Lilium – Electric vertical take-⁠off and landing jet | Hacker News Reader

Lilium – Electric vertical take-⁠off and landing jet

lilium.com

291 pointsptrptr308 comments

Very skeptical of any claims until I hear some hands-on opinions by individuals far smarter than I am. They didn't show anything about the inside of the aircraft or the controls.

However, to speculate for a moment. If it is possible to create a vehicle such as this, then this is what I would love to see as the real direction of all those self-driving car companies (Google,Lyft,Apple,Uber,etc).

I trust humans in land-craft far more than I trust humans in aircraft, and I might even consider the problems to solve by AI in shuttling humans from point A to point B through the air might actually easier than those you have to solve navigating the roads and ground-based hazards... way less human-driven vehicles and dumb animals (including humans) up in the air and a lot more ways to maneuver and avoid them.

I think a much better future is the one where our tech companies use their AI to control these air taxis and have them pickup and dropoff between tons of mini-airstrips (including the tops of apt buildings?) and we get a new ubiquitous form of fast public transportation which takes the load off of the rest of the transportation infrastructure without creating a weird human/AI dynamic on the roads.

But, as has been said... probably too good to be true for right now.

Their useful range is almost nil.

300km cruise speed with 300km range = 1 hour endurance. General flight planning guidelines call for at least 45 minutes of reserve fuel in case of things like weather or landing holds.

So really the useful range is more like 50km.

50 km fully loaded in that thing would be amazing with present day technology. I don't think it can be done.

General flight planning guidelines do not take into account VTOL capability!

In the case of helicopters, they most certainly do.

Good point!

Real world policy aside, if you're taking off and landing vertically, would the 45 minutes of reserve fuel really be necessary if you're not constrained to use an airfield?

Also, if they could magically double it, would it then be useful for a high-end taxi service?

Don't get me wrong, even with a working prototype, I see this moving really slowly unless the company is commanded by an exceedingly talented team that understands how to influence governments to update policies.

As a taxi service, the unit would have to travel to the client, do the client's run (repeat those two steps if possible), then return to base where the batteries can be swapped out, all while maintaining some degree of emergency reserve. I'm not sure how useful it would be for a taxi service if it only had an hour or two's endurance.

If the batteries can't be easily swapped out, then there's quite a bit of downtime in charging as well.

5-10 minute charge time is just as good as swap out without the overhead. It's difficult with current tech, but is indeed possible.

> would the 45 minutes of reserve fuel really be necessary if you're not constrained to use an airfield?

Yup. High winds in an area would make it unsafe to land anywhere in that area. Ditto for low cloud cover (need a minimum of 1000') or low visibility (need more than 2 miles).

From an overview of the differences in regulations that cover Helicopters (which are likely more maneuverable at low speeds than this aircraft):

>>> Helicopters must complete the flight to the first airport of intended landing, then fly from that airport to the alternate airport; and then fly after that for 30 minutes at normal cruising speed. Normally, other aircraft are required to have 45 minutes. <<<

http://www.cfidarren.com/hpart91.htm

Long story short, batteries are heavy, heavy beasts. Generally available electric vehicles have trouble going much over 300 miles on a single charge; aircraft are going to have even more problems.

> I see this moving really slowly unless the company is commanded by an exceedingly talented team that understands how to influence governments to update policies.

Isn't that what Uber's talent really was? Getting policy challenged and the hundreds of local and state lobbying efforts?

Fortunately the FAA is far less susceptible to such "talent". State and local governments have very little authority over aviation.

FAA Minimum reserve requirement is 30 minutes. 50 ~ 150 Km is plenty to avoid most cities heavy traffic.

FAA allows helicopters to operate with only 20 minutes fuel reserve under VFR conditions.

the current airtime with current power/weight battery technology should be around 10-15 minutes with 1 passenger.

fixed wing required reserve is 30min, rotorcrafts 20min depends how this vehicle is classified, nevertheless current total airtime is less than reserva.

Level flight or in VTOL mode?

Level flight you're probably right (assuming it is even capable of the transition and level flight, I'm not convinced of that, those forward pods add a lot of drag), depending on how much energy you'd lose just from the take-off, landing and the transition. This will give range anxiety a whole new (third) dimension.

However that would make it very useful in urban environments, where people can move between high-rises without having to move through traffic, and can charge in-between. This would likely be their first market.

The vast majority of urban high rises are incapable of accommodating landing pads.

Interesting. Why is that? Seems like a fairly obvious extension to keep in mind, at least at this stage.

Roofs aren't flat, aren't designed to support extra weight, and/or filled with antennas and HVAC equipment. If you want a building to have a helipad the architect usually has to plan for that from the start; retrofitting existing high rises would be extremely expensive. Plus upper floor occupants will complain about the noise.

Thanks. Hoping architects start planning for it then :-)

Manhattan outlawed rooftop landings and takeoffs after 9/11.

It would be interesting to see if they have "solved" the software and design engineering problem of VTOL, transition from vertical to forward flight, and GPS+Glonass guided drone like operation, but the bottleneck to implementing it is the problem of the batteries.

In which case the whole design will need to sit on a shelf for 5 to 10 years until some radical change in Wh stored per kilogram of battery comes along. The density of 92 octane petrol, aviation fuel or diesel fuel in terms of kilojoules (or watt hours) per kilogram is still ridiculously higher than the best batteries.

I'll preface this by saying that humans are terrible pilots[1], but the reality of the problem is much worse than just navigating a quadcopter around on GPS coordinates. Pilots are responsible for a complex decision making chain way before the flight happens. Is the weather safe to fly in (no thunder storms, winds low enough, density altitude, etc. which is not trivial when you're running such a small aircraft)? Is the aircraft in good condition and safe to fly? Is the cargo weight and position within the operating envelope?

[1]: https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?E...

I'm no aviation expert, but that sounds like a checklist that can potentially checked by a computer.

It's really not. Weather is such a dynamic factor that if you went by forecasts alone or a wx briefer, you'd never be able to go. Computers can't also do preflight inspections where you physically inspect the condition of the aircraft, sump fuel, etc.

what you see flying it's an empty shell.

That thing's empty. It's a giant carbon-fiber drone. Cool and all, but that is not a test flight.

Initially I thought it was using those spinning-cylinder wings to produce the VTOL behavior! Decent approach, though.

No sound. I'd like to hear how noisy it is: the wind alone will be pretty loud, even if the electric motors are silent. And again, there's nobody in that: with a passenger it's going to work maybe three times as hard, depending on how light and dronelike it is empty. They might have next to no batteries in there, it behaves like it's quite staggeringly light.

Clever to use dronelike autostabilization to avoid having much in the way of control surfaces. This vehicle absolutely depends on having those fans working, and probably couldn't glide to a landing of any sort.

Ducted fans run high RPM and screech like banshees. Just another little detail to work out. I just noticed Zennstrom (of Skype fame) is one of their investors.

on the video the transition from lift to forward movement is absent, because it's normally the hardest thing to get right on a VTOL aircraft and i doubt that is solved.

I guess I'll just have to do it myself. Fair warning, the result is liable to be goofy and insufficiently Jetson-like, but all the same it's bound to arrive eventually. I'm sure the autostability stuff will be part of the eventual result, because CPU chips are way lighter than aerodynamic control surfaces.

I'm sure the Jetsons-hype guys will continue making the direct play for venture capital money. Let 'em.

They could probably fit a parachute to compensate for the lack of gliding ability for emergency landings.

How high would it need to fly for the parachute to be effective?

Even with a rocket deployed parachute you need to be at least about 200ft above the ground for it to work. So there's a dead zone during takeoff and landing where you're too high to survive a crash but too low to parachute down. Military VTOL jets like the Harrier and F-35B address that risk using zero/zero ejection seats which can launch the pilot straight up high enough for a parachute to work but that's obviously not feasible for general aviation.

Since ejection wouldn't be feasible, wonder if an undercarriage airbag, perhaps like bumper rails to keep weight down and work around landing gear, would be effective in a crash?

If the aircraft is falling out of control there's no guarantee it will impact the ground with the undercarriage side down. Plus airbags would have to be huge and heavy to do any good.

If the wings are intact it will have gliding ability. In flight breakups are really rare, and the only other reason why I'd consider a parachute is total electrical failure while in meteorological conditions: i.e. can't see with my eyes or instruments. Night time in the middle of nowhere could also be such a case. If you can't see the ground you're probably gonna hit it faster than you want.

No it won't. Not with a wing there and canards of that size. Without power, that is a lawn dart. The only possible behavior of the rear wing is to point the nose straight at the ground in a ballistic trajectory for maximum speed of impact. That's a wide tail fin, not a wing.

and they are talking about making a five seat model, Stop the madness.

I see Uber buying this company for $1B in a couple of months.

> And again, there's nobody in that: with a passenger it's going to work maybe three times as hard, depending on how light and dronelike it is empty.

How much do you think it masses empty? 30kg? The Gossamer Albatross was 32kg!

It's got to be at least 100kg empty.

That's a nice achievement. The question is battery life. They've built a big drone. The cockpit is empty except for a GoPro.[1] How far can they go with a payload?

