Lilium - Point to point small air transport reinvigorated?

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Well-Known Member
besides being electric/sexy/trendy I don't see what the benefit of this is over something like a robinson R44.. which is proven, carries 4 people and has basically the same specs of speed and range that this is aiming for. a new robinson is like $400k right?? I would highly doubt if one of these is made for less. I doubt it'll be significantly cheaper too. The difference is in the running cost. A helicopter is a mechanical geek's wet dream, but an accountants nightmare; so much mechanical stuff that moves that it's going to eat up complex expensive parts all the time and maintenance is measured in US$ cubed.

Electric has the potential to reduce this enormously.

I've talked to several owners of electric sailplanes. Most owned 2-stroke self-launchers before and happily paid more for an electric system. Dependent on who you ask, reliability (MTBF) is increased 10 to 100+ fold while running cost are decreased by about the same amount.

As long as battery lifetime (not 1000 but 10^6 charge cycles) can be reasonably solved, I don't see why you can't operate something like the Lilium far below the cost of running a normal car, assuming normal GA price levels for components etc.

Himat

Well-Known Member
Indeed, you are right on many points there. However, there is a large difference between a helicopter with large rotary wings and a strong tail rotor to align it's fuselage as it pleases - and this Lilium project. Helicopters have control over the wind because the airflow of the blades is stronger than the wind. In other words, a helicopter can overcome wind by pure motoric force. What do you think, would the same be possible with these tiny little fans? Could they ever compensate the force of the wind acting on the wing&canard in a strong windgust or a crosswind? Just multiply the disc area of one canard or wing (left or right) and simple physics might show that this aircraft would be tossed around like a plastic toy in a hurricane.
A little rhetorical, do “crosswind” even exists in the airplanes reference frame?
The question about stability in gusty wind, where a change in wind direction and the planes inertia make the plane heading not point into the oncoming air is valid. But is not this only a question about directional stability? If the airplane is made directional stable without a fin, the fin is superfluous. It look like it could be done, still I would not be surprised if a fin is added later on to get more directional stability in cruise mode.

Hovering a fin only would add to the side area that the gust could grab. Less side area should make the impact of a gust less, as the inertia to side area ratio then get larger.

DangerZone

Well-Known Member
HBA Supporter
A little rhetorical, do “crosswind” even exists in the airplanes reference frame?
The question about stability in gusty wind, where a change in wind direction and the planes inertia make the plane heading not point into the oncoming air is valid. But is not this only a question about directional stability? If the airplane is made directional stable without a fin, the fin is superfluous. It look like it could be done, still I would not be surprised if a fin is added later on to get more directional stability in cruise mode.

Hovering a fin only would add to the side area that the gust could grab. Less side area should make the impact of a gust less, as the inertia to side area ratio then get larger.
There's so much more than directional stability in question.

Actually, winds mean a bit more than people expect. Specially with a ducted fan design like the one designed by Lilium. Ducted fans rely on laminar flow into the duct, while a helicopter or propeller blade easily works in turbulent air. In other words, IF the wind creates turbulence and makes the pressure drop at the duct entry, there will be no laminar flow into the duct to feed the fan some air. Turbulence often prevents air from entering the duct like a crowd prevents easy entrance through a narrow gate if they all push forward at the same time. Or you could try breathing in low pressure at 9km high to get the idea what I'm writing about - without air flow most suffocate pretty quickly. Simple physics apply to airplanes and ducted fans too, so these pretty expensive drones would fall from the skies and drop like flies in moderate wind gusts or turbulence.

So, either the guys at Lilium are missing some Learnium (some people never learn and repeat the same mistakes over and over again) or they know about it all yet keep sucking on EU funds.

