> > improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy
> Again, this can be done for any aircraft, not just the electric ones.
Not only that: you burn the fuel, so for the second half of the flight you only need to carry half the fuel. But you have to carry the full battery mass (modulo E=mc^2) all the way.
Well, that’s in part a point for the batteries, though. You spend a lot of energy to lift all that fuel that you just blow out with all its potential energy up in the air, whilst the batteries provide you with that very potential energy on the way down as well.
Glider planes quiet commonly are filled with water to make them heavier so they can make more use of the potential energy they gain from the externally powered take off and so that they can bridge longer distances without lift generating upwind.
Would electric towplanes be doable for passenger aircraft? (Long or short haul, electric or otherwise).
If one of the downside of electric planes is the range, while fuel is cheap, making them cheaper to operate, and take-off uses a significant portion of the total energy, I could see very powerful electric towplanes as a way to reduce the amount of fuel needed for takeoff. This would:
* Allow to travel longer distances with the same amount of fuel (enabling electric airplanes to fly longer distances). Alternatively, allow planes to fill up with less fuel for the same distance.
* Improve fuel efficiency of big airliners, and their carbon footprint if you consider regular ones.
One last question: aircraft that fly shorter routes typically embark less fuel, but would that be doable with electric planes?
Actually, gliders with water ballasts have the same L/D full or empty. The difference is that they can fly faster when the tanks are full, but they don’t travel larger distances
That's not a point for batteries. I cannot imagine a circumstance where, during cruise or even descent, you'd wish that you'd be carrying more mass (except possibly to have a higher AoA and thus higher V_a if you want to fly through turbulence faster).
Indeed, there are various ways to handle "staging" of aircraft, including parachuting batteries, electric towplanes, assisted groundlaunch, piggyback, etc. These may have niche uses, particularly for cargo flights, but I suspect that will only happen if 1) jet air travel pays for its full climate cost and 2) we stop making any progress in battery technology.
Taking seriously the idea for a moment: you don't consume batteries one at a time, they are in various degrees of parallelism. Also the balance of the plane is affected by mass ejection.
> Again, this can be done for any aircraft, not just the electric ones.
Not only that: you burn the fuel, so for the second half of the flight you only need to carry half the fuel. But you have to carry the full battery mass (modulo E=mc^2) all the way.