Will the Lilium Jet Work? A detailed analysis by an independent expert.
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- Опубліковано 1 сер 2024
- Download PDF versions of the video: drive.google.com/drive/u/1/fo...
| Timestamps |
0:00 Prologue
3:30 Chapter 1: Fundamentals
42:28 Chapter 2: Aerokurier vs Lilium
1:18:59 Chapter 3: Evolution of Lilium
1:41:51 Conclusion
| About me |
For an aircraft engineer like myself, the advent of the eVTOL industry is exciting. The industry's current state is that many companies are exploring different aircraft designs and innovations. Some will work, but many will fail because they will ultimately be less economical or technically inferior. I aim to be an independent analyst, educator, and commentator about what aircraft concepts are sensible and feasible and what could be more challenging. I want to share those insights, hoping that they will accelerate the learning curve that the industry is on.
| Disclaimer |
It is important to note that I do not provide investment advice. I am not telling you to buy or sell a particular stock. Instead, I provide opinions on the aircraft design. Whether or not companies will be successful depends on numerous factors, of which the aircraft design is only a fraction. With teaching as my priority, I aim to boost our understanding of maths, physics, and engineering by using this exciting industry as the motivating context.
My research and reports express my opinions, which I have based upon generally available public information, field research, inferences, and deductions through my due diligence and analytical process. To the best of my ability and belief, all information contained herein is accurate and reliable and has been obtained from public sources I believe to be accurate and reliable. I strive for accuracy and completeness to support my opinions, and I have a good faith belief in everything I write; however, all such information is presented “as is” without warranty of any kind - whether express or implied. I make no representation, express or implied, as to the accuracy, timeliness, or completeness of any such information or with regard to the results to be obtained from its use. You agree that the use of my research is at your own risk. In no event will I be liable for any direct or indirect trading losses caused by any information available on this report. Think critically about my opinions and do your own research and analysis before making any decisions.
I am entitled to my opinions and to the right to express such opinions in a public forum. I believe that the publication of my opinions about public companies that I research is in the public interest. This report and all statements contained herein are my opinions and are not statements of fact. You can publicly access any piece of evidence cited in this report or that I relied on to create this report. All expressions of opinion are subject to change without notice, and I do not undertake to update or supplement any reports or any of the information, analysis, and opinion contained in them.
| References |
See the comment section below. - Наука та технологія
Great to see UA-cam recommend a small channel like this. I'm sick of the fluff click-bait videos. Thanks for your work.
its recommending it? thats great.
This was one of the best lectures on electric aircraft design and certainly the principles explained can be applied to other vtol aircrafts. Very comprehensive.
This is a 12/10 analysis
Such a great video material! The best is that with your high-level technical work on this video, you attracted a really knowledgable crew of commentors that only enrich more this. Please continue doing these analysis at this level or even higher. I loved to see the technical details, the backed-up data, and conclusions. I just discovered your channel and I am subscribed now
Very much look forward to watching this in full a bit later today. Looks great and like a much needed report.
What an amazing 100+mins of content! Can't wait for your future analysis
Interesting and highly professional analysis of this concept and somewhat inline with my gut feeling after 40 years in the industry - good job
Lilium successfully passed their 4th & final DOA audit. It fully disproves John's lies about Lilium. Don't always go for the gut when Germans are engineering hm?
@@robitwhisperr Good for them, and as might be expected from German engineering diligence. We can learn most from being proved wrong, so lets see if it passes the real World usability test.
This is a death trap.
@@denisw398 can this plane handle the weather, such as wind gusts working at high elevations I notice it to be always windy. massive gusts of winds at high altitude most likely is even more
@@rezasaba1602 wind is surprisingly a non-issue for aircraft, it only becomes a problem with crosswind landings. But crosswind landings are only performed because its physically impossible to reorient a paved runway to align with the prevailing wind. A VTOL aircraft can easily along itself into the wind and therefore doesn't need to perform a crosswind landing.
I welcomed your very candid, clear and uninhibited analysis. I hope that you will continue your efforts to educate the public. I hope that lilum will take your service to heart. Better yet, I hope that they seek you out as an advisor and advocate. Thank you.
im goings to let the video play through without watching it again because i don't want the algorithm to think i got bored and bailed. i never care about that stuff but this video deserves it.
Love the detail and analysis, thanks for taking the time making this video and posting it, very interesting.
Thank you!
Stoked to see you get the recognition you deserve mate! Such refreshing and well delivered analysis/information. Let's see how battery technology over the next 24 months impacts the sector. Thank you!
Thank you, Harry!
@@zhihenglou Pleasure man, really love this type of work and sometimes wish I was more an engineer than a marketer! It's pretty wild how all this new and increased battery density news is coming out a week after the release of this video. Let's see how long it takes to play out in reality for the leaders, I also think I've got the topic/title of your next analysis! aha.
Yes, I've been reading the news on CATL's 500Wh/kg battery. I haven't found any useful resources that describe the batteries in depth; I only found a few short news articles thus far. I'm still very intrigued about this new battery. What's your topic/title idea for my next analysis?
It's the same old story; design an airplane that's needs power that's currently beyond what's on the market!
Even military aircraft get caught in this cycle. One of the most famous experimental kit planes that did this was the BD-5 in the 70's. They sold lots of kits but most were never complete because a reliable, affordable and available motor never happened. Here we are 50 years later and there's still no motor that really checks all the boxes as a powerplant for those airplanes.
@@harryseagar He deserves egg on his face at least. Lilium passed their 4th & final DOA audit from EASA. If verifies their battery tech & wing flight fully. So John here spent an hour successfully fooling you all.
This 2 mo video didn't age well 😂
Great video. Please keep up the good work. Very much enjoy you videos, John!
As an RC aviation modeller and pilot in the 1980’s I am perplexed these engineers started this project from a top-down approach. (First some calculations, then a model).
In an RC modellers mind you start with a general concept, then you start adapting until it works. Low cost development, high return. Make it crash and build better. I designed a canard glider with a special wing design in the 90’s, first model were flat balsa surfaces to have a rudimentary proof of stability of the design. It worked. Then you can start upgrading. Due to life’s duties that project is still on my shelf.
What I remark in your analysis is that a designer drew a manta-like flying object, but I wonder if he realizes how aerodynamics work. By the way, VTOL can save lives for short distances, but it’s not suited for long flights. Best in between choice would be STOL then, but also requiring a lot of power. VTOL electric is quite crazy if it consumes 10 times more to go up or down.
Some interesting information for you to consider: Building an aircraft is not close to building RC planes when it comes to processes. I have experience at Airbus. One of the biggest cost eaters is design changes, increasing with time within the process. Thus, its the complete opposite to your RC planes with the slogan "high developtment cost, low probability of failure or big design changes". About Lilium: changing their design shows uncertainty and is a cost eater.
The top down approach is also common at Airbus aircraft design, and with my experience id like to say that you are making the wrong argument.
But as a Startup Lilium makes something completly different than Airbus:
There is no fixed mission assigned before building the plane. The argument you make is about the order in which they calculate which is actually fine. What is not so much fine is:
1. As stated in the Video, after the first theoretical calculations there is yet lack of confirmation by proof of 1:1 scale flight test (lets see what this year brings).
