The Lilium Jet
lilium.com
lilium.com
In this case, there's really one big benefit at the cost of a lot of negatives.
It can VTOL/VSTOL. Most fixed wing airplanes cannot do that. So it can theoretically take off in a parking lot or a helipad or a small field. That's really the only plus as I can tell.
The negatives are many compared to a traditional plane. In no particular order:
Less efficient cruising due to much more drag from all the ducts and engines.
Much less likely to fly with engine failures as they can dramatically affect control (since they are essential parts of the control system).
Less control surface stability with mechanical or hydraulic failures. Those engines mounted on the surfaces hanging off a hinge are very heavy, and in some failure cases they would hang low and create immense drag.
Yaw (rotational) control is highly dependent on working engines on both sides.
The glide ratio of the aircraft would be very poor with all the drag, even assuming the surfaces were still controllable (not hanging).
I didn't see, but I assume a parachute is part of the plan for this. I doubt it could pass certifications (at least to carry passengers) without it.
I don't know if electric motors are more reliable than ICE, but I speculate that they are.
------ Edit, my opinion below:
VTOL is a HUGE WIN. It's the holy grail of flight. Fixed wing aircraft are inconvenient because they need a mile of flat blacktop for takeoff and landing.
Affordable eVTOL craft could change general aviation forever. The problem with helicopters is insane maintenance overhead and low fuel efficiency. The problem with fixed wing is you can't land it in your back yard. EVTOL is interesting in that it could bridge the gap between these two to provide a personal aircraft that has the best of both. Napkin math shows it's possible, and we're seeing some really cool products now.
That said, both terms have been used for a very long time for a very wide range of overlapping things. MIT has a nice history[0] of the words and why they are essentially synonyms in most cases (with engine being more appropriate to use in non-mechanical contexts like search engines and economic engines and motor being more appropriate to use as a gerund like motoring through something or motoring around the countryside).
[0] https://engineering.mit.edu/engage/ask-an-engineer/whats-the...
From there we tend to shorten it to either motor or engine. Perhaps in current times people here the terms "combustion engine" and "electric motor" most commonly and assume there is an implied distinction.
Typical general aviation aircraft (which this seems comparable to) need <1/4 mile runway (e.g. a Cessna 172 is less than 1000ft) which in the US means ~20k available airports.
My point being, the reason those airports are lightly used is driven by cost not that they inconvenient.
My family had a weekend at a popular vacation spot about 80 miles from where we live (about 2 miles from the downtown area of Melbourne, Australia).
The drive takes roughly two hours door to door.
We’re in a suburb that happens to be on the right side of the city to be close to the GA airport, but it would be a 20 minute drive to the airport, say a 30-minute flight, and another 20 minute drive from the destination airport to our accommodation. If you could do the transitions between car-plane-car in less than 20 minutes total I’d be very surprised; net result, you’re saving maybe 30 minutes on the trip.
If you could put VTOL ports within 10 minutes walk of each destination (say 500 metres) you could cut the trip down to less than an hour.
To be fair, the amount of luggage you’d have to carry/push in this scenario might well still tip the balance in favour of the car for the holiday trip, but there are plenty of other scenarios where similar trips are made without the need to carry a mass of luggage where the VTOL is a massive win.
Cost to drive (.50/mile) = $40x2 (round trip)= $80 @4hrs
General aviation 20min+45min (Cessna 172) + 20min= 1hr 25min x2 is 2hr 50 min (let’s call it 3hr) 1.5 hrs flying time @$300hr (let’s exclude cost of ground transport) means $450. So $270 to save an hour
If vtol saves another 2.5hrs for $270 and has the same cost profile, Than that’s great, you’re still spending >$100hr on time savings (and this optimistic, because I think most uses cases have lower ratio of airport travel time to flight time, you would then need to value your time at >$285k a year (pre tax @30% and 2000 hrs a year), which is not that huge a group of people
A motor is metal spinning in a magnetic field, powered by chemical reactions in a battery.
Which seems more likely to fail?
If a plane engine fails, you can glide, but you need a nearby road or field. If a helicopter engine fails, you can auto-rotate but have very little margin for error and need forward momentum. There are also more single point failure parts in both helicopters and fixed wing planes.
