric motors when spun will generate power, you'd have to do some work to get one not to generate power when driven.
        m4x 10y ago
        AC induction motors are the most common type of motor for anything other than small electronics and turning one by hand will not generate any output power. They are definitely not identical to an alternator. The armature of an induction motor doesn't have an associated magnetic field so turning it won't generate any power in the windings. Permanent magnet motors are the only motor that will generate power if you just pick one up and turn it by hand, and they are quite rare (and expensive) at scales larger than a RC toy motor
        jacquesm 10y ago
        Sorry, but you're wrong there. Remanent magnetism will allow you to use an AC induction motor as a generator just fine. Absent any remaining magnetism you can 'flash' the motor core with a short DC pulse and then start rotating it with your chosen driver afterwards. Just one sample (of many) of people using this trick for all kinds of interesting small RE applications: http://www.smallhydropower.com/induction.htm http://www.smallhydropower.com/induction.htm
  - ars 10y ago
    > Do we know if there's a lot or a little lost electricity that is generated as a result of the main engines running? That's not how it works. Car use an alternator instead of a generator because it lets them control how much electricity to make regardless of the speed at which the alternator spins. They basically vary the strength of the magnet in the alternator. If they didn't the effect of "extra electricity" is a higher voltage, which would obviously be bad. > I know cars waste a bunch of electricity (which is how hybrid batteries charge themselves when driving). Hybrid batteries mostly save energy by capturing wasted energy when braking and when going downhill. Charging batteries from the engine makes the engine consume more gas.
    - jhayward 10y ago
      > Hybrid batteries mostly save energy by capturing wasted energy when braking and when going downhill Only for some workloads. A remarkable portion of the efficiency gain in hybrid vehicles is due to letting the ICE run at only the most efficient portion of the torque and power curves. In my experience (10 years in a Prius) regenerative braking is a distant second.
  - jacquesm 10y ago
    The waste energy in a regular car is not electricity, it is mostly simply heat. Instead of heating up a brake-disc by clamping it with calipers and pads an electric car or a hybrid will engage the motor by allowing it to be driven by the car instead of the other way around. The resulting energy at the output terminals of the motor is rectified and used to charge the batteries. So when you brake your regular car you lose some heat to the environment, you don't 'waste a bunch of electricity'.
- Retric 10y ago
  There is a huge gap between ~600mph vs much lower speeds of electric planes or windmills. As to energy requirements, it's likely fairly low in large part due to the expected altitude of 30,000+ feet. But also because the goal is stabilizing the airflow. PS: Drag force is velocity ^2; energy lost to drag Drag force * Distance or v^3.
  - fnj 10y ago
    Power, not energy.
    - fnj 10y ago
      Could you justify the downvote for a factual correction?
aardvark291 10y ago
> It goes to show how much energy just deals with drag in the current system. All of the energy used during cruise flight (straight and level, accelerated) goes to drag.
- abakker 10y ago
  I am not a physicist, but, doesn't fighting gravity by way of lift mean that at cruise altitude the plane is still fighting gravitational acceleration constantly? Drag is friction, right?
  - solidsnack9000 10y ago
    It's true that at least some energy must be expanded to lift the plan, even were there no drag; otherwise planes would lift themselves. Drag is more like vacuum than friction.
    - kd5bjo 10y ago
      Keeping an object at a constant altitude requires force, but it doesn't necessarily cost any energy. For example, there's no energy being expended keeping my coffee cup elevated, just a table exerting a force. From my admittedly limited understanding of aerodynamics, a plane's engines are only fighting against drag to keep the airspeed up, and it's the airspeed passing by the wings that generates lift -- if engines are necessary to generate lift, gliders and kites wouldn't be able to work at all.
      - jasonwatkinspdx 10y ago
        There's more too it than that. The airfoil causes a net downwash, and via newton we know the acceleration of that mass of air will cause an upward force. The finer details of this are something a lot of textbooks get wrong. Wikipedia's article about it is pretty good. With a kite the wind is the engine, the string allows the kite to use it. Or you can run on a windless day. With a glider the tow plane or ground tow rope provides the initial energy to get to altitude, giving the glider potential energy. As it glides that potential energy is converted to kinetic energy. The pilot uses their knowledge and skill to glide to places where they can gather more energy from updrafts of various sorts. I think it's really amazing how after that initial injection of energy, it's just all just skill and ambient energy.

by Feneric 10y ago

phkahler 10y ago

>> It's surprising that even with the energy it takes to generate a plasma strong enough and in enough quantity to achieve the desired effects, it can still result in an estimated 25% energy savings. It goes to show how much energy just deals with drag in the current system. You've made an assumption that they are taking the energy required to create the plasma into account in their aerodynamic efficiency calculations. I didn't see any indication of the power required to produce the plasma, much less that number of power already required to fly. I did see the suggestion of using it on electric planes or wind turbines where larger amounts of electric power are readily available - one can interpret that availability as a convenience (high voltages and power are already there meaning less complexity) or an oversight (we're just neglecting the energy required). Nowhere in the article is this directly addressed. It would not surprise me if the truth were somewhere in between - it takes a lot of power, but saves even more. I've seen a similar situation in the hybrid car world when making certain comparisons.