The video looks like a Kickstarter promotion. Too many neckbeards, not enough video of product working. A few minutes of uninterrupted flight video would be more impressive. They don't show the transition from vertical to horizontal flight, either.

There have been several battery-powered human carrying aircraft. Most are scaled-up quadcopters.[2] Here are five of them.[3] All have flown and none are shipping.

[1] https://youtu.be/ohig71bwRUE?t=65 [2] https://www.youtube.com/watch?v=hrZwt9KIvWs [3] https://www.youtube.com/watch?v=eYsDcoS5Gt8

> There have been several battery-powered human carrying aircraft. Most are scaled-up quadcopters

Umm.. wat? Afaik most serious attempts for electric (battery-powered) aircraft have been fairly conventional fixed-wing designs. As you seem to like youtube videos, here are couple:

https://www.youtube.com/watch?v=Uoy3Efsxp3o from Airbus

https://www.youtube.com/watch?v=fiu8TFnXYFY Siemens

https://www.youtube.com/watch?v=WiADDbeFanU Pipistrel

https://www.youtube.com/watch?v=Xe1g1JrRRkY Electroflight

I think the Pipistrel one is actually already shipping today.

I was just looking at the VTOL aircraft, since the parent article was about a VTOL.

[1] is the Lilium Jet that the article is about.

[2] is the Volocopter (18 rotor drone), but some weird video (titled "The Amazing Biggest Drone in the World"). This video is published by Volocopter, and more comprehensive: https://www.youtube.com/watch?v=OazFiIhwAEs

[3] covers the eHang 184 (4 twin rotors), the Quadro UAS (20 rotors), the Aero-X ("flying bike" with 2 ducted fans), the Flike (3 twin rotors, coming to market in 2016 (?)), and the Volocopter (18 rotors).

As a pilot I would never step foot in this thing. The thought of being in an aircraft with zero aerodynamic control, or ability to glide in a dead stick situation is a complete nightmare. It doesn't matter how redundant your systems are if you have a fundamentally unstable airframe with no yaw control. In a total power loss situation, you must have some type of glide profile. All other forms of aircraft have this. Such a design would be fine for drones, but this will never carry humans.

How is the glide profile any worse than a helicopter's?

Helicopters glide or 'autorotate' tolerably well after engine or driveshaft failure, at least enough to land controllably.

In the R22 two-seater the best glide ratio is about 4:1 ( 4ft horizontal for 1ft drop ) and those at my local airfield practice autorotation to landing all day long.

Apparently the worst helicopters for autorotation are those with Kamov's superimposed coaxial rotor system, which struggle to reach 2:1 for some aerodynamic reason I don't know.

In a helo you can attempt auto-rotation, which while tricky at least gives you a fighting chance.

>How is the glide profile any worse than a helicopter's?

This is a common misconception. Helicopters can glide to a landing just like airplanes.

Helicopters glide quite nicely. Learning to autorotate is something you learn early on when getting your license.

Rockets, balloons, most military aircraft? Shove a ballistic parachute on it.

> "Rockets, balloons, most military aircraft? Shove a ballistic parachute on it."

As far as I know, no rocket or military fighter jet has ever been certified to carry paying passengers for exactly this reason. We're talking about shuttling people around, not highly trained test pilots.

Balloons are actually far safer than fixed wing aircraft for other reasons. It would take a complete loss of the canopy for a balloon to fall out of the sky. When they run out of fuel, they just drift slowly to the ground.

Ballistic parachutes are a last resort option, and add a large amount of weight and complexity to the aircraft. Not to mention that they do not scale up to larger passenger aircraft. It's not even comparable to the safety afforded by a stable airframe.

You cant dead stick a cessna in an urban environment, and current ballistic parachutes aren't that heavy.

https://aviation.stackexchange.com/questions/24946/what-is-t...

>You cant dead stick a cessna in an urban environment, and current ballistic parachutes aren't that heavy.

Except a ballistic parachute does absolutely nothing for you in the scenario where > 90% of accidents happen: take off and landing. Even the most advanced BRS systems on Cirrus planes require 1000 feet AGL. There's simply no getting around the basic physics of this problem.

Yeah but dead sticking is less effective during take off and landing as well.

I watched someone who wouldn't make the runway (pilot error, didn't switch the fuel tanks fully on approach) dead stick onto a perpendicular highway.

With a light plane, you can do a lot with a dead stick. They have remarkably generous glide slopes (nearish to a mile horizontal travel for every 1,000 vertical feet). Not to mention being inherently stable whether under power or not.

Well a 0/0 safety system seems like a solvable problem in the scheme of things. airbag + chute? Who knows.

You can't dead stick most aircraft in an urban environment. Unless you are Sully...

Let me clarify that, you can dead stick a cessna and land it outside your local bar in NYC (someone did) but its not easy.

https://en.wikipedia.org/wiki/Thomas_Fitzpatrick_(pilot)

https://cityroom.blogs.nytimes.com/2013/06/04/long-ago-a-pil...

Once a parachute is deployed there is no control among many high rise buildings.

On the technology page under the safety first section they talk about a parachute being installed as a last resort.

Is this dissimilar to a helicopter though?

Helicopters can auto-rotate, "gliding" on the momentum of the main rotor. This allows for a controllable landing under loss of power.

There have been rare cases where a mechanical failure seizes the main rotor, such as the crash of the WNBC news chopper (N8617B) in 1986. This particular incident was caused by poor maintenance, however.

https://en.wikipedia.org/wiki/Autorotation

http://www.check-six.com/Crash_Sites/Dornacker-N8617B.htm

A helicopter can auto-rotate, though that's really the least-bad option if you're in that sort of situation. It turns an assuredly fatal scenario into a hopefully, maybe, possibly survivable one: https://aviation.stackexchange.com/questions/14605/how-does-...

Here's a demonstration: https://www.youtube.com/watch?v=BTqu9iMiPIU

Haha! That Neil DeGrasse Tyson, what a dummy.

(Good sport, though. And I also thought a helicopter would drop like a rock without power.)

It drops like a rock if the Jesus Nut (https://en.wikipedia.org/wiki/Jesus_nut) fails, but that situation is freakishly rare.

So similar to how a maple seed glides?

Not really. Watch the video. A maple seed has less control over how it spins.

Roughly as dissimilar as a sack of bricks versus a helicopter. Those small ducted fans will do absolutely nothing while you fall down. Maybe they'll spin a little bit to recharge the batteries, sort of a built in confusion generator for the people doing the autopsy: "Why didn't they just land the thing, it's got some charge left?".

Where do people get the idea that helicopters just fall from the sky when there's a power failure?

Do people think that others are flying around everyday in machines that will likely kill them in case of a malfunction? Is the media is covering up all the helicopter related fatalities?

People just don't realize there is such a thing as auto-rotation.

Yes, that is exactly what I thought. Me and Neal DeGrasse Tyson!

This guy!

If equipped with a parachute like a Cirrus I would not be so scared of it. In its current iteration it's about as scary as the eHang giant octocopter.

Parachutes generally need 1K feet to be effective, and VTOL cabs will operate at fairly low altitudes. Maybe there are special ops low-altitude parachute designs that can be adapted for airframes.

As a non-pilot, that's ultimately the reality every time we fly already. Sure there's redundancy, but ultimately if things go wrong all we can do is sit powerlessly in our chair as the ground roars up at us.

The post is talking about unpowered glide profile - the vast majority of air travel is in commercial jetliners which can and do glide, providing a major advantage in case of problems.

The plane they are planning to build looks like it could glide by itself.

I have to say I'm impressed. This is a game changer for several reasons. The first is that full autonomy is much easier in aviation than with ground transport. Second is successful implementation of flying cars would change things (for the middle class and rich) in a major way: potentially for everyone if the economics of sharing these works out where regular folks could afford to hail these and the system could scale.

Something like this that connects the exurbs to the city would be a game changer. I would imagine inner city luxury housing would take a big hit. Anyways, super cool to see that thing take off.

I am squarely middle class... how in the hell would I be able to afford this, pilot training, maintenance and more if I can't afford to buy a 1960's Cessna 172? Nevermind the maintenance, training and more?

Flying cars for the masses are a delusional pipe dream.

If it's fully autonomous, which as has been noted is easier for aviation, you don't buy it, you rent it for a few minutes.

Imagine ordering a Lyft and this show up. This is amazing.

I laughed at the thought that you might one day use a ride sharing app and forget to specify that you wanted a car.

They're aiming to make it a taxi service. You wouldn't have to own one or deal with maintenance, you'd just pay the $X for your trip. And if it's fully autonomous (which it appears to be), then you -- as a passenger -- wouldn't have to be licensed any more than if you were flying commercial. I have no idea what sort of regulatory hurdles would exist or how easily they'd be overcome. But the fact that they've already built the plane would indicate that they've already taken that into consideration.

> And if it's fully autonomous (which it appears to be),

It's clearly not, since they describe situations in which onboard systems would provide notifications to "the pilot" directing them to land the plane.

alistproducer2 is operating under the premise that full autonomy, or a self-driving VTOL is easier than self-driving cars, or at least that flying cars for the masses would hinge on top-tier automagical flying to deal with the training issue.

