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Comment by momenti | Hacker News Reader

Lilium's plane has 30 engines, multiple independent battery packs, and electric motors are way more reliable than jet engines (due to being so much simpler). A Lilium plane may have a 1000x higher chance of a crash in case of full engine failure, but perhaps that can be compensated for by 1000x times simpler/redundant propulsion technology. This seems to be very hard to assess in theory, so we probably just have to wait and see how it performs in practice.

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That's all very well, as long as there's no common modes of failure. Redundancy can be a means to achieve reliability, but not always. Imagine the cause of failure is a bug which kicks in at a specific time of day, or an integer overflow which happens after a certain amount of uptime, or all the motor drivers are susceptible to a specific RF frequency. It doesn't matter how many motors you have if they're all susceptible to the same failure mode.

That's what certification is there for, isn't it?

> integer overflow which happens after a certain amount of uptime

It’s not just electric powered planes that have to worry about such things… this was an issue for the Boeing 777 Dreamliner too. If it was powered on for longer than 248 days, it could lose all electrical power due to an overflow in the generator.

https://www.engadget.com/2015-05-01-boeing-787-dreamliner-so...

I’m not saying it isn’t a concern, but rather it is a concern for all planes (and vehicles for that matter). Many commercial passenger planes are now fly by wire. If you lose electrical power, you’ll also lose control. So, while we’re talking about purely electric planes, the problems are universal.

But many planes can glide to a certain degree.

This thing would just fall or glide with zero pilot control. No control surfaces.

At some point at least their design also included a whole plane parachute. I don't know if that's still the case.

> 1000x times simpler/redundant propulsion technology

This is a contradiction.

A system with that level of redundancy will have a corresponding increase in complexity of management systems. That means software (multiple copies of software on multiple independently powered computers all somehow coordinating). This makes the management software the single point of failure, and frankly I'd sooner trust a 50 year old pair of mechanical engines to a 5 year million line of code program.

You can always build things more safely with more resources (more maintenance, more checks, more testing etc.), the question at the end of the day is whether it is economical. I don't think this question can be answered upfront in this case.

30 engines = 30x the chance that at least one will fail. Maybe one is tolerable. How many can it lose and still fly?

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