2. The first theoretical calculations are used as data for investors, which is very risky.
3. The biggest risky thing to do in my opinion, there is no fixed mission. For example at Airbus, you would define the whole mission(s) of all possible customers, then do some basic calculations if those missions are even possible in theory, and if confirmed, THEN you would proceed. Lilium just changes their performance in the process, before having a fixed mission.
The argument you make is in my opinion worthy, but not factually correct. You are saying Liliums design process is risky and uncommon in the industry. Comparing RC planes to real planes is wrong on alot of levels, but your point in the end is valid in my opinion due to different facts then what you stated. Lilium takes alot of risks. LILIUM HAS TO TAKE RISKS. None company would develop such a design otherwise, which would maybe not push battery suppliers on the huge scale (you could argue with automobile here). So they are not "stupid", they are risky. Lilium is a Startup. Lets see what happens.
@@TecTrendsThank you for your answer, I appreciate it, after all, I know RC modeling is in no way to be equaled with real planes. I agree you need a top down approach for production, but you need a bottom up approach for development
@@TecTrends Small scale flying model prototypes have been used in industries since the dawn of aerospace development. It is just that such works are not well published and tend to be company internal information.
@@grasuh Considering what I already said, here my opinion which I try to express neutrally as an aerospace engineer, Airbus insider and privat pilot:
You did not understand what I said. Small models are used in different scenarios to get some information, eg at same Reynold Number windtunnel testing. But what I said is something completely different then what you inferred, even tho I have been more then clear.
I was talking about processes on how aircraft are developed. A model aircraft is, as the first commenter stated, built up by big radical steps, to cite him „make it crash and built it better“. It doesn’t fly straight, so you change the rudder.
Airplanes are NOT designed this way. Development changes are getting more and more expensive as development state rises. Thus, there are first made (even in times before computer) heavy calculations, which get iterative more and more advanced. A clear mission is defined and the physics need to align, meaning from that definition comes the powersystem, the wing design and everything else. After the physics align in some kind of calculated model, every single part is being optimized, BUT NOT YET BULILT as a WHOLE AIRPLANE. This is the huge difference which I was talking about. And trust me, I’ve seen Liliums early designs. Shown at a local conference, not allowed to talk about it. Like for everything it’s just to display the general form. A model airplane is BUILT and then OPTIMISED holistically by big changes. Opposed to airplanes which develop after the „physics fit model“ after heavy calculations in tiny steps.
That model approach is what we see from Lilium, which as a startup they kinda have to do but I still don’t think it’s optimal as stated. Because it’s a cost, time eater and high risk.
Please read all my lines carefully, it all makes sense.
Thank you.
@@TecTrends Here is an example of a scale model usage. Search Google for "ADAPT Scaled Demonstrator" and read the paper through ResearchGate, called "System Identification and Stitched...".
| References |
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(Anonymous, 2020) www.aerokurier.de/static-download/8/3/7/8/5/9/6/aerokurier_Konzeptberechnung_Lilium_Jet.pdf
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(ecosummitTV, 2016) ua-cam.com/video/htaeARwse1w/v-deo.html
(Gapper, 2023) www.ft.com/content/87b1ee8b-e856-40a5-aa57-62340ff3d8c8
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(LinkedIn, 2022) Potentially available upon further request
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Velice přínosné dokumentární video. Fandím lidem, jako jsou ti ve společnosti "Lilium".
Very good and calm analysis, thank you very much. It’s hard to believe that so much money can be raised for a quite obviously flawed concept.
Exactly my thoughts😂
Amazing work, very detailed presentation! Thank you for the effort given
Dear John, nice video, nice work from your side, keep this ongoing, I will just add a remark to what you said: In 2017 i sent an email to Lilium telling them that this eVTOL will never fly, (they announced 2019 as a first fly), I explained to them that they should reduce the number of EDF and increase the diameter, guess what, after millions of € and 5+ years, they increased the diameter of the EDF (also the number is reduced). But after all this is a new startup, they should keep iterating the design/system, maybe it will fly.
Hi there! Thanks for sharing this story and your comments. Sadly, I did not discuss the change from 36 to 30 EDF's in this video. But I have analyzed this change in my previous video. In hindsight, I should have included this detail for completeness...
@@zhihenglou Hey, you did yeoman's work in this long video. Don't worry about that one change. You can mention it, and its expected impact on the flight/range performance, in a follow-up video.
(Which I will watch. Duly subscribed, so I won't miss it)
Thanks for your positive feedback, Nicolas! This video analysis is based on the 7-seater with 30-motors (see Chapter 2), so the video's conclusion regarding flight performance should not be impacted by this change from 36 to 30 EDF's. But I should have explicitly mentioned this change in the timeline (Chapter 3). Thanks again for your comment and your sub! What would you like to see in my next video?
Great Video,
Keep up the good work!
A ballistics parachute is certainly possible. A ballistics parachute with rocket extraction and pyrotechnical instant inflation is possible to allow inflation at zero speed and zero altitude. A ballistics parachute with a high speed ribbon drogue is possible. I would argue only a plain simple parachute designed for low speed deployment at a modest altitude is required.
Ilium now has designed the Lilium Jet to land n a runway. This may mean that the aircraft no longer needs a ballistics parachute so long as it is in flying distance of a runway.
Ballistics parachute might be very expensive to develop and the weight will detract from other more important sofety factor.
this is a great video. i was worried that you deleted it when i couldn't find the original. its as good as a video can be.
Thank you so much for this clear and helpful analysis!
I eagerly watched the report by John Lou. Although difficult for me to understand the technical language and calculation, It was informative for me as a potential investor, and want to say Thank You for taking the time and review it for all of us. Not sure it was stated what the weight of the batteries are, and how long it takes to recharge them, Just as an observer the wing span length to the fuselage length. Planes need long wing span for lift to happen. If it is Li batteries, they weigh a lot,
The Lilium looks more like a Drone than a plane from what I have seen
this video was so good i watched it again. i don't even bother arguing about lilium anymore i just link this and they quit.
They have quietly slipped the in service date back another year, to 2026. And for a company that issues a press release claiming a watershed moment every time they so much as partner with a new supplier of widgets, the lack of candour about the slipping timeline speaks volumes. Reality is they have not even built the conforming prototype for evaluation test flights so no way will they be in service in 2026. Joby and Vertical have both had catastrophic failure of their full size prototypes, so EASA and the FAA are bound to take a most cautious approach to certification of this untried technology for which no prior operational data exists. In my view, few if any of the eVTOL start ups can meet the exacting requirements of certification with an aircraft that will still deliver their bold performance claims.
Good analysis, that kind of reminds me of the concept of the 80% solution being much easier than the the 100%. I read down below, pilots are pointing out some failure possibilities which seemingly don't have "autorotation" or glide to landing fall backs.
Ballistic parachutes will also increase in quality and fall in price. Wright's Law will prevail...it's quite predictable
Thank you for in-depth insight. 👍🏻👍🏻👍🏻
Congratulations on this very sound analysis!
