Personal aircraft aiming to take off from your home

May 6, 2016, European Space Agency
ESA BIC Bavaria start-up Lilium is developing a  two-seater electric powered plane for personal use. Although taking off and landing like a helicopter, by rotating its engines it also functions as a very efficient fixed-wing aircraft that can travel at up to 400 km/h and have a range of 500 km. Credit: Lilium

A start-up company hosted in an ESA business incubator is developing the world's first vertical takeoff and landing aircraft for personal use. The electric two-seater will open the door to a new class of simpler, quieter and environmentally friendly planes available from 2018.

"Our goal is to develop an aircraft for use in everyday life," explains Daniel Wiegand, CEO and one of the company's four founders.

"We are going for a plane that can take off and land vertically and does not need the complex and expensive infrastructure of an airport.

"To reduce noise and pollution, we are using electric engines so it can also be used close to urban areas."

Founded in February 2015 by four engineers and doctoral students from the Technical University of Munich in Germany, Lilium has already proved the concept with several scale, 25 kg prototypes and is now developing its first ultralight and landing aircraft.

Simpler and easier air transportation

Today, general public aviation offers fixed-wing aircraft and helicopters. Conventional aircraft are efficient, fast and available in many sizes but require airports often 20–50 km from city centres because of their space-hungry runways and the high noise levels.

Airports are expensive bottlenecks for transportation. This is especially so for short-haul flights, where travel time to and from airports can easily double the duration of a trip. This is not a problem for helicopters, which can take off almost anywhere and are therefore often used for short shuttle flights and special applications.

The electric aircraft under development by ESA BIC Bavaria start-up Lilium needs only an open flat area of about 15x15 m for vertical takeoff and landing. The environmentally friendly aircraft is planned to be available from 2018. Credit: Lilium

However, helicopters are very noisy and difficult to fly – which requires expensive licences. They also have no backup in case of rotor failure, making them expensive to build and maintain.

The Lilium vehicle combines the benefits of helicopters and fixed-wing aircraft while avoiding their drawbacks. While initially restricted to airfields, the goal is for it to take off vertically from almost anywhere – even from back gardens – it needs only an open flat area of about 15x15 m.

Although taking off and landing like a helicopter, by swivelling its engines it also functions as a very efficient aircraft that can travel at up to 400 km/h.

ESA BIC Bavaria start-up Lilium is developing a two-seater electric powered plane for personal use. Although taking off and landing like a helicopter, by rotating its engines it also functions as a very efficient fixed-wing aircraft that can travel at up to 400 km/h and have a range of 500 km. Credit: Lilium

Entirely electric, the plane is much quieter during takeoff than helicopters thanks to its ducted fan engines. Its batteries, engines and controllers are redundant, making it a much safer design than conventional helicopters.

The plane is classed as a Light Sport Aircraft for two occupants, with the pilot's licence requiring 20 hours' minimum training – almost like taking a driving licence.

It is intended for recreational flying during daylight, in good weather conditions and in uncongested airspace up to 3 km altitude.

ESA BIC Bavaria start-up Lilium is testing concepts for their electric-powered aircraft, which is planned to be ready by 2018. Several small-scale prototypes are being flown at Special Airport Oberpfaffenhofen, next to the company’s development site. Credit: Lilium

Using computer control for vertical takeoff and landing is essential for a vehicle targeted at the consumer market for personal transportation.

Powered from a simple wall plug

Highly efficient in its cruising mode, the vehicle will have a range of 500 km. It features a touchscreen and fly-by-wire joystick controls, retractable landing gear, wing doors, large storage, panoramic windows, and a battery that can be recharged from any wall plug.

Entirely electric, the Lilium plane is much quieter during takeoff than helicopters thanks to its ducted fan engines. The fans are positioned vertical during takeoff and landing, and turned horizontal for flying to make the plane a very efficient fixed-wing aircraft that can travel at up to 400 km/h. Credit: Lilium

Satnav is crucial to the high degree of automation and wind compensation during takeoff and landing.

