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Electrifying flight: very different aircraft may end up taking to the sky

economist.com

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Re: Electrifying flight: very different aircraft may end up taking to the sky

#21

Post by obataroter »

akiselev wrote: post #14
waqf wrote: post #11

Earlier quoted context omitted.

How about solar-powered planes? I would assume not having to carry an energy source (except for emergency use) is a huge efficiency win. And it's always sunny in the stratosphere (well, not at night).

There's a very strict limitation on solar planes that depends on the panel efficiency and other material science avances as well as the shape and, especially, its height. The bigger you make the jet, the more of its surface you have to cover with solar panels. However, while the mass grows geometrically with the size because of volume, the surface area of the panels only grows exponentially (x^3 vs x^2). Just like wi…

> geometrically [...] exponentially

Cubically and quadratically?

Re: Electrifying flight: very different aircraft may end up taking to the sky

#22

Post by erikpukinskis »

ams6110 wrote: post #5

Li ion batteries still have a LONG way to go in energy density compared to Jet A kerosene. Jet A, about 43 MJ/kg. Lithium ion, <1 MJ/kg.

If the density doubles every 10 years that means we're 50 years to parity. And we don't need to get to parity in order for there to be at least one economically feasible design. there might be some cases where reliability and availability of fuel are at a premium and an aircraft could be viable in half that. Which means now is exactly the right time to start experimenting if you're a plane manufacturer.

Re: Electrifying flight: very different aircraft may end up taking to the sky

#24

Post by ohazi »

PietdeVries wrote: post #19
ams6110 wrote: post #5

Li ion batteries still have a LONG way to go in energy density compared to Jet A kerosene. Jet A, about 43 MJ/kg. Lithium ion, <1 MJ/kg.

There might not be a need to equal the energy density of jet fuel in a battery. If the efficiency of the engine and propulsion improve significantly compared to fuel jets, an electrical system might not need that much energy after all. See the hybrid car: the efficiency of a regular engine (VW Diesel not taken into account ;-) is relatively low. If an electrical engine can be twice as efficient, you only need half th…

Wait, what? A good electric motor is already ~90% efficient. How are you going to double that?

Re: Electrifying flight: very different aircraft may end up taking to the sky

#25

Post by alkonaut »

ams6110 wrote: post #5

Li ion batteries still have a LONG way to go in energy density compared to Jet A kerosene. Jet A, about 43 MJ/kg. Lithium ion, <1 MJ/kg.

You have to consider the system as a whole. The kerosene tank with kerosene, plus the motor and gearboxes = X kg. The battery + The electrical motors and driveline = Y kg.

Example take a small aircraft as an example:

- Combustion: Motor 150kg (1kW per kilo) fuel 100kg (43MJ/kg) = 250 kg, 4300MJ

- Electrical: Motor 20kg (5kW per kilo) batteries 230kg (1MJ/kg) = 250kg, 230MJ

The amount of batteries carried is more than twice the weight of the fuel, so the difference in carried energy between those planes is now no longer 43x, its Now consider any additional weight we didn't count here (gearboxes or other drive line components), the complexity of those planes, e.g. the number of moving parts. Also consider noise level, fuel economy, environment, reliability. For multi-engine craft it becomes even more pronounced. I don't think batteries will ever need to come close to the energy density of combustible fuels for electric flight to be viable.

Re: Electrifying flight: very different aircraft may end up taking to the sky

#26

Post by kruczek »

ohazi wrote: post #24
PietdeVries wrote: post #19

Earlier quoted context omitted.

There might not be a need to equal the energy density of jet fuel in a battery. If the efficiency of the engine and propulsion improve significantly compared to fuel jets, an electrical system might not need that much energy after all. See the hybrid car: the efficiency of a regular engine (VW Diesel not taken into account ;-) is relatively low. If an electrical engine can be twice as efficient, you only need half th…

Wait, what? A good electric motor is already ~90% efficient. How are you going to double that?

By reducing wasted energy by half, thereby increasing efficiency to ~95%.

Re: Electrifying flight: very different aircraft may end up taking to the sky

#28

Post by gambiting »

The batteries have also another problem not mentioned in the article - you have to carry their weight for the entire duration of the flight, while with regular fuel you burn it up during the flight, making the aircraft lighter and more efficient. Not to mention, that many aircraft can't land with their tanks full - but electric aircraft will have to be able to land with the same weight they took off with.

Re: Electrifying flight: very different aircraft may end up taking to the sky

#29

Post by leoedin »

tajen wrote: post #27

The article raises all hopes, then finishes with the necessity of developing superconductivity.

We have developed superconductivity. MRI scanners wouldn't work without it. The problem is that it needs to be cooled to very low temperatures, which requires complicated plumbing and expensive cryogenic gases. Not really something viable on an aircraft. Superconductors have been slowly improving in operating temperature though - perhaps the temperatures found at aircraft cruising altitude are within reach?
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