[HN Gopher] Technology Behind the Lilium Jet ___________________________________________________________________ Technology Behind the Lilium Jet Author : dnst Score : 103 points Date : 2021-12-22 16:31 UTC (6 hours ago) (HTM) web link (lilium.com) (TXT) w3m dump (lilium.com) | SkyPuncher wrote: | If you work at Lilium, you need to make some tweaks to your | website. This was an incredibly frustrating experience, to the | point that I gave up. | | * Scroll jacking - looks pretty, impossible to use. | | * Cookie consent - It's both too large and takes to long to find | the right action. | hagbard_c wrote: | I never saw any cookie prompt since I block _cookiebot.com_. | Things seem to work just as good /bad without it, try blocking | that domain and see if it works for you - not just on this site | but all others which use these "services". | Centmo wrote: | I was a core engineer in a different manned eVTOL project, so | have spent a lot of time thinking about this technology and | watching the space. Lilium raised some eyebrows recently with | their SPAC IPO valuation of over $3B, without having released | footage of a single manned flight. The prototype is unique and | aesthetically appealing, but my engineering mind recoils at the | complexity of the design. The variable pitch blades, the | adjustable exhaust nozzles, the tilt-wing vectored thrust system, | etc. With complexity comes cost, maintenance, and exponentially | increasing failure modes. Safety is paramount in aviation, so all | flight-critical failure modes require redundant backup systems, | which further increase cost and complexity. It's a slippery | slope. | | The eVTOL space is currently seeing a Cambrian explosion of | different design concepts, but the first to see economic | viability I think will be the simpler ones. | anonymouse008 wrote: | > The eVTOL space is currently seeing a Cambrian explosion of | different design concepts, but the first to see economic | viability I think will be the simpler ones. | | Mind expanding a bit on this? And curious where you are now | instead of this space... is it because you see the tech too far | out? | | My original interest began with the SkyCar 400 from Moller. The | same design theory of a lot of eVTOLs today; just with a petrol | motor. The petrol motor reduced responsiveness of the control | system, but I always thought it would work out in software. | | eVTOLs are wonderful, but I think any eVTOL without a 'hot | swap' battery is going to be DOA in terms of the personal | transport revolution. | Centmo wrote: | I ended up moving on for personal and geographic reasons, | nothing to do with the tech. The tech is all there for short- | haul flights with batteries as the only limiting factor for | range and speed. | | There are various paths to economic viability for an eVTOL | aircraft but I don't see how Lilium's current prototype fits | into any of them. Unlike an ultralight design, it will | require a certified pilot to chauffer passengers around until | the day when full automation moves into the aviation space. | Other than selling as an extravagant toy, this limits it to | air taxi service. The design is complex so will be very | expensive to buy and to maintain, so I don't see it as an | improvement over existing helicopters beyond the 'green' | energy source and claimed lower noise. | | I am familiar with the Moller SkyCar. Lots of promises were | made and broken, and lots of money burned on that project. | Many modern eVTOL concepts suffer from the same basic design | flaw: forward flight hanging from small propellers is | inefficient. If you care about range, you need the lift of a | large airfoil. Moller also had stability issues, but the | responsiveness of electric propulsion and the advances in | IMUs have solved this problem. | | I think you can have a viable eVTOL product without a hot- | swappable battery in the same way that electric cars have | shown. | semi-extrinsic wrote: | Meh. | | The US is somehow singularly incapable of implementing decent | public transport. Thus venture capitalists are throwing stupid | amounts of money at exotic technology that could potentially | alleviate some of the problems arising from this stupidity. | | First we had the "full" self-driving cars and robotaxis coming | any day now. Then there's Musk's attempts at tunnel digging and | Hyperloop that have gone nowhere. And now eVTOLs that will go | nowhere. | | It's kinda fun to watch from afar though. | dsego wrote: | Don't worry, EU has money to throw around on stupid projects | as well. Even worse, it's public money. | | https://seenews.com/news/croatias-rimac-to-get-200-mln- | euro-... | semi-extrinsic wrote: | Oh sure, and countries in Asia as well, we don't hesitate | to join in on these things. | | I'm just saying, if you trace these ideas back to their | original motivation, it's the lack of decent public | transport in California specifically and the US generally. | kiba wrote: | Roads required public money to build though. | kiba wrote: | _The US