Have been watching Lilium. Started on this but skipped through. Its looks to be 'German' comprehensive and well delivered. I note the many positive comments below, well done! For a potential (not yet) investor, in between the marketing hype and your comprehensive analysis (and also for the math, physics, areo competent), a 5 minute, compelling, executive summary would be awesome - though certainly not demanded. Thank you for your great work.
Hi Brendan,
I am not doing further work on my project about Lilium, except for some light maintenance work, like replying to comments. Because I have other exciting ideas and projects coming up!
You can find a summary in 'Conclusion' (see 1:41:51). You can also find a PDF version of this video, which might help (see drive.google.com/drive/u/1/folders/16IEpl-tQwd244ZVuoIncWn4l8evGRIwH ).
Lastly, I must remind you of my disclaimer. I am not giving investment advice, so please read the disclaimer in full.
Best,
John
@@zhihenglou Thanks again John. Great content. Disclaimer noted and understood. Will look for your other content.
This is a very good evaluation. However, I don't quite understand the overly negative reaction to Lilium in the comments. The evaluation concludes that Lilium is viable, but the 7 seater version is overly optimistic with current battery technology, with a simple solution - exchange passengers for additional batteries. Alternatively, keep 7 passengers, but take much shorter routes in the initial years of service (sub 100km). Most of the initial business is likely to be for sub 50km routes, in any case. Initial business is likely to be aimed at the semi-luxury market, so having more expensive tickets to cover the loss of passenger numbers, is viable. It is likely to be competing with helicopter services initially, which it should still be able to undercut by a pretty solid margin. I do think that we're looking at the (mid) 2030s before this, and other EVTOLs, become regular means of transport for the general public. A big advantage of Lilium is that it can perform short running landings, if necessary, reducing the essential need for hover duration during the landing phase. Initial trips could be carried out where there is sufficient space for a short running landing, in the unlikely event that this is required, if the trip is long enough to be pushing the maximum range.
Exactly. 300km might be highly optimistic, but smaller fractions of this are absolutely possible with today's battery technology (which is pushing into the 300Wh/kg range). This can be commercially successful without hitting all the named goals.
Very good analysis! Thanks.
Your analysis it really amazing and I admire the way you diplomatically avoid saying that this is utter BS. I also agree that it can not be more absurd to blow though hundreds of millions of dollar for last 8 years, employ tons of people when they can barely make a small unmanned empty weight version carefully go from vertical to horizontal flight mode while flying in the near vicinity of the airfield. Now believing in catching all that wasted design work up in one year is totally ridiculous.
I find it just as absurd that you can win awards for things that don't exist/don't work at all as long as you can present nice images of a model. Our world makes it easy for cheaters of all kinds to gain public visibility and create completely wrong impressions. We should overthink the concept of giving awards, because they are supposed to highlight excellence, which in this case they just don't.
Your analysis and presentation is so great that I instantly subscribed - fantastic work 👍
Nice work. I like how your analysis sticks to the applied science. The company’s analysis seems biased by fundraising and marketing concerns.
He fooled you I'm afraid. Lilium has been issued their long awaited DOA license from Europe. If John Lou was correct about anything he disparaged Lilium for, EASA would never have given them their DOA. It verifies everything from their battery to wing flight. It also allows them to scale up their craft without further approval because they have proven their engineering competency.
It in turn proves John Lou is incompetent and a pathological liar.
Finally an engineer published a rational analysis for that lil jet!
Very well done John.
Thank you for te detailed report.
An excellent calm, objective and factual evaluation of the hype that surrounds this project. As someone who's spent a lot of time using electric-power propellor and ducted fan model aircraft I can tell you that in "the real world" there's just no way an electric ducted fan can come close to a traditional propellor in terms of efficiency when you've got high disk loadings such as those proposed by Lilium. Also, how convenient that one of the requirements for their promised performance is battery tech that is not yet readily available.
It was also very interesting to note that their prototype self-incinerated because one thing very rarely discussed by eVTOL companies is how they plan to mitigate the risk of in-air fires caused by battery malfunction. Multiply redundant power systems and ballistic parachutes do *nothing* to save passengers from a fiery death in such an event.
in the case of vertical flight, really large propellers have an advantage, while this vehicle is supposed to fly like an airplane to make optimal use of the engines.
@@EverynyanSan The concept of using many small EDFs as opposed to a lesser number of fan-units with a larger diameter is still flawed. The "wetted area" of the ducting on those fan units is much greater per area of cross-section than would be the case with one or two larger-diameter fans producing the same amount of thrust and that means increased drag hence lower efficiency. There's a reason we're seeing a lot more twin-engine commercial airliners than four-engined ones and some of that is down to the greater efficiency of larger fans over multiuple smaller fans.
In the world of electric flight, efficiency is *everything* so this concept is immediately flawed through its use of many, many small (and thus less-efficient) fan units. There's a very good reason that all the other players are using lower disk-loadings than the Lilium -- they've prioritized efficiency over gimmicky styling.
@@xjet I guess lilium wanted to add extra lower pressure to the top of the wings to increase lift. I have no illusions that this project has no chance of success without a new type of batteries. I am not an aviation engineer but it seems to me that propellers powered only by electricity have certain limits that cannot be overcome compared to internal combustion engines.
The theoretical batteries and the theoretical motor bearings. "we will get it working when reality catches up with our fringe science" ( get Walter Bishop onto it ( Fringe ))
@@alanhilder1883 Walter would have it solved yesterday.
You can now download PDF versions of the video: drive.google.com/drive/u/1/folders/16IEpl-tQwd244ZVuoIncWn4l8evGRIwH
very nice analysis, thank you
I believe that it’s really profitable to focus at cities transportation, for example carrying 16 persons with 30 KM distance is better than carrying 7 for 175 KM ?
Serving like a bus stations from one block to another
Very professional analysis!
Excellent analysis. Thank you.
Thanks, Chris!
Thank you for sharing.
Well done!!
John, it would be great to see a similar video on the Jetoptera from the US.
I have done some drag analysis and optimization for canard plane like Lilium as a personal project . The drag of the canard was significant.
Liliums latest test flight range was over 13 km.
Thanks for the in depth video.
Pls more content about lilium :)
Not sure they were carrying any payload at all at the time?
@@amazingdiyprojects From my observation and analysis, Lilium has not flown a full-scale prototype to date. As the video explains, the current prototype, the Phoenix 2, differs significantly in weight and the variable nozzle. The variable nozzle is critical for aircraft performance, as shown in Lilium's paper. Yet, the absence of the variable nozzle in Lilium's current prototype is seemingly missed by many other commentators.
So short the stock and get a billionair @@zhihenglou 👍
Good job on the analysis. I think they ran into the same issue all other air taxi ventures have. They thought hover stability was the difficult part until they got off the ground and found that electric power doesn't keep you airborne for very long. The one thing they have going for themselves is looks. It looks more futuristic than most other designs. Doesn't perform any better and is arguably worse than a propeller design, but it sure looks purty. Just like all other air taxies, they will delay and delay as long as they can until the electric power plants get to where they need to be. Like most others, they will eventually go with a hybrid approach in the mean time.
Interesting! Well reasoned.
excellent video
Dayumn! This was very detailed, great work.
