Andres125sx wrote: ↑23 Oct 2019, 11:33
Just_a_fan wrote: ↑23 Oct 2019, 09:58
Andres125sx wrote: ↑23 Oct 2019, 07:45
True. Do you say the same about combustion aircrafts? Because they need several orders of magnitude more energy as ICE are not even a half efficient compared to electric motors
Electric aircraft face the same issue that electric cars face - energy density. Electric motors may be more efficient than combustion engines, but the energy density of oil-derived fuels is so high that batteries can't compete. Jet fuel is 43MJ/kg compared to batteries that are mostly significantly less than 1 MJ/kg.
If an aircraft requires 100 tonnes of jet fuel to fly three hundred people over several thousand miles, even with the efficiency savings of an electric motor over a high-bypass turbofan, you're going to need more than 100 tonnes of batteries. Indeed, you're going to need several hundred tonnes of batteries. And then your aircraft won't fly because it'll be too heavy.
If/when batteries can give 30+MJ/kg energy density, then electric aircraft for commercial use will be possible. Until then? Nope, not going to happen.
Sorry but you're missing the key point of the discussion, Alair batteries are around 6MJ/kg which changes the whole scenario. Nobody talked about airliners, no electric setup can replace a turbine tough. But for prop planes it may be possible, and specially for personal multirotors. They would obviously be very expensive, but as any new technology is. ICE cars also were a luxury when first released.
The main point IMO is with this new batteries now they're feasible, and that's a huge step forward
6MJ/kg compared to 43MJ/kg does not make them feasible. You're still talking about 7 times the mass of batteries compared to fuel for a given trip. So a 10 tonne fuel requirement becomes a 70 tonne battery requirement. Are electric motors 7 times as efficient as modern turbofans / turboprops? I'm betting no where near - if they were, we'd be using them already.
Remember also one big "advantage" of fuel over batteries in aircraft - as the flight goes on, the mass reduces. This means that the aircraft becomes more efficient the further it flies - you need less lift to hold the aircraft up so you can trim it for a lower angle of attack / lower drag or fly higher which gives reduced drag (and so more efficiency). The battery-powered aircraft will be the same mass at the end of the flight as at the beginning and so doesn't benefit from this lowering of drag as the flight progresses.
Then there is the very big issue that aircraft can take off at weights higher than they can land. A battery aircraft will land at the same weight that is takes off. So you're limited to the maximum weight that the landing gear etc. can handle - more weight then being needed to make stronger landing gear to land a heavier aircraft.
I think we're stuck with fuelled aircraft for the foreseeable future. Better to develop carbon-neutral, low pollutant fuels to reduce the impact of aircraft.
Sure, there are limited cases where an electric aircraft is practical but they're limited to things like high altitude sensor platforms for the military i.e. relatively small, no need to fit in people and keep them alive etc. so can be built for aero efficiency above all else. They're going to be a very high aspect ratio winged, powered gliders, in effect.
If you are more fortunate than others, build a larger table not a taller fence.