A fleet of these forming an aerial taxi service would be the next step

The vision is an air taxi service serving the public, not personal aircraft owned or piloted by members of the general public.

> The first is that full autonomy is much easier in aviation than with ground transport.

> potentially for everyone if the economics of sharing these works out where regular folks could afford to hail these and the system could scale.

The idea is:

- You don't need pilot training

- The cost of the aircraft is shared among many people. You're not meant to buy one for yourself, you're meant to hail it like a taxi or Uber.

Plus, the only price I could find for a 1960s Cessna 172 is $12k. If you can't afford that, you can't buy a decent car either.

> Plus, the only price I could find for a 1960s Cessna 172 is $12k.

Seems unusually low, compared to the offer prices listed here: http://www.aircraftdealer.com/aircraft_for_sale/Cessna_172/9...

I was looking at this, though I admittedly know little about purchasing used aircraft: https://www.trade-a-plane.com/search?category_level1=Single+...

Ditto, I just though it might be useful to look at a larger sample size (taking "a 1960's Cessna 172" as more of a general example than an exact requirement).

Even if it's a real price, that's hardly the only cost to owning an airplane, if you actually fly it.

Similarly, the purchase price of a car isn't the only cost of owning it. Someone else later in the thread broke down small plane ownership costs (about $8000, without flying, about $10k if you actually want to fly some).

I was just replying to the price comparison with a car. Going up the thread, part of the premise was that they couldn't afford to buy a Cessna "Nevermind the maintenance, training and more".

Anyhow, the point's already been made (several times) that the purchase price isn't the only consideration.

~30k-40k for a mid 60's 172 that will actually fly, after some maintenance.

Plenty of decent cars available for $12K.

And don't forget about fuel. My horse, for example, costs me only $50/mo to keep well fed and gives me transportation year round. These sound like a huge drain on the wallet just to keep them running.

You ride it to work?

Horses were and are pretty expensive.

I think that underestimates the TCO of horses - shoes, medical care, grooming etc!

$300/month is a more realistic figure.

You dont afford it. You hail it like an uber. And its autonomous, so you dont need a pilots license. And because its picking up and dropping off dozens and dozens of 'rides' a day, the cost is shared by the user base. A short flight 2 hours away could be $100. Hell of a lot better than spending your time stuck in traffic. Also begins the process of easing congestion on highways.

The other thing is that they could still be flown a few feet above ground but without an actual road. It would eliminate the need to maintain a road system and if the thing fails at least it will not be the high altitude crash landing that kills you( although traveling at 300km/hour and loosing power will still be really bad even if you are just a few feet above ground). I think it would make it an easier sell to the public.

[Edit] Obviously I know nothing about aviation. So based on the comments below I stand corrected.

That's totally unrealistic. Low altitude flight is extremely dangerous due to the risk of hitting trees, towers, power lines, hills, etc. Military helicopter pilots are well trained and have good equipment but they still have frequent crashes during low-level training missions. If anything goes wrong you impact the ground and die with no chance to recover. The general public won't tolerate that level of risk, and the FAA would certainly never permit it.

> And because its picking up and dropping off dozens and dozens of 'rides' a day, the cost is shared by the user base.

I imagine charging time would be an issue; there would have to be well-stocked supplies of batteries near each dropoff point, and some way to quickly swap them out.

$39K for 1967 Cessna 172 seems affordable

http://www.aircraftdealer.com/aircraft-for-sale-detail/Cessn...

Annuals are at least $1000 a year, with insurance, taxes, and other costs you'd probably spend $8K a year to have it sit not flying. Add in flying costs and engine reserve you'd spend $10K or more a year.

Source: Am a pilot.

Taxes for what exactly?

Insurance is about ~600 a year from what I gather.

So not sure how you go from 1k to 8k

When you have large assets, the gov makes sure to charge property tax.

Local tax of a few hundred up to $1k, $300 loan a month, insurance is more like $1200 depending on experience. Hangar and tie down fees...

Cant find anything on taxes on personal aircraft (past purchase of course).

Loan?

Hangers are indeed expensive depending on the area, but tie down fees are like $60 a month

Many states/counties have a property tax on airplanes. But compared to other costs (insurance, maintenance, fuel) it's a drop in the bucket.

I'm calling bullshit. See my calculations in the other thread. ~1600lbs of batteries to hit their specs with current tech and that's VERY generous. Likely closer to 2k. Lipo capacity going up at 5% a year so 2025 isn't happening unless new battery tech is announced and commercialized in the next 8 years.

Also, steering appears to be entirely based on differential thrust. Power loss = uncontrolled descent. Good luck getting that certified...

I'm not a pilot, but the fan pods are flaps, so I think there's some steering there.

Also, it has a full aircraft parachute as a last resort.

Air frame parachutes are great at high altitude but under ~500ft (where you're going to have the highest load on your electrical system during landing/takeoff) they do absolutely nothing.

As far as the flaps, they are not sufficient for controlled flight. Increasing the angle of one of them increases both lift and drag on that wing so you have at best a dutch roll/adverse yaw and at worst a flat spin.

https://www.faa.gov/regulations_policies/handbooks_manuals/a...

Helicopters, as opposed to this vehicle, have the ability to be controlled even when power is lost. This is a much safer failure mode for personal aircraft then depending on a chute: useless at altitudes high enough to be fatal but low enough to result in a failed chute deployment.

Similarly, winged aircraft can glide, where this one cannot, given enough forward velocity.

This thing will drop like a rock in an incidence of power failure at low altitude and the operator will have no way to control where it hits the ground (for either their safety or the safety of those on the ground).

That's why this is so frustrating. It seems like everyone is just missing the point. Flying cars are not a mechanical design problem. We have the tools, engines, designs, etc. all nailed down at this point. Any aerospace engineering grad could design a flying car tomorrow if the energy source existed in such a density that would make it feasible. It is fundamentally an energy problem, not a mechanical one. Maneuvering around that fact, and spending time on problems that aren't solving the core issue of battery technology is a massive waste of resources.

Yes, and it always has been. From the Moller Sky car to the Lilium here, making the craft is the easy bit (well, apart from the thrust vectoring but with modern computers that's solvable). Getting it to run for more than 2 minutes with a realistic load is the hard part. Those small ducted fans are horribly inefficient by the way, a regular shaped plane with a pusher prop and the wingspan of a glider would have a much better chance achieving the range (but no VTOL).

Too good to be true usually isn't true.

Thank you, my thoughts exactly. We need to be focusing on high density energy storage. An electricity source with a similar or greater specific energy to gasoline would transform transportation to the point of being unrecognizable within a couple years. It would be as much of a singularity as AI, high temp super conductors or low cost graphene. Just putting electric motors in current generation airframes would cut costs ten-fold.

> Just putting electric motors in current generation airframes would cut costs ten-fold.

Absolutely. I didn't mean to disparage the idea of an electric drivetrain for aircraft in general. Check out Pipistrel (https://www.youtube.com/watch?v=WiADDbeFanU) they're doing some incredible things right now. They have a LiPo powered twin seat LSA trainer in production that gets an hour of flight time at 80 knots and 600lb useful load with hotswap batteries. This is the future of trainers IMO.

Please use SI units: 150 km/h speed, 300kg useful load.

Thank you for the Pipistrel link!

Aviation units/specifications are unfortunately almost always specified in knots and pounds.

A liquid-hydrocarbon fueled turbogenerator would appear to meet your criteria. You can use synthetic or biofuels if you're worried about the environmental impact. Of course the aircraft will be more efficient if you omit the generator and mechanically couple the turbine to the props.

I talk about this elsewhere in this section. Pipistrel tried this on the Panthera and the system complexity is enormous. The whole advantage of electric propulsion is it's simplicity. Might as well just use the turbine for lift.

Yes that was exactly my point. Barring major advances in battery technology, if you want to build a powered lift VTOL aircraft safe enough for civilian passengers with useful range and payload then you probably need to use a turbine engine. Batteries just aren't good enough yet.

Why energy density storage and not wireless power transmission and/or reception?

Sure, it's possible, but it's a much longer way off at the moment. There are all sorts of technical problems that need to be solved in that space for it to be viable. You need to be able to transmit in excess of 100kW through clouds without any dispersal and not set the target on fire. We at least have the groundwork laid for potentially very high capacity batteries (LiAir, LiS, etc).

I thought a fixed wing or even heli/drone type aircraft for one, two pax could fly with, say, 50 kW?

50kw is still an incredible amount of power to transmit wirelessly without cooking the target and anything that may pass between the power transmitter and the target. Go put an egg in your microwave and watch what 1kw does to it.

It would also almost certainly require line of sight and a directional antenna that can track the aircraft. Batteries could be used in the aircraft to at least land safely if there were a loss in power.

But currently we have trouble transmitting 5 watts across the 7mm gap between a wireless charger and a phone. 50kw over a distance of 1-300km is a very long way away.

Thanks. (Note that I think the wireless transmission idea is entirely fanciful and can safely be discarded for the foreseeable future. Just got hung up on the 100 kW figure...)

It may need 100kw during certain phases of flight --take off and landing for a VTOL craft, or just take-off for a standard aircraft. Cruise power is generally far less than take off/hover power.

