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Would be a turbo-electric config using 2 turbofans as generators for a 150 pax. aircraft more efficient than a very high bypass rationed Turbofan that burns hydrogen?

If not, then why are all companies like Airbus, Rolls Royce and Safran etc. working towards this?

Also, why would they just use their Highby pass Turbo-fans, that ways they don't have to invest billions and also have very high efficiency and less pollution (CO2, Nox, etc.)?

If we can argue about 15 years down the line, what would be a better solution? And why?

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    $\begingroup$ It's called greenwashing. Everybody in the industry knows that hydrogen and electric propulsion are impractical for airliners, but the press, woke activists and politicians don't listen but think they know it better. Hence the theater. $\endgroup$
    – Peter Kämpf
    Commented May 24, 2021 at 18:56
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    $\begingroup$ @Frog Simple physics seems not convincing, so why don't you read some of the answers here? $\endgroup$
    – Peter Kämpf
    Commented May 25, 2021 at 10:10
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    $\begingroup$ @Peter Kämpf - with no disrespect to your standing in this forum and elsewhere, citing your own statements as evidence that everyone in the industry knows something is not entirely compelling. I understand that there’s no arguing with the state of the art regarding physics, but perhaps you could clarify whether you think that electric airliners will ever be viable; if so then it follows that the ongoing efforts in this direction are justified. $\endgroup$
    – Frog
    Commented May 26, 2021 at 1:05
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    $\begingroup$ @Frog I linked to questions, not answers. Feel free to read the insights of others, too. I'm not holding you back. Now you ask about electric airliners ever to be viable. From first principles, an energy source that uses resources which are readily available at the place of consumption will always be superior to one which needs to carry all energy along with it. So an electric airliner might become viable one day but will always be at a disadvantage to one which uses a chemical reaction with oxygen. Regarding development: Put the effort in a field where it pays sooner, like electric cars. $\endgroup$
    – Peter Kämpf
    Commented May 26, 2021 at 6:55
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    $\begingroup$ @Peter Kämpf - hesitant as I am to continue shaking this particular tree, are you perhaps equating electric power with battery power? Something like an ethanol fuel cell would indeed dispose of its fuel load progressively in flight. Although I note that the OP is asking about turbo-electric propulsion, which could be powered by normal jet fuel. $\endgroup$
    – Frog
    Commented May 29, 2021 at 9:51

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Turbo-electric configurations do not offer any meaningful advantages for commercial airliners.

  1. Aircraft engines have extremely high power-to-weight ratios. These would be greatly degraded by adding motors and generators.
    For instance, the RR T406 offers power in excess of 10 kW/kg. Large turbofans are even better. Most electric generators and motors are worse. The best have the same power-to-weight, but since they only transfer power, this increases the weight of the engine system by a factor of 2.5-3.

  2. Wings are already the optimal location for both the generator and the propulsor.
    You want your heavy engine where the lift is created, and that's the wings. You want your propulsors away from the fuselage, and that's either the wings or the tail. Thus, there is no need to move the power any distance.

Hydrogen is a suitable fuel for turbofan engines and requires no other intermediate devices to convert it to thrust.

There is no significant need for hybrid airliners, as there's no stops to recover energy in flight.

Weight means fuel burn. Engines are heavy: in an A320neo, for example, they take up 14% of the weight. Increasing it 2.5x will make the aircraft 20% heavier. After adding payload and unusable fuel, this results in 15% more fuel burn, if the motors and generators were perfectly efficient.

Since they are not perfectly efficient, a naive replacement would result in even worse fuel consumption. This could be offset by perfecting propulsor size, speed, and placement, but the end result is still that a turbo-electric aircraft will be less efficient than a similar turbofan aircraft.

As to hydrogen itself, it is not the best aviation fuel. However, it is usable. The overall energy efficiency will be worse, due to the loss of cabin space to tanks. Whether that can be offset by clean production is a question outside of aviation.

Regardless, a 15-year horizon is so short that it can be safely said that hydrogen or electric or hybrid airliners will not be anything more than concepts and experiments in this timespan. 75 years, that could be a topic for debate, on appropriate sites.

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