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The Lilium Jet

The Lilium Jet

143 comments

·October 1, 2022

z9znz

I'm glad people take on crazy projects and push them to some level of completion. That's how we learn and progress overall. Unfortunately for the people who do follow through with unconventional ideas, actually getting a thing to work doesn't necessarily mean (financial) success.

In this case, there's really one big benefit at the cost of a lot of negatives.

It can VTOL/VSTOL. Most fixed wing airplanes cannot do that. So it can theoretically take off in a parking lot or a helipad or a small field. That's really the only plus as I can tell.

The negatives are many compared to a traditional plane. In no particular order:

Less efficient cruising due to much more drag from all the ducts and engines.

Much less likely to fly with engine failures as they can dramatically affect control (since they are essential parts of the control system).

Less control surface stability with mechanical or hydraulic failures. Those engines mounted on the surfaces hanging off a hinge are very heavy, and in some failure cases they would hang low and create immense drag.

Yaw (rotational) control is highly dependent on working engines on both sides.

The glide ratio of the aircraft would be very poor with all the drag, even assuming the surfaces were still controllable (not hanging).

I didn't see, but I assume a parachute is part of the plan for this. I doubt it could pass certifications (at least to carry passengers) without it.

jasonwatkinspdx

I think you're mistaken about a few things.

> Less efficient cruising due to much more drag from all the ducts and engines.

So, I read through some of Boeings research in this area years ago. The array of fans ends up acting like an insanely high bipass ratio turbofan. In the case of hybrid aircraft the combination is more efficient when cruising. The efficiency of a fan producing a given thrust or drag goes up with disk area, as it can spin slower and the local speed mismatch to the airstream is less. The array of fans acts like a giant disaggregated disk in this regard.

> Much less likely to fly with engine failures as they can dramatically affect control (since they are essential parts of the control system).

These are electric motors and batteries. Electric motors are extremely reliable, and in this case we have a high degree of redundancy. This thing is almost certainly more reliable than a single engine helicopter.

> Yaw (rotational) control is highly dependent on working engines on both sides.

The flaps can help with that, it's not solely reliant on differential thrust. There's plenty of precedent for yaw control of flying wings.

> The glide ratio of the aircraft would be very poor with all the drag, even assuming the surfaces were still controllable (not hanging).

You can't evaluate aerodynamics by eyeball, and that goes doubly for active devices like these wings. It's the net circulation pattern around the wing that matters, and you have no actual information about that, just assumptions. Likewise that there's some novel fault problem with a movable flap just because it has fans on it. You realize airliners have huge flaps that deal with much more substantial forces?

ehnto

On top of being reliable, an array of electric motors in a control loop will be able to compensate for a loss of one or more motors. I imagine this thing could probably fly with a number of it's motors offline.

crhulls

I'm not sure if all your comments are fair. For example, fly by wire is extremely reliable, and the large number of engines provides huge redundancy and arguably much more safety in certain constrained environments.

If a plane engine fails, you can glide, but you need a nearby road or field. If a helicopter engine fails, you can auto-rotate but have very little margin for error and need forward momentum. There are also more single point failure parts in both helicopters and fixed wing planes.

If you get a partial failure on a Lilium you probably have much more flexibility to do an emergency landing as you have the other engines for control and redundancy.

I'm sure it will take a while to work the kinks out, and sure there are tradeoffs, but I'm not sure this is a jack of all trades master of none situation. I could see the jet carving out its own niche.

And yes, it could be a huge flop, just sharing a counterpoint.

_hypx

All VTOL aircraft have the same issue: Insane energy consumption. There's a reason why quadcopters have flight times measured in minutes, and why helicopters never came close to displacing small aircraft. This will be no different.

zlsa

Quadcopters have short flight times because they need to use batteries. Commercial helicopters regularly have 3+ hours of flight time.

(Of course, Lillium's aircraft is battery-powered. But it's not fair to say that an aircraft capable of VTOL will always have a dramatically reduced endurance compared to a non-VTOL aircraft, especially since this one can transition to fixed-wing flight.)

_Microft

I commented elsewhere here on the video of a test flight. In that video they achieved that the aircraft flew like a normal plane with lift provided by its wings.

