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I think you're mistaken about a few things.

> Less efficient cruising due to much more drag from all the ducts and engines.

So, I read through some of Boeings research in this area years ago. The array of fans ends up acting like an insanely high bipass ratio turbofan. In the case of hybrid aircraft the combination is more efficient when cruising. The efficiency of a fan producing a given thrust or drag goes up with disk area, as it can spin slower and the local speed mismatch to the airstream is less. The array of fans acts like a giant disaggregated disk in this regard.

> Much less likely to fly with engine failures as they can dramatically affect control (since they are essential parts of the control system).

These are electric motors and batteries. Electric motors are extremely reliable, and in this case we have a high degree of redundancy. This thing is almost certainly more reliable than a single engine helicopter.

> Yaw (rotational) control is highly dependent on working engines on both sides.

The flaps can help with that, it's not solely reliant on differential thrust. There's plenty of precedent for yaw control of flying wings.

> The glide ratio of the aircraft would be very poor with all the drag, even assuming the surfaces were still controllable (not hanging).

You can't evaluate aerodynamics by eyeball, and that goes doubly for active devices like these wings. It's the net circulation pattern around the wing that matters, and you have no actual information about that, just assumptions. Likewise that there's some novel fault problem with a movable flap just because it has fans on it. You realize airliners have huge flaps that deal with much more substantial forces?

On top of being reliable, an array of electric motors in a control loop will be able to compensate for a loss of one or more motors. I imagine this thing could probably fly with a number of it's motors offline.

I'm not sure if all your comments are fair. For example, fly by wire is extremely reliable, and the large number of engines provides huge redundancy and arguably much more safety in certain constrained environments.

If a plane engine fails, you can glide, but you need a nearby road or field. If a helicopter engine fails, you can auto-rotate but have very little margin for error and need forward momentum. There are also more single point failure parts in both helicopters and fixed wing planes.

If you get a partial failure on a Lilium you probably have much more flexibility to do an emergency landing as you have the other engines for control and redundancy.

I'm sure it will take a while to work the kinks out, and sure there are tradeoffs, but I'm not sure this is a jack of all trades master of none situation. I could see the jet carving out its own niche.

And yes, it could be a huge flop, just sharing a counterpoint.

All VTOL aircraft have the same issue: Insane energy consumption. There's a reason why quadcopters have flight times measured in minutes, and why helicopters never came close to displacing small aircraft. This will be no different.

Quadcopters have short flight times because they need to use batteries. Commercial helicopters regularly have 3+ hours of flight time.

(Of course, Lillium's aircraft is battery-powered. But it's not fair to say that an aircraft capable of VTOL will always have a dramatically reduced endurance compared to a non-VTOL aircraft, especially since this one can transition to fixed-wing flight.)

That's the point. Lillium is also battery powered. It will have minutes of runtime in all likelihood.

They're saying 190 mile range and 170 MPH cruise speed. So I guess that's around 60 minutes.

https://en.wikipedia.org/wiki/Lilium_Jet#Specifications

More than that because FAA mandates at least a half hour of reserve fuel.

No, quadcopters have short flight times because they choose to generate thrust using multiple fast and small propellers instead of a larger and slower one. Quadcopters will always lose to a single rotor of the same overall diameter.

Multiple rotors do decrease efficiency and this flight time somewhat, but nowhere near as much as switching from fuel to batteries. The mass energy density of batteries is less than 0.1x fuel. There are some gas-powered quadcopters out there which much longer fight times than the electric ones. Compare an electric CP RC heli to nitro and nitro has much longer fight time. Of course, a combustion engine is usually heavier than electric motors too, so there are diminishing returns from switching to fuel as your fuel or battery to engine mass ratio decreases. But, the main consideration in this regard for flying things is almost always: fossil fuel is way, way more energy dense than batteries in a mass sense. See e.g https://www.batterypowertips.com/comparing-ev-battery-and-fu...

It is, it falls out of the physics of VTOL vs. fixed wing flight. It's so extreme that cargo helicopters have to fly forwards to take off at MTOW, because it dramatically lowers the power required to get the aircraft off the ground relative to taking off vertically. You can minimise the impact in the mission requirements, but there's a reason hover and VTOL are typically specialist requirements. They tend to be very costly in terms of endurance.

To put some numbers on this, down in the large quadcopter/fixed-wing size of aircraft, you can expect about 200W/kg of power required for the quadrotor/VTOL phase and more like 20W/kg once you’re in fixed-wing mode, assuming you have wings and speeds that provide a reasonable L/D ratio. Literally a factor of 10 (or more, if your fixed-wing design is more like a glider.)

I commented elsewhere here on the video of a test flight. In that video they achieved that the aircraft flew like a normal plane with lift provided by its wings.

This mode of flight is said to be ten times more efficient than the helicopter mode during VTOL. That is: for each minute that they can cut from flying like a helicopter during starts and landing, they gain ten minutes of normal flight time.

I think the energy argument does not apply that much more than for other small electric aircraft.

The key difference is that VTOL / hovering with its associated energy consumption will only be required for start and landing.

Fly by wire sucks because you don’t get feedback from the control surfaces. Are you even a pilot or just an avgeek?

For what purpose?

Enthusiasts and race car drivers like lots of feedback through the control surfaces of their cars.

Most people don’t care, lack the skill to interpret that feedback anyway, and rely on driving well within the car’s limits and/or electronic safety nets to save them when they get it wrong.

