Simplicity was our Most Complicated Goal
At Lilium, we have invented a completely new aircraft concept for the modern age. While vertical take-off and landing (VTOL) itself is not new – after all, quadcopters, tilt rotors and tilt wings are well-known concepts – we did not want to accept the compromises inherent to these configurations.
Quadcopters excel with their simplicity but are highly inefficient in cruise flight. Transition aircraft can fly three times faster and ten times further with an equally sized battery, but system complexity is usually much higher.
So, the goal was set: defining a transition aircraft concept with better performance in safety, noise, speed, range and payload than existing concepts, while cutting complexity to one third.
We challenged physical limitations, mechanical complexity and energy laws, until we came up with something new and unique. Something simple and efficient.
Sounds quite complicated? Find out what we did.
Two Modes. Seamless Transition.
The Lilium Jet consists of a rigid winged body with 12 flaps. Each one carries three electric jet engines. Depending on the flight mode, the flaps tilt from a vertical into a horizontal position. At take-off, all flaps are tilted vertical, so that the engines can lift the aircraft. Once airborne, the flaps gradually tilt into a horizontal position, leading the aircraft to accelerate. When they have reached complete horizontal position, all lift necessary to stay aloft is provided by the wings as on a conventional airplane.
Covering it All.
The beauty of this system is its simplicity. In comparison to existing concepts, Lilium Jets require no gearboxes, no foldable or variable pitch propellers, no water-cooling, and no aerodynamic steering flaps. Just tiltable electric engines.
What’s more: The Lilium Jet has the highest possible structural efficiency. As we can provide differential thrust from the engines in cruise flight, no stabilizing tail is necessary.
Efficient and Fast.
The design of the electric engines ensures a very low drag coefficient in cruise flight, leading to a higher speed and range. The energy consumption per seat and kilometer thereby becomes comparable to an electric car – but the jet is 3 times faster.
More Efficiency at Low Speeds.
The Lilium Jet uses an integrated high-lift system. The objective is to increase the lift of the wings even at low speeds to save energy. While hovering is very energy-consuming, as an aircraft must provide thrust equal to its own weight, dynamic lift of wings consumes much less energy to stay aloft. So, it is important to create as much dynamic lift from the wings as possible, even at very low speeds.
Full Maneuverability in Transition Flight.
As the engines always maintain attached flow on the surface of the flaps, the Lilium-Jet is highly maneuverable in any flight condition. It can do climbing, curves and high-rate sinking in any phase of a transitional flight. This feature is highly important when flying in narrow corridors in urban areas or for avoiding unexpected objects during a transition flight.
Electric Jet Engines
The electric jet engines work like turbofan jet engines in a regular passenger jet. They suck in air, compress it and push it out the back. However, the compressor fan in the front is not turned by a gas turbine, but by a high performance electric motor. Therefore, they run much quieter and completely emission-free.
Reliability and Maintenance
The Lilium Jet engines have only one moving part - the central shaft of the rotor holding both the fan in the front and the magnets of the electric motor. This ensures highest reliability in operation and low maintenance costs of the propulsion system. The high redundancy of the system allows large inspection intervals to keep costs much lower than for helicopters or reciprocating engines.
Low Noise & Vibrations
The large open rotors of a helicopter induce vibrations into the cabin. The whole vehicle vibrates in the frequency of the rotor blades passing. Our electric jet engines, however, run smoothly. This ensures a quality passenger experience during the entire flight. Likewise a big advantage of electric jet engines is their low noise signature for people on the ground.
Safety First. Safety Second.
A key objective for the Lilium Jet is to bring a new safety paradigm into general aviation. As we develop vertical takeoff flights for everyone, we had to develop a safety concept compatible with a consumer product: it has to be foolproof. In case of an emergency, regardless of the failing component, the computer informs the pilot to land the jet. Since vertical landing is still possible no complex decisions need to be made under time pressure as in conventional planes.
To fulfill our safety objectives, we chose the concept of ultra-redundancy. We equip the Lilium Jet with small independent components, so that, for example, a single engine failure does not have consequences for the aircraft’s safety or stability. The system can still do a vertical landing with a loss of multiple engines. This philosophy of redundancy has been applied to all flight systems.
Flight Envelope Protection
The Lilium Jet is a full fly-by-wire system. This means a set of fully redundant computers are flying the airplane and controlling all functions of the engines and actuators at all times. The pilot commands high level directions with a joystick, which the computer puts into action. This makes flying a Lilium Jet as easy as steering a toy quadcopter. Furthermore, the system has a built-in flight envelope protection: meaning that even if the pilot requests a dangerous maneuver, the computer does not exceed safety limits of speed, roll, and pitch.
Electric jet engines also excel in safety. The duct around the fan is designed to contain the loss of a fan blade at full power. If an engine fails, for example due to ingestion of a foreign object, it is guaranteed that this event does not cause the adjacent engine to fail as well. The only way to prevent a cascade effect, in case of a blade loss event, is using shielded engines.
The Lilium Jet’s battery pack is comprised of several thousand Lithium-Ion cells similar to those in electric cars. It is designed to fully contain a thermal runaway of several cells while still delivering enough power to the propulsion system. To achieve this, it is built with many independent parallel strings of cells ensuring multi-redundancy also on the energy supply.
In case all precautions won’t help and a regular landing is impossible, there is still a safety net. Every Lilium Jet is equipped with a full aircraft parachute – bringing the jet safely down to the ground if necessary. By the way: The cabin is water-resistant in case of descending onto water.
Air Travel Made Comfortable
The Lilium Jet features elegant gull-wing doors. This enables easy boarding and exit - it also lets you literally slide into the comfortable seats the way you would in a premium car. Once in the jet, passengers can easily store their luggage under their seat or in the trunk behind them. There is enough legroom even for tall passengers, and the huge panoramic window ensures an almost 360° view.
Every Gram Counts
Lightweight design has become almost a religion here at Lilium. For a VTOL jet, such a design is even more important than for a normal airplane. The whole structure of the jet is made from carbon fiber custom built for Lilium. Carbon fiber is five times stronger and three times stiffer than aluminum. We use the world’s lightest known material – and still we continue to strip off the last kilogram.