When business aviation was a baby there were lots of early private jet contenders, and a properly diverse bunch they were. The JetStar with four engines at the back, the VFW614 with engines over the wings, the sleek Learjet, not to mention the 125, Sabre and Mystere. All of these were simple fodder for aircraft spotters, who could identify them easily from a mile off, but not all achieved long-lasting commercial success. Now, as the wind-tunnels and supercomputers have pushed every manufacturer in the direction of the optimal design, the latest aircraft are less easily distinguished.

That's part of the reason why truly innovative designs are rare, and turn heads. Designs like the Lilium Jet, with its rows of electric fans along two fixed wings.

But with innovation comes risk, and with new technology comes a heightened burden of proof in terms of safety, regulation and certification. Investors must take realistic views of the amount of money needed to jump through every hoop and start earning.

Lilium filed for insolvency in October, and has been working with a potential saviour ever since. Now it says that, while talks about alternative solutions are still ongoing, the chance for restructuring is highly unlikely and therefore operations will be stopped.

This is not end of the electric VTOL. There are many other models mooted, in testing, and even heading for certification. I'm sure they will bring considerable diversity to future fleets - but I can't help thinking that the Lilium Jet would be a sad loss.