Justsignedup 10y ago
Do we know if there's a lot or a little lost electricity that is generated as a result of the main engines running? I know cars waste a bunch of electricity (which is how hybrid batteries charge themselves when driving).
- hx87 10y ago
  Cars and planes don't "lose" electricity when their engines are running; otherwise their batteries would be constantly overcharged. Hybrid cars just have more powerful alternators.
  - JonathonW 10y ago
    Hybrid cars don't necessarily have an alternator in the sense that an all gasoline car does-- for example, Toyota's hybrid system uses a pair of motor/generators (electric motors which can be configured to generate power too) connected to each other and to the gasoline engine through a planetary gearset.
    - jacquesm 10y ago
      Electric motors and alternators are mostly equivalent, the difference is that the diode assembly on a car alternator would stop you from using one as a motor. Otherwise, they are roughly identical. That you don't find a 'traditional' alternator in an electric or hybrid car is simply because the electric motor doubles in that role when required. Almost all electric motors when spun will generate power, you'd have to do some work to get one not to generate power when driven.
      - m4x 10y ago
        AC induction motors are the most common type of motor for anything other than small electronics and turning one by hand will not generate any output power. They are definitely not identical to an alternator. The armature of an induction motor doesn't have an associated magnetic field so turning it won't generate any power in the windings. Permanent magnet motors are the only motor that will generate power if you just pick one up and turn it by hand, and they are quite rare (and expensive) at scales larger than a RC toy motor
        jacquesm 10y ago
        Sorry, but you're wrong there. Remanent magnetism will allow you to use an AC induction motor as a generator just fine. Absent any remaining magnetism you can 'flash' the motor core with a short DC pulse and then start rotating it with your chosen driver afterwards. Just one sample (of many) of people using this trick for all kinds of interesting small RE applications: http://www.smallhydropower.com/induction.htm http://www.smallhydropower.com/induction.htm
- ars 10y ago
  > Do we know if there's a lot or a little lost electricity that is generated as a result of the main engines running? That's not how it works. Car use an alternator instead of a generator because it lets them control how much electricity to make regardless of the speed at which the alternator spins. They basically vary the strength of the magnet in the alternator. If they didn't the effect of "extra electricity" is a higher voltage, which would obviously be bad. > I know cars waste a bunch of electricity (which is how hybrid batteries charge themselves when driving). Hybrid batteries mostly save energy by capturing wasted energy when braking and when going downhill. Charging batteries from the engine makes the engine consume more gas.
  - jhayward 10y ago
    > Hybrid batteries mostly save energy by capturing wasted energy when braking and when going downhill Only for some workloads. A remarkable portion of the efficiency gain in hybrid vehicles is due to letting the ICE run at only the most efficient portion of the torque and power curves. In my experience (10 years in a Prius) regenerative braking is a distant second.
- jacquesm 10y ago
  The waste energy in a regular car is not electricity, it is mostly simply heat. Instead of heating up a brake-disc by clamping it with calipers and pads an electric car or a hybrid will engage the motor by allowing it to be driven by the car instead of the other way around. The resulting energy at the output terminals of the motor is rectified and used to charge the batteries. So when you brake your regular car you lose some heat to the environment, you don't 'waste a bunch of electricity'.
Retric 10y ago
There is a huge gap between ~600mph vs much lower speeds of electric planes or windmills. As to energy requirements, it's likely fairly low in large part due to the expected altitude of 30,000+ feet. But also because the goal is stabilizing the airflow. PS: Drag force is velocity ^2; energy lost to drag Drag force * Distance or v^3.
- fnj 10y ago
  Power, not energy.
  - fnj 10y ago
    Could you justify the downvote for a factual correction?

aardvark291 10y ago

> It goes to show how much energy just deals with drag in the current system. All of the energy used during cruise flight (straight and level, accelerated) goes to drag.

abakker 10y ago
I am not a physicist, but, doesn't fighting gravity by way of lift mean that at cruise altitude the plane is still fighting gravitational acceleration constantly? Drag is friction, right?
- solidsnack9000 10y ago
  It's true that at least some energy must be expanded to lift the plan, even were there no drag; otherwise planes would lift themselves. Drag is more like vacuum than friction.
  - kd5bjo 10y ago
    Keeping an object at a constant altitude requires force, but it doesn't necessarily cost any energy. For example, there's no energy being expended keeping my coffee cup elevated, just a table exerting a force. From my admittedly limited understanding of aerodynamics, a plane's engines are only fighting against drag to keep the airspeed up, and it's the airspeed passing by the wings that generates lift -- if engines are necessary to generate lift, gliders and kites wouldn't be able to work at all.
    - jasonwatkinspdx 10y ago
      There's more too it than that. The airfoil causes a net downwash, and via newton we know the acceleration of that mass of air will cause an upward force. The finer details of this are something a lot of textbooks get wrong. Wikipedia's article about it is pretty good. With a kite the wind is the engine, the string allows the kite to use it. Or you can run on a windless day. With a glider the tow plane or ground tow rope provides the initial energy to get to altitude, giving the glider potential energy. As it glides that potential energy is converted to kinetic energy. The pilot uses their knowledge and skill to glide to places where they can gather more energy from updrafts of various sorts. I think it's really amazing how after that initial injection of energy, it's just all just skill and ambient energy.