[blutack]

Electric motors would need to be orders of magnitude more efficient than turbofans (which they aren't). You also need to compare the overall efficiency developed as thrust, not just thermal efficiency.

There's also the issue of the mass of batteries not going away during the flight, unlike fuel, which will require maximum landing weight to equal maximum takeoff weight - this will impose a structural penalty versus IC aircraft.

[cjrp]

> There's also the issue of the mass of batteries not going away during the flight

Excellent point; currently as fuel is burned off, planes can climb to higher, more efficient altitudes (known as a step climb). What's the performance penalty for not being able to do this as your batteries aren't getting lighter as the flight progresses.

[gsnedders]

Such short flights also spend a large proportion of time on the ground taxiing, etc., where turbofans are very inefficient. They spend incredibly little time at their most efficient high-altitude cruise.

One can imagine an electric aircraft relying on powered landing gear (as previously trialled by Airbus/Lufthansa Technik) which would further improve efficiency during taxiing.

[neolefty]

Maximum efficiency is ... 100%. So if a turbofan is 30% efficient, then the best you can do is about 3x.

[ericd]

Good point, but something to keep in mind is that the efficiency of the motors in turning stored energy into motion is only one part of the efficiency of the aircraft. If a plane is able to fly much higher due to the engines no longer being air breathing, that would also change the equation, as drag would be much lower with the thinner atmosphere.

[Gravityloss]

Also you can tune the location and amount of propulsors, and have a high efficiency rotation rate with direct drive electric motors.

The current turbofan engines are close to the size limits in relative fan size and bypass ratio without a gearbox, which adds cost and mass. (Only one manufacturer is in the process of introducing a geared turbofan.)

Because of no high speed jet exhaust and large area thrusters, these aircraft have the potential to be able to take off really steeply and to be really quiet.