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Lilium Jet Demonstrator Achieves First Main Wing Transition For All-Electric Aircraft

Lilium · Youtube · 442 HN points · 0 HN comments
HN Theater has aggregated all Hacker News stories and comments that mention Lilium's video "Lilium Jet Demonstrator Achieves First Main Wing Transition For All-Electric Aircraft".
Youtube Summary
Watch as Phoenix 2, our 5th Generation all-electric Technology Demonstrator plane, achieves main wing transition – the first time a full-size electric jet aircraft has ever made the transition from hover to wing-borne flight.

Although a landmark moment for electric aviation, it’s only one small step for Lilium towards achieving our mission to transform regional air mobility. Next steps are to continue the Flight Test campaign and expand the flight envelope further, including transition of the forward canards and high-speed flights. We look forward to sharing more progress soon.

Flight details:
Flight Test Objective: Main Wing Transition
Aircraft: Phoenix 2 Technology Demonstrator
Pilot: Remote
Location: ATLAS Flight test center, Spain
Propulsion: 36 electric engines

Find out more about transition:
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Hacker News Stories and Comments

All the comments and stories posted to Hacker News that reference this video.
Jun 12, 2022 · 442 points, 392 comments · submitted by tomohawk
I'm skeptical.

They're claiming they'll be able to store 300kWh of energy on board. That's the equivalent of about 4 Tesla Model Y cars. Even if they could pack this much energy on board, flying that much weight 200km is almost certainly going to take more than 300kWh, especially with 7 passengers.

Lilium is very proud of their ducted fan designs and their power usage profiles -- and they should be! -- but they're counting on advancements in battery tech that are unlikely to happen in the timeframe they need. It's much more likely they will be limited to 100km range or 30-minute flights at a maximum when reserves are factored in.

This says nothing about how fast they can recharge those massive batteries. If they have the equivalent of four Tesla superchargers available they can probably recharge completely in 40 minutes or so, which is probably good enough. But that charging infrastructure needs to be in place at virtually every pad where the plane lands, so the "ordinary helipads" they brag about using are not going to work without roughly a $million of power infrastructure upgrades at each. If they try to go cheap on this, they will have to live with multi-hour recharge times.

> Even if they could pack this much energy on board, flying that much weight 200km is almost certainly going to take more than 300kWh, especially with 7 passengers.

The Pipistrel Alpha Electro can fly 2 people more than 100km today, with an aircraft that's not at all optimised for electric flight. The battery pack is 21kWh. Increasing that to 200km seems entirely reasonable with a more optimised design and newer battery technology. Let's say you could fly 2 people 200km with a 50kWh pack, then you can by definition fly 12 people 200km with a 300kWh pack. Trade 4 people for the trade-offs needed for VTOL, and you're down to 8.

> but they're counting on advancements in battery tech that are unlikely to happen in the timeframe they need

Are they? They're using Zenlabs batteries, which claims to have already been verified their energy/power densities with a third party laboratory. Question is as always if plans for mass manufacturing works out.

Seems like they're assuming numbers that are entirely reasonable for early mass manufacturing within the next 5 years. With the amount of money pouring into battery R&D, and the number of companies now in trial production phase with next generation cells, it seems more or less inevitable to me.

They can afford to pay more for the batteries than mass-market BEV companies. So it's also not unreasonable to assume they'll be able to buy batteries at the early stage of manufacturing.

> This says nothing about how fast they can recharge those massive batteries.

Charging these in 40minutes would take at most 500kW (I'm assuming 250kWh charged at 2C rate). Often it'd be much less (not always going to fly its full range). We have plenty of charging stations around me with way more total power than that. Chargers running at up to 350kW is already being built routinely. So you just need two of those, and they are usually built in pairs already. This is really not going to be a major issue at all in the initial phase. Maybe down the line when they've already built out the easiest locations, it could be a bigger challenge. But nothing bigger than the mass electrification of cars and trucks. The economics of the charging stations will be better than with BEV stations, since they'll be built on fixed routes, and have high utilisation during the daytime.

Doesn't feel like the skepticism passes the back of the napkin calculation tests. It's definitely within the realm of possibility. Hard? Yes, very, but if it was easy someone else would already have done it, as with all new development.

If you're going to be skeptical, at least look at the numbers of what's being done today, and see how far what they require is from that.

> Pipistrel Alpha Electro can fly 2 people more than 100km today, with an aircraft that's not at all optimised for electric flight.

Pipistrel Alpha Electro is basically a sailplane with an engine. It's designed to glide long distances without an engine. It's a beautiful design but it derives 0% of its lift from engine thrust, it has no VTOL capability, it's slow, and it's much lighter than the Lilium jet. And by the way it's marketed as a training aircraft rather than a passenger aircraft because Pipistrel is an honest company. There's no comparison.

> Are they? They're using Zenlabs batteries, which claims to have already been verified their energy/power densities with a third party laboratory.

Here's an article about the now-CEO of Zenlabs:

> Charging these in 40minutes would take at most 500kW (I'm assuming 250kWh charged at 2C rate).

You're assuming linear charging, and LiIon batteries don't work that way. You have to reduce the charge rate as the battery gets closer to full. This means if you want fast charging you have to break the battery into multiple pieces [electrically speaking] and charge each piece separately with its own high-current charger. And I seriously doubt they'd ever get FAA cert without a commitment to fully charge before takeoff.

1,000 times this, and this is why they are mired in an investor lawsuit.
Looks like I was overly optimistic. After doing some more research I found that the company has been saying "Our ducted fans are often assessed based on methodologies better suited to assessing open propellers, which are generally less efficient in flight than ducted fans" and "It is accepted in the aerospace expert community that ducted fans are aerodynamically more efficient than open propellers." [0]

This is just thinly-disguised lying. Ducted fans are more efficient than open propellers of the same diameter, which is a telling detail that they conveniently leave unstated. A ducted fan of 10 cm diameter cannot be compared with an open propeller of 4 m diameter, which is closer to what Lilium's competitors use. This doesn't by itself mean the ducted fan idea won't work, but it's ridiculous to imply that the ducted fan is somehow "more efficient" without talking about the propellers' respective diameters.


> but it's ridiculous to imply that the ducted fan is somehow "more efficient" without talking about the propellers' respective diameters.

Why? Their point is that it's misleading to use data from open propellers and apply it to a ducted fan design. I would certainly hope that the critics tried to scale according to the diameter of the rotors. That is, they should at least assume something like a 10cm open rotor. But then it'd still be misleading to use data based on open propellers. Their point is that there are aspects of their design that increases efficiency that must be taken into account, and that's true as far as I can tell.

And why do you assume that scaling down the size of the rotor would make it less efficient, rather than more? I mean yes, if that's the only thing you do, it probably would be. But they're also changing the whole design of the aircraft specifically for distributed propulsion.

NASA is already demonstrating with the Maxwell X-57 that moving to many smaller rotors is more efficient than 1-2 big rotors, since you get additional lift distributed over the wing allowing for a smaller wing with less drag. I think NASA knows what they're doing.

The small distributed motors on the X-57 are only used on takeoff and landing to augment lift. The small propellers fold away in cruise, when the entirety of the aircraft’s thrust is provided by two large propellers at the wingtips.
Making a comment to represent all aerospace professionals getting major gell-man amnesia vibes from this thread.
This has been one of my “shower thoughts”..

If jet fuel is very efficient and dense for the more demanding take off and low altitude legs of the flight, we aren’t there concepts that do a hybrid of jet fuel and electric powered flights that use the electric propellers only where they are efficient, leaving the existing system for the more challenging tasks like take off?

Then you have two different energy storage areas plus two different drive trains, and the associated weight gain that implies. Hybrid road vehicles make it work because they have the weight supported by the ground, plus the additional benefit of regenerative braking, which evens out energy usage in stop-and-go and hilly travel. Planes don’t work at all in either scenario.
Same problem as all hybrid power systems; weight and complexity. You can't get away with generalist designs in an aircraft the way you can with a land or water vehicle. Carrying around the weight and drag penalties of an unused engine would more than detract from any efficiency gain with an electric auxiliary.
Also unlike with sea where efficiency gains from hybrids out gain the mass and volume losses, same doesn't apply to air.

Also, some of the engine types like turboprops are pretty good already. And hybrid systems likely won't make gains and probably even lose quite a bit.

There are some electric gliders which at least use the same intuition -- you need a ride for takeoff, but then there's an electric sustaining motor for once you're in the air (and don't have lift).
Because we use the engines to generate hydraulic power and electric power, and on larger planes it drives the air conditioning. The engines do a lot more than just provide thrust.
Or can you have a 100' long cable to directly power the lift off and first hundred feet of the flight? (For a conventional runway takeoff, some kind of powered tracks.)
Aircraft carriers effectively have powered tracks. As I understand it, this is currently quite dangerous and expensive.
In addition to other comments here about increased weight and complexity...

There's an area where it makes sense, and it's being trialed in few places. Namely electric propulsion for taxiing.

You see, Taxiing on jet engines is very, very, very inefficient - you stay pretty much in worst fuel economy all the time to the point that taxiing burns more fuel than few hundred kilometers of cruise on the heaviest airliners. In fact optimizing taxiing is important enough that landings are calculated to ensure you have shorter distance and can reuse kinetic energy from landing, and depending on plane it might be norm to shut off all engines except one during taxi.

So there's experimentation with either adding electric drivetrain to main gear or having remote-controlled pulling car or quick-detachable (and also remote controlled) drive blocks that could attach to main gear. This way the plane would only start the engines just before going onto its designated runway.

This all just furthers my idea that if I’m ever a time traveler, I’ll try and convince the past to make airplanes that all have aircraft carrier sling shot systems… for fun.
Taxiing is the process of getting the plane to the slingshot.
Yeah, you'd need to convince the past that "tugboats but for aircraft" is a good thing to standardize.
Is then issue the turbines themselves, or the jet fuel engine?

I was wondering why they don't do what Prius did andnhabe a gas motor charge batteries.

I am not an expert

This doesn’t seem to make any sense to me. If taxiing is so inefficient, why not use the pushback carts to push/pull the planes into position?

I’ve been to many more airports that make the plane taxi for quite a distance, like 20 minutes (not just sitting and waiting, but moving) to get to the gate than ones that “ensure you have shorter distance and can reuse kinetic energy from landing”

That's essentially what the prototype projects are doing, except optimized for taxiing vs. "just" pushback or maintenance moves - normal pushback truck is not exactly prepared to handle high traffic taxiing, partially due to how communication between aircraft and pushback is handled.

So those projects investigate a solution that is optimized for the whole taxi trip at full traffic at the airport, including electric solutions to avoid currently heavy diesel pushback trucks.

Shower thought: Is anyone working on ground-assisted takeoff of aircraft using something like an aircraft catapult? It seems like it would be fairly straightforward to provide the initial momentum of an aircraft and save a bit of fuel & weight. Sure, you're not gaining much just getting the aircraft up to takeoff speed, but it seems like an easy way to make commercial flights more efficient.
The short answer is that catapult systems are expensive and require a lot of maintenance. Even many Navies don’t use catapult assisted launches for that very reason. Additionally, commercial aircraft aren’t designed for that kind of force applied to their main gear. They’d most likely have to be modified.
I wonder what sort of force you could generate with a series of electric coils in the ground? It lacks moving parts, so it should be low maintenance. You'd need magnets on the gear of the plane, offsetting the weight savings though. Yeah, you'd definitely need to reinforce the landing gear, but I think that's doable.
Naval catapults don't apply force to the main gear either. Mostly is to the nose gear now, but it used to through the use of bridles to points on the wing (and wing spar). The bridles were a pain though, so they transitioned everything to the nose gear attachment. You can tell when a carrier transitioned, because they took the bridle catchers off the bow (the little narrow ramps at the front).
I think I am going to stick with the commercial flights without the catapult if this ever happens
Yes, for gliders:

Also related:

Last summer, I rode in a Rubik R-26 Góbé glider, invented by the father of the man who invented the Rubik's cube.óbé

Pretty fun experience. And if commercial airplanes ever start using this sort of launching technology, I imagine the takeoff would feel a lot smoother.

It's always so fascinating to read about EVTOL outside of industry forums, especially where commenters are highly inquisitive (both in the physics/engineering of these vehicles and in their proposed business models.)

For those who've read into Lilium and their business model, some comments:

1. There are lots of very talented people at the company, including several friends of mine. They also have strong leadership and a very well connected board. However, their design has several unproven aspects to it.

2. The biggest issue Lilium has is their battery, which is predicated on technology that doesn't exist yet. Battery technology doesn't improve like the semiconductor. There is no Moore's Law. What Lilium needs is an Einstein-level breakthrough in chemistry. Who knows if and when that will happen?

3. Lilium, like several other EVTOL manufacturers, managed to SPAC itself last year. Many of its investors are now retail investors who do not understand aerospace platform development, the challenges and risks of this nascent EVTOL domain, nor the necessary timelines for development, certification, or infrastructure development (a much bigger challenge IMHO than certification.) As a result, thanks in part to the reveal about above issue #2 some months ago (which may or may not be related to a major drop in stock price,) there is now a class-action investor lawsuit against the company. Uh oh!

Btw, I do a lot of work in aerospace safety standards around emerging tech, and therefore have a lot of tentacles into this new domain of aerospace, although I do not work commercially in AAM/EVTOL/UAM. As an engineer and leader, I think broadly and connect dots. This is uncommon in the industry, which is highly siloed.

In short, there is a good deal skepticism in these comments. I think that's warranted, and I tend to agree with that skepticism. Lilium and others will have a positive and positively transformative effect on aviation--especially in the general and business aviation space (what we aerospace nerds call Part 23, even though EVTOL is now Part 21.17b--another issue to read up about!) However, I wouldn't bet a dime on the current business models of most of these EVTOL/UAM OEMS.

> What Lilium needs is an Einstein-level breakthrough in chemistry.

Do you have details for this claim? Is their needs anything more than what their supplier Zenlabs claims to have developed?

If so, it doesn't seem to me that they require anything more than what has already been proven in the lab, and is somewhere in the stages of late lab development to early pilot production by several companies (Zenlab, SES, QuantumScape, Sila, etc)

Nothing is guaranteed until one of these companies have actually started shipping massive amount of batteries to a finished commercial product. But seems almost inevitable now that a step improvement in energy density will be achieved in a shipping product in the next 5-10 years.

It's well known in the industry that Lilium's claims on range are well outside available technology. Read up on AirCurrent, AVWeek, and other trade publications to understand what other manufacturers and 3rd parties are saying about battery tech.

The only major EVTOL OEM basing their battery tech on readily available technology is Archer. They are claiming ~40 miles of useable range after reserves and loss to battery inefficiency at various stages of flight. Lilium is claiming 186 miles of range.

Yes battery tech is improving, but change is very incremental. The idea that we can go from 40 usable miles to 186 useable miles in a timeframe compatible with Lilium's business plans is suspect.

