[phkahler]

>> 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.

[Retric]

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]

Power, not energy.

[fnj]

Could you justify the downvote for a factual correction?

[Justsignedup]

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).

[ars]

> 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]

> 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]

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'.

[hx87]

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]

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]

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]

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]

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