If the craft were entirely wirelessly powered, then of course the system would have to be able to transfer 100kw. But the link(if even 50kw were ever feasible) could be designed for a lower power level, and the aircraft could draw from an onboard battery bank for extra power during these phases of flight.

Kind of like how hybrid drive vehicles undersize the internal combustion engine and then draw power from the ICE and the electric system during heavy acceleration.

But we still need to find a reasonable way to wirelessly transmit large amounts of power safely and efficiently.

100kW is the likely cruise power for that aircraft at 300kmph. It's likely many times that for VTOL

Very possibly. I'm by no means an aerospace engineer.

A quick google turned up this[1] which has a top speed of 296km/h with a 120hp(89kw) engine, and it's likely a good bit lighter than the Lilium with a full battery load.

[1] http://www.aircraftspruce.com/catalog/kitspages/nexaer.php

edit: added [1]

Any aerospace engineering grad could design a flying car tomorrow if the energy source existed in such a density that would make it feasible.

Beamed power?

Impossible for safety reasons in populated areas. And even ignoring safety issues, the conversion efficiency on beamed power is so low as to make it uneconomical.

I thought the conversion efficiency for microwaves was 80%.

Maybe in a kitchen microwave oven. You're not accounting for transmission path losses and receiver conversion efficiency.

Actually, I think that's a figure including transmission and receiver conversion efficiency, but it doesn't include path losses. That's still quite impressive, though.

http://spectrum.ieee.org/energywise/green-tech/solar/japan-d...

That's for short range transmission to a fixed receiver. So not really relevant for powering aircraft.

Such microwave systems have been proposed for solar power satellites. They have useful ranges up to 100's of miles.

Maybe, but unlikely. Lasers need line of sight and would generally be a bad idea at the power levels required (basically a weapon), and microwave power transmission requires large receiving apertures. Current "wireless charging" technologies are pretty much universally near field.

How would this work through clouds? The water vapor would in theory block or scatter everything from UV to microwave radiation. Also, I don't want to be near a 1W laser/maser, and if our energy budget is 100kW, you'd need at least a 100,000W laser pointed at your tiny air taxi.

That's called target practice.

These guys do it all the time:

https://www.youtube.com/watch?v=JtxwT6PQIw8

I'm surprised they didn't include an internal combustion engine in it to charge the battery. That's the solution for the terrafugia tf-x. https://www.terrafugia.com/tf-x/

Lipo capacity going up at 5% a year so 2025 isn't happening unless new battery tech is announced and commercialized in the next 8 years.

What about a small fuel/turbogenerator drop pod for just the takeoff/climb?

Pipistrel was trying to do this (along with a few other companies). At that point, the mechanical complexity is prohibitive along with the insane operating costs. You still need enough batteries to get back on the ground if something fails but you have the added weight of a combustion engine and it's fuel as well.

The whole appeal of electric motors is that they are basically solid state. You don't need to change oil or perform a ton of regular maintenance. Just replace bearings every few years if ever and you're good to go. Gas/jet engines need to be overhauled regularly which contributes a large portion of the operating costs. For instance, a Cessna 172R/SP uses a 180 hp I/O-360 engine that needs to be overhauled (completely disassembled) every 4000 hours at a cost of around $20,000. That's $5 an hour just for the engine replacement assuming no excessive wear or metal flakes in the oil are found.

you have the added weight of a combustion engine and it's fuel as well

Note I said drop pod.

The whole appeal of electric motors is that they are basically solid state.

I think beamed power has a lot of potential for electric jets. It's sort of magic. You get to ditch the heavy fuel tanks/batteries, and you still get the benefits of low maintenance costs for electric motors.

Even still, you would need to have the thrust to lift it in addition to your regular operating equipment and some way for it to be recovered (more weight, complexity, operating and upfront cost)

I'll pass on sitting in the tiny plane with a 100kw laser pointed at it.

> I'll pass on sitting in the tiny plane with a 100kw laser pointed at it.

Now that's one place where a tinfoil hat might come in really handy.

> It's sort of magic.

It's not sort of magic, it would be actual magic.

Perhaps Magnet bearing mounted flywheel as your kinetic energy storage would be better and lighter than battery power?

Range is helped A LOT by good lift to drag. In fact, range is proportional to lift to drag. A quadcopter cannot get very good range, but add wings, and you all of a sudden can go places.

300km is probably optimistic for this prototype. Wings are pretty short. But with extremely good lift to drag ratio (as seen in gliders, the best of which can get over 70 lift to drag), you could definitely get even 1000km range even with existing battery tech.

Range = (ratio of battery mass used for horizontal flight to total mass) * (lift to drag ratio) * (efficiency of propulsion system) * (specific energy of batteries)/(acceleration due to gravity)

So, if cruise-batteries are 0.5 of the total mass, lift to drag is 50, propulsion system is 0.75 efficient (75%), battery specific energy is 1MJ/kg (or 10^6 m^2/s^2 in alternate units, about 300Wh/kg, as good as very best lab-scale lithium ion batteries... lithium-sulfur is better), and gravity is 10m/s^2 (rounded), you have a range of:

0.5 * 50 * .75 * 1(MJ/kg)/(10m/s^2) = 0.5 * 50 * .75 * 10^6(m^2/s^2)/(10m/s^2) = 1875km.

Of course, 50% useful cruise battery weight is probably optimistic (although not too different from long distance airliners whose take-off mass can be roughly half fuel) and a lot of weight will be needed for the vertical take off and landing motors plus the payload, but it does show you what's possible even with existing battery tech.

I tend to think the prototype they showed probably won't get 300km range. Probably need longer wings for that. But their eventual goal is achievable. By the way, for long range, they're not likely using LiPo but lithium ion, perhaps those ubiquitous 18650 cells that Panasonic makes (of Tesla fame). And greater range is possible, especially as lithium-sulfur batteries start becoming more widely available (to speak nothing of lithium air).

As far as losing power to an engine, well, there are lots of engines. Also, electric motors and batteries are very simple and can be built to have extremely high reliability. The batteries and propulsion system can be built to be totally distributed, in which case there's really no feasible scenario where power is lost (unless control is lost, in which case you'd be screwed in a conventional airplane or helicopter, too). Additionally, a ballistic parachute can be and is used.

I don't think this flight is a breakthrough. A decent team could do the same thing they just did, and lots of people (including at NASA Langley) have been working on the same goal. Teaming a bunch of electric motors capable of tilting is a thing that several groups are pursuing, lots of people have done at smaller scale already, and it's only a matter of time before it's done at a large scale as well.

How do you cancel out the total system mass? I'm not completely following your derivation. Keep in mind with your math that you have to account for the VTOL component of flight too. Also, the ducted fans they're using are not efficient at all in your stated flight regime.

There are other considerations at work here as well. Having a 70l/d ratio means huge wings on something that will be this heavy. Gliders have big wings for their size and they have a very very low gross weight (ASK 21 2 seater at 900kg and a 17m wingspan). On top of just being absolutely massive, having all that wing area can cause problems in other than optimal weather situations. An ultra low wing loading will mean that the craft responds like a kite to any air movement so it would be very uncomfortable for the passengers who just want to get where they're going.

I agree that the chances of power loss are remote, especially compared to the current tech in use, but especially with new designs, you need a way of handling it. The issue isn't so much any individual motor but the batteries and support systems. They'll need a cooling system most likely and any failure will turn the whole thing into a Note 7. Also, sorry about using LiPo as a generic term. LiS batteries will definitely help the situation somewhat.

And intra-pack screening of batteries to avoid cascading failures.

It's all in that first 0.5 ratio. Basically, that ratio says that if I have a 10 ton aircraft, 5 tons is for the payload, airframe, engines, miscellaneous structure, and takeoff/landing batteries while 5 tons is for the cruise batteries. That 0.5 ratio is probably very optimistic for a real-world vehicle, but not crazily so. Burt Rutan's Voyager and the Virgin Globalflyer got much more ambitious figures, like 0.75 and 0.83, respectively (in this case referring to fuel mass instead of battery mass).

You refer to L/D ratio and lack of wing loading as if it's the same thing but it isn't. High performance gliders are generally ballasted (sometimes about half the weight is ballast) in order to increase the wing loading and increase flight speed. Our aircraft would have a 300km/h cruise speed, and so will similarly have a fairly high wing loading, even if it does need long, high aspect-ratio wings. This is helped by the fact that the sort of high performance lithium-ion batteries that you'd be likely to use (i.e. like Tesla uses) would be a good twice as dense as fuel. This increases your effective wing loading for the same outer mold line, allowing higher speed efficient cruise at the same altitude.

As far as battery and support system being a central failure point:

One interesting thing with electric propulsion is it's fairly easy to split the batteries and subsystems up /as well/ as the motors. So each motor pod could have its own small battery nearby for (possibly emergency) take-off and landing (this could also help reduce cabling mass, especially for the high currents you're likely to need for the vertical takeoff and landing portions). The cruise batteries could remain centralized, since you'll need a lot more of them and mass efficiency will be critical (and you could rely on your very good glide ratio).