Well-Known Member
Sure dude. This is why ducted tail rotors lead to instant obliteration...

gtae07

Well-Known Member
Third, how many of these guys are pilots? I bet 99% of them are neither pilots nor airspace engineers.
So? I work at a company that makes "real" airplanes. I'd bet that maybe 1-2% of the people working there are pilots (not counting the people we employ as test pilots etc., I'm talking about the engineers/mechanics/HR/management/marketing/etc.). The same is probably true at most aircraft companies--heck, I'd bet that even most of the employees at Van's aren't pilots. And most non-pilots at these companies have no interest in it either--I know Toobuilder has related before that even when flying and instruction was dirt cheap at the company/base flying club, they had few takers.
And who cares what kind of engineering was listed on their diplomas? Our chief structures guy was a civil engineering major. Most of the guys in my department (systems) were mechanical or electrical majors. Your specialty gives you a leg up, but any competent engineer can probably slot into almost any other engineering role given time to learn the job. That's the real purpose of an engineering education, IMO--to teach you how to solve unknown problems by finding the material and figuring it out, from first principles if need be, not to focus you on one specific type of problem.

Fifth, such an aircraft would have no stability in high winds or if power goes out. Who would fly in such a safety neglecting aircraft?
Why does everyone keep assuming this won't be stable in high winds because it doesn't have a given aerodynamic control surface? It vectors its thrust to achieve the same result. You have fans running almost all the way down the length of the wing so that gives you plenty of yaw control.

Dependence on electricity for stability isn't a new thing. Look at fly-by-wire aircraft and helicopters. Some have really rudimentary means of manual control (e.g. I think the A320 family provides some means of rudder and elevator control) but many of them are completely dependent on some level of electric power to retain control. So they have multiple levels of redundancy--multiple generators, batteries, standby wind-driven turbines, etc.--to ensure they retain power. And when you look at aircraft like the F-16, F-22, F-35, Rafale, etc. if they lose all power for the flight controls, they go unstable very very quickly.

besides being electric/sexy/trendy I don't see what the benefit of this is over something like a robinson R44.. which is proven, carries 4 people and has basically the same specs of speed and range that this is aiming for. a new robinson is like \$400k right?? I would highly doubt if one of these is made for less.
As autoreply mentioned, it's operational cost. Something like this may well have fewer moving parts in the whole power and flight control system than that R-44 does on its tail rotor.
And if they're able to make it so that you don't need to be a pilot to operate it (get in, hit "go here", and sit back for the ride), and if a reasonable means of accommodating them in the airspace system can be found, you have a potential for massive sales and economy of scale. Imagine something like a Tesla factory churning these things out (though how you would actually do this in practice, with the massive legally-mandated paperwork burden that accompanies certified aircraft production, I have no idea).

also the test unit was missing some of it's core components listed on the web page... canard, winglets, retractable landing gear and pilots... this adds a LOT of weight and significantly changes the dynamics. given the efficient cruise mode claims they seemed to ditch that aspect to get it in the air with a 2x3 arrangement of the ducted fans instead of straight 6 along the canard as depicted...
Again... so? This is a proof-of-concept demonstrator. A true prototype, not a production test vehicle. A loose comparison would be the X-35B compared to the F-35B--the former had no mission systems, could carry no payload, and was a fair bit different in many respects from the aircraft that's in service. But that wasn't its job. Its purpose was to demonstrate the feasibility of the shaft-driven lift fan concept, which it did.

Or, it's like the XV-15, which had no payload capability, limited range, and no actual usefulness beyond demonstrating the feasibility of a tiltrotor.

This prototype is intended to prove out the arrangement of the fans, the power and control algorithms, and the mechanism of transition to and from hover. This is the hard part. To do so it doesn't need to carry people or indeed be full-scale at all--that would simply be a waste of time, money, and materials at this point. It need not have the full range of the intended production vehicle, only enough to fly the test program. Assuming things work more or less as intended, they will take the lessons they've learned from this prototype and build one much closer to an intended final production vehicle.

A lot of the work at this stage is validating the models they're using for development (which is also part of why flight testing of large civilian and military aircraft takes so long these days--they do a lot of flying gathering data to fine-tune their CFD, FEA, and performance models). If they can show their CFD and control models work on a smaller cheaper prototype, then they can be reasonably confident that they'll work on a larger, more expensive version.

DangerZone

Well-Known Member
HBA Supporter
Sure dude. This is why ducted tail rotors lead to instant obliteration...
Hopefully you do realize these tail rotors are shrouded props, not ducted fans?