One small addendum, small fans=very, very low efficiency
That is something no amount of money or buzzwords can change, ever. When i first saw this, i just dismissed it as another CGI money grab for the uninformed.
Excellent video and analysis. If only we had one of these for each of the other eVTOL concepts, as the vast majority of them are hiding mountains of "bad news" data from their investors as well. This is precisely why Beta suddenly shifted to marketing Alia as CTOL.
There are no doubt technical challenges. I've seen ilium go from being described as impossible by 'professors' in learned papers, to full fore and main plane transition (also said to be impossible). Aeronautical engineers are no more qualified to talk of battery tech than civil or mechanical. The batteries to make Lilliium achieve its performance goals already exist. Lilums economic success will depend on battery tech that allows much more than 600 cycles and battery tech scientists should be asked and they will probably say its a matter of when not if. It's eaither 3 years or 10 years.
What kind of battery exists today that can produce enough current for 10 turbine-looking motors? and how much do these batteries weigh?@@williamzk9083
One question I have about all E-VTOLS, is are they designed to operate in windy and rainy conditions too? I haven't seen any mention of climatic conditions other than calm winds and sunshine from any of the designs that are currently in development.
I was the 1000th like! Thanks for the info
i would love to see actual test data. this should be continuously published. Such transparency would be better than the question of "techno-scam?". Even if this data might have a negative impact on fund-raising, it could nevertheless keep the company alive for longer, due to confidence in the reality of the product. could it be so bad that they would want to hide it? i remember hearing that the hover efficiency of this duct configuration was better than expected, given lift produce by the rigid portion of the wing with ducts pointed at angles downward. i did not hear that mentioned in this analysis.
Also curious on this. In Liliums last test flight, you could definitely see that the air "attached" to the wing in the last part of the vertical descent, so that would suggest that some lift might be generated by the fixed wing part.
Well said and great analysis.
It is insane the capital that these firms like
Lilian generate from people and companies that do no due diligence
Tencent, tech company and one of the top 10 biggest in the world and biggest in China does no due diligence? But you do right? Lol
@@octavicolom4562 why don't they take the lilium out for a fight and record it? they only show short clips of a short flight a couple of times a year.
@@octavicolom4562 Tencent is an IT company not an aviation company. It should be easy to attract non aviation investors with tiktok videos.
@@frankyflowers I've read the LILIUM can only fly for 15 minutes, thus the Lilium is a piece of junk. JOBY has already flew 1,000 of times and 150 minutes at up to 200 mph. JOBY is the West leading EVTOL. Thus JOBY is the world leader, and copy cat Archer is not far behind per my research.
In hover those wingflaps canted vertically are going to introduce a horrendous gust response dynamic. Control logic can probably be figured out(space x can land rockets with millisecond control response challenges after all). But i expect for certification the weather maximums will be very very low
I'm not an engineer of any kind, but am enjoying this video very much. I only used to fly model aircraft when I was young. I see this as university quality lecture material. I would suggest perhaps consider breaking future videos up into 30 minute segments, to increase your UA-cam rankings, by more frequent uploads etc... however I'm not a UA-cam expert either. However that simply might not be important to you and that's fine. I'm 30% through this video and expect to have a few questions by the end of it. I'm taking some notes.
I have an early hypothesis that 4 motors with variable pitch mounted in the inner wing areas ( two on each side ) might be worth considering. That covers your 224 kW for cruise plus a bit extra to help cover drag inefficiencies of the other rotors. Possibly 6 motors if you want a bit more redundancy for variable pitch. That still leaves the bulk of motors for VTOL.
NOTE: There are claims out there that CATL claim just released a 500 Wh/kg battery. Even if that were true, I remain a bit sceptical of this Lilium Jet.
Agree that hover capability should be the higher priority.
The first manned flight is no longer going to happen this year, according to Lilium. The pattern of quietly slipping back tangible results continues. This latest failure should surprise no astute person who has been following the PR of this company for these last 10 years.
Good analysis. Can you do MAEVE next? Delft start-up, less futuristic.
Can you do an update on Lilium?
A better comparison than the Tesla would be a Sea King. It can definitely achieve VTOL and can definitely carry 5 people, and it does that with 2000kW.
I watched the whole video and think it is very good. However, there is a small elephant in the room here called final reserve energy. I don’t know what it will end up being for this new class of aircraft, but it is most likely going to be the same as for helicopters. So minimum 20 minutes VFR. I did not see this discussed in the video. This is going to have a big adverse impact on the range/weight. What I am saying is, it is not
even going to be able to achieve the performance estimates seen here, given it will be lugging about a 3rd more battery deadweight as a legal contingency.
One other point. I find it very odd that the mission profile is for a climb and cruise at 3000 m. In the helicopter world you would typically be in the 150 - 1000m range above ground level. Obviously it offers a modest advantage in terms of true airspeed to be higher. Maybe cooling of the electrics. Against that you have the adverse effect of low temps on battery. There is much that could be discussed from the technical POV. But in the end it just isn’t a good operational fit with short to medium range VFR hops across Northern Europe and the like. And if they think this thing is going to be doing IFR work for a living then they will certainly need a bigger battery
Hi there,
Thanks for leaving so many detailed comments - I have read them all!
The final reserve energy, to which you are referring, is honestly a big elephant in the room, even for someone like me who is generally supportive of eVTOL development. There is no doubt that this problem will require changes to the regulation. Because removing 30 minutes (I do not think it is 20 minutes; I could be wrong here) from an eVTOL's cruise flight means there is essentially no battery energy left for revenue generation.
I think most eVTOL proponents are working on the assumption that battery technology will improve and regulations will change favourably. Whether these assumptions are realistic is another discussion (for example, if I am honest, battery improvement has been more sluggish in the last 5-10 years than I hoped).
Opinions change over time, often in light of new information. So you might see me change my mind about eVTOL, in one way or another!
Thanks again for all your comments. It is clear to me that you are very knowledgeable in this field.
Best,
John
@@zhihenglou thank you John. It has been refreshing to watch a video that does a rigorous and objective analysis. And I learned a thing or two which is the reason to watch.
Ilike the overall concept. I am an inventor and an eVTOL reseacher.
With newer battery technology this concept could be viable.
Watching this in 2024, CATL has just introduced 500 wh/kg batteries. Might be an interesting option if they can mass produce them.
Could it be made viable with the addition of a 2kw generator, weighing 38lbs, with fuel?
I love VTOL but……. If one still must utilize and airport for takeoff and landing….. just buy a Cessna 182. All this effort and money spent on VTOL but nobody wants to talk about all the noise and prop-wash you’d have to deal with landing one of these at your house or the mall. Great video. Thank you.
Thank you for this highly interesting and impressive in-depth analysis. It seems that the Aerokurier paper is too conservative, but the Lilium paper is (far?) too optimistic.
I was surprised to hear that no results from the test flights have yet been included in the published papers. If too many uncertain parameters actually have to prove realistic for the concept to fly, the risk for investors increases considerably.
A first manned test flight is now announced for end of 2024 - let's see how it goes.
…first manned flight has quietly been slipped back to 2025. Service entry 2026, but that won’t happen either.
I have no academic qualifications whatsoever in design nor aviation but just a hobbyist. When I first saw this concept I have already had a few doubts about the project.
