
Lilium unveils five-seater air taxi prototype after a successful maiden flight - FrojoS
https://techcrunch.com/2019/05/15/lilium-5-seater/
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lazyjones
What are the tech specs of this thing? What altitude does it fly at? Does it
use the ground effect for efficiency? If not, the claimed range seems a little
too futuristic with current battery technology. 150 KW for flight (" _it will
require less than ten per cent of its maximum 2000 horsepower during cruise
flight_ ") x 1 hour range = 150 KWh and that's going to weigh more than the
maximum takeoff weight of 640 Kg according to
[https://en.wikipedia.org/wiki/Lilium_Jet](https://en.wikipedia.org/wiki/Lilium_Jet)
...

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donquichotte
In my experience, specs are omitted in technical articles IFF somebody is
trying to hide something. Like super short flight time.

The MIT battery primer [1] states a specific energy of 150Wh/kg for Li-Ion
cells. 150kWh would therefore weigh 1000kg.

Even at double the specific energy, the battery would still weigh in at 500kg,
almost 80% of the maximum takeoff weight.

If there is a future for electric airplanes, it is going to be in fixed-wing
applications.

[1]
[http://web.mit.edu/2.009/www/resources/mediaAndArticles/batt...](http://web.mit.edu/2.009/www/resources/mediaAndArticles/batteriesPrimer.pdf)

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FrojoS
But it is fixed wing! Anyway, thanks for looking into it and doing the math.

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fock
which means it's a little less stupid than what airbus is doing...

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dmitrygr
300km/h and 300km range means 1hr endurance. That means it probably cannot be
used at all for paid flights in the USA. Reserves required are greater than
that (enough fuel to fly to destination, to alternate, and then 45 mins).

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_fizz_buzz_
Those rules will be changed for electric VTOLs. There are already proposals in
the working at the FAA as well at EASA.

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beenBoutIT
The reserves are just as important for electrical VTOLs as they are for gas,
when the power runs out the thing drops out of the sky. If anything the
electric VTOLs need stricter requirements, not lower standards.

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vidarh
The point being that it doesn't need a runway. There might be opposition to
changing the rules, but rules intended for planes that needs to land at an
airport makes little sense for something that can land on pretty much any
small flat-ish surface.

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dmitrygr
Please tell me. You're over center of LA. Where's that mythical flat area
you'll land on? Oh, and how will you find it through the fog bank below you
for miles...

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m463
I think float planes might be an untapped market.

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beenBoutIT
Right above propeller boats.

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bouvin
Once in a while it is nice to be reminded that we do indeed live in the
future.

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turk73
Too bad the future is so unevenly distributed.

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bpiche
I see u

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newshorts
I love how in the video it shows 100+ people cheering and hugging each other
in blissful victory for essentially making a drone fly.

It looks extremely unstable and dangerous.

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TeMPOraL
> _I love how in the video it shows 100+ people cheering and hugging each
> other in blissful victory for essentially making a drone fly._

Agree. The plane looks cool, and there definitely were a lot of people happy
it flew, but the reactions on video look _ridiculously_ staged. It reminds me
of videos of rocket launches, except in those there's a high risk the rocket
(and last X months of work) will just blow up on the pad, and you don't get to
test-fly it beforehand. I don't think there were any outcomes possible for
Lilium other than "it works" and "it almost works".

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syntaxing
I have mixed feelings about their "electric jet engines". I'm curious if those
are more efficient than a quadcopter/plane hybrid. Though seems like the
benefits is that they are using them for flight controls. If that is the case,
they can change the airplane wing characteristics when they want which can be
a game changer.

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ricardobeat
It is a quadcopter/plane hybrid...

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syntaxing
Hmm, I would probably put this in the class of planes with VTOL functionality,
not a quad-copter/plane hybrid like Amazon and Google X's delivery drone. For
instance, a V22 is considered a plane with VTOL but not a quad-copter/plane
hybrid.

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pizzabear123
Interesting that they are using electric jet engines, 300km range and speed
isn't bad

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kwelstr
Taxi service, from airports or from any open field? Because, how loud is this
thing? I wouldn't enjoy it landing close to my house.

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LeonM
Not an expert, but I'd expect it to be less loud than a helicopter (because no
turbine engine).

But how often do helicopters land near your house? Sounds more like a case of
NIMBY.

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newshorts
Growing up on a street where the neighbors landed a helicopter at their house
a few times per month I can tell you it’s extremely disruptive. As a kid you
think it’s fun, I’m sure my dad was annoyed when he was trying to hear the tv
though.

