German start-up Lilium has completed the first phase of testing with its electric-powered Lilium Jet, which includes the crucial transition from vertical to horizontal flight.
Munich-based Lilium says that in the six months since the aircraft's maiden sortie on 4 May it has performed increasingly complex and aggressive manoeuvres and safety tests such as engine and flap failures.
So far it has flown with only three of its 36 engines out, although trials involving a "complete system failure" will eventually be required.
And while speeds have so far been modest – hitting just over 54kt (100km/h) – the developer points out that the initial phase of trials have enabled validation of its flight modelling.
"We are very impressed with how it performed compared with our predictions."
In addition, Lilium says that a second phase of flight testing which is to commence shortly, will see it "pushing through to high-speed manoeuvres".
Lilium claims the jet will be able to cover a journey of 161nm (300km) in 1h on a single battery charge.
Second-phase evaluations will run for about a year and will involve solely unmanned flights. While Lilium has been able to complete initial test flights within the confines of its Oberpfaffenhofen airfield home, the distances soon required will see the Lilium Jet flying in national airspace.
This will require special permission from Germany's safety regulator; Lilium says conversations have already begun and it has been “encouraged” by the level of engagement.
A second, manned prototype will also be used for certification flights.
The five-seat Lilium Jet is powered by 36 electrically driven fans distributed across two sets of wings.
Service entry, initially as a manned aircraft, is planned for 2025, with the jet designed for inter-city and short regional flights.
Lilium has also completed construction of its initial 3,000sq m (32,200sq ft) final assembly plant at its Oberpfaffenhofen headquarters.
This will be complemented by a second facility at the same site which is currently being built.
The two plants will be able to support production of hundreds of aircraft per year, the company says.
Those high output levels will require the "scale of automotive [manufacturing] but with the quality of aerospace", says Lilium, which hopes to benefit from southern Germany's long experience with car making.
Lilium intends to produce significant parts of the aircraft in house, including the engines and battery packs. It will also operate the Lilium Jets, making it a combination of "OEM and airline".
Although the company acknowledges the complexity of that model – which will be further complicated by it designing the ground infrastructure for the aircraft – "that doesn't mean it can’t be done.
"We believe the returns are good enough to make it a viable business model."
Reports on the TechCrunch website suggest that Lilium is looking to raise a further $400-500 million in a third fund-raising round to help bring the jet to market.
However, the company declines to comment on its future financing requirements.