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The new wave of electric VTOL aircraft concepts (Joby Aviation, Zee, Lilium, Airbus A$^3$, etc...) has produced some audacious unconventional designs.

Now my question, is how Lilium's concept can be stable and/or maneuverable, given the following configuration:

Lilium's concept

What strikes me is a lack of a surface that creates a force to counteract the momentum generated by the distance between the wing's lift and the gravitational force.

And although control around the yaw axis seems possible with differential thrust, I wonder how the aircraft is controlled around the pitch axis.

From the forward part of the fuselage some canard-like surfaces with integrated propellers are deployed to provide hovering capabilities, however it seems these are supposed to be retracted during forward flight.

Deployed "canard"

Some might suggest the pictures are pure artwork, but Lilium and its investors appear to believe in the concept: First model

10m€ funding from London-based venture capital firm

Ginger
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mezzanaccio
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    Those images represent art, not engineering. – J W Feb 10 '17 at 15:14
  • Must be an anti-gravity system. I don't think the wings would generate any lift with the motors in the way of the airstream. – Ron Beyer Feb 10 '17 at 16:05
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    @JonathanWalters At first glance, that's what I would think too. However, Lilium claims to be developing exactly this aircraft. Someone appears to believe in this: https://medium.com/lilium-aviation/10million-funding-b49addcdfa71#.udrqmr9nv – mezzanaccio Feb 10 '17 at 16:12
  • Well then, I would love to know the expected operating limitations for turbulence and wind gusts. I have trouble imagining such a design could handle conditions such as 20 gusting to 39, orographic turbulence, and low level wind shear very well. A calm-weather-only design? – J W Feb 10 '17 at 16:18
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    Could be body of the aircraft be generating lift? – Notts90 Feb 10 '17 at 16:41
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    I was going to say it can't glide, but then I read it has a whole-airframe parachute, so I stand corrected. – Nick T Feb 10 '17 at 21:51
  • I don't understand the question. – user6035379 Feb 11 '17 at 08:19
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    While I don't think the magnitude would be enough to solve the problem, if all of the weight of the motors and batteries were at the trailing edge of the wing, the CG might be further aft than it intuitively appears. But probably not enough further. It would seem like you could move the wing forward a fair amount while still maintaining good downward visibility, question is if it would be enough visibility for a vertical hover landing, or only an extremely steep descent. – Chris Stratton Feb 12 '17 at 19:53
  • http://www.esa.int/var/esa/storage/images/esa_multimedia/images/2016/05/ducted_fans_on_wings/15974606-2-eng-GB/Ducted_fans_on_wings.jpg – Richard Feb 12 '17 at 20:36
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    I imagine that that beautiful thing will fly like a shuttlecock. – Ismael Miguel Feb 13 '17 at 10:43
  • Some clips of a test flight were published in the media today, if that helps at all. – Robie Basak Apr 20 '17 at 23:13
  • @RobieBasak just as fake as everything else about the thing. Note how the 'retractable forward surfaces' could never retract and leave room for a pilot's legs, or even at all because they together are wider than the room they have to retract into... – jwenting May 29 '17 at 06:15
  • That test flight is clearly a scale model drone and it never retracts its forward "hovering" jets. It looks from the t if it did retract those it would nose down and fall quickly to its destruction. @Notts90 It does look like it might be designed as a lifting body. – TomMcW Sep 06 '17 at 00:12

6 Answers6

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What strikes me is a lack of a surface that creates a force to counteract the moment generated by the distance between the wing's lift and the gravity force.

You are not alone. Believe it or not, Lilium contacted me for advice, and I asked them basically the same thing. They never responded.

I agree with you, this thing will never fly and investors will get burned.

My advice to them would be to sweep the wings forward. This allows to keep the fuselage basically unchanged - you don't want the main spar to go where the pilot sits. But given the small wings this needs substantial sweep.

Update to this answer, February 2020:

Now they have beefed up their canard and skipped retractability, but all they can show is hovering flight for a few minutes at most. Sill no aerodynamic flight. The 300 km range and hour long flight time still are impossible with near-term technology. My verdict stands: Investors will get burned.

KorvinStarmast
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Peter Kämpf
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  • It's surprising that they would get to the full scale model without running wind tunnel tests or even modeling it in X-Plane to determine its characteristics. I'm guessing that this design would only work in VTOL configuration or where the front motors can act as a canard. – Ron Beyer Feb 10 '17 at 17:52
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    Their development page shows several flight tests, but all appear to have a forward ducted fan in the position where the circles are in the picture above:

    http://lilium-aviation.com/development.html

     – SteveS Feb 10 '17 at 18:46
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    "Lilium contacted me for advice..." -- we all knew Peter was good. I don't know that many of us knew he was that good! – FreeMan Feb 10 '17 at 19:44
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    I'd only ask whether those "wings" are indeed wings, or just streamlined mounting pylons for the electric motors. I also wonder why the artwork isn't showing the extension cord, 'cause there's not room for enough batteries for more than a few minutes of flight :-) – jamesqf Feb 10 '17 at 20:29
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    Maybe there's a few tons of batteries in the tail. /eyeroll – Nick T Feb 10 '17 at 21:37
  • @SteveS so it's a multicopter with some things sticking out of it that look like wings to make the occupants feel better. – Nick T Feb 10 '17 at 21:41
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    Their 2:1 scale demonstrator model is definitely flying as a multicopter, there's not enough forward motion. It's not as heavy as the 300kg it should weigh either (as a 2:1 model). I think the only viable strategy for them is to use the investment capital to first build a time machine, which they could then use to steal Graphene engineering technologies and Graphene lithium-ion batteries from the future. – Adrian Thompson Phillips Feb 10 '17 at 22:31
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    @Adrian Thompson Phillips: I don't think even graphene lithium-ion batteries are going to provide enough energy. They need to go sideways into the Star Trek universe and bring back a bunch of dilithium crystals :-) – jamesqf Feb 11 '17 at 05:09
  • "this thing will never fly and investors will get burned": it apparently does fly, according to some short clips of a test flight published in the media today. Looks like it is using downwards pointing fans rather than using the wings for lift. – Robie Basak Apr 20 '17 at 23:12
  • @RobieBasak: Thanks for the link. What you see is something that uses its wings only to place propellers, but not to create lift, as you rightly say. It is flying slowly and the movie even loops back and forth to create the impression of a longer flying time. I do not see a reason to reverse my judgement. – Peter Kämpf Apr 21 '17 at 07:03
  • Here's a better video of their first drone flight – Bergi Apr 21 '17 at 12:19
  • @Bergi: I wouldn't exactly call this flying - hovering yes, but not flying. For now the wings are purely for keeping the inefficient ducted props in place. – Peter Kämpf Apr 22 '17 at 15:03
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    @SteveS I've seen many a kickstarter or similar website designed to lure venture capitalists and other investors with grandiose claims "supported" by videos and pictures that are clearly fakes to anyone with a bit of knowledge about physics or another related science exceeding primary school levels. This appear from the looks of it to be no different. – jwenting May 29 '17 at 06:11
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    @m2as3registeredservicesohmone: They have hovered something that looks quite different to what it looked when I wrote this answer. – Peter Kämpf Feb 24 '20 at 04:30
  • I guess buying an airline is not the only way to become millionaire in aviation business... – Jpe61 Feb 24 '20 at 21:15
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    It just goes to show one of my fundamental rules about aerospace: always beware of the Silicon Valley whiz kid claiming to be able to do what others have struggled to make for decades. – Romeo_4808N Feb 24 '20 at 23:36
  • @PeterKämpf https://lilium-aviation.com/files/redaktion/refresh_feb2021/investors/Lilium_7-Seater_Paper.pdf a detailed performance assessment from Lilium. – slitvinov May 05 '21 at 11:13
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    @slitvinov What is needed is outside company engineers saying it will work, not based on the people asking for the money. If they want a vehicle that uses lift then that needs to be inherent in he design. We already know that blowing air at the ground really hard will get something off the ground. That isn't new technology. My issue with the pop out canard design is there is no place inboard to hide both of those units and then push them out, lock them into place to use them without being really heavy. Where do you put the the lever with nearly no space between the units when they are inboard? – Rowan Hawkins Dec 13 '21 at 03:58
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This looks a lot like many other similar technology projects which are really more designed to generate a fast buck by farming grants and crowdfunding than with any realistic expectation of ever producing a working product.

Given that there is no technical detail apart from concept art and there are no remotely similar designs which do fly the question of how it might fly is purely speculative and there is no meaningful engineering data to comment on.

Chris Johns
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Looks like they've noticed their stability issues and are trying to update the design. Permanent fixed wing forward now and winglets the rear wings.

SMS von der Tann
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oeste
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Unless the body has some significant lifting properties, the nose will sink and the plane will not fly (without the canards extended).

In a no power situation, without a vertical stabilizer and some fore/aft lifting balance, this plane would be a lawn dart.

Michael Teter
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It probably cant. This wing configuration is designed for extreme performance, as in, its extremely unstable. Military planes are often unstable, which makes them turn faster. Civilian planes are supposed to be stable, making them turn slow, comfortable, and safe.

Creating an unsafe air transport that is very uncomfortable and difficult to fly so to create dogfight capability for a civilian craft is either A: Madness, or B: attempt to make it look cool at the cost of everything else. So its a scam for investors.

One possibility is that the top of the engine housing is designed to work as an elevator, but the question once again is "why?".

J.W.
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Consider the third picture: look at the chord of wing and compare it to the attitude of the nose (angle of incidence). It is clear that the nose will point fairly high, with a substantial amount of air hitting the belly of the aircraft, thus moving the centre of pressure forward, possibly close enough to the centre of mass.

There is an angle of incidence that neutralises the rotation around the pitch axis, although this does not result in a stable equilibrium condition. Some active control is required to avoid to flip the plane either downwards of backwards.

DarioP
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    This is a comment (trying to convince myself), not an answer. -1 – Thorsten S. Feb 12 '17 at 19:41
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    There is no way the nose can be very light since it's supposed to seat two people. – mezzanaccio Feb 13 '17 at 08:28
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    The lift, if there is any, could only emerge at high speed. Presumably you can get there from low speed regime without flipping over by pointing the front thrustors downward. But even then, it is going to be unstable. – Hans Feb 26 '20 at 00:11