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Wildgoose
This is described as an 'electric jet' which doesn't make sense to me.
Enclosed propellors perhaps?

Edit: Apparently the rotors that compress the air are electrically powered, so
sort of.

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TeMPOraL
AFAIK the "jet" in classical jet engines is a jet of _air_. Unlike rocket
engine, where hot combustion gases are your reaction mass, jet engines in
aircraft use fuel primarily to spin turbines that compress and move _air_ from
the front of the engine to the back of it. You don't need combustible fuel to
spin turbines - you can do that with electricity too.

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ClassyJacket
Isn't that also what a propeller does?

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moonrobin
IANAAE (I Am Not An Aerospace Engineer), but I think the key difference here
is the compression that happens with turbines as opposed to propellers which
only move the air.

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larkeith
I've always wondered what exactly differs a jet from a ducted fan - this makes
a lot of sense, thank you!

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dTal
Modern "high bypass" jet engines are actually ducted fans, with the shaft
powered by a "gas turbine" whose role is mostly to provide torque. All
propulsion units compress the air to some extent, even propellers - if they
didn't, they would be silent. However, in a gas turbine, the function of the
"compressor stage" (which is NOT the "turbine" part) is to get a lot of oxygen
in one place, where it can be combined with a lot of fuel, which makes it very
hot, which causes it to adiabatically expand a lot, driving the turbine at the
back (this is what a 'turbine' does - extract power). If the air weren't
compressed, you wouldn't be able to burn much fuel with it, and it wouldn't
get so hot and expand so much. (By the way, this is the same reason for
superchargers and turbochargers in piston engines. More air = more fuel = more
heat and expansion)

This process isn't actually very efficient at _moving_ air though, which is
why gas turbines are now mostly used to power ducted fans, propellors, and
helicopter rotors.

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magtux
This is so cool. This is the one company I was really trying to get into as an
electronics engineer. Must be fucking fantastic for everybody who worked on
it.

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optymizer
What happened? Did you go through the interview?

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grenoire
Eagerly anticipating the VTOL to horizontal flight tests, looks wobbly but
promising!

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FrojoS
Video of the two seater flight from 2 years ago
[https://m.youtube.com/watch?v=uGrAwc-
cbrY](https://m.youtube.com/watch?v=uGrAwc-cbrY)

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KentGeek
That original video looked phony to me two years ago, and in comparison to the
latest, it looks even worse. Am I completely alone in this?

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JustSomeNobody
At least they didn’t tether it:

[https://youtu.be/shlZySkGq6g](https://youtu.be/shlZySkGq6g)

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jansan
That's actually quite funny. The Lilium guys also did a much better job
cleaning all leaves near the testing area.

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Gatsky
Must be an extraordinary feeling to design something like this, bring it forth
into the world and then watch it take off.

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hef19898
Yeah, the cool thing about this company us that besides the founders all other
senior positions are held by people with a ton of relevant experience.

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et2o
Very cool. Interested in the design requirements which made 36 small jets
better suited to the task than two larger jets.

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throwaway55554
My lay person take is they're using what is basically an EDF, you spin the
impeller at high speeds sucking air in and ramming it out the back that is a
lower diameter than the front. Surely many smaller engines would be safer than
a couple of larger ones at those speeds. Also, maybe they found out it was
more efficient to use many smaller ones.

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vbuwivbiu
very cool but video way too emotional

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bond
More like a first hover... Congrats!

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ptah
surely it's intra-city not inter-city?

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vidarh
300km range, so inter-city a lot of places. I live in London - with 300km
range I could reach Manchester in an hour instead of spending an hour _getting
to the right train station_ to get onto a 3 hour train journey. Or I could
reach Calais, France in less time. Not quite enough range to reach Paris, but
still fast enough that you could pop over to Calais, go through passport
control/customs, and take another one in to Paris in maybe 90 minutes - about
the at which I could expect to have gotten onto a Eurostar train.

If they'll be able to land them enough places, close enough, and be cheap
enough, this is just about enough range to cause massive changes in
transportation patterns. I currently have one international airport within 20
minutes of my nearest transport hub. If I could get into one of these there,
I'd be able to go direct to a lot of nearby locations, or reach 6
international airports within 20 minutes and probably 20+ within an hour. I'd
be able to commute to the majority of England in the same time I can commute
to the centre of London today.... It both opens fantastic possibilities and is
a bit terrifying at the same time (in terms of driving energy demand..)

