Originally Posted by
etudiant
I'd thought cruise thrust was usually only about 25% of takeoff power, suggesting the requirements are correspondingly more modest.
I think for turboprops it's typical to cruise at 70-80% torque. Since many turboprop engines are thermodynamically flat-rated, the actual energy consumption to maintain cruise torque can still be quite significant -- certainly more than 25%.
A large electric-powered propeller-driven air transport vehicle with Tu-114-level payload and performance would have to expend about the same energy. It appears that would equate to over 30 megawatts sustained cruise output for a two-hour short-haul flight, or over 60 megawatt hours, not counting reserves or takeoff.
It's true that batteries don't get lighter as they discharge, so expended units could hypothetically be progressively jettisoned in flight. That would help but would require a large new infrastructure. At current energy densities that would equate to over 1 million lb of batteries per plane, so it's not really possible with current technology. It would require at least a 10x improvement in battery energy/mass ratio just to achieve short-haul capability for something the size of a prop or fan-powered 737. To recharge the planes, each airport would require one or more on-site dedicated multi-gigawatt power plants.
You could pick up a little more efficiency using unducted fans, but that's just nibbling at the edges of a much larger problem.