It would be cheaper (and far more effective) to just run a rail line to the exurbs in question. Why don't we do that first if connecting them is that valuable/important.

Because fundamentally thats still less convenient for the customer. In a perfect world, you want to be picked up from your front door and dropped off at the front door of your destination. And if you can avoid highways and traffic, even better. This provides the infamous 'last mile' solution to transportation, instead of forcing everyone onto mainline routes and artery networks.

I don't see something like this scaling in the way that a rail network can. Shuttling a few people at a time won't be enough for morning/evening rush hour, you'd need loads of these to match the carrying capacity of a train, and then you've reinvented the problem of traffic (although presumably much less dense; e.g. I imagine you'd join a queue and have to wait until the airspace isn't congested before your journey is permitted).

That's also an optimistic outlook. One contributor to traffic is people using a whole car just for themselves; since we've not figured that out after several decades of having cars, I doubt making them fly will solve the problem.

I can imagine niches for this, and wish them luck, but I don't think it'll make a dent in mass commuter transport.

This doesn't even remotely provide a last mile solution because even if they get the aircraft working the landing pads will be more than a mile apart. Just because it's a VTOL aircraft didn't mean you can land it on a city street. A large, securely fenced area free of nearby obstacles will be needed. Where are you going to put those in a dense city? And don't try to tell me that they're going to land on building roofs; most roofs are unsuitable because they're too small or not flat or full of ventilation equipment and antennas.

Parking lots we don't need after autonomous cars.

And even the ones that are large, flat, and uncluttered won't take the weight of an aircraft.

There's a NASA study ("Concept of Operations", CONOPs) on VTOL taxis in Silicon Valley:

"Silicon Valley Early Adopter CONOPs and Market Study"

https://nari.arc.nasa.gov/sites/default/files/attachments/An...

Running a rail line point to point is cheap? More like impossible.

It's also impressive that it can each 300KM already. In 10 years, it could be about 1,500 or 1,000 miles. But 300 is a great start.

I'd be surprised if their current prototype had a range of 300km. I think that's what they hope to achieve.

You're joking, right?

It would be impressive if it could reach 300km already, but the actual evidence we have is of it flying a small circle above the middle of a runway, implying a range of the order of 300m

and physics of course, that would suggest a 300km range to be exceptionally unlikely. But what use is physics in the face of such reckless marketing hype?

> It's also impressive that it can each 300KM already.

That's a target, not what they've demonstrated.

For a speculative look at how a global network of flying cars might play out 'Too Like The Lightening'[1] was a pretty enjoyable read for me last year.

One of the consequences was that global borders essentially become worthless, and people instead join hives that best represent their ideals.

[1] http://www.npr.org/2016/05/10/476483675/science-fiction-and-...

The elephant in the room is the weight of the batteries (a few 100 Kg at least) and the range / max flight duration given those specific batteries. That's a dealbreaker with a design like this if it doesn't work out.

Wonder how heavy the demo was and what part of the weight was batteries. Everything else is just along for the ride. Short wings -> needs lots of speed to get any advantage from the wings.

It's the first point they mention on the landing page:

- 300 km range - Travel from London to Paris in one hour.

Yes, the could have written anything there. What matters is what the weight of the combination is to achieve that range (even in theory). It takes a lot of energy to fly a plane with aerodynamics such as this one, far more than your typical glider and batteries are very very heavy. Also there wasn't anybody on board.

If this whole contraption weighed more than 100 KG for the demo I'd already be very impressed, even more so if 80% of that wasn't battery weight and if it could stay aloft for more than the one minute demo.

This is not so simple.

That's what they claim they will do, not what they've demonstrated. This seems to be a modernized version of Moller International's "just around the corner" hype of the last, what, 30 or so years, only Lilium's hype seems more oriented toward potential investors/acquirers rather than selling pre-orders to aspiring individual owners of flying cars that'll never be commercially viable.

Aka investor bait. It's been awfully quiet around Moller since 2010 or so, maybe that's why this company is able to do what it does. Normally you'd be sent home to do your homework if you came up with a battery powered VTOL with short stubby wings.

The first and only interesting problem these guys should solve is how they are going to power it. Everything else can wait until then.

Well, there's an interesting, tangentially related bit in their March 2017 newsletter [0]

---

Moller International has received a number of emails from newsletter subscribers who have expressed concern that MI’s lead in VTOL capable flying cars is being upstaged by companies like Airbus, Ehang, Embraer, Google, and Joby. Nothing that is presently contemplated as a battery powered flying car is a threat to the technology that has been developed by MI.

---

Incidentally, it it wrong that a kind of want a Moller v. Lilium PR battle to be a thing?

[0] http://us2.campaign-archive1.com/?u=84c20a8ab4539585a29aaaa5...

That will only happen if they see each other as going for the same sources of funds. The one is in .de the other in the United States to I doubt that that would happen.

Even so, it would be hilarious. Maybe we can set them up? Mail them both saying you're ready to pre-order but are also looking at the other?

Incredible that Moller is still going at it and that he still manages to get more money. Elizabeth Holmes could learn a thing or two from Moller.

I give them kudos for getting past the Moeller air-car stage and actually having something flying. I think if they had been a bit more plugged into the typical fraud patterns from this sort of pitch they might have shot that video a bit differently. In particular it has exactly zero frames where it is in an environment that can authenticate its scale. Consider that this airbus380 (https://www.youtube.com/watch?v=-Rt9zX1rZFU) is a really big model but when it is in the air and there are no scale references you could believe it was full size if you had seen a static mock-up of one on the ground. To avoid this you need the unit to fly by, or operate near items that set its scale accurately. A good one is to have people near it when it takes off or lands.

That they flew it without a person is understandable (its a new aircraft after all and who wants to kill a test pilot really?) but the cockpit area was completely empty and that is a problem. Test flight data is really only valid if you're testing actual flight conditions. So they really should have had crash test dummy and enough ballast to at least simulate the mass of a pilot in command. The thing that was even more challenging was that the lift moment of the vertical fans in the rear of the wing are behind the center of mass for the pilot. So all of the pilots mass is going to create a pitch down moment on the much smaller front fans. There are really good engineering reasons that most flying car prototypes put the weight over (or under) the wing. They could of course be counter balancing the weight of the batteries that are all located behind the wing, but that would make carrying the weight in the pilot seat even more important.

It's full size, that I believe without any problem. But it really is just a scaled up model, there is no payload and it probably would not be able to stay aloft much longer than the video. (you can see the interior is totally empty in the overhead shot at the beginning of the video).

The wing being behind the pilot was probably done for visibility reasons but it will make it very hard to get those front fans retracted or at least out of the way (because of the extra drag they create).

At a guess and judging from the way it takes off the COG is just aft of the leading edge of the wing so adding a pilot would have the effect you describe.

Scaling a model is hard enough so they definitely should get some credit for that but the way it is spec'd right now it would very much surprise me if they ever go to any level of airworthiness with passengers. Battery tech would have to go through some kind of revolution (and then you'll immediately have a ton of competitors, quite a few of those are much further along in creating viable aircraft but none based on the VTOL model because of its obvious limitations).

https://en.wikipedia.org/wiki/Pipistrel_Alpha_Trainer

Has 126 Kg of batteries, can regenerate when it loses altitude (forget that with ducted fans) and has a pretty good wing surface compared to the Ilium:

https://www.youtube.com/watch?v=WiADDbeFanU

Not being VTOL it manages to get about 1 hours worth of flying time (but you'd need to keep a reserve).

So there is no question about whether or not electric aircraft are possible. It's just that I don't see the VTOL/short fixed wing and small ducted fan combination work out, especially not at 300 Km/h where drag forces would be considerable, no matter how nice the body looks.

It really is an electric version of the Moller Skycar.

This is cool... and let me say I am no aerospace engineer. I am a flight enthusiast... mostly R/C quadcopter and plane as real planes are $$$.

It looks like an extremely large ducted fan R/C plane with VTOL. Calling it a "jet" in the parlance of today seems like a stretch. Are ducted fans "jets"? I guess the argument could be made. I would think the people buying these would very well think of a jet as propulsion from combustion. Also, the FAA and turbine (jet) rating... I could go on...

The VTOL is awesome, and something I think we'll see more of as quadcopter technology scales to more robust .gov missions. The applications for this tech are limitless...

It's a "jet" in the sense that it doesn't have a visible propeller, which is really the only meaning that word has any more. Virtually all the thrust produced by aircraft that people call "jets" comes from shrouded fans of some sort.

"Jets" are called "jets" because they produce a jet of matter (water or air) behind them, causing motion via Newton's third law. If the illustrations on the technology page are accurate, this fits the bill fine.

What useful definition of jet am I missing (beyond the trivial "can't be electric") where this can't usefully be called a jet?

Well, the only definition that matters would be the regulating body with jurisdiction. In the case of the US, that would be the FAA. It is squarely an experimental plane.

That's mostly what I'm getting at. They're called "jets" because the first ones used a turbojet engine, whose exhaust jet provided the thrust. The term is a colloquial contraction of the engine name, not a formal description of its operation.

Designers (of subsonic devices) rapidly moved to a more efficient turbofan design where the exhaust provides very little thrust and the engine core is used as merely a torque engine to turn a rather larger shrouded fan which actually produces the thrust.

