It has been a busy time for Lilium behind the scenes as the company prepares for its anticipated public listing this month. On Sept. 10, shareholders of the special purpose acquisition company Qell Acquisition Corp. (Nasdaq: QELL) will vote on whether to approve a combination with Lilium, which could generate up to $830 million in gross proceeds for the German eVTOL developer. This week, Lilium announced that David Neeleman is expected to join the company’s board following successful completion of the merger. Neeleman is the chairman of Azul Brazilian Airlines, which last month said it may place an order for Lilium Jets worth up to $1 billion.

Lilium’s unconventional eVTOL design, which has high disc loading and thus high power demands in a hover, has attracted considerable skepticism from some aerospace engineers. In parallel with its outreach to investors, Lilium has also been making efforts to engage with the engineering community, starting in March with publication of a technical paper by Lilium co-founder Dr. Patrick Nathen. On Sept. 1, Nathen along with three of his colleagues — chief technology officer Alastair McIntosh, chief strategy officer Alex Asseily, and chief engineer Luigi Ricci Moretti — took to r/AerospaceEngineering on Reddit for an “Ask Me Anything” (AMA).

You can find the full AMA here. We sorted through the 160-plus comments and pulled out some of the highlights.

Lilium Jet in flight
Lilium Jet’s original five-seat technology demonstrator in flight. Lilium Photo

1. Lilium expects to conduct full transition and long endurance flight tests later this year.

After its first five-seat demonstrator aircraft was destroyed in a ground fire in February 2020, Lilium suspended flight testing for well over a year, finally resuming its flight test campaign with an upgraded five-seat demonstrator in July. Referencing the recent 150-mile eVTOL test flight made by competitor Joby, Redditor MikeCZ_ asked about Lilium’s own longest flight to date, and the weight of the prototype that made it.

Nathen (who congratulated Joby on its “amazing milestone”) didn’t provide a distance figure, explaining that Lilium is “currently in the first stages of our flight test campaign with our current demonstrator including long endurance flight tests later this year. This will include our full transition flights” — flights in which the aircraft transitions from hovering to wing-borne flight and back. He said the company has conducted approximately 100 hours of tests to date, reaching a maximum speed of around 100 kilometers per hour (62 mph).

According to Nathen, Lilium’s five-seater has a targeted maximum take-off weight of 1,300 kilograms (2,865 pounds). The company plans to go to market with a larger, seven-seat version of the Lilium Jet, and aims to start a flight test campaign with that version at the end of next year. In response to a question from Redditor Kooky_Damage5633, Nathen said that the first test flights with an onboard pilot will take place with that larger prototype.

Lilium Lake Nona vertiport
A concept for a Lilium vertiport in Orlando, Florida. Lilium Image

2. Lilium plans to launch U.S. operations in Florida with four vertiports in 2024, and is exploring other key markets in the U.S. — and China.

Redditor MochaCocao asked about Lilium’s go-to-market plans in North America. Asseily confirmed that Lilium’s first U.S. regional network will be in Florida, where it’s planning to launch commercial operations in 2024 along with its infrastructure partners Tavistock and Ferrovial.

“We expect to start with four vertiports at launch and then expand to a network of 14 locations across Florida — using over 100 Lilium Jets eventually to serve them,” Asseily wrote. “We are of course looking closely at routes and commercial partnerships in a number of other U.S. regions such as the Northeast, California, Texas, etc.”

In response to a similar question from Redditor imasifkhan, Asseily added: “Likewise, we believe China will before long become a significant market — and we’ll be working with our investor Tencent to begin planning that launch in due course.”

Lilium cabin
Lilium’s eVTOL Lilium Jet incorporates 36 small electric ducted fans. Lilium Photo

3. Lilium continues to believe in electric ducted fans (EDFs).

Redditor Zymosis asked why Lilium based its eVTOL design on EDFs versus conventional propellers, observing: “I know EDFs are cool and all, but for something bigger than an RC [remote control aircraft] it seems like too big of a performance/weight design tradeoff.”

McIntosh acknowledged that “ducted fans versus open rotors is always a point for discussion. The key parameter is disc loading and for a given aircraft size and noise the disc loading is [two times] higher for the ducted fan in hover. Not good on face value. The key is that we only spend a very short time in hover as we don’t operate like a helicopter.”

Meanwhile, he said, ducted fans are around 40% more efficient compared to an open rotor at the same disc loading, thanks to the lack of blade overtip leakage and swirl losses. “Noise is the other key parameter — the ducted fans fitted with acoustic liners allows us to tune out the tonal noise which is something you cannot do with open rotors,” he added.

Speaking of noise, Redditor CrazyCommission7553 asked why Lilium hasn’t released any videos with audio of its eVTOL aircraft. Nathen promised, “We’re definitely planning to share more footage in the near future so you can hear just how quiet the jet is — watch this space!”

Lilium Jet cargo
An image from Lilium’s investor materials touting the Lilium Jet’s advantages for the cargo market.

4. Lilium is looking seriously at the cargo market.

Lilium has primarily marketed its eVTOL Lilium Jet as a regional air taxi. However, careful readers of its investor materials will have noticed that the company also expects to sell fleets of aircraft to corporations and governments. In its recent Capital Markets Day presentation, Lilium touted the advantages of the Lilium Jet for cargo applications, including a spacious 210-cubic-foot cabin. Lilium claims that the aircraft’s low noise will allow it to access urban warehouses while also being able to connect remote regions flexibly and more efficiently than trucks.

Redditor Charlie-Oh-No asked, “Why not go cargo-first with the Lilium Jet and use proceeds from aerial logistics missions to certify a passenger-rated aircraft?” To which Asseily replied: “A shrewd and prescient question.”

“Moving goods is definitely a part of our strategy,” he said, “for some of the reasons you raised and others too. Ultimately, it’s the same core aircraft architecture, which incidentally will have 50-100% more volumetric capacity than some of our peers in the eVTOL space.”