is somehow singularly incapable of implementing | decent public transport. Thus venture capitalists are | throwing stupid amounts of money at exotic technology that | could potentially alleviate some of the problems arising from | this stupidity._ | | With trains you don't need self driving cars! | | Rather, why don't we imagine a differently configured | society? If you have streetcar suburbs, then it's possible to | have a lot of last mile delivery delivered by light rail. | Animats wrote: | The whole thing hinges on battery energy density more than | anything else. The planning document says 20 seconds of hover | at landing, with a 60 second reserve. The demo flight has 45 | seconds of VTOL mode/hover at landing. That's cutting it close. | You don't get a second chance at landing. No go-around. | | Regard this as a bet on improved batteries. With current | batteries, it's a nice demo. | jhgb wrote: | Sounds basically like the Apollo lander...only today we have | better computers and control systems. | semi-extrinsic wrote: | Yes, and it's a bet they will probably lose, if they really | need 500 Wh/kg in three years time. Their battery graph is a | fairytale at best. | | The current state-of-the-art batteries that researchers build | in laboratories that last 10-20 cycles can put out about 400 | Wh/kg. You're simply not going to achieve first a 20% | improvement over that, then a development of the tech to | increase lifetime to something useable, and then scaling that | to widespread commercial availability, within three years | time. | joering2 wrote: | This was my take as well - and was wondering what is Fig. 11 | based off of? We can predict, but we don't know how the | market for batteries will form in the next decade or so. I.e. | the COVID disturbed all sorts of markets bad enough that | price of many commodities went up X-fold and haven't gotten | down yet. | spacecity1971 wrote: | Agree re simplicity. Ehang has been using what is essentially a | consumer drone design for some time, and has demonstrated | success with many flight tests. Although they aren't using the | most efficient design, I wouldn't be surprised if they dominate | the short range air taxi field. | aj7 wrote: | Exactly. And a seven-seater gets to pay for this. | | The V-22 was how many years late? How many billions over | budget? | walrus01 wrote: | when you say "simpler", do you mean something somewhat more | conventional that is a multi-rotor/tilt-rotor design like the | joby evtol? | Centmo wrote: | From a safety perspective (ignoring cost, though which is | also critical for viability), I mean minimizing the number of | 'Jesus bolts' in the design - single components that if they | fail, you are in a world of trouble. In the Lilium for | example, what if the tilt mechanism for one of the main wings | locks up while in cruise, and you only discover this while | coming in for a vertical landing? This could be due any one | of many possible reasons: SW bug, electrical failure, | mechanical failure, debris jamming the mechanism, etc. You've | got one wing producing forward thrust and the rest producing | vertical thrust which is not likely to end well. You need to | either prove that every part of this particular system is | extremely reliable or you need a redundant backup system in | place. Due to the design, neither of these options are easy | here. | | Obviously you need to assume there will be motor-out | situations in any eVTOL design and the system needs to handle | this with full payload over the flight envelope needed for a | safe landing. Lilium has the advantage of many propulsion | systems to take over the lost thrust, but many other eVTOLs | are questionable here. | | The same thinking has to be applied throughout the entire | aircraft design (electrical and mechanical) and then you need | to test, test, test. Each failure mode, using full payload | over the full flight envelope, stability testing under | differing weather conditions, the list goes on. To give you a | rough idea, having a flying prototype is great but once you | are comfortable enough with the design to put in a test pilot | under controlled, monitored, and ideal conditions, you are | maybe 20% of the way towards something you can responsibly | put into service. If you want to see a simple design, check | out the Opener Blackfly. | papertokyo wrote: | Is an airframe parachute essentially a requirement for a | vehicle like this to be viable? | Centmo wrote: | It certainly increases the safety factor, but should | never be relied upon as the sole redundant backup system. | There are situations where it will not do you any good | such as hovering at low altitude. If the aircraft does | not have a reasonable glide slope, most people would feel | a lot more comfortable with one. | aj7 wrote: | More cost. | rayiner wrote: | One of my senior projects in college was designing a ducted | lift fan UAV. One of the things that was apparent from digging | through the old research was the monstrous total complexity | even of