So... if you pull out the internal combustion engine and replace it in a straightforward way with an electric motor that drives the same shaft, are you really changing the nature of the device?

> So... if you pull out the internal combustion engine and replace it in a straightforward way with an electric motor that drives the same shaft, are you really changing the nature of the device?

Just like "turbojet" derives from it being a turbine-powered jet, I think the new electric version should be called a "magnejet". Or just "jet" for short.

Why spend the time pontificating, asking others for things that are clearly explained on the website, when you could answer these questions yourself?

https://lilium.com/technology/

I saw that and it is not a jet in today's parlance of what most pilots would call a "jet". Hell, it looks like there are 36 extremely large brushless outrunner motors.

In order to avoid a goalpost-moving exercise, what is concrete the working definition of jet you feel most pilots would agree with? Is the difference between that and this as trivial as "has an ICE"?

From an engineering perspective, if something produces thrust primarily by producing a jet of surrounding matter (water or air) and taking advantage of Newton's third law, I'm not sure I see the issue. There's no exposed airfoil, and it doesn't appear to care about Bernouilli's law (except for lift).

Thanks, I missed that (I have to say I never even bothered looking; I've seen this kind of website before). It's pretty sparse on information. I managed to find that:

- they use lithium ion batteries.

- they use LEAPTech style engine layout with multiple small engines (they don't name check it, I just recognise it from https://www.nasa.gov/content/experimental-wing-tests-electri...).

- there's a backup parachute.

- they don't mention autonomous flying, but you also don't have direct control of the vehicle --- a computer mediates.

- for some reason they insist on calling ducted fans 'electric jet engines'.

That's about it. Anything I missed?

This page is completely devoid of any actual information. It's a SquareSpace marketing site.

You find somebody that calls by "jet" anything that does not have exposed propellers. They also probably only use the name on their marketing material. Nobody goes out of their way to have regulators classify their engines as "jets".

Many people are failing to appreciate the "tesla for the skies" model that is coming. Uber is actively pursuing the acquisition of companies like Lilium. Long term, roads aren't a great solution to increasing populations. The Ubers of the sky which land in your front yard or the top of your building and whisk you anywhere within 200-300 miles is coming... fast. And by making the eletric VTOL aircraft autonomous with waypoints, no one has to be a pilot. You simply hail a plane with your app, hop in, fly to your destination and depart. Many companies are testing full-size models like Lilium... for example, http://www.jobyaviation.com/. No one has carried a human passenger yet, and none with autonomous waypoint flying. But soon... within a year.

> No one has carried a human passenger yet

Volocopter, first manned flight, April 2016:

https://www.youtube.com/watch?v=OazFiIhwAEs

Biggest problem, given they're German: these things won't fly in Germany outside of airports.

In Germany, it's not even allowed to do agricultural aircraft flying based on anything but a licensed airstrip - the only kind of aircraft permitted to start and land anywhere are SAR and military aircraft, and gliders can only land anywhere (simple physics) but have to be started from a licensed airstrip. Helicopters (SAR/military excepted) also may start and land only on licensed helipads, which won't be licensed in cities.

And to those imagining a future of living in rural countryside and flying to work... no way cities are going to permit random people flying over it, not after 9/11.

Given that this is an electric aircraft, their range estimate is delusional.

Couldn't this be solved with a small diesel generator mounted in the back?

But you'd need to cut weight by getting rid of the batteries.

Those are pretty heavy and would remove all their listed advantages.

Google 'battery energy density trend'...

I dunno. Remember it's got wings, which means once it shifts into forward flight mode, the engines are used solely for propulsion and not for lift, which is vastly more efficient.

Playing with the numbers here:

http://web.mit.edu/lochie/www/erange/main.html

...shows it can be made to work, provided the thing has very low drag (I was using a battery specific energy of 200 for a LiPoly cell). Given it's a streamlined blob with stubby wings, that seems vaguely plausible.

Anyone with a better grasp of the principles want to comment?

Update: I found their tech page (see link upthread). They use lithium ion. They have about the same specific energy as lithium polymer.

Look at the power requirements for similar aircraft to get an idea of range. An SR-20 (similar size, speed and composite) needs 180hp and probably 140 for the roughly 300kmph cruise. That's 104 kW for an hour plus the FAA 30min minimum remaining at maybe 80 kW (higher for commercial ops) that's 720kg of batteries or roughly the the empty weight of a cessna 172

edit: this is also very generous because it assumes you don't need to takeoff and climb. Max cruise on the SR-20 is 155kn so the power requirement is as much as 20% greater

I wonder how head-wind factors into that as well, I know on our EV I can easily see 10-15% consumption difference if I run into a strong one at freeway speeds.

Wind will always affect flight speeds regardless of configuration. To use physics terminology, the air around you becomes your frame of reference. 10kt tail wind and 100kt True Air Speed = 110kt ground speed

A SR-20 has a single engine at the front of the plane rather than 36 scattered over the wings. They claim, at least, that that makes a big difference in aerodynamic efficiency.

It does in some cases (see NASA X-57 where the fan is used to accelerate air over the wing, leading to a smaller wing with lower drag overall) but I'm not convinced in this case. Having a system that is efficient at high airspeed and high thrust generally requires a variable geometry propeller (constant speed prop in GA terms) because a 'lift fan' at high relative airspeed, would have to spin much faster than a 'cruise fan' like you would see on a regular aircraft meaning airflow over the blades is higher leading to higher drag on the blade than necessary.

Lift and drag are inherently connected; you can't have one without the other. So it doesn't really make sense to say that engines are not used for lift, when the drag that the engines are countering at least partially is induced by lift.

https://en.wikipedia.org/wiki/Lift-induced_drag

The problem though is with safety. This kind of design can work fine for drones, because if the power fails and a drone is lost it's not a big deal. But for a passenger carrying aircraft, you must have some semblance of aerodynamic control and glide in a dead stick situation. This thing would be a complete deathtrap.

I'm not in the aerospace industry, but couldn't it deploy a parachute in the case of power loss? Or are the batteries too heavy?

Also, what about helicopters? I guess the pilot might still have control after losing power because the blades would still be spinning?

Weight and altitude are the problem with the chute. This thing would result in a fatal accident at low altitude with power loss (total, they say it can operate with some systems lost) that are too low for a chute to deploy before you hit the ground. A similar problem exists with many ejection systems for military aircraft (pilot will escape the aircraft if it's on the ground, but not reach sufficient altitude for the chute to help when they return to the ground). Helicopters can auto-rotate, allowing for degraded performance during the descent but still controllable and survivable.

Good luck falling from 100 m or so while deploying your chute. That's the problem zone, high enough and a chute would work, closer to the ground and there just isn't time enough for the chute to slow you down. Even a crash into water from that altitude and you'd likely be dead.

I'd also emphasize that they have 9 years on their runway (pun intended) until they plan to have it operational for consumers. That's a long time for battery tech to get better.

Not necessarily. Don't be fooled by the improvements in semiconductors and storage in the last decades: not everything doubles every 2 years. Battery specific energy seems to grow at around 5% per annum, doubling only every 14 years.

You can source Li-ion/Li-Poly fairly easily (as a company, almost impossible as an individual) with 250 Wh/kg, I believe I read somewhere that Tesla hit about 260/270 with their latest power walls. Even so, I still have to doubt they'll reach more than 200km range with current technology.

Their mission is to release to the public in 2025 however, which makes the goal much more likely to be hit with improvements in technology.

I don't see how something like this is workable unless practical lithium-air or zinc-air batteries are developed. Looking at their founding team, I don't see any who come from a battery/electrical background, they mostly seem to be aerospace/mechanical folks.

Rest assured they work with a company that is really good at packaging [1]. However true, chemistry innovations will need to come from the lower end of the R&D pipeline.

[1] wrote my thesis with them, http://openbatt.org

Don't get me wrong, this is super cool technology. But imagine putting a 1500kg Tesla 100kWh battery into a much more efficient Cessna type design that is lighter and has larger wings. It would need to dish up about 80kw to maintain cruising speed, which is only about 180km/h. Factoring in the tiny wings and incredible weight, this thing would be hard pressed to stay airborne for a hour at 100km/h. I just hope is capable of gliding to a landing if the Battery dies or fails. Then it could be safer than a helicopter.

A whole Cessna weighs maximum 1100 Kg or so on take-off. With the batteries unshielded and a bare minimum for motors, structure, avionics and parachute there wouldn't be any margin for a passenger.

> imagine putting a 1500kg Tesla 100kWh battery into a much more efficient Cessna type design

Can't put 1,500kg into a Cessna - but if you are happy with 130kg of batteries for 50-60 minutes of max flight time, you can buy the Pipistrel Alpha Electro today.

...well, by 2025 it will all work because batteries will be 10x more powerful.

What would be interesting would be a very long power cable - a mains lead - that took the thing to some useful altitude before detaching. I can't see myself having a reel of copper, 1km long in the back garden any time soon though.

They didn't mention any battery specifications. Chemistry, capacity, weight, nothing. Just a wistful "300km'.