This mode of flight is said to be ten times more efficient than the helicopter mode during VTOL. That is: for each minute that they can cut from flying like a helicopter during starts and landing, they gain ten minutes of normal flight time.

I think the energy argument does not apply that much more than for other small electric aircraft.

mschuster91

The key difference is that VTOL / hovering with its associated energy consumption will only be required for start and landing.

captainredbeard

Fly by wire sucks because you don’t get feedback from the control surfaces. Are you even a pilot or just an avgeek?

coredog64

Boeing engineer from Everett has just logged in :) Seriously though, Airbus has had FBW for decades and there’s an entire subset of the population of commercial pilots that rave about it.

crhulls

Yes I’m a private pilot and I enjoy aerobatic planes with lots of direct feel. This is a robotic air taxi - what is the relevance of tactile feedback?

And your premise is more broadly incorrect. The f16, which was developed to dogfight, has had fly by wire for decades. The fly by wire allowed far greater control.

https://www.f-16.net/articles_article13.html

rgmerk

For what purpose?

Enthusiasts and race car drivers like lots of feedback through the control surfaces of their cars.

Most people don’t care, lack the skill to interpret that feedback anyway, and rely on driving well within the car’s limits and/or electronic safety nets to save them when they get it wrong.

Who do you think represents the closest analogue to the majority of Lilium aircraft operators in the long term?

engineer_22

You repeatedly mention engines, but I'd point out there are no engines on this craft. This craft has electric motors.

I don't know if electric motors are more reliable than ICE, but I speculate that they are.

------ Edit, my opinion below:

VTOL is a HUGE WIN. It's the holy grail of flight. Fixed wing aircraft are inconvenient because they need a mile of flat blacktop for takeoff and landing.

Affordable eVTOL craft could change general aviation forever. The problem with helicopters is insane maintenance overhead and low fuel efficiency. The problem with fixed wing is you can't land it in your back yard. EVTOL is interesting in that it could bridge the gap between these two to provide a personal aircraft that has the best of both. Napkin math shows it's possible, and we're seeing some really cool products now.

balderdash

The VTOL only matters if it’s cheap. Most of the airports in the US are lightly used because general aviation is expensive, not because people are thinking “I would buy/charter a plane, but driving 20min to the local airfield is just not convenient enough”.

Typical general aviation aircraft (which this seems comparable to) need <1/4 mile runway (e.g. a Cessna 172 is less than 1000ft) which in the US means ~20k available airports.

My point being, the reason those airports are lightly used is driven by cost not that they inconvenient.

rgmerk

In any decent sized metro area inconvenience is a big deal.

My family had a weekend at a popular vacation spot about 80 miles from where we live (about 2 miles from the downtown area of Melbourne, Australia).

The drive takes roughly two hours door to door.

We’re in a suburb that happens to be on the right side of the city to be close to the GA airport, but it would be a 20 minute drive to the airport, say a 30-minute flight, and another 20 minute drive from the destination airport to our accommodation. If you could do the transitions between car-plane-car in less than 20 minutes total I’d be very surprised; net result, you’re saving maybe 30 minutes on the trip.

If you could put VTOL ports within 10 minutes walk of each destination (say 500 metres) you could cut the trip down to less than an hour.

To be fair, the amount of luggage you’d have to carry/push in this scenario might well still tip the balance in favour of the car for the holiday trip, but there are plenty of other scenarios where similar trips are made without the need to carry a mass of luggage where the VTOL is a massive win.

a_shovel

For most people, "motor" and "engine" are synonyms. Is there a technical difference between the two terms?

yodon

There are people who feel strongly that one is only for electric, on non-electric, or combustion, or thermodynamic, or other classes of thing, kind of like a boat-vs-ship distinction. It is certainly more common to talk about an electric motor than an electric engine, for example.

That said, both terms have been used for a very long time for a very wide range of overlapping things. MIT has a nice history[0] of the words and why they are essentially synonyms in most cases (with engine being more appropriate to use in non-mechanical contexts like search engines and economic engines and motor being more appropriate to use as a gerund like motoring through something or motoring around the countryside).

