Slashdot is powered by your submissions, so send in your scoop

 



Forgot your password?
typodupeerror

Comment Re:The technical problems with this are immense. (Score 1) 240

Is he? I didn't get the impression of that from TFA that it would switch over. TFA talks about both electric and VTOL but not about using conventional power during flight. If that's what he meant, that's much more potentially reasonable but given his long-term goals of dealing with global warming and fossil fuel dependence (which is why he's so in favor of electric cars) that doesn't seem like that's what he means. Do you have a citation or source that he means that?

Comment Re:The technical problems with this are immense. (Score 1) 240

You can recharge/refuel more frequently with an electric car. A bit hard to land and recharge in the middle of the Atlantic ocean. So the reduced range of an electric car (around 200 miles for an electric car as opposed to 300-400 miles for a gas car) doesn't matter as much. Also, cars are less dependent on fuel in some sense than planes since planes need to go fast. So you need a lot more fuel proportionally, so its efficiency matters more for planes.

Comment The technical problems with this are immense. (Score 5, Insightful) 240

Batteries do not have the energy density of jet fuel. The primary thing that matters here is energy density, which has two forms, energy per mass and energy per volume. https://en.wikipedia.org/wiki/Energy_density Both need to be much better than they are today for electric airplanes to have any chance (lifespan and and number of cycle uses also need to improve but that's in some ways less of a barrier.) Energy density of batteries by both metrics batteries has increased by 5%-10% a year depending on the exact metric and choice of examples https://www.quora.com/Is-it-true-that-battery-energy-density-improves-5-8-per-year which is exponential growth ( but with a much slower doubling time than something like Moore's Law. One has a doubling about once every 8 or 10 years.) Jet fuel has an energy density of around 45 MJ/kg, The most efficient batteries have a little under 1 MJ/kg. So one needs at least about 5 doublings before batteries can reasonably compete which will start to occur if they have an energy density of around 32/ MJ/kg. Similar remarks apply to energy density measured by joules per volume. However, there are technical reasons to think that batteries will stop doubling before that (see theabove quora link for details which argues that we can't make batteries much than four times as efficient before we start running into serious theoretical limits). At around 20 MJ/kg, one maybe could run planes practically but they would be much less convenient and practical than today's jets and that would be at the very upper end of the plausible limits just from a straight energy density estimate.

However, the situation is even worse than that. When you use jet fuel, you use it up. Depending on the type of airplane, at take off fuel is generally 25% to 50% of the mass of the plane. So one gets serious savings that one doesn't have to move all the used fuel the entire way. That doesn't work with batteries: they are the same mass and volume whether or not they are charged, and dumping them would defeat most of the point. It might be possible to do some sort of staging approach where one uses some set of batteries to nearly empty and then have them break off in a modular plane that returns to the ground site. But that itself would lead to all sorts of additional problems.

So it is likely that we will still see fossil fuels used for jets for the next 40 or 50 years. Indeed, it is likely that they will be the very last use of fossil fuels.

Comment Re:"people are more connected today", really? (Score 1) 86

Maybe "connectedness" contributes to the partisanship.

The most stable societies often seem to be the ones with the least diversity. It seems like the fewer the internal differences among the population, the fewer reasons to be partisan -- the other guy looks like you, speaks like you, prays the same, eats the same, lives the same.

Connectedness makes people aware of differences -- the other guy looks different, talks different, prays different, eats different, lives different.

Something about humans makes the other a competitor or an enemy.

Slashdot Top Deals

At the source of every error which is blamed on the computer you will find at least two human errors, including the error of blaming it on the computer.

Working...