1. The "over-the-wing" multi-turbine fans design has already compromised hugely on "flying" efficiency as that is the area that a plane would generate its lift.
2. Multi-fan design...regardless how efficient each motor can be, the design required a housing assembly that creates more frontal area hence reduced overall efficiency.
3. Mult-fan design...the more parts the more lost in power efficiency, as simple as that.
Apart from Mr. Lou's detailed analysis, the above is my personal observation on the failure of Lilium Jet.
I would like to fly a machine that can -at least theoretically- glide safely to the ground in case of power loss. The current VTOL propositions seem to be riddled with too many "death zones" in case of power loss. I like your first principle analysis and style. What do you think of e-STOL hybrid proposition like Electra ? Thanks
Has anyone tried an e-gyrocopter yet? Still think they are the cinderella of the rotor aircraft industry. The other issue for me is, how much do we want vertical takeoff? There is a case for first responders, but for the rest of the world a 100 metre runway would be fine. Take offs from skyscraper roofs may still be possible, but I don't think apartment owners or office workers would want large amounts of traffic coming and going. Electric vtols are going to be noisy. OK for busy high income earners only, IMO.
@@travelbugse2829 There are several unmanned ones
@@sUASNews I will try to check them out - tks!
Add a parachute.
Conventional small airplanes can land safely without power. For example, airplanes like Cessna 150, 152, 170, 172, 182 and so forth. Typically they need 300 feet or so ... but that can be a dirt or paved road, often even a road with traffic on it, since you can lower yourself between cars to just above the road while flying at typical traffic speeds, then land between cars. Better is a school with a baseball or football field. In a message above I suggested that a better configuration for eVTOL (or other) "flying cab" aircraft would have the entire wings and canards capable of being rotated, which would make landing them in small places even easier ... a lot easier in fact, and in a much shorter landing area.
Your thoughts on Lillium now they've successfully completed hover to aerodynamic flight to hover test flights? It seems the question of range viability comes down to battery power density and aero drag. It seems entirely reasonable that Lillium anticipate further enhancements in battery chemistry and design the aircraft well ahead of current battery technology - so long as their investors are patient. It also seems reasonable that they develop multiple models of aircraft over time, waiting for battery technology to catch up.
This seems to be the approach that Eviation are taking, even though they're not an eVTOL company. Iterate the design, allow battery technology to mature.
First of all thank you for an amazing video - I learned a lot
Secondly I would like to ask - How would the situation look like if we had a battery with much higher energy density. Perhaps something like a solidstate battery or the one being developed by Enovix. Would love to see a video on this topic.
I think its fair to say that the batteries Lilium needs to achieve its performance objectives (range, VTOL) are already available. Over 300WHr/kg energy density, over 2500 W/kg power density and the ability to provide that power down to about 20% SOC state of Charge.
-What is missing is a battery that can do this economically. If this battery has a cycle life of 600 it is perfect for a car but the economics for a eVTOL suggest it would do a 60% charge every flight ie life of 1000 flights which might exhaust the batteries in l0.5 to 1 year pending on use. The batteries will still be usable but will have a 0.2% reduced range after each flight thereafter. I assume an aerial taxi will need to perform an average of 10 flight/day. It looks like there are batteries that may offer 3000 cycles possible so technical advances are needed to make economics viable.
@@williamzk9083 Thank you for elaborating on this, very helpful
Another glaring problem with Lilium's concept is the ballistic parachute they were initially envisioning to employ. A damn heavy vehicle spinning very fast on top of a forward speed of 300km/h will be difficult to rescue and it is not easier when in low-level hover, in which a chute cannot be used but adds weight. Furthermore putting the thrusters directly on top of the wing also disturbs the airflow over the wing once the thrusters stop to operate (or operating no well in sync with environmental factors). Therefore after a safety-shutoff the wings become ineffective and just add as dead weight.
Hi there,
This detail regarding the ballistic parachute is something I have genuinely forgotten about! Thank you for bringing it up. I think other viewers will find your comment helpful in building a comprehensive picture of this story.
I have not worked with ballistic parachutes before, so I cannot comment on the technical details, but I read your comment with great curiosity and interest. Thanks again!
Best,
John
@@zhihenglou I'm just a light sport aircraft enthusiast and probably not qualified to comment on the technical details. But Lilium once stated they want to certify their vehicles as LSA. But whatever happened since then they never produced a prototype that could carry a test pilot (being it only for a short hover flight). That parachute issue just comes to my mind when I go through my everyday pre-flight checklist. That said I really enjoyed your technical analysis. I used to write software for the aircraft maintenance world and I always wanted to switch to engineering the other side that actually flies. In so far thanks for providing your educational outreach here.
When I was researching Lilium's history, I also found that the company wanted to certify its vehicles as LSA (see this German webpage: webarchiv.typo3.tum.de/AR/ls-id/id/design-fuer-startups/project-showcase/lilium-aviation/index.html ). I believe the initial concept was intended as a personalized air vehicle: an airplane with wings but also a ground vehicle that can be driven like a normal car. The wings could be folded to create a more space-efficient geometry (see this picture: ua-cam.com/video/htaeARwse1w/v-deo.html ).
I know nothing about light sport aircraft. I assume you use a parachute there because you mentioned it in your checklist? Thanks again for your comments!
Ballistic whole-airframe parachutes are utilized on several aircraft that wouldn't make much sense unless you understand the philosophy of use.
E.g. Cirrus Jet has a parachute that has a maximum deployable airspeed so low that the aircraft would be well below its operating speed to utilize the chute in an emergency. It is completely and totally inadequate for most high speed scenarios.
But its there for one specific scenario that kills many private pilots. That is departure from controlled flight after exceeding the critical angle of attack while performing the base-final leg turn to landing at low airspeed and low altitude. Being high wing loaded and rather fast, that mistake will absolutely be fatal at traffic pattern altitudes. If the pilot is able to deploy the recovery parachute in time, it probably will be survivable. The most likely scenario is deploying the chute at an altitude of 500-1,000ft AGL, at a velocity of around 150ktas. Also, the vertical descent velocity in a fully developed spin is likely right around the parachutes maximum deployment speed, so in the case of a spin, it is recoverable with less risk of injury to passengers. Also, at high-altitude long range cruise/loiter velocity, the Dynamic Pressure may well be low enough to safely deploy the chute in the case of rapid cabin depressurization or pilot incapacitation being a single pilot certified aircraft. If one slowed down to a low indicated airspeed at 37,000' just above stall, the chute might work fine for that.
Same with this Vtol. Its not meant for maximum speed. Its meant to save lives if the power fails in a hover between around 250'-1,000ft AGL. An automatic deployment on power failure such as the F-35 ejection seat would be ideal.
@@zhihenglou Thanks to your reference, some details become clear. The propulsive efficiency of these small electric driven fans is rather poor due to Reynolds scaling, (Ackeret efficiency scaling formula) I have analysed solar cell powered aircraft like the Swiss one that did fly in sections around the world ( Piccard)
If you carry 2 persons , with today's storage batteries (4 kg/kwh) reaching 500 km seems inadequate or the reason, that a sufficient minimum reserve flight time must be provided any less requires a mayday call , that forces ATC to give priority. Even flying at altitude, the flight time with reserves is less than 2 hrs. Without a substantial increase in span, laminar airfoils, and optimal design, the range is not achievable.