[0] https://engineering.mit.edu/engage/ask-an-engineer/whats-the...

andyferris

I thought the term was originally "motor engine" (a piece of engineering that produces motion) in the same way we can have a "compute engine" or a "siege engine" or a similar name for any other _ingenious_ creation.

From there we tend to shorten it to either motor or engine. Perhaps in current times people here the terms "combustion engine" and "electric motor" most commonly and assume there is an implied distinction.

NonNefarious

I would trust motors over an engine any day. Look at the contraption that is an ICE: You have fuel-, oil-, and air-delivery systems... you have ignition systems... you have mechanical parts violently changing directions thousands of times per minute...

A motor is metal spinning in a magnetic field, powered by chemical reactions in a battery.

Which seems more likely to fail?

14

I agree with your assessment but also think with the size of this plane it is a good candidate for the parachute system some planes already have. Maybe making that a requirement is a good middle ground.

anovikov

As for the engine failures, it's a lot safer because it has so many of them. It can fly with engine out, probably counterbalanced with another engine being switched off on the other side.

kybernetikos

This is very cool. But it's also spending a lot of novelty points. I thought energy density was still a huge problem, so it seems weird to try to solve the problem of electric planes with acceptable range at the same time as tackling the enormously energy intensive problem of VTOL.

tlb

Those are related. Part of what makes engine-powered VTOL difficult is the engines. The V-22 Osprey has two propellors and two engines, but in order to handle an engine failure, there's a complicated driveshaft and gear arrangement across the middle of the aircraft to send power from the working engine to the other propellor. I don't know that anyone has seriously tried more than 2 engines for a VTOL system.

Electric power allows you to have lots of small fans, a few of which can fail without disaster.

Also, throttling turbines up and down fast enough to stabilize an aircraft doesn't seem to work well.

scarier

There are a number of VTOL aircraft that have used multiple engines. The Yak-38 used two lift engines and one lift-cruise engine, the VJ101 used four lift-cruise engines and two lift engines, and the Do 31 used two lift-cruise engines and eight(!) lift engines. Out of these, only the Yak-38 was remotely successful, and not nearly as much as the single-engined Hawker Siddeley Harrier (and its derivatives).

There are plenty of ways to stabilize an aircraft without relying on pure engine thrust, and turbofan aircraft have some advantages here.

The distributed electric propulsion systems do have awesome redundancy, but they have significant losses in efficiency compared to fewer, larger props, which really isn't what you want in an aircraft with severe energy density limitations. I'm curious to see what the production Lillium's payload, range, and power margin end up being.

nradov

There have been a few flying VTOL prototype designs with more than two turbine engines. The extra engines were used for powered lift during takeoff and landing. But that approach turned out to be impractical due to safety, cost, and weight.

https://vtol.org/vstol/wheel.htm

lordofgibbons

It makes sense why they'd do this.

Given current energy density of batteries, electric planes are only useful on very short flights. If you can only operate out of airports (without vtol), the useful range of the airplane will be significantly reduced

kybernetikos

Great point. Reading a little more https://lilium.com/newsroom-detail/technology-behind-the-lil... you're exactly right, and the same thinking drives the requirement of low noise and the ability to utilise helipads.

nradov

There aren't many helipads either. Outside of regular airports, only a few urban areas have any helipads available for commercial use. More can potentially be built but that requires large open areas free of obstructions. Adding helipads to existing building roofs is generally impractical due to weight and safety issues.

NonNefarious

"If you can only operate out of airports (without vtol), the useful range of the airplane will be significantly reduced"

Why do you say that? That's backward. VTOL consumes a huge amount of energy, far more than a traditional rolling takeoff.

vidarh

"Acceptable" range is short - they're not really trying to compete with planes, but with other modes of transport.

trollied

I had this pop up as a recommendation on youtube. Video of a test flight, VTOL: https://www.youtube.com/watch?v=ywJWka1evH8

_Microft

The interesting part seems to be happening around 1:20-1:30 minutes into the video. The main wings and canadards (that's the smaller wings at the front) are oriented fully parallel to the direction of flight. The threads indicating the flow of air over the surfaces are no longer moving around and therefore air is moving smoothly over the wings. The aircraft seems to be relying fully on lift provided by the wings instead of the engines. As far as I know they hadn’t achieved that before.