The company is hosted at ESA's Business Incubation Centre in Bavaria, which offers a workshop for developing and building the prototypes and final plane.

Located directly next to the Special Airport Oberpfaffenhofen, the company has direct access to test fields and an inspiring aviation-friendly environment.

ESA BIC Bavaria start-up Lilium is building the world’s first vertical takeoff and landing two-seater electric airplane for personal use. Credit: Lilium
"The half-size prototype is already flying and now under test. The full-size unmanned prototype is planned for this summer," says Thorsten Rudolph, CEO of AZO, which runs the incubator, one of many in ESA's Technology Transfer Programme throughout Europe.

"We are helping the Lilium team to turn their idea into a viable business. They are the aircraft experts, and we provide the expertise on how to make a business out of their dream."

Supported by a venture capital investor, the company is planning its first manned experimental flight in 2017 and rollout of the completed vehicle for licensing by 2018, ready for initial production to begin meeting orders. Serial production will follow later.

The retail cost will be far less than similar-sized aircraft of today and with much lower running costs.

"In the longer term, our target is to build an that not only the super-rich can afford, and that can make private air transportation possible for a much wider number of people," adds Daniel.

"With the concept of taking off and landing almost everywhere, we could see that one day our plane will be used for quick and daily transportation almost like a car today."

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25 comments

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Eikka
5 / 5 (4) May 06, 2016
500 km on batteries? That's going to be one hell of a battery.
Eikka
5 / 5 (3) May 06, 2016
The lightest most fuel efficient passenger aircraft seem to come down at just about the same fuel consumption as a regular passenger car, so it might juuust be possible to pull off 500 km or about 300 miles in optimum conditions.

Such batteries are available at least. Trouble is, the air drag is proportional to the lift requirement, and the required amount of cells weighs about 1,200 lb which in itself is nearly the weight of a Cessna 172 at 1,470 lbs.

The maximum takeoff weight is 2,500 lbs, so If we assume the aircraft is about as heavy as a Cessna, and it's carrying a 1,200 lbs battery, it just can't take off. It's 170 pounds overweight with no passengers or cargo inside.

Close, but not quite. That's an engineering challenge.
Eikka
5 / 5 (1) May 07, 2016
Of course the difference between a battery powered aircraft and a petrol powered aircraft is that the latter gets lighter as it runs out of fuel, so the lift requirement gets less and less and the remaining fuel lasts longer.

The weight-lift-drag problem is kinda like the rocket equation: the less you're trying to lift, the less fuel or batteries you need to bring along, which means you're trying to lift less which means you need less fuel... although of course if you take zero fuel along, you go nowhere.

That means there's going to be some optimum amount of batteries relative to the aircraft mass that takes it the furthest distance. Any more will result in higher specific energy consumption and reduce the range.
gculpex
not rated yet May 07, 2016
I wonder how it handles in a crosswind (no rudder)?
I like the design but there are a few things that worry me, like what to do in an emergency.
ab3a
not rated yet May 07, 2016
I have observed that where design subtleties are important, that there are always a few amoral jerks who will take advantage of the ignorance of the masses.

There are designs such as the CarterCopter which are actually close to being able to deliver such performance. But they're not simple. Furthermore, as Eikka points out, the batteries alone make this aircraft improbable. I also note that the wing loading on this design would have to be quite high, and yet to take advantage of such wing loading, one would have to have some rather impressive propulsion performance.

I see this as yet another example of the Moller skycar concept. There are unfortunately too many investors who won't take the time to run some elementary numbers.

Also note that no amount of computer control can alleviate issues with weather. Even if this design were legit, I predict endless lawsuits as these aircraft encounter storms and are thrown out of the sky.
Eikka
5 / 5 (1) May 08, 2016
one would have to have some rather impressive propulsion performance.


