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from the airline-spelled-backwards-is-enalpria dept.
[...] Assuming these electric aircraft could be built, would they actually lower emissions? At present, no. Given the average emissions involved with powering the US grid, the emissions involved with powering an electric aircraft (including losses during transmission) would be about 20 percent higher than those generated by a modern, efficient jet engine. That doesn't mean they'd be entirely useless from a climate perspective, though. Once the additional warming effects of aircraft are taken into consideration, the electric aircraft comes out ahead by about 30 percent.
Future considerations complicate things pretty quickly, though. The price of renewable energy is expected to keep dropping, which will make renewables a larger part of the grid, lowering the emissions. The authors estimate that the vast majority of charging will take place during daylight hours—the peak of solar production—as well. Assuming future solar production leads to a discount on electric use during the day, it could help the economics of electric aircraft; currently, they only make sense economically with fuel at about $100/barrel.
How all of this would affect air travel is very sensitive to the capacity of future batteries. The authors estimate that an effective range of about 1,100 kilometers would allow electric aircraft to cover 15 percent of the total air miles (and corresponding fuel use) and nearly half the total flights. That would raise the total electricity demand by about one percent globally, although most of that would affect industrialized nations. Upping the range to 2,200 kilometers would allow 80 percent of the global flight total to be handled by electric aircraft.
Zeppelins still don't seem to figure into the answer.
(Score: 3, Interesting) by Runaway1956 on Saturday December 15 2018, @10:55AM (3 children)
Regarding charging planes - it seems obvious to me that they would need to change batteries, rather than wait for the chargers to do their job. No airline wants their planes sitting on the tarmac for half of eternity while the batteries charge! Somehow, though, I can't see the authorities approving of pulling tons of batteries out of the aircraft, then slapping a bunch of new ones in place. For efficiency, you would almost have to redesign the air frame, so that a very large forklift drives up to the belly of the plane, the batteries are disconnected as a unit, then unlatched from the aircraft, and the whole power unit hauled away as a unit.
I also question how fast these things can be. Jets are fast - faster than just about anything other than rockets. With batteries, you're moving backward to propellors, or at best, turbines. How fast can you make those? Jets pretty much took over aviation by reason of their speed.
For battery powered craft, we need a whole lot of tech breakthroughs, and probably a more leisurely approach to air travel. I don't see either of those happening real soon.
(Score: 2) by Dr Spin on Saturday December 15 2018, @11:48AM
Jets pretty much took over aviation by reason of their speed.
Having taken over, people were able to realise that fuel economy and reliability were also important. And no one has any plans to produce a piston engine that competes with high bypass turbojets.
You could reasonably expect fare paying passenger planes with the battery life of a sub $100 drone, Above that, you have unreasonable expectations.
Warning: Opening your mouth may invalidate your brain!
(Score: 2, Interesting) by khallow on Saturday December 15 2018, @04:14PM
Most jets are turbines, let us note. Turbines can go a little into the supersonic regime. The key is to slow incoming supersonic air to subsonic speeds (expansion and heating) for the turbine to grip, and then eject at supersonic speed (reverse of the initial process). Certainly, they'd be able to function at the normal high subsonic speeds that passenger jets currently travel at.
The big problem is the battery mass.
(Score: 4, Interesting) by subs on Saturday December 15 2018, @05:14PM
A few little details:
- Modern turbofan engines derive around 85 - 90% of their thrust from the bypass fan.
- A bypass fan is little more than a glorified high-speed fixed pitch propeller.
- If you replace the turbine engine core with an electric motor, in principle there's nothing preventing you from building an electric fan engine that would achieve the same speeds that a turbofan could (M0.75 - M0.84).
- "or at best, turbines" - this makes no sense from an engineering perspective. All aviation jet engines ARE turbine engines.
If you look at things such as propfans [wikipedia.org] or unducted fans / ultra high-bypass turbofans, the differences between a turbofan and turboprop engine get blurred until there's basically no distinction left.
In short, the propulsor / engine tech isn't really what's holding electric aircraft back. That's pretty much a solve engineering problem and we have all the tech needed for it available today (in fact we've probably had for the last half century). What kills it is the battery energy density.