conceptually simple designs that had 1-2 ducted fans | embedded in the body or wings. Computers make the complexities | of controlling these things tractable, which was a much bigger | problem in the 1960s. But even with relatively modern | technology e.g. Lockheed has had a hell of a time with the | F-35B. | madengr wrote: | [deleted] | textcortex wrote: | There is one fundamental error in this blog; the battery energy | density graph. Battery tech does not follow Moore's law. | Batteries are not transistors.. | aidenn0 wrote: | "Simple by design, there are no ailerons..." then goes on to | describe a vectored-thrust control scheme consisting of | essentially 36 blown elevons. Clearly we mean something very | different by the word "simple." | conradev wrote: | I know very little about aerospace, but from a manufacturing | perspective it seems like having a single part or unit that you | need to manufacture and test would be simpler | | but I imagine that this offloads complexity to the flight | control software, though - is that what you are referring to? | GravitasFailure wrote: | Moving to an electric ducted fan instead of an internal | combustion engine with a variable pitch propeller definitely | simplifies things, though replacing that ICE and prop with 36 | ducted fans mounted to elevons seems like you're just | swapping one set of complexities for a different set, though | gaining complexity through redundancy isn't really the worst | thing. | | My biggest concern with this system is what kind of glide | ratio this has in a power loss scenario. | skykooler wrote: | It's fly-by-wire. Uncontrollable in a power loss scenario. | null0ranje wrote: | My biggest concern is how you maintain directional control | in a power loss scenario. | aidenn0 wrote: | ballistic parachute? | GravitasFailure wrote: | Maybe. Not sure I've seen one that will work on a 7 | seater, especially with the extra mass of batteries. | Tuxer wrote: | There is a ballistic chute on the cirrus SF50 (their | single-engine jet). It's a 7 seater IIRC (6 minimum), and | roughly the same weight (2.7T for the cirrus, 3.1 for the | lilium). | bewaretheirs wrote: | Design for hot-swap batteries, and eject the batteries | (with their own smaller chute or chutes)? | GravitasFailure wrote: | Forgive me if I don't consider dropping lithium batteries | from several hundred meters up a safety feature. | | A parachute on this system is a lot of extra mass to | compensate for a problem solved when the Wright brothers | were around. | aidenn0 wrote: | I mean will a 7-seater helicopter autorotate sufficient | to provide control in a power-loss situation? | GravitasFailure wrote: | That too. As far as I can tell, this thing has all the | control and glide capabilities of a brick. At least the | brick has the inherent safety feature of not being | mistaken for a passenger aircraft. | Centmo wrote: | A way around this risk is to come up with a design for | which a total power loss is extremely unlikely (i.e. it | would take multiple simultaneous non-correlated failures in | a short span of time). This could be achieved through a | distributed battery system where each motor has its own | battery physically and electrically separated from the | others, and critical flight electronics have their own | backup batteries. A ballistic parachute is always nice as a | last-resort hail mary. | GravitasFailure wrote: | Redundancy does go a long way, but that also introduces a | lot of extra weight and complexity into an already heavy | aircraft and can screw with your weight distribution. | | The parachute can work since there are ones for air | dropping tanks, but at the same time I'm not sure I've | seen anyone try to use a parachute as safety equipment on | an aircraft this heavy. | Centmo wrote: | Agreed, the distributed battery system does not seem | practical for the Lilium design but you could get at | least part way there by segmenting the central battery | into parallel modules with separate safety disconnects. | Not sure about the feasibility of the parachute system, | it may be impractical due to the aircraft weight as you | mention. | faeyanpiraat wrote: | Would it be enough for the safety batteries at the motors | to be only as big as to provide power for the aircraft | for an emergency landing? Like for a 30 sec full thrust? | | That might not bother the weight distribution that much. | samstave wrote: | "It's simple! We KILL the Aileron!" | mysterydip wrote: | "The landing gear is fixed and there are no hydraulics." | | Will this cause issues during landing? I've seen helicopters land | and it can be a bumpy/sketchy experience. | kwhitefoot wrote: | That's a very unconvincing video clip on that site. | | Here's a better one: https://www.youtube.com/watch?v=5ukmS9ZJm40 | Dunedan wrote: | Note that the video you linked doesn't show their latest | "demonstrator". Here is a video of their latest one: | https://www.youtube.com/watch?v=jqvMXoVZfDw | beaconstudios wrote: | why are all these new variants of sport aircraft