The thrust required for level flight with lift provided by wings is said to be ~ 10% of what is required for vertical take-off and landing.

https://youtu.be/ywJWka1evH8?t=82

narrator

The hydrogen conversion of the Cessna Caravan seems a little more practical. Hydrogen is bulky, but light. Fuel cells aren't cheap though. However, hydrogen is quick to refuel unlike battery charging. I think the weight to power is better with hydrogen than li-ion and weight is the most important thing for aviation.

https://www.militaryaerospace.com/commercial-aerospace/artic...

stareatgoats

Hydrogen will likely win out ultimately, once they have figured out which high density solid-state hydrogen storage solution is the most viable for aviation. It's not going to be the most energy efficient (many big losses in the process of converting to water to solid-state hydrogen), but it is vastly safer than the alternatives and will likely at least enable long range green air travel, at long last.

coderenegade

Solid state hydrogen storage typically only gets you to a maximum of 20% hydrogen by weight, which is equivalent to ammonia. Ammonia also lets you liberate all of the hydrogen, whereas hydrides don't.

If you want to use hydrogen for aviation, LH2 is really the best answer, since the percentage hydrogen by weight is much higher. The next best thing would probably be an sofc using hydrocarbon fuel, if you really wanted to go electric, but still needed endurance.

chroma

Hydrogen fuel cells won't happen. There are too many downsides.

Hydrogen must be stored as a compressed gas or as a deep cryogenic liquid. Either way such tanks are expensive, heavy, and create safety concerns. Hydrogen is a very pernicious molecule, and leaks cannot be detected by human senses. All hydrogen vehicles and fueling stations need special sensors to detect leaks. Hydrogen is much easier to ignite than gasoline. Any concentration from 4-74% will explode in air, and the flame is nearly invisible.

Refueling a hydrogen tank involves going from high pressure to low pressure, which causes the fuel line and nozzle to get extremely cold. Even in southern California, refueling a few Toyota Mirais causes the nozzle to freeze to the valve. This limits refueling speeds and duty cycles.

Lastly, hydrogen is far less efficient as an energy storage medium. With a battery, you put electricity in and get electricity out. It's 80-90% efficient. With hydrogen, you use electricity to split water, then compress and liquefy the hydrogen, then run it through a fuel cell. The fuel cell itself is 40-60% efficient. At the end of the whole process, around 30% of your initial electricity comes out of the fuel cell.

narrator

Sure, hydrogen is not good compared to batteries as an energy storage medium, but making synthetic fuels from solar power is also massively inefficient. Biofuels is a huge waste of farmland, fertilizer, etc. This downside compared to batteries is why hydrogen will not be used in cars or boats, but the weight of hydrogen is a big enough advantage that it will probably be used in medium haul planes. Long haul planes will probably rely on biofuel or synfuel, but zeroavia.com claims they'll get to 5000 nm range eventually.

pfdietz

Very long term, I'd bet (if I could live that long) on long haul planes powered by lasers from space.

_hypx

Long-distance battery airplanes are literally impossible. If you don't agree with hydrogen powered aircraft, you are advocating for conventional airplanes forever.

jamiek88

That’s ridiculously short sighted to think out only options are hydrogen or the status quo.

Off the top of my head I can think of biofuels plus carbon neutral recaptured co2 from excess renewable energy.

Diesel electric motors for example with the ‘diesel’ being carbon neutral biofuel. This is actually being tested on large airbus jets currently.

Hydrogen is one of the worst possible options for aircraft. Energy density is crap, tankage is heavy, failure modes catastrophic.

chroma

I don't have a dog in this fight. I'm just explaining why hydrogen will never be popular. For a new technology to be adopted, it has to be better than the status quo. Compared to current aircraft, hydrogen costs more, has new safety concerns, and requires new infrastructure to transport and store the fuel. If that means aircraft will keep using fossil fuels, well then I guess we'll keep using fossil fuels.

null

[deleted]

ZeroGravitas

I think hydrogen (or something made from it) and fuel cells will win in the medium term. It's energy inefficient, but we're going to have a lot of cheap energy which will make lots of energy inefficient things reasonable, as long as you can store the output in some way.

