Lilium and the thirty-six ducted electric jets that went bankrupt before they could prove the physics

Lilium, the German eVTOL company, staked its future on a propulsion concept no competitor would touch: 36 small ducted electric jet engines embedded in the wing and canard surfaces. The approach promised superior cruise efficiency and lower noise, but unresolved questions about hover power consumption helped drive the company into insolvency in late 2024. New investors acquired the assets, and Lilium is now targeting type certification in the 2027–2028 timeframe with a smaller team and tighter budget.

Why Did Lilium Choose Ducted Electric Vectored Thrust?

Most eVTOL companies follow variations of the same aerodynamic playbook. Joby uses six tilting propellers. Archer uses twelve rotors. Wisk adopted a lift-plus-cruise layout. All rely on large, exposed rotors for vertical lift, then transition to wing-borne flight for efficiency.

Lilium rejected that approach entirely. Their design embeds 36 small ducted fans in the trailing edges of the main wing and forward canard. No exposed propellers, no tilt mechanisms, no folding rotors. The fans vector thrust downward for vertical takeoff, then rotate aft for cruise flight.

The motivation was cruise efficiency. Hovering devours battery capacity, and every second in vertical flight reduces range. Most multicopter designs accept this penalty and minimize the hover phase. Lilium’s bet was different: by eliminating the drag of exposed rotors during cruise, the aircraft could recover the energy spent hovering by being dramatically more efficient at 200 mph. The configuration also offered extraordinary redundancy—losing five of 36 motors still leaves enough thrust to land safely.

What Is the Disc Loading Problem?

This is where the physics gets uncomfortable. Ducted fans at Lilium’s scale—roughly eight inches in diameter—face a fundamental aerodynamic constraint called disc loading. A large rotor sweeps a wide area and generates lift relatively gently. A small ducted fan must accelerate air much faster through a much smaller area to produce the same force, demanding significantly more power.

Multiple independent aerodynamicists raised this concern publicly starting around 2020. Their calculations suggested Lilium’s hover power requirement could be so extreme that batteries couldn’t deliver enough energy for a useful mission. The first two minutes of vertical takeoff might consume so much power that meaningful range would be impossible.

Lilium countered that their proprietary fan design and duct geometry addressed the disc loading issue. They pointed to their fifth-generation demonstrator, a smaller technology prototype that successfully achieved vertical takeoff and transitioned to wing-borne flight. Those flights were real—the concept was not fantasy.

But the demonstrator was significantly smaller and lighter than the planned production aircraft, the Lilium Jet, designed to carry six passengers plus a pilot over roughly 170 miles. Scaling matters enormously in electric aviation. A concept that works at 2,000 pounds can collapse at 6,000 pounds because battery energy density doesn’t scale proportionally. Lilium never publicly demonstrated the full-scale production aircraft in flight.

How Did Lilium Rise and Fall Financially?

Lilium was founded in Munich in 2015 by four engineers from the Technical University of Munich, with Daniel Wiegand as CEO. The company progressed through venture capital rounds before going public via a SPAC merger in 2021, reaching a peak market valuation exceeding $7 billion. At its height, Lilium employed over 1,000 people and was constructing a large production facility in Germany.

The burn rate was staggering. By some estimates, Lilium was spending over $100 million per quarter with zero revenue—no deliveries, no paying customers, only engineering development and overhead.

Timelines kept slipping. The original target of paying passengers by 2024 became 2025, then 2026. Each delay eroded investor confidence. In late 2024, Lilium filed for insolvency in Germany, effectively declaring bankruptcy. Over a thousand employees faced layoffs, the production facility went quiet, and flight testing stopped.

How Did Lilium Come Back From Bankruptcy?

Weeks after insolvency appeared terminal, a consortium of investors—including European aerospace interests and reportedly Middle Eastern capital—acquired Lilium’s assets out of insolvency proceedings. The new ownership group expressed confidence in the technology and committed to continuing development.

By early 2025, Lilium was operating again with a reduced workforce, tighter budget, and revised certification target of 2027–2028. However, the restructuring came at a cost. Key engineers departed, taking institutional knowledge with them. Certification discussions with EASA (European Union Aviation Safety Agency) must now account for the organizational disruption.

Where Does Lilium Stand Against Competitors?

While Lilium navigated insolvency, competitors advanced. Joby accumulated flight test hours. Archer built a manufacturing facility in Georgia. The window for first-mover advantage in eVTOL is narrowing, and Lilium is now behind companies it was once considered a peer of.

The competitive question reduces to an engineering philosophy divide. One school—represented by Joby and Archer—says use proven components in new configurations. Take existing rotor and motor technology and combine them cleverly. The other school—Lilium’s approach—says if the end state demands new physics, develop the new physics rather than optimizing the wrong solution.

History supports both philosophies. The jet engine replaced the piston engine not because pistons were poorly optimized, but because jet propulsion was fundamentally superior at speed. But history also has no shortage of technically superior solutions that arrived too late or cost too much to matter.

What Needs to Happen in the Next 18 Months

The critical question remains unresolved: nobody outside Lilium has independently verified that the full-scale aircraft achieves the hover efficiency numbers the company claims. The disc loading concern didn’t disappear with the change in ownership. Battery technology has improved since 2020, but potentially not by the margin Lilium needs if the skeptical aerodynamic models are correct.

If Lilium gets the full-scale production aircraft into flight testing and demonstrates competitive hover efficiency, this becomes one of aviation’s great comeback stories. If they can’t, the company becomes an expensive lesson in the gap between simulation and reality.

Either outcome advances the field. The ducted fan research, distributed electric propulsion data, and vectored thrust control algorithms contribute to the broader knowledge base. That’s how aerospace has always worked—the projects that fail feed the projects that succeed.

Key Takeaways

• Lilium’s 36 ducted electric fans offer potential advantages in cruise efficiency, noise reduction, and motor redundancy, but face unresolved questions about hover power consumption due to disc loading physics
• The company went bankrupt in late 2024 after burning through billions with no revenue, then was rescued by a new investor consortium
• No independent verification exists for Lilium’s claimed full-scale hover efficiency numbers—the demonstrator that flew was significantly smaller than the planned production aircraft
• Competitors have pulled ahead during Lilium’s restructuring, with Joby and Archer advancing through flight testing and manufacturing buildout
• The 2027–2028 certification target depends on Lilium’s ability to rebuild engineering capacity and prove full-scale performance under new ownership