appearing at the | moment? There must be something in the water because I've seen so | many re-interpretations of the flying car in the past year or | two. They look cool in movies but how are they at all a practical | method of transportation outside of being toys for the ultra- | rich? | qzw wrote: | I think everyone is trying to replicate the Tesla formula where | the first Roadster was a toy for the rich, then followed by | real products and now $Trillion in market cap. But there are a | few steps in there that are probably hard to copy, like being | able to sell carbon credits to other manufacturers, federal tax | credit for buyers, etc. Oh, and one Elon Musk. | HPsquared wrote: | Electric cars have increased the availability of mobile | electric power systems: experience with batteries, motors, | controllers etc in cars is transferable to aircraft. It's "in | the air" so to speak. | | Edit: Also the mass market adoption of small quadcopters; these | "distributed electric propulsion" flying car type things are | basically the same concept: flight control by altering the | speed of an array of propellers. | | Also a lot of university teaching/research on both of the | above. | Dunedan wrote: | One of the main backers of Lilium is Frank Thelen | (https://en.wikipedia.org/wiki/Frank_Thelen), a VC from | Germany, best known for his participation in the German version | of Shark Thank ("Die Hohle der Lowen"). | | He seems to believe that eVTOL are the future of mass | transportation, like an airborne version of taxis. I personally | don't find that plausible at all, but maybe I'm just not | creative enough to imagine a future where this would work. | beaconstudios wrote: | I really hope that's not the case. Mass transit that's just | cars that are even more noisy and can drop on people from the | sky? | fh973 wrote: | Be aware that you are usually looking at prototypes, not | available products. | | Currently its mostly another set of startups to invest in. They | might look attractive to VCs because they're ambitious, require | lots of capital, and the technical feasability of a specific | approach is complex enough to find merits in. The jury is still | out if any of them are actually viable from a technology and | economic perspective. | | Lilium's approach specifically has been publicly critized by | aviation experts to not be make sense when looking at the basic | physics. | brightball wrote: | I could see these being a more cost effective option than | helicopter transport. Especially in island areas. | kensai wrote: | Lilium, as I see it, has by far the most secure design of all air | carrier designs we have seen recently. And there have been a lot | including some really nice! | | Lilium is the only company going for this distributed propulsion | system with so many rotors, adding the the safety of the whole | thing. Safety should be paramount! A couple of deadly accidents | can literally ground a fleet otherwise. | | Volocopter also tries a similar approach, but the lack of eVTOL | probably makes that bird much slower than the Lilium product. | fh973 wrote: | However, Volocopter seems to be further with their product | development, while there are serious doubts if the Lilium | concept works at all. | _Microft wrote: | What do you mean that their concept might not work at all? | They have flown several iterations of their prototypes | already but maybe you have something different in mind, e.g. | doubts about the possibility to scale the concept up? | | Here are videos of recent test flights: | | https://www.youtube.com/watch?v=0idI3sJJKZw | | https://www.youtube.com/watch?v=SqMEFdbuzQY | | https://www.youtube.com/watch?v=jqvMXoVZfDw | AeZ1E wrote: | Cool, but the event is not unmannedly flying around in a | circle for 1 minute but to transport up to 7 people over | several hundred miles. | antoniuschan99 wrote: | It's all unmanned unfortunately. Still waiting for them to | demo at least a dummy payload like Joby did a few months | back. | | Also, Joby, Ehang, and Volocopter are much further ahead in | the sense they have done point to point or are building out | the factory (same time last year Ehang got hit by being | called a scam by Citron, however). | | From what I read, rumor is the big issue is battery density | which is holding Lilium from being viable. We shall see! | | Also, Joby is most likely the one to look at to track the | progress of this air taxi segment since they have just | Spac'ed and their aircraft is the most conventional. | KentGeek wrote: | From those videos, it's difficult to be sure those are full | size prototypes and not scale models. | mrfusion wrote: | How do the engines point down for take off? | w0mbat wrote: | I am not at all an expert in this field, but is "jet" the right | word? | | I thought that required combusting fuel and using the flaming | exhaust to propel something. This is propellors in tubes. | | Also this vehicle is about a third of the speed of what most | people think of as a "jet plane". | nickff wrote: | 