As winter sets in at its headquarters near Munich, Germany, Lilium is preparing to relocate its “Phoenix 2” eVTOL technology demonstrator to Spain for continued flight testing.
Lilium co-founder and CEO Daniel Wiegand told eVTOL.com that demonstrator has performed around 25 flights since its test campaign launched this summer at Lilium’s facilities at the Oberpfaffenhofen Airport.
Phoenix 2 is the updated version of the demonstrator that was destroyed in a fire during ground maintenance activities in February 2020. Nominally a five-seat, 2,865-pound (1,300-kilogram) aircraft, the uncrewed demonstrator incorporates lessons learned from the first Phoenix’s flight test campaign and untimely demise.
“It’s flying very nice,” Wiegand said during an interview at Lilium’s headquarters. “It’s much more reliable than the predecessor. The build quality is excellent. We’ve had no incidents, nothing in that whole test campaign, from the ground test up until now.”
Lilium’s first full-scale demonstrator completed an initial phase of low-speed flight testing up to around 62 miles per hour (100 kilometers per hour) before it was destroyed. In a Nov. 15 letter to shareholders, Lilium reported that Phoenix 2 has fully explored the GPS position controlled hover envelope at 12 mph (19 km/h) and conducted airspeed envelope expansion up to 46 mph (74 km/h) with full maneuverability.
However, the company has yet to demonstrate full transitions between hovering and wingborne flight, which will be a critical milestone for the program due to the aerodynamic challenges associated with that phase of flight. Wiegand said that full transitions are impractical to accomplish at Oberpfaffenhofen, where the demonstrator is restricted to flying over the airport.
“That’s what we want to do in Spain, and what we cannot do here, because . . . 50 to 60 knots is the limitation of what we can test here on this airport,” he said. “So we’re going to pack the airplane and go to a test site where there’s a big free space without houses . . . where we can also fly potentially beyond visual line of sight.”
Compared to Munich, Spain’s sunnier climate should also be much more conducive to winter flight testing, he added.
Wiegand said that Lilium is evaluating two possible test sites in Spain and expects to confirm the final location within the next six weeks. Lilium anticipates receiving a permit to fly in Spain in early to mid-2022.
Results from the Phoenix 2 flight test campaign will inform the development of the much larger seven-seat Lilium Jet, which is the aircraft that Lilium plans to certify for passenger-carrying operations by 2024.
With a wingspan of around 45 feet (14 meters) and a length of 28 feet (8.5 m), the fully electric seven-seat Lilium Jet is around twice the size of the Phoenix 2, although it shares the same basic architecture of 36 ducted fans distributed across a main wing and forward canard.
Wiegand said the seven-seat model and smaller demonstrator have roughly the same disc loading, a driver of power consumption in the hover. The Lilium Jet’s high disc loading compared to competing eVTOL designs has led some skeptics to question whether the aircraft will be able to achieve its stated performance targets, which are currently given as a range of over 155 miles (250 km) at a cruise speed of 175 mph (280 km/h).
Lilium maintains, however, that the Lilium Jet will only spend a very short time in the hover, making its higher disc loading less of a handicap. Wiegand noted that the ducted fans in the seven-seat Lilium Jet, unlike the Phoenix demonstrator, will have variable outlet nozzles, enabling the fixed-pitch fans to run at optimal efficiency in both hovering and cruise flight. He estimated that restricting the mass flow in cruise will improve efficiency in that flight regime by around 20%.
In its letter to shareholders, Lilium reported that it entered the preliminary design review phase for its seven-seat aircraft this month. “As we head into 2022, we will be working towards securing further supplier contracts that will support initial aircraft production and progress towards first flight of a fully conforming aircraft,” the letter states.