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Comment by noodlesUK | Hacker News Reader

At what point does it become simpler to do hydrogen powered flight and use renewables to break water? Hydrogen is much easier to fly a plane with than batteries from what I understand.

edit: I mean that we would split water on the ground to make hydrogen.

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Synthetic liquid methane would probably be more practical because it is so much more energy dense than hydrogen. Audi already has a pilot plant that does this.

https://en.wikipedia.org/wiki/Power-to-gas

You can also run standard jet engines on biodiesel.

https://en.wikipedia.org/wiki/Aviation_biofuel

Both options are far more realistic than electric airliners, which simply aren't possible with any battery technology which will exist in the foreseeable future.

https://www.youtube.com/watch?v=VNvzZfsC13o

NASA's interest in electric aircraft is most likely motivated by the possibility of flying them on other planets.

https://en.wikipedia.org/wiki/JPL_Mars_Helicopter_Scout

https://www.bbc.com/news/business-48630656

"This week's Paris Airshow saw the launch of the world's first commercial all-electric passenger aircraft - albeit in prototype form.

Israeli firm Eviation says the craft - called Alice - will carry nine passengers for up to 650 miles (1,040km) at 10,000ft (3,000m) at 276mph (440km/h). It is expected to enter service in 2022."

"Eviation has already received its first orders. US regional airline Cape Air, which operates a fleet of 90 aircraft, has agreed to buy a "double-digit" number of the aircraft."

Carrying 9 passengers 1040 km at 440 km/h is quite a lot different than carrying 180 passengers 6150 km at 840 km/h (Airbus A320). Because batteries do not get lighter as you discharge them (fuel tanks do), simply adding more batteries gets you rapidly diminishing returns. Short range electric aircraft already exist, but transcontinental flights are likely out of reach. And if you are only traveling 1040 km, wouldn't you be better off taking a train anyway?

Surely you can't fly with only 1 engine right on the wingtip even if it has the thrust?

It has three engines, not 1?

Yeh but the media on it keep banging on about having redundant engines. I don't think redundancy counts when if that one the fails is a wingtip.

Looks like some of these proposals in the article are for hybrid systems with electric motor assist to the turboprop/fan during takeoff and landing so that the liquid fueled jet engine can be sized for the most efficient cruise at altitude.

On the other hand, Musk sees an electric plane in about 5 years so there are differences of opinion by people in the know.

https://electrek.co/2019/07/01/tesla-electric-airplane-elon-...

Has anyone got a sense of what the issues are with moving to bio fuels/ liquid methane for aircraft?

It looks as if it's going to have to be at least a medium term solution, I havent really heard much talk about them though. Is that just because they aren't sexy compared to electric planes?

„In 2013 the round-trip efficiency of power-to-gas-storage was well below 50%, with the hydrogen path being able to reach a maximum efficiency of ~ 43% and methane of ~ 39% by using combined-cycle powerplants.“

Not great, not terrible.

Seeing the ecological catastrophe that biofuels are, I hope they never make planes fly on that. Entire ecosystems are being burnt down to replace them with plantations :(

Just because biofuel production is not currently done responsibly doesn't mean it can never be. The same sustainable organic farming techniques that are used to grow food crops can be used to grow fuel crops, and should be. And don't forget that most biodiesel is currently made from waste products like used cooking oil.

Our farming's sustainability, on a global scale, is best illustrated by Amazon being burned down to create more farmland.

The roundtrip energy efficiency of such a system is less than 50%, and hydrogen is a very inconvenient liquid fuel (it requires cryogenic storage, very strong pressure vessels, and it leaks away rapidly). There are likely better ways to convert energy into a tractable liquid fuel.

Imagine you could store the hydrogen (protons) in a convenient, safe form called a "battery"

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