'Jet' has been used to describe many different types of | propulsion system. The first jets were what you'd call rocket | engines. Then we got 'turbojets' (mostly on aircraft), followed | some time later by 'turbofans'. Most confusingly, ducted | propellers on submarines are called 'pump-jets'. | | I would agree with you that this seems better-described as a | ducted fan (which the author also says), but this use of 'jet' | is not beyond the pale. | divbzero wrote: | Jet propulsion involves ejecting a jet of fluid [1] and does | not require combustion of that fluid. | | [1]: https://en.wikipedia.org/wiki/Jet_propulsion | Karliss wrote: | There is also waterjet and jet stream. Not uncommon dictionary | of jet is narrow,forceful stream of fluid or the nozzle | producing it. Taking that into account difference between jet | and propeller in tube is matter of speed and compression. It's | just that fuel combustion is one the most practical energy | sources including for producing jets of gas. | HPsquared wrote: | Interesting stuff. Haven't heard of the Lilium specifically, but | have seen other distributed electric propulsion concepts here and | there. DEP is such a nice idea, eliminating a lot of the problems | with helicopters/fixed wing aircraft (noise, space requirements | etc.) to carve out a new category of aircraft that is perfectly | suited to an emerging technology (high energy density batteries). | | If we ever do get flying cars, they will use distributed electric | propulsion. | dmitrygr wrote: | "fifth evolution of our technology over our six year history" | reads: "it still doesn't work, we aren't sure if it can, but need | more investor cash" | | Their rosy projections of how they expect battery systems to | magically materialize and double in density over the next few | years to make this device actually work are also quite funny. | aj7 wrote: | "So, the Lilium aircraft requirements can be summarised as | follows... | | *High seat capacity to achieve attractive unit economics and | affordable pricing over time" | | devolves to | | "Yes, we are building a 7-Seater!" | rikeanimer wrote: | This paper "Electric VTOL Configurations Comparison" [ | https://www.mdpi.com/2226-4310/6/3/26/pdf ] presents a pretty | decent energetic analysis of a few of these eVTOL projects | (including Lilium) and is _very_ generous to them. | | Lilium is vaporware. Ask anyone who has worked in the space. Or | just look at it. Or their promotional materials. | | Ducted fans huh... meh. I don't think they have an interest in | people understand how fly-y/hover-y things actually work. | | I do applaud the investors for their vigorous desire to increase | the velocity of money throughout society, it is important | econometrically. Somehow I doubt they'll be happy to see their | currency shredded by 36 rc brushless motors struggling to thrust | an anemic wing into the sky though (before its glorious ~250km/h | cruise to destination [of course])--and then ~15s landing hover. | | What exciting times to fly in. | rickreynoldssf wrote: | What Brilliant Web Designer thought it was a good idea to pulse | the text? Are you trying to give me a seizure? SMH WTF | kevincox wrote: | And that 2px per full spin of the scroll wheel ensures I really | had time to absorb the content. | Timothycquinn wrote: | I've been watching this space for quite a long time and this | company seems to have the engineering and backing to make it | happen. From a safety perspective, this design has a potential | for massive redundancy over several other designs being promoted | out there. | | Considering that their marketing is not to desperate, and their | releases of footage is slow and stead, I predict that they are | very confident in their designs. | | If I had a few million to throw around, I would definitely be | investing in this company. | djrogers wrote: | These are som pretty impressive goals. If they can truly achieve | a hover state as quiet as 60db, and get the efficiency they've | outlined, these could truly change the way we look at short-haul | travel. | | The idea of a 2 hour drive from a small town to the big city | being reduced to a 1hr flight (with no airport - yay helipads) is | already a market where helicopters are making money. Doing that | in even less time, in more comfort (ugh - choppers are loud), and | at lower cost per hour/mile will change things dramatically. | axiosgunnar wrote: | How is 2h to 1h any ,,revolution"? And wouldn't simple (bullet) | trains be better for that? | orangepurple wrote: | New train lines won't be built ever again in the United | States | dragonwriter wrote: | > New train lines won't be built ever again in the United | States | | New train lines are being built now in the United States. | renewiltord wrote: | There's construction ongoing on new train lines in the | United States. Whether they're being built is up for | debate. | deepnotderp wrote: | A small town doesn't have the density for a HSR link, see eg | China's HSR debt. | | A 120 mile link at 14 million