If you get a partial failure on a Lilium you probably have much more flexibility to do an emergency landing as you have the other engines for control and redundancy.
I'm sure it will take a while to work the kinks out, and sure there are tradeoffs, but I'm not sure this is a jack of all trades master of none situation. I could see the jet carving out its own niche.
And yes, it could be a huge flop, just sharing a counterpoint.
(Of course, Lillium's aircraft is battery-powered. But it's not fair to say that an aircraft capable of VTOL will always have a dramatically reduced endurance compared to a non-VTOL aircraft, especially since this one can transition to fixed-wing flight.)
This mode of flight is said to be ten times more efficient than the helicopter mode during VTOL. That is: for each minute that they can cut from flying like a helicopter during starts and landing, they gain ten minutes of normal flight time.
I think the energy argument does not apply that much more than for other small electric aircraft.
Enthusiasts and race car drivers like lots of feedback through the control surfaces of their cars.
Most people don’t care, lack the skill to interpret that feedback anyway, and rely on driving well within the car’s limits and/or electronic safety nets to save them when they get it wrong.
Who do you think represents the closest analogue to the majority of Lilium aircraft operators in the long term?
https://thelacesout.com/for-christmas-2016-i-give-the-world-...
And your premise is more broadly incorrect. The f16, which was developed to dogfight, has had fly by wire for decades. The fly by wire allowed far greater control.
> Less efficient cruising due to much more drag from all the ducts and engines.
So, I read through some of Boeings research in this area years ago. The array of fans ends up acting like an insanely high bipass ratio turbofan. In the case of hybrid aircraft the combination is more efficient when cruising. The efficiency of a fan producing a given thrust or drag goes up with disk area, as it can spin slower and the local speed mismatch to the airstream is less. The array of fans acts like a giant disaggregated disk in this regard.
> Much less likely to fly with engine failures as they can dramatically affect control (since they are essential parts of the control system).
These are electric motors and batteries. Electric motors are extremely reliable, and in this case we have a high degree of redundancy. This thing is almost certainly more reliable than a single engine helicopter.
> Yaw (rotational) control is highly dependent on working engines on both sides.
The flaps can help with that, it's not solely reliant on differential thrust. There's plenty of precedent for yaw control of flying wings.
> The glide ratio of the aircraft would be very poor with all the drag, even assuming the surfaces were still controllable (not hanging).
You can't evaluate aerodynamics by eyeball, and that goes doubly for active devices like these wings. It's the net circulation pattern around the wing that matters, and you have no actual information about that, just assumptions. Likewise that there's some novel fault problem with a movable flap just because it has fans on it. You realize airliners have huge flaps that deal with much more substantial forces?
Given current energy density of batteries, electric planes are only useful on very short flights. If you can only operate out of airports (without vtol), the useful range of the airplane will be significantly reduced
https://www.beaconhealthsystem.org/beacon-medical-transport/...
You need roughly a football field of clear flat land for human-piloted helicopters.
In the US at least, that's nothing. It's comparable to one quarter of a clover-leaf offramp.
Medical transport helicopters have somewhat greater freedom to land in random places like roads and fields when necessary to pick up emergency patients. But that only works because police are on the ground to secure the area. And local residents don't complain about the noise from a single emergency flight. Those situations don't apply to air taxis.
Again, maybe you aren't in America, but outside of SF and NYC, literally every major city is brimming with already loud highway interchanges/off-ramps.
Just cap those and put the landing pad on top. Space is not the issue.
Say what you will about America, but we built our environment to accommodate decentralized forms of transit, it's sort of our thing.
Oh, and the cto was telling so much bullshit that it was hard to listen to. Blockchains was of course there, but also stuff I already forgot. I guess it's mostly to impress investors and to collect money, but bs is still bs.
Why do you say that? That's backward. VTOL consumes a huge amount of energy, far more than a traditional rolling takeoff.
Electric power allows you to have lots of small fans, a few of which can fail without disaster.
Also, throttling turbines up and down fast enough to stabilize an aircraft doesn't seem to work well.
There are plenty of ways to stabilize an aircraft without relying on pure engine thrust, and turbofan aircraft have some advantages here.
The distributed electric propulsion systems do have awesome redundancy, but they have significant losses in efficiency compared to fewer, larger props, which really isn't what you want in an aircraft with severe energy density limitations. I'm curious to see what the production Lillium's payload, range, and power margin end up being.