I don’t care how skeptical or how much of a downer you want to be - if you can’t look at this and think “damn that’s cool” then maybe you need to take a step back.
Is hydrogen gas dense enough to power an aircraft? I don't think battery technology will be dense enough to power aircraft in our lifetimes, but I feel like hydrogen could play a part
Hydrogen has an excellent energy-to-weight ratio, but in terms of energy-to-volume it's even worse than lithium-ion batteries as a gas. This is why proposals for hydrogen airliners usually need a complicated cryogenic setup to store it as liquid hydrogen instead.
You don't need a "complicated" cryogenic setup. You just need insulated tankage. But it won't fit in the wings, so you need new airframes or fuel nacelles.

We have a very great deal of experience with fuel nacelles already, because that is what a "drop tank" looks like; you just omit the "drop" complication. The advantages over inboard tankage are safety, possible retrofitting of existing fleets, and short plumbing runs.

Once LH2 aircraft are used on any route, kerosene craft will be wholly unable to compete, even without carbon taxes. Carbon taxes could be spent on accelerating the transition.

Or a radically different airframe design. One that perhaps is much bigger and flies slower but is very low weight (by virtue of being mostly full of hydrogen).
A different airframe design would take a long time to field, and with inboard tankage arguably less safe.
Lithium Battery are already enough to power some airplanes. Airplanes now in development using current battery tech are already targeting many niches.

They will not fly across oceans for a while but a lot of aviation is limited to one continent.

And beyond that, the cheaper operational cost, can change how flights routes significantly and even open more markets.

The problem with airplanes is partly that it takes a very long time to design a new one and the cost are significant. To create a longer range electric plane, you need to really start from the ground up, and rethink the airplane. Even with cars this took 10-15 years. For planes it will be even more difficult.

Lots of comments saying it's impractical but there are already several companies working on hydrogen (both gas and liquid) powered designs. Airbus/Delta and ZeroAvia/Alaska for example.

Hydrogen has been tested, including in Soviet Union which considered it the future fuel for airliners, tested on Tu-154M modified for cryogenic hydrogen fuel.
There are a few flying prototypes of various sizes, so clearly there's a big flaw in your argument.

In principle you can burn hydrogen in a jet or even in an internal combustion engine. Both have already been shown to work. Fuel cells are another possibility of course. As far as I understand it, most plane manufacturers are already designing planes with hyrdogen as a power source. Particularly for big Jets, the consensus seems to be that that is happening.

The main challenge in the market is similar with what we've seen with existing car manufacturers. Changing technology disrupts them and threatens their profitability. So, you see companies that are talking the talk but not really committing to much beyond that. E.g. Airbus and Boeing have lots of fancy concept planes but not much in the line of actual planes being designed and marketed yet.

As for battery, there are several battery powered planes flying and certified (or in the process of being certified). Most of the companies behind those are following up with longer range versions that they've already announced.

Maybe aviation fuel goes a bit further but it is very expensive. Especially for general aviation, the value proposition might look pretty good a few years down the line with better ranges and charging speeds and lower cost. That does not even require that much in terms of breakthroughs in energy density either. Anything certified today is using battery tech that is several years old and was probably picked conservatively to speed up the process. That's just the nature of the certification process. What's flying legally today was the state of the art about half a decade ago in terms of batteries. Probably not that impressive compared to the latest electrical cars.

There is already a type-certified electric aircraft.
Hydrogen looks like the perfect storage medium for aviation, except that every way people created to store it is either very dangerous or reduces its energy density enough that it becomes similar to batteries.
Hydrogen looks good on paper but has a lot of practical issues.

- Currently, the most economically efficient method to obtain hydrogen is by methane steam reforming. This releases a lot of CO2.

- If you want to get hydrogen without making CO2, you'll need to use electricity to split water. That's around 60-70% efficient. If you used the same electricity to charge a battery, it would be over 90% efficient.

- Hydrogen embrittlement is a problem for tanks and pipes. This means you can't easily repurpose natural gas infrastructure.

- Hydrogen has no odor, and adding an odorant can foul fuel cells. The most effective solution is to add hydrogen sensors everywhere, increasing costs.

- Hydrogen burns with an invisible flame. It's also much more easily ignited than gasoline and will burn in a wider range of concentrations. (Though unlike gasoline, it won't pool up.)

- Hydrogen is a small enough molecule that it will slowly permeate through a sealed tank. Newer tanks have coatings that reduce this, but research is ongoing.

- Remember the ideal gas law? The pressure change involved in refilling a hydrogen tank causes the nozzle to get very cold. Even in southern California this can freeze the nozzle to the tank, limiting refill speeds.

- Hydrogen is light, but tanks are heavy. The Toyota Mirai's tanks weigh 87.5kg but can only store 5kg of hydrogen.

Considering all of these disadvantages, I don't think hydrogen aircraft are going to happen.

> Remember the ideal gas law?

For anyone else who doesn't: "also called the general gas equation [...] is a good approximation of the behavior of many gases under many conditions". It seems to relate how pressure, volume and temperature interact (combined with some constant and how much gas there is). (Bit of a weird name; 'general gas equation' makes more sense to me.)

But okay so this reference is about "know how gas behaves?" and actually seems to mean "gas gets cold when it expands", if I understand the comment correctly (since I didn't have this in school). Not sure why the tank you're filling can't just have the same pressure if this is a problem (plunger on both ends, push the gas over, don't let the available space expand or shrink).

To transfer gas into a tank, it has to go from higher pressure to lower pressure. If the pressure is equal, you won't transfer any gas. Also an empty tank is pretty much at atmospheric pressure. Gas has to expand to pressurize it.

The easiest solution is probably to add heating coils around the parts that get cold. I haven't heard of any the hydrogen filling stations having such devices, but that's probably because hydrogen stations are only in California.

I am (perhaps unreasonably) annoyed by the mixed units. The narrator and captions are using knots for speed, which is standard for aviation in most of the world. The on-screen display is using km/h, which is standard for everything else in most of the world.
Interestingly, glider pilots use metric units in metric countries. So altitudes are in m, airspeed in km/h, and vertical speed in m/s.
And ft/s for vertical speed. Really got a bit of everything going on there!
That is standard for vertical speed everywhere
So if both wings break off, I need to do unit conversion to calculate my remaining lifespan? Jesus Christ, what a horror show.
That's funny for someone with aero-glide2 as user name. I'm used to metric variometers in gliders.
And yet, excepting two countries (IIRC), altitude is normally in feet for ATC. Which means instruments are in feet.
Not in the countries you refer to, and not in gliders in many European countries. Not 'everywhere' then.
Having motors along the whole trailing edge of the wing surely kills the glide ratio of this, right?

Losing power on one side seems like an even more frightening prospect. Even if the motors were somehow allowed to freely windmill, that's a lot of surface area for drag.

At the very least, it must have some unusual aerodynamic properties.

Why is the airflow so turbulent over the trailing edge? Is it even considered a full transition?
> Having motors along the whole trailing edge of the wing surely kills the glide ratio of this, right?

The motors are running at reduced thrust and changed geometry during all parts of the flight.

Regarding power loss: Last time I read about it in more detail, the impellers were organised in groups of 3, and you could lose one such module anywhere on the plane, even on the front canards, without issues. On the wings you could probably lose several.

If you lose all electricity everywhere that would be a bad day, but the same is true for a modern airliner with fly by wire controls.

Modern airliners are equipped with ram air turbines to provide electrical power for critical systems even if they lose all engines and the APU.
What percentage of available battery did that 4 minute loop take?
I would guess a considerable percentage because launching and landing takes a disproportional amount of power. Iirc their information correctly then launching and landing takes 10x as much power as level flight. That's because in these situations lift has to be generated by the fans instead of the wings. So short flights are actually disadvantageous.
Pretty exciting. I consider this a real proof of concept for shuttlepods AKA flying cars. I'm sure there's a lot of work left to do this shows how much is already possible with relatively little effort by a relatively small company.

Seems like there's a few advances that should enable it to finally happen:

Automated: so there's no pilot to make mistakes and drive up costs. Automated flying is easier than navigating streets, so this is probably already doable at scale even though self-driving cars are taking longer than hoped.

Electric: so the at-scale/long-term cost per flight can be nearly zero. Seems possible something like this could be manufactured for $100k at scale and fly (with maintenance) for multiple years.

Multi-rotor w/efficient DC motors, multi-battery pack w/advanced batteries, and multi-computer w/advanced processors: so there's no single point of failure and lots of opportunity to recover from failure, and to enable easy VTOL without runways.

The Wright brothers would love it. Their initial vision was to not need specially built runways or airports. It turns out that was "too early" of an idea to be practical but we're getting close.

An "infinite highway of the air" (Wilbur Wright) is an exciting goal.

This is a major milestone for them. Very nice to see the indicators suddenly transitioning to laminar flow.

It is a shame that they only stayed in this flight regime for a few seconds, but they will now gradually expand the envelope.

Here is a good article explaining the tradeoffs they make vs. more traditional VTOL craft with larger propellers: . TLDR: they accept more inefficient performance during hover because they won't stay in this flight regime for long.

Really cool seeing the telltales on the top of the wing briefly show laminar flow as airflow over the upper section becomes smooth when they lower the angle of attack enough. Most of the time the entire airfoil is in a stalled state with the airfoil having exceeded the critical angle of attack and lift being provided purely by vertical thrust. Until that airfoil rotates enough and the aircraft has enough forward speed to achieve laminar flow and lift from the airfoils.

I don’t know anything about this project and it’s the first time I’ve seen it so apologies if I’ve misunderstood what’s happening, but visually that’s my read on what they’re doing.

I’ll bet there’s a lot of opportunity here to use software and an autopilot to optimize fuel efficiency. Eg define takeoff direction and transition to main wing lift as soon as possible versus letting the human do it. Using thrust to maintain altitude has to be brutally inefficient.

Without a vertical stabilizer, I guess it relies on thrust vectoring to control yaw.

One would question why that uncommon decision was made (deleting the stabilizer), and the most likely reason I can imagine is weight. If that's the case, and considering composite structures, that would also suggest that payload (passengers and luggage) would be quite limited.

Ultimately it seems this total package depends very much on the array of ducted fans. While there are many of them, it is still a serious single point of failure. In a no power situation with a crosswind, how would one control the direction of the aircraft? I notice from this film that the windsock showed virtually no wind, and I doubt this was a coincidence.

> (deleting the stabilizer), and the most likely reason I can imagine is weight

More likely than weight is drag.

I considered that, but forward speed doesn't seem to be the priority. I think the VTOL aspect is what matters, and that suggests weight is most important.

But who knows. I would much sooner ride in a helicopter than this. At least a heli can potentially autorotate in a no-power scenario.

Not really a plane so much as a expense, semi-hovering, large drone, inefficient consumer of electricity.

An efficient vehicle would have significant aerodynamic properties like a glider. Instead, it's mostly pushing itself up rather than using an airfoil.

Also, in terms of climate change, widespread use of anything similar would be devastating for the environment as it's an inherently extremely uneconomical mode of transportation.

If we wanted better transportation for less energy, it look like a train.

Recently read unleaded aviation fuel seems to be an insurmountable problem for the FAA. Will it be that hard with electric aircraft or is it further along?
Completely unrelated.

The issue with unleaded fuel is that the goal is to make it a drop-in replacement on all engines that currently use AVGAS100LL, which is the only remaining leaded fuel in large use (a lot of small planes can actually fly on unleaded aviation fuels and there are some available, it's just 100LL is "default" fuel when thinking of piston engines). So they have to certify that if you swap the fuel, preferably without any modifications, then it's safe to fly.

Battery powered aircraft go through normal certification process for a new design.

It has vertical take off? It must burn so much electricity for that?

Wouldn't be classic horizontal take off more efficient?

I guess since they're mainly competing with helicopters, the advantage of being able to go to a random building rather than requiring huge runways in the place you want to go (usually somewhere in the middle of a city) is bigger than the advantage of improved fuel efficiency.
I think the ideal personal aircraft would work like a quadcopter during takeoff and landing, but unfold wings for cruising flight with much better efficiency. It seems there's already such a drone called Transwing, I hope they make a personal aircraft like that.
That really is the basic idea here, except with more redundancy. Pulling the air over the wings and canard generates a lot of lift.
Very nice, but the mechanics of the vehicle remind me of the Moller Skycar and the V22 Osprey, both of which were famous failures. So I'll remain skeptical until it starts doing manned airport-to-airport flights.
Is 120km/h considered a high enough speed for aircraft now? That looked like a very short span of time to use the main wings, and it was still going barely faster than a car.
Transportation economics are dominated by the passengers per pilot ratio. Small vehicles aren't economic unless they are piloted by a passenger or an AI.

AI piloting should be easier with aircraft than cars.

Fuel costs are in the order of hundreds of thousands of dollars per flight. Surely that’s much more expensive than the pilot costs?
For commercial jetliners? Yes, but they have a very high passenger:pilot ratio already.

Also, the order is tens of thousands (for a typical transatlantic flight).

Across transportation modalities, fuel costs are usually a minor contributor to total cost. For a commercial airline flight, about 10% of ticket price.

See also, this comment of mine on a recent story about the Joby eVTOL:

According to [1] fuel costs are in the tens of thousands for intercontinental flights. Pilot training is around 200k USD [2] and thousands of hours to be accepted to fly reputable companies' planes. I wouldn't call pilot costs negligible.

[1] -

[2] -

Consider that, as a ballpark average, a commercial pilot gets paid maybe ~$200/hour for their work. Double that if you're feeling generous. Whereas total operating costs for a 737 is somewhere in the $5000-$10000/hour range. That doesn't include airport fees, either.

The cost of pilots next to the cost fuel+maintenance+everything else is...pretty negligible.

We are living in a world were co-pilots sometimes pay to be allow?d to fly in order to get flight hours in towards type ratings and promotions. Initial pilot trainig through airlines, and paid by those with almost guaranteed employment afterwards, is a thing of the past. Most pilots pay for their own training now. Ehich leaves salaries, which are indeed negligable.

Even if you accoubt for training costs, those are negiligable whem compared to fuel, maintenance,...

This is simply incorrect. The dominant costs are maintenance, followed by fuel.

Even the tiniest and cheapest of trainer airplanes usually break down their cost structure as follows:

engine/maintenance costs: ~$90/hour fuel costs: ~$60/hour instructor fee: ~$60/hour

As airframes get larger and engines get more powerful, the cost of maintenance and fuel goes up astonishingly quickly - but it's rare to pay more than $100/hour for instruction. Once you get into turboprop and very small jet aircraft, you're talking one to several thousand dollars an hour in operating costs, which no pilot has ever been paid.

Sorry if it wasn't clear, my comment doesn't just refer to aircraft but to all means of mass transportation, with units of USD per passenger mile. It's based on extensive analysis but is also pretty obvious when you think about it. Yes, as the passenger:pilot ratio gets high, other costs will exceed the pilot's salary.

In the case of a Cessna 172 (for example), even if the pilot works for free, 25% of the vehicle's capacity is wasted, unless the pilot is also a passenger. This isn't true in the case of the general population so these planes aren't used for mass transportation.