a mile is more than a billion | dollars. | loudmax wrote: | A bullet train is better if there's one that already happens | to go from your location to your destination. If they manage | to make these VTOL planes safe and cheap enough, they'll be | far easier to deploy than any train system. Also while | there's overlap between short haul aviation and train | markets, the infrastructures don't have to be mutually | exclusive. | bostonsre wrote: | Yea, 60 decibels at 100m would be pretty crazy to achieve. | avidiax wrote: | 60dB @ 100m is 77db @ 15m | | For comparison, in Washington state, the legal limit for an | automotive exhaust is 72db@15m. | | Still an achievement, but definitely not something you want | your neighbor to land at 3 am. | wmf wrote: | Obviously aircraft are louder than cars. It seems like this | should be compared to a helicopter since it uses the same | pads. | ananonymoususer wrote: | Can we please use dBa (a measure of absolute sound pressure) | rather than dB (a relative term used in many domains)? | fh973 wrote: | It might actually be too good to be true. The German magazine | Aerokurier is citing experts that seem to have doubts about | feasibility [1]. | | The category is called air taxis, other competitors are | Volocopter and Archer, with different concepts. | | [1] https://topgear-autoguide.com/category/sports- | car/futuristic... | gibolt wrote: | Experts always have questions about disruptive technology. | | They are often not right, since disruptions are not | incremental change, but tons of nuanced ones that lead to a | significantly better overall system. | | Edit: "Often" does not mean always, or the majority of the | time. Lilium is clearly not a scam, and seems to be making | steady progress towards their goals. | chefkoch wrote: | ...but physics isn't something that cares If you want to | disrupt. | hn_throwaway_99 wrote: | I think this is such an important point to differentiate. | Yes, incumbent experts can be caught flat-footed when a | new technology comes along that is essentially just _much | better_ at what they do. Best example in my mind is the | iPhone, where essentially the big old-school cell phone | execs totally poo-poo 'ed Apple's ability to create a | compelling cell phone in 2008: "A computer company | doesn't know what they're doing." | | But that is fundamentally different than pointing out | real physical limitations of an idea, and the danger is | you get exactly the OP response, "The old guard always | dismisses you until you change the world!" yada yada. | This is basically _exactly_ what happened with Theranos - | anyone in the actual field of microfluidics knew it was | all bullshit. | wmf wrote: | Of course, but it seems like the gap between what is | physically possible and what has been demonstrated is | pretty large when it comes to aircraft. Has anyone made a | specific argument that Lilium violates the laws of | physics? | kiba wrote: | How energy efficient is this concept? Can't this air taxi | thing be done with better public transport and urban | design? | rayiner wrote: | > Experts always have questions about disruptive | technology. They are often not right | | They're usually right, because most technology that seeks | to be disruptive doesn't end up working. | RandallBrown wrote: | My take was actually the opposite. I can't see this changing | anything. | | Since this thing won't be able to take off from my driveway or | land at my destination, I figure it will still take 2 hours to | go door to door. Once you arrive, you'll still need your own | transportation too. | | Unless this is somehow cheaper and more comfortable than | driving, I can't imagine ever using something like this. | akrymski wrote: | Why not use hydrogen instead of heavy batteries? | | Why not use jet engines instead of propellers? | twp wrote: | What is missing from this blog: | | Where is the safety margin? i.e. what happens if something goes | wrong? Can the aircraft make a safe landing if the motors fail? | Do the limited control surfaces give it enough maneuverability to | make an emergency landing in a tight field, especially in bad | weather? | | tl;dr great blog, thank you for the technical insight, it sounds | like you've designed Lilium for a perfect world. Popular aviation | needs to have basic safety margins and there are no safety | margins evident here. | samstave wrote: | Multiple questions for aerospace folks here: | | Why are designs with multiple wings no longer developed, not just | bi/tri wing planes with wings stacked, but why aren't their rows | of smaller wings, or multiple wings? Do the vortices of the trail | of a leading wing fuck up themlift potential on wings behind it? | | --- | | We simple golf balls for greater distance through the air, and | Wales see an advantage to the barnacles that grow on the leading | edge of their flippers which have shown to create eddys behind | the tail edge of the flipper which aids in greater vortices and | greater propulsion.. | | Why don't we dimple wing surfaces? Or