The thrust required for level flight with lift provided by wings is said to be ~ 10% of what is required for vertical take-off and landing.
https://www.militaryaerospace.com/commercial-aerospace/artic...
Battery swapping has repeatedly faceplanted when it comes to cars, but it's a pretty different scope of challenge, and it seems like every major issue is more favourable to aircraft.
On the other hand, planes are often on the ground for 2+ hrs between flights anyway, so maybe it could be realistic with enough power delivery capability to just charge a big pack in situ. Certainly simpler to plug in a big umbilical at the gate than having to have another ground vehicle reaching into the belly of the thing.
It seems like an obvious choice to me.
Perhaps if you store it in a balloon? But then volume would bed a problem for an aeroplane.
If you want to use hydrogen for aviation, LH2 is really the best answer, since the percentage hydrogen by weight is much higher. The next best thing would probably be an sofc using hydrocarbon fuel, if you really wanted to go electric, but still needed endurance.
Hydrogen must be stored as a compressed gas or as a deep cryogenic liquid. Either way such tanks are expensive, heavy, and create safety concerns. Hydrogen is a very pernicious molecule, and leaks cannot be detected by human senses. All hydrogen vehicles and fueling stations need special sensors to detect leaks. Hydrogen is much easier to ignite than gasoline. Any concentration from 4-74% will explode in air, and the flame is nearly invisible.
Refueling a hydrogen tank involves going from high pressure to low pressure, which causes the fuel line and nozzle to get extremely cold. Even in southern California, refueling a few Toyota Mirais causes the nozzle to freeze to the valve. This limits refueling speeds and duty cycles.
Lastly, hydrogen is far less efficient as an energy storage medium. With a battery, you put electricity in and get electricity out. It's 80-90% efficient. With hydrogen, you use electricity to split water, then compress and liquefy the hydrogen, then run it through a fuel cell. The fuel cell itself is 40-60% efficient. At the end of the whole process, around 30% of your initial electricity comes out of the fuel cell.
Off the top of my head I can think of biofuels plus carbon neutral recaptured co2 from excess renewable energy.
Diesel electric motors for example with the ‘diesel’ being carbon neutral biofuel. This is actually being tested on large airbus jets currently.
Hydrogen is one of the worst possible options for aircraft. Energy density is crap, tankage is heavy, failure modes catastrophic.
Having said that, with future automatiion, I do feel there's room for aircraft that combine and re-assemble themselves in mid air. For example, a VTOL tug that lifts off and starts a craft flying, but then detaches and returns to base.
This can potentially be repeated on the landing side, and even mid-air "re-fueling" via battery drones.
Possibly I just watched too many kids shows where vehicles did this and it's now my equivalent of the Jetson's flying cars.
Feels like the next crazy project for Silicon Valley Billionaires to look into now that electric flight, jetpacks, rockets that land vertically etc. are all solved problems.
Trains are a solved problem, Japan, China and France show how it's done. No need to wait for miracles or SV billionaires - ffs, Hyperloop was (likely) only created to disturb the planning of California's HSR [1]!
[1] https://jalopnik.com/did-musk-propose-hyperloop-to-stop-cali...
Trains are cool though. One big EU project currently is to connect up the train lines better across borders which are often still country centric in their network layout, which defaulted the medium distance capital to capital journeys to air transport.
The CA HSR project was started in 2008, when voters passed Proposition 1A to provide $10 billion to fund high speed rail between SF and LA with a maximum travel time of 2 hours and 40 minutes. Initial estimates were that trains would be running by 2022 with the project completed by 2029 at a cost of $33 billion.[1] Construction started in 2015. Now the official projection is to have trains running between SF & LA in 2033 at a cost around $100 billion, though in reality the two cities will likely never be connected.[2]
High speed rail doesn't make much sense in most of the US. The country is so big that most routes would take significantly longer than aircraft, even counting the extra time spent in security and traveling to/from the airport.
1. https://en.wikipedia.org/wiki/History_of_California_High-Spe...
2. https://www.theguardian.com/us-news/2022/may/29/california-h...
[0] https://www.researchgate.net/publication/347258594_Operation...
