# How can this aircraft be stable/manoeuvrable?

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 manoeuvrable, given the following configuration:

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.

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.

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

10m€ funding from London-based venture capital firm

• Those images represent art, not engineering. – J Walters Feb 10 '17 at 15:14
• @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: medium.com/lilium-aviation/… – mezzanaccio Feb 10 '17 at 16:12
• Could be body of the aircraft be generating lift? – Notts90 Feb 10 '17 at 16:41
• 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
• 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

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.

• 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: lilium-aviation.com/development.html – SteveS Feb 10 '17 at 18:46
• "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
• 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
• Maybe there's a few tons of batteries in the tail. /eyeroll – Nick T Feb 10 '17 at 21:37
• 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

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.

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.

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.

• What wonderful progress. What will they think of next, a vertical tail? – Koyovis May 28 '17 at 15:10

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?".

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.

• This is a comment (trying to convince myself), not an answer. -1 – Thorsten S. Feb 12 '17 at 19:41
• There is no way the nose can be very light since it's supposed to seat two people. – mezzanaccio Feb 13 '17 at 8:28