plane bodies? | | Or helicopter blades? | | What happens when we simulate the leading edge barnacle bumps on | the leading edge of a wing, or more aptly, the leading edge of a | blade on a helicopter? | | What software is used to model the airflow over a wings surface, | such as solid works... | | -- | | How much overlap is there between fluid hydro and aero dynamics? | (Specifically the observation of the impact to flow/eddy creation | over a surface?) | gfody wrote: | I always loved the look of Burt Rutan's dragonfly, there's a | list of issues mostly related to conventional (non-vtol) flying | - https://www.nestofdragons.net/weird- | airplanes/tandemwings/qu... | dmitrybrant wrote: | Off topic, sorry, but: Why do web designers think that they can | provide a better _scrolling_ experience than the default system | behavior that the user expects in every other interaction? | | By the way, hijacking scrolling behavior often breaks other | things, such as searching for text in a page. Go ahead, try it, | search for a term in that article. | aidenn0 wrote: | I hate scrolljacking too, but to answer your question, | overriding the default system behavior in general isn't about | providing a _better_ experience but rather a more consistent | (from the POV of the designer) experience. | | The downside of course is that it looks less consistent with | other apps and webpages from the user POV. | fikama wrote: | I just wanted to add that scrolling works normal on mobile. | Including searching. It's only loading a bit too long. | tailspin2019 wrote: | I was about to say that it's quite smooth for me on Safari - | then I searched for something as per your suggestion and the | whole page was vertically offset and effectively broken... oh | dear. | | Edit: The scroll hijacking makes more sense in the context of | the home page, which actually uses it to reasonable effect (not | endorsing the technique, but the home page is attractive at | least). | | I think the mistake was leaving it on for heavy content pages | like the one linked where it adds very little but breaks other | basic behaviour. | skykooler wrote: | It's quite smooth with a trackpad. With a mouse scroll wheel, | it's basically non-functional. | [deleted] | systemvoltage wrote: | The sexier the blogpost, the less believable it is for me. Make | this page in Times New Roman or Computer Modern typeface, | preferably in a PDF format, and I am automatically convinced | :-). It just means that they have better things to do than | aesthetics! | tommoor wrote: | Yea, it's atrocious on this article - makes it unreadable tbh | as scrolling muscle memory is completely messed up. | AeZ1E wrote: | Can we make sustainable public transport attractive again - an | stop hyping gadgets for the rich? | oh_sigh wrote: | Lilium Jet has 600 employees. What do you think they could | contribute to sustainable public transport that the millions of | people employed across the globe directly involved in public | transport can't do? | mrshadowgoose wrote: | Those are not mutually exclusive endeavors. | | Please be aware though, that there's always going to be a large | population segment that will desire to proceed directly from | point A to B in comfort. | | Unless by "public transport" you're including "government owned | autonomous taxis", public transport will never be attractive to | that population segment. | OnlineGladiator wrote: | > Please be aware though, that there's always going to be a | large population segment that will desire to proceed directly | from point A to B in comfort. | | How large do you consider this population segment to be? | sokoloff wrote: | Order of magnitude as large as the group that commutes by | car today. | [deleted] | mrshadowgoose wrote: | Quite large, certainly a good chunk of the population that | currently drives. There's also a segment of the public | transit riding population that would prefer personal | transit, but do not have the option. | | People generally prefer to a) be comfortable, and b) | proceed directly from point A to B with no interstitial | bullshit. | | You almost never get b) with public transit as commonly | realized today. | Maarten88 wrote: | A high-speed train can connect inner cities just as fast as | this gimmick jet. It is orders of magnitude more efficient | and scalable, and much more safe. A good train could easily | be more comfortable, if there is a market for that. Do you | think that jet will have dining rooms, sleeping cabins, ample | room for luggage? Do you think it will even have a toilet? | | Just. Build. A. Train. | mrshadowgoose wrote: | High-speed trains are awesome. We absolutely should be | building more of them for the people who'd like to use | them. | | But if someone wants to go directly from point A to B in a | "gimmick jet", why should we try to prevent that? | | I'll reiterate with your example. Building high-speed | trains, and developing "gimmick jets" are not mutually | exclusive endeavors. It's clear that you are not personally | interested