Electric propulsion is, ironically, quite capable. You get massive performance out of ducted electric fans compared to piston engines or microturbines. The limiting factor is again the batteries.

A piston engine or a turbine doesn't go past open throttle. That's all you get. Electric motors have the ability to be overdriven well past their design by simply applying more input power, which gives you high peak performance from a light motor. They overheat of course, but that's manageable.

Eikka
5 / 5 (1) May 08, 2016

Also note that no amount of computer control can alleviate issues with weather. Even if this design were legit, I predict endless lawsuits as these aircraft encounter storms and are thrown out of the sky.


Hence why

"It is intended for recreational flying during daylight, in good weather conditions and in uncongested airspace up to 3 km altitude."
ab3a
5 / 5 (1) May 08, 2016
Hence why

"It is intended for recreational flying during daylight, in good weather conditions and in uncongested airspace up to 3 km altitude."


Unfortunately, even with those limits, experienced private pilots routinely screw up and kill themselves quite regularly. Now figure that in to the general population and you'll see accidents all over the place.

Regarding your over-power condition for electric motors, that might be appropriate in a car where the motor output averages 30% or less. However an aircraft engine has to be able to function at 65% or better in cruise configurations. Takeoff conditions are usually 100% output for several minutes and then 75% or better to climb toward the cruising altitude. This is not a casual stomp on the accelerator pedal to merge in to traffic on the highway. I have doubts a motor could be designed for a reasonable lifetime while building up that much heat.
Eikka
5 / 5 (1) May 08, 2016
Unfortunately, even with those limits, experienced private pilots routinely screw up and kill themselves quite regularly. Now figure that in to the general population and you'll see accidents all over the place.


Hence why

"Using computer control for vertical takeoff and landing is essential for a vehicle targeted at the consumer market"
"Satnav is crucial to the high degree of automation and wind compensation during takeoff and landing."

It's basically a self-driving airplane and the driver is just telling it where to go.

Regarding your over-power condition for electric motors, that might be appropriate in a car where the motor output averages 30% or less. However an aircraft engine has to be able to function at 65% or better in cruise configurations


Electric motors are generally rated and designed for full continuous output, unlike engines/turbines that are rated for ther peak output. An electric car could do with a 40 HP motor and drive like 100 HP
Eikka
5 / 5 (1) May 08, 2016
I have doubts a motor could be designed for a reasonable lifetime while building up that much heat.


You forget that ducted fans are pumping tremendous amounts of air.

As long as the motor shaft and bearings can take the torque/forces involved, and the wiring insulation can withstand the voltage you put in, the only limit to power is keeping the motor cool. The more you cool it, the more continous power you get.

And another advantage is that electric motor efficiency increases with running speed, so there's less heat to get rid of in the first place.
ab3a
not rated yet May 08, 2016
Eikka, as a licensed pilot, allow me to point out that computer controls alone can not handle issues of judgment regarding weather. Flying around thunderstorms, mountainous terrain, canyons, and the like, one can encounter severe updrafts and downdrafts that even a fighter jet would have difficulty with. Flying in freezing rain or virga can knock an aircraft right out the sky --no matter how good the computer controls may be.

As for electric motor efficiency, going faster is not necessarily better. Once the propeller blade tips reach mach speed, there is no additional thrust, just heat and noise. Ducted fans can improve propeller efficiency and speed, but the ducting weighs more and as such it usually negates any meager gains in performance.
Da Schneib
5 / 5 (3) May 08, 2016
Electric motors are generally rated and designed for full continuous output, unlike engines/turbines that are rated for ther peak output. An electric car could do with a 40 HP motor and drive like 100 HP
This is especially true since the torque curve of an airbreathing engine depends upon the air intake, whereas the torque curve of an electric motor is dependent upon the current draw and the magnetic coupling between the rotors and stators. Most electric motors have a relatively flat curve, with high torque even at zero speed, up to their breakover torque, after which they quickly decline to their maximum speed. Airbreathers have zero torque at zero speed, building to a peak and then having the same decline after the peak.

