Technology Behind the Lilium Jet

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&#x27;s a slippery slope.<p>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.

&quot;Simple by design, there are no ailerons...&quot; 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 &quot;simple.&quot;

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.<p>* Scroll jacking - looks pretty, impossible to use.<p>* Cookie consent - It&#x27;s both too large and takes to long to find the right action.

This paper &quot;Electric VTOL Configurations Comparison&quot; [ <a href="https:&#x2F;&#x2F;www.mdpi.com&#x2F;2226-4310&#x2F;6&#x2F;3&#x2F;26&#x2F;pdf" rel="nofollow">https:&#x2F;&#x2F;www.mdpi.com&#x2F;2226-4310&#x2F;6&#x2F;3&#x2F;26&#x2F;pdf</a> ] presents a pretty decent energetic analysis of a few of these eVTOL projects (including Lilium) and is <i>very</i> generous to them.<p>Lilium is vaporware. Ask anyone who has worked in the space. Or just look at it. Or their promotional materials.<p>Ducted fans huh... meh. I don&#x27;t think they have an interest in people understand how fly-y&#x2F;hover-y things actually work.<p>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&#x27;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&#x2F;h cruise to destination [of course])--and then ~15s landing hover.<p>What exciting times to fly in.

No doubt the whole eVTOL&#x2F;AAM space will lead to positive and long lasting developments for aviation, but the amount of money chasing specifically the air taxi&#x2F;uam space (Joby, Lilium, Archer, Volocopter, etc.) is staggering given how utterly nonsensical the business plans and projections are.<p>Right now everyone is in a race to certify. I guarantee that will be the easy part. The whole list of issues this community is not thinking through and addressing dwarfs those that they are. Energy density is just the start.<p>For instance: Power requirements for these business models at scale will require a sudden turnaround and mass embrace of nuclear. Infrastructure build will require government investment and widespread use of eminent domain. City laws and ordinances allowing for uam flight need to be rewritten. I could go on…<p>Btw I am in the industry.

I am not at all an expert in this field, but is &quot;jet&quot; the right word?<p>I thought that required combusting fuel and using the flaming exhaust to propel something. This is propellors in tubes.<p>Also this vehicle is about a third of the speed of what most people think of as a &quot;jet plane&quot;.

That&#x27;s a very unconvincing video clip on that site.<p>Here&#x27;s a better one: <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=5ukmS9ZJm40" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=5ukmS9ZJm40</a>

Can we make sustainable public transport attractive again - an stop hyping gadgets for the rich?

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!<p>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.<p>Volocopter also tries a similar approach, but the lack of eVTOL probably makes that bird much slower than the Lilium product.

why are all these new variants of sport aircraft appearing at the moment? There must be something in the water because I&#x27;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?

What Brilliant Web Designer thought it was a good idea to pulse the text? Are you trying to give me a seizure? SMH WTF

&quot;fifth evolution of our technology over our six year history&quot; reads: &quot;it still doesn&#x27;t work, we aren&#x27;t sure if it can, but need more investor cash&quot;<p>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.

Lilium and other electric vtol would benefit greatly in my eyes from a cable assisted starting. Just have 500 m of powercord on take-off and once you are over that initial peak you just drop the cable. Not as sci-fi, but alot of kilometers in ex-change.

These are som pretty impressive goals. If they can truly achieve a hover state as quiet as 60db, and get the efficiency they&#x27;ve outlined, these could truly change the way we look at short-haul travel.<p>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&#x2F;mile will change things dramatically.

Interesting stuff. Haven&#x27;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&#x2F;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).<p>If we ever do get flying cars, they will use distributed electric propulsion.

They could test the market for these in Norway, the Scottish Islands or the Greek Islands. Places where 15 min flights with low passenger numbers over a distance of 50-100km would have a high value compared to a 1-2hr ferry crossing. Wouldn’t need to go anywhere near max range and would still mostly over land not much other air traffic to bump into.

Multiple questions for aerospace folks here:<p>Why are designs with multiple wings no longer developed, not just bi&#x2F;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?<p>—-<p>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..<p>Why don’t we dimple wing surfaces? Or plane bodies?<p>Or helicopter blades?<p>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?<p>What software is used to model the airflow over a wings surface, such as solid works…<p>—<p>How much overlap is there between fluid hydro and aero dynamics? (Specifically the observation of the impact to flow&#x2F;eddy creation over a surface?)

What stands out to me about all this eVTOL&#x2F;air taxi vehicles are that they operate in 3D space instead of 2D like cars.<p>This means, even though more inefficient than cars, you can have more “lanes” to operate in.<p>On roads, you have to have traffic lights and stop streets, traffic itself, and cars driving inconsistent speeds or braking when turning.<p>In the air this can all fall away, so people can live further away from city centres, streets can be left for cycling, and less concrete&#x2F;asphalt infrastructure is required.

I&#x27;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.<p>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.<p>If I had a few million to throw around, I would definitely be investing in this company.

&gt; Lilium’s greatest breakthrough is not accepting that traditional approach to trade-offs but rather getting to first principle understanding of the physics and then systematically innovating and optimising each subsystem in an integrated and coherent manner such that the resulting aircraft achieves all stated performance objectives.<p>You cannot &quot;innovate such that ...&quot;, you can only &quot;innovate and hope to achieve ...&quot;<p>There is too much assertiveness in this post.

&quot;The landing gear is fixed and there are no hydraulics.&quot;<p>Will this cause issues during landing? I&#x27;ve seen helicopters land and it can be a bumpy&#x2F;sketchy experience.

I have to wonder about the glide ratio. All those fans will probably create a ton of drag. If for some reason you have a complete power&#x2F;engine(s) failure, that thing is likely to become a lawn dart.<p>At least with a helicopter you can autorotate if you lose your engine. Unless this plane will get an airframe parachute, I would not fly in it.

&gt; Zero operating emissions<p>Could it be clear to everybody that this thing will require energy and thus will, in a way or another, emit somthing (either CO2 from electricity production or CO2 from the construction of means of electricity production).<p>Besides, why not just invest in trains ? (or lighter alternative if any)

I don&#x27;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.

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..

“So, the Lilium aircraft requirements can be summarised as follows…<p>•High seat capacity to achieve attractive unit economics and affordable pricing over time”<p>devolves to<p>“Yes, we are building a 7-Seater!”

What is missing from this blog:<p>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?<p>tl;dr great blog, thank you for the technical insight, it sounds like you&#x27;ve designed Lilium for a perfect world. Popular aviation needs to have basic safety margins and there are no safety margins evident here.

Why not use hydrogen instead of heavy batteries?<p>Why not use jet engines instead of propellers?

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.

How do the engines point down for take off?

Off topic, sorry, but: Why do web designers think that they can provide a better <i>scrolling</i> experience than the default system behavior that the user expects in every other interaction?<p>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.

What is missing from the presentation is anything about recharging. The reasonable conclusion is they have no good story, there.<p>Most of the profitability of an air transport, when there is any, comes from quick turnaround. Having to wait to charge for an hour eliminates any possibility of that. An alternative is to have removable batteries, so when you land, you drop off dead batteries and slot in charged ones; and charge at the airport.<p>A better design would have an aft liquid-hydrogen tank and fuel cell, instead of batteries, for longer range and much lower mass. LH2 would be produced at the airfield during minimum energy spot prices, and stored underground.