I'm impressed by how quiet 36 electric turbines can be. (Of course, that's almost certainly a function of whoever mixed the audio...)
The ducted fans help reduce the noise.
1. We already have VTOLs - helicopters. How do the economics of this compares to helicopters?

2. Surely hydrogen is a better fuel source for VTOL?

1. Helicopters are technically VTOL, but what you'd really want is something that can transition between vertical takeoff and horizontal flight using conventional wings, which is much more efficient and stable when travelling from A to B.

2. VTOL requires engines which provide very high thrust and very short response time during vertical ascent. This is incredibly hard to do using combustion engines - which includes hydrogen - but trivial using electric engines, which is why every cheap drone can easily fly using only vertically mounted propellers.

1. I'm interested in the economics of this vs helicopters. Why would someone buy one? Is it cheaper? Faster? More energy efficient per mile?

2. Hydrogen fuel cells drive an electric motor, no combustion needed. Battery weight seems to be a huge factor for VTOL. Hydrogen drones can easily fly for hours for example.

Also what about safety? Helicopters can be landed even in case of power failure.

> VTOL requires engines which provide very high thrust and very short response time during vertical ascent

Not necessarily. That's how you do it with electric multirotors, because it's simple and electric motors are good at it. With turbine powered VTOLs, the rotor blades are actuated to change their angle of attack, and consequently how much lift they're producing, using swashplates and cyclic controls. That's what traditional helicopters do, and what tiltrotors like the V-22 do too.

Incidentally I think tiltrotors are what you're describing as the VTOL ideal; they take off like helicopters then transition into horizontal flight using conventional (albeit stubby) wings. They're not exactly a runaway success and have had a rocky history, but they do work.

There is so much mechanical complexity in the existing tiltrotor systems. Especially with the V-22, where each turbine can cross-drive the other rotor.
Another area where electric propulsion shines. You can simply drive each propeller with its own motor and not blow up your weight/complexity budget even if you go crazy with the number of fans line Lilium did. That's precisely why almost noone bothered with tiltrotors until batteries became so good that they are almost useful for flying aircraft.
>the rotor blades are actuated to change their angle of attack, and consequently how much lift they're producing, using swashplates and cyclic controls

Correct, but that is just the workaround to achieve more immediate thrust variability from a combustion engine - which in turn made these aircraft insanely complex and highly expensive to operate. An electric motor can immediately give you the required torque over a wide range of speeds, finally making these designs safe and possibly even economical. Batteries are the only reason why we aren't seeing these things everywhere and a tiltrotor capable of VTOL and winged horizontal flight could finally make them viable.

> Correct, but that is just the workaround to achieve more immediate thrust variability from a combustion engine

Well no, it's not just a work-around to the thrust response of combustion engines. Cyclic control is also how traditional rotorcraft control their pitch and roll. It actually works quite well, helicopters are a huge success and the main reason why tiltrotors aren't more popular is because helicopters are generally good enough; nobody really needs the extra endurance of a tiltrotor enough to make the extra complexity worth it. In most cases when you need more range, a fixed wing aircraft is better. The intersection of "needs to be VTOL" and "needs better range than a helicopter" seems to be "military".

Anyway, saying that Helicopters are "technically" VTOLs is silly; they are VTOLs in every sense of the term. If you think they aren't in some way VTOLs then you're operating with some pet definition of VTOL. You seem to think electric multirotors are the ideal form of VTOL and anything other than that doesn't really count... but VTOL doesn't mean that. VTOL means vertical takeoff and landing. Helicopters are VTOL, not just technically but conceptually, spiritually, and in every other sense you can conceive of.

> Batteries are the only reason why we aren't seeing these things everywhere and a tiltrotor capable of VTOL and winged horizontal flight could finally make them viable.

I disagree. Electric VTOLs perform much worse than electric fixed-wing airplanes, and always will. Fixed wing electric airplanes don't have the power or endurance to do much that's useful. That's the upper bound for VTOL performance, and it sucks.

Why is the speed in metric (km/hr) and the vertical acceleration in imperial (ft/min). Hurts my brain!
i don't know what the proper term is, so i'm just going to make bjork happy and call them aerodynamic scientifical tassles.

are they just recorded visually by a camera and then inspected manually for a test flight or are they part of some kind of active sensor system.

cool stuff.

Tufts and they are recorded on video.
I love that tell-tales are still part of vessels thousands of years later.
the hover power density is insane, 2500W/kg
Oh, wow, that is intense indeed. Where did you get these numbers? Was it in the vid?
and again, we see an amazing german engineering.
impressive, what a smooth landing!!!
Why does this look like it's entirely CGI?
Resolution and framerate. What were you watching the video in?
Lilium is a shady company

First, it's people without even most basic aeronautic backround designing an aircraft.

Second, the number of flaws with their scheme being pointed by experts is so huge they cannot possibly get certified without throwing out everything, and redesigning completely from scratch.

Third, they finally hired somebody with the background, but so far nobody seen any change from "submarine ramen startup," to a serious company happening. Unlike with SpaceX, where Elon promptly yielded to professional engineers shutting down his fantasies like an SSTO design, 3D printing the whole rocket, or developing an ion engine to replace chemical one for last stages.

Fourth, they lash out on all criticism with "you have no vision," it's "aircraft 2.0," and similar dismissal.

Fifth, they courted investors with physically unachievable performance figures.

To me it's very clear, the company is heading the way of "HTML supercomputer"

P.S. Speak of the devil, it's already starting:

I'm also highly skeptical. I've heard from someone in the industry that their original demos were intentionally misleading. They had images of the Lilium aircraft taking off and flying for a bit, but what they didn't tell you was that the thing that was flying was essentially a large foam model that probably weighed 1/10th of what the real thing would. I don't know if that's the case anymore, but I wouldn't personally invest my own money in them though. Joby seems like they have a much more promising electric aircraft.

I don't have a position in either company nor in any electric aircraft stocks.

That law firm looks like quite active on stock market [1]. There are like hundreds of them I saw on the news.


> Unlike with SpaceX, where Elon promptly yielded to professional engineers shutting down his fantasies like an SSTO design, 3D printing the whole rocket, or developing an ion engine to replace chemical one for last stages.

What's the source for that?

Looking at their location in Munich, they probably have hired engineers with background in Airbus Helicopter and Marenco.
They have 600 people, onboarding a veteran Airbus exec as CEO and are located in the south of Germany which is the center of the German aircraft and high tech manufacturing industry. On the surface they pass my smell test.

From their website: > As Co-founder and VP Product, Patrick leads the global digital and physical product strategy owning the technical operation readiness of the aircraft and its mobility service . He holds a PhD in Aerospace Engineering from the Technical University of Munich.

Claiming they have no clue seems to be without facts.

Their website isn't exactly up to date.

Dr. Patrick Nathen who published Lilium's white paper detailing their aircraft architecture has left his VP role and is now an engineer within their flight mechanics team [0].


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I was actually just thinking that VTOL aircraft could solve the housing crisis considering we’re using 1000s of acres of prime real estate in every city for airports. Anyone want to flesh out that idea and write it up?

(I’d be curious if anyone could correct my thinking instead of downvoting)

I didnt downvote, I think those VTOLs also at the end gonna land somewhere, its reminds me this pic [1].

That’s true but runways are quite long and we need several of them at least.

And we wouldn’t need the same level of centralization for small landing pads.

No city will be scrapping its runways. Period. So if you add VTOL pads that takes more of high value real estate.
They can land on roofs, in parks, any open area large enough basically.

That kind of is the whole point being able to land anywhere. Short term, anything that already accommodates helicopters would be good enough. The problem with those is mainly that helicopters are very noisy so people don't like to have helipads everywhere.

But considering, these VTOL planes tend to be a lot less noisy, having them land in more places might end up being less controversial.

Either way, it would be a perfectly valid way to commute 50-80 miles in ten minutes or so and skip the 2 hour car ride. I could see that become a popular thing. Initially probably quite expensive but the pitch for these devices seems to be that they could be mass produced cheaply.

Yes my answer was for the airport, I definitely would like to see them around and try it!
Any powered aircraft large enough to carry a person is inherently noisy and dangerous. All serious vertiport proposals I have seen for quiet electric aircraft assume a dedicated facility at least as large as a city block. And even those are only feasible if there is no significant NIMBYism in the area.

Rooftop landing pads could work, at least in principle. They are however risky enough that Western cities often outright ban them in urban areas or limit their use to emergency situations.

When people got thousands of cars, railway stations and bus stations didn’t disappear. This will be even more apparent with the really expensive VTOL aircraft for the mega rich. Plus you can’t really land anywhere since you do need charging infrastructure. Unless you are willing to spend days when recharging this beast from a 220V outlet.
There's no way airports use enough land to be able to 'solve the housing crisis' by using it for housing.

The housing crisis is an entirely self-created problem by the societies it exists in, and it has little to do with amount of land. For example, Japan and South Korea have relative little land -- and in the case of Japan, very little non-mountainous land -- relative to their population, and yet rent prices there are quite affordable, even in the megacities of Tokyo and Seoul.

Western cities tend to have some combination of greater restrictions on density/housing forms, and harder/more ambiguous red tape to develop new buildings. Relaxing these regulations would at least alleviate, it not outright solve the crisis, but people just don't wanna do that. It's not a technical issue, it's just that the political will isn't there.

As an example of ambiguous red tape, take the ubiquitous "community meetings" that are common in US cities any time there's a major new development. It's common for neighbors to raise random objections that may or may not relate to any building codes or zoning regulations, and then a planning board to force the developer to adapt to those objections, or just block the project outright.

What this means, is that there's really two sets of laws: one on the books, that was developed through normal democratic processes like city council members voting on them, or local initiatives passing, and then the second set is whatever the local residents feel like accepting in their heads.

We would never accept this for other laws, the idea of, "well sure you didn't break any laws on paper, but local residents don't like what you did and a few raised a stink about it at a community meeting, so you're going to jail anyway." But that's how building permitting actually works. You can't just follow actual laws, you have to make the subset of people who show up to community meetings all happy.

This is kind of cool, but I'm skeptical that these sort of planes will ever be practical as much more than rich people toys. The power density of even speculative near-future batteries favors small airplanes and short flights. This doesn't really mesh into the existing aviation industry, so proponents of these small electric planes usually propose creating new markets entirely; e.g. Uber for Helicopters. But I'm pretty skeptical that laws will allow regular operation of these in residential neighborhoods for long, if at all.

Also, where is the vertical stabilizer and rudder? I assume they're using differential thrust in powered flight, but what if they lose power? Can this plane be controlled in a glide?

This was posted on HN a while ago; of course the numbers are aspirational but this explains their business model:

> If we imagine for a moment that you work in an office in Palo Alto, you could now choose to live in Hayward (5 min flight, $25), downtown San Francisco (10 min flight, $50), or even San Rafael (15 min flight, $70).

> Or maybe you want to escape to Lake Tahoe for a long weekend? That would be less than an hour on a Lilium Jet, at a cost of around $250 at launch and less in the near future. It might not be something you’d do every weekend, but saving you three hours each way might well make it worthwhile for an occasional trip.

Obviously at first this will be a luxury good, but it's not obvious that it'll remain out of reach for the middle class. (Sure, it'll never be cheaper than a bus.)

It's a fair question exactly how much regulatory change this approach requires, but my impression is that they are trying to operate within existing constraints (I'd appreciate any insight from experts in the aviation space though).

You would have to be making a lot of money to justify 2 such flights per day.

25 * 2 * 22 = $1100/mo = $13.2K / year.

Bay bridge toll + gas + parking + amortized car ownership + insurance is pretty plausibly less than that already.
You will have less mobility than with a car, though,so it won't replace all of it. But I agree with your main point, the actual premium will be much lower and probably worth it, considering the time saved.
There's likely a reason they picked Switzerland, Munich, New York and California as examples ;)

I'm interested in how those prices break down. Without any more details, it's hard to know if they're realistic at all.

But if you can live in a cheaper place than Palo Alto, you’ll make back that $15K per year in lower house payments. And if you only have a comfortable commute of 15-20 min each way as opposed to an hour (or more), your standard of living will be much nicer too.
House prices will adjust once air taxis take off (no pun intended).
Perhaps not. A recent study (can't remember where, but industry specific) proposed that EVTOL economics--at scale--will settle at a CASM of $3. (CASM = cost per available seat mile. Note RASM, or revenue per available seat mile, will be higher or these businesses won't make a profit.) With a CASM of $3, this study showed that only 0.03% of the Bay Area will be wealthy enough to commute on these vehicles on anything resembling a regular basis.
I wonder if the buildings these aircraft should land on can take the load of the downwash and the noise.

In Europe there is a tilt rotor initiative. This has a smaller and more intensive downwash than a helicopter.

I also recently read a report about the effects of rattle noise from Chinook helicopters affecting houses above 75dB noise levels.

If my concerns are valid, I estimate travel times to increase. You would need to visit a vertiport first.

I wonder if the buildings these aircraft should land on can take the load of the downwash and the noise.

In Europe there is a tilt rotor initiative. This has a smaller and more intensive downwash than a helicopter.

I also recently read a report about the effects of rattle noise from Chinook helicopters affecting houses above 75dB noise levels.

If my concerns are valid, I estimate travel times to increase. You would need to visit a vertiport first.

The main issue is not cost, but safety and the disturbance of others.

Safety: If you crash in a car, its very likely that you survive. With these a crash is very likely deadly. To reach safety levels like commercial airplanes costs will need to rise tremendously. A commercial jet needs maintenance and checks after each flight by trained personnel, high quality parts that can be tracked from the refinery,...

Privacy: You dont want these flying over your house 7/24. They fly much lower than commercial planes, with a mediocre camera you could spy on anyone.

Crime: What if you divert one? Will there be security checkpoints at the entrance?

Weather: I'm no aviation expert, but these look... flimsy. Are they able to run on cold weather? (batteries last much less in cold) Are they able to run in storms? Likely not, even commercial planes avoid them. Then I guess they suspend the service during storms, since with their "local" distances as big as the circumference of a storm cloud?

Safety can be solved with a parachute that lands the whole aircraft in the event of a catastrophic failure. These are already fitted to high end GA aircraft like Cirrus.
Safety and weather are covered by certification requirements. Those will be somewhere between small aircraft and helicopters with some eVTOL specifics. If it gets certified those bases are covered.

Privacy: Regulated airspace is your friend, plis why wait for one those if you can have your own drone for the price of one Lilium ticket.

Crime: Regulations also cover airport operations, so that base will be covered as well.

For me the question is not if those aircraft are goong to fly (they will if it os technically possible and people fund development), but rather whether there is an actual market for those big enough to make the manufactirers and operators viable businesses. The last qiestion is hard (IMHO impossible) to answer without getting them to market first.

There are certification requirements for both the aircraft and Ops Spec approvals for Part 135 (on-demand charter) operations. I can see that these would be certified to fly (and thus eligible for Part 91 (private) operations) far more easily than the more stringent requirements for Part 135 charter operations.