DangerZone

Well-Known Member
HBA Supporter
So? I work at a company that makes "real" airplanes. I'd bet that maybe 1-2% of the people working there are pilots (not counting the people we employ as test pilots etc., I'm talking about the engineers/mechanics/HR/management/marketing/etc.). The same is probably true at most aircraft companies--heck, I'd bet that even most of the employees at Van's aren't pilots. And most non-pilots at these companies have no interest in it either--I know Toobuilder has related before that even when flying and instruction was dirt cheap at the company/base flying club, they had few takers.
This comes as a surprise non-engineers and non-pilots could successfully perform engineering jobs at Van's and most aircraft companies. I had the impression that people working on research, development and design needed some formal education to know what they are doing. Sure, assembly might hire uneducated workers (and marketing might use economists) but I was convinced most of the people working in engineering and design would need aviation specific competences. Besides Van's, which other companies hire non-engineers and non-pilots for aircraft design?

And who cares what kind of engineering was listed on their diplomas? Our chief structures guy was a civil engineering major. Most of the guys in my department (systems) were mechanical or electrical majors. Your specialty gives you a leg up, but any competent engineer can probably slot into almost any other engineering role given time to learn the job. That's the real purpose of an engineering education, IMO--to teach you how to solve unknown problems by finding the material and figuring it out, from first principles if need be, not to focus you on one specific type of problem.
True, agreed. As long as someone is competent to do the job, let them do it.

Why does everyone keep assuming this won't be stable in high winds because it doesn't have a given aerodynamic control surface? It vectors its thrust to achieve the same result. You have fans running almost all the way down the length of the wing so that gives you plenty of yaw control.
Because of physics?

Fans require airflow, laminar airflow into the duct. If a ducted fan can't provide lift and direction/thrust, magic ain't gonna help much. Only some other aerodynamic surfaces could. Like wings, winglets, elevators, rudders, parachutes, props and the likes. Without these, any aircraft is stalled. And we all know how that ends up - with gravity problems.

Dependence on electricity for stability isn't a new thing. Look at fly-by-wire aircraft and helicopters. Some have really rudimentary means of manual control (e.g. I think the A320 family provides some means of rudder and elevator control) but many of them are completely dependent on some level of electric power to retain control. So they have multiple levels of redundancy--multiple generators, batteries, standby wind-driven turbines, etc.--to ensure they retain power. And when you look at aircraft like the F-16, F-22, F-35, Rafale, etc. if they lose all power for the flight controls, they go unstable very very quickly.
It seems we missed each other by a mile. I am all pro-electricty for stability control. It works, it works great. Yet a couple of small electric ducted fans work horribly worse than one large ducted fan or a shrouded prop. Such small fans would not be redundancy, that would be poor engineering, lousy efficiency, running of five to 30 minutes max before battery cells run dead dry. Using batteries to the max equals fifty cycles (charging-discharging) tops. Discharge the batteries down to 50% and you might get 500 to 1000 cycles depending on the cell technology. Discharge down to only 70% of capacity and you'd get up to 2000 cycles before the battery capacity drops bellow upper top useful specs. A well designed aircraft of such size would use shrouded props for better efficiency and safety, not toy ducted fans. There is a reason why many electric motor producers write 'NOT FOR AIRCRAFT USE' on their products, because some incompetent schmuck might come to the idea to transport humans in such a thing. Sure, it could work if one knows what he is doing. But if you are right and only 1% to 2% of people working on airplane development & design are neither engineers not pilots - safety would be a problem. No matter how many toy gadgets they'd install.

gtae07

Well-Known Member
This comes as a surprise non-engineers and non-pilots could successfully perform engineering jobs at Van's and most aircraft companies. I had the impression that people working on research, development and design needed some formal education to know what they are doing. Sure, assembly might hire uneducated workers (and marketing might use economists) but I was convinced most of the people working in engineering and design would need aviation specific competences. Besides Van's, which other companies hire non-engineers and non-pilots for aircraft design?
...

But if you are right and only 1% to 2% of people working on airplane development & design are neither engineers not pilots - safety would be a problem.
Nowhere did I say that Van's or anyone else hired non-engineers to do design work. I said that the vast majority of all of the employees--engineers and everyone else--were not pilots. Big difference.