That's a bad sign. Battery technology is the gating factor for electric planes and not even calling that out suggests they have not solved it.

Great design, great prototype, now give us the power consumption specs. Show me where that 300km is coming from.

Energy Density:

Jet fuel - 46 MJ/kg

Lithium-ion battery - less than 1 MJ/kg

This is an electric VTOL craft which runs off an energy source that is renewable, unlike jet fuel. If it can be done that is what should be important here.

Can we find a better name than VTOL for these things?

Flypod or something that can be used by anyone in a regular conversation.

Impossible?

Energy density is "good enough". Cities like New York banned helipads on the top of high-rises after the Panam crash in the 70's because of the risk of jet fuel flowing down a high-rise and igniting.

Electric powered vehicles like this would solve that issue and allow quick travel around high density cities, they could land on top of buildings to pick up passengers. Current battery technology should be enough to support these short range trips around a city.

A good example would be a corporate executive traveling from their NYC headquarters to the local airport to board their business jet. It's not a long distance trip but helicopters are not suitable.

By what metric is it "good enough"? Appears to me to be not good enough by a long shot. VTOL is especially energy intensive.

Idea: vertical take-off via a detachable umbilical. On landing... well, gravity is on your side :)

That would have to be a pretty long cable, high voltage (to keep it light) and you'd have to stay connected roughly until you reach cruising speed for maximum effect.

Recovering the cable would also be fun (assuming it stays on the ground to save weight).

Maybe they can partner with uBeam for wireless energy transmission and screw two sets of investors in one go.

By the metric of range. The website says the range is 300km which is more than enough to travel in/out of the core of most major cities.

You must be new to the internet. These numbers are very wishful thinking for some undetermined future date.

One thing to keep in mind, though, is that internal combustion engines are quite inefficient, piston engines typically convert less than 20% of the chemical energy into work. Electrical engines are much more efficient, so that gives you a factor of about 5 to 10.

In other words, getting batteries with, say, 4 times the current specific energy would already make a lot of electric flight applications practicable.

At the current rate of improvement (5% to 8% per year), we should be there in about 20 to 30 years :-)

So, putting huge numbers of small electric motors on your wings has big efficiency advantages. But is there any reason this has to be stricktly battery powered? This seems like a situation very well suited to hybrid electric power with a internal combustion generator providing the power for level flight.

Hi Hacker News,

Several people in this thread have pointed out the major reason that this airplane design is not viable, which is the weight of the batteries.

I have developed an alternative that I would like to patent. I asked for an introduction here:

https://www.reddit.com/r/AskEngineers/comments/65cazg/i_need...

But I did not receive responses. Subsequent to this, I reached out directly to patent attorneys I thought would be qualified. Here I ran into a big problem. I will quote my reply email:

>"After speaking with the partner who handles our firm’s major aviation client, we have determined that taking you on as a client would likely result in a conflict of interest. This is more than just a matter of potentially overlapping subject matter. The fact that you wish to license your IP to other aviation companies would actually mean we couldn’t represent both you and our other client in those negotiations. In effect, we’d be on both sides of the discussion, which is by definition a conflict of interest."

This is actually an issue with any qualified patent attorney who might take on this case.

I would therefore like to work with an aviation engineer. I believe we could draft the patent language ourselves.

I don't want to include a terrible amount of information here, but I want to list one benefit of the invention:

- Solves the distance issue.

jacquesm's analysis in this thread is absolutely correct. This is what motivated me to ask if there were any aviation engineers in this thread. The cost to entering the aviation market is extremely high and the only viable means of doing so is via the patent approach, so I would like to work with someone who has had patents in their own name.

Please let me know if you would be someone who might be able to collaborate with me on this project, and I will get in touch with you. Thank you!

> This is actually an issue with any qualified patent attorney who might take on this case.

Why?

Because they're qualified if they have aviation patent experience. They would have aviation patent experience if they have clients.

I want to license to those clients. It's kind of a Catch-22.

The most qualified attorneys I can find easily (by Googing) are right out.

At this point I think the best approach is to pair with an aviation engineer who has gone through all this... hence my comment here.

It's by no means a simple situation. That said, I'm not really sure where I can find such engineers. I assume most of them are working with large companies and are not open to this sort of collaboration.

The following isn't legal advice and I'm not your attorney. Keep looking for someone with related but not direct experience. Many of the details of patent prosecution are procedural and legal, not exactly technical. Anyone who has done patent prosecution is better than a technical expert.

Even if you get a patent passed the examiner, you might have gotten claims that were too broad or too narrow. You might have made statements during prosecution that make asserting the application difficult. You might have written the claims in a way that is difficult to enforce.

thanks for this feedback. if you don't mind replying with an email address I have some more questions along the same lines, since it sounds like you know what you're doing. (if not you can ignore this reply.) thanks again.

Do you have a working prototype?

Hi. Thank you for your reply. I am never going to build any airplane (well never say never - I should say, it's completely orthogonal to any of my plans). I have a mathematical (-type, obviously it's physics and aerodynamics) proof that it should be possible, so that the person reviewing it would be quite easily assured that what I propose is theoretically possible - but then so is a space elevator. I do not have the level of qualifications necessary to show that it is actually easily possible at airplane scales and with present materials.

If I built a prototype (doing so is not in my plans) then it would be at a very small scale and I personally don't know how to do the calculations to see how it applies to larger scales. In other words, if I had the prototype flying around me right now it wouldn't help convince me that it's possible and plausible. Further calculations are necessary and only an aviation company (or an aviation engineer) is able to perform those.

Are you an aviation engineer? Do you know someone who could spend a few minutes on this case? I will need a small NDA but I am not very concerned of IP theft, just the formalities; the assurance can be verbal via email.

Unfortunately the medium would have to be via email as public disclosure prevents patenting and I don't know at what point (if ever) I would get to that stage. Let me know if you or someone you can put me in touch with could look at this briefly. Your profile here does not list an email.

Thank you for your assistance.

Anyone interested in the actual future of electric powered flight should check out Pipistrel https://www.youtube.com/watch?v=WiADDbeFanU

These folks are doing exactly what I've been saying for ages that someone should do once battery tech gets good enough. With a couple of brilliant additions like making the engine pods part of the lifting body, and using many smaller engines instead of a few larger ones. You can't use powered lift for long-distance travel, it isn't energy efficient enough for batteries to work. But you need to use electric motors because you get away with much lower mechanical complexity.

This is a disruptive concept regarding where people will choose to live, assuming that the details can be solved.

> The system can still do a vertical landing with a loss of up multiple engines.

I'm more than skeptical about the quality of the safety features if there are glaring mistakes in the language describing it.

I assume they used to specify the number ("loss of up to 6 engines"), then switched to the vague "multiple", and screwed up the editing.

Here's Aurora Flight Sciences, contracted by DAPRA, flight testing their similar but smaller prototype a year ago:

https://www.youtube.com/watch?v=fgWSuZbGh0s

This is part of DAPRA's VTOL X-Plane program:

https://en.wikipedia.org/wiki/VTOL_X-Plane

This seems way too good to be true. Seeing as the timeline on their mission page puts the first manned flight at some time in 2019 and their technology page states that the vehicle is built primarily with aluminum and carbon fiber, I'm guessing that this thing is incredibly light, maybe even under 500kg. The video seems to back this up with how easily the craft drifts side-to-side in the air with cross-breezes.

That low weight is an impressive feat of engineering, but it's also a big disadvantage for any real world applications because passenger and cargo weight is going to be a huge problem. You can't build passengers out of aluminum and carbon fiber. Even combustion-powered, light aircraft have serious problems with weight, and their pilots frequently have to work passenger weight into their fuel calculations.

My guess is that this technology will do wonders for aerial photography, scientific research and maybe even military reconnaissance, but transportation and any kind of serious shipping are still a very long way off.

I could easily imagine it picking me up from the top floor of my apartment building, taking me to the heliport at the top floor of an office building.

My current commute is 10 km of horrendous traffic. Driving time on rush hour = 1.5 hours Flying time @ 100kph (average of speed up, slow down and cruise) 6 minutes!

Then it would just fly on it's own to pick up the next customer.

Imagining it is as close as you'll ever come to flying this thing. It just isn't going to happen. See also: Moller Skycar.

While there are reasons to be skeptical it is worth noting that this effort is carried out in the south of Germany which is where there is a cluster of high tech resources within driving distance <2h

- BMW

- Mercedes

- Audi

- Porsche

- Airbus suppliers

- Military aerospace companies

- Key tech universities (Munich, Stuttgart) including aerospace oriented engineering

- World class glider manufacturer Schempp-Hirth

I'm curious on how they get "less noise than a motor bike". There are plenty of quad copters that i feel are more loud than most bikes, let alone the weight this thing has to put out some significant thrust requirements...

From the bottom of their mission page..

First full scale prototype has already been flown.

First manned flight planned for 2019.

On demand air transport planned for 2025.

https://lilium.com/mission/

Was the flight test done at full weight capacity ? (Passengers and/or cargo)

Congratulations. you've made life somewhat easier for the top 1%. I'm glad someone is taking up their cause for a change.

I have a hard time believing the range. We have a hard time creating 300km range on cars, how would they do it on a freaking plane?