[contd]
Da Schneib
5 / 5 (1) May 08, 2016
[contd]
Since most people who drive cars rate their acceleration in terms of the "hole shot," starting from a dead stop to freeway speeds, electric motors can give a far better performance even at lower total horsepower since they have far more low-end torque than any airbreather can achieve. In fact I'd be surprised if there wasn't a designed-in limit on the torque curve, determined by a computer, on electric cars to prevent loss of traction and injury to the passengers, not to mention stress on the infrastructure of the car, from abrupt accelerations. It's so antithetical to the way people are used to cars behaving that I can't imagine they don't have to allow for this effect.

I might think you're exaggerating just a bit, @Eikka, but not much and I wouldn't be surprised if it were only because they tone the starting torque down in the computers; the motors probably can handle far more than the passengers can.
Da Schneib
5 / 5 (1) May 08, 2016
So how plausible is this technology?

I have to point out here that demonstrating this technology using smaller models is inherently unsound; lift will only scale as the square of size, whereas weight will scale as the cube. So I will watch, but overall I'd say that you have it right, Eikka; this will be a very difficult engineering challenge. On the plus side, electric motors have possibilities that are inherently suited to the challenge, and with computer-controlled transition from vertical to level flight, this has some possibilities that might not have been feasible before. That transition has always been the most challenging design task for engineers dealing with human factors; eliminating the human factors would make such transportation systems far easier to develop. We'll see if it's enough.

I think the real question here is how much battery power vs. mass changes over the development time of the aircraft.
ab3a
not rated yet May 08, 2016
I think the real question here is how much battery power vs. mass changes over the development time of the aircraft.


Let's just say that I've seen others try to build similar aircraft to what ESA BIC Bavaria is trying to build going all the way back to the 1970s at least. More than a few models have flown, but carrying enough payload for a human being to go anywhere has not happened even in prototypes.

I wouldn't invest in this endeavor.
Eikka
5 / 5 (1) May 09, 2016
As for electric motor efficiency, going faster is not necessarily better. Once the propeller blade tips reach mach speed, there is no additional thrust, just heat and noise

Hence why the design uses many smaller rotors instead of one large.

And you can still use simple and robust planetary gears to make the motor spin faster than the prop. The point was simply that if you can get an electric motor spinning close to 10,000 RPM or more, it can be made very efficient and light.

as a licensed pilot, allow me to point out that computer controls alone can not handle issues of judgment regarding weather


So you're still objecting that a fair weather hobby airplane might be used by some in conditions that it's not meant for, like flying around canyon passes or when the weather report says chance of rain.

Don't hang gliders have the same problem, and yet we allow their use?
Eikka
5 / 5 (1) May 09, 2016
In fact I'd be surprised if there wasn't a designed-in limit on the torque curve,


There is, exactly due to the overheating problem.

When you apply a voltage to an inductor, such as the pole coil in an electric motor, the current begins to rise and energy is stored in the magnetic field at a rate determined by the reactance of the coil. The faster the motor is designed to spin, the smaller the reactance and the faster the current rises.

The energy is being transferred only when the current is growing. Once the current flattens out because the supply can't give any more, or the resistivity of the coil begins to limit it, no more energy is being transferred to torque and the rest of the switching cycle is just holding the field and wasting power into heat.

So electric motors in cars, driven by a variable frequency inverter, are very inefficient at low speeds and they have to be torque limited or they'd burn up.

Eikka
5 / 5 (1) May 09, 2016
You can take for example:

http://www.turbin...tor.html

nner shroud diameter: 128mm
Fan swept area: 94cm²
Weight incl. motor, wires, connectors and
Secure Fan Fix: 1330g
Thrust range: 10.19kg to 13.25kg (100-130N)
Overall efficiency: 70-71%


So that's about 10:1 thrust to weight ratio which is better than most jet engines, and the efficiency is better than any jet engine, and that's just an RC hobby motor.
Eikka
5 / 5 (1) May 09, 2016
The more impressive bit is really this:

the new DSM 6740 Schuebeler motor has a diameter of 67mm and a magnet length of 40mm.