The FAA thinking is that you have greater understanding as a passenger on a Part 91 operation and are better able to judge the risk yourself, whereas a Part 135 (charter) or Part 121 (scheduled airline) operation, the public cannot effectively judge the safety of the operation so the FAA holds them to a higher standard.

Single engine Part 135 is possible, but there's a large amount of focus on redundancy:

I work for one of these startups, Beta.

We are focusing on a slightly different market than the other entrants; we're focusing initially on cargo rather than passenger transit. One initial customer is United Therapeutics, for transporting organ transplants and artificial organs to hospitals. Another is UPS, for getting air freight from airports to distribution centers; cutting out the truck trip can save a ton of time there. We are also making a passenger variant, but since the regulatory and NIMBY concerns for the passenger air taxi market present a lot of risk, we're not betting solely on that market like a lot of the other companies are.

This helps with a lot of the concerns raised in this thread. In fact, another one that I'm not sure has been brought up is vertiport design and siting concerns; right now standards on vertiports are still a work in progress, and there are questions about whether it will be feasible to get them installed, because even with vertical takeoff and landing you generally need to keep approach angles of about 15° clear, which means once a vertiport is installed you need to limit the heights of any surrounding buildings to keep the approach clear.

To address a few of your other concerns: we're located in northern Vermont, we know cold weather. Actually, for our use case hot weather tends to be more of a concern; batteries and motors heat up when used, especially in the very high power vertical lift phase, so our limitations there tend to be thermal and cold air provides better cooling.

Our charging stations also include air for cooling and warming the batteries; so you should be able to avoid the issues with batteries being cold on startup with our air system.

All aircraft have limitations on weather that they can be flown in; crosswind limits for takeoff and landing, etc. As very lightweight aircraft, with high lift/drag, these will be somewhat lower than the limits for your big jumbo jets, but will be high enough to be useful in a lot of weather. All aircraft have requirements for design and testing for HIRF (high intensity radiated field/lightning), so these will all be certified to the same standard there. Aircraft can optionally be certified for flight into known icing conditions (FIKI); I believe our plan is to have the capability, but as an optional add on, as it requires a number of heating elements which add weight and complexity. But overall, the weather concerns shouldn't be too much different than for other small aircraft.

As far as safety goes, that's obviously a concern in any aircraft. One advantage of electric aircraft is that electric propulsion systems are far mechanically simpler, with far fewer moving and wearing parts. The only real wear item of concern are the main bearings on the motors, and the landing gear. So maintenance intervals can be much longer than with ICE aircraft, and I expect reliability to be considerably higher. Additionally, electric motors can be much smaller and lighter, and thus can be made redundant. Each propeller on our aircraft will be driven by multiple independent motors (probably can't say the exact configuration at the moment), so that motor failures can be tolerated without catastrophic consequences.

> crosswind limits for takeoff and landing

Most aircraft have a “maximum demonstrated crosswind capability” which is a required test flight item but is not a limitation. It has to be demonstrated during flight testing to a figure of not less than 20% of Vso, but once that’s hit, they don’t have to find a greater crosswind to determine an actual limit.

You're right. The maximum demonstrated crosswind velocity isn't a limit, but more of a guideline, based on what was tested for.

However, many aircraft do that testing to a higher level than is required. For instance, for a Cessna 172, 20% of Vso would be 8.2 knots, but it has a maximum demonstrated crosswind velocity of 15 knots.

Anyhow, all I'm saying is that at least for our aircraft, it looks likely that the maximum demonstrated crosswind velocity will be on the low side; at least the mandated limit based on Vso, possibly a few knots higher, but like most small aircraft, much much lower than what you have for big jets.

Pilots will care more about the aircraft’s capabilities than the demonstrated crosswind limits. My A36 was demonstrated to only 15knots IIRC, but easily handles a 25 knot direct crosswind. Whether Beech test flew it to 11, 15, or 20 knots I wouldn’t care the least bit about.

(In VTOL mode, could you wheel the aircraft into the prevailing wind for takeoff and/or land it pointed into the wind to reduce crosswind effects? [I’m a fixed wing guy with I think only 0.7 dual received in a helo.])

Yes, in VTOL mode you are generally going to want to land into the wind or wheel the aircraft into the wind for takeoff. I think that would probably be possible.

But we are also concerned with CTOL performance; in order to add more flexibility, CTOL performance is something that we are focusing on heavily, as if a runway is available you can do a takeoff and/or landing with lower energy use and thus get more range, so we're designing to be able to takoff and land either CTOL or VTOL. For example, one of our use cases is cargo, such as UPS getting packages from an airplane at the airport, to its distribution center. At an airport, you have a runway available for takeoff, so you might do a CTOL takeoff, and then a VTOL landing at the distribution center, and vice versa for the return trip.

And what I'm saying is that our aircraft, at least, won't have crosswind capabilities that are terribly high when doing CTOL takeoff and landing. It's pretty light and floaty and has a strong weathervaning tendency, and control surface sizes are kept limited in order to save weight and drag. It will be able to handle the minimum and maybe a bit more, but I wouldn't expect it to do well significantly above what the demonstrated crosswind velocity is. Ours is designed more as a glider that happens to have electric propulsion and lift capabilities, rather than a conventional powered aircraft, in order to be able to eke more range out of our batteries and provide a greater safety margin in the event of loss of propulsion power, but there are some tradeoffs to that design.

Also, I should say that I'm a software guy, this is my first aviation related job, and I only have about 2 hours in my logbook for dual received, and our certified design is not finalized and we are still doing some trades on things like control surface sizes, so anything I say here might be wrong now or in the future. But right now, we have a fairly limited crosswind envelope.

That might not be as big of a concern as it first appears. You’re rarely more than 50 miles from an airport with either a crossing runway or a taxiway better aligned to the unusual wind (naturally, airports tend to have a primary runway aligned with the prevailing winds when terrain permits).

In an emergency, landing on an aligned taxiway is probably not materially different in risk profile from a VTOL landing on an uncontrolled ramp or parking lot under those same wind conditions.

Yep, I'm not saying it's a big limitation, given the VTOL capabilities and availability of airports. Just that there will be few windy days in which we might not be able to fly, but that's the case for pretty much all small aircraft.
These seem to compete more in the helicopter realm than the airliner realm. That's likely to be true of the relative level of safety of this vs a helo vs an airliner. (I've sometimes quipped that helicopters are one of the primary predators of billionaires.)

While the stated/projected costs (which I doubt will be achievable), these would compete very favorably against a helicopter on a cost basis. Without the ability to auto-rotate (or a functional equivalent level of safety system), there's no way I'm getting in one nor recommending my family get in one [and I'm perfectly happy flying my family in single engine piston aircraft at night].

eVTOL have to be designed to the same safety standards as other aircraft; and in fact, they will be held to slightly higher design safety standards due to their novelty, required to meet safety standards that otherwise only apply to larger transport category aircraft.

You are right, eVTOL cannot autorotate, but electric motors can be far more reliable than internal combustion engines, with many fewer failure modes. Additionally, they are much lighter, and so you can have much greater redundancy. There is considerable redundancy in the lift motors on these aircraft, so one or in many cases more than one lift motor can fail while still providing safe and controllable flight. The exact level of redundancy needed is verified via probabilistic risk analysis, considering failure probabilities of different components, and as mentioned the target failure rate will be lower for these than for equivalent sized conventional aircraft due to their novelty.

While there's still a lot of design and development work to do, I'd be very surprised if these didn't end up much more reliable and less prone to failure than helicopters and single engine airplanes.

Note: I work for one of these startups, so I may be a bit biased, but I also have insight into the design process and safety and redundancy of systems are absolutely a top concern.

We shall see… I can make a strong counter argument for your first paragraph.

The EVTOL community has long lobbied for, and for some time, has gotten away with a whole new set of performance based standards not previously used to certify other aircraft of similar size and weight. This was, of course, until several weeks ago when the FAA made the abrupt rule change going from Part 23 to 21.17b for these vehicles. Much has been said about this in the industry, but I understand that questioning the performance based standards is at the core. We’ll see where the dust lands, but it’s clear that some in the EVTOL community are not interested in applying airliner safety standards to these vehicles.

Questions: is your firm following ARP 4754A and 4761 to the letter? What systems are being mandated to DAL A (requiring a 10 to the minus 9 failure rate?) Are these the usual components found in other jets, or new components that typically haven’t required the same level of safety criticality?

These are a whole new type of aircraft—there are so many unknowns that it’s impossible to compare safety standards to other aircraft, even if the intent is to meet something like Part 25.1309. Case in point: power distribution systems in airliners are rarely DAL A, but I’d recon they’re pretty damn safety critical in an EVTOL. No power distribution = no spinning propellers = no thrust, and all on a “powered lift vehicle…” cue the classic line about the V22, “a plane that can’t glide AND a heli that can’t autorotate—all in one!”

You're right, some other entrants in the eVTOL community seem to have strategies that rely on some kind of regulatory magic. The company I'm working for, Beta, is taking a very different strategic approach, with much less reliance on "then some regulatory magic happens;" we are focusing on cargo first, and a passenger variant later. We are not particularly concerned with the change to 21.17b, we're willing to work with the FAA on that rather than fighting it. And because our initial target is cargo, such as transporting organs between hospitals with existing helipad infrastructure or cargo from airport to distribution center, there are a lot fewer regulatory hurdles about where we operate than the air taxi market.

We are following ARP4754A and 4761, yes. We are still in the process of doing our safety assessments at the aircraft and systems levels and finalizing our type certified design, so I can't say which systems are going to be required to be DAL-A, but I expect that the pilot inputs, flight controller, battery systems, high voltage distribution system, low voltage distribution system, lift motors, and control surface servos will be designed to that level. Our strategy is to build ourselves the critical components for an electric aircraft, so we are doing the battery, high voltage distribution, and electric motors, while we are buying the other components (pilot inputs, flight control computer, control surface servos, primary flight displays, etc) from existing suppliers who already have experience in this space.

In the meantime, we are also learning a lot from flight test of our experimental proof-of-concept airframes, which we can feed into this process. We've already built one experimental eVTOL under a previous design, and then two proof of concept airframes with a design much closer to the type certified design that we're now working on; so while we go through the process of breaking down the requirements per 4754A and doing safety assessments per 4761 and working on our final type certified design, we're also learning a lot about operational concerns and refining our design on our experimental proof of concept airframes.

As for the V22 line, well, our aircraft can't autorotate, but it's not bad as a glider. That was a primary design criterion; it should mostly be a glider that happens to have electric power. We recently did a cross-country trip halfway across the country on our PoC aircraft in CTOL configuration (, with a number of stops on the way, of course, our range is limited by physics, and the majority of that trip was done such that there was an airport within the glide cone of our aircraft; we did allow for a few legs in which that wasn't always the case, and we would need to ditch in the event of power failure, but for most of the trip there was an airport within our glide cone if we had a power off event.

Oh, I should also say, for a helicopter autorotation is only particularly helpful if you have enough forward airspeed or height to initiate it. Helicopters come with an HV diagram indicating safe flight envelope, such that autoration could be initiated in case of an engine failure, or you are low enough for a crash to be survivable if you do not have enough height or airspeed for autoration.

In an eVTOL, if you have enough height or velocity, you should be able to glide on the wing. So you'll be wanting to keep yourself in the appropriate region of the HV curve, and your emergency engine out procedure will be much more like a conventional fixed wing aircraft, rather than a helicopter.

Lilium's plane has 30 engines, multiple independent battery packs, and electric motors are way more reliable than jet engines (due to being so much simpler). A Lilium plane may have a 1000x higher chance of a crash in case of full engine failure, but perhaps that can be compensated for by 1000x times simpler/redundant propulsion technology. This seems to be very hard to assess in theory, so we probably just have to wait and see how it performs in practice.
At some point at least their design also included a whole plane parachute. I don't know if that's still the case.
> 1000x times simpler/redundant propulsion technology

This is a contradiction.

A system with that level of redundancy will have a corresponding increase in complexity of management systems. That means software (multiple copies of software on multiple independently powered computers all somehow coordinating). This makes the management software the single point of failure, and frankly I'd sooner trust a 50 year old pair of mechanical engines to a 5 year million line of code program.

You can always build things more safely with more resources (more maintenance, more checks, more testing etc.), the question at the end of the day is whether it is economical. I don't think this question can be answered upfront in this case.
30 engines = 30x the chance that at least one will fail. Maybe one is tolerable. How many can it lose and still fly?
That's all very well, as long as there's no common modes of failure. Redundancy can be a means to achieve reliability, but not always. Imagine the cause of failure is a bug which kicks in at a specific time of day, or an integer overflow which happens after a certain amount of uptime, or all the motor drivers are susceptible to a specific RF frequency. It doesn't matter how many motors you have if they're all susceptible to the same failure mode.
That's what certification is there for, isn't it?
> integer overflow which happens after a certain amount of uptime

It’s not just electric powered planes that have to worry about such things… this was an issue for the Boeing 777 Dreamliner too. If it was powered on for longer than 248 days, it could lose all electrical power due to an overflow in the generator.

I’m not saying it isn’t a concern, but rather it is a concern for all planes (and vehicles for that matter). Many commercial passenger planes are now fly by wire. If you lose electrical power, you’ll also lose control. So, while we’re talking about purely electric planes, the problems are universal.

But many planes can glide to a certain degree.

This thing would just fall or glide with zero pilot control. No control surfaces.

A lot of the electric (mostly fuel cell) aviation startup industry is funded/supported by currently profitable aviation companies. The 1000hp motors for them are, like the airframes, one of the mostly off-the-shelf elements of their development.

I agree that even modern batteries are pretty absurd for any human scale flight, though scaling laws make smaller aircraft more reasonable.

Isn't synthetic fuel much more promising?
There's been an EU funded research project that did some projections on the electricity needed for e-fuels. See the graphic on page 44:

For pure e-fuels they project 32 PWh. That is, to put it in perspective, more than the total world electricity production today. You'll want to use every technology available to do this in a more efficient way - batteries for very short ranges, hydrogen for mid ranges, e-fuels only for long range where nothing else works. It'll still be very challenging and likely the current growth projections of the aviation industry will be seen as unrealistic fantasies at some point in the future.

> For pure e-fuels they project 32 PWh. That is, to put it in perspective, more than the total world electricity production today.

Total annual electricity production is 161 PWh. THe PDF you linked puts it in perspective by saying that if it were purely powered by renewable energy it would increase the size of the renewable energy sector by 3 to 5 times. In other words this doesn't sound hard at all from an electricity standpoint. If electrical generation were half the cost it would be economical right now.


> We find that an electricity emissions factor of less than 139 g CO2e per kW h is required for this [Direct Air Capture system paired with Fischer–Tropsch synthesis] pathway to provide a climate benefit over conventional diesel fuel.

The grid averages in most regions are higher than that. I don't think multiplying current renewable generation just for jet fuel is easy.

Yeah they are, and this fact is just overlooked by people who aren't thinking through the implications of abundant renewable energy. With a surplus of renewable energy it makes much more sense to manufacture synthetic liquid fuels and burn them, than it does to power airplanes with batteries. The energy cycle is grossly inefficient but nobody is going to care because the energy inputs will be nearly cost-free.
CAISO hits about 100gCO2e/KWh during the day. And I run a solar surplus that I don't put back on the grid.