If you put it on a bootstrap template, it must be true!

There's no people sitting in the vehicle in all these videos. Is 300km with or without load?

They've never done a manned flight[0]. Presumably they expect 300km with typical load, but they haven't actually demonstrated it yet.

[0] https://lilium.com/mission/

Looking a bit more at this, here (at the bottom) are two more videos of earlier prototypes. All appear to be extremely light.

https://www.youtube.com/c/LiliumAviation

I do expect to live to see the day that such things are ferrying people around. But I also do think that it'll take a major breakthrough in energy storage technology. And if that happens, then all kinds of things become possible.

This looks awesome! Hopefully more companies build stuff like this and drive adoption.

Fun coincidence I was just reading about SuperCar https://en.wikipedia.org/wiki/Supercar_(TV_series)

Quite amazing if the claims are true. They are too good to be true.

It's been a while since my jaw dropped when I saw a video. Even if this goes nowhere I'm impressed with what they've done so far. Best of luck Lilium!

Ok, I'm calling it, this is technically a flying car!

Technically, it's a large drone.

Are we sure it's not an over-powered leaf blower?

[This](https://en.wikipedia.org/wiki/Helicopter) is a flying car.

When I read the part about "Order your air taxi to the nearby landing pad," I immediately thought of the old Commodore 64 game SpaceTaxi.

`Pad 1 please` :)

What are the fail safeties? Parachute? Alternate motor? It would suck to have one of these things fall on my head.

Found the following at the bottom of https://lilium.com/news/

What makes it so safe? Safety has been the top priority from day one of Lilium’s development. We’ve incorporated the concept of what we call ‘ultra redundancy’. The aircraft is designed such that it does not have a single point of failure, which means any component can fail in any flight condition and the aircraft will always be able to do an ordinary vertical landing automatically. The objective behind this concept is to make flying a Lilium Jet as simple as driving an electric car. At the same time, we provide an unprecedented level of safety both through a failure-tolerant aircraft and through avoiding pilot errors in stressful situations. For the duration of the flight, the software’s Flight Envelope Protection system rejects unsafe pilot commands. No matter what you do as a pilot, the system will always maintain safe flight conditions. Additionally, the Jet is equipped with a whole-aircraft parachute.

I'm sure it would be none-too-pleasant for the person flying inside it, either.

But that's their choice, not mine ;)

Besides the obvious things like seat belts, airbags, &c, I'd hope these have those whole-vehicle parachute systems you see on some small private planes.

Helicopters can autorotate, planes can glide. like the Moeller contraption, this type of thing falls. I would insist on a ballistic parachute.

It has one, though I'd go further and insist it have a deployment mechanism that does not rely on any computers or complex electronics.

So, everyone can "drive" it, it would fly above and land into cities…

Regulating this is going to be fun.

Probably as much as for helicopters.

That said, what's the differential why one would want this instead of an helicopter? It it cheaper? Faster? The site is certainly not telling this.

Probably smaller, faster, and safer.

This thing cannot autorotate. Sure, it could withstand the loss of a few motors, but it can't survive power loss. A chopper can.

Yes, but some of the helicopter accidents happen because rotor blades hit something. Those would be avoided here.

Sorry, I didn't mean those cannot be made safer. I do sense a tradeof however: chopper blades can hit things, and this aircraft cannot handle power loss. Which is safer? I have no idea.

>what's the differential why one would want this instead of an helicopter

From the homepage:

"Access inner cities with less noise than a motorbike"

That's a huge difference.

I have a lot of trouble believing that. Ever been in the vicinity of a large drone?

If they actually achieve their goals, then this would be a lot faster, quieter, more accessible, and quite a lot cheaper than renting a helicopter. Check the "mission" section on their site for estimated costs -- cheaper than or on-par with a traditional taxi.

Aside from not being easily bookable, helicopter rentals today are quite expensive (hundreds to thousands of dollars an hour, depending on the helicopter, origin, and destination).

Not everyone and the regulation is already done. Easy, cut and dry.

This is the part about the "flying car" that literally everyone gets wrong. If we are talking USA, ask the FAA if everyone can fly. There is the Class 3 flight physical that is required to fly as a PPL pilot... it is very, very thorough. If you can't pass that, there is a massive and growing sport class of flyers who are not full PPL's but still require pretty expensive training to get certified... and you are quite limited in size and scope.

In short, there is not going to be a massive "flying car" moment in this country unless they are autonomous or remotely piloted by ultra qualified people.

Hey, I'm basing this on the hype they are rousing on their website. From the second paragraph of their "mission" page:

> We are bringing personalized, clean and affordable air travel to everyone.

Either they're trying to con someone, or they intend to drastically lowers the bars to entry: it must be affordable, legal, and mustn't require much skill. I'm also seeing a beautiful rendering of those things flying over a dense city lower than some rooftops, and a landing pad with people standing on them, just after one craft took off.

They're gonna need one hell of a lobbying force to pull that off. Or a couple decades proving this stuff is mighty safe.

> Either they're trying to con someone, or they intend to drastically lowers the bars to entry: it must be affordable, legal, and mustn't require much skill.

They explicitly say that the "for everyone" part isn't everyone can fly (or afford to own) one, just that you will be able to hail them via a smartphone app and they'll come to you where you need them, because building suitable landing sites will be relatively inexpensive and attractive to property owners.

Still, there's the problem of volume. "Everyone" has to mean "more than 1% of the traffic" to be at all meaningful. Air traffic controllers are gonna have to become bloody efficient to absorb that.

In Germany, there is talk of a new category/class of aircraft for certification of the Volocopter and similar designs, and possibly a new airmen license, as well, as operations are just so different. (I mean, landing consists of choosing a spot and then pulling the thumb switch downwards until touchdown...)

FAA and EASA are increasingly looking at performance based, rather than narrow implementation based certification. I agree that the regulatory hurdles are monumental, but they're not insurmountable.

> So, everyone can "drive" it

It's described as an air taxi, it references guidance to the pilot; there's no indication that it is self-flying. So, AFAICT, it would be flown by people licensed under whatever regime there is for pilots in the jurisdictions it operates in.

> Regulating this is going to be fun.

It's basically a faster, quieter helicopter taxi. It's not a particularly novel regulatory problem.

> We are bringing personalized, clean and affordable air travel to everyone.

No way that'll happen under current regulations of the crushing majority of western countries.

Why not? Are you taking issue with their use of the word "personalized"?

The implied statement that I take from what they are pitching is "I can request my pickup and destination" vs. having to head to the airport where I pick up a fixed route flight. That form of personalization.

I'm taking issue with "everyone". Which can easily mean they intend to take up a sizeable fraction of the commuting traffic, I imagine up to 10%, perhaps even more.

The sheer strain this would put on air traffic controllers is unworkable, unless they change how air traffic control is made —'cause there's no way the air above cities is currently uncontrolled, and going through those zones take up at least 30 seconds worth of air controller's attention and talking. (Source: last time I got on a small plane for hobby purpose, we flew close to my city at some point.)

Ok, that's a different situation, thank you for the clarification.

Automation will most likely force a reworking of the ATC network in the near future. For example, if delivery drones really do take of at scale updates will be needed.

Well, even those might not be allowed right now. In France for instance, they're not, for a host of reasons: limited weight, limited range, and the need for authorization requests come to mind. There's also making sure there is no human within 30m of the drone, limited wireless power (don't pollute the spectrum!)…

We're not there yet.

Why do they cakl it a jet? all I see are bunches of small ducted fans. And it's electric powered.

Who cares? Once batteries can get as much, or more energy density than fuel, those types of machines will appear naturally.

I'm not really impressed by this project to be honest, I'm more interested by cost and energy density of batteries. Can't wait to see how the giga factory impacts the price of batteries.

Do you know much about the Gigafactory? How do you expect it to affect the price of batteries?

Also on that note, are there any limitations on the number of batteries we keep creating? Eg, Lithium supply?

I don't think it's fair to assume that rechargeable batteries will ever have a higher usable energy density greater than Jet A.

There's no wheels - would a plane be required to taxi to fly at a US airport?

Helicopters aren't required to have wheels. They just land directly on a designated helipad and stay there. Then if the ground crew needs to move it they attach temporary wheels and a tow cart.

How would this compare with the TriFan 600?

It totally looks like a rendering.

This looks like cars all over again. Massive energy waste for transporting single persons. Looking at this reminds me of people driving alone on heavy massive gas consuming 4 seat vehicles to drive the same way everybody else is driving. Except that now its in the air and for rich people only. I don't see flying cars happening, well at least not like this. There probably will be flying shuttles that take people to different places like buses or metros that would make way more sense then this.

>There probably will be flying shuttles that take people to different places like buses or metros that would make way more sense then this.

Airplanes exist. The future is now!

No I mean small shuttles like buses that start vertically and transport people short distances across a city for example.

The future is here - but for rich people only.

The future is here; it's just not evenly distributed yet.

That's been true for a long, long time, though, and rich people always take the role of vanguarding expensive new technologies. Later it'll get developed into more efficient forms and commoditized.

To the extent that Uber is only for rich people, maybe. At least given the prices they say they're targeting.

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