Who do you think represents the closest analogue to the majority of Lilium aircraft operators in the long term?

Boeing engineer from Everett has just logged in :) Seriously though, Airbus has had FBW for decades and there’s an entire subset of the population of commercial pilots that rave about it.

Any thoughts on the ParaWing idea that is based on the lift / stall advantages of the humpback whale fin tubercles?

https://thelacesout.com/for-christmas-2016-i-give-the-world-...

Yes I’m a private pilot and I enjoy aerobatic planes with lots of direct feel. This is a robotic air taxi - what is the relevance of tactile feedback?

And your premise is more broadly incorrect. The f16, which was developed to dogfight, has had fly by wire for decades. The fly by wire allowed far greater control.

https://www.f-16.net/articles_article13.html

Yeah every pilot I know loves fly by wire and once the auto industry gets it right more people will get to enjoy it.

You repeatedly mention engines, but I'd point out there are no engines on this craft. This craft has electric motors.

I don't know if electric motors are more reliable than ICE, but I speculate that they are.

------ Edit, my opinion below:

VTOL is a HUGE WIN. It's the holy grail of flight. Fixed wing aircraft are inconvenient because they need a mile of flat blacktop for takeoff and landing.

Affordable eVTOL craft could change general aviation forever. The problem with helicopters is insane maintenance overhead and low fuel efficiency. The problem with fixed wing is you can't land it in your back yard. EVTOL is interesting in that it could bridge the gap between these two to provide a personal aircraft that has the best of both. Napkin math shows it's possible, and we're seeing some really cool products now.

For most people, "motor" and "engine" are synonyms. Is there a technical difference between the two terms?

There are people who feel strongly that one is only for electric, on non-electric, or combustion, or thermodynamic, or other classes of thing, kind of like a boat-vs-ship distinction. It is certainly more common to talk about an electric motor than an electric engine, for example.

That said, both terms have been used for a very long time for a very wide range of overlapping things. MIT has a nice history[0] of the words and why they are essentially synonyms in most cases (with engine being more appropriate to use in non-mechanical contexts like search engines and economic engines and motor being more appropriate to use as a gerund like motoring through something or motoring around the countryside).

[0] https://engineering.mit.edu/engage/ask-an-engineer/whats-the...

I thought the term was originally "motor engine" (a piece of engineering that produces motion) in the same way we can have a "compute engine" or a "siege engine" or a similar name for any other _ingenious_ creation.

From there we tend to shorten it to either motor or engine. Perhaps in current times people here the terms "combustion engine" and "electric motor" most commonly and assume there is an implied distinction.

The VTOL only matters if it’s cheap. Most of the airports in the US are lightly used because general aviation is expensive, not because people are thinking “I would buy/charter a plane, but driving 20min to the local airfield is just not convenient enough”.

Typical general aviation aircraft (which this seems comparable to) need <1/4 mile runway (e.g. a Cessna 172 is less than 1000ft) which in the US means ~20k available airports.

My point being, the reason those airports are lightly used is driven by cost not that they inconvenient.

In any decent sized metro area inconvenience is a big deal.

My family had a weekend at a popular vacation spot about 80 miles from where we live (about 2 miles from the downtown area of Melbourne, Australia).

The drive takes roughly two hours door to door.

We’re in a suburb that happens to be on the right side of the city to be close to the GA airport, but it would be a 20 minute drive to the airport, say a 30-minute flight, and another 20 minute drive from the destination airport to our accommodation. If you could do the transitions between car-plane-car in less than 20 minutes total I’d be very surprised; net result, you’re saving maybe 30 minutes on the trip.

If you could put VTOL ports within 10 minutes walk of each destination (say 500 metres) you could cut the trip down to less than an hour.

To be fair, the amount of luggage you’d have to carry/push in this scenario might well still tip the balance in favour of the car for the holiday trip, but there are plenty of other scenarios where similar trips are made without the need to carry a mass of luggage where the VTOL is a massive win.

Fair points, but it think my point is this

Cost to drive (.50/mile) = $40x2 (round trip)= $80 @4hrs

General aviation 20min+45min (Cessna 172) + 20min= 1hr 25min x2 is 2hr 50 min (let’s call it 3hr) 1.5 hrs flying time @$300hr (let’s exclude cost of ground transport) means $450. So $270 to save an hour

If vtol saves another 2.5hrs for $270 and has the same cost profile, Than that’s great, you’re still spending >$100hr on time savings (and this optimistic, because I think most uses cases have lower ratio of airport travel time to flight time, you would then need to value your time at >$285k a year (pre tax @30% and 2000 hrs a year), which is not that huge a group of people

Yep, agreed - though I suspect it's a rather larger group than those who currently charter helicopters for transport.

I would trust motors over an engine any day. Look at the contraption that is an ICE: You have fuel-, oil-, and air-delivery systems... you have ignition systems... you have mechanical parts violently changing directions thousands of times per minute...

A motor is metal spinning in a magnetic field, powered by chemical reactions in a battery.

Which seems more likely to fail?

I agree with your assessment but also think with the size of this plane it is a good candidate for the parachute system some planes already have. Maybe making that a requirement is a good middle ground.

As for the engine failures, it's a lot safer because it has so many of them. It can fly with engine out, probably counterbalanced with another engine being switched off on the other side.