4 ms·

The fuel burn of take-off and climb substantially lightens the aircraft for cruise. Electric batteries have no such effect, you're carrying all that dead weight

The fuel burn of take-off and climb substantially lightens the aircraft for cruise. Electric batteries have no such effect, you're carrying all that dead weight for the rest of the flight. This reduces the passenger or cargo capacity of the aircraft, which reduces potential revenue. And what if you need two go-arounds?

0cf8612b2e1e 3mo ago
Energy density of liquid fuels cannot be beat by batteries, so this is not competitive if you are looking to maximize cargo. However, there are plenty of short haul flights: private jets, island hopping, regional routes where you need to move little mass.
xattt 3mo ago
Exactly. A hybrid passenger car can tolerate unpredictable power output that may come with an auxiliary power setup that may or may not be available when stronger dynamics are called for. A plane doesn’t have this luxury and needs predictable output. The fossil fuel engine either needs a sacrificial “overboost” mode for emergencies (at the cost of wear/long-term longevity), or has to be sized for full power at the ultimate cost of efficiency.
- Melatonic 3mo ago
  So theoretically if the electric motors fail (or battery is dead) an engine could be sized and designed smaller (for cruise efficiency) but have some sort of boost mode that still ensures safety ? At the cost of increased maintenance or wear or something if it must be used
hobonation 3mo ago
Valid. Perhaps it's not all negative: the electric portion could give a pilot a bit more glide than the gas portion dies.
Tade0 3mo ago
On anything but very short flights most of the fuel is spent on cruising.
- dmoy 3mo ago
  I would classify 290 miles as a very short flight, that's like 1-2 hours or something?
arijun 3mo ago
> you're carrying all that dead weight for the rest of the flight If you're recharging the batteries for extra go-arounds during landing, they are as dead weight as the fuel you would otherwise reserve for that purpose. And if you have 30% more efficient engines, meaning less fuel and smaller engines, it's possible you could come out ahead, weight-wise. > what if you need two go-arounds I assume that a go-around requires less sustained power output than a full climb from takeoff, so you will probably get more than one go-around anyway, and we don't know how much over-capacity they're designing for. In any case, any design will require tradeoffs in safety, and having more engine-out capabilities might improve safety enough to overcome the higher risk with go-arounds. Not saying this project is will work out or that you're even wrong necessarily (this could be the equivalent of a concept car for Pratt & Whitney).
- dmitrygr 3mo ago
  > I assume that a go-around requires less sustained power output than a full climb from takeoff, No. Source 1: PE = mgh Source 2: am pilot
  - arijun 3mo ago
    You don't do a full climb after a go-around, so the heights are not equal, and the mass is less since you've expended fuel. You also retain some kinetic energy but I assume that is closer to a negligible effect. Also, PE = mgh is probably an not a great formula for energy cost of takeoff/go-around, as there are probably large costs it ignores (gravity loss, less efficient engine use, maybe less efficient turbines?). For your source 2 I have no rebuttal so will have to defer to you, but would ask for an explanation.
    - SoftTalker 3mo ago
      Not a pilot, but on approach for landing you bleed off a lot of energy. For a go-around you need to reverse your descent and build up enough energy to fly away again. Take-off/Go-around tends to be the same throttle setting, AFAIK. Of course it also depends on how early you decide to throw away the approach and go around. Doing it at 1000 feet is different from bouncing it off the runway.
repiret 3mo ago
Don’t conflate airplanes with rockets. On an airplane, most of the energy in cruise is spent overcoming parasitic drag, not induced drag. It’s spent pushing the airmass out of the way as it moves forward, not creating lift to stay aloft. For that reason, a change in weight does not significantly change cruise fuel usage. Weight is still precious, but that’s because airplanes’ load are more often weight constrained than volume constrained, and capital and operating costs are such that you want to maximize the load.
deleted 3mo ago
[deleted]
usrusr 3mo ago
"And what if you need two go-arounds?" Easy: you don't try the second landing approach before the battery is sufficiently recharged to contain enough energy for the second abort. Chances are this does not take any longer than going through the pattern anyways. The saving is not just the dead weight of the bigger engine you'd need to do take-off, climb and abort without electric assist, it's also the fuel saved during cruise from running an engine that is completely designed for efficiency at cruise load instead of for some compromise between cruise efficiency and sufficient peak power for start and abort.