Having said that, with future automatiion, I do feel there's room for aircraft that combine and re-assemble themselves in mid air. For example, a VTOL tug that lifts off and starts a craft flying, but then detaches and returns to base.

This can potentially be repeated on the landing side, and even mid-air "re-fueling" via battery drones.

Possibly I just watched too many kids shows where vehicles did this and it's now my equivalent of the Jetson's flying cars.

Feels like the next crazy project for Silicon Valley Billionaires to look into now that electric flight, jetpacks, rockets that land vertically etc. are all solved problems.

nradov

Forever is a long time, but our grandchildren will still be taking long-haul flights on conventional aircraft powered by turbine engines burning kerosene (possibly synthetic). The advantages of liquid hydrocarbons over hydrogen fuel are overwhelming in terms of safety, handling, and aerodynamics.

pfdietz

Or synfuels from atmospheric CO2 capture, or laser power beaming.

mattmaroon

I’ve been wondering also why fuel cells aren’t used. Hydrogen is less energy dense than fossil fuels in terms of energy per unit of volume, but much more dense in terms of weight (almost 3) and far far more than batteries, which matters more in aviation.

It seems like an obvious choice to me.

6stringmerc

I bet they will be for transport zeppelins when an in between for cargo ships and planes becomes viable, kind of like a nuclear submarine.

sacrosancty

Squared-cubed law for tank weight and fuel weight. So hydrogen will have poor energy density at small scales. Not sure where it dips below that of batteries but rockets are OK with it, so smaller than that.

Perhaps if you store it in a balloon? But then volume would bed a problem for an aeroplane.

mattmaroon

The square cubed law argues in favor of something that is more energy dense by weight but less by volume right? You make the wings a little bigger and the surface area increases a lot less than the volume. There’s also the potential of enlarging the fuselage and storing some there too.

pfdietz

Rockets are in fact often not ok with that. Using hydrogen in the first stage of a launcher is a bad idea.

VBprogrammer

Hydrogen is light but tanks capable of 10,000psi don't tend to be. Nor particularly are cryogenic tanks but at least that improves the situation volume problem by an order of magnitude.

conradev

When you get to the size of airliners, though – so much money, time and effort has gone into designing, producing and operating the existing airliner fleet that it makes sense to invest in biofuels rather than completely new airliners:

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

senectus1

why not Ammonia? Ammonia has a higher energy density, at 12.7 MJ/L, than even liquid hydrogen, at 8.5 MJ/L. Liquid hydrogen has to be stored at cryogenic conditions of –253 °C, whereas ammonia can be stored at a much less energy-intensive –33 °C. And ammonia, though hazardous to handle, is much less flammable than hydrogen.

jsjohnst

You sure of those numbers? While this [0] compares liquid ammonia to pressurized hydrogen rather than liquid hydrogen, I doubt the energy density would drop that much to give up the advantage of hydrogen over ammonia.

[0] https://www.researchgate.net/publication/347258594_Operation...

joe_the_user

If you can switch battery packs, refueling could be very quick.

mikepurvis

And even though they're heavy and bulky, it's much more tractable to install that infrastructure at a few dozen key airports, and also to manage the tracing/ownership of "fleets" of batteries.

Battery swapping has repeatedly faceplanted when it comes to cars, but it's a pretty different scope of challenge, and it seems like every major issue is more favourable to aircraft.

On the other hand, planes are often on the ground for 2+ hrs between flights anyway, so maybe it could be realistic with enough power delivery capability to just charge a big pack in situ. Certainly simpler to plug in a big umbilical at the gate than having to have another ground vehicle reaching into the belly of the thing.

_hypx

Absolutely not. Airplanes have to be aerodynamic, and it would be incredibly challenging to make the entire bottom portion of the plane something that can open up and fit a giant battery. Never mind the weight of the whole system plus battery. The whole idea is absurd and completely impractical.

nradov

Batteries power will only be feasible for short-haul flights, and those have much shorter turn around times. Southwest Airlines has it down to 35 minutes. Recharging within that time limit might eventually become feasible but it's going to take some further battery innovations.

consumer451

Wisk[0], backed by Kittyhawk and Boeing seems like they may have a more practical vehicle, and in some ways it is much further along.