The motor itself is but two inches long, smaller than a hockey puck, and it's handling between 7-10 kW of power. Nearly all the mass in the fan is from the ducting and the prop.
antialias_physorg
5 / 5 (1) May 09, 2016
not to mention stress on the infrastructure of the car, from abrupt accelerations.

I was looking at the smart fourtwo electric drive - which is by no means a high end sports vehicle. The salesperson told me they had to incorporate torque limiters in their second generation vehicles because the standard gearbox they use couldn't handle the stresses.

Flying around thunderstorms, mountainous terrain, canyons, and the like, one can encounter severe updrafts and downdrafts that even a fighter jet would have difficulty with

Apart form the fact that they say this is specifically for 'nice weather' flying, only: There's a big difference between a combustion engine and an electric engine in terms of how fast it can respond to changing conditions. This makes automated/intelligent controls far easier to implement (the complexity of software behind the stabilization of a quadcopter is a joke. A similar software for a combustion engine would be a nightmare to write)
krundoloss
5 / 5 (1) May 09, 2016
I like the concept, a multitude of reliable motors reduce chance of failure, computer controlled with multiple safeguards. More than likely the thing would not let you fly in certain weather conditions, controlled by a some sort of group that will decide such things. The battery weight problem may be solved by going with some other technology, much as we are seeing with Drones that use Hydrogen Fuel Cells instead of batteries. Bottom line, if enough people want it to happen, then it will. http://www.geek.c...1650724/
ab3a
not rated yet May 09, 2016
Don't hang gliders have the same problem, and yet we allow their use?


We allow them because the aircraft is lightweight, the risk is only the pilot's. and they don't fly terribly fast or fly over populated territory.

In this aircraft the wing loading is likely to be high, so it would have to fly fast. It will be heavier, and the risk of something like this coming down on people or property would be significant. Furthermore, weather conditions can change very fast. I've seen more than a few weather forecasts turn to garbage in minutes. The problem isn't just that the weather changes, but that there is no turn-around.

There is much more to this than just watching a weather radar image. This is not just a matter of seeing where you're going, but knowing things such as what an elevated K-index is, knowing what lenticular clouds imply, or what happens to aircraft performance as the temperature rises.
Eikka
not rated yet May 11, 2016
The salesperson told me they had to incorporate torque limiters in their second generation vehicles because the standard gearbox they use couldn't handle the stresses.


That's not so much due to the high torque of the motor, but the jerk of the motor, or the rate of change of acceleration. An electric motor is on and off so fast that it causes stress fractures in the driveshafts. This is made worse by the fact that the gearbox only has one gear that goes from zero to top speed.

Same thing happens when you drive a normal engine too slow on a high gear. The drivetrain vibrates and eventually snaps.
Eikka
not rated yet May 11, 2016
We allow them because the aircraft is lightweight, the risk is only the pilot's. and they don't fly terribly fast or fly over populated territory.


So apply the same limits here. No flying over populated areas and the risk is yours.

Hang gliders, paragliders, paramotors, small ultralight aircrafts all have the same troubles and they're all restricted to be fair weather hobbies because of that.

In this aircraft the wing loading is likely to be high, so it would have to fly fast


It has effectively tilt rotor capabilty, so it can derive some of its lift by hovering. It doesn't necessarily need to fly fast, but it will be most efficient covering distance at speed.
gculpex
not rated yet May 12, 2016
Sorry there are limits to this, mass air flow through the fans. the flow would have to be quite fast for the inner diameter- near sonic air flow.
The motors would have to run continuously at full power in hover mode.

they could hide the fans inside the wings...

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