Occasionally you do see people without formal engineering educations working in certain engineering roles, but typically those people have extensive experience as mechanics or electricians and have worked their way up from the floor by demonstrating exceptional skill and ability. And for some roles you much prefer those people over some kid out of school with an engineering degree and no practical sense. And there are still roles equivalent to draftsmen where you're basically a CAD driver. But the overwhelming part of the design, calculation, and certification (and flight test analysis) is being done by people with formal engineering educations.

Because of physics?

Fans require airflow, laminar airflow into the duct. If a ducted fan can't provide lift and direction/thrust, magic ain't gonna help much. Only some other aerodynamic surfaces could. Like wings, winglets, elevators, rudders, parachutes, props and the likes. Without these, any aircraft is stalled. And we all know how that ends up - with gravity problems.

It seems we missed each other by a mile. I am all pro-electricty for stability control. It works, it works great. Yet a couple of small electric ducted fans work horribly worse than one large ducted fan or a shrouded prop. Such small fans would not be redundancy, that would be poor engineering, lousy efficiency, running of five to 30 minutes max before battery cells run dead dry. Using batteries to the max equals fifty cycles (charging-discharging) tops. Discharge the batteries down to 50% and you might get 500 to 1000 cycles depending on the cell technology. Discharge down to only 70% of capacity and you'd get up to 2000 cycles before the battery capacity drops bellow upper top useful specs. A well designed aircraft of such size would use shrouded props for better efficiency and safety, not toy ducted fans.
These aren't the only people looking at distributed propulsion with smaller ducted fans. Yes, there may be scaling issues. But maybe it's also possible they have something that works--and seeing as they're actually flying some hardware, something is working. They're doing a lot more than any of us sitting around here grousing on the interwebs.

There is a reason why many electric motor producers write 'NOT FOR AIRCRAFT USE' on their products, because some incompetent schmuck might come to the idea to transport humans in such a thing.
They put it there because someone might try to put it on a certified airplane and then someone's lawyer will come after them for selling airplane parts without a PMA or TSO. Not to mention the absurd liability problems.
The Facet cube pumps Van's recommends for boost pump usage, and which Spruce carries, also say "not for aircraft use" on them. People use them anyway.

BBerson

Light Plane Philosopher
HBA Supporter
I doubt they have any engineers with VTOL experience that understand the power density needed for tiny high disc loaded propulsion.

Jay Kempf

Curmudgeon in Training (CIT)
I am not sure why people are questioning the engineering talent on this team. There is actually quite a bit of press on this effort. They have quite a few ringers. That doesn't necessarily make a successful project but it doesn't hurt. High disc loading is a compromise to get redundancy while sacrificing most likely endurance. But the tilt wing aspect buys some of that back depending on how the mission profile is put together. I am curious to see if this thing gets to real trials and evolves as a design to have a reasonably low drag cruise. The Joby craft is moving along the same trajectory.

pictsidhe

Well-Known Member
The difficulties I see with Lilium:
Regulatory, loads of these flying around cities?
Range, getting a good L/D is going to be challenging with all those dinky DFs.
Cost, they are going to need a lot of high energy density batteries. Those just aren't particularly cheap, and won't be without new chemistry. Life is part of that.

BBerson

Light Plane Philosopher
HBA Supporter
I asked Joby about the thrust to weight ratio of his propulsor systems. He didn't have an answer.

Jay Kempf

Curmudgeon in Training (CIT)
I agree with the regulatory stuff. Just because they can build something they can test doesn't mean it is viable. Steep hill to climb there with any multirotor concept. But they are getting more prevalent.

L/D vs. range: Not sure whether this is clear or not to most. I see this as designing aero wings that work and being able to run the cruise power down low enough to save watts per mile. This project and Joby are optimizing around the same mission, short distance point to point, no runway transport of 1 or 2 humans. I actually really have hope for this mission. It's a start in the right direction. endurance can be expanded later. If this can work, it would be quite an accomplishment on it's own. A whole new category of aero craft.