Flight Chops has a great video[1] showing a bunch of details, including the addition of "Digital Flight Rules" to VFR and IFR. Though I do love Lilium's aircraft, it is definitely more of a sports car.

[0] https://wisk.aero

[1] https://www.youtube.com/watch?v=yrEeCp5xJj8

googlryas

Why is kittyhawk investing in airplane startups, when they themselves are an airplane startup? Is that just a sign of too much cash to burn with too few ideas?

Not that it matters much anymore...

addaon

Wisk was spun off from Kitty Hawk when Boeing invested.

rootusrootus

Sounds like Kittyhawk is shutting down [0]. Is the future of Wisk in question?

[0] https://aviationweek.com/business-aviation/kittyhawk-shut-do...

psadri

I always wondered if this could work, that is if it'd be more energy efficient that using fuel/batteries to reach cruising altitude:

- use lighter than air balloon to life an aircraft to cruising altitude

- transition to powered flight while collapsing the balloon (by compressing the gas into liquid form?). Or maybe detaching from it?

- cruise

- at destination, glide towards touch down?

lmm

> use lighter than air balloon to life an aircraft to cruising altitude

Interesting thought, but that would mean you've got aircraft ascending slowly right through the entire airspace with limited control. Difficult to imagine it would be workable at busy airports.

> Or maybe detaching from it?

Consuming a balloon's worth of helium every flight is a non-starter, and hydrogen is probably unacceptable to passengers. Landing a balloon is also not cheap or easy, even without passengers.

> at destination, glide towards touch down?

Almost all planes essentially do this already, they'll reduce thrust and start descending a long way out.

pqdbr

Those are crazy ideas. I love them. Anywhere they have been experimented with before?

psadri

Looks like quite a few companies worked on the idea for orbital launches -- lift a rocket with a balloon and then launch from a high altitude.

Ekaros

Rocketry really isn't about height but speed. And balloons don't actually help so much with that. At least if you want to stay up there once the lift is gone.

6stringmerc

There is a lot of talk about horizontal launch for spacecraft - I’m pretty sure steam catapults and aircraft designed to use them could change things as well.

cpursley

Can we pass a federal law prohibiting scroll-jacking?

bestest

Absolutely. I closed the tab once I felt being molested by the scrolling mechanism hijack.

Sophistifunk

Or kickstart a team of black-ops mofos.

zac23or

All electric airplane designs today appear to be frauds (like all crypto currency projects), because no one airplane project answers the most important problem: battery power density.

karamanolev

Kind of tongue-in-cheek, but I want to know what's the project that scores the most fraud points, while still being serious - blockchain, electric-powered, self-driving/flying airplane/car/submersible hybrid sold as NFTs?

yencabulator

... with quantum 5G edge cloud AI self-driving.

nradov

That's not quite fair. The Pipistrel Alpha Electro trainer aircraft is FAA certified and in active use by flight schools today. Endurance is very limited due to low battery power density, but it is adequate for basic flight training.

https://www.pipistrel-usa.com/alpha-electro/

But these other eVTOL designs are probably just too early. It will take several more generations of battery improvements until they become economically viable.

kybernetikos

zac23or

It's nothing, it's a Pr text.

kybernetikos

I don't disagree, but what do you expect to be shared with the public? They've acquired battery IP, they show the power charts, they talk about the difficulties of discharge at low states of charge. Their whole design is focused on short distances with very short time spent in hover.

They may not be correct (and they seem to have assumed at least 5 more years of basic improvements) but the suggestion that they haven't addressed the problem at all is just wrong.

nharada

I feel like they make it pretty clear the design constraints (and thus business constraints) they're operating under. They have a working prototype. I think this project is incredibly risky, especially from a regulatory and safety perspective, but there's nothing in the laws of physics and our current battery understanding preventing this plane from existing.

You're not flying NY to LA in this thing and that's fine.

6stringmerc

Nope there’s already one flying in England testing for commercial service and its twin is about to get FAA clearance to start testing here as well.

It’s an electric aircraft with a hydrogen fuel cell system.

zac23or

> hydrogen fuel cell system.

It's not a battery.

