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This has been one of my “shower thoughts”.. If jet fuel is very efficient and dense for the more demanding take off and low altitude legs of the flight, we are

This has been one of my “shower thoughts”.. If jet fuel is very efficient and dense for the more demanding take off and low altitude legs of the flight, we aren’t there concepts that do a hybrid of jet fuel and electric powered flights that use the electric propellers only where they are efficient, leaving the existing system for the more challenging tasks like take off?

ramesh31 4y ago
Same problem as all hybrid power systems; weight and complexity. You can't get away with generalist designs in an aircraft the way you can with a land or water vehicle. Carrying around the weight and drag penalties of an unused engine would more than detract from any efficiency gain with an electric auxiliary.
- Ekaros 4y ago
  Also unlike with sea where efficiency gains from hybrids out gain the mass and volume losses, same doesn't apply to air. Also, some of the engine types like turboprops are pretty good already. And hybrid systems likely won't make gains and probably even lose quite a bit.
krallja 4y ago
Then you have two different energy storage areas plus two different drive trains, and the associated weight gain that implies. Hybrid road vehicles make it work because they have the weight supported by the ground, plus the additional benefit of regenerative braking, which evens out energy usage in stop-and-go and hilly travel. Planes don’t work at all in either scenario.
cjbprime 4y ago
There are some electric gliders which at least use the same intuition -- you need a ride for takeoff, but then there's an electric sustaining motor for once you're in the air (and don't have lift).
rwmj 4y ago
Or can you have a 100' long cable to directly power the lift off and first hundred feet of the flight? (For a conventional runway takeoff, some kind of powered tracks.)
- amluto 4y ago
  Aircraft carriers effectively have powered tracks. As I understand it, this is currently quite dangerous and expensive.
p_l 4y ago
In addition to other comments here about increased weight and complexity... There's an area where it makes sense, and it's being trialed in few places. Namely electric propulsion for taxiing. You see, Taxiing on jet engines is very, very, very inefficient - you stay pretty much in worst fuel economy all the time to the point that taxiing burns more fuel than few hundred kilometers of cruise on the heaviest airliners. In fact optimizing taxiing is important enough that landings are calculated to ensure you have shorter distance and can reuse kinetic energy from landing, and depending on plane it might be norm to shut off all engines except one during taxi. So there's experimentation with either adding electric drivetrain to main gear or having remote-controlled pulling car or quick-detachable (and also remote controlled) drive blocks that could attach to main gear. This way the plane would only start the engines just before going onto its designated runway.
- SV_BubbleTime 4y ago
  This all just furthers my idea that if I’m ever a time traveler, I’ll try and convince the past to make airplanes that all have aircraft carrier sling shot systems… for fun.
  - stavros 4y ago
    Taxiing is the process of getting the plane to the slingshot.
    - simonsarris 4y ago
      Yeah, you'd need to convince the past that "tugboats but for aircraft" is a good thing to standardize.
- dwighttk 4y ago
  I am not an expert This doesn’t seem to make any sense to me. If taxiing is so inefficient, why not use the pushback carts to push/pull the planes into position? I’ve been to many more airports that make the plane taxi for quite a distance, like 20 minutes (not just sitting and waiting, but moving) to get to the gate than ones that “ensure you have shorter distance and can reuse kinetic energy from landing”
akira2501 4y ago
Because we use the engines to generate hydraulic power and electric power, and on larger planes it drives the air conditioning. The engines do a lot more than just provide thrust.

ramesh31 4y ago

Same problem as all hybrid power systems; weight and complexity. You can't get away with generalist designs in an aircraft the way you can with a land or water vehicle. Carrying around the weight and drag penalties of an unused engine would more than detract from any efficiency gain with an electric auxiliary.

Ekaros 4y ago
Also unlike with sea where efficiency gains from hybrids out gain the mass and volume losses, same doesn't apply to air. Also, some of the engine types like turboprops are pretty good already. And hybrid systems likely won't make gains and probably even lose quite a bit.

krallja 4y ago

Then you have two different energy storage areas plus two different drive trains, and the associated weight gain that implies. Hybrid road vehicles make it work because they have the weight supported by the ground, plus the additional benefit of regenerative braking, which evens out energy usage in stop-and-go and hilly travel. Planes don’t work at all in either scenario.

cjbprime 4y ago

There are some electric gliders which at least use the same intuition -- you need a ride for takeoff, but then there's an electric sustaining motor for once you're in the air (and don't have lift).

rwmj 4y ago

Or can you have a 100' long cable to directly power the lift off and first hundred feet of the flight? (For a conventional runway takeoff, some kind of powered tracks.)

amluto 4y ago
Aircraft carriers effectively have powered tracks. As I understand it, this is currently quite dangerous and expensive.

p_l 4y ago

In addition to other comments here about increased weight and complexity... There's an area where it makes sense, and it's being trialed in few places. Namely electric propulsion for taxiing. You see, Taxiing on jet engines is very, very, very inefficient - you stay pretty much in worst fuel economy all the time to the point that taxiing burns more fuel than few hundred kilometers of cruise on the heaviest airliners. In fact optimizing taxiing is important enough that landings are calculated to ensure you have shorter distance and can reuse kinetic energy from landing, and depending on plane it might be norm to shut off all engines except one during taxi. So there's experimentation with either adding electric drivetrain to main gear or having remote-controlled pulling car or quick-detachable (and also remote controlled) drive blocks that could attach to main gear. This way the plane would only start the engines just before going onto its designated runway.

SV_BubbleTime 4y ago
This all just furthers my idea that if I’m ever a time traveler, I’ll try and convince the past to make airplanes that all have aircraft carrier sling shot systems… for fun.
- stavros 4y ago
  Taxiing is the process of getting the plane to the slingshot.
  - simonsarris 4y ago
    Yeah, you'd need to convince the past that "tugboats but for aircraft" is a good thing to standardize.
dwighttk 4y ago
I am not an expert This doesn’t seem to make any sense to me. If taxiing is so inefficient, why not use the pushback carts to push/pull the planes into position? I’ve been to many more airports that make the plane taxi for quite a distance, like 20 minutes (not just sitting and waiting, but moving) to get to the gate than ones that “ensure you have shorter distance and can reuse kinetic energy from landing”

akira2501 4y ago

Because we use the engines to generate hydraulic power and electric power, and on larger planes it drives the air conditioning. The engines do a lot more than just provide thrust.