[SupersonicScrub]

There's a better electrically driven solution that takes advantage of the fact that take-off and climb-out requires the most power.

Maximum power requirements come from take-off and climb-out, so the engine size is designed around the max take-off power. This means that the engine is over-designed and less-efficient for the majority of the flight.

By implementing a hybrid engine, the gas-powered component and the electric powered component work together to provide take-off power requirements. By the time the aircraft reaches cruising altitude, the batteries are dead, and the gas-powered component works alone. This allows the engine to be designed for the cruise power requirements, which results in a much more efficient engine. UTC is currently experimenting with this concept.

https://www.flightglobal.com/news/articles/utc-to-test-hybri...

Yes it's not carbon neutral, but it's a step in the right direction.

[iguy]

Not just for take-off, but for the possibility of finishing the take-off with one engine failure. That's quite a bit of spare capacity.

However I also wonder why, if electric motors are a solution here, there hasn't been a comparable fuel-powered extra-takeoff-engine. Why would this not have the same benefits? Or are extra engines simply too complicated mechanically unless they are motors?

(The liked article is about modifying a Dash 8, which is a turboprop, and perhaps it's easy to have oversize propellers for takeoff, and just connect a motor to the same gearbox.)

[mikepurvis]

Probably because a jet engine costs like $30MM. It may well be that the incremental cost ($, weight, complexity) of adding an electric booster to an existing engine design is much more practical than just adding more engines.

[WalterBright]

> take-off and climb-out requires the most power

Military aviation has dealt with this in various ways:

1. Carried aloft by a larger plane

2. Towed aloft be multiple other planes

3. Jet assisted takeoff

4. catapults

5. drop tanks

6. mid-air refueling

[mhandley]

You still need enough power to make a late go-around at the destination, in case of problems due to weather on final approach, arrival spacing, or a problem on the runway. I've been on planes that had to go around from low altitude three times, so it's not even that rare. Either the engine needs to be large enough to generate full take-off power, or you need a large margin of battery power that will never be used on an uneventful flight.

[_ah]

Wouldn't this also mean that full engine power is unavailable in the event of an emergency? Seems like this solution makes edge cases more likely to be fatal.