As the Lilium Phoenix eVTOL demonstrator reached its maximum speed in a flight test over rural Spain last month, the crew piloting it remotely from the ground savored the moment.
This was the first time Phoenix achieved its target maximum speed of 136 knots (155 miles per hour or 250 kilometres per hour), and it marks a crucial milestone as Lilium works toward the first crewed flight of the Lilium Jet production aircraft in late 2024.
“It was a really good moment,” said Andy Strachan, chief test pilot for Lilium, in an interview with Vertical. “We’ve changed what was theory and expected performance, into known and validated performance.”
While the Phoenix demonstrator is less than half the targeted weight of the Lilium Jet, the demonstrator is configured identically to the planned production aircraft. Achieving maximum speed with Phoenix is seen as proof of the aircraft’s stability and maneuverability at high velocity, and a significant milestone in its certification path.
“This represents everything you’d want to be a test pilot for — getting involved in something new and challenging, but which has the potential to have huge benefit,” said Strachan, who previously worked as a test pilot with Leonardo Helicopters. “We effectively confirmed the flight envelope we wanted to define with it.”
Phoenix is designed as an unmanned demonstrator, and it was not carrying any passengers or pilots during the test flight. Its only payload was the instrumentation, recording devices, and radios to ensure it functioned properly and could be monitored from the ground.
One pilot maneuvered the aircraft from mission control as it took off and flew in a loop over the Spanish countryside. The entire flight lasted about five and a half minutes, and it consisted of several stages that gradually brought the demonstrator up to speed.
Flight test approval requirements from the European Union Aviation Safety Agency (EASA) required this staged, gradual progression. As a result, it is not yet possible to confirm how quickly Phoenix can accelerate to its maximum speed.
“All of that’s designed to keep it within the constraints of the regulation,” Strachan said. “There were pauses in acceleration at different speeds as we accelerated up to 136 knots.”
Lilium has designed its Lilium Jet production aircraft to achieve the same 136 knot maximum speed while carrying a pilot and six passengers, plus baggage.
The company completed its preliminary design review for the Lilium Jet last year. After a bit of fine-tuning, engineers have a clear idea of how the aircraft will be configured.
“We’re more or less at the frozen design now, and cracking on with that,” Strachan said.
As part of its flight test at maximum speed, crews verified Phoenix’s flight physics and flight control system and tested Phoenix’s battery system, engine, and powertrain, all of which performed well, with few complications.
“There were a couple of things that came up,” Strachan said. “There were no major unexpected events. Obviously, there were bits and pieces; we learned as we went. But genuinely, there was nothing major.”
In the months ahead, Phoenix will continue its test flight regime at the ATLAS Test Flight Center, about 30 kilometers (20 miles) east of the town of Ubeda, Spain.
Lilium aims to have the first crewed flight of its production aircraft toward the end of next year, with a target of initial type certification as soon as possible after.
Strachan compares the ramp up to commercial electric flight with the Wright Brothers’ first airplane flight in 1903.
“This is a new and developing part of a big aviation story,” he said. “What we are aiming to do is eventually provide a much greener, efficient means of air transport. We are advancing, all of us, together.”