Batteries are a problem for all electric craft. Nothing specific to this project there. Don't put this in with airplanes when doing comparisons. This is a hybrid mission, VTOL, tilt wing. And it hasn't even gotten through final design yet. That happens after testing a mock up. This thing get's lumped in with things like the Osprey and multi-copters.

cheapracer

Well-Known Member
Log Member
So what if it's a model?
Issue to me is nobody here, in other media outlets, or their Youtube video, is clear as to what it is.

A lot less bollshot on themselves, manhugz with feelgood music and a little more detail of what's going on technically would be of great benefit to most.

They're doing a lot more than any of us sitting around here grousing on the interwebs.
It's 11PM right now on a Saturday night and I am detailing my aileron linkage in 3D, I might get to bed before 3. I'll be at the factory before 10 am in the morning. Sunday morning.

I'm also sure a number of other members I could name have at least their minds on their work and or projects as well, if they are not actually hands on as we speak.

You need to stop apologizing for this group, their presentation/information is poor, it's they by themselves who have created the confusion and doubt, not "Us".

Well-Known Member
Issue to me is nobody here, in other media outlets, or their Youtube video, is clear as to what it is.

A lot less bollshot on themselves, manhugz with feelgood music and a little more detail of what's going on technically would be of great benefit to most.
But not to them. They have their funding. Only thing they need is more good engineers and a good image for future lobbying.

You or we are simply not the target audience.

pictsidhe

Well-Known Member
If they want engineers, they aren't doing a great job of attracting them. Looks more like a funding drive.

Himat

Well-Known Member
There's so much more than directional stability in question.

Actually, winds mean a bit more than people expect. Specially with a ducted fan design like the one designed by Lilium. Ducted fans rely on laminar flow into the duct, while a helicopter or propeller blade easily works in turbulent air. In other words, IF the wind creates turbulence and makes the pressure drop at the duct entry, there will be no laminar flow into the duct to feed the fan some air. Turbulence often prevents air from entering the duct like a crowd prevents easy entrance through a narrow gate if they all push forward at the same time. Or you could try breathing in low pressure at 9km high to get the idea what I'm writing about - without air flow most suffocate pretty quickly. Simple physics apply to airplanes and ducted fans too, so these pretty expensive drones would fall from the skies and drop like flies in moderate wind gusts or turbulence.

So, either the guys at Lilium are missing some Learnium (some people never learn and repeat the same mistakes over and over again) or they know about it all yet keep sucking on EU funds.
Ducted fans experience better performance and efficiency if the inlet flow is unobstructed and laminar. Still, they work reasonable without.

Just have a look at one of the early radio control model ducted fan installations. Especially the Byron F-16 comes to mind. Engine in pusher mode in front of fan, tuned pipe extending forward of fan into intake duct, fan deep in the fuselage, one small forward air inlet and the front wheel forward of the main air inlet, a “cheater” hole.

The Lilum ducted fan inlets look overly refined compared that old RC plane ducted fan inlet. Have a look at a Byron F-16 at RcGroups: https://www.rcgroups.com/forums/showthread.php?971166-Bryon-f16-e-dynamax-the-dynabyro-fan#post11177199

There is the main undercarriage in front of the fan too.

Himat

Well-Known Member
I am not sure why people are questioning the engineering talent on this team. There is actually quite a bit of press on this effort. They have quite a few ringers. That doesn't necessarily make a successful project but it doesn't hurt. High disc loading is a compromise to get redundancy while sacrificing most likely endurance. But the tilt wing aspect buys some of that back depending on how the mission profile is put together. I am curious to see if this thing gets to real trials and evolves as a design to have a reasonably low drag cruise. The Joby craft is moving along the same trajectory.
What is available is another possible reason for the selected ducted fan size. Selecting the largest commercial available electric ducted fan intended for model aircraft can speed up development of the vehicle while cutting cost. Then, as the vehicle is developed better propulsion units may be available. That is without the vehicle developer spending any money or time. Not so if they have to develop their own lift units.

If the performance differences between smaller or larger fans are a draw depending on the criteria, availability and cost often is the deciding factors. I must confess that I have designed some part bin specials in my day time job.:gig: