[HN Gopher] The Lilium Jet ___________________________________________________________________ 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 ___________________________________________________________________ (page generated 2022-10-04 23:00 UTC)