in a "gimmick jet", but there are people who | would be. Why exactly should we be stopping those people? | natechols wrote: | I like trains too (and short-haul aircraft frighten me), | but it's much easier to find an unobstructed path for a | small aircraft than a high-speed train. There's also more | latitude for experimentation with these piecemeal private | sector experiments. I would expect a high-speed rail line | between San Jose and San Francisco, for example, to cost | far more than Lilium's current market cap. I'm not even | sure where you'd put the track, without killing an existing | train line. | thescriptkiddie wrote: | Not only is this company obviously a scam, if their product | actually did exist it would be extremely expensive as well as | louder and more dangerous than a regular helicopter. | AeZ1E wrote: | What a useless startup | Timothycquinn wrote: | What gives you this impression? They have amazing engineers and | huge backers. My impression is that they are one of the most | likely to succeed in this space. | AeZ1E wrote: | They won't be able to deliver on their spec. Not even close. | https://www-aerokurier- | de.translate.goog/elektroflug/lilium-... | orangepurple wrote: | After reading your article I came to one conclusion: RUN, | don't walk from Lilium. They are obviously tricking people | who don't know a single thing about airplane engines. | | Lilium responded to the aerokurier article on Monday with | an email in which our experts were accused of having set | the hover efficiency of the drives far too low with an | efficiency of 20 percent. Lilium, on the other hand, claims | that values "of 85-95% are the industry standard for turbo | fan levels". According to Lilium, this mistake should have | been noticed by any industry expert. | | Lilium is right with regard to the efficiency of turbofan | engines viewed in isolation, as they are standard today on | all high and fast flying airliners. However: There are no | turbo fans installed on the Lilium Jet. They are jacketed | propellers driven by electric motors. | icefox11 wrote: | That is precisely the problem: believing that one can succeed | in this space. Flying personal transport is not economical. | On a side note, it doesn't matter how brilliant an engineer | is if you set impractical goals to him. Neither good | engineers not deep pocketed backers could make Theranos real. | deepnotderp wrote: | And why are you so certain that flying personal transport | is not economical? | | Certainly the history of the automobile should show that | such statements can look ridiculous in hindsight. | rmah wrote: | He's certain because of energy budgets, weight | constraints, safety reasons and more. The history of the | automobile vs aircraft shows he's right. | | To move something in the air inherently uses more energy | than any sort of ground transport. To make the aircraft | more efficient, you have cut weight, which means more | exotic (i.e. expensive) materials. The powerplant has to | have a higher power:weight ratio (again more expensive). | It's more dangerous to be flying, so you need additional | safety equipment that ground vehicles don't need. Etc, | etc. | | And if any aviation technologies manages to gain | price/performance better than the stuff used for ground | transport... it will be adopted by ground transport. | Which still leaves air transport more expensive for the | reasons listed above and many others. Hell, in WW2, they | stuck an aircraft engine into the most common US tank | (sherman). Interestingly, sherman tank crews didn't have | to worry about falling out of the sky and dying if their | engine failed (though they had lots of other worries, of | course). | | Long story short: there is nothing magical about electric | motors turning propellers. And battery energy density is | utterly horrible vs gasoline/kerosene. Air transport will | ALWAYS be more expensive than ground transport. Perhaps | someday it will be cheap enough to be common. But | personally, I doubt that such a day is anytime soon. | | Last aside... You can buy a small used two or four seater | plane NOW for < $100k. Get a pilots license and you can | fly around to your heart's content. General passenger | aviation today is not reserved for the ultra rich. | karmicthreat wrote: | I don't doubt this concept could ferry people around. But its | safety margin is razor thin. 60s reserve? That is barely time for | an operator to figure out where to ditch. | Ancapistani wrote: | If I'm reading it correctly, they're claiming 60s of reserve | _at hover_. That would translate to roughly 10m of reserve in | level flight. | sokoloff wrote: | On a windy day or two, I've done multiple go-arounds in a | fixed wing aircraft. In low weather, missing an approach to | land is also relatively common. | | "Don't worry, your pilot has 60 seconds of reserve with which | to land safely" is terrifying rather than reassuring. ___________________________________________________________________ (page generated 2021-12-22 23:00 UTC)