I'd be really happy if there were a good way for me to turn excess electricity into something I could use later. Maybe that's hydrogen. Maybe that's capturing carbon and putting it into liquid fuels. Maybe that's creating graphite that I can use for fun personal projects.

But regardless, I don't expect grid electricity prices to fall. Probably not in the US. Definitely not in CA.

I had that thought recently. Renewable energy sources like wind need a lot of energy storage. That is, unless you over-provision them so much that they can always meet demand even at peak times. This leaves you with over-production at other times, which could be used for other purposes that don't need to run continuously: synthetic jet fuel production, water desalination, etc.

Basically, overprovision and then set electricity rates based on demand, and the renewable energy "storage problem" might just sort itself out. Of course, all those windmills and solar panels will cost an awful lot, so it might not be as simple as "overprovisioning".

> That is, unless you over-provision them so much that they can always meet demand even at peak times.

Overprovisioning solar to power the grid on ice cold, windless new moon night is going to be hard. Having somewhere to put excess energy and some overprovisioning is always good, but it won't solve all storage problems.

If we can build a superconducting grid, we can transport power from the parts of the planet where it is sunny or windy to the parts where it isn't. Assuming that everyone remains friendly and operational, that is.
Burning any fuel in our atmosphere produces nitrous oxides. Synthetic/carbon neutral fuels won't help with that.
These can possibly be addressed by catalytic converters in the exhaust (not sure how feasible that is in a turbine engine though). In any event, it's a small fraction of total greenhouse emissions, dwarfed by CO2. Let's not let perfect be the enemy of good.
Oh I wasn't concerned about their greenhouse effect contribution. NOx can cause asthma and bronchitis and can aggravate pre-existing heart conditions. They also form smog.

Did I mention that they are bad for the ozone layer?

From a CO2 perspective, synthetic fuels don't have an intrinsic advantage, unless you use biomass as your source of carbon. Traditionally, synthetic fuel has been made using coal or natural gas as the source of carbon. There is still some advantage to this, the nitrogen and sulfur content of the fuel can be dramatically reduced, which is great. But with regard to C02 specifically, you're basically burning coal. With biofuels, I think care needs to be taken to ensure we don't ruin the price of food for people by incentivizing farmers to grow fuel feedstock instead. Biofuels made from algae might be the best, since this wouldn't require the use of arable farmland.

Another approach is to pull the CO2 straight out of sea water. Apparently the US Navy thinks this might be a viable approach, since their nuclear aircraft carriers have power to spare.

Obviously in the present context "synthetic" refers to fuel produced using renewable energy. If you are willing to use petroleum, you don't need to synthesize anything because that is where you started, unless maybe you are turning NG into kerosene. But that would be a dead end technology, so would not return investment.

Energetically, the principal synthetic fuels will be anhydrous ammonia and hydrogen. Capturing CO2 to make methane and kerosene is possible but more expensive. In particular, you need hydrogen as input, and must both capture and crack the CO2.

But for some uses you still need hydrocarbons, at least for now. Given carbon taxes subsidizing synthetics, the synthetics could be competitive.

In the longer term, aviation does much better with liquid hydrogen fuel, but it takes new airframes or, at least, extensive retrofits.

I recently commented about synthetic jet fuel in another thread

> A problem with biofuel is scaling it up, see: According to that article the U.S. would need to devote "an area bigger than Texas and California and Pennsylvania combined" to crops specifically for its own jet biofuel needs. That's just for flying, not for food or fuel for ground transportation or anything else.

Also that article says that from 2009-2013 a $100 million effort was made to figure out how to get sufficient synthetic fuel from algae but they eventually gave up and went back to the drawing board.

Biofuel is an obvious dead end.

The future has no place for biofuel in any substantial amount.

Ethanol made from food (like corn) is a dead end.

Firewood and derivatives have always had an important place in heating and cooking, and are likely to continue in that role for a while. Other types of biomass based hard fuels (from recycled garbage/waste, algae, etc) will most likely also play a role in electricity production and heating, but perhaps a small one (unless algae based biomass takes off).

And for liquid fuels for transportation use, algae may also end up being a competitor to hydrogen when oil runs out. I remember there were a lot of companies working in that space 10 years ago, but then there was the oil price crash in 2015, and it seems many switched away.

For instance algenol was positioning itself as a fuel company, but appear to have diversified:

If oil prices remain at current levels, though, algae may be only a few years away from scaling up to take a significant part of the market.

Firewood does not constitute a "substantial amount", by any industrial measure. It will continue being used, in decreasing amounts as very cheap efficient stove designs gradually penetrate the tropics.

Growing algae occupies >10x the area of floating solar panels producing the same usable energy. Harvesting and processing algae costs >>1 orders of magnitude more than delivering electrical power via wire.

The reasonable expectation is that transitions will be toward cheaper alternatives, with societal inertia acting to delay transition well beyond the point of obvious benefit. Thus, existing nukes will continue operating well after building solar + storage and then switching to that would be cheaper.

I keep thinking the direction kitchens are headed in developing countries is a solar powered microwave, induction cooktop, and fridge.

Does the lady of the house want to collect scraps of firewood and then cook in a hot already smokey kitchen or on a only heats the pan induction cooktop? Yeah.

The bottom billion people have no counter to put a microwave on. A solar panel, battery, microwave, induction cooktop, and fridge would cost several years' income preferentially spent (e.g) eating.

Getting together $10 for a stove that needs 5x less firewood is a challenge. They need a new one every year because making one that lasts costs more.

In Norway, biofuel (mostly firewood) accounts for a bit more energy used than coal and a little less than natural gas:

Here is similar data from Sweden:

Here is for the world, my understanding is that "Traditional Biomass" is mostly firewood there too:

Can we allow CO2 emissions if we can sequestrate it somewhere else? Synthetic fuels sounds like a good idea.

It's capturing energy in point A and being used at point B. You can't just look at point B and yell "CO2 emissions!".

> if we can sequestrate it somewhere else?

That seems to be the big if.

I believe when people say synthetic fuel they mean carbon neutral fuels that are made from renewable electricity.

The general idea is to use electrolysis to produce hydrogen, then combine that with atmospheric CO2 to produce methanol.

For instance:

Atmospheric carbon capture seems like an petroleum industry scam to me (check the 'Members' page of that website.) In principle it's what plants do, but plants do it using scale; there's a whole bunch of them. CO2 is under 500ppm in our air, and air isn't particularly dense in the first place; the amount of air you'd need to move through your capture plant is immense.

On the Costs & Outlook page of this site, they list their potential feedstocks; it's all biomass, except for the 'Technical Potential "Unlimited"' column, which mentions Power-to-Liquids. But how does that actually work and does it actually make sense?

Related parody of carbon capture:

I fully agree with the bit about atmospheric carbon capture. What a pointless waste of energy. But if you start thinking of plant biomass not as the energy source, but just as the carbon provider for making carbohydrates from your hydrogen, then energy crops vs food crops conflict suddenly disappears, because the nutritious parts usually come alongside plenty of lower energy "plant waste" that should be good enough as a carbon provider for hydrogen "carbonation". Certainly much better for the task than atmospheric CO2. And all that plant carbon would soon continue it's cycle as atmospheric CO2 anyways, so it's just as good as atmospheric capture.
It is possible, it’s just expensive.

The U.S. navy is interested in a fuel synthesizer that works on co2, seawater and uranium and they can pay more than you per gallon because you don’t have to refuel an aircraft carrier in a war zone.

>This doesn't really mesh into the existing aviation industry, so proponents of these small electric planes usually propose creating new markets entirely; e.g. Uber for Helicopters. But I'm pretty skeptical that laws will allow regular operation of these in residential neighborhoods for long, if at all.

I can see it becoming more of "Greyhound for Helicopters". Practically every town in the US greater than a few thousand population has at least a local municipal airport. With electrification, aviation can become so cheap that all of these fields will just have a few commuter size electric aircraft that feed into to the rest of our existing airport infrastructure. And with the planes being so small, there's really no need for TSA security or anything, it becomes as simple as buying a ticket on your phone and hopping on the plane like a bus.

> And with the planes being so small, there's really no need for TSA security or anything

There's no need for larger planes either for zero-risk travelers.

Have you heard of 9/11?
> With electrification, aviation can become so cheap…

Fuel is not the dominant cost in general aviation. Electrification alone won’t make it cheap.

>Fuel is not the dominant cost in general aviation. Electrification alone won’t make it cheap.

It's not about fuel efficiency. In fact, any electric aircraft with current battery tech is always going to be less efficient than a jet, because jets burn oxygen from the air.

It's about maintenance. The fixed hourly cost of aviation is almost entirely based on the cost of maintenance. And a fleet of electric aircraft will be orders of magnitude cheaper to maintain than turboprops and jets. That can unlock whole new business models of small scale commercial aviation that aren't possible today.

When you say "orders of magnitude cheaper" you can't possibly mean even 10×. There is more to aircraft maintenance than just engine repairs and overhauls. Electric aircraft will still require similar amounts of maintenance on the airframe, control surfaces, avionics, and interior. And some of the powered lift designs have literally dozens of separate motors and rotors, each of which require periodic manual inspection.
Electrification alone won't make air charters cheap. The aircraft themselves, pilot salaries, maintenance, and facilities will all still be nearly as expensive. We are decades away from the FAA allowing autonomous or remote piloted aircraft to carry paying customers in commercial service.
Granted, this is a new type of transport.. but the current metrics on air flight safety do not support this idea. Take offs and landings are the most dangerous part of flight, and still account for planes being more dangerous _per trip_ than most other modes of transport.

Planning to create a plane that fills this space is planning to create a plane that suffers a lot of accidents for almost no real gain over current options.

Buses are incredibly safe. If you want better busses, build those instead. This obsession with floating to your destination above the ground does not seem wise or worthwhile.

It's trivial to create a luxury "bus" in just about any form factor you want to from a full-size motor coach down to a limo. Presumably the economics don't work in most cases. Of course, if you're talking small municipal airports in the US, the vast majority of people living there, especially those who can afford somewhat upscale transportation, probably own a car.
Yes. Most small towns don't even have bus service to the nearest hub airport, because economically it doesn't work. And there is no arrangement of costs that will work out to electric aircraft being cheaper to own and operate than a bus.
In a sufficiently river/sea/ /hill/valley rich environment it might work if one can save on infrastructure cost for extra expensive roads. This is not most of the world though.
You already have bush planes in places like Alaska. A cheaper/better bush plane has probable merit but, as you say, that's not most places.
>[The electric airplane] doesn't really mesh into the existing aviation industry

The reason small electric planes haven't taken off [1] is that they simply haven't proven their cost advantage. About one-sixth of the cost of a flight is fuel, which can be difficult to tax because of jurisdiction shopping. A third is labor, including taking care of the plane. Seven percent goes to building the plane. From:

Optimistically, electric planes could be cheaper to fuel, build and maintain. That's enough to upset an entrenched industry. But it's not clear how it should be organized, and the infrastructure mostly doesn't exist. Plus, the scale you expect to operate at depends on battery technology, which has been a little up in the air [2], and you don't want to design your operations around 1000-mile ranges if it's going to be 2000 in ten years.

1: Sorry.

2: Sorry. But see:

There's other aspect than the pure economic aspect:



When both are combined, this makes Urban flight closer to feasable.

Enjoy the engineering achievement in the moment.
I'm guessing that if it loses power during flight then it's curtains for the airframe and anyone unlucky enough to be in it.

There's lots more work to do to push it out to the mass market, but I could definitely see a niche for it.

Check out their other video posted around the same time as this one, especially the part about changing the wheel design to allow for rolling landings. Seems like regulators had the same concern.

Why not add a parachute? Some small planes actually build one in.
I like those a lot but they only help above some altitude (I think it’s something like 300 or 600 ft). Ie they won’t save you during VTOL
Airplanes glide. Some better than others, but they do glide.
I think this “plane” has a glide ratio that’s only slightly better than a thrown rock.
Powered lift aircraft are not controllable in a glide, nor are they capable of autorotation like a helicopter. Any complete loss of power will result in an unrecoverable spin. For safety these aircraft rely on redundant systems, plus a parachute.
That's the whole point of GP's comment. Planes glide with the control afforded by a rudder and a vertical stabilizer. Without that, it ain't pretty.
The Lilium plane has 12 sets of 3 electric motors. Each pair of sets is powered by its own battery pack, and each set is individually actuateable. So it basically has 12 control surfaces. Separate aerodynamic controls aren't needed.

Writing control software that can handle arbitrary failures isn't easy, but there is plenty of redundancy with the three separate flight computers.

That's the same if a jet engine losses power
Passenger jets have very good glide ratios. A 747 gliding with no power (all four engines somehow broken) from 10,000ft will get even further than a small Cessna 172 doing the same.

This is counter intuitive to even most pilots, but it's how efficient the wing design on a passenger jet is. Their lift to drag ratio is better than small planes.

Is this achievable by the size of the craft itself? Or the fact that these bigger planes have 1000s of engineers behind them optimizing every possible factor to squeak out the best possible lift to drag ratio?
It's the overal effort that goes into the design, combined with a different design goal. Airliners are specifically optimised for low drag because it saves fuel. A Cessna 172 is a design from the 1960s that wasn't much optimised after that, and the design goal was stability and benign flying not the lowest possible drag. Later similarly sized small aircraft like the DA40 and SR20 are better at low drag because they're computer designed and fuel cost became more of a thing in modern times.

For airliners the retractable gear saves tons of drag, but they also have things like winglets, and lots of smaller things like optimisation on the wing-root (airliners have smooth transitions here, trainers are sort of just square) that all reduce drag.

An airliner is also much less friendly to handle in a stall condition, while a trainer almost recovers on it's own. And similar for yaw stability, if you get the rudder a bit wrong in a trainer nothing much happens, while an airliner will typically start to oscillate. Both of these are solved on the airliner by electronics, a stick shaker or pusher to avoid the stall and a yaw damper to enhance stability. The Cessna 172 doesn't have any electronics involved in flying, only for navigation and those are optional.


Look at the tiny wings, and at what speed it still depended on vertical thrust. It's going to have horrible glide ratio, which means unpowered landings might be, well, not a thing, which leaves you only with emergency full-plane parachute as an option.

Pretty much all jet engine planes can do unpowered landings in glide, though admittedly some have pretty high speeds involved - but then they operate by default only on airports that have facilities for such speeds.

See this famous example, where a jet airliner ran out of fuel in flight and glided to a successful landing:

Also Air Transat Flight 236.
The movie Sully [0] opened my eyes to the amazing glide ratio of a commercial passenger plane like the A320. (I'm assuming that the movie was pretty accurate in that regard.)


Yes, the movie was accurate in that regard.
If a [civilian] jet aircraft loses an engine, it's still a strong favorite to end that flight upright, intact, and on a runway. There are a couple dozen jet engine failures per year; the overwhelming majority end up in a safe conclusion.

