Vertiflite May/June 2021

Lilium also noted that its propulsion systems architecture — embedded ducted fans on a wing and canard — are conducive to scaling up to larger capacity designs, while still being able to use the same infrastructure. The company contrasted that with a notional five-seat (four-passenger) tilt-propeller aircraft with a 50-ft (15-m) wingspan. A 16-Seater Lilium Jet, planned for launch in 2028, would have the same wingspan but 3.75 larger passenger capacity. Big Database In conjunction with the March 30 announcement, Lilium, for the first time, revealed significant new information on its aeropropulsion approach. The company posted an informally peer-reviewed paper, “Architectural performance assessment of an electric vertical take-off and landing (e-VTOL) aircraft based on a ducted vectored thrust concept,” by founder Patrick Nathen, and reviewed by four European academics. While no data was provided, it laid out the basic approach of the company’s proprietary Ducted Electric Vectored Thrust (DEVT) technology, and why the company believes it has a breakthrough in aeropropulsion performance. The paper indicates an incredible lift-to-drag (L/D) ratio of 18.4, similar to airliners flying at 35,000 ft (10,000 m), and a wing thickness ratio (t/c) of 12% — less than a turboprop and half that of the V-22 Osprey. The company has conducted extensive ground testing. In Lilium’s investor video, Brian Phillipson, Deputy Chief Technology Officer, noted that the company has “more than 50 different test facilities and the manufacturing facilities required to support them… They allow us to assess structural performance, aerodynamic performance, thrust, propulsion, acoustic and — particularly today, we’re standing in the acoustic wind tunnel, which allows us to assess the acoustic performance of different fan types, different rotor types and to measure the radiated noise, as well as the propulsion efficiency of the motor.” Images showed a full-scale, three-fan segment in a wind tunnel test. Lilium says it has successfully developed, tested and refined the underlying technology for its eVTOL jets, DEVT, along with key control systems, aircraft and battery architecture. DEVT technology enables Lilium to scale to higher-capacity aircraft and keep noise emissions and ground footprint low, according to the company. The 7-Seater Lilium Jet will be Lilium’s first aircraft to go into serial production, but it has plans for larger aircraft in the future. Lilium notes that its aircraft will have one-thirtieth the number of parts than a commercial airliner (fewer than 100,000 components vs. about three million) and is designed for ease of manufacturability and scalability. Lilium plans to apply automotive-style design for manufacturing methods and is designing for fully automated, high-quality production of its engines, actuators and batteries. In its investors briefing, the company highlighted some of these approaches for manufacturability and scaling. This included using very few but highly repetitive components, such as a single type of electric motor, actuator and battery module. As more data and information come out, it can be analyzed and considered in proving its breakthrough in eVTOL technology.

after that COVID hit and we said, okay, then let’s use the time to upgrade the aircraft.”

However, a Feb. 10, 2021, article on Forbes.com, revealed that the company was working on a seven-seat version of its Lilium Jet, and had aspirations for even larger models. In fact, the article quoted that Alexander Asseily, an early investor in Lilium and now the company’s chief strategy officer, had long abandoned the five-seat design. “We were never going to ship it, we were never going to certify it.” A Bigger Aircraft The Lilium “7-Seater Jet” — indicating six passengers and a pilot — has a projected cruise speed of 175 mph (280 km/h) at 10,000 ft (3,000 m) and a range of 155+ miles (250+ km), including reserves. The company also published its dimensions: the wingspan is 45.6 ft (13.9 m) and overall length is 27.9 ft (8.5 m); its five-seater has a wingspan of about 36 ft (11 m). The company says its eVTOL aircraft will “revolutionize regional travel, saving people hours not minutes.” Its “regional shuttle service will enable sustainable, high-speed transportation.” The 7-Seater Lilium Jet has market-leading capacity — company founder Wiegand noted that it has 50% more passenger capacity than its leading competitor, the four-passenger Joby air taxi — and is “capable of quiet vertical take-off, allowing Lilium access to more landing sites and the opportunity to build higher network density, avoiding the need for expensive ground infrastructure.” In an interview with Vertiflite , Wiegand said that Lilium hired its commercial team four years ago, in 2017, and they looked extensively at the different business models, such as air taxi, shuttle flights, etc. After a year of study, the company “decided to fully exploit the ability of our technology to go for a bigger airplane, because we found that a shuttle business model going into a city would give us two big advantages. Firstly, we would get higher time savings. We would get hours of time savings for our customers, not 10, 20 minutes or so. And because of that, it would enable us to bring more passengers on one flight.” He noted that “this is crucial to get better unit economics and to get the prices down, because it allows us to distribute the cost of the pilot and the landing fees —which are always the same [regardless of number of passengers] — over more passenger tickets.” Lilium applied for concurrent type certification for a high- capacity aircraft with the European Union Aviation Safety Agency (EASA) and the US Federal Aviation Administration (FAA) in 2018. Development of the 7-Seater Lilium Jet began in stealth mode following this milestone. In late 2020, the 7-Seater Lilium Jet received CRI-A01 certification basis from EASA. The EASA Special Condition SC-VTOL draft was published in October 2018 and finalized the following July. Explaining the process, Wiegand said, “You start with the requirements and the regulators. Then, you talk about your means of compliance with the regulators. Once you have clarity on this, you pursue into the detailed design, you have your preliminary and critical design reviews, and then you’re going to ground tests and flight testing… we are now in the detailed design of the 7-Seater.” Thus, with this 2018 decision to go to a larger aircraft, the five-seat Phoenix became a technology demonstrator before its first flight.

May / June 2021

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