4 ms·

There is a physics problem with carrying both fuel and oxidizer and not dumping spent fuel into the atmosphere. I suppose one could use lithium air batteries a

There is a physics problem with carrying both fuel and oxidizer and not dumping spent fuel into the atmosphere. I suppose one could use lithium air batteries and then land heavier than takeoff. The reason petroleum fuel works so well is because you scavenge 2/3 of the fuel from the air.

CrazyStat 6y ago
This is an underappreciated factor, particularly for long-haul flights. For transatlantic/transpacific flights the fuel can be over a third of the total takeoff weight of a modern airliner. Burning that mass off as you go means you get more efficient the longer you've been flying. Even if/when batteries match the energy density of aviation fuel (appropriately adjusted for motor/engine efficiency), they will still be at a substantial disadvantage for long flights.
- deleted 6y ago
  [deleted]
- arcticbull 6y ago
  The efficiency is worse the further you go, because you have to burn extra fuel just to carry extra fuel the whole way, so that it be used for the incremental distance travelled. It's why the A340-500 flying gascan is such a disaster from a unit economics perspective. It's also why Emirates, Etihad and Qatar did such good business for so many years connecting east and west with a stop in the Gulf as compared to eastern and western carriers who had to go the whole distance without stopping.
  - CrazyStat 6y ago
    That's a different efficiency comparison. You are correct that for a given type of plane, efficiency is worse for father distances. When comparing battery vs. hydrocarbon-fueled planes, however, hydrocarbon does relatively better the longer the distance, for the reasons discussed above. Battery-powered planes may soon be practical for regional short-haul flights but they're not going to be competing on transatlantic routes anytime soon.
arcticbull 6y ago
It's not a problem per se, but it is of course a factor. On the other hand, the thermal efficiency of driving an electric motor from a battery is ~99%. The thermal efficiency of jet and propeller planes is in the mid-30s.
- jcampbell1 6y ago
  A long haul jet is at takeoff roughly evenly split by weight between fuel, passengers, and plane. Yes, it becomes lighter, but the more importantly it scavenges it’s entire takeoff weight in oxygen which conventional lithium ion batteries can’t do. Lithium batteries have improved, but you have to carry both sides of the redox. The only way I can think to get similar physics is to use lithium air batteries and then dump them with a parachute when discharged.
  - Dylan16807 6y ago
    That's not the point of the comment you replied to. Pulling in oxidizer from the air gets you a 3x efficiency boost, but using a combustion engine has a 3x efficiency penalty. It cancels out.

CrazyStat 6y ago

This is an underappreciated factor, particularly for long-haul flights. For transatlantic/transpacific flights the fuel can be over a third of the total takeoff weight of a modern airliner. Burning that mass off as you go means you get more efficient the longer you've been flying. Even if/when batteries match the energy density of aviation fuel (appropriately adjusted for motor/engine efficiency), they will still be at a substantial disadvantage for long flights.

deleted 6y ago
[deleted]
arcticbull 6y ago
The efficiency is worse the further you go, because you have to burn extra fuel just to carry extra fuel the whole way, so that it be used for the incremental distance travelled. It's why the A340-500 flying gascan is such a disaster from a unit economics perspective. It's also why Emirates, Etihad and Qatar did such good business for so many years connecting east and west with a stop in the Gulf as compared to eastern and western carriers who had to go the whole distance without stopping.
- CrazyStat 6y ago
  That's a different efficiency comparison. You are correct that for a given type of plane, efficiency is worse for father distances. When comparing battery vs. hydrocarbon-fueled planes, however, hydrocarbon does relatively better the longer the distance, for the reasons discussed above. Battery-powered planes may soon be practical for regional short-haul flights but they're not going to be competing on transatlantic routes anytime soon.

arcticbull 6y ago

It's not a problem per se, but it is of course a factor. On the other hand, the thermal efficiency of driving an electric motor from a battery is ~99%. The thermal efficiency of jet and propeller planes is in the mid-30s.

jcampbell1 6y ago
A long haul jet is at takeoff roughly evenly split by weight between fuel, passengers, and plane. Yes, it becomes lighter, but the more importantly it scavenges it’s entire takeoff weight in oxygen which conventional lithium ion batteries can’t do. Lithium batteries have improved, but you have to carry both sides of the redox. The only way I can think to get similar physics is to use lithium air batteries and then dump them with a parachute when discharged.
- Dylan16807 6y ago
  That's not the point of the comment you replied to. Pulling in oxidizer from the air gets you a 3x efficiency boost, but using a combustion engine has a 3x efficiency penalty. It cancels out.