[HN Gopher] The Lilium Jet
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The Lilium Jet
Author : trollied
Score : 48 points
Date : 2022-10-01 07:30 UTC (3 days ago)
(HTM) web link (lilium.com)
(TXT) w3m dump (lilium.com)
| trollied wrote:
| I had this pop up as a recommendation on youtube. Video of a test
| flight, VTOL: https://www.youtube.com/watch?v=ywJWka1evH8
| _Microft wrote:
| 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
| 6stringmerc wrote:
| This seems viable especially as next generation power storage
| comes into the fold. Finally using the wings for sustained flight
| - something that doesn't take nearly as much energy as getting
| whatever payload off the ground in the first place.
| zac23or wrote:
| 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.
| johndevor wrote:
| Talyn does: https://www.talyn.com/
| J5892 wrote:
| My crypto project is powered by D batteries.
|
| I don't know how dense they are, but they're pretty heavy.
| LightG wrote:
| Your batteries are my ... my density ... I mean, I mean, my
| destiny ...
|
| (someone will get this).
| kybernetikos wrote:
| What level of detail do you want? https://lilium.com/newsroom-
| detail/technology-behind-the-lil... has some discussion of it
| in Item 3 as does https://lilium.com/newsroom-detail/liliums-
| battery-strategy
| zac23or wrote:
| It's nothing, it's a Pr text.
| karamanolev wrote:
| 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?
| narrator wrote:
| 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...
| VBprogrammer wrote:
| 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.
| stareatgoats wrote:
| 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.
| chroma wrote:
| 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.
| joe_the_user wrote:
| If you can switch battery packs, refueling could be very quick.
| mikepurvis wrote:
| 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.
| mattmaroon wrote:
| 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.
| sacrosancty wrote:
| 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 wrote:
| 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.
| z9znz wrote:
| 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.
| engineer_22 wrote:
| 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.
| crhulls wrote:
| 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.
| cpursley wrote:
| Can we pass a federal law prohibiting scroll-jacking?
| kybernetikos wrote:
| 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 wrote:
| 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.
| nradov wrote:
| 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
| scarier wrote:
| 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.
| dingaling wrote:
| XC-142 tiltwing, four turboprops
|
| https://vought.org/products/assets/images/1758_005_o.jpg
| lordofgibbons wrote:
| 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 wrote:
| 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 wrote:
| 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.
| w10-1 wrote:
| 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
| consumer451 wrote:
| 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 wrote:
| 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 wrote:
| Wisk was spun off from Kitty Hawk when Boeing invested.
| rootusrootus wrote:
| Sounds like Kittyhawk is shutting down [0]. Is the future of
| Wisk in question?
|
| [0] https://aviationweek.com/business-aviation/kittyhawk-shut-
| do...
| jimbru wrote:
| Does anyone know why you would choose a ducted engine design
| here? Why not a more traditional propellor?
| chroma wrote:
| Ducted engines make less noise, which is handy for helipads in
| cities. They also increase thrust efficiency. If done right,
| the duct can contain any shrapnel if the fan blades come apart.
| The disadvantage of a duct is extra weight.
| nharada wrote:
| What kind of range does this specific vehicle get? They've said
| they're aiming for 300km but that will require density increases
| to get there, curious what it is _now_
| psadri wrote:
| 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?
| pqdbr wrote:
| Those are crazy ideas. I love them. Anywhere they have been
| experimented with before?
| polar8 wrote:
| Why do electric planes like this one have many smaller motor, as
| opposed to 1-4 engines like typical planes do?
| pvorb wrote:
| Perhaps it has to do with being failure-safe?
| mikepurvis wrote:
| 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 wrote:
| 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.
| iijj wrote:
| 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
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