New developments in boundary layer suction may overcome this problem . See University of Delft research. Have a tail dōng fēng in tropical latitudes.
What happens if the motor fails? Can it then glide to a safe landing, or are you dead?
with a canopy like that it will get hot in there and it can't have air conditioning if it can't even cover its connectors to save weight.
A correction - my last post had an error in attributing the wrong duct size of Lilium to Sripad et al it was in fact in a paper on Aerospace MDPI "Electric VTOL configurations comparison' Pub Feb 28 2019 by Basshini and Cestino --the figure for the duct/fan diameter was 0.15 mtrs - the actual diameter is about 0.3 mtrs (so the disc loading was overestimated by four times ) apologies for the mistake , I was working from memory and just found the original paper .
I cant wait for 2019
@48.31 Hover efficiency is not equal to FM, but to FM*Ideal propulsive efficiency.
Therefore you shouldn't compare the 0.4-0.7 FM to the overall efficiency indicated by the anonymous author.
Please let me know if I'm mistaken.
Very detailled, thank you very much for your insights! I believe there is one fundamental issue with our contemporary construction of eVTOL flight however: We keep thinking in hover+cruise, insisting that such an aircraft must begin and end its flight in a hover phase. I believe this to be a flawed and counter-productive way of thinking. This may be an oversimplified example, but we should take inspiration from how birds (hummingbirds excluded) fly. They expand a great amount of energy in their initial flight phase and almost none in their terminal flight phase. When a bird lands, it does not go to 'hover', it comes in at a rather high speed, opens up its wings to a huge flare, then two or three flappings of their wings later, they are landed. Their whole flight-envelope (at least for short to medium distances) looks more like an extended, semi-parabolic jump than the rectangular profile of hover+cruise. If we started to design eVTOLs around this concept, we might be able to achieve significant increases in efficiency as well as a deeper integration of electric propulsion as a whole. Two examples for the latter: Electric motors (given some thermal capacity) are great at providing short, intense bursts of energy, exactly what a bird would need at takeoff / launch. No need to burn through energetic or thermal headroom through extended periods of hover. Second, given a relatively high 'cruise' / vertex altitude and substantial overspeed headroom, the last quarter (or so) of the flight could be used to windmill, re-capturing some of the energy that was expended to get to that height, recuperating the energy reserves required for this bird-like flare in the terminal flight phase. If (future stuff) we were able to integrate hydrogen fuel cells, we could further exploit this framework by using (possibly) liquid hydrogen to cool the motors in the launch-phase to further increase thermal headroom and possibly even - through the use of superconducting materials - increase motor efficiency. Overall, and I might be wrong with all of this, but I believe that what we need is not (only) more energy dense batteries etc. but to re-think the fundamental framework of flight that we envision eVTOLs upon. There are so many cool, eVTOL-related technologies out there, I think what we need is an adequate framework to stitch all of them together.
More people need to see this type of level-headed analysis. Then we would see more emphasis on proven technology (like HS trained) and less on these ducted pipe-dreams.
It's a low brow attempt at exaggerating his low brow concerns. They passed all 4 DOA audits and passed 3 before he posted this video. He should have known better
Makes total sense. What do you think about the design of Convair XFY Pogo, will that work with an electric double prop system? I am looking into building something similar asap I can get batteries from Amprius
I do not know what to think of the design because I have not examined it in detail. But I would look forward to you building it and sharing your results (a UA-cam video? I would subscribe). Good luck!
Why not incorporate ground powered air assist from take off? Upward air forces under the wings from a ground based launch pad could dramatically reduce battery drain during the lift off.
There is possibility for development with such concept but the realization of it is not going to be as easy as portraited by lillium, reminds me of the same situation aptera is right now sadly. Really enjoyed the somber and technical dissection of both papers.
Thank you for putting the time and effort o break it down in detail for the public.
aptera don't have to fly lol
Very good analysis. The true range and payload capabilities, with realistic and reasonable values, are probably significantly higher than the Aerokurier paper but not as high as Lilium postulated in their paper, which should have been far more robust in its calculation and validation of key parameters.
I suspect a 5 person version of the design would have a range closer to that demonstrated by Joby, probably nearer 100-150km, and cruising at more like 150-200km/h, not 300km/h.
As for the 450km/hr and 500km range estimates put forward in 2015, they were fantasy. So were the project timelines.
One elephant in the room the video did not mention is battery cycle life. Even if a battery with sufficiently high specific energy (Wh/kg) and specific power (W/kg) is produced, its cycle life is likely to be low (maybe a few hundred cycles). Cycle life has a huge effect on operating costs because short life = more battery replacements, which are very expensive. This has the potential to wreck the business model and leave VIP transport as the only market sector. Difficult to see how it can be a mass-market “Uber like” proposition.
joby never demonstrated its range just said they did. where is the demonstration of the range? they are both scams and vaporware
…yes, battery life is a big problem (I think he did touch on it). It is most likely that EASA will impose short battery ‘TBO’ based on the 700 hour limit they slapped on the Pipistrel with its relatively tried and tested battery technology. Compared with the equivalent piston engine, that battery replacement costs more than the 2000 hr engine overhaul and needs done 3 times as often. So even if a new type of battery becomes available for Lilium that can provide the performance, there will be no operational experience to prove its safety and longevity. They will have the devil’s own job trying to convince the powers that be to certify it, in this post 787 Dream-burner battery fiasco and post 737 MCAS debacle certification environment.
Would love a deep dive into why evtol systems don’t use PEM fuel cells or a hybrid approach to reduce battery weight.
Green politics and delusional denial of basic facts of physics as things scale. Dunning-Kruger ignorance coupled with wishful thinking.
Just look at current German politics, they want to electrify transportation plus heating which would require about 500GW additional power plus large amounts of minerals and materials like copper, lithium, neodymium etc but instead of expanding electricity production they are reducing it.
And no one even thinks about securing the minerals. No one is investing and building the new mines except for the Chinese. They don't care that solar output in the winter is low and sometimes PV might even be covered in snow when most power for heating will be needed. They don't care that wind power is negligible for weeks in the winter months in some years. They don't care that the storage needed will be gigantic if they don't use fossil fuel power or nuclear but they are neither allowing nuclear nor working on backup storage.
Green and electric is sexy and clean in the minds of the willfully ignorant woke left-green fascists and their sheep. The consequences will be great destruction of wealth. But in the end they will blame capitalism for their impoverishment and demand even more socialism and government intervention in the markets.
Because thats way more complicated. Hydrogen is a beast that is hard to tame. Batteries and electric engines are easy, as long as you stay below a certain power consumption and range
Me too. I've also wondered if these concepts could use spring loaded legs to help leap into the air?
Very good job. Non-bias annalists.