Flight Chops has a great video[1] showing a bunch of details, including the addition of "Digital Flight Rules" to VFR and IFR. Though I do love Lilium's aircraft, it is definitely more of a sports car.
Not that it matters much anymore...
[0] https://aviationweek.com/business-aviation/kittyhawk-shut-do...
https://twitter.com/wiskaero/status/1572677287455358976?s=46...
- use lighter than air balloon to life an aircraft to cruising altitude
- transition to powered flight while collapsing the balloon (by compressing the gas into liquid form?). Or maybe detaching from it?
- cruise
- at destination, glide towards touch down?
If you could first lift the rocket to a high altitude, you could get away with far less fuel. The smaller mass would mean faster acceleration (think a rocket fired from a jet fighter).
note: I'm not a rocket scientist or physicist :-)
Interesting thought, but that would mean you've got aircraft ascending slowly right through the entire airspace with limited control. Difficult to imagine it would be workable at busy airports.
> Or maybe detaching from it?
Consuming a balloon's worth of helium every flight is a non-starter, and hydrogen is probably unacceptable to passengers. Landing a balloon is also not cheap or easy, even without passengers.
> at destination, glide towards touch down?
Almost all planes essentially do this already, they'll reduce thrust and start descending a long way out.
I don't know how dense they are, but they're pretty heavy.
(someone will get this).
They may not be correct (and they seem to have assumed at least 5 more years of basic improvements) but the suggestion that they haven't addressed the problem at all is just wrong.
In five years, the problem may no longer exist. Perhaps the plan is to wait for battery technology to advance...
You're not flying NY to LA in this thing and that's fine.
https://www.pipistrel-usa.com/alpha-electro/
But these other eVTOL designs are probably just too early. It will take several more generations of battery improvements until they become economically viable.
It’s an electric aircraft with a hydrogen fuel cell system.
It's not a battery.
I would add: in a highly-regulated domain that segregates risk. FAA wants designs that won't kill people (including bystanders) when systems fail.
Battery: using lithium with silicon anodes: unproven at scale?
For landing, the Illium offers only a 60-second reserve after a expected 20-second hover. But can take time to land, particularly in wind: 20-80 seconds is too short. And since it is landing on rooftop helipads, without more reserve you could kill people just by blocking the helipad.
Perhaps they could take-off via hover and land conventionally, but that would require stronger gear placed differently.
Design: This relies completely on fans for directional stability?
FAA even for experimentals, helicopters, etc. requires controllability on power failure, and e.g., 30 minutes of reserve power, more at night.
It's doubling risk to integrate power and control, and engines into the wing. If some fans fail, you're adding controllability to power loss; it's unclear other fans could depower dynamically as required. And what if a fan goes catastrophic -- breaking the wing or nearby fans or control lines? Commercial airplanes can fly even when their engines blow up because the engines are largely segregated from flying and control surfaces (unlike military jets).
I could imagine a more conventional hybrid stepping-stone to this ultimate concept.
If you put fixed horizontal ducted fans at the front and rear of the fuselage, you get the benefit of lower disc loading for the bulk of vertical hover thrust. With colocated batteries, this would reduce power transit. On failure of both, fall back to conventional landing. On failure of one, balance out with tandem-wing alternate.
As an aside: for homebuilt tandem-wing airplane, search for Rutan Quickie or Q200
None of this applies with electric, particularly a cleansheet design.
Single vs dual engine helicopter is a big safety distinction. There's heavy lift and military helicopters with 3 engines.
I guess I mean is there a channel where air is sucked in like a Dyson ‘bladeless’ ‘fan’?
Imagine a huge two-engine jetliner.
Replace the jet turbines with electric motors. Shrink the entire nacelle. Keep shrinking it, and then multiply it until you have 24 tiny motors in 24 tiny nacelles.
Then integrate those nacelles into the flaps on the back of the wings.
That, and 12 more tiny motor-nacelle-flaps on the front canards, is how their diagram looked.
Turbo fan engines work more efficient, because with their huge fan diameter, they have lower disk loading than turbo jet engines without bypass.
Lilium has a very high disk loading, resulting in low efficiency, resulting in short possible hovering times.
It is NOT a jet. I'm fully supportive of these innovators, but lying about what the product is hurts EVERYBODY.
Grow up.