6stringmerc

Would you consider graphene based next generation power storage a battery or something different? I'm pretty keen on the RC hobby realm and the up and downstream innovations for batteries is still on the uptick I believe. I believe there are some Experimental (by FAA standards) battery based planes flying today, which again, simply is proof of concept to counter the doom and gloom potential outcome. For what it's worth, I felt the same way for years - batteries will never work - but now I'm not so sure.

ilrwbwrkhv

Yup this is the new meta for pushing dirty money through the VC system.

J5892

My crypto project is powered by D batteries.

I don't know how dense they are, but they're pretty heavy.

LightG

Your batteries are my ... my density ... I mean, I mean, my destiny ...

(someone will get this).

hef19898

Great Scott! 1.21 GW, what was I thinking????

leveraction

Back to the Future?

loufe

I took a small plane for a work flight a couple months ago, and I feel something that's misleading about their ostensibly 7-seat configuration is the lack of space for luggage. People don't travel 200km+ often without at least a backpack. Sure some flights will be ok but I think many operators would use a configuration for this size of 5 seats with the back row for luggage.

yencabulator

This is a rich people toy, they'll have fresh clothes waiting at their destination...

w10-1

kybernetikos said it well: "spending a lot of novelty points"

I would add: in a highly-regulated domain that segregates risk. FAA wants designs that won't kill people (including bystanders) when systems fail.

Battery: using lithium with silicon anodes: unproven at scale?

For landing, the Illium offers only a 60-second reserve after a expected 20-second hover. But can take time to land, particularly in wind: 20-80 seconds is too short. And since it is landing on rooftop helipads, without more reserve you could kill people just by blocking the helipad.

Perhaps they could take-off via hover and land conventionally, but that would require stronger gear placed differently.

Design: This relies completely on fans for directional stability?

FAA even for experimentals, helicopters, etc. requires controllability on power failure, and e.g., 30 minutes of reserve power, more at night.

It's doubling risk to integrate power and control, and engines into the wing. If some fans fail, you're adding controllability to power loss; it's unclear other fans could depower dynamically as required. And what if a fan goes catastrophic -- breaking the wing or nearby fans or control lines? Commercial airplanes can fly even when their engines blow up because the engines are largely segregated from flying and control surfaces (unlike military jets).

I could imagine a more conventional hybrid stepping-stone to this ultimate concept.

If you put fixed horizontal ducted fans at the front and rear of the fuselage, you get the benefit of lower disc loading for the bulk of vertical hover thrust. With colocated batteries, this would reduce power transit. On failure of both, fall back to conventional landing. On failure of one, balance out with tandem-wing alternate.

As an aside: for homebuilt tandem-wing airplane, search for Rutan Quickie or Q200

carstenhag

About the helipad blocking thing: supposedly these rooftop things have similar security gates like on airports. The helipad itself would be a restricted area. Would be relatively safe imo. But of course, that's not enough for regulators in the US/EU.

polar8

Why do electric planes like this one have many smaller motor, as opposed to 1-4 engines like typical planes do?

iijj

It's called Distributed Propulsion, and it theoretically has advantages over normal aircraft propulsion. Presumably using dozens of piston or turbine engines has enough drawbacks to make it not worth it, which is why it hasn't been a thing until electric planes became possible.

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

pvorb

Perhaps it has to do with being failure-safe?

mikepurvis

With a conventional turbofan (or basically gas-anything) the bigger it is the more efficiency gains can be realised. So I'd expect that conventional jets would really ideally have just one engine, and they typically have 2 or 4 for reasons of fault tolerance and isolating noise from the fuselage.

None of this applies with electric, particularly a cleansheet design.

UncleOxidant

But then they would've been using many smaller ICE or jet engines already to get redundancy. I suspect the reason is that it's easier to get that kind of redundancy with electric motors - they're more compact, lighter weight, less overhead for each.

jasonwatkinspdx

We do. It wasn't until the 80s that twin engine airliners were certified for long flights. Before then it was 3 or 4 engine only. It took a lot of effort to get jet engines that reliable too.

Single vs dual engine helicopter is a big safety distinction. There's heavy lift and military helicopters with 3 engines.

entropicgravity

Here's a youtube (June 2022) about Lillium by the company and it covers off a lot of the engineering questions. [1]

[1]https://www.youtube.com/watch?v=qZ73PftBfFg