For an urban aircraft to be usable, it needs to be able to safely handle strong, gusty winds, rain and snow and turbulence due to low level operaration. Density altitude is also a huge issue. All tests seem to be no-wind tests in calm sunny weather. If you have ever done a rooftop landing in a helicopter, you know how tough that is
yes, I noticed that too planes just like cars need to have some weight for basic stability, how much? am not sure ? more questions than answers came up after this review
That is an astute observation. What is most noteworthy about the Lilium YT channel is not what they show us of a big r/c model flying about with agility that would be underwhelming on the bridge of a super tanker, but the absence of a single flight in so much as a moderate wind. There is not one example of it performing a spot turn, nor even so much as a ground taxi. And yet they cling to the line that they are on track to have a 7 seat version certified and in commercial service within 2 years. It is deluded. We are seeing a version of ‘The Emperor’s new clothes’ fable play out in front of our very eyes, and it is apparent that most of the people watching are the idiots of that tale.
Can you please do a video on the Jetson One?! I feel like that concept done in a price reduced way could be the answer to evtols.
Why do evtols have to have multiple passenger. You could have ten of thousands of adults flying inside of a year with a cheaper mass produced jetson one
An excellent summary of the state of Lilium's technology. I ran the numbers in 2018 as well. That was less thorough, but I also used Leishman's standard analysis techniques and results from modern ducted fan research from projects like the XV-24.
A crucial pin in Lilium's (and Joby's) forward flight L/D was the NASA research leading up to their founding regarding blown wings and distributed propulsion concepts. Joby pivoted away from this concept for a number of reasons, and I am not aware of any full-scale demonstrator that has flown at relevant Reynolds numbers. An L/D of 18 could be legitimate if and only if the promises of distributed propulsion drastically increasing stall C_L are true, but this has yet to be proven out at scale.
For their sake, I hope investors are taking note of your analyses. They are in line with my previous estimates and with what I'd expect of my colleagues at the University of Maryland.
The "marketing" of Lilium expecting huge leaps in technology to improve their business cases only seem, based on my knowledge, to be borne out in the event that a new battery chemistry matures in the very short term.
Work has been in progress on Lithium Sulfur batteries for years as an eVTOL energy storage mechanism, but I have not heard of the chemistry problems drastically shortening the cycle life at high specific energy being solved as yet.
Check out Jeff Dahn's research. He's actively working on relatively high energy density batteries with a lifespan over 10,000 charge cycles. An actual test cell is demonstrating nearly zero degradation after thousands of cycles with a projected lifespan of a whopping 19,500 cycles!! The secret sauce is silicon carbide that allows for high energy density and long battery life.
The Lilium demonstator has flown with full transition of main and fore-wing now. Batteries are improving to allow the necessary performance and economics.
@@williamzk9083 Lilium has a design that potential customers far prefer to the likes of the Joby S4, Archer, Vertical VX4, etc. with their many exposed props flailing the air. Pass.
The efficiency and performance disadvantages are forgotten when the customer experience is superior. That's why regional jets are preferred over much more efficient turboprops. Batteries are only getting better and will make longer range flights a reality. It really is just a matter of time.
@@williamzk9083 "Batteries are improving to allow the necessary performance and economics" Practical examples please.
Or are you telling us your wishful thinking?
@@wolfgangpreier9160 There are laboratory devices available in small quantities and excess 400 what hours per kilogram. This is above the 300 watt hours per kilogram that Lilium needs to get its ranges objectives. In fact 500 hours per kilogram laboratory devices. Why don’t you spend some time researching batteries maybe take a positive mindset to things and stop listening to nonsense speculation by some aerodynamics Proffesor unqualified in the area of batteries, who wrote stuff five years ago.
oh and the Pipistrel weighs 1200 lbs vs 6000 for the Lilium. So battery density might have to be more like 10x -20x current lithium batteries.
What would be the opportunity to change the design to rex/hybrid solution? Try to get the best of both worlds.
I would be very interested in seeing what the power requirements of a STOL take-off and landing of the Lilium would be when a short ground roll is possible. By taking off with the propulsor arrays at an angle that is somewhere around 45 degrees the upper surface suction at low speed would result in a very large lift coefficient. As such most of the force necessary to lift the aircraft then comes from lift on the wing and canard with a lesser portion from the vertical component of the thrust from the propulsors. With such a high lift coefficient, the stall speed is correspondingly low. The result should be a very short take-off distance (~50-100 m?) along with a very steep departure and approach angles at a power level that is likely 2-3 times that of cruise as opposed to 10 times.
With less energy used during take-off and landing, more remains available for cruise, and so increasing cruise distance. So I would hope that anywhere the Lilium can avoid take-off and landing vertically it probably should do so.
This is all about Physics & Chemistry and with current Li-ion battery tech & many small fans (which are less efficient w high disc loading than larger fans) 300km & 5 ppl isn't happening. Lillium has no incentive to be honest & fair as they need to raise money. It looks cool but won't work as advertised. Excellent video. Lillium using calculated thrust not tested is mad! And using battery mass ratios from Kittyhawk (which is bust) misleading.. And the lift to drag ratio nuts. Basically Lillium are using best case models, not experimental data. Inexcusable. They will likely go bust without a battery revolution. Test. Test. Test!!!! Not numbers numbers numbers!!!
If there was a battery paradigm shift then we wouldn't need lilium because could make one.
Many also laughed at Hunter Kawald's e-hover board for being engineering impossible but there he rode it in Times Sqr, and every where.
So as many big auto makers laughed at Tesla when its inventors came up with a prototype... saying engineering impossible.
The SECRET sauce is the trick to supply enough consistent electric juice and software energy planning.
People might pay to fly in it because of the fine design and the fame.
To have a Lilium arrive at a ski resort and fly down to Innsbruck airport would be special for wealthy people. It's a long descent down the valley from St. Moritz, for example, which would help with the battery problems.
There is a stream of videos about new battery technology that is going to change everything. In the meantime, to have something providing such a service would help further the dream.
…a stream of videos about batteries isn’t going to get this thing certified.
@@XPLAlN
That's true. They expect it can be certified with existing battery technology. New batteries may open up more possibilities.
The Lillium concept is a brilliant idea but VTOL is very wasteful of energy so short take off and landing would be a better route to follow.
What a great Idea , those lithium batteries really do burn like rockets !!
Another thing that has not been discussed is spillage drag. If this thing is meant to be only using 10% of maximum thrust in its cruise condition, there will inevitably be a great deal of spillage drag over the large array of ducted fans. It makes the claimed L/D ratio of over 18:1 seem all the more implausible.
18:1 is about normal for a modern jet airliner. A B787 perhaps 21:1.. The small wing area means parasitic drag is reduced.. The suction across the top of the wing ensures laminar flow.
@@williamzk9083 18:1 is in the region of a modern airliner but therein lies the issue, it is a bold claim for any eVTOL to achieve drag as low as an airliner. Saying “small wing reduces parasitic drag” is beside the point as the area reduction also reduces lift in the same proportion as drag so you cannot improve L/D that way.