0cf8612b2e1e 3mo ago

Energy density of liquid fuels cannot be beat by batteries, so this is not competitive if you are looking to maximize cargo. However, there are plenty of short haul flights: private jets, island hopping, regional routes where you need to move little mass.

xattt 3mo ago

Exactly. A hybrid passenger car can tolerate unpredictable power output that may come with an auxiliary power setup that may or may not be available when stronger dynamics are called for. A plane doesn’t have this luxury and needs predictable output. The fossil fuel engine either needs a sacrificial “overboost” mode for emergencies (at the cost of wear/long-term longevity), or has to be sized for full power at the ultimate cost of efficiency.

Melatonic 3mo ago
So theoretically if the electric motors fail (or battery is dead) an engine could be sized and designed smaller (for cruise efficiency) but have some sort of boost mode that still ensures safety ? At the cost of increased maintenance or wear or something if it must be used

hobonation 3mo ago

Valid. Perhaps it's not all negative: the electric portion could give a pilot a bit more glide than the gas portion dies.

Tade0 3mo ago

On anything but very short flights most of the fuel is spent on cruising.

dmoy 3mo ago
I would classify 290 miles as a very short flight, that's like 1-2 hours or something?

arijun 3mo ago

> you're carrying all that dead weight for the rest of the flight If you're recharging the batteries for extra go-arounds during landing, they are as dead weight as the fuel you would otherwise reserve for that purpose. And if you have 30% more efficient engines, meaning less fuel and smaller engines, it's possible you could come out ahead, weight-wise. > what if you need two go-arounds I assume that a go-around requires less sustained power output than a full climb from takeoff, so you will probably get more than one go-around anyway, and we don't know how much over-capacity they're designing for. In any case, any design will require tradeoffs in safety, and having more engine-out capabilities might improve safety enough to overcome the higher risk with go-arounds. Not saying this project is will work out or that you're even wrong necessarily (this could be the equivalent of a concept car for Pratt & Whitney).

dmitrygr 3mo ago
> I assume that a go-around requires less sustained power output than a full climb from takeoff, No. Source 1: PE = mgh Source 2: am pilot
- arijun 3mo ago
  You don't do a full climb after a go-around, so the heights are not equal, and the mass is less since you've expended fuel. You also retain some kinetic energy but I assume that is closer to a negligible effect. Also, PE = mgh is probably an not a great formula for energy cost of takeoff/go-around, as there are probably large costs it ignores (gravity loss, less efficient engine use, maybe less efficient turbines?). For your source 2 I have no rebuttal so will have to defer to you, but would ask for an explanation.
  - SoftTalker 3mo ago
    Not a pilot, but on approach for landing you bleed off a lot of energy. For a go-around you need to reverse your descent and build up enough energy to fly away again. Take-off/Go-around tends to be the same throttle setting, AFAIK. Of course it also depends on how early you decide to throw away the approach and go around. Doing it at 1000 feet is different from bouncing it off the runway.

repiret 3mo ago

Don’t conflate airplanes with rockets. On an airplane, most of the energy in cruise is spent overcoming parasitic drag, not induced drag. It’s spent pushing the airmass out of the way as it moves forward, not creating lift to stay aloft. For that reason, a change in weight does not significantly change cruise fuel usage. Weight is still precious, but that’s because airplanes’ load are more often weight constrained than volume constrained, and capital and operating costs are such that you want to maximize the load.

deleted 3mo ago

[deleted]

usrusr 3mo ago

"And what if you need two go-arounds?" Easy: you don't try the second landing approach before the battery is sufficiently recharged to contain enough energy for the second abort. Chances are this does not take any longer than going through the pattern anyways. The saving is not just the dead weight of the bigger engine you'd need to do take-off, climb and abort without electric assist, it's also the fuel saved during cruise from running an engine that is completely designed for efficiency at cruise load instead of for some compromise between cruise efficiency and sufficient peak power for start and abort.