If they aren't stupid (And I bet they aren't), they made several independent redundant power system. I think distributed power systems (i.e. lots of small engines) is actually on of Lilium's main strength, can be made very reliable.

Lost 2 batteries and 7 rotors, fine, there's still 6 batteries and 25 rotors left. Or something like that

> The power density of even speculative near-future batteries favors small airplanes and short flights. This doesn't really mesh into the existing aviation industry,

How short are these short flights? The hugely popular Ponte Aérea ( has a flight duration of one hour.

That flight is about 230 miles (365 km) as the crow flies, and they're doing it with 737s that seat 100+ each and fly dozens of these flights a day.

Compare that to this battery plane that can fly 200 miles:

These aren't in the same ballpark; they aren't even playing the same game. If you want something to replace that plane route, I suggest buying a lot of buses.

> The power density of even speculative near-future batteries favors small airplanes and short flights.

Use a hydrogen fuel cell instead:

It used to mesh a lot better, when general aviation was much bigger than it is now and we had lots of tiny airports. Maybe we could get back to that. VTOL makes it a bit easier.
If you have even a tiny airport with a real runway then you can operate fixed-wing aircraft (possibly electric powered) without the extra cost and risk inherent to VTOL. Lillium and their competitors in the e-VTOL space are trying to create a new market for urban air mobility by bypassing airports and building new heliports, but even if they can solve the technical and legal challenges it's unclear if the economics will work.
Powered lift aircraft are not controllable in a glide, nor are they capable of autorotation like a helicopter. Any complete loss of power will result in an unrecoverable spin. For safety these aircraft rely on redundant systems, plus a parachute.

Finding landing sites is going to be a major challenge even if they can solve the battery problems. New York City could be a prime market but there are only a few heliports. Politics and safety issues make it difficult to construct more.

Any idea what the minimum height for the parachute to be effective as a life saving device?
The Cirrus SR22 needs ~1000ft above ground to effectively deploy the airframe parachute in a spin.
Minimum effective altitude for parachutes on light aircraft is about 400 ft agl, but the exact number varies depending on the flight regime. For powered lift aircraft there is likely a small "dead zone" in the flight envelope: too high to survive a crash, too low for the parachute to be effective. This may or may not be acceptable depending on mission risk tolerance and the reliability of other systems.

> too high to survive a crash, too low for the parachute to be effective

This is probably a silly question, but couldn't the pilot just wait until the plane dropped below the dead zone before deploying the parachute?

The lower the craft drops, the deader the zone.
You're thinking about the dead zone in the wrong way: There's a height X where you can drop the aircraft and it'll absorb all the forces to have the people live. There's a height Y where the parachute has enough time to deploy and bring the aircraft to terminal velocity. If X is less than Y, there's a height where there's nothing to save you.

Options to resolve this are: make X higher by making the structure able to absorb more energy, or make Y lower by having it deploy faster.

> New York City could be a prime market but there are only a few heliports.

Afaik rooftop helipads have been banned in NYC ever since an accident in 1977 killed five people.

There are three heliports on the rivers around Manhattan. There’s plenty of space to build more but noise complaints prevent that from happening. Bezos wanted to build one on the Queens waterfront (LIC) but the city killed the idea.
I assume that in a glide the wings are functional. The issue with all of these coaxial, non-contra rotating VTOL aircraft is that they don't allow autorotation, which usually allows helicopters to land using the deceleration generated by natural blade rotation in descent. This is a regulation and many of these VTOL aircraft will never make it to production unless they solve this problem.
The energy density of gasoline does not matter at all. Batteries are good enough for some applications, like short distance flights. And the operating costs for use cases where batteries work strongly favour batteries.

Power density has not been a problem for a while. We are not anywhere near the theoretical limits of battery energy density. So as soon as there are some commercial applications for battery powered flight, there will be a strong economic incentive to get closer to the theoretical limits.

Current jet engines are absolute engineering miracles that go very close to the physical limits to get maximum efficiency. But it took several decades to get there.

There is already a lot of economic incentive for lighter batteries.
Yes, and they are improving by a few percent every year. No major breakthroughs, but compounding improvements year over year, which do add up.

Batteries have improved incredibly in my lifetime. As a kid I had an electric RC plane that barely made it off the ground. Now you can get pretty cheap aerobatic RC planes that easily compete with gasoline powered models.

Battery powered screwdrivers used to be incredibly underpowered. Now I have a very decent battery powered rotary hammer...

> The energy density of gasoline does not matter at all.

Well if we're talking about commercial aviation, we're talking about jet fuel not gasoline. Regardless, it obviously matters a lot. A fully loaded 747 freighter has somewhere around 200 tons of jet fuel and a max payload of about 130 tons. They already need more fuel than cargo, and that's with the excellent energy density of jet fuel. Furthermore, traditional planes get lighter the longer they fly as they burn off their substantial fuel loads. The last 20% of the fuel goes a lot further than the first 20%. Batteries don't get this advantage at all. (Dropping batteries from the plane with parachutes is a terrible idea, but I've lost count of the number of times I've seen it proposed..)

> We are not anywhere near the theoretical limits of battery energy density.

This doesn't jive with what I've read. It's my understanding that we're already near the limits of what electrochemistry can give us, and future advancements are likely to come from improved electrode designs, with maybe 2-3x better performance possible if we're lucky.

Dropping batteries from the plane with parachutes is a terrible idea, but I've lost count of the number of times I've seen it proposed

Perhaps, but there is also the middle-ground solution to use a booster rocket assembly similar to what the space shuttle uses. The booster can use its own battery packs and if needed its own additional engines, and when the plane has reached cruising altitude, the booster can decouple and return to the airport of departure.

> Well if we're talking about commercial aviation, we're talking about jet fuel not gasoline. Regardless, it obviously matters a lot. A fully loaded 747 freighter has somewhere around 200 tons of jet fuel and a max payload of about 130 tons.

You only need giant quantities of kerosene for transoceanic or transcontinental travel. The lilium business model requires a range of a few 100 km, which is possible with today's batteries.

Very long distance air travel is impossible with today's commercially available batteries, but is possible with exotic chemistries (see below) or with hydrogen fuel cells.

> This doesn't jive with what I've read. It's my understanding that we're already near the limits of what electrochemistry can give us, and future advancements are likely to come from improved electrode designs, with maybe 2-3x better performance possible if we're lucky.

There are several battery chemistries such as lithium sulfur or lithium air that have extremely high energy densities. But cycle life remains very low, which makes them uneconomical.

There has been decent progress made in improving cycle life, but it is still too low to be economical. There are military applications where a low cycle life is acceptable.

Lilium's quoted range goal is not possible with today's batteries--not by a long shot. This is why in part there is an investor lawsuit agains the company.

The only company touting range achievable with today's battery tech is Archer, and their range, when you factor out reserve and inefficiencies, is about ~40 miles (~65KM.)

> a range of a few 100 km, which is possible with today's batteries.

Not with a meaningful amount of cargo it isn't; look up the electric planes that are actually flying today (and it's certainly not for want of trying, this is a very trendy field.) I can think of only a few niches where very light but expensive cargo needs to go somewhere close-by, but faster than is possible with a truck. Organs for transplant, and rich people.

The cargo here is humans
But can you carry enough of them to make the whole thing worth it?
I mean, why should regulations me more lenient on sci-fi chopper/plane crossovers than on regular choppers?
I think there's a segment for flight instruction. I think flight lessons are usually short in duration.
I can’t possibly comment on any specific design, but what I’d like is something that can replace road ambulances.

This is partly because I live right next to a busy crossroads and often get multiple simultaneous sirens; but I do also wonder how faster they can arrive by going as the crow flies rather than following street layouts, and how much they have to slow down both for traffic and for blind corners.

For critical patients helicopters are already used. For patients who need to get to a hospital but are short-term in stable condition, is the extra expense of an air ambulance justified, in a health care system that is already unaffordable?
The ability to replace road ambulances is, I think, inherently a cost claim. After all, capability is already solved with, as you say, helicopters.
> For critical patients helicopters are already used.

I'm sure they are used based on a cost/benefit calculation - not everyone gets them. If eVTOL reduces the cost, many more can benefit, or those funds can be shifted to something else.

I keep thinking remotely controlled cargo operations, especially around bad terrain and difficult water features. Great for proving design and catching bugs for initial years.
This is one of the primary reasons I've bought into the eVTOL revolution. I'm also skeptical about these filling city skies, due to safety, noise pollution, etc. But the market for emergency and special purpose vehicles alone is enormous.

The US market size for existing _air_ ambulances is itself $4.5 billion dollars annually. The market size for standard ambulances is nearly 10x that.

When you expand this to the rest of the world, you can easily see a 100+ billion market for these sorts of vehicles, whether in ambulance services, firefighting, agricultural, or any number of other activities.

It's still possible we develop near-to-city eVTOL airport systems for short distance travel. But even absent that, I still think there's a big market opportunity.

Dropbox vs rsync moment right here
Wendover "Why Electric Planes are Inevitably Coming" to save others a click... please don't post only a random UUID as an answer.

I also find linking videos as a reply to something a bit weird, like how many minutes is one supposed to invest in understanding your point? Are you even making a point / answering a specific question, or is it just an interesting video on the topic? Articles are much easier to quote from or skim, depending on what you mean to say.

Air taxi is their market
Zero chance of helicopters in cities after 9/11. You can’t fly helicopters over SF or Manhattan anymore except for medical purposes.
> can’t fly helicopters over SF or Manhattan

Both cities have plenty of potential even with overland banned. New York has a thriving helicopter business between boroughs, up and down both sides of Long Island and to and from the airports. The Bay Area isn’t similarly knitted together, but there is no good argument for not having an electric hop from e.g. Mountain View to SFO.

Can someone comment on why the parent would be (as of this writing) downvoted?

I'm wondering if there's some context I'm missing.

Best guess? Because the helicopter restrictions have nothing to do with 9/11.
Worth noting that the "thriving" helicopter business is uniformly disliked by residents, due to noise pollution[1].


There are also big cities outside America. Plenty of helicopters in Sao Paulo...

How is Blade flying people between Manhattan and the Hamptons?

The helipads are all on the rivers not inside Manhattan
Zero chance in the US which - increasingly - is not the center of the world.
Helicopters aren't banned over Manhattan, etc, despite repeated efforts to do so.

In the late 1970's, all the building-top helipads stopped operation after repeated accidents.

Still, there's the helipads along the river and a VFR corridor in and out of Manhattan. In 2009, the altitude rules for the corridor got a lot stricter because of repeated fatal accidents.

I was under the impression you can only fly over the rivers. Is that not true?
There's a VFR corridor over the rivers where you don't have to talk to air traffic control. Otherwise, you're going to need to talk to LaGuardia.

If you're a tour operator and want to use a city heliport, you need to sign a very restrictive agreement about operations, too-- which allows only limited overland stuff (e.g. flying over Yankee's Stadium/the Bronx). Mostly because people were sick of tourist helicopters constantly hovering over Central Park.

None of this has anything directly to do with 9/11. Crashes of tourist helicopters and noise concerns has caused the city to clamp down on use of helipads. Crashes of air taxi operations in the 1970s caused the removal of the vast majority of helipads.

This might give you some insights...

...of the idea. Witch is essentially, advertisement aside, "the wealthy who happen to live nearby cities, witch happen to be open-sky prisons^w^w factories stuffed with services to achieve the Chinese lockdown with workers who live in the factory, to work, of course ehrm, to achieve the best work life balance (better not say the best to who) can came and go from such erh smart cities in full comfort with means that made things closer, like if they live inside the city and goes with cars.

...In the LONG term, that means we can benefit from the economy of scale living "near" but far less dense than today so at that point in time we have finally found a way to live sufficiently flexible to withstand the technological, social and climate change still being near enough to be social and have economy of scale phenomenon.

Or: in the short term we need a good solution for those who can pay, in the medium terms slaves ahem citizens have built a new society and new generations will finally benefit from such progress...

In theoretical terms: maintaining roads network is expensive, far expensive if we also need to build new ones, like a potential future arctic "anthropization" due to climate change, so better made few railroads and waterways for heavy loads transports and live humans in the air, far more flexible and cheap. At a certain point in time if we are still alive as a species we will reach that point. Then the "self-sufficiency push" will be the key to reach that goal in an unspecified future.

Ps if they loose power there is AFAIK only an emergency parachute for the entire plane. Only it demand, I suppose, a certain altitude to being able to be deployed...

The low energy density of batteries favors large planes and short distances.

The only reason you are seeing them in small planes is that electric propulsion makes VTOL viable, and VTOL favors small planes. There is just this niche in aviation that can't be filled at all by fossil fuel engines, so it's the first to adopt electric ones.

And yes, regulations will be the most important factor for those. I imagine it all depends on how silent those planes can be. But I doubt safety will be the limiting factor.

> I imagine it all depends on how silent those planes can be.

I agree. I’d say, though, not just how silent, but how pleasant sounding. Aesthetics of sound could make or break this industry.

You either get a chop-chop-chop, or a bzzzt, both incredibly loud. It's not the engine that makes the noise, it's mostly the propeller/rotor. The only advantage of electric VTOLs is easier manufacturing and better control.
There is plenty of space to change the number of propellers, total area, and rotational velocity and change the sound profile of the plane.

There is also a lot of space on how you maneuver it on the landing and take-out, so you make less sound when it matters the most.

There is the entire thing about minimizing weight too, that also reduces sound, but it's also not clear how much can be done.

Overall, it's not clear at all how much noise the eVTOL planes will make.

Props need feathers.
> You either get a chop-chop-chop, or a bzzzt

Well, for instance, if they could line up the harmonics to create a missing fundamental (eg with the addition of external sounds), they could make propellers present an artificially lower pitch.

Your solution to them being too loud and annoying is to make them louder and hopefully less annoying?
Yes. It’s possible that louder but less annoying is more viable, wouldn’t you say?
I would say the most viable solution is to not subject hundreds of thousands of people to an incredible amount of noise pollution, so that a couple of playboys get to skip a taxi ride to the airport.

Private-transport helicopters or equivalents have no place in cities. The gain is in no way worth the cost.

To complement that: they are only viable because they are heavily subsidized by the suffering of city dwellers. If you placed the cost of air pollution on the bill, they'd be much more expensive.

Its not just unreasonable because the person flying gets less utility that is otherwise lost. It is also an unfair form of theft.

do you have any references to back these statements up? I am not an expert but I did read in a hacker News comment that the energy density of gasoline is about 14 (reading that article, its 50) times higher than a "normal" battery.

if that is true (I do not think that he left references either) then I would think that your statements seem less plausible.

a replier who later deleted their comment left a reference saying the energy density is 50 to 1, comparing lithium-ion battery to diesel:

Combustion aircraft also benefit from the weight reduction as fuel is consumed.
While that’s true, and makes a huge difference for rockets, it only makes a relatively small difference for airplanes. In cruise, most of an airplane’s energy is spent overcoming air resistance to move forward through the air mass (parasitic drag) rather than to create lift (induced drag).
> I am not an expert but I did read in a hacker News comment that the energy density of gasoline is about 14 times higher than a "normal" battery.