The key parameter for good aerodynamic efficiency in the subsonic regime is high aspect ratio. The Lilium jet appears to have an aspect ratio that would be unremarkable on a typical light airplane (where 15:1 L/D would already be exceptionally good). They claim distributed thrust is going to make all the difference, but it is a stretch, and given the lack of evidence to back this rhetoric everyone should treat this number with great skepticism. The large array of ducted fans is extra drag. The bottom line here is those fans need to increase lift by 18 pounds, for every pound of nacelle drag, otherwise the airframe L/D ratio is degraded rather than enhanced. Nobody is denying that blowing the wing will increase lift - that isn’t new - but is that going to net you 18 pounds extra lift for every extra pound of drag? Particularly given it is meant to cruise at only 10% of rated power so high spillage drag is implied. It would be futile to try and estimate nacelle drag, suffice to say that those EDFs are likely to spill a lot of air in the cruise.
@@williamzk9083….if 18:1 is normal for an airliner cruising with optimal spillage drag, how is the Lilium going to be able to match that with the extremely sub optimal spillage drag? The answer is it won’t. And why do you say “the suction across the top of the wing will ensure laminar flow”? The rhetoric rolls off the tongue easily but it requires a theoretical basis that may or may not be credible…
@@XPLAlN I don’t think there is any spillage drag as the Lillium jets electric ducted fans as there is no compressor that will need to reject excess air. It’s a fan and doesn’t have spillage drag.
@@williamzk9083 You get spill drag with or without a compressor. It depends on mass flow through the fan, airspeed and inlet area. The Lilium mass flow is 158 kg/s according to their white paper. They don’t state inlet area, but based on fan diameter they will need to spill 30 kg/s in the 300 km/h cruise. That is over 30 000 litres per second. The extra drag is anyone’s guess, which is effectively all they do. Coefficient of drag of the nacelle is, quote, “set at 0.017 because it is a lifting surface”, a number dropped into the paper without explanation. Just calling the nacelle a flap won’t make additive drag go away.
But that isn’t the biggest problem. The entire drag analysis of their white paper is full of holes. The claimed cruise L/D of 18.26 leads to an L/D max exceeding 20. Just no way is that credible with fixed gear at the aspect ratio of the Lilium. The Cirrus Vision Jet is a similar sized modern composite airframe with L/D max of 15 - gear up.
The canard is not included in the profile drag. Only its ‘flap’ is included. A plan view photo on their blog shows the flap is only 70% of the area of the canard assembly. Why is the rest not included?
The estimated ‘flap’ area is itself bogus. They simply multiply fan diameter by duct length and number of fans. But that ignores the nacelle surrounding the fan! Hence the ‘flap’ area used for the drag estimate is a clear and wilful underestimate.
I can get their induced drag estimate from the theory they cite. However, Lilium claim a span efficiency factor of 0.83 and I cannot get this without including the area of canard that is missing from the profile drag estimate. In other words, there is some real estate ignored to the benefit of the profile drag estimate that is then included to benefit the induced drag estimate. Dodgy.
Cooling drag is overlooked but will likely be significant. The all electric Pipistrel Velis has a 13% deficiency in L/D max to its piston sibling - due in all likelihood to the extra cooling air scoops.
Lilium estimate induced drag is only 36% of total drag in the 300 km/h cruise. But L/D max occurs when induced drag is 50% of total drag, so using Lilium’s claimed Cdo and efficiency factor the L/D max ends up being an astonishing 20.4! We are expected to believe this thing with its fixed gear is going to be more slippery than the best airliners out there.
A favourable estimate of the wetted aspect ratio is around 2.4 which suggests an L/D max of about 14 based on extrapolation from the known L/Ds of fixed gear airplanes (re Raymer’s Aircraft Design fig 3.6). With a modern composite airframe they may exceed 14 but getting to 20.4 is fantasy land.
The white paper in no way validates the suspiciously low drag count claimed for this concept. On the contrary, it shows all they did was ignore multiple sources of drag. Nonetheless, the elephant in the room remains the battery specific energy.
Jetoptera has been silent for years, I wonder if their tech has run into problems. Would Lilium have use for such bladeless fan tech?
I guess we have to know, what most Projects are for? It is for how to make it works!
How do you feel about EHang?
Thanks John -it seems that any 'lengthy' response gets treated as spam from what I can work out . My laptop is pretty ancient and has some other quirks like 'striknig out' text at random.
The whole eVTOL scene is like the wild west at present and has been driven by irrational exuberance fueled by cheap money and ignorance plus the easily exploited desire for flying cars in the public mind . The vertical flight society seems to have taken a hands off policy with Darwinian selection expected to winnow out the 'unfit' but those included in the directory also claim the imprimatur of the organization just by being listed ; it is hard to know what else could be done but at least some sort of disclaimer might be made ( it might have been but if so I am unaware of it ) The situation is reminiscent of the ultralight boom of the 1970s that was a free for all with predictable results and bad publicity from fatal accidents (maybe moreso in Australia since we had had a total ban on local experimental aircraft design ,only imports, and thus a dearth of engineering experience -- the hiatus in VTOL activity for many years after the burst of new designs in the 1960s (the tri service competition etc ) and failed experiments leading to the 'wheel of misfortune' of VTOLs created a similar 'know how'/ ' know-how-not-to , gap. ( I think it was a Lockheed engineer who dubbed it as such - a similar thing could be done for unsuccessful flying cars of any type ,including VTOL which bridges the new field of 'air taxis' .
Just substituting battery power and computer software is not enough to solve the inherent defects in basic design. The tilting lifting duct was pioneered by Alexander Lippisch and adopted by Dornier in several drones and later again by Paul Moller (with a caveat - he expected that FIXED ducts with venetian blind flaps in the duct exits would give him VTOL -- look at the first depictions eg popular Mechanics covers . After Martin Cole ,then vice president of the Australian institute of engineers, extoled the great promise of the Moller Skycar in an editorial in ~1993, which was brought to my attention (he wanted Australia to get behind Moller ) I advised him of the NACA research that debunked the possibility of so much flow turning ( I had access to the complete set of NACA/AGARD etc research reports while working for our aeronautical research organization DSTO ) The tilting duct 'aerodynes' had to hover about 45 degrees nose up -- soon after Cole visited my home/design office he advised Moller and then Moller 'redesigned' his design with - you guessed it- TILTING ducts . And commenced to make his usual claims as if the thing had flown successfully - by tilting, the fans did not interfere as previously - (just as the Joby now does in forward flight) Ignorance of the findings from vast amounts of prior research means that all the old mistakes are being repeated . The staggering diseconomy built in to the lippisch concept as adopted by Lilium is matched by the shortcomings in contollability in gusty conditions that will become apparent (the induced airflow is inadequate to negate gust effects on the fixed surfaces and is not comparable to slipstream blown wings /tails - the fixed wing areas are a big liability in hover but are needed to support the huge hidden mass in batteries -unlike earlier gas turbine VTOLS that had much smaller wings sized for cruise .... enough for now . regards,
If you can, would you give your best estimate given current aerodynamic, propulsion, and battery theory as to the best and worst range capabilities?
You seem to have sufficient information available to ascertain Lillium's flight range assuming a best-case demonstrator.
Hi there,
Regarding your question, I can suggest the following study, conducted by a German professor: iceberg-research.com/2022/08/31/liliums-misrepresentations-over-its-technology-keep-mounting/ You need to scroll down until you find the PDF file. Then, you can skip to section 6 of the PDF file).
Best,
John