I understand you get more out of talking to a person who can (hopefully) explain the nuance of something, but this seems like a simple enough thing to google?

Any idea how reliable electric motors/systems are compared to fossil fuel systems (primarily piston driven as opposed to jets)?
My understanding is that electric motors are generally more reliable than piston engines. I'm not sure how that compares to jets (which are also considered generally more reliable than piston engines). Nearly all modern helicopters are jet powered.
In that niche, why are batteries needed? Couldn't those planes be constructed with gas turbines that generate the necessary electricity?
VTOL works fine with turbines, nearly all large helicopters use turbine engines. They don't use the turbines as generators but instead connect both engines to the rotor via a gearbox.
It's a matter of the weight/power relation. While batteries suck on weight/energy, their weight/power is great.

The lower that relation, the smaller you can make your VTOL vehicles, and the smaller the vehicles, the cheapest and more economical they are on total.

Did the Harrier just get skipped by the rest of the world?

fossil fuel VTOL was cracked in the late 60s.

When talking about practical small plane with relatively acceptable noise levels and fuel efficiency, I don't think Harrier counts as it "being cracked". 125dB at 100 feet from the plane, very limited time it can spend on vertical takeoff while loaded, limited situations (fuel/weight/thrust ratio) in which it can hover at all...If it was cracked, the newer iteration of the "same thing" - F-35B - wouldn't be so complex and take so many billions to develop...
And the Harrier only barely worked at all. For most operational missions, they couldn't really make true vertical take-offs and landings. Instead they usually had to make short ground rolls to get some lift from the wings, or have a carrier ship sail into the wind. And the mishap rate was appalling.
Whenever I hear air taxi, I think about water bottles and airport security.

I don't want some rich dude flying over my house just because he/she can afford to take a airtaxi from the airport to city center while everyone else uses car or train.

For other use cases they can do what they want. Australian outback perhaps.

But airspace pollution and a potential small airplane crashing down in a city? No way.

They do this already. They're called helicopters.
On the one hand, yes.

On the other hand, making it cheap enough that mono-millionaires can do it regularly is going to make a big difference compared to the status quo.

> mono-millionaires

Ah right, moving it from 0.1%-ers to 1%-ers is really going to make a big difference.

About 10x, right?
Roughly 10% of Americans are millionaires, for reference (though I doubt all of that is liquid).
Alright, the actual figure is $1,2M for the 90-percentile household net worth. For the individual that's to be divided by 3 (since there are about 120M households in the U.S.). We are at the 96-percentile for $3M household net worth.

So yeah, 4%-ers then. Really makes a big difference to my point. This is totally gonna change everybody's life. (I.e. those who can afford it, while the majority is scraping by from paycheck to paycheck.)

Owning a house doesn't just allow you to fly business all the time
this comment reminded me of this
Sources online show that about 8% of Americans are millionaires, with a significant bump during COVID (probably because of the stock market.) About 10% of households are.

It's hard to find precise qualifications for how they determine that, though. The households figure doesn't include primary residence value (why?), and the individual statistics don't mention liquidity. I suspect that only a small percent of that 8% actually has $1+ million liquid.

Definitely not liquid cash, but assuming that a not insignificant portion of those people are retirees or planning to retire soonish (which is when net worth peaks), I wouldn't be surprised if the percentage of decently liquid assets like stocks and bonds are higher than you might think.
I don't know. The idea that a bunch of people with a couple of millions of dollars in wealth can now zip around above my house (and further alienate themselves from civic reality, even more so than cars do) seems like a pretty bad outcome.
That is essentially how progress begins in every industry. Wealthy people pay for new tech with their vast fortunes, and many times, their lives. Once they work out the kinks and economies of scale take over, the less wealthy enjoy the same tech at higher levels of safety and lower prices.
I wonder how often that's true, or a myth of uber-capitalism - sort of a trickle-down theory for tech. AFAIK, it's often government that pays for new tech, and then once it has a profitable nitch, corporations.
That is true to a large extent today. Sadly, most of the foundations of the tech we have today is based on tech we had developed before governments were involved to level they are today. Cars, trains, engines, CRT, film, computers, telephone, building materials, and much much more, are seemingly only being tweaked. The rapid pace of truly innovative tech has waned. Is this because of government involvement? Is this because our understanding of basic science allowed us to pass some threshold, only to be stymied by the increasing complexity and having to devote more time and material to test the nuances?

Blockchain was supposedly created by a single person. The Federal Reserve Bank of the United States has mentioned creating a digital currency. As they pump more money into that idea and develop some neat tweaks or totally control blockchains, will we look back in 50 years and say, "Look at how much the government did for blockchain." forgetting that it exists in the first place to spite them?

Yes exactly! I'm traveling business all the time because it's so cheap.

Ah wait let me rephrase this: while more people can fly now economy got shittier than ever.

Also we live in 2022, the narrative that rich risk there life's was probably never true (they have test personal) and we have enough capital in our society to do certain things without the money of the rich.

> Also we live in 2022, the narrative that rich risk there life's was probably never true (they have test personal)...

> Earhart was the daughter of Samuel "Edwin" Stanton Earhart (1867–1930) and Amelia "Amy" (née Otis; 1869–1962).[13] She was born in Atchison, Kansas, in the home of her maternal grandfather, Alfred Gideon Otis (1827–1912), who was a former federal judge, the president of the Atchison Savings Bank and a leading citizen in the town. Amelia was the second child of the marriage after an infant was stillborn in August 1896.[14]

She for one, looks to me to have been wealthy.

> and we have enough capital in our society to do certain things without the money of the rich.

Part of the reward for pioneering tech is the taking of the risk and getting the reward while at the end of the day being able to feel a sense of accomplishment having done it largely of your own initiative and cost. The spirit of exploration that existed in early humans, that led to our expansion to the furthest points of the earth, exists today in the form of innovation and invention. While it is enticing of course to create at the behest of government or corporations like was done in Bell Labs or DARPA, there is a severe risk that liabilities and bureaucracy stifle innovation. I cannot imagine a governmental system of incentives that creates an atmosphere quite like the USA had prior to the 1960s that led to innovation, invention, and implementation that we had never seen before, and may never see again.

Well, _electric_ helicopters or electric helicopter-equivalent-vehicles would be a step forwards, correct?
> They do this already. They're called helicopters.

This is dangerously close to the infamous HN Dropbox critique[1] :-D

And it's likely wrong in the same way.


Past performance is not an indicator of future performance?
I think you're trying to be clever but missing the point.

HN Dropbox critique is saying "why bother building this bc there are already equivalents"

The reply you quoted is saying "you're objecting to this as impossibly unsafe, but it has the same safety properties as something that exists today"

Reply isn't saying electric VTOL is pointless bc helicopters exist. They're saying this whole line of objection is silly (rich people will fly over your house, what if they crash?!?) bc it also applies to helicopters.

Helicopters are expensive to rent. If Lilium achieves even 10x the cost they've suggested they can reach in the past, they'll be attractive to a customer base who'd never be able to afford regular helicopter rides.
Air taxis are really useful in places divided by natural obstacles.

Hop over a fjord, hop over a mountain range. Much cheaper and eco-friendly than building bridges and tunnels everywhere, especially if the population density isn't high.

These kinds of places are also generally suitable for hydropower and geothermal energy which gives considerable amounts of cheap electricity.
If population density is not high than it will not be cost efficient for the normal surprised how many people here think that rich people who can afford to fly over a mountain regularly is a good thing.

Perhaps in 20-50 years when we solved climate change.

Those companies are not trying to just create a cheap and easy to use carplane they want to become rich which needs business viability.

And I don't mind if they solve some niche problems. I mind that they want to fly over my head every 10 minutes.

"rich people who can afford to fly over a mountain regularly"

Look at the rural countryside in places like Norway. I am not talking about rich people primarily, but semi-isolated communities whose older citizens might need specialized healthcare etc.

Also, this was originally a discussion about electric planes, so their effect on climate change is probably neutral-ish.

>I don't want some rich dude flying over my house just because he/she can afford to take a airtaxi from the airport to city center while everyone else uses car or train.

Why not? He's funding the employment of the air taxi people, plus their technology development, and reducing congestion.

I understand the safety concern, but I don't see how "just because" they can afford it is a reasonable objection.

How would a few rich people flying above the lower ones reduce congestion ... on the ground?

Congestion would be reduced by people using trains and maybe, I would be actually willing to see this as an option, autonomously driving cars.

It's not 'just' a safety concern.

It's the safety concern and it's flying over my head.

There is always a risk/benefit ratio and just because a handful of people want to spend more money so that they can fly faster from the airport to the city center than others is not worth the security implications.

You are aware how much security is involved whenever you fly?

We talk an expensive license, regular flying hours per year (also not cheap), air control, restricted air zones, very regular safety plain checks.

Every single object on a commercial plane for example is tracked, every replacement etc.

Congestion is not solved by small expensive air taxies. If a normal taxi costs x, an airtaxi has to cost 4x and more.

We the people don't need to allow everyone everything just because they have the money into do so.

Like I said, safety concerns are fine, these things should be properly regulated like any aircraft, but if they can be safely regulated then I don't see a problem.

>Congestion is not solved by small expensive air taxies

If you expect a new transport to 'solve congestion' as a requirement for it to be allowed, we're not going to allow anything. Incremental improvements can add up.

I just find these "I can't have it, so you can't either" arguments so short sighted. Lots of technologies start out the domain of the wealthy before achieving scale and mass adoption. Maybe we won't all be mass adopting air taxis, but some of the technologies that come out of these things may well end up in our cars, or houses, or benefiting us indirectly.

I say 'not over my head'.

I also say 'do not start polluting the sky's

And ' keep the noise down'

You don't have a lawn?
Even existing regulated airplanes kill people on the ground every now and then. The risk is small, but I feel like the benefit of transporting ~100 people weighs out the risk much better than transporting ~1.
Fair enough, as I said in my first comment and have re-iterated in my later comment, that's fine. It's a reasonable concern. The safety issue is not really in contention.

My issue is with the argument that simply being wealthy enough (literally 'just because' he is wealthy enough. Check the comment I was replying to.) to do this is by itself reason enough to ban it.

All this redirection back to safety is a smokescreen to distract from the actual issue I'm concerned with.

Funny you mention Australia, back when people worked in offices you could sit down on the banks of the Yarra on a Friday night, and watch chopper after chopper flying the wealthy from their Melbourne offices to their Mornington peninsula weekend homes. There’s already a pretty big rich guys who won’t take the train market.
> airspace pollution

Bit of a fake concern, no?

>potential small airplane crashing down in a city

Is that really much worse than a SUV driving into a building?

> Is that really much worse than a SUV driving into a building?


Why? You’d expect there to be far more people at the street level than on top floors.

And in any case, even if such accidents would be worse, they’d also be vast less common. It’s more difficult to fuck things up in the air, and the level of training required to operate an aircraft is far higher than the level of training required to operate a SUV.

Drivers famously can’t even keep track of which pedal is the brake and which is the throttle

> Why?

All of the things that wrote, and:

> You’d expect there to be far more people at the street level than on top floors.

There are far more people who live near the sky than live near a large road.

> It’s more difficult to fuck things up in the air,

No, it really isn't? Aircraft driver licencing and training is notoriously much harder, longer than the equivalent motor-car licencing and training. Car drivers don't have to learn about stalls for starters. The training is there because a) it's much harder to do right, there are more ways to go wrong and b) potentially greater impact.

The common failure mode for a car is that it stops moving at the side of the road. The equivalent for an aircraft is that it falls out of the sky onto whatever is below. We are not ready for a lot more of that.

remember this?

So, terminal velocity of a relatively aerodynamic shape (like a bullet falling, or a skydiver who is head down and pulled their arms in) is about 200mph, according to

How many SUVs do you know of that are crashing into houses at 200mph?

Also, what is the relative mass of the electric airplane with a bunch of lithium batteries, versus the SUV?

What parts of the house might be hit by a falling airplane, versus an SUV crashing into the house from the road?

What is the fire risk of a bunch of lithium batteries having fallen out of the sky, versus the SUV crashing into the house?

There's lots of factors to be considered here, but overall I'd say there's a lot more risk of damage, injury, and death with the falling electric airplane than with the SUV.

Why focus on houses? SUVs drive into ground level shops and restaurants every single day. Places which tend to exists at ground level for accessibility reasons, and contain much more people than your average house.

I could find thousands of these.

An airplane falling from the sky is far less likely to hit anyone than a car suddenly accelerating into a store because the driver is flooring the accelerator instead of the brake. These incidents are so common that they have an extensive wikipedia article

You can find some numbers at They claim this happens around 60 times a day.

It could be any structure, but the probability is that it will be a house or other type of housing. There are a lot more residential buildings than commercial.
And you think that having the same amount of air taxies in the air that. SUVs on the street would still make the SUVs look bad?

Again at least with streets I know that an SUV will only crash close to streets with an air taxi it could crash everywhere.

Kindergarden? Yes.

Can we protect a kindergarden from an accidental SUV acceleration? Of course we can. Easy.

> And you think that having the same amount of air taxies in the air that. SUVs on the street would still make the SUVs look bad?

Yes of course, per passenger mile SUVs are far more likely to drive into a building than an air taxi is to fall out of the sky.

> Can we protect a kindergarden from an accidental SUV acceleration? Of course we can. Easy.

But we don’t.

Think of it this way. If an SUV drives into your building you can sue and make some money. But if some really rich person crashes their flying gizmo into your building you can sue and make a lot of money!
So, are you saying that you think that the worst that happens in car crashes is "someone could sue"?

please don't waste our time.

I can't sue if I've been incinerated by an uncontrolled lithium battery fire.
Neither could you sue if you had been struck and killed by an SUV. The end state of your reasoning is that nobody can ever do anything that involves risk because someone might die and be unable to sue. Sounds like an awful world
Emphasis on "killed." I don't want to be struck by an SUV, but one hitting my apartment at ordinary NYC residential street speeds (at least, pre-COVID) is less likely to kill me than a plane crash.

Risk is a community exercise. You don't (or rather, shouldn't) get to externalize disproportionate risks upon the commons because it makes your life easier.

(An example of such a consideration: what happens when the fire department shows up? They know how to deal with a car accident; are they going to have the presence of mind not to douse a vehicle that looks like a normal personal aircraft in water?)

>but one hitting my apartment at ordinary NYC residential street speeds

Why ordinary speeds? Someone driving into a building is likely to be going significantly faster, perhaps because they confused the brake pedal and accelerator.

Things like this happen all the time

You have only that much of momentum from ground in comparison to something already in the air and just falling down.

We currently have a billion cars on the road. Of course we have plenty of accidents.

But that's not a valid comparison.

And perhaps we should also get rid of carsnow your argument is totally invalid

You also don't get to invent risks that don't exist. I hate to break it to you, but small planes fly over your apartment all the time.
With more and more SUVs and truck beimg EVs that doesn't change much. Well, eVTOLs will burn longer, not that it matters because a large SUV will burn long enough to not matter to you.

And I'd bet a lot more on the crash safety of aerospace cerrified batteries than those of the automotive sector.

> And I'd bet a lot more on the crash safety of aerospace cerrified batteries than those of the automotive sector.

Why? Aircraft are optimized for weight far more than automobiles. Making airplane batteries safer than car batteries would make them even less energy dense than they already are. Add to that fact that cars have a crumple zone built into them, while an airplane AFAIK does not -- at least not one that matters when it crashes into my house at 100mph.

Furthermore, some Tesla crashing on the freeway on the way to Tahoe is unlikely to start a forest fire. But what about some rich yahoo making the same trip while flying their personal electric plane who crashes in the Oakland hills?

These problems are non trivial particularly because every personal electric plane company wants to scale into the millions.

Yes it is. A SUV rarly crashes into a building and when it does, it's often possible that humans die.

An airtaxi crashes down from a hight and speed. They will crash into and through your roof or into a street or directly into humans.

Airspace pollution is not a fake concern.

Why would we allow one company to fly over my head and another not?

Either it is so niche that it doesn't add any benefit to our society or it becomes so normal that air space pollution is a real issue.

I'm very very happy when I look into an empty/nearly empty sky.

This is a valid concern.

> Yes it is. A SUV rarly crashes into a building and when it does, it's often possible that humans die.

This is something that happens on a daily basis.

The NHTSA estimates that there are 16000 crashes per year in the US caused by drivers confusing the brake and accelerator pedals. A huge chunk of these do end up with the vehicle inside a building.

> An airtaxi crashes down from a hight and speed. They will crash into and through your roof or into a street or directly into humans.

The odds of a SUV driving into humans is far greater than the odds of a falling airtaxi hitting anyone.

SUVs end up inside stores every single day because of unintended acceleration on parking lots.

> Why would we allow one company to fly over my head and another not?

What does that even mean?

>Either it is so niche that it doesn't add any benefit to our society or it becomes so normal that air space pollution is a real issue.

The “airspace” is very big 3D space that can simultaneously accommodate thousands of flights over a city before congestion becomes an issue.

Now scale that up to a number which actually makes any difference and your SUV argument falls appart.

And yes it's totally valid as well to not allow it at all if only a handful of other people can benefit from it.

We are the people and I don't care if a rich person wants to do that. My airspace is more important than that one rich person.

I always saw cars / roads as the great equaliser in the cities ... I lived in Sydney for a while where there were a couple of traffic snare points that were unavoidable, no matter your position in life. The Sydney Harbour bridge is one that comes to mind. There would be incidents all the time that would briefly close the bridge and you'd have execs in their batmobiles bumper to bumper with sparkies in their ford transits, nowhere to go and nothing to do. There was literally no way short of commandeering a helicopter that would get you over that bridge faster than the next bozo. Unless you wanted to slum it on public transport or a bike.

Re. Australian outback, air taxi already kind of exists in light planes, helis and of course flying doctor.

“There was literally no way…” in a car. But bikes, walking, etc. Bikes are better for cities.

Biking is not slumming it. There are some pretty fancy eBikes out there.

For sure. I cycled my ~16km return route to work almost every day (starting with a killer hill) ... tho must be said cycling in Sydney is not for the faint of heart.

That said, the particular generation of execs I was referring to largely exist in a culture devoid of bicycle commutes :)

> But airspace pollution and a potential small airplane crashing down in a city? No way.

Why is this fine with big planes, but bad with small ones?

It's not. The big plane fly area at a hard area to life in due to all the noise.

But small air taxies would first of fly much lower, always in the city and if it is cheap enough for all of us, you need more than just one.

And if it's not affordable for us, than there is no real reason for us to accept this at all.

And yes the big planes when they travel very high you can not hear them but it's also totally valid to have the discussion about air pollution and sky visual pollution.

But air transport for goods is actually something were we all benefit. Airmail as well.

> a potential small airplane crashing down in a city? No way.

Drones ought to have megaphones that scream DRONE CRASH IMMINENT before impact.

Boy, that would scare the crap out of those Russian T-72 tank drivers just before they die....
> No way.

Wait until you see the motor carriages they claim are going to replace horses one day.

The motor carriage and its consequences have been a disaster for the human race.
We know much more today than when no one knew what a car is.

And honestly we didn't do a good job. After all climate change is real, lead poisoning was real too.

When a motor carriage loses power, it stops. When a helicopter loses power, it kills people.
When a helicopter loses power it glides, safely, to the ground - assuming it's being flown by a qualified pilot.

That is a fantasy that almost never works out in real life. Autorotation is only feasible with enough forward air speed and control authority. Most helicopter crashes happen outside that narrow zone of survivability. Even if an autorotation is semi-pulled off it's likely to be a hard landing that causes significant injuries.
Autorotations are regularly trained (and often taken all the way to touchdown during training). The checkride for private and commercial rotorcraft has a power failure at hover taken all the way to touchdown as part of the standard.

Autorotations are by no means a "gimme", but if every autorotation "likely" caused significant injuries, there wouldn't be enough helicopters or pilots to go around (no pun intended).

Well to be fair those training exercises are probably done in near ideal conditions of altitude, landing zone, forward airspeed, and you know it's coming have studied mentally ahead of time. It's one thing to pull it off during training and another when the engine fails at a random point during a flight in LA/SF/NYC.
Don't you think pilots would tend to try and stay within that "safe autorotation" envelope most of the time while flying? It seems mostly a case of having sufficient altitude and/or speed, similar to what fixed wing pilots try and maintain - a safety margin.
Why would they?

They will probably want to fly across non easy terrain because otherwise you could just use some other means than an expensive helicopter.

Hight perhaps but you will fly across water, woods, power lines, cities.

Watch a helicopter take off sometime. It (almost) never lifts into a hover and climbs straight up. Instead, it lifts slightly off the ground and accelerates forward following the recommended takeoff profile.

That’s so the craft can stay in the “autorotation possible” section of the HV diagram as much as possible.

I’m not at all qualified here, but it sounds like autorotation might not be involved in crashes because when autorotation works, there is no crash :P
> That is a fantasy that almost never works out in real life.

Can you quantify this?

> Most helicopter crashes happen outside that narrow zone of survivability.

AFAIK the majority of helicopter crashes are not caused by a loss of engine power, but autorotation is relevant specifically in that context. It's not relevant to helicopters crashing into hills during storms, or hitting wires with the rotor, or anything like that. We're discussing what happens if the engine stops, not all accident scenarios.

> Even if an autorotation is semi-pulled off it's likely to be a hard landing that causes significant injuries.

Yes, but it's better than being dead.

Autorotation generally works just fine. Most helicopter crashes involve things unrelated to possibility of autorotation or not, and sometimes autorotation won't help when you hit something too hard at the end, with all of it happening because client pushed too hard and overworked the crew (I might be quoting a specific crash here...)
Also I suspect the majority of autorotation failures are from using the helicopter for things only a helicopter can do like hovering.

This is why you rarely see them do that, instead they circle - which any small plane could do but the helicopter can hover if needed. It’s just the most dangerous part.

if a helicopter hovers high in the air it's not dangerous because they have time to turn that height/energy into forward motion. see "dead man's curve"
Yes - at height, they tend to move forwards rather than hovering in one spot to avoid getting stuck in a column of downwards moving air:
Hovering is the signature helicopter move for laymen, but it's also considerably hard, and "high hover takeoff/landing" is, IIRC, one of the hardest maneuvers (it's been years since I've read the pilot's textbook, though)

There's also a lot of other things that can impact the event - for example, the crash I mentioned involved bad weather, tired crew, and losing both engines at once due to icing. They autorotated and nobody died... but they fell into a forest, landed hard enough to destroy undercarriage, and the first officer survived by accident due to helping get passengers into position when a tree smashed his station.

EDIT: corrected captain to first officer, as visible in this photo: (it's Mi-8, so captain sits on the left, not on the right as is normal in western helicopters)

> Autorotation is only feasible with enough forward air speed and control authority.

Control authority yes, but altitude is always a substitute for forward air speed (and is an even better substitute for the eVTOL planes than helicopters).

Most helicopter mishaps start at low altitude.
And you need a place with enough room to land--extremely difficult to find in a city. I really don't like flying single-engine aircraft over large cities.
> Most helicopter crashes happen outside that narrow zone of survivability.

That’s kind of a given, since the successful autorotations do not qualify as crashes.

Wrong. Most helicopter crashes are non-fatal:

2020: 94 accidents, 19 fatal accidents, 35 fatalities, 22% decrease in accidents compared to 2019, 36% decrease in accidents compared to 2013

2019: 121 accidents, 24 fatal accidents, 51 fatalities

2018: 122 accidents, 24 fatal accidents, 55 fatalities

2013: 146 accidents, 30 fatal accidents, 62 fatalities

I guess the question is - can we maintain the standard that is ‘qualified pilot’ as it is today while making it accessible enough for this to scale.

Learning to drive and learning to fly isn’t the same bar today.

And if Lilium think Palo Alto to San Francisco could be $50, they’re gonna need _alot_ of flights to balance their costs.

I think it's safe to assume this class of vehicles (and likely any new class of vehicles from here on out) is not designed to be piloted by a human past its prototype stage.
And it then glides onto what?

Humans? A uneven roof? A busy road?

And for whom? The rich? People who can afford a few hundred dollars for a quick flight from the airport to the city?

How about no?

I don't know about other parts of the world, but in the UK, helicopters are quite carefully controlled so that they can land safely in such an event.

For example, to fly a helicopter over London requires pilots to fly only over well defined routes - although those with multiple engines are allowed more scope.

You can recognize that cars are going nowhere and it's best if we embrace this fact in our own ways (either by being a car owner, or working around car-designed cities the way we prefer), but still note that our cities could have been designed better from scratch that doesn't favor cars. Similarly, avoiding the same mistake now for helicopters wouldn't be inconsistent with living with cars.
The difference is we don't live in the sky. As long as there isn't noise pollution (and electric planes are supposedly a lot quieter), you have to try really hard to create and issue here. Aviation is getting ever more automated and safer.
It’s very energy inefficient to leave the ground.
So is building and maintaining transportation networks of massive proportions on the ground. Somehow that never gets looked at, people just compare the running costs and completely ignore construction and maintenance. Plus the cost of all the deaths it causes, human and non-human. Plus the space it takes up and how it destroys environments. All these are costs.

Planes will not be a solution for all transportation needs, but where it makes sense they're great. A flying bus basically, routes can be very flexibly changed depending on evolving needs.

That's not true.

Public transport is factors more efficient than air travel.

And yes including initial cost.

We build infrastructure to last not to throw it away 5 years later.

You need to understand how much more energy it actually costs to bring a plain up in the air and down again. We talk magnitude more energy than trains.

We can talk about this again in 20 years when solid state batteries are broken through.and sustainable energy sources are the norm.

Air taxi's ate not hard to build on a technical level. We know how to build them.

That seems reasonable, but what is missing (at least in this branch of the debate) is data and counter arguments that will not clearly peter out while the technology matures, if they are even trying to be factual to begin with.

As an example, just on the topic of safety: Why would we assume these machines are relatively dangerous once they reach production? Just because they fly? I know of at least one category of vehicles where on that basis our intuition fails us to this day.

And what happens when they do fail? They are not going to explode randomly or purposefully target the closest building. So what are the chances of all fail-safes failing, and catastrophic outcomes occurring?

Why would we assume whatever this technology eventually enables will be operated by human pilots? I for one would be fairly surprised if that was to happen at any noteworthy scale. Clearly, the interesting part about this prototype is electric flight, not its HID, agreed?

So let's build cool things (electric flight is potentially a cool thing) and then gather actual data about other things it brings (some maybe not so cool), before we "no way" it without any facts on the basis of weak conjecture and personal feelings.

> Why would we assume these machines are relatively dangerous once they reach production? Just because they fly?

I don't have a particularly positive or negative opinion of the technology here, but the one good reason I can see to treat these machines as inherently dangerous is because they take all the kinetic energy of something traveling faster than a car and add the gravitational potential energy of something hundreds of feet off the ground, while not being constrained to a well-defined corridor that you can protect with safety barriers.

When cars meet stationary objects at speed they tend to make a mess. These things are likely to be lighter, but when out of control they'll be going faster, and this thing specifically, when it goes bad, will go bad carrying several hundred kilos of lithium into an uncontrolled energetic event.

If risk is probability times expected outcome, my estimate would be that Lilium comes out worse than driving on both sides of the formula. That's not a reason per se not to do it because, like you say, let's gather data. But the basic physics of the situation is also not something to ignore.

Those aircrafts can be easily fitted with a parachute actually.
I think there are reasons to be a bit more optimistic about the dangers.

A) The reason that cars crash (crash meaning doing damage in the process of failure) is by a large margin not mechanical failure, but human error. While in this case the technology is still infantile and will, even after a couple of years of testing, certainly be more prone to mechanical failure, I see no real reason to assume that it would ever be permitted for actual inner city usage before it beats a certain range/failure-ratio, because that seems trivial to secure and exactly what regulatory bodies are made for.

B) Let's assume there will be no humans piloting these things in an urban transportation scenario, ever, because that does indeed seem incredibly dangerous and silly. I don't think we as a species have the capacity to manually navigate these things in a 3d space filled with them. I don't see any reason we have to. Let's not do that.

C) If you think about it, physics are impossibly bad for car safety. There is no time to decelerate safely and then also no safe space to evade to. In contrast, in the case of flying thingies however, you have space and time working for you: Even if parts of the machine fail, it definitely has at least an order of magnitude more seconds to manoeuvre to relative safety. Of course, catastrophic failure (big fireball in the sky) can possibly still occur (I assume), but you are not working against physics, which is great, because then all you need is outstanding engineering and appropriate fail safes. Engineers will take that over having to beat physics any day.

A and B are solid, sensible suggestions. Inevitably someone stupid (possibly multiple someones, possibly in positions of power) will ignore them. We can leave that to one side.

With C, we're well into "what do the safeties look like" because the assumption that you can manoeuvre at all after something Unexpected And Exciting happens is possibly rash. I don't trust that designs like this one have much unpowered lift or even that much flight control at all in a power-out state. And remember too that the whole point of these things is that they're flying over presumably dense areas. The idea that there will be somewhere safe to manoeuvre to in the seconds you may or may not have is definitely on the optimistic side.

But still, even given all that, a parachute should go a long way to being a workable "emergency stop" equivalent. There are failure states which it doesn't help with (for instance: a birdstrike goes badly enough wrong that a short-circuit starts a lithium fire which, thanks to our parachute, slowly drifts an incendiary path across entire city blocks) but in general I'd expect the benefits to outweigh the risks.

I don't want to say that the world might look different in 20 years (probably even more)

Advances in ai, energy storage etc.

But right now, air taxi is just inherently stupid.

We know how to build those things. There is nothing really you need to invent. you just need to build them.

The problem are things like safety, airspace (who owns it), co2, terrorism, airspace Management...

Let's talk air taxi again when we can fly fully